< draft-bms-optical-sdhsonet-mpls-control-frmwrk-00.txt		draft-bms-optical-sdhsonet-mpls-control-frmwrk-01.txt >
	MPLS Working Group Greg Bernstein		CCAMP G. Bernstein
	Internet Draft Ciena		Internet Draft Ciena
	Document: <draft-bms-optical-sdhsonet-mpls-		Document: <draft-bms-optical-sdhsonet-mpls- E. Mannie
	control-frmwrk-00.txt>		control-frmwrk-01.txt> Ebone
	Category: Eric Mannie		Category: Informational V. Sharma
	Expires: May 2001 GTS		Metanoia
			Expires January 2002 July 2001
	Vishal Sharma
	Tellabs
	November 2000
	Framework for MPLS-based Control of Optical SDH/SONET Networks		Framework for GMPLS-based Control of SDH/SONET Networks
	<draft-bms-optical-sdhsonet-mpls-control-frmwrk-00.txt>		<draft-bms-optical-sdhsonet-mpls-control-frmwrk-01.txt>
	Status of this Memo		Status of this Memo
	This document is an Internet-Draft and is in full conformance with		This document is an Internet-Draft and is in full conformance with
	all provisions of Section 10 of RFC2026 [1].		all provisions of Section 10 of RFC2026 [1].
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF), its areas, and its working groups. Note that		Task Force (IETF), its areas, and its working groups. Note that
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	Drafts. Internet-Drafts are draft documents valid for a maximum of		Drafts. Internet-Drafts are draft documents valid for a maximum of
	six months and may be updated, replaced, or obsoleted by other		six months and may be updated, replaced, or obsoleted by other
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	as reference material or to cite them other than as "work in		as reference material or to cite them other than as "work in
	progress."		progress."
	The list of current Internet-Drafts can be accessed at		The list of current Internet-Drafts can be accessed at
	http://www.ietf.org/ietf/1id-abstracts.txt		http://www.ietf.org/ietf/1id-abstracts.txt
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	http://www.ietf.org/shadow.html.		http://www.ietf.org/shadow.html.
	1. Abstract		1. Abstract
	The suite of protocols that define Multi-Protocol Label Switching		The suite of protocols that defines Multi-Protocol Label Switching
	(MPLS) is in the process of enhancement to generalize its		(MPLS) is in the process of enhancement to generalize its
	applicability to the control of non-packet based switching, that is,		applicability to the control of non-packet based switching, that is,
	optical switching. One area of prime consideration is to use this		optical switching. One area of prime consideration is to use these
	generalized MPLS in upgrading the control plane of optical transport		generalized MPLS (GMPLS) protocols in upgrading the control plane of
	networks. This paper illustrates this process by describing how		optical transport networks. This document illustrates this process
	MPLS is being extended to control SONET/SDH networks. SONET/SDH		by describing those extensions to MPLS protocols that are directed
	networks are exemplary examples of this process since they possess a		towards controlling SONET/SDH networks. SONET/SDH networks make
	rich multiplex structure, a variety of protection/restoration		very good examples of this process since they possess a rich
	options, are well defined, and are widely deployed. The extensions		multiplex structure, a variety of protection/restoration options,
	to MPLS routing protocols to disseminate information needed in		are well defined, and are widely deployed. The document discusses
	transport path computation and network operations are discussed		extensions to MPLS routing protocols to disseminate information
	along with the extensions to MPLS label distribution protocols		needed in transport path computation and network operations together
	needed for provisioning of transport circuits. New capabilities that		with the extensions to MPLS label distribution protocols needed for
	an MPLS control plane would bring to SONET/SDH networks, such as new		the provisioning of transport circuits. New capabilities that an
			MPLS control plane would bring to SONET/SDH networks, such as new
	restoration methods and multi-layer circuit establishment, are also		restoration methods and multi-layer circuit establishment, are also
	discussed.		discussed.
	Mack-Crane et al Expires May 2001 1		Bernstein, Mannie, Sharma Informational - January 2002 1
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000
	2. Conventions used in this document		2. Conventions used in this document
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in		"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
	this document are to be interpreted as described in RFC-2119 [2].		this document are to be interpreted as described in RFC-2119 [2].
	3. Introduction		3. Introduction
	A few years ago, the Internet Engineering Task Force (IETF) began		A few years ago, the Internet Engineering Task Force (IETF) began
	work on the specification of a new connection-oriented transport		work on the specification of a new connection-oriented transport
	technology called Multi-Protocol Label Switching (MPLS). The MPLS		technology called Multi-Protocol Label Switching (MPLS). The MPLS
	forwarding plane was inspired mainly by concepts from virtual		forwarding plane was inspired mainly by concepts from virtual
	circuit switching in ATM, while its control plane was inspired		circuit switching in ATM, while its control plane was inspired
	mainly by the routing protocols found in IP. As work on defining		mainly by the routing protocols found in IP. As work on defining the
	the components of MPLS progressed, it soon became apparent that the		components of MPLS progressed, it soon became apparent that the
	principles upon which MPLS was based were generic, and were		principles upon which MPLS technology was based were generic, and
	applicable to multiple layers of the network. As such, MPLS-based		were applicable to multiple layers of the transport network. As
	control of other network layers, such as the TDM and optical layers		such, MPLS-based control of other network layers, such as the time
	was also possible. The motivation behind introducing such control		division multiplexing (TDM) and optical layers was also possible.
	was to provide new services, such as dynamic establishment of TDM		The motivation behind introducing such control was to provide new
	and optical circuits, which were hitherto not possible in transport		services, such as dynamic establishment of TDM and optical circuits,
	networks. With MPLS-based control, transport operators or service		which were hitherto not possible in transport networks. With MPLS-
	providers would be able to offer on-demand services to their		based control, transport operators or service providers would be
	customers, due to the reduction in provisioning time of their		able to offer on-demand services to their customers, due to the
	circuits, thus adding considerable flexibility in their service		reduction in provisioning time of their circuits, thus adding
	portfolios.		considerable flexibility in their service portfolios.
	The MPLS Working Group of the IETF is currently extending MPLS		The CCAMP Working Group of the IETF is currently working on
	protocols to support these non-packet layers and these new services.		extending MPLS protocols to support multiple network layers and
	This extended MPLS, which was initially known as Multi-Protocol		these new services. This extended MPLS, which was initially known as
	Lambda Switching, is now better referred to as Generalized MPLS (or		Multi-Protocol Lambda Switching, is now better referred to as
	GMPLS). The authors of this work are among the co-authors of the		Generalized MPLS (or GMPLS). The authors of this work are among the
	GMPLS specifications, and - focus mainly on those aspects of GMPLS		co-authors of the GMPLS specifications, and - focus mainly on those
	that relate to the control of SDH/SONET networks.		aspects of GMPLS that relate to the control of SDH/SONET networks.
	The GMPLS effort is, in fact, extending IP technology to control and		The GMPLS effort is, in effect, extending IP technology to control
	manage lower layers. Using the same framework and the same kinds of		and manage lower layers. Using the same framework and similar
	signaling and routing protocols to control multiple layers not only		signaling and routing protocols to control multiple layers can not
	has the potential to reduce the overall complexity of designing,		only reduce the overall complexity of designing, deploying and
	deploying and maintaining networks, but also has the potential to		maintaining networks, but can also make it possible to operate two
	make it possible to operate two contiguous layers by using either an		contiguous layers by using either an overlay model, a peer model, or
	overlay model, a peer model or an integrated model. The benefits of		an integrated model. The benefits of using a peer or an overlay
	using a peer or an overlay model between the IP layer and its		model between the IP layer and its underlying layer(s) will have to
	underlying layer(s) will have to be clarified and evaluated in the		be clarified and evaluated in the future. In the mean time, GMPLS
	future. In the mean time, GMPLS is very suitable for controlling		could be used for controlling each layer independently.
	each layer completely independently.
	The goal of this paper is to highlight how MPLS could be used to		The goal of this work is to highlight how GMPLS could be used to
	dynamically establish, maintain and tear down SDH/SONET circuits.		dynamically establish, maintain and tear down SDH/SONET circuits.
	The objective is to provide at least the same kind of SDH/SONET		The objective of using these extended MPLS protocols is to provide
			at least the same kinds of SDH/SONET services as are provided today,
	Bernstein, Mannie, Sharma Expires May 2001 2		but using signaling instead of provisioning via centralized
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000
	services as provided today, but using signaling instead of		Bernstein, Mannie, Sharma Informational - January 2002 2
	provisioning to establish those services. This will allow operators		management to establish those services. This will allow operators to
	to propose new services, and will allow clients to create SONET/SDH		propose new services, and will allow clients to create SONET/SDH
	paths on-demand, in real-time, through the provider network. We		paths on-demand, in real-time, through the provider network. We
	first review the essential properties of SDH/SONET networks and		first review the essential properties of SDH/SONET networks and
	their operations, and we show how the labelÆs of MPLS can be		their operations, and we show how the label concept in MPLS can be
	extended to the SONET/SDH case. We then look at important		extended to the SONET/SDH case. We then look at important
	information to be disseminated by a link state route protocol and		information to be disseminated by a link state routing protocol and
	look at the important signal attributes that need to be conveyed by		look at the important signal attributes that need to be conveyed by
	a label distribution protocol. Finally, we look at some outstanding		a label distribution protocol. Finally, we look at some outstanding
	issues and future possibilities. [3], [4], [5], [6], [7],[8], [9],		issues and future possibilities. [3], [4], [5], [6], [7],[8], [9],
	[10], [11], [12].		[10], [11], [12].
	3.1 MPLS Overview		3.1. MPLS Overview
	An advantage of the MPLS architecture is the clear separation		A major advantage of the MPLS architecture for use as a general
	between the forwarding plane, the signaling plane, and the routing		network control plane is its clear separation between the forwarding
	plane. This allows the work on MPLS to focus on the forwarding and		plane (or data plane) the signaling (or connection control) plane,
			and the routing (or topology discovery/resource status) plane. This
			allows the work on MPLS extensions to focus on the forwarding and
	signaling planes, while allowing well-known IP routing protocols to		signaling planes, while allowing well-known IP routing protocols to
	be reused in the routing plane. This clear separation also allows		be reused in the routing plane. This clear separation also allows
	for MPLS to be used to control networks that do not have a packet-		for MPLS to be used to control networks that do not have a packet-
	based forwarding plane.		based forwarding plane.
	In MPLS terminology, an MPLS node is called a Label Switch Router		An MPLS network consists of MPLS nodes called Label Switch Routers
	(LSR) and a circuit is called a Label Switched Path (LSP). An LSP is		(LSRs) connected via circuits called Label Switched Paths (LSPs). An
	unidirectional and could be of several different types such as		LSP is unidirectional and could be of several different types such
	point-to-point, point-to-multipoint, and multipoint-to-point. Border		as point-to-point, point-to-multipoint, and multipoint-to-point.
	LSRs in an MPLS cloud, act either as ingress or egress LSRs		Border LSRs in an MPLS network, act either as ingress or egress LSRs
	respective to the direction of the traffic being forwarded.		depending on the direction of the traffic being forwarded.
	MPLS allows the establishment of LSPs between ingress and egress		Each LSP is associated with a Fowarding Equivalence Class (FEC),
	LSRs. Each LSP is associated with a Fowarding Equivalence Class		which may be thought of as a set of packets that receive identical
	(FEC), which may be thought of as a set of packets that receive		forwarding treatment at an LSR. The simplest example of an FEC might
	identical forwarding treatment at an LSR. The simplest example of an		be the set of destination addresses lying in a given address range.
	FEC might be the set of destination addresses lying in a given		All packets that have a destination address lying within this
	address range. All packets that have a destination address lying		address range are forwarded identically at each LSR configured with
	within this address range are forwarded identically at that LSR.		that FEC.
	To establish an LSP, a signaling protocol such as LDP/CR-LDP or		To establish an LSP, a signaling protocol (or label distribution
	RSVP-TE is required. Between two adjacent LSRs, an LSP is locally		protocol) such as LDP/CR-LDP or RSVP-TE is required. Between two
	identified by a short, fixed length identifier called a label. This		adjacent LSRs, an LSP is locally identified by a short, fixed length
	label is only significant between these two LSRs. The signaling		identifier called a label, which is only significant between these
	protocol is responsible for the inter-node communication that		two LSRs. The signaling protocol is responsible for the inter-node
	assigns and maintains these labels.		communication that assigns and maintains these labels.
	When a packet enters an MPLS packet-based network, it is classified		When a packet enters an MPLS-based packet network, it is classified
	according to its FEC and, possibly, additional rules, which		according to its FEC and, possibly, additional rules, which together
	together determine the LSP along which the packet is sent. For that		determine the LSP along which the packet must be sent. For this
	purpose, the ingress LSR attaches an appropriate label to the		purpose, the ingress LSR attaches an appropriate label to the
	packet, and forwards the packet to the next hop. The label may be		packet, and forwards the packet to the next hop. The label may be
	attached to a packet in different ways. For example, -it may be in		attached to a packet in different ways. For example, it may be in
	the form of a header encapsulating the packet (the "shim" header) or		the form of a header encapsulating the packet (the "shim" header) or
	it may be written in the VPI/VCI field (or DLCI field) of the layer
	Bernstein, Mannie, Sharma Expires May 2001 3		Bernstein, Mannie, Sharma Informational - January 2002 3
	"		it may be written in the VPI/VCI field (or DLCI field) of the layer
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000		2 encapsulation of the packet. In case of SDH/SONET networks, we
			will see that a label is simply associated with a segment of a
	2 encapsulation of the IP data. In case of SDH/SONET networks, we
	will see that a label is simply associated with a segment of a
	circuit, and is mainly used in the signaling plane to identify this		circuit, and is mainly used in the signaling plane to identify this
	segment (e.g. a time-slot) between two adjacent nodes.		segment (e.g. a time-slot) between two adjacent nodes.
	When a packet reaches a core packet LSR, this LSR uses the label as		When a packet reaches a core packet LSR, this LSR uses the label as
	an index into a forwarding table to determine the next hop and the		an index into a forwarding table to determine the next hop and the
	corresponding outgoing label, writes the new label into the packet,		corresponding outgoing label (and, possibly, the QoS treatment to be
	and forwards the packet to the next hop. When the packet reaches the		given to the packet), writes the new label into the packet, and
			forwards the packet to the next hop. When the packet reaches the
	egress LSR, the label is removed and the packet is forwarded using		egress LSR, the label is removed and the packet is forwarded using
	adequate forwarding, such as normal IP forwarding. We will see that		appropriate forwarding, such as normal IP forwarding. We will see
	for a SONET/SDH network these operations -do not occur in quite the		that for a SONET/SDH network these operations do not occur in quite
	same way.		the same way.
	3.2 SDH/SONET Overview		3.2. SDH/SONET Overview
			There are currently two different multiplexing technologies in use
			in optical networks: wavelength division multiplexing (WDM) and time
			division multiplexing (TDM). This work focuses on TDM technology.
	SDH and SONET are two TDM standards widely used by operators to		SDH and SONET are two TDM standards widely used by operators to
	transport and multiplex different tributary signals over optical		transport and multiplex different tributary signals over optical
	links, thus creating a multiplexing structure, which we call the		links, thus creating a multiplexing structure, which we call the
	SDH/SONET multiplex. SDH, which was developed by the ETSI and later		SDH/SONET multiplex. SDH, which was developed by the ETSI and later
	standardized by the ITU-T, is now used worldwide, while SONET, which		standardized by the ITU-T, is now used worldwide, while SONET, which
	was standardized by the ANSI, is mainly used in the US. However,		was standardized by the ANSI, is mainly used in the US. However,
	these two standards have several similarities, and to some extent		these two standards have several similarities, and to some extent
	SONET can be viewed as a subset of SDH. Internetworking between the		SONET can be viewed as a subset of SDH. Internetworking between the
	two is possible using gateways.		two is possible using gateways.
	The fundamental signal in SDH is the STM-1 that operates at a rate		The fundamental signal in SDH is the STM-1 that operates at a rate
	of about 155 Mbps while the fundamental signal in SONET is the STS-1		of about 155 Mbps, while the fundamental signal in SONET is the STS-
	that operates at a rate of about 51 Mbps. These two signals are made		1 that operates at a rate of about 51 Mbps. These two signals are
	of contiguous frames that consist of a transport overhead (header)		made of contiguous frames that consist of transport overhead
	and a payload. To solve synchronization issues, the actual data is		(header) and payload. To solve synchronization issues, the actual
	not directly transported in the payload but rather in another		data is not transported directly in the payload but rather in
	internal frame that is allowed to float over two successive		another internal frame that is allowed to float over two successive
	SDH/SONET payloads. This internal frame is named a Virtual Container		SDH/SONET payloads. This internal frame is named a Virtual Container
	(VC) in SDH and a Synchronous Payload Envelope (SPE) in SONET.		(VC) in SDH and a Synchronous Payload Envelope (SPE) in SONET.
