< draft-malis-sonet-ces-mpls-04.txt   draft-malis-sonet-ces-mpls-05.txt >
Network Working Group Andrew G. Malis Network Working Group Andrew G. Malis
Internet Draft Ken Hsu Internet Draft Ken Hsu
Expiration Date: October 2001 Vivace Networks, Inc. Expiration Date: February 2002 Vivace Networks, Inc.
Jeremy Brayley Jeremy Brayley
Steve Vogelsang Steve Vogelsang
John Shirron John Shirron
Laurel Networks, Inc. Laurel Networks, Inc.
Luca Martini Luca Martini
Level 3 Communications, LLC. Level 3 Communications, LLC.
Tom Johnson Tom Johnson
Marlene Drost Marlene Drost
Ed Hallman Ed Hallman
Litchfield Communications Litchfield Communications, Inc.
April 2001 July 2001
SONET/SDH Circuit Emulation Service Over MPLS (CEM) Encapsulation SONET/SDH Circuit Emulation Service Over MPLS (CEM) Encapsulation
draft-malis-sonet-ces-mpls-04.txt draft-malis-sonet-ces-mpls-05.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 RFC 2026 [1]. all provisions of section 10 of RFC 2026 [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
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
skipping to change at page 1, line 49 skipping to change at page 1, line 49
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.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
1. Abstract 1. Abstract
This document describes a method for encapsulating SONET/SDH Path This document describes a method for encapsulating SONET/SDH Path
signals for transport across an MPLS network. signals for transport across packet-switched networks (PSNs). The PSNs
explicitly supported by this document include MPLS and IP.
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 this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [2]. document are to be interpreted as described in RFC 2119 [2].
3. Introduction 3. Introduction
This document describes a method for encapsulating time division This document describes a method for encapsulating time division
multiplexed (TDM) digital signals for transmission over a packet- multiplexed (TDM) digital signals for transmission over packet-
oriented MPLS network. The transmission system for circuit-oriented switched networks.
TDM signals is the Synchronous Optical Network (SONET) [3], [6] /
Synchronous Digital Hierarchy (SDH) [4]. To support TDM traffic, The transmission system for circuit-oriented TDM signals is the
which includes voice, data, and private leased line service, the Synchronous Optical Network (SONET) [3], [6] / Synchronous Digital
MPLS network must emulate the circuit characteristics of SONET/SDH Hierarchy (SDH) [4]. To support TDM traffic (which includes voice,
payloads. MPLS labels and a new circuit emulation header are used data, and private leased line services) PSNs must emulate the
to encapsulate TDM signals and provide the Circuit Emulation Service circuit characteristics of SONET/SDH payloads. MPLS labels and a
over MPLS (CEM). new circuit emulation header are used to encapsulate TDM signals and
provide the Circuit Emulation Service over MPLS (CEM) function. The
MPLS encapsulation may be further encapsulated in IP for carriage
across IP PSNs [8].
This document also describes an optional extension to CEM called This document also describes an optional extension to CEM called
Dynamic Bandwidth Allocation (DBA). This is a method for Dynamic Bandwidth Allocation (DBA). This is a method for
dynamically reducing the bandwidth utilized by emulated SONET/SDH dynamically reducing the bandwidth utilized by emulated SONET/SDH
circuits in the packet network. This bandwidth reduction is circuits in the packet network. This bandwidth reduction is
accomplished by not sending the SONET/SDH payload through the packet accomplished by not sending the SONET/SDH payload through the packet
network under certain conditions such as AIS-P or STS SPE network under certain conditions such as AIS-P or STS SPE
Unequipped. Unequipped.
This document is closely related to references [5], which describes This document is closely related to references [5], which describes
the control protocol methods used to signal the usage of CEM, and the control protocol methods used to signal the usage of CEM, [7],
[7], which describes a related method of encapsulating Layer 2 which describes a related method of encapsulating Layer 2 frames
frames over MPLS and which shares the same signaling. over MPLS and which shares the same signaling, and [11] which
describes a MIB for controlling and observing CEM services.
4. Scope 4. Scope
This document describes how to provide CEM for the following digital This document describes how to provide CEM for the following digital
signals: signals:
1. SONET STS-1 synchronous payload envelope (SPE)/SDH VC-3 1. SONET STS-1 synchronous payload envelope (SPE)/SDH VC-3
2. STS-Nc SPE (N = 3, 12, or 48)/SDH VC-4, VC-4-4c, VC-4-16c 2. STS-Nc SPE (N = 3, 12, or 48)/SDH VC-4, VC-4-4c, VC-4-16c
3. Unstructured SONET Emulation, where the entire SONET bit-stream
(including the transport overhead) is packetized and transported
across the PSN.
For the remainder of this document, these constructs will be For the remainder of this document, these constructs will be
referred to as SONET/SDH channels. referred to as SONET/SDH channels.
Other SONET/SDH signals, such as virtual tributary (VT) structured Other SONET/SDH signals, such as virtual tributary (VT) structured
sub-rate mapping, are not explicitly discussed in this document; sub-rate mapping, are not explicitly discussed in this document;
however, it can be extended in the future to support VT and lower however, it can be extended in the future to support VT and lower
speed non-SONET/SDH services. OC-192c SPE/VC-4-64c are also not speed non-SONET/SDH services. OC-192c SPE/VC-4-64c are also not
included at this point, since most MPLS networks use OC-192c or included at this point, since most PSNs use OC-192c or slower
slower trunks, and thus would not have sufficient capacity. As trunks, and thus would not have sufficient capacity. As trunk
trunk capacities increase in the future, the scope of this document capacities increase in the future, the scope of this document