	The SDH/SONET architecture identifies three different layers, each		The SDH/SONET architecture identifies three different layers, each
	of which corresponds to one level of communication between SDH/SONET		of which corresponds to one level of communication between SDH/SONET
	equipment. These are, starting with the lowest, the regenerator		equipment. These are, starting with the lowest, the regenerator
	section/section layer, the multiplex section/line layer, and (at the		section/section layer, the multiplex section/line layer, and (at the
	top) the path layer. Each of these layers has its own overhead		top) the path layer. Each of these layers in turn has its own
	(header). The transport overhead of a SDH/SONET frame is mainly sub-		overhead (header). The transport overhead of a SDH/SONET frame is
	divided in two parts that contain the regenerator section/section		mainly sub-divided in two parts that contain the regenerator
	overhead and the multiplex section/line overhead. In addition, a		section/section overhead and the multiplex section/line overhead. In
	pointer (in the form of the H1, H2 and H3 bytes) indicates the		addition, a pointer (in the form of the H1, H2 and H3 bytes)
	beginning of the VC/SPE in the payload.		indicates the beginning of the VC/SPE in the payload of the overall
			STM/SDH frame.
			Bernstein, Mannie, Sharma Informational - January 2002 4
	The VC/SPE itself is made up of a header (the path overhead) and a		The VC/SPE itself is made up of a header (the path overhead) and a
	payload. This payload can itself be subdivided into sub-elements		payload. This payload can be further subdivided into sub-elements
	(signals) in a fairly complex way. In the case of SDH, the STM-1		(signals) in a fairly complex way. In the case of SDH, the STM-1
	frame itself may contain either one VC-4 or three multiplexed VC-3s.		frame may contain either one VC-4 or three multiplexed VC-3s. The
	Indeed, SDH and SONET both define a complete multiplexing structure.		SONET multiplex is a pure tree, while the SDH multiplex is not a
	The SONET multiplex is a pure tree, while the SDH multiplex is not a		pure tree, since it contains a node that can be attached to two
	Bernstein, Mannie, Sharma Expires May 2001 4
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000
	pure tree since it contains a node that can be attached to two
	parent nodes. The structure of the SONET/SDH multiplex is shown in		parent nodes. The structure of the SONET/SDH multiplex is shown in
	Figure 1. In addition, we show reference points in this figure that		Figure 1. In addition, we show reference points in this figure that
	will be explained later on.		are explained in later sections.
	xN x1		xN x1
	STM-N<----AUG<----AU-4<--VC4<------------------------------C-4 E4		STM-N<----AUG<----AU-4<--VC4<------------------------------C-4 E4
	^ ^		^ ^
	Ix3 Ix3		Ix3 Ix3
	I I x1		I I x1
	I -----TUG-3<----TU-3<----VC-3<----I		I -----TUG-3<----TU-3<---VC-3<---I
	I ^ C-3		I ^ C-3 DS3/E3
	DS3/T3/E3		-------AU-3<---VC-3<-- I ---------------------I
	-------AU-3<---VC-3<-- I -----------------------I
	^ I		^ I
	Ix7 Ix7		Ix7 Ix7
	I I x1		I I x1
	-----TUG-2<----TU-2<----VC-2<---C-2		-----TUG-2<---TU-2<---VC-2<---C-2 DS2/T2
	DS2/T2
	^ ^		^ ^
	I I x3		I I x3
	I I------TU-12<---VC-12<--C-12 E1		I I----TU-12<---VC-12<--C-12 E1
	I		I
	I x4		I x4
	I---------TU-11<---VC-11<--C-11		I-------TU-11<---VC-11<--C-11 DS1/T1
	DS1/T1
	xN		xN
	STS-N<-------------------SPE<---------------------------------		STS-N<-------------------SPE<------------------------------DS3/T3
	DS3/T3		^
	^		Ix7
	Ix7		I x1
	I x1		I---VT-Group<---VT-6<----SPE DS2/T2
	I---VT-Group<---VT-6<----SPE		^ ^ ^
	DS2/T2		I I I x2
	^ ^ ^		I I I-----VT-3<----SPE DS1C
	I I I x2		I I
	I I I-----VT-3<----SPE DS1C		I I x3
	I I		I I--------VT-2<----SPE E1
	I I x3		I
	I I--------VT-2<----SPE E1		I x4
	I		I-----------VT-1.5<--SPE DS1/T1
	I x4
	I-----------VT-1.5<--SPE
	DS1/T1
	Figure 1. SDH and SONET multiplexing structure and typical PDH		Figure 1. SDH and SONET multiplexing structure and typical PDH
	payload signals.		payload signals.
	Bernstein, Mannie, Sharma Expires May 2001 5		Bernstein, Mannie, Sharma Informational - January 2002 5
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000
	The leaves of these multiplex structures are time slots (positions)		The leaves of these multiplex structures are time slots (positions)
	of different sizes that can contain tributary signals. These		of different sizes that can contain tributary signals. These
	tributary signals (e.g. E1, E3, etc) are mapped into the leaves		tributary signals (e.g. E1, E3, etc) are mapped into the leaves
	using standardized mapping rules. In general, a tributary signal		using standardized mapping rules. In general, a tributary signal
	does not fill a time slot completely, and the mapping rules define		does not fill a time slot completely, and the mapping rules define
	precisely how to fill it.		precisely how to fill it.
	What is important for the goal of this paper is to identify the		What is important for the MPLS-based control of SDH/SONET circuits
	elements that can be switched from an input multiplex on one		is to identify the elements that can be switched from an input
	interface to an output multiplex on another interface. These		multiplex on one interface to an output multiplex on another
	elements are only those that can be re-aligned via a pointer, i.e. a		interface. The only elements that can be switched are those that can
	VC-x in the case of SDH and a SPE in the case of SONET.		be re-aligned via a pointer, i.e. a VC-x in the case of SDH and a
			SPE in the case of SONET.
	An STM-N/STS-N signal is formed from N x STM-1/STS-1 signals via		An STM-N/STS-N signal is formed from N x STM-1/STS-1 signals via
	byte interleaving. The VCs/SPEs in the N interleaved frames are		byte interleaving. The VCs/SPEs in the N interleaved frames are
	independent and float according to their own clocking. To transport		independent and float according to their own clocking. To transport
	tributary signals in excess of the basic STM-1/STS-1 signal, the		tributary signals in excess of the basic STM-1/STS-1 signal rates,
	VCs/SPEs can be concatenated, i.e., glued together. In this case		the VCs/SPEs can be concatenated, i.e., glued together. In this case
	their relationship with respect to each other is fixed in time and		their relationship with respect to each other is fixed in time and
	hence this relieves, when possible, an end system of any inverse		hence this relieves, when possible, an end system of any inverse
	multiplexing bonding processes. Different types of concatenations		multiplexing bonding processes. Different types of concatenations
	are defined, with specific rules.		are defined in SDH/SONET.
	For instance, the standard SONET concatenation allows the
	concatenation of M x STS-1 signals within an STS-N signal with M <=
	N, and M = 3, 12, 48, 192,...). The SPEs of these M x STS-1s can be
	concatenated to form an STS-Mc. The STS-Mc notation is short hand
	for describing an STS-M signal whose SPEs have been concatenated.
	3.3 The Real World of Circuit Establishment with SDH/SONET		For example, standard SONET concatenation allows the concatenation
			of M x STS-1 signals within an STS-N signal with M <= N, and M = 3,
			12, 48, 192,...). The SPEs of these M x STS-1s can be concatenated
			to form an STS-Mc. The STS-Mc notation is short hand for describing
			an STS-M signal whose SPEs have been concatenated.
	Today, SDH and SONET networks are statically configured. When a		3.3. The Current State of Circuit Establishment in SDH/SONET Networks
	client of an operator requests a point-to-point circuit or a ring,
	it sets in motion a process that can last for weeks. This process is
	indeed a chain of shorter administrative and technical tasks, some
	of which can be fully automated, resulting in significant
	improvements in provisioning time and in operational savings. In the
	best case, the entire process can be fully automated allowing, for
	example,. a CPE to contact a SDH/SONET switch to request some
	bandwidth. This is, in fact, the ultimate objective that we would
	like to achieve using MPLS to control SDH/SONET networks.
	In the current setup, however, the provisioning process involves the		Today, June 2001, SDH and SONET networks are statically configured.
	following components.		When a client of an operator requests a point-to-point circuit, the
			request sets in motion a process that can last for several weeks or
			more. This process is composed of a chain of shorter administrative
			and technical tasks, some of which can be fully automated, resulting
			in significant improvements in provisioning time and in operational
			savings. In the best case, the entire process can be fully automated
			allowing, for example, customer premise equipment (CPE) to contact a
			SDH/SONET switch to request a circuit. Currently, the provisioning
			process involves the following tasks.
	3.3.1. Administrative Tasks		3.3.1. Administrative Tasks
	The administrative tasks represent a significant part of the		The administrative tasks represent a significant part of the
	provisioning time. Most of them can be automated using IT		provisioning time. Most of them can be automated using IT
			applications, e.g., a client still has to fill a form to request a
			circuit. This form can be filled via a Web-based application and can
			be automatically processed by the operator. A further enhancement is
	Bernstein, Mannie, Sharma Expires May 2001 6		Bernstein, Mannie, Sharma Informational - January 2002 6
			to allow the client's equipment to coordinate with the operator's
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000		network directly and request the desired circuit. This could be
			achieved through a signaling protocol at the interface between the
	applications, however, and MPLS does not help in that case. However,		client equipment and an operator switch, i.e., at the UNI interface,
	a client still has to fill a form to request a circuit. This form		where GMPLS signaling can be used.
	can be filled via a Web-based application and can be automatically
	processed by the operator. A further step is to allow the client's
	equipment to coordinate with the operator's network directly and
	request the desired circuit. This has to be achieved through a
	signaling protocol at the interface between the client equipment and
	an operator switch, i.e. at the UNI interface, where MPLS can play a
	role.
	3.3.2. Manual Operations		3.3.2. Manual Operations
	Another significant part of the time may be consumed by manual		Another significant part of the time may be consumed by manual
	operations that involve installing the right interface in the CPE		operations that involve installing the right interface in the CPE
	and installing the right cable or fiber between the CPE and the		and installing the right cable or fiber between the CPE and the
	operator switch. This time can be especially significant when a		operator switch. This time can be especially significant when a
	client is in a different time zone than the operator's main office.		client is in a different time zone than the operator's main office.
	This first-time connection time is frequently accounted for in the		This first-time connection time is frequently accounted for in the
	overall establishment time. To support our fully automated model we		overall establishment time.
	must, of course, assume that CPEs are pre-connected to the
	operatorÆs network.
	3.3.3. Planning Tool Operation		3.3.3. Planning Tool Operation
	Another portion of the time is consumed by planning tools that run		Another portion of the time is consumed by planning tools that run
	simulations using heuristic algorithms to find an optimized		simulations using heuristic algorithms to find an optimized
	placement for the required circuits and/or rings. These planning		placement for the required circuits. These planning tools can
	tools can require a significant running time, sometimes of the order		require a significant running time, sometimes on the order of days.
	of days. These simulations are, in general, executed for a set of		These simulations are, in general, executed for a set of demands for
	demands for circuits and/or rings to improve the optimality of the		circuits, i.e., a batch mode, to improve the optimality of network
	solution. Today, we do not really have a means to reduce this		resource usage and other parameters. Today, we do not really have a
	simulation time. On the contrary, to support fast, on-line, circuit		means to reduce this simulation time. On the contrary, to support
	establishment, we will most probably skip this phase. It means that		fast, on-line, circuit establishment, this phase may be invoked more
	the network will have to be re-optimized periodically, implying that		frequently, i.e., we will not "batch up" as many connection
	the signaling should support re-optimization without hurting too		requests before we plan out the corresponding circuits. This means
	much the service. Indeed, the optimization of the network is then		that the network may need to be re-optimized periodically, implying
	taken out of the chain and becomes a background activity. Smart		that the signaling should support re-optimization with minimum
	circuit re-routing required for re-optimization is available in		impact to existing services.
	MPLS.
	3.3.4. Circuit Provisioning		3.3.4. Circuit Provisioning
	Once the first three steps have been executed, the circuits must be		Once the first three steps have been completed, the circuits must be
	effectively provisioned by the operator using the outputs of the		provisioned by the operator using the outputs of the planning
	planning tool. The time required for this provisioning is fairly		process. The time required for provisioning varies greatly. It can
	short, on the order of a few minutes. In many cases, operators		be fairly short, on the order of a few minutes, if the operators
	already have tools that help them to do the provisioning over		already have tools that help them to do the provisioning over
	heterogeneous equipment more or less automatically. In general, the		heterogeneous equipment. Otherwise, the process can take days.
	provisioning is a grouped activity, a few times per week an operator		Developing these tools for each new piece of equipment and each
	launches the provisioning of a set of circuits in one shot. MPLS		vendor is a significant burden on the service provider. A
	will reduce this provisioning time from a few minutes to a few		standardized interface for provisioning, such as GMPLS signaling,
	seconds and will help to transform this periodic process into a		could significantly reduce or eliminate this development burden. In
	real-time process.		general, provisioning is a batched activity, i.e., a few times per
			week an operator provisions a set of circuits. GMPLS will reduce
	Bernstein, Mannie, Sharma Expires May 2001 7		this provisioning time from a few minutes to a few seconds and could
			help to transform this periodic process into a real-time process.
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000
	When a circuit or a ring is provisioned it is not delivered directly
	to a client. First, its performance and behavior is tested by the
	operator and if this is successful, the circuit is delivered to the
	client. This testing phase lasts, in general, for up to 24 hours.
	The operator instalsl test equipment at each end and uses pre-
	defined test streams to verify the performance. If successful, the
	circuit is officially accepted by the client. Thus, to speed up this
	process, brief automated performance testing will have to be
	supported in some way.
	So, it results that most of the time that can be saved is mainly due
	to the fact that we change the work model of an operator. In
	addition, note that signaling other than MPLS can achieve the same
	result. Even an architecture based on a centralized management
	achieves the same without MPLS. The benefits of using MPLS can,
	however, be realized both with the use of a distributed architecture
	or a centralized architecture, since MPLS supports explicit routing
	(and a centralized architecture with signaling support, could
	compute the route and then use signaling to establish it). Below
	we will briefly look at both the centralized and the distributed
	approaches to circuit provisioning.
	3.4. Centralized Approach versus Distributed Approach
	The debate between a centralized approach and a distributed approach
	to control an SDH/SONET network or an optically switched network is
	still on-going. There is probably no outstanding characteristic any
	approache that will make it the universal solution. Each approach
	has advantages and disadvantages. Depending on the particular
	network to be controlled and operator requirements, either solution
	could be the right one. The application of MPLS to SONET/SDH
	networks does not preclude either model although MPLS is itself a
	distributed technology. In particular, the explicit route
	capability in MPLS combined with a "soft permanent LSP" (SPLSP) type
	functionality could fully support a centralized approach to circuit
	provisioning that would also be interoperable.
	The centralized approach is typically implemented using a Network
	Management System dynamically provisioning circuits. Although no
	signaling protocol is used, a routing protocol is used to route the
	management messages. Indeed, the management protocol acts as a
	signaling protocol. Network elements stay relatively simple and are
	not involved in decision making. CPEÆs can implement a simple
	signaling interface with the NMS, such as the one being proposed in
	the ODSI. This approach has a number of advantages in the short
	term. The typical network management model used today for TDM
	networks is TMN.
	A distributed approach consists of using one or more distributed
	routing protocols, such as IP routing protocols, and a distributed
	signaling protocol. The MPLS architecture fits very well in that
	case. This solution has the potential to be scalable and robust, and
	enable future services like inter-domain routing. Obviously, it adds
	Bernstein, Mannie, Sharma Expires May 2001 8
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000
	more complexity but this is the "price" to pay if we want to build a
	network of SDH/SONET networks, i.e. an SDH/SONET inter-network.
	A centralized approach can benefit from the management information
	that is collected constantly, e.g. performance alarms, failure
	alarms and traps. Once filtered and analyzed, this information can
	be used to detect failure in almost real-time. However, sometimes
	this approach can also be penalized if the number of management
	messages is not controlled appropriately, as we will see later.
	On the other hand, a distributed routing protocol relies mainly on
	timers and missing routing PDUs to detect a failure between two
	adjacent switching nodes. It can also use indications from the
	underlying layer, if available, but it does not communicate directly
	with some network elements, like amplifiers, and transponders, that
	could detect problems sooner.
	In addition, a NMS maintains a consistent view of all the layers,
	including the physical topology, at any time. Centralized decisions
	can be taken based on accurate information and can use physical
	information about fibers and ducts. On the other hand, a routing
	protocol builds and maintain a logical model of the network. Not all
	routing entities have the same view of the network at all times, and
	re-routing and crank-back are needed for the signaling protocol.
	A centralized management is easier to operate, new features can be
	introduced with a simple upgrade. On the contrary, updating switches
	with new routing software is harder. One could easily change the
	parameters of the constrained routing algorithm or the metrics of
	the links. These changes will take effect instantaneously. Several
	added-value tools can run in the background and easilty easily
	information with the centralized decision point. Such tools might
	be, circuit planning tools (for network optimization, diversity
	design, performance analysis), circuit reservation tools, and VPN
	tools,for example.
	Finally, this approach fits well with the current network operation
	structure. The major upgrade is a an IT upgrade at the operatorÆs
	network operations center. The DCN used to transport the management
	protocol now becomes now a critical part of the operator
	infrastructure and consequently must be protected. Its availability
	has a direct impact on the on-demand circuit provisioning. Of
	course, ideally new SDH/SONET non-blocking switching fabrics need to
	be deployed in the network. Note that this approach could have been
	supported since years with the actual SDH/SONET switching fabrics,
	if we took into consideration the limitations of these fabrics.
	The DCN used to transport management PDUs can be a mix of out-of-
	band links and in-band communication links in the SDH/SONET overhead
	(like the DCC). A routing protocol is run over these links to route
	the management PDUs. The TMN model uses CMIP as the network
	management protocol. The interface between a NE and the NMS is
	referred to as the Q3 interface and is based on the OSI model. The
	Bernstein, Mannie, Sharma Expires May 2001 9
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000
	upper part of the protocol stack at the Q3 interface is defined in		When a circuit is provisioned, it is not delivered directly to a
	Q.812. Different profiles are defined in Q.811 for the lower part,		client. Rather, the operator first tests its performance and
	they cover LAN and WAN interfaces. Note that the upper part can also		behavior and if successful, delivers the circuit to the client. This
	be supported over an IP infrastructure. In general, IS-IS is the
	network layer routing protocol that is used.
	The topology of the DCN is more complex than the topology considered		Bernstein, Mannie, Sharma Informational - January 2002 7
	for the distributed approach, since all network elements, and not		testing phase lasts, in general, for up to 24 hours. The operator
	just the switches, must be reached. In case of failures in a		installs test equipment at each end and uses pre-defined test
	SDH/SONET network, bursts of hundreds or thousands of alarms can be		streams to verify performance. If successful, the circuit is
	sent to the management system over the DCN. In that case,		officially accepted by the client. To speed up the verification
	provisioning related messages can be delayed by the treatment of the		(sometimes known as "proving") process, it would be necessary to
	alarms if no mediation function filtering and message aggregation is		support some form of automated performance testing.
	available between the NMS and NEs.
	In the case of the distributed approach, the routing protocol must		3.4. Centralized Approach versus Distributed Approach
	only abstract the physical links between the switches and the
	signaling protocol must only flow between these switches. The DCN
	used for the management of the network could be re-used, or a
	separate signaling network could be setup. Surprisingly, the
	requirements of a DCN could be much higher than the requirements for
	the distributed signaling network.
	An NMS has scalability limitations. For instance, it can be limited		Whether a centralized approach or a distributed approach will be
	in the number of network elements that can be managed (e.g. one		used to control SDH/SONET networks is an open question, since Eech
	thousand). It is quite common for operators to deploy several NMSÆs		approach has advantages and disadvantages. The application of GMPLS
	in parallel at the Network Management Layer, each managing a		to SONET/SDH networks does not preclude either model although MPLS
	different zone. In that case, a layer on the top of several		is itself a distributed technology.
	individual NMS at the Service Management Layer must be built to take
	care of end-to-end on-demand services. On the contrary, the
	scalability is much better in the distributed approach, clients are
	co-located with switches and distributed among these switches.
	An NMS can also be a bottleneck, it has already to deal with all		The basic tradeoff between the centralized and distributed
	traditional management messages; now in addition, it has to take		approaches is that of complexity of the network elements versus that
	care of reliably handling provisioning messages, and, sometimes, UNI		of the network management system (NMS). Since adding functionality
	messages as well. The load due to additional and more dynamic		to existing
	operations, such as dynamic circuit establishment and fast		SDH network elements may not be possible, a centralized approach may
	restoration is also not negligible. Indeed, the distributed approach		be needed in some cases. The main issue facing centralized control
	has the advantage of being isolated from the burden that can be		via an NMS is one of scalability. For instance, this approach may be
	placed on the NMS due to network conditions.		limited in the number of network elements that can be managed (e.g.
			one thousand). It is, therefore, quite common for operators to
			deploy several NMS’s in parallel at the Network Management Layer,
			each managing a different zone. In that case, however, a Service
			Management layer must be built on the top of several individual
			NMS’s to take care of end-to-end on-demand services. On the other
			hand, in a complex and/or dense network, restoration could be faster
			with a distributed approach than with a centralized approach.
	It could be expected that in a complex and/or dense network,		Let's now look at how the major control plane functional components
	restoration could be faster with a distributed approach than with a		are handled via the centralized and distributed approaches:
	centralized approach. In the first case, signaling messages travel
	over exactly the same path as the affected circuits and only through
	the affected. In the second case, a signaling message has to go
	first to the NMS , which transmits signaling messages (in parallel)
	to all concerned nodes. However, this comparison requires further
	investigations.
	In general , an NMS is not a single point of failure, since all		3.4.1. Topology Discovery and Resource Dissemination
	operators have systems in hot stand-by and disaster recovery plans
	Bernstein, Mannie, Sharma Expires May 2001 10		Currently NMS's maintain a consistent view of all the networking
			layers under their purview. This can include the physical topology,
			such as information about fibers and ducts. Since most of this
			information is entered manually, it remains error prone.
			A link state GMPLS routing protocol, on the other hand, could
			perform automatic topology discovery and dissemination the topology
			as well as resource status. This information would be available to
			all nodes in the network, and hence also the NMS. Hence one can
			look at a continuum of functionality between manually provisioned
			topology information (of which there will always be some) and fully
			automated discovery and dissemination as in a link state protocol.
			Note that, unlike the IP datagram case, a link state routing
			protocol applied to the SDH/SONET network does not have any service
			impacting implications.
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000		Bernstein, Mannie, Sharma Informational - January 2002 8
			3.4.2. Path Computation (Route Determination)
	for the NMS. The DCN must now be as well protected as the transport		In the SDH/SONET case, unlike the IP datagram case, there is no need
	network itself. However, the survivability of the distributed		for network elements to all perform the same path calculation. In
	approach is likely to be better since the intelligence is		addition, path determination is an area for vendors to provide a
	distributed, and could even survive to a network partitioning.		potentially significant value addition in terms of network
			efficiency, reliability, and service differentiation. In this sense,
			a centralized approach to path computation is easier to operate and
			upgrade. For example, new features such as new types of path
			diversity or new optimization algorithms can be introduced with a
			simple NMS software upgrade. On the other hand, updating switches
			with new path computation software is a more complicated task. In
			addition, many of the algorithms are quite computationally intensive
			and may be completely unsuitable for the embedded processing
			environment available on most switches. In restoration scenarios
			the ability to perform a reasonably sophisticated level of path
			computation on the network element can be particularly useful for
			restoring traffic during major network faults.
	A distributed signaling and routing approach also appears a		3.4.3. Connection Establishment (provisioning)
	reasonable solution for inter-domain operations. Having hundreds of
	NMSs organized in a tree with a root NMS that controls the various
	NMSs from different operators can be rather difficult, especially in
	the absence of adequate NMS interoperability standards. This is
	probably a significant motivation for resorting to a distributed
	approach.
	Having signaling and routing at each inter-domain interface does not		The actual setting up of circuits, i.e., a coupled collection of
	imply that we need the same inside each individual domain. However,		cross connects across a network, can be done either via the NMS
	inter-working between intra- and inter-domain operations will be		setting up individual cross connects or via a "soft permanent LSP"
	greatly facilitated if we a distributed approach is also supported		(SPLSP) type approach. In the SPLSP approach, the NMS may just kick
	internal to a domain. This is particularly true for the signaling,		off the connection at the "ingress" switch with GMPLS signaling
	using the same protocol for both intra and inter-domain operations -		setting up the connection from that point onward. Connection
	seems a sensible approach.		establishment is the trickiest part to distribute, however, since
			errors in the connection setup/tear down process are service
			impacting.
	Distributed approach Centralized approach		Distributed approach Centralized approach
	Control plane like MPLS or Management plane like TMN or		Control plane like MPLS or Management plane like TMN or
	PNNI SNMP		PNNI SNMP
	Do we really need it? Being Always needed! Already there,		Do we really need it? Being Always needed! Already there,
	added/specified by several proven and understood.		added/specified by several proven and understood.
	standardization bodies		standardization bodies
	High survivability (e.g. in Potential single point(s) of		High survivability (e.g. in Potential single point(s) of
	skipping to change at line 602 ¶		skipping to change at line 467 ¶
	PNNI SNMP		PNNI SNMP
	Do we really need it? Being Always needed! Already there,		Do we really need it? Being Always needed! Already there,
	added/specified by several proven and understood.		added/specified by several proven and understood.
	standardization bodies		standardization bodies
	High survivability (e.g. in Potential single point(s) of		High survivability (e.g. in Potential single point(s) of
	case of partition) failure		case of partition) failure
	Distributed load Bottleneck: #requests and		Distributed load Bottleneck: #requests and
	actions to/from NMS		actions to/from NMS
	Individual local routing Centralized routing decision,		Individual local routing Centralized routing decision,
	decision can be done per block of		decision can be done per block of
	requests		requests
	Routing scalable as for the Assumes a few big		Routing scalable as for the Assumes a few big
			Bernstein, Mannie, Sharma Informational - January 2002 9
	Internet administrative domains		Internet administrative domains
	Complex to change routing Very easy local upgrade (non-		Complex to change routing Very easy local upgrade (non-
	protocol/algorithm intrusive)		protocol/algorithm intrusive)
	Requires enhanced routing Better consistency		Requires enhanced routing Better consistency
	protocol (traffic		protocol (traffic
	engineering)		engineering)
	Ideal for inter-domain Not inter-domain friendly		Ideal for inter-domain Not inter-domain friendly
	Suitable for very dynamic For less dynamic demands		Suitable for very dynamic For less dynamic demands
	demands (longer lived)		demands (longer lived)
	Probably faster to restore, Probably slower to restore, but		Probably faster to restore, Probably slower to restore,but
	Bernstein, Mannie, Sharma Expires May 2001 11
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000
	but more difficult to have could effect reliable		but more difficult to have could effect reliable
	reliable restoration. restoration.		reliable restoration. restoration.
	High scalability Limited scalability: #nodes,		High scalability Limited scalability: #nodes,
	(hierarchical) links, circuits, messages		(hierarchical) links, circuits, messages
	Planning (optimization) Planning is a background		Planning (optimization) Planning is a background
	harder to achieve centralized activity		harder to achieve centralized activity
	Easier future integration		Easier future integration
	with other control plane		with other control plane
	layers		layers
	Table 1. Qualitative comparison between centralized and distributed		Table 1. Qualitative comparison between centralized and distributed
	approaches.		approaches.
	3.5 Why SDH/SONET will not Disappear Tomorrow		3.5. Why SDH/SONET will not Disappear Tomorrow
	If the IP traffic becomes the unique traffic transported over any
	transmission network, we could consider that the statistical
	multiplexing of IP would completely replace the time division
	multiplexing of SDH and SONET. In that case, IP over WDM will be
	used everywhere and lambdas could be optically switched. A carrier's
	carrier will sell dynamically controlled lambdas with each customer
	building its own IP backbone over these lambdas.
	This simple model implies that a carrier will sell lambdas instead
	of bandwidth. The carrier will try to maximize the number of lambdas
	per fiber and each customer will have to fully support the cost for
	each of his end-to-end lambdas. Inthe near future, we may have
	technology to support several hundreds of lambdas per fiber.
	However, a world where lambdas are so cheap and abundant that every
	customer can buy them, from one point to any other point, appears an
	unlikely scenario today.
	More realistically, there is still room for a multiplexing
	technology that provides circuits with a lower granularity than a
	wavelength. Not everyone needs a minimum of 10 Gbps or 40 Gbps per
	circuit, and IP does not yet support all the telecom applications
	(e.g. telephony).
	SDH and SONET possess a rich multiplexing hierarchy that permits a
	finer granularity and provides a very cheap and simple physical
	separation of the transported traffic between circuits. We can
	easily multiplex any kind of traffic, IP or not, synchronous or
	asynchronous.
	Moreover, IP is not used directly over a wavelength, a framing or		As IP traffic becomes the dominant traffic transported over the
	encapsulation is always required to delimit IP datagrams. The Total		transport infrastructure, it is useful to compare the statistical
	Length field of an IP header cannot be trusted to find the start of		multiplexing of IP with the time division multiplexing of SDH and
	a new datagram, since it could be corrupted and would result in a		SONET.
	loss of synchronization. The typical framing used today for IP over
	DWDM is defined in RFC1619/RFC2615 and is also known as POS (Packet
	Bernstein, Mannie, Sharma Expires May 2001 12		Consider a scenario where IP over WDM is used everywhere and lambdas
			are optically switched. In such a case, a carrier's carrier would
			sell dynamically controlled lambdas with each customer building
			his/her own IP backbone over these lambdas.
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000		This simple model implies that a carrier would sell lambdas instead
			of bandwidth. The carrier’s goal will be to maximize the number of
			wavelengths/lambdas per fiber, with each customer having to fully
			support the cost for each end-to-end lambda whether or not the
			wavelength is fully utilized. Although, inn the near future, we may
			have technology to support up to several hundred lambdas per fiber,
			a world where lambdas are so cheap and abundant that every
			individual customer buys them, from one point to any other point,
			appears an unlikely scenario today.
	Over SONET/SDH). It is indeed IP over PPP (in HDLC like format) over		Bernstein, Mannie, Sharma Informational - January 2002 10
	SDH/SONET.		More realistically, there is stillroom for a multiplexing technology
			that provides circuits with a lower granularity than a wavelength.
			(Not everyone needs a minimum of 10 Gbps or 40 Gbps per circuit, and
			IP does not yet support all telecom applications in bulk
			efficiently.)
	SDH and SONET are actually efficient encapsulations for IP. For		SDH and SONET possess a rich multiplexing hierarchy that permits
	instance, with an average IP datagram length of 350 octets, an IP		fairly fine granularity and that provides a very cheap and simple
	over GBE encapsulation using an 8B/10B encoding results in 28%		physical separation of the transported traffic between circuits,
	overhead, an IP/ATM/SDH encapsulation results in 22% overhead and an		i.e., QoS.
	IP/PPP/SDH encapsulation result in 6% overhead. New simplified		Moreover, even IP datagrams are not transported directly over a
	encapsulations could reduce this overhead to as low as 3%, but the		wavelength. A framing or encapsulation is always required to delimit
	gain is not huge compared to SDH and SONET -, which have other		IP datagrams. The Total Length field of an IP header cannot be
	benefits as well.		trusted to find the start of a new datagram, since it could be
			corrupted and would result in a loss of synchronization. The typical
			framing used today for IP over DWDM is defined in RFC1619/RFC2615
			and known as POS (Packet Over SONET/SDH), i.e., IP over PPP (in
			HDLC-like format) over SDH/SONET. SDH and SONET are actually
			efficient encapsulations for IP. For instance, with an average IP
			datagram length of 350 octets, an IP over GBE encapsulation using an
			8B/10B encoding results in 28% overhead, an IP/ATM/SDH encapsulation
			results in 22% overhead and an IP/PPP/SDH encapsulation results in
			only 6% overhead. (New simplified encapsulations could reduce this
			overhead to as low as 3%, but the gain is not huge compared to SDH
			and SONET -, which have other benefits as well.)
	Any encapsulation of IP over WDM should at least provide error		Any encapsulation of IP over WDM should at least provide error
	monitoring capabilities (to detect signal degradation), error		monitoring capabilities (to detect signal degradation), error
	correction capabilities, such as FEC (Forward Error Correction) that		correction capabilities, such as FEC (Forward Error Correction) that
	are particularly needed for ultra long hau transmission, sufficient		are particularly needed for ultra long haul transmission, sufficient
	timing information, to allow robust synchronization (that is, to		timing information, to allow robust synchronization (that is, to
	detect the beginning of a packet), and capacity to transport		detect the beginning of a packet), and capacity to transport
	signaling, routing and management messages, in order to control the		signaling, routing and management messages, in order to control the
	optical switches. SDH and SONET cover all these aspects natively,		optical switches. SDH and SONET cover all these aspects natively,
	except FECs that can be (are) supported in a proprietary way.		except FEC, which tends to be supported in a proprietary way.
	Since the SDH/SONET encapsulation is a good candidate and is anyway		Since IP encapsulated in SDH/SONET is efficient and widely used, the
	used, the only real difference between an IP over WDM network and an		only real difference between an IP over WDM network and an IP over
	IP over SDH over WDM network is the layers at which the switching or		SDH over WDM network is the layers at which the switching or
	forwarding can take place. In the first case, it can take place at		forwarding can take place. In the first case, it can take place at
	the IP and optical layers. In the second case, it can take place at		the IP and optical layers. In the second case, it can take place at
	the IP, SDH/SONET and optical layers. What we are arguing here is		the IP, SDH/SONET, and optical layers.
	that it makes sense to do switching or forwarding at all these		Almost all transmission networks today are based on SDH or SONET. A
	layers.
	Almost all transmission networks today are based on SDH or SONET. A
	client is connected either directly through an SDH or SONET		client is connected either directly through an SDH or SONET
	interface or through a PDH interface, the PDH signal being		interface or through a PDH interface, the PDH signal being
	transported between the ingress and the egress interfaces over SDH		transported between the ingress and the egress interfaces over SDH
	or SONET. The SDH and SONET technologies are widespread, very well		or SONET. What we are arguing here is that it makes sense to do
	understood		switching or forwarding at all these layers.
	4. MPLS Applied to SDH/SONET
	4.1. Controlling the SDH/SONET Multiplex
	Different parts of the SDH/SONET multiplex can be switched, and we		4. GMPLS Applied to SDH/SONET
	have to decide which of these we would like to control through MPLS.
	Basically, every SDH/SONET element that is referenced by a pointer
	can be switched, through pointer adjustment. These elements are the
	VC-4, VC-3s, VC-2s, VC-12s and VC-11s in the SDH case; and the SPEs
	in the SONET case. The SONET case is more difficult to explain
	since, unlike in SDH, SPEs in SONETdo not have individual names.
	We will refer to them by identifying the structure that contains
	them, namely the STS-1, VT-6s, VT-3s, VT-2s and VT-1.5s.
	Bernstein, Mannie, Sharma Expires May 2001 13		Bernstein, Mannie, Sharma Informational - January 2002 11
			4.1. Controlling the SDH/SONET Multiplex
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000		Controlling the SDH/SONET multiplex implies deciding which of the
			different components of the SDH/SONET multiplex that can be switched
			do we wish to control using GMPLSEssentially, every SDH/SONET
			element that is referenced by a pointer can be switched. These
			component signals are the VC-4, VC-3, VC-2, VC-12 and VC-11 in the
			SDH case; and the VT and STS SPEs in the SONET case. The SONET case
			is a bit difficult to explain since, unlike in SDH, SPEs in SONET do
			not have individual names. We will refer to them by identifying the
			structure that contains them, namely the STS-1, VT-6, VT-3, VT-2 and
			VT-1.5.
	The STS-1 SPE corresponds to a VC-3, a VT-6 SPE corresponds to a VC-		The STS-1 SPE corresponds to a VC-3, a VT-6 SPE corresponds to a VC-
	2, a VT-2 SPE corresponds to a VC-12, and a VT-1.5 SPE corresponds		2, a VT-2 SPE corresponds to a VC-12, and a VT-1.5 SPE corresponds
	to a VC-11. The SONET VT-3 SPE has no correspondence in SDH, and the		to a VC-11. The SONET VT-3 SPE has no correspondence in SDH, however
	SDH VC-4 has no correspondence in SONET. A continuous flow of one of		SDH's VC-4 corresponds to SONET's STS-3c SPE.
	such elements constitutes an SDH or SONET signal.
	In addition, it is possible to concatenate some of the structures		In addition, it is possible to concatenate some of the structures
	that contain these elements to build bigger elements. For instance,		that contain these elements to build larger elements. For instance,
	SDH allows the concatenation of X contiguous AU-4s to build a VC-4-		SDH allows the concatenation of X contiguous AU-4s to build a VC-4-
	Xc and of m contiguous TU-2s to build a VC-2-mc. In that case, a VC-		Xc and of m contiguous TU-2s to build a VC-2-mc. In that case, a VC-
	4-Xc or a VC-2-mc can be switched and controlled by MPLS. Note that		4-Xc or a VC-2-mc can be switched and controlled by MPLS. Note that
	SDH defines also the virtual (non-contiguous) concatenation of TU-		SDH also defines virtual (non-contiguous) concatenation of TU- 2s,
	2s, but in that case each constituent VC-2 is switched individually.		but in that case each constituent VC-2 is switched individually.
	4.2. SDH/SONET LSR and LSP Terminology		4.2. SDH/SONET LSR and LSP Terminology
	Let a SDH or SONET Terminal Multiplexer (TM), Add-Drop Multiplexer		Let a SDH or SONET Terminal Multiplexer (TM), Add-Drop Multiplexer
	(ADM) or cross-connect (i.e. a switch) be called an SDH/SONET LSR. A		(ADM) or cross-connect (i.e. a switch) be called an SDH/SONET LSR. A
	SDH/SONET path or circuit between two SDH/SONET LSRs now becomes an		SDH/SONET path or circuit between two SDH/SONET LSRs now becomes a
	MPLS LSP. An SDH/SONET LSP is a logical connection between the point		GMPLS LSP. An SDH/SONET LSP is a logical connection between the
	at which a tributary signal (client layer) is assembled into its		point at which a tributary signal (client layer) is adapted into its
	virtual container, and the point at which it is disassembled from		virtual container, and the point at which it is extracted from its
	the virtual container. The position taken r by a tributary signal in		virtual container.
	a virtual container will be referred to as an SDH/SONET signal.
	To establish such an LSP, a signaling protocol is required to		To establish such an LSP, a signaling protocol is required to
	configure the input interface, switch fabric, and output interface		configure the input interface, switch fabric, and output interface
	of each SDH/SONET LSR along the path. An SDH/SONET LSP can be point-		of each SDH/SONET LSR along the path. An SDH/SONET LSP can be point-
	to-point or point-to-multipoint, but not multipoint-to-point, since		to-point or point-to-multipoint, but not multipoint-to-point, since
	no merging capability is possible.		no merging is possible with SDH/SONET signals.
	To facilitate the signaling and setup of SDH/SONET circuits, an		To facilitate the signaling and setup of SDH/SONET circuits, an
	SDH/SONET LSR, therefore, must identify each possible signal		SDH/SONET LSRmust, therefore, identify each possible signal
	individually per interface, since each signal corresponds to a		individually per interface, since each signal corresponds to a
	potential LSP that can be established through the SDH/SONET LSR. It		potential LSP that can be established through the SDH/SONET LSR. It
	turns out, however, that not all signals correspond to an LSPs and		turns out, however, that not all SDH signals correspond to an LSP
	therefore not all of them need be identified. In fact, only those		and therefore not all of them need be identified. In fact, only
	signals that can be switched need identification.		those signals that can be switched need identification.
	5. Decomposition of the MPLS Circuit-Switching Problem Space		5. Decomposition of the MPLS Circuit-Switching Problem Space
			Bernstein, Mannie, Sharma Informational - January 2002 12
	Although those familiar with MPLS may be familiar with its		Although those familiar with MPLS may be familiar with its
	application in a variety of application areas, e.g., ATM, Frame		application in a variety of application areas, e.g., ATM, Frame
	Relay, etc. we quickly review its decomposition when applied to the		Relay, and so on, here we quickly review its decomposition when
	optical switching problem space.		applied to the optical switching problem space.
	(i) Information needed to compute paths must be made globally		(i) Information needed to compute paths must be made globally
	available throughout the network. Since this is done via the link		available throughout the network. Since this is done via the link
	state route protocol, any information of this nature must either be		state routing protocol, any information of this nature must either
	in the existing link state advertisements (LSAs) or the LSAs must be		be in the existing link state advertisements (LSAs) or the LSAs must
	supplemented to convey this information. For example, if its		be supplemented to convey this information. For example, if it is
	desirable to offer different levels of service in a network based on		desirable to offer different levels of service in a network based on
	whether a circuit is routed over SDH/SONET lines that are ring		whether a circuit is routed over SDH/SONET lines that are ring
			protected versus being routed over those that are not ring protected
	Bernstein, Mannie, Sharma Expires May 2001 14		(differentiation based on reliability), the type of protection on
			a SDH/SONET line would be an important topological parameter that
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000		would have to be distributed via the link state routing protocol.
	protected versus not being protected (differentiation based on
	reliability), the type of protection on a SDH/SONET line would be
	an important topological parameter that should be distributed via
	the link state route protocol..
	(ii) Information that is only needed between two "adjacent" switches		(ii) Information that is only needed between two "adjacent" switches
	for the purposes of connection establishment is appropriate for		for the purposes of connection establishment is appropriate for
	distribution via one of the label distribution protocols. In fact		distribution via one of the label distribution protocols. In fact,
	this information may form the "virtual" label. For example in SONET		this information can be thought of as the "virtual" label. For
	if we are distributing information to switches concerning an end-to-		example, in SONET networks, when distributing information to
	end STS-1 path traversing a network, it is critical that adjacent		switches concerning an end-to-end STS-1 path traversing a network,
	switches agree on the multiplex entry used by this STS-1 (but this		it is critical that adjacent switches agree on the multiplex entry
	information is only of local significance between the two switches).		used by this STS-1 (but this information is only of local
	Hence, the multiplex entry number in this case can be used as a		significance between those two switches). Hence, the multiplex
	virtual label. Note that it is virtual in that it is not appended to		entry number in this case can be used as a virtual label. Note
	the payload in any way, but it is still a label in the sense that it		that the label is virtual in that it is not appended to the payload
	uniquely identifies the signal local to the link between the two		in any way, but it is still a label in the sense that it uniquely
	switches.		identifies the signal locally on the link between the two switches.
	(iii) Information that all switches in the path will need to know		(iii) Information that all switches in the path need to know about a
	about a circuit will also be distributed via the label distribution		circuit will also be distributed via the label distribution
	protocol. Example of such information can include bandwidth,		protocol. Examples of such information include bandwidth, priority,
	priority, and preemption information.		and preemption for instance.
	(iv) Information intended only for end systems of the connection.		(iv) Information intended only for end systems of the connection.
	Some of the payload type information in may fall into this category.		Some of the payload type information in may fall into this category.
	[8],[10].		[8],[10].
	6. MPLS Routing for SDH/SONET		6. MPLS Routing for SDH/SONET
	Modern transport networks based on SONET/SDH excel at		Modern transport networks based on SONET/SDH excel at
	interoperability in the performance monitoring (PM) and fault		interoperability in the performance monitoring (PM) and fault
	management (FM) areas, however, they do not inter-operate in the		management (FM) areas., They do not, however, inter-operate in the
	areas of topology discovery or resource status. Although link state		areas of topology discovery or resource status. Although link state
	route protocols, such as IS-IS and OSPF, have been used for some		routing protocols, such as IS-IS and OSPF, have been used for some
	time in the IP world to compute destination-based next hops for		time in the IP world to compute destination-based next hops for
	routes (without routing loops), their value in providing timely		routes (without routing loops), their value in providing timely
	topology and network status information in a distributed manner,		topology and network status information in a distributed manner,
	i.e., at any network node, is immense. If resource utilization		i.e., at any network node, is immense. If resource utilization
	information is disseminated along with the link status (as was done		information is disseminated along with the link status (as was done
	in ATM's PNNI routing protocol) then a very complete picture of		in ATM's PNNI routing protocol) then a very complete picture of
			Bernstein, Mannie, Sharma Informational - January 2002 13
	network status is available to a network operator for use in		network status is available to a network operator for use in
	planning, provisioning and operations.		planning, provisioning and operations.
	Information needed to compute the path a connection will take		The information needed to compute the path a connection will take
	through a network is important to distribute via the routing		through a network is important to distribute via the routing
	protocol. In the optical TDM case this information includes, but is		protocol. In the optical TDM case, this information includes, but
	not limited to: the available capacity of the network links, the		is not limited to: the available capacity of the network links, the
	switching and termination capabilities of the nodes and interfaces,		switching and termination capabilities of the nodes and interfaces,
	and the protection properties of the link.		and the protection properties of the link.
	When applying routing to circuit switched situations it is useful to		When applying routing to circuit switched networks it is useful to
	compare and contrast this situation with the datagram routing case.		compare and contrast this situation with the datagram routing case.
			In the case of routing datagrams all routes on all nodes must be
	Bernstein, Mannie, Sharma Expires May 2001 15		calculated exactly the same to avoid loops and "black holes". In
			circuit switching, this is not the case since routes are established
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000
	In the case of routing for datagrams all routes on all nodes must be
	calculated exactly the same to avoid loops and "blackholes". In the
	circuit switching, this is not the case since routes are establish
	per circuit and are fixed for that circuit. Hence, unlike the		per circuit and are fixed for that circuit. Hence, unlike the
	datagram case, routing is not service impacting in the circuit		datagram case, routing is not service impacting in the circuit
	switched case. This is helpful, since to accommodate the optical		switched case. This is helpful, because to accommodate the optical
	layer new information must be supplemented to the routing protocols,		layer routing protocols need to be supplemented with new
	much more than the datagram case. This information will also be used		information, much more than the datagram case. This information is
	in different ways for implementing different user services. Due to		also likely to be used in different ways for implementing different
	the increase in information transferred in the route protocol it is		user services. Due to the increase in information transferred in
	important to separate the relatively static parameters concerning a		the routing protocol, it is important to separate the relatively
	link with those that may be subject to frequent changes. This is		static parameters concerning a link from those that may be subject
	particularly important in the case of available capacity		to frequent changes. This is particularly important in the case of
	advertisements.		available capacity advertisements.
	6.1. Switching Capabilities		6.1. Switching Capabilities
	The main switching capabilities that characterize a SONET/SDH end		The main switching capabilities that characterize a SONET/SDH end
	system and thus get advertised into the link state route protocol		system and thus need to be advertised via the link state routing
	are: the switching granularity, supported forms of concatenation,		protocol are: the switching granularity, supported forms of
	and the level of transparency.		concatenation, and the level of transparency.
	6.1.1. Switching Granularity		6.1.1. Switching Granularity
	From Error! Reference source not found. and the overview section on		From references [3], [4]and the overview section on SONET/SDH we see
	SONET/SDH there are a number of different signals that compose the		that there are a number of different signals that compose the
	SONET/SDH hierarchies. Those signals that are referenced via a		SONET/SDH hierarchies. Those signals that are referenced via a
	pointer, i.e., the VCs in SDH and the SPEs in SONET are those that		pointer, i.e., the VCs in SDH and the SPEs in SONET are those that
	will actually be switched within a SONET/SDH network. These signals		will actually be switched within a SONET/SDH network. These signals
	are subdivided into lower order signals and higher order signals as		are subdivided into lower order signals and higher order signals as
	shown in Table 2.		shown in Table 2.
	Table 2. SDH/SONET switched signal groupings.		Table 2. SDH/SONET switched signal groupings.
	Signal Type SDH SONET		Signal Type SDH SONET
	Lower Order VC-11, VC-12, VC-2 VT-1.5 SPE, VT-2 SPE,
	VT-3 SPE, VT-6 SPE
	Higher VC-3, VC-4 STS-1 SPE
	Order
	Many manufacturers today switch signals starting at VC-4 for SDH or		Lower Order VC-11, VC-12, VC-2 VT-1.5 SPE, VT-2 SPE,
	STS-1 for SONET (i.e. the basic frame) and above (see concatenation		VT-3 SPE, VT-6 SPE
	section), but they don't allow to switch lower order signals. Some
	of them allow only to switch aggregates (concatenated or not) of
	signals such as 16 VC-4s, i.e. a complete STM-16, and nothing below.
	Some manufacturers go down to the VC-3 for SDH. Finally, some
	manufacturers allow to go lower than the VC-3/STS-1, down to lower
	order signals such as VC-12s. Some combinations are also possible,
	such as down to VC-12 for unprotected circuits and nothing below VC-
	4 for fast restoration.
	Bernstein, Mannie, Sharma Expires May 2001 16		Higher VC-3, VC-4 STS-1 SPE
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000		Bernstein, Mannie, Sharma Informational - January 2002 14
			Order
	We can see that very different granularities can be considered.		Manufacturers today differ in the types of switching capabilities
	These granularities can even vary between services. In order to		their systems support. Many manufacturers today switch signals
	cover the needs of all manufacturers and operators, we don't limit		starting at VC-4 for SDH or STS-1 for SONET (i.e. the basic
	the scope of our work to higher order signals and we consider that		frame) and above (see concatenation section), but they do not
	we have to design a solution able to control the complete SDH/SONET		switch lower order signals. Some of them only allow the switching
	multiplex. Of course, one could just use it to control the higher		of entire aggregates (concatenated or not) of signals such as 16 VC-
	order signals.		4s, i.e. a complete STM-16, and nothing finer. Some go down to the
			VC-3 level for SDH. Finally, some offer highly integrated switches
			that switch at the VC-3/STS-1 level down to lower order signals such
			as VC-12s. In order to cover the needs of all manufacturers and
			operators, GMPLS must consider both higher order and lower order
			signals.
	6.1.2. Signal Concatenation Capabilities		6.1.2. Signal Concatenation Capabilities
	As stated in the SONET/SDH overview, to transport tributary signals		As stated in the SONET/SDH overview, to transport tributary signals
	in excess of the basic STM-1/STS-1 signal, the VCs/SPEs can be		with rates in excess of the basic STM-1/STS-1 signal, the VCs/SPEs
	concatenated, i.e., glued together. Different types of		can be concatenated, i.e., glued together. Different types of
	concatenations are defined: contiguious standard concatenation,		concatenations are defined: contiguous standard concatenation,
	arbitrary contiguous concatenation, and virtual concatenation with		arbitrary concatenation, and virtual concatenation with different
	different rules concerning their size, placement, and binding.		rules concerning their size, placement, and binding.
	Standard SONET concatenation allows the concatenation of M x STS-1		Standard SONET concatenation allows the concatenation of M x STS-1
	signals within an STS-N signal with M <= N, and M = 3, 12, 48,		signals within an STS-N signal with M <= N, and M = 3, 12, 48,
	192,...). The SPEs of these M x STS-1s can be concatenated to form		192,...). The SPEs of these M x STS-1s can be concatenated to form
	an STS-Mc. The STS-Mc notation is short hand for describing an STS-M		an STS-Mc. The STS-Mc notation is short hand for describing an STS-M
	signal whose SPEs have been concatenated. The multiplexing		signal whose SPEs have been concatenated. The multiplexing
	procedures for SONET and SDH are given in references [3], [4], [5],		procedures for SONET and SDH are given in references [3]and [4].
	Constraints are imposed on the size of STS-Mc signals, i.e., they		Constraints are imposed on the size of STS-Mc signals, i.e., they
	must be a multiple of 3, and on their starting location and		must be a multiple of 3, and on their starting location and
	interleaving. This has the following advantages: (a) restriction to		interleaving.
	multiples of 3 helps with SDH compatibility (there is no STS-1
	equivalent signal in SDH); (b) the restriction to multiples of 3		This has the following advantages: (a) restriction to multiples of 3
	reduces the number of connection types; (c) the restriction on the		helps with SDH compatibility (there is no STS-1 equivalent signal in
	placement and interleaving could allow more compact representation		SDH); (b) the restriction to multiples of 3 reduces the number of
	of the "label"; The major disadvantages of these restrictions are:		connection types; (c) the restriction on the placement and
			interleaving could allow more compact representation of the "label";
			The major disadvantages of these restrictions are:
	(a) Limited flexibility in bandwidth assignment (somewhat inhibits		(a) Limited flexibility in bandwidth assignment (somewhat inhibits
	finer grained traffic engineering). (b) The lack of flexibility in		finer grained traffic engineering). (b) The lack of flexibility in
	starting time slots for STS-Mc signals and in their interleaving		starting time slots for STS-Mc signals and in their interleaving
	(where the rest of the signal gets put in terms of STS-1 slot		(where the rest of the signal gets put in terms of STS-1 slot
	numbers) leads to the requirement for re-grooming (due to bandwidth		numbers) leads to the requirement for re-grooming (due to bandwidth
	fragmentation).		fragmentation).
	Due to these disadvantages some SONET framer manufacturers now		Due to these disadvantages some SONET framer manufacturers now
	support "flexible" or arbitrary concatenation, i.e., no		support "flexible" or arbitrary concatenation, i.e., no restrictions
	restrictions on the size of an STS-Mc (as long as M <= N) and no		on the size of an STS-Mc (as long as M <= N) and no constraints on
	constraints on the STS-1 timeslots used to convey it, i.e., the		the STS-1 timeslots used to convey it, i.e., the signals can use any
	signals can use any combination of available time slots.		combination of available time slots.
			Bernstein, Mannie, Sharma Informational - January 2002 15
	Standard and flexible concatenations are network services, while		Standard and flexible concatenations are network services, while
	virtual concatenation is a SONET/SDH end system service recently		virtual concatenation is a SONET/SDH end-system service recently
	approved by the committee T1 of ANSI and ITU-T. The essence of this		approved by the committee T1 of ANSI and ITU-T. The essence of this
	service is to have SONET/SDH end systems "glue" together the VCs or		service is to have SONET/SDH end systems "glue" together the VCs or
	SPEs of separate signals rather than the signals being carried		SPEs of separate signals rather than requiring that he signals be
	through the network as a single unit. In one example of virtual		carried through the network as a single unit. In one example of
	concatenation two end systems supporting this feature could		virtual concatenation, two end systems supporting this feature could
	essentially "inverse multiplex" two STS-1s into a virtual STS-2c for		essentially "inverse multiplex" two STS-1s into a virtual STS-2c for
	Bernstein, Mannie, Sharma Expires May 2001 17
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000
	the efficient transport of 100Mbps Ethernet traffic. Note that this		the efficient transport of 100Mbps Ethernet traffic. Note that this
	inverse multiplexing process can be significantly easier with		inverse multiplexing process can be significantly easier to
	SONET/SDH signals rather than for packets. Virtual concatenation,		implement with SONET/SDH signals rather than packets. Since virtual
	being provided by end systems, is compatible with existing SONET/SDH		concatenationis provided by end systems, it is compatible with
	networks. Virtual concatenation is defined for higher order signals		existing SONET/SDH networks. Virtual concatenation is defined for
	and low order signals. Table 3 shows the nomenclature and capacity		both higher order signals and low order signals. Table 3 shows the
	for several low order virtually concatenated signals contained in		nomenclature and capacity for several lower-order virtually
	different higher order signals.		concatenated signals contained within different higher-order
			signals.
	Table 3 Capacity of Virtually Concatenated VTn-Xv ( 9/G.707)		Table 3 Capacity of Virtually Concatenated VTn-Xv ( 9/G.707)
	Carried In X Capacity In steps		Carried In X Capacity In steps
	of		of
	VT1.5/V STS-1/VC-3 1 to 28 1600kbit/s to 1600kbit/s		VT1.5/ STS-1/VC-3 1 to 28 1600kbit/s to 1600kbit/s
	C-11-Xv 44800kbit/s		VC-11-Xv 44800kbit/s
	VT2/VC- STS-1/VC-3 1 to 21 2176kbit/s to 2176kbit/s		VT2/ STS-1/VC-3 1 to 21 2176kbit/s to 2176kbit/s
	12-Xv 45696kbit/s		VC-12-Xv 45696kbit/s
	VT1.5/V STS-3c/VC-4 1 to 64 1600kbit/s to 1600kbit/s		VT1.5/ STS-3c/VC-4 1 to 64 1600kbit/s to 1600kbit/s
	C-11-Xv 102400kbit/s		VC-11-Xv 102400kbit/s
	VT2/VC- STS-3c/VC-4 1 to 63 2176kbit/s to 2176kbit/s		VT2/ STS-3c/VC-4 1 to 63 2176kbit/s to 2176kbit/s
	12-Xv 137088kbit/s		VC-12-Xv 137088kbit/s
	6.1.3. SDH/SONET Transparency		6.1.3. SDH/SONET Transparency
	The purposed of SONET/SDH is to carry its payload signals in a		The purposed of SONET/SDH is to carry its payload signals in a
	transparent manner. This can include some of the layers of SONET		transparent manner. This can include some of the layers of SONET
	itself, i.e., the path overhead can never be touched since it		itself. For example, situations where the path overhead can never be
	actually belongs to the client. This was another reason is why we		touched, since it actually belongs to the client. This was another
	didnÆt want to code any explicit label in SDH/SONET path overhead.		reason for not coding an explicit label in SDH/SONET path overhead.
	It may be useful to transport, multiplex and/or switch lower layers		It may be useful to transport, multiplex and/or switch lower layers
	of the SONET signal transparently.		of the SONET signal transparently.
	As mentioned in the introduction SONET overhead is broken into three		As mentioned in the introduction, SONET overhead is broken into
	layers: Section, Line and Path. All these layers are concerned with		three layers: Section, Line and Path. Each of these layers is
	fault and performance monitoring. Section overhead is primarily		concerned with fault and performance monitoring. The Section
	concerned with framing and Line overhead is primarily concerned with		overhead is primarily concerned with framing, while the Line
	multiplexing and protection. To perform multiplexing, a SONET		overhead is primarily concerned with multiplexing and protection.
	network element should be line terminating. However, not all SONET		To perform multiplexing, a SONET network element should be line
	multiplexers/switches perform SONET pointer adjustments on all the		terminating. However, not all SONET multiplexers/switches perform
	STS-1s contained within them or if they perform the pointer
	adjustments they do not terminate the line overhead. For example, a
	multiplexer may take four SONET STS-48 signals and multiplex them
	onto an STS-192 without performing standard line pointer adjustments
	on the individual STS-1s. This can be looked at as a service since
	it may be desirable to pass SONET signals, like an STS-12 or STS-48,
	with some level of transparency through a network and still take
	advantage of TDM. Transparent multiplexing and switching can also
	be viewed as a constraint, since some multiplexers and switches may
	Bernstein, Mannie, Sharma Expires May 2001 18
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000
	not switch at as fine a granularity as others. Table 4 summarizes		Bernstein, Mannie, Sharma Informational - January 2002 16
	the levels of SONET/SDH transparency.		SONET pointer adjustments on all the STS-1s contained within a
			higher order SONET signal passing through them. Alternatively, if
			they perform pointer adjustments, they do not terminate the line
			overhead. For example, a multiplexer may take four SONET STS-48
			signals and multiplex them onto an STS-192 without performing
			standard line pointer adjustments on the individual STS-1s. This
			can be looked at as a service since it may be desirable to pass
			SONET signals, like an STS-12 or STS-48, with some level of
			transparency through a network and still take advantage of TDM
			technology. Transparent multiplexing and switching can also be
			viewed as a constraint, since some multiplexers and switches may not
			switch with as fine a granularity as others. Table 4 summarizes the
			levels of SONET/SDH transparency.
	Table 4. SONET/SDH transparency types and their properties.		Table 4. SONET/SDH transparency types and their properties.
	Transparency Type Comments		Transparency Type Comments
	Path Layer (or Line Standard higher order SONET path		Path Layer (or Line Standard higher order SONET path
	Terminating) switching. Line overhead is terminated or		Terminating) switching. Line overhead is terminated
	modified.		or modified.
	Line Level (or Section Preserves line overhead and switches the		Line Level (or Section Preserves line overhead and switches
	Terminating) entire line multiplex as a whole. Section		Terminating) the entire line multiplex as a whole.
	overhead is terminated or modified.		Section overhead is terminated or
			modified.
	Section layer Preserves all section overhead, basically		Section layer Preserves all section overhead,
	does not touch any of the SONET/SDH bits.		Basically does not touch any of the
			SONET/SDH bits.
	6.2. Protection		6.2. Protection
	SONET and SDH networks offer a variety of protection options at both		SONET and SDH networks offer a variety of protection options at both
	the SONET line and SONET path level. Standardized SONET line level		the SONET line (SDH multiplex section) and SONET/SDH path
	protection techniques include Linear 1+1 and Linear 1:N automatic		level[5][6]. Standardized SONET line level protection techniques
	protection switching (APS) and both two-fiber and four-fiber bi-		include Linear 1+1 and Linear 1:N automatic protection switching
	directional line switched rings (BLSRs). At the path layer, SONET		(APS) and both two-fiber and four-fiber bi-directional line switched
	offers uni-directional path switched ring protection. Both ring and		rings (BLSRs). At the path layer, SONET offers uni-directional path
	1:N line protection also allow for "extra traffic" to be carried		switched ring protection. Both ring and 1:N line protection also
	over the protection line when that line is not being used, i.e.,		allow for "extra traffic" to be carried over the protection line
	when it is not carrying traffic for a failed working line. These		when that line is not being used, i.e., when it is not carrying
	protection methods are summarized in Table 5. It should be noted		traffic for a failed working line. These protection methods are
	that these protection methods are completely separate of any MPLS		summarized in Table 5. It should be noted that these protection
	layer protection or restoration mechanisms.		methods are completely separate from any MPLS layer protection or
			restoration mechanisms.
	Table 5. Common SONET/SDH protection mechanisms.		Table 5. Common SONET/SDH protection mechanisms.
	Protection Type Extra Comments		Protection Type Extra Comments
	Traffic		Traffic
	Optionally		Optionally
			Bernstein, Mannie, Sharma Informational - January 2002 17
	Supported		Supported
	1+1 No Requires no coordination		1+1 No Requires no coordination
	Unidirectional between the two ends of the		Unidirectional between the two ends of the
	circuit. Dedicated		circuit. Dedicated
	protection line.		protection line.
	1+1 Bi- No Coordination via K byte		1+1 Bi- No Coordination via K byte
	directional protocol. Lines must be		directional protocol. Lines must be
	consistently configured.		consistently configured.
	Dedicated protection line.		Dedicated protection line.
	1:1 Yes Dedicated protection.		1:1 Yes Dedicated protection.
	1:N Yes One Protection line shared		1:N Yes One Protection line shared
			by N working lines.
	Bernstein, Mannie, Sharma Expires May 2001 19
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000
	by N working lines. N @
	1
	4
	4F-BLSR (4 Yes Dedicated protection, with		4F-BLSR (4 Yes Dedicated protection, with
	fiber bi- alternative ring path.		fiber bi- alternative ring path.
	directional		directional
	line switched		line switched
	ring)		ring)
	2F-BLSR (2 Yes Dedicated protection, with		2F-BLSR (2 Yes Dedicated protection, with
	fiber bi- alternative ring path		fiber bi- alternative ring path
	directional		directional
	line switched		line switched
	ring)		ring)
	UPSR (uni- No Dedicated protection via		UPSR (uni- No Dedicated protection via
	directional alternative ring path.		directional alternative ring path.
	path switched Typically used in access		path switched Typically used in access
	ring) networks.		ring) networks.
	It may be desirable to route some connections over lines that		It may be desirable to route some connections over lines that
	support protection of a given type, while others may be routed over		support protection of a given type, while others may be routed over
	unprotected lines, or as "extra data" over protection lines. Also to		unprotected lines, or as "extra traffic" over protection lines.
	assist in the configuration of these various protection methods it		Also, to assist in the configuration of these various protection
	can be extremely valuable to advertise the link protection		methods it can be extremely valuable to advertise the link
	attributes in the route protocol. For example suppose that a 1:N		protection attributes in the routing protocol. For example suppose
	protection group is being configured via two nodes. One must make		that a 1:N protection group is being configured via two nodes. One
	sure that the lines are "numbered the same" with respect to both end		must make sure that the lines are "numbered the same" with respect
	of the connection or else the APS (K1/K2 byte) protocol will not		to both ends of the connection or else the APS (K1/K2 byte) protocol
	correctly operate.		will not correctly operate.
	Table 6. Parameters defining protection mechanisms.		Table 6. Parameters defining protection mechanisms.
	Protection Comments		Protection Comments
	Related Link		Related Link
			Bernstein, Mannie, Sharma Informational - January 2002 18
	Information		Information
	Protection Type Indicates which of the protection types		Protection Type Indicates which of the protection types
	delineated in Table 5.		delineated in Table 5.
	Protection Indicates which of several protection		Protection Indicates which of several protection
	Group Id groups (linear or ring) that a node belongs		Group Id groups (linear or ring) that a node belongs
	to. Must be unique for all groups that a		to. Must be unique for all groups that a
	node participates in		node participates in
	Working line Important in 1:N case and to differentiate		Working line Important in 1:N case and to differentiate
	number between working and protection lines		number between working and protection lines
	Protection line Used to indicate if the line is a		Protection line Used to indicate if the line is a
	number protection line.		number protection line.
	Extra Traffic Yes or No		Extra Traffic Yes or No
	Supported		Supported
	Layer If this protection parameter is specific to		Layer If this protection parameter is specific to
	Bernstein, Mannie, Sharma Expires May 2001 20
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000
	SONET then this parameter is unneeded,		SONET then this parameter is unneeded,
	otherwise it would indicate the signal		otherwise it would indicate the signal
	layer that the protection is applied.		layer that the protection is applied.
	How much information to disseminate concerning protection is an open		An open issue concerning protection is the extent of information
	issue with the contents of Table 6 representing one extreme and a		regarding protection that must be disseminated. The contents of
	simple enumerated list of: Extra-Traffic/Protection line,		Table 6 represent one extreme whilea simple enumerated list of:
	Unprotected, Shared (1:N)/Working line, Dedicated (1:1, 1+1)/Working		Extra-Traffic/Protection line, Unprotected, Shared (1:N)/Working
	Line, Enhanced (Ring) /Working Line, representing the other.		line, Dedicated (1:1, 1+1)/Working Line, Enhanced (Ring) /Working
			Line, represents the other.
	There is also a potential implication for link bundling, that is,		There is also a potential implication for link bundling, that is,
	for each link, the routing protocol could advertise whether it is a		for each link, the routing protocol could advertise whether that
	working or protection link and possibly some parameters from Table		link is a working or protection link and possibly some parameters
	6. A possible drawback of this scheme is that the routing protocol		from Table 6. A possible drawback of this scheme is that the routing
	would be burdened with advertising properties even for those		protocol would be burdened with advertising properties even for
	protection links in the network that could not in fact be used for		those protection links in the network that could not, in fact, be
	routing working traffic, e.g., dedicated protection links. An		used for routing working traffic, e.g., dedicated protection links.
	alternative method, would be to bundle the working and protection		An alternative method, would be to bundle the working and protection
	links together and advertise the bundle instead. Now, for each		links together, and advertise the bundle instead. Now, for each
	bundled link, the protocol would have to advertise the amount of		bundled link, the protocol would have to advertise the amount of
	bandwidth available on its working links, as well as the amount of		bandwidth available on its working links, as well as the amount of
	bandwidth available on those protection links within the bundle that		bandwidth available on those protection links within the bundle that
	were capable of carrying "extra traffic." This would reduce the		were capable of carrying "extra traffic." This would reduce the
	amount of information to be advertised. An issue here would be to		amount of information to be advertised. An issue here would be to
	decide which types of working and protection links to bundle		decide which types of working and protection links to bundle
	together. For instance, it might be preferable to bundle working		together. For instance, it might be preferable to bundle working
			Bernstein, Mannie, Sharma Informational - January 2002 19
	links (and their corresponding protection links) that are "shared"		links (and their corresponding protection links) that are "shared"
	protected separately from working links that are "dedicated"		protected separately from working links that are "dedicated"
	protected.		protected.
	6.3. Available Capacity Advertisement		6.3. Available Capacity Advertisement
	Internally to each SDH/SONET LSR interface, a table is maintained
	indicating each signal allocated in the multiplex structure. This is
	the most complete and accurate view of the link usage and available
	capacity.
	This information needs to be advertised in some way to all others
	SONET/SDH LSRs in the same domain for use in path computation. There
	is a trade off to be reached concerning:
	the amount of detail in the available capacity information to be
	reported via a link state routing protocol,
	the frequency or conditions under which this information is updated,
	the percentage of connection establishments that are unsuccessful on
	their first attempt,
	the extent to which network resources can be optimized.
	There are different levels of summarization that are being
	considered today for the available capacity information. At one
	extreme all signals that are allocated on an interface could be
	Bernstein, Mannie, Sharma Expires May 2001 21
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000		Each SDH/SONET LSR must maintain an internal table per interface
			that indicates each signal in the multiplex structure that is
			allocated at that interface. This internal table is the most
			complete and accurate view of the link usage and available capacity.
	advertised, or on the other extreme, an single aggregated value of		For use in path computation, this information needs to be advertised
	the available bandwidth could be advertised.		in some way to all others SONET/SDH LSRs in the same domain . There
			is a trade off to be reached concerning: the amount of detail in the
			available capacity information to be reported via a link state
			routing protocol, the frequency or conditions under which this
			information is updated, the percentage of connection establishments
			that are unsuccessful on their first attempt due to the granularity
			of the advertised information, and the extent to which network
			resources can be optimized. There are different levels of
			summarization that are being considered today for the available
			capacity information. At one extreme, all signals that are allocated
			on an interface could be advertised, while at the other extreme, a
			single aggregated value of the available bandwidth per link could be
			advertised.
	Consider first the relatively simple structure of SONET and its most		Consider first the relatively simple structure of SONET and its most
	common current and planned usage. DS1s and DS3s are the signals most		common current and planned usage. DS1s and DS3s are the signals most
	often carried within a SONET STS-1. Either a single DS3 occupies		often carried within a SONET STS-1. Either a single DS3 occupies
	the STS-1 or up to 28 DS1s (4 each within the 7 VT groups) are		the STS-1 or up to 28 DS1s (4 each within the 7 VT groups) are
	carried within the STS-1. With a reasonable VT1.5 placement		carried within the STS-1. With a reasonable VT1.5 placement
	algorithm within each node it may be possible to just report on		algorithm within each node it may be possible to just report on
	aggregate bandwidth usage in terms of number of whole STS-1s		aggregate bandwidth usage in terms of number of whole STS-1s
	(dedicated to DS3s) used and the number of STS-1s dedicated to		(dedicated to DS3s) used and the number of STS-1s dedicated to
	carrying DS1sallocated for this purpose. . This way a network		carrying DS1s allocated for this purpose. This way a network
	optimization program could try to determine the optimal placement of		optimization program could try to determine the optimal placement of
	DS3s and DS1s to minimize wasted bandwidth due to half-empty STS-1s		DS3s and DS1s to minimize wasted bandwidth due to half-empty STS-1s
	at various places within the transport network.		at various places within the transport network. Similarly consider
			the set of super rate SONET signals (STS-Nc). If the links between
	Similarly consider the set of super rate SONET signals (STS-Nc). If		the two switches support flexible concatenation then the reporting
	the links between the two switches support flexible concatenation		is particularly straightforward since any of the STS-1s within an
	then the reporting is particularly straightforward since any of the		STS-M can be used to comprise the transported STS- Nc. However, if
	STS-1s within an STS-M can be used to comprise the transported STS-		only standard concatenation is supported then reporting gets
	Nc. However, if only standard concatenation is supported then		trickier since there are constraints on where the STS-1s can be
	reporting gets trickier since there are constraints on where the		placed. SDH has still more options and constraints, hence it is not
	STS-1s can be placed. SDH has still more options and constraints		yet clear which is the best way to advertise bandwidth resource
	hence it is not yet clear yet the best way to advertise bandwidth		availability/usage in SONET/SDH. However, due to the multiplexed
	resource availability/usage in SONET/SDH. However, due to the		nature of the signals reporting of bandwidth particular to signal
	multiplexed nature of the signals reporting of bandwidth particular		types rather than as a single aggregate bit rate is highly
	to signal types rather than as a single aggregate bit rate is highly
	desirable.		desirable.
	6.4. Path Computation		Bernstein, Mannie, Sharma Informational - January 2002 20
			6.4. Path Computation
	Although a link state route protocol can be used to obtain network		Although a link state routing protocol can be used to obtain network
	topology and resource information, this does not imply the use of an		topology and resource information, this does not imply the use of an
	"open shortest path first" route. The path must be open in the sense		"open shortest path first" route. The path must be open in the sense
	that the links must be capable of supporting the desired signal type		that the links must be capable of supporting the desired signal type
	and that capacity must be available to carry the signal. Other		and that capacity must be available to carry the signal. Other
	constraints may include hop count, total delay (mostly propagation),		constraints may include hop count, total delay (mostly propagation),
	and hop count. In addition, it may be desirable to route traffic in		and underlying protection.In addition, it may be desirable to route
	order to optimize overall network capacity, reliability, or some		traffic in order to optimize overall network capacity, or
	combination of the two. Dikstra's algorithm computes the shortest		reliability, or some combination of the two. Dikstra's algorithm
	path with respect to link weights for a single connection at a time.		computes the shortest path with respect to link weights for a single
	This can be much different than the paths that would be selected in		connection at a time. This can be much different than the paths that
	response to a request to set up a batch of connections between a set		would be selected in response to a request to set up a batch of
	of endpoints in order to optimize network link utilization. One can		connections between a set of endpoints in order to optimize network
	think along the line of global or local optimization of the network.		link utilization. One can think of this along the lines of global or
	Due to the complexity of some of the route algorithms (high		local optimization of the network in time.
	dimensionality non-linear integer programming problems) and various
	criteria by which one may optimize their network it may not be		Due to the complexity of some of the connectionrouting algorithms
			(high dimensionality, non-linear integer programming problems) and
			various criteria by which one may optimize a network, it may not be
	possible or desirable to run these algorithms on network nodes.		possible or desirable to run these algorithms on network nodes.
	However, it may still be desirable to have some basic path		However, it may still be desirable to have some basic path
	computation ability running on the network nodes, particularly in		computation ability running on the network nodes, particularly for
	restoration situations. Such an approach is in line with the use of		use during restoration situations. Such an approach is in line
			with the use of MPLS for traffic engineering, but is much
	Bernstein, Mannie, Sharma Expires May 2001 22		different than typical OSPF or IS-IS usage where all nodes must
			run the same routing algorithm.
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000
	MPLS for traffic engineering but is much different than typical OSPF
	or IS-IS usage where all nodes must run the same route algorithm.
	6.5. Link Bundling in Routing: Reducing Adjacencies
	A brief mention is in order here about how the SDH/SONET links can
	be advertised in routing protocols. We have alluded to routing
	issues before, but a point worth advertising that link bundling may
	be used to announce bundles of SDH/SONET links. This would
	considerably reduce the amount of information advertised in routing,
	as well as the number of IP addresses actually consumed by SDH/SONET
	links and interfaces. Furthermore, bundled links could, in turn, be
	advertised in IGP routing tables as forwarding adjacencies (Fas) for
	use by subsequent lower speed circuits.
	While the issue of exactly how to bundle links and the specifics of
	how to advertise them have received attention in the IETF for
	packet-based links, some of the details of this process, especially
	for SDH/SONET networks is still under study.
	7. LSP Provisioning/Signaling for SDH/SONET		7. LSP Provisioning/Signaling for SDH/SONET
	Traditionally, end-to-end circuit connections in SDH/SONET networks		Traditionally, end-to-end circuit connections in SDH/SONET networks
	have been set up via network management systems (NMSs), which issue		have been set up via network management systems (NMSs), which issue
	commands (usually under the control of a human operator) to the		commands (usually under the control of a human operator) to the
	various network elements involved in the circuit, via an equipment		various network elements involved in the circuit, via an equipment
	vendor's element management system (EMS). Very little multi-vendor		vendor's element management system (EMS). Very little multi-vendor
	interoperability has been achieved via management systems. Hence,		interoperability has been achieved via management systems. Hence,
	end-to-end circuits in a multi-vendor environment typically require		end-to-end circuits in a multi-vendor environment typically require
	the use of multiple management systems and the infamous		the use of multiple management systems and the infamous
	configuration via "yellow sticky notes". As discussed in Section 2,		configuration via "yellow sticky notes". As discussed in Section 2,
	a common signaling protocol, such as RSVP with TE extensions or CR-		a common signaling protocol, such as RSVP with TE extensions or CR-
	LDP appropriately extended for circuit switching applications, could		LDP appropriately extended for circuit switching applications, could
	therefore help to solve these interoperability problems. In this		therefore help to solve these interoperability problems. In this
	section, we examine the various components involved in the automated		section, we examine the various components involved in the automated
	provisioning of SONET/SDH LSPs and the associated signaling.		provisioning of SONET/SDH LSPs.
	7.1.1. What do we Label in SDH/SONET? Frames or Circuits?		7.1.1. What do we Label in SDH/SONET? Frames or Circuits?
	MPLS was initially introduced to control asynchronous technologies		MPLS was initially introduced to control asynchronous technologies
	like IP, where a label was attached to each individual block of		like IP, where a label was attached to each individual block of
	data, such as an IP packet or a Frame Relay frame. SONET and SDH,		data, such as an IP packet or a Frame Relay frame. SONET and SDH,
	however, are synchronous technologies that define a multiplexing
	structure (see Section 1.2), which we referred to as the SDH (or
	SONET) multiplex in Section 1.2. This multiplex involves a hierarchy
	of signals, lower order signals embedded within successive higher
	order ones (see Fig. 1). Thus, depending on its level in the
	hierarchy, each signal consists of frames that repeat periodically,
	with a certain number of slots per frame, and these signals can be
	controlled using MPLS.
	Bernstein, Mannie, Sharma Expires May 2001 23		Bernstein, Mannie, Sharma Informational - January 2002 21
			however, are synchronous technologies that define a multiplexing
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000		structure (see Section 3.2), which we referred to as the SDH (or
			SONET) multiplex. This multiplex involves a hierarchy of signals,
			lower order signals embedded within successive higher order ones
			(see Fig. 1). Thus, depending on its level in the hierarchy, each
			signal consists of frames that repeat periodically, with a certain
			number of byte time slots per frame.
	The question then arises: is it these frames that we label in MPLS?		The question then arises: is it these frames that we label in GMPLS?
	It will be seen in what follows that we do not consider that each		It will be seen in what follows that each SONET or SDH "frame"
	SONET or SDH "frame" has its own label and that we switch frames		need not have its own label, nor is it necessary to switch frames
	individually. Rather, the unit that is switched is a "flow"		individually. Rather, the unit that is switched is a "flow"
	comprised of continuous time slots that appear at a given position		comprised of a continuous sequence of time slots that appear at a
	in such a frame. That is, we switch an individual SONET or SDH		given position in a frame. That is, we switch an individual SONET or
	signal, with a label associated with each given signal.		SDH signal, and a label associated with each given signal.
	For instance, the payload of an SDH STM-1 frame does not fully		For instance, the payload of an SDH STM-1 frame does not fully
	contain a complete unit of user data. In fact, the user data is		contain a complete unit of user data. In fact, the user data is
	contained in a virtual container (VC) that is allowed to float over		contained in a virtual container (VC) that is allowed to float over
	two contiguous frames for synchronization purposes. A pointer in the		two contiguous frames for synchronization purposes. A pointer in the
	Section Overhead (SOH) indicates the beginning of the VC in the		Section Overhead (SOH) indicates the beginning of the VC in the
	payload. Thus, frames are now inter-related, since each consecutive		payload. Thus, frames are now inter-related, since each consecutive
	pair may share a common virtual container. From the point of view of		pair may share a common virtual container. From the point of view of
	MPLS, therefore, it is not the successive frames that are treated		GMPLS, therefore, it is not the successive frames that are treated
	independently or labeled, but rather the user signal. An identical		independently or labeled, but rather the entire user signal. An
	argument applies to SONET.		identical argument applies to SONET.
	Observe also that the MPLS signaling used to control the SDH/SONET		Observe also that the GMPLS signaling used to control the SDH/SONET
	multiplex must honor its hierarchy. In other words, the SDH/SONET		multiplex must honor its hierarchy. In other words, the SDH/SONET
	layer should not be viewed as homogeneous and flat, because this		layer should not be viewed as homogeneous and flat, because this
	would limit the scope of the services that it can provide. Instead,		would limit the scope of the services that SDH/SONET can provide.
	MPLS tunnels should be used to dynamically and hierarchically		Instead, GMPLS tunnels should be used to dynamically and
	control the SDH/SONET multiplex. For example, one unstructured VC-4		hierarchically control the SDH/SONET multiplex. For example, one
	LSP may be established between two nodes, and later lower order LSPs		unstructured VC-4 LSP may be established between two nodes, and
	(e.g. VC-12) may be created within that higher order LSP. This VC-4		later lower order LSPs (e.g. VC-12) may be created within that
	LSP can, in fact, be established between two non-adjacent internal		higher order LSP. This VC-4 LSP can, in fact, be established
	nodes in an SDH network, and later advertised by a routing protocol		between two non-adjacent internal nodes in an SDH network, and
	as a new (virtual) link called a Forwarding Adjacency (FA).		later advertised by a routing protocol as a new (virtual) link
			called a Forwarding Adjacency (FA).
	An SONET/SDH-LSR will have to identify each possible signal		A SONET/SDH-LSR will have to identify each possible signal
	individually per interface to fulfill the MPLS operations. In order		individually per interface to fulfill the GMPLS operations. In order
	to stay transparent the LSR obviously should not touch the SONET/SDH		to stay transparent the LSR obviously should not touch the SONET/SDH
	overheads; this is why an explicit label is not encoded in the		overheads; this is why an explicit label is not encoded in the
	SDH/SONET overheads. Rather, a label is associated with each		SDH/SONET overheads. Rather, a label is associated with each
	individual signal. This approach is similar to the one considered		individual signal. This approach is similar to the one considered
	for lambda switching, except that it is more complex, since SONET		for lambda switching, except that it is more complex, since SONET
	and SDH define a richer multiplexing structure.		and SDH define a richer multiplexing structure. Therefore a label
	Therefore a label is associated with each signal, and is local and		is associated with each signal, and is locally unique for each
	unique for each signal at each interface. This signal could, and		signal at each interface. This signal could, and will most probably,
	will most probably, occupy different time-slots at different		occupy different time-slots at different interfaces.
	interfaces.
	7.2. Label Structure in SDH/SONET		Bernstein, Mannie, Sharma Informational - January 2002 22
			7.2. Label Structure in SDH/SONET
	The signaling protocol used to establish an SDH/SONET LSP must have		The signaling protocol used to establish an SDH/SONET LSP must have
	specific information elements in it to map a label to the particular		specific information elements in it to map a label to the particular
	signal type that it represents and to the position of that signal in		signal type that it represents, and to the position of that signal
	the SONET/SDH multiplex. As we will see shortly, however, with a		in the SONET/SDH multiplex. As we will see shortly, with a
	carefully chosen label structure, the label itself can be made to		carefully chosen label structure, the label itself can be made to
	function as this information element.		function as this information element.
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	In general, there are two ways to assign labels for signals between		In general, there are two ways to assign labels for signals between
	neighboring SDH/SONET LSRs. One way is for the labels to be		neighboring SDH/SONET LSRs. One way is for the labels to be
	allocated completely independently of any SDH/SONET semantics; e.g.		allocated completely independently of any SDH/SONET semantics; e.g.
	labels could just be unstructured 16 or 32 bit numbers. In that		labels could just be unstructured 16 or 32 bit numbers. In that
	case, in the absence of appropriate binding information, a label		case, in the absence of appropriate binding information, a label
	gives no visible information about the flow that it represents. From		gives no visible information about the flow that it represents. From
	a management and debugging point of view, therefore, it becomes		a management and debugging point of view, therefore, it becomes
	difficult to match a label with the corresponding signal, since , as		difficult to match a label with the corresponding signal, since , as
	we saw in Section 4.1.1, the label is not coded in the SDH/SONET		we saw in Section 7.1.1, the label is not coded in the SDH/SONET
	overhead(s)of the signal.		overhead of the signal.
	Another way is to use the well defined and finite structure of the		Another way is to use the welldefined and finite structure of the
	SDH/SONET multiplexing tree to devise a clever signal numbering		SDH/SONET multiplexing tree to devise a signal numbering scheme that
	scheme that makes use of the multiplex as a naming tree, and assigns		makes use of the multiplex as a naming tree, and assigns each
	each multiplex entry a unique associated value. This allows the		multiplex entry a unique associated value. This allows the unique
	unequivocal identification of each multiplex entry (signal) in terms		identification of each multiplex entry (signal) in terms of its type
	of its type and position in the multiplex tree. By using this		and position in the multiplex tree. By using this multiplex entry
	multiplex entry value itself as the label, we automatically add		value itself as the label, we automatically add SDH/SONET semantics
	SDH/SONET semantics to the label! Thus, simply by examining the		to the label! Thus, simply by examining the label, one can now
	label, one can now directly deduce the signal that it represents, as		directly deduce the signal that it represents, as well as its
	well as its position in the SDH/SONET multiplex. We refer to this as		position in the SDH/SONET multiplex. We refer to this as
	multiplex-based labeling. This is the idea that was incorporated in		multiplex-based labeling. This is the idea that was incorporated in
	the GMPLS signaling specifications.		the GMPLS signaling specifications [7].
	In the following sections, we look at this label structure in more
	detail.
	7.2.1. SDH/SONET Multiplex Entry Name
	We will use the SDH multiplex, defined in recommendation G.707
	Figure 6-1, as the basic reference to identify signals. It defines a
	tree, whose root is an STM-Nsignal, and whose leaves are the signals
	that can be transported (hierarchically) within the STM-N. This tree
	will be used as a naming tree to create unique multiplex entry
	values as discussed in the previous subsection. This entry will
	identify at the same time the type of signal and its position in the
	multiplex. Figure 1 shows the SDH and SONET multiplexes.
	The possible leaves of that tree are VC-4, VC-3, VC-2, VC-12 or VC-
	11. According to the multiplex structure there is a maximum of 1 VC-
	4, 3 VC-3s, 21 VC-2s, 63 VC-12s or 84 VC-11s in one STM-1. Of
	course, different VCs may be combined according to the combination
	rules of the SDH multiplex.
	A maximum of 172 (1+3+21+63+84) different signals, therefore, may be
	identified in one STM-1. Although some of them use the same
	physical space, and are therefore incompatible, for simplicity we
	will give a unique name to each of them. For that purpose we extend
	the well-known (K, L, M) numbering scheme defined in G.707 section
	7.3..N STM-1 signals may be interleaved together to form an STM-
	Nsignal. It results that we must identify the STM-1 that is itself
	decomposed in sub-signals. We discuss concatenation in Section 4.3.
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	This method is directly applicable to SONET as shown in Fig. 1,
	since the SONET multiplex can be seen as a sub-tree of the SDH
	multiplex tree.
	7.2.2. SDH/SONET Multiplex Entry Notation
	We propose the - following hierarchical multiplex entry notation:
	(S, U, K, L, M) or S.U.K.L.M (in dot notation), where
	S: 1 -> N : indicates a specific STM-1/STS-1 inside an STM-N/STS-
	N multiplex.
	U: 0 -> 4 : index of an SDH Administrative Unit (AU-4 or AU-3).
	K: 0 -> 4 : index indicating the content of a VC-4.
	L: 0 -> 8 : index indicating the content of a TUG-3, VC-3 or STS-
	1 SPE.
	M: 0 -> 10 : index indicating the content of a TUG-2 or VT Group.
	Each letter indicates a possible branch number starting at the
	parent node in the naming tree. Branches are numbered in the
	increasing order, starting from the top of the naming tree. The
	numbering starts at 1, and zero is used to indicate a non-
	significant field.
	S is the index of a particular STM-1/STS-1. S=1->N indicates a
	specific STM-1/STS-1 inside an STM-N/STS-N multiplex. For example,
	S=1 indicates the first STM-1/STS-1, and S=N indicates the last STM-
	1/STS-1 of this multiplex.
	U is only significant for SDH and must be ignored for SONET. It
	indicates a specific VC inside a given STM-1. U=1 indicates a single
	VC-4, while U=2->4 indicates a specific VC-3 inside the given STM-1.
	K is only significant for SDH and must be ignored for SONET. It
	indicates a specific branch of a VC-4. K=1 indicates that the VC-4
	is not further sub-divided and contains a C-4. K=2->4 indicates a
	specific TUG-3 inside the VC-4. K is not significant when the STM-1
	is divided into VC-3s (and is easy to read and test).
	L indicates a specific branch of a TUG-3, VC-3 or STS-1 SPE. It is
	not significant for an unstructured VC-4. L=1 indicates that the
	TUG-3/VC-3/STS-1 SPE is not further sub-divided and contains a VC-
	3/C-3 in SDH or the equivalent in SONET. L=2->8 indicates a specific
	TUG-2/VT Group inside the corresponding higher order signal.
	M indicates a specific branch of a TUG-2/VT Group. It is not
	significant for an unstructured VC-4, TUG-3, VC-3 or STS-1 SPE. M=1
	indicates that the TUG-2/VT Group is not further sub-divided and
	contains a VC-2/VT-6. M=2->3 indicates a specific VT-3 inside the
	corresponding VT Group, these values MUST NOT be used for SDH since
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	there is no equivalent of VT-3 with SDH. M=4->6 indicates a specific
	VC-12/VT-2 inside the corresponding TUG-2/VT Group. M=7->10
	indicates a specific VC-11/VT-1.5 inside the corresponding TUG-2/VT
	Group. Note that M=0 denotes an unstructured VC-4, VC-3 or STS-1 SPE
	(easy for debugging).
	SDH SONET
	unstructured VC-4/VC-3 unstructured STS-1 SPE
	VC-2 VT-6
	1st VT-3
	2nd VT-3
	1st VC-12 1st VT-2
	2nd VC-12 2nd VT-2
	3rd VC-12 3rd VT-2
	1st VC-11 1st VT-1.5
	2nd VC-11 2nd VT-1.5
	3rd VC-11 3rd VT-1.5
	4th VC-11 4th VT-1.5
	Table 7. Encoding of the M field in the SDH/SONET multiplex entry.
	This may be illustrated with the following examples.
	Example 1: S>0, U=1, K=1, L=0, M=0
	Denotes the unstructured VC-4 of the Sth STM-1.
	Example 2: S>0, U=1, K>1, L=1, M=0
	Denotes the unstructured VC-3 of the Kth-1 TUG-3 of the Sth STM-1.
	Example 3: S>0, U=0, K=0, L=0, M=0
	Denotes the unstructured STS-1 SPE of the Sth STS-1.
	Example 4: S>0, U=0, K=0, L>1, M=1
	Denotes the VT-6 in the Lth-1 VT Group in the Sth STS-1.
	Example 5: S>0, U=0, K=0, L>1, M=9
	Denotes the 3rd VT-1.5 in the Lth-1 VT Group in the Sth STS-1.
	7.2.3. SDH/SONET Multiplex Entry Encoding:
	A multiplex entry name may be used directly as a label, or may be
	used in an information element of a signaling protocol to associate
	a label with the corresponding multiplex entry (signal). In both
	cases, a multiplex entry can be coded as described in Figure 3 .This
	coding has also been proposed for the SDH/SONET labels in GMPLS.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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	| S | U | K | L | M |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The current SDH standards only allow N to take the discrete values
	0, 1, 4, 16 or 64. Today, in practice all of them are used: STM-0
	(51.840 Mb/s), STM-1 (155.52 Mb/s), STM-4 (622.08 Mb/s), STM-16
	(2488.32 Mb/s) and STM-64 (9953.26 Mb/s). In the future, it is
	likely that N will grow up to 256 or 1024. This fixes the number of
	possible different multiplex entry names to 1024 x 172 = 176128.
	Note that an SDH LSR does not need to maintain a table of this
	size, it just needs to maintain a list of multiplex entries that it
	has allocated at any given time.
	7.2.4. Hierarchical Label Allocation:
	At any particular point in time, a given position in the SDH/SONET
	multiplex may either be a valid position or not, according to the
	signals already allocated, and if valid, may either be used or be
	free. Thus, a multiplex entry (time-slot) must be interpreted in
	relation tothe already allocated multiplex entries (time-slots).
	The fact that two neighboring SDH/SONET LSRs allocate a label for a
	particular LSP implies that the corresponding time-slot will be
	enabled in the multiplex between the two LSRs. When an SDH/SONET LSP
	is removed, the corresponding local label is released, and the
	corresponding multiplex space may be re-used. An MPLS conservative
	label retention mode must be implemented when using multiplex based
	labeling.
	For instance, for a downstream-on-demand label allocation, the
	upstream LSR must indicate the type of signal it wants to forward.
	The downstream SDH-LSR must check if such a signal is available in
	its multiplex, and, if it is available, return the corresponding
	label. With multiplex-based labeling, the upstream SDH/SONET LSR
	can easily verify if the right type of signal was allocated by the
	downstream SDH/SONET LSR , just by looking at the label.
	In this case, the downstream SDH-LSR is applying a straightforward
	SDH/SONET call admission control (CAC) function based on the space
	available in the multiplex. Note that the two SDH/SONET LSRs should
	have identical multiplex tables, so that even before requesting a
	label, the upstream SDH/SONET LSR could even check its own multiplex
	table for that particular interface, to see if space is available
	for that signal.
	The two neighboring SDH/SONET LSRs could also have a mechanism to
	periodically check if their multiplex tables are identical, i.e.
	fully synchronized. This can be achieved through the MPLS signaling
	simply by exchanging the complete multiplex tables or the list of
	currently allocated signals (labels). If the neighboring SDH-LSRs
	discover that their multiplex tables are not identical, a fault
	should immediately be triggered to alert a NMS
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	Note that since an SDH-LSR may have a neighbor relationship at
	different levels of the SDH/SONET hierarchy, the multiplex table
	that is common between two neighboring SDH/SONET LSRs should be
	understood in the context of that relationship. That is,
	neighboring SDH-LSRs should compare only the list of LSPs that they
	negotiated as peers at a particular level of the hierarchy
	For instance, in Figure 3 (please refer to pdf document; available
	from authors), SDH/SONET LSR2 and SDH/SONET LSR3 may have an
	unstructured VC-4 established between them, while SDH/SONET LSRs 1
	and 4 may have a VC-12 established within that VC-4. If LSR2 and
	LSR21 compare their multiplex tables, LSR2 must ensure that is sends
	just the view that LSR21 has of the multiplex. For example, LSR21
	knows nothing about the contents of the VC-4, and so should not be
	sent information about it.
	7.3. Signaling Elements		7.3. Signaling Elements
	In the preceding sections, we defined the meaning of a SDH/SONET		In the preceding sections, we defined the meaning of a SDH/SONET
	label and specified its structure. A question that arises naturally		label and specified its structure. A question that arises naturally
	at this point is the following. In an LSP or connection setup		at this point is the following. In an LSP or connection setup
	request, how do we specify the signal for which we want to establish		request, how do we specify the signal for which we want to establish
	a path (and for which we desire a label)?		a path (and for which we desire a label)?
	Clearly, information that is required to completely specify the		Clearly, information that is required to completely specify the
	desired signal and its characteristics must be transferred via the		desired signal and its characteristics must be transferred via the
	label distribution protocol, so that the switches along the path can		label distribution protocol, so that the switches along the path can
	be configured to correctly handle and switch the signal. As we		be configured to correctly handle and switch the signal. This
	explain ahead, this information is specified in three parts, each of		information is specified in three parts, each of which refers to a
	which refers to a different network layer. The first specifies the		different network layer.
	nature/type of the LSP or the desired SDH/SONET channel, in terms of
	the particular signal (or collection of signals) within the
	SDH/SONET multiplex that the LSP represents, and is used by all the
	nodes along the path of the LSP. The second specifies the payload
	carried by the LSP or SDH/SONET channel, in terms of the termination
	and adaptation functions required at the end points, and is used by
	the source and destination nodes of the LSP. The third specifies
	certain link selection constraints, which control, at each hop, the
	selection of the underlying link that is used to transport this LSP.
	In the following subsections, we discuss each of these in more
	detail.
	7.3.1. Nature of the LSP: LSP Encoding Type, Signal Type, and
	Connection Bundling
	The nature of the SDH/SONET signal is specified collectively by the
	LSP encoding type and signal type fields, which identify (via
	appropriate rules) the specific connection point types on a
	particular interface/port that may be used to switch this signal or
	LSP. Another element specifying the nature of the desired LSP is the
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	extent, if any, of connection grouping, which is specified by a
	combination of two fields that denote respectively, the type of
	grouping requested by the LSP and the number of components in that
	grouping.
	Recall that in TDM networks, the link connection points (or the
	type of signals within a SDH/SONET multiplex that the link can
	switch) provided by a link are limited to a fixed, discrete set.
	Thus, the link connection points that are suitable for carrying a
	given LSP are limited to those that match the LSP type and the
	signal type, or to which the LSP type and signal type can be readily
	adapted (by mapping to a container).
	7.3.1.1. LSP Encoding Type and Signal Type
	In particular, the LSP encoding type indicates the technology of the
	LSP being requested, and includes, for example, ANSI PDH, ETSI PDH,
	SDH, and SONET. The signal type field indicates the specific signal
	type of the LSP being requested, and is interpreted in the context
	of the technology specified in the LSP encoding type. Thus, the
	signal type provides transit switches with information required to
	determine the connection point types (timeslots/labels) that can
	suppor t this LSP. As an example, the permitted LSP encoding types
	with their permitted signal types for SDH are shown in Table 8. A
	detailed discussion of the encoding types appears in [7].
	LSP Encoding Type Signal Type
	SDH
	1 VC-11
	2 VC-12
	3 VC-2
	4 TUG-2
	5 VC-3
	6 TUG-3
	7 VC-4
	8 STM-1
	9 STM-1 MS
	10 STM-1 RS
	12 STM-4
	13 STM-4 MS
	14 STM-4 RS
	16 STM-16
	17 STM-16 MS
	18 STM-16 RS
	20 STM-64
	21 STM-64 MS
	22 STM-64 RS
	24 STM-256
	25 STM-256 MS
	26 STM-256 RS
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	Table 8 Permitted LSP encoding types and their corresponding signal
	types for SDH.
	By way of example, a DS3 LSP can be supported by link connections of
	type DS3, or by link connections of type STS-1, if a DS3/STS-1
	adaptation function is available at the source (and a corresponding
	one is available at the destination of the DS3 LSP). A DS3 LSP
	cannot, for instance, be routed on link connections of type VT1.5,
	no matter how many are available, since the associated links do not
	have the capability to switch DS3 signals. Therefore the LSP
	encoding type and signal type are fundamental in indicating the
	nature of the LSP requested, and in enabling the determination of
	which available link connections may carry the signal.
	7.3.1.2. Connection Bundling
	Since a number of non concatenated STS-1s may be routed together as
	a group (that is, all contained within the same SONET line or WDM
	signal) and receive essentially the same delay and propagation, they
	are specified by a requested grouping type (RGT) field in GMPLS.
	This denotes how many connections of a given signal type are
	requested together, which ensures that they meet similar routing
	constraints. Since the specific group routing constraints depend on
	technology, this parameter also is interpreted in the context of the
	LSP encoding type. The values for SONET/SDH are no grouping, virtual
	concatenation, and continuous arbitrary concatenation (or flexible
	concatenation), and continuous standard concatenation, as explained
	in Section 3.1.2. For virtual concatenation, all components in the
	group must be routed via the same higher order container. For
	contiguous standard concatenation, there must be a standard number
	of components (3, 12, 48, etc.), and they must be in one higher
	order container. For contiguous arbitrary concatenation, the number
	of components is arbitrary (2, 3, 4, à) and they still must be
	routed in one higher order container.
	Such concatenation simplifies connection establishment (especially
	for batches of DS-3s that are being wholesaled) and speeds re-
	routes. Since bundling may be important when establishing STS-1s
	that will be used between end-systems implementing virtual
	concatenation, it is recommended that the labels chosen for SONET
	paths be capable of incorporating the concept of STS-1 bundling. The
	bundling of larger signals, i.e., groups of STS-Mc, is for further
	study.
	Finally, there is also a field that indicates the requested number
	of components (RNT), that is, the number of identical signal types
	that are requested to be grouped into an LSP, as specified in the
	RGT field. All components are assumed to have identical
	characteristics, of course, and the field is set to zero when no
	grouping is requested.
	7.3.2 Payload Type
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	As discussed earlier, the label request must also carry an
	identifier of the payload that is carried by the LSP. The payload
	identifies the client layer of that LSP, is interpreted in the
	context of the LSP encoding type, and is used by the end-points of
	the LSP. As an example, Table 9 depicts a suggested organization of
	the generalized payload identifier (GPID) values for SDH and SONET..
	LSP Encoding Type Payload/Client Type
	SDH Unknown
	Asynchronous mapping of E4
	Asynchronous mapping of DS3
	Asynchronous mapping of E3
	Bit synchronous mapping of E3
	Byte synchronous mapping of E3
	Asynchronous mapping of DS2
	Bit synchronous mapping of DS2
	Byte synchronous mapping of DS2
	Asynchronous mapping of E1
	Byte synchronous mapping of E1
	Byte synchronous mapping of 31 *
	DS0
	Asynchronous mapping of DS1
	Bit synchronous mapping of DS1
	Byte synchronous mapping of DS1
	ATM mapping
	SONET Unknown
	DS1 SF Asynchronous
	DS1 ESF Asynchronous
	DS3 M23 Asynchronous
	DS3 C-Bit Parity Asynchronous
	VT
	STS
	ATM
	POS
	Table 9. The payload type indicator in the context of the LSP
	encoding type for SDH/SONET.
	A value of "unknown" indicates that the payload carried by the LSP
	is either unknown or not relevant to know for the end points of the
	current LSP.
	7.3.3. Link Protection Type
	The link protection type carried in the label request indicates the
	level of protection that an LSP desires on the links at each hop
	along its path. In other words, the link protection is local to the
	interface between two adjacent nodes, and controls how the
	underlying link at a particular hop is protected. It is, therefore,
	distinct from MPLS-level protection (see [12]), which involves
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	protection of the actual LSP (which may be done either end-to-end,
	via path-based protection, or locally, via bypass tunnels).
	The link protection may be represented as a vector of flags, where
	one or more protection levels may be turned on simultaneously. A
	value of 0 implies that this connection does not care about which,
	if any, link protection is used. More than one bit may be set to
	indicate when multiple protection types are acceptable. When
	multiple bits are set and multiple protection types are available,
	the choice of protection type is a local (policy) decision. The
	following flags are defined:
	Extra Traffic
	Indicates that links that are reserved for automatic recovery in
	case of a fault elsewhere in the network may be used for this LSP.
	Observe that this means that the LSP can be disrupted whenever such
	a link is needed for its assigned recovery purpose. In other words,
	the LSP can be dropped even if there is not fault on the links along
	which this LSP is routed.
	Unprotected
	"Unprotected" indicates that unprotected links may be used by this
	LSP. This means that the LSP will only lose service on this hop, if
	there is a fault along this particular link (a fault elsewhere will
	not affect this link and therefore this LSP). In other words,
	"unprotected" can be regarded as a "neutral" form of protection. The
	LSP does not lose service as long as the link is up, but loses
	service once this link goes down, since the link itself is not
	protected by a backup link.
	Shared
	Indicates that protected (working) links whose protection resources
	are shared with some number, say N, of other working links may be
	used by this LSP.
	This means that if there is a fault along this particular link, the
	LSP will lose service on this hop, only if the backup link is
	already in use by traffic from one of the remaining N-1 working
	links (due to an earlier fault on one of those links). Thus, the
	"shared" option can be regarded as a better form of protection,
	since the LSP is protected as long as there is no fault on any of
	the remaining N-1 working links that share the same backup link.
	Dedicated
	Indicates that links with dedicated protection, e.g., 1:1 or 1+1
	protection, may be used by this LSP.
	This means that a protection link is reserved for the working link
	over which this LSP is routed, so that this LSP is always protected
	against any fault on its working link. Thus, the "dedicated" option
	offers a higher form of link-level protection.
	Enhanced
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	Indicates that links that are multiply protected, such as via a ring
	switch and a span switch in a 4-fiber BLSR/MS-SPRING.
	Thus, the LPFs represent both a property of a link (which needs to
	be appropriately advertised in routing), as well as a constraint on
	which links may be used for a given path (which is signaled during
	connection setup as specified above).
	8. Choices for Control Channel Implementation
	One question that we have not yet addressed is how the so-called
	MPLS "control channel" is implemented?
	It turns out that there are several implementation choices for the
	control channel. One way is to use out-of-band (OOB) signaling. An
	OOB control channel that has been implemented using a dedicated
	wavelength works as follows.
	The incoming signal on a fiber is first demultiplexed into the data
	bearing wavelengths and the control bearing wavelength. While the
	data wavelengths are switched by the cross-connect, the control
	wavelength is passed to a control element, where it undergoes O/E
	conversion to produce a digital bit stream. This bit stream is
	interpreted and processed by the MPLS signaling/control element, and
	the resulting control bits are converted via E/O conversion, back
	into a optical signal that is multiplexed onto the outgoing fiber.
	An alternative implementation is to use a dedicated network (such as
	an IP network) as a control network connecting the controllers on
	the optical elements.
	An alternative to OOB signaling is to implement the control channel
	using in-band signaling. Again, there are several ways to accomplish
	this:
	The first is to use a portion of a wavelength to carry control
	information, which is useful when the number of wavlengths is
	limited and it is not possible to dedicate an entire wavelength for
	carrying control information. Essentially, the incoming signal is
	demultiplexed into the data channels, which are switched by the
	cross-connect, and the control bearing wavelength, which undergoes
	O/E conversion to produce a data stream and control information. The
	data stream is switched electronically while the control information
	is interpreted and processed by the MPLS signaling/control element.
	The resulting control bits and the data stream are both converted
	back, via E/O conversion, into a optical signal that is multiplexed
	onto the outgoing fiber.
	A second option is to use sub-carrier modulation, modulating the
	data carrying wavelength with an additional sub-carrier that carries
	control information. This sub-carrier signal is split from the data
	carrying wavelength, and processed (after O/E conversion) by the
	MPLS signaling/control element, and then is used to re-modulate the
	outgoing wavelength.
	Bernstein, Mannie, Sharma Expires May 2001 34		The first specifies the nature/type of the LSP or the desired
			SDH/SONET channel, in terms of the particular signal (or collection
			of signals) within the SDH/SONET multiplex that the LSP represents,
			and is used by all the nodes along the path of the LSP.
	draft-bms-sdhsonet-mpls-control-frmwrk-00.txt November 2000		Bernstein, Mannie, Sharma Informational - January 2002 23
			The second specifies the payload carried by the LSP or SDH/SONET
			channel, in terms of the termination and adaptation functions
			required at the end points, and is used by the source and
			destination nodes of the LSP.
	A third option is to use the overhead bytes in SONET frames or		The third specifies certain link selection constraints, which
	overhead bits in a digital wrapper. This requires, of course, that		control, at each hop, the selection of the underlying link that is
	all devices be O-E-O capable.		used to transport this LSP.
	9. Summary and Conclusions		8. Summary and Conclusions
	In this paper, we gave a detailed account of the issues involved in		We provided a detailed account of the issues involved in applying
	applying MPLS-based control to TDM networks (a general overview of		MPLS-based control to TDM networks.
	these issues for applying GMPLS to optical networks appears in
	[11]).
	We began with a brief overview of MPLS and SDH/SONET networks,		We began with a brief overview of MPLS and SDH/SONET networks,
	discussing current circuit establishment in TDM networks, and		discussing current circuit establishment in TDM networks, and
	arguing why SDH/SONET technologies will not be "outdated" in the		arguing why SDH/SONET technologies will not be "outdated" in the
	forseable future. We then looked at MPLS applied to SDH/SONET		foreseeable future. We then looked at MPLS applied to SDH/SONET
	networks, where we consider why such an application makes sense, and		networks, where we considered why such an application makes sense,
	reviewed some MPLS terminology as applied to TDM networks. We then		and reviewed some MPLS terminology as applied to TDM networks. We
	considered the two main areas of application of MPLS methods to TDM		then considered the two main areas of application of MPLS methods to
	networks, namely routing and signaling. We considered in detail the		TDM networks, namely routing and signaling. We considered in detail
	switching capabilities of TDM equipment, and the requirement to		the switching capabilities of TDM equipment, and the requirement to
	learn about the protection capabilities of underlying links, and at		learn about the protection capabilities of underlying links, and how
	how these influence the available capacity advertisement in TDM		these influence the available capacity advertisement in TDM
	networks. We focused briefly on path computation methods, pointing		networks. We focused briefly on path computation methods, pointing
	out that these were not subject to standardization. We then examined		out that these were not subject to standardization. We then examined
	optical path provisioning or signaling, considering the issue of		optical path provisioning or signaling, considering the issue of
	what constitutes an appropriate label for TDM circuits, how this		what constitutes an appropriate label for TDM circuits, how this
	label should be structured, and we focused on the importance of		label should be structured, and we focused on the importance of
	hierarchical label allocation in a TDM network. We then reviewed the		hierarchical label allocation in a TDM network. We then reviewed the
	signaling elements involved when setting up an optical TDM circuit,		signaling elements involved when setting up an optical TDM circuit,
	focusing on the nature of the LSP, the type of payload it carries,		focusing on the nature of the LSP, the type of payload it carries,
	and the characteristics of the links that the LSP wishes to use at		and the characteristics of the links that the LSP wishes to use at
	each hop along its path, for achieving a certain reliability.		each hop along its path, for achieving a certain reliability.
	We believe our work provides a comprehensive overview of the issues		9. Security Considerations
	arising in the dynamic control of optical SDH/SONET networks, and
	points to several issues that will certainly require more work and
	industry consensus to realize interoperable implementations of a
	dynamically controlled transport network.
	10. Security Considerations
	This draft raises no new security issues in the MPLS specifications.		This draft raises no new security issues in the MPLS specifications.
	11. References		10.References
	[1] Bradner, S., "The Internet Standards Process -- Revision 3",		[1] Bradner, S., "The Internet Standards Process -- Revision 3",
	BCP 9, RFC 2026, October 1996.		BCP 9, RFC 2026, October 1996.
	[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement		[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
	Levels", BCP 14, RFC 2119, March 1997		Levels", BCP 14, RFC 2119, March 1997
	[3] Synchronous Optical Network (SONET) Basic Description including		Bernstein, Mannie, Sharma Informational - January 2002 24
	Multiplex Structure, Rates, and Formats, ANSI T1.105-1995.
	[4] G.707, Network Node Interface for the Synchronous Digital Hierarchy		[3] Synchronous Optical Network (SONET) Basic Description including
	(SDH), International Telecommunication Union, 03/96.		Multiplex Structure, Rates, and Formats, ANSI T1.105-1995.
	[5] Synchronous Optical Network (SONET) Transport Systems: Common		[4] G.707, Network Node Interface for the Synchronous Digital
	Generic Criteria, Bellcore GR-253-CORE, Issue 2, December 1995.		Hierarchy (SDH), International Telecommunication Union, 03/96.
	Synchronous Optical Network (SONET) Transport Systems: Common Generic
	Criteria, Bellcore GR-253-CORE, Issue 2, December 1995.
	[6] Peter Ashwood-Smith and Lou Berger, Editors, "Generalized MPLS:		[5] ANSI T1.105.01-1995, Synchronous Opical Network (SONET)
	Signaling Functional Description," Internet Draft,		Automatic Protection Switching, American National Standards
	draft-ietf-mpls-generalized-signaling-01.txt, Work in Progress,		institute.
	November 2000.		[6] G.841, Types and Characteristics of SDH Network Protection
			Architectures, ITU-T, 07/95.
	[7] Ben Mack-Crane, V. Sharma, Greg Bernstein, Eric Mannie, et al,		[7] Peter Ashwood-Smith and Lou Berger, Editors, "Generalized MPLS:
	Enhancements to GMPLS Signaling for Optical Technologies, Internet		Signaling Functional Description," Internet Draft,draft-ietf-mpls-
	Draft, Work in Progress,		generalized-signaling-04.txt, Work in Progress, May 2001.
	draft-mack-crane-gmpls-signaling-enhancements-00.txt, November 2000.
	[8] E. Mannie, Greg Bernstein "Extensions to OSPF and IS-IS in support		[8] E. Mannie, Editor, "GMPLS Extensions for SONET and SDH
	of MPLS for SDH/SONET Control", Internet Draft, Work in Progress,		Control", Internet Draft, draft-ietf-ccamp-gmpls-sonet-sdh-01.txt,
	draft-mannie-mpls-sdh-ospf-isis-00.txt, July 2000.		Work in Progress, June 2001.
	[9] Greg Bernstein, "Some Comments on the Use of MPLS Traffic		[9] E. Mannie, Greg Bernstein "Extensions to OSPF and IS-IS in
	Engineering for SONET/SDH Path Establishment", Internet Draft, Work in		support of MPLS for SDH/SONET Control", Internet Draft, Work in
	Progress, draft-bernstein- mpls-sonet-00.txt, March 2000.		Progress, draft-mannie-mpls-sdh-ospf-isis-00.txt, July 2000.
	[10] E. Mannie, "MPLS for SDH Control", Internet Draft, Work in		11.Acknowledgments
	Progress, draft-mannie-mpls-sdh- control-00.txt. March 2000.
	[11] Greg Bernstein and Vishal Sharma, Some Comments on GMPLS and		12.Author's Addresses
	Optical Technologies, Internet Draft, Work in Progress,
	draft-bernstein-gmpls-optical-00.txt, November 2000.
	[12] Vas Makam, V. Sharma, Ben Mack-Crane, et al, Framework for		Greg Bernstein
	MPLS-based Recovery, Internet Draft, Work in Progress,		Ciena Corporation
	draft-ietf-mpls-recovery-frmwrk-00.txt, September 2000.		10480 Ridgeview Court
			Cupertino, CA 94014
			Phone: +1 510 573-2237
			E-mail: greg@ciena.com
	Bernstein, Mannie, Sharma Expires May 2001 35		Eric Mannie
			EBONE
			Terhulpsesteenweg 6A
			1560 Hoeilaart - Belgium
			Phone: +32 2 658 56 52
			Mobile: +32 496 58 56 52
			Fax: +32 2 658 51 18
			E-mail: eric.mannie@ebone.com
			Bernstein, Mannie, Sharma Informational - January 2002 25
			Vishal Sharma
			Metanoia, Inc.
			335 Elan Village Lane, Unit 203
			San Jose, CA 95134
			Phone: +1 408 943 1794
			Email: v.sharma@ieee.org
			Bernstein, Mannie, Sharma Informational - January 2002 26
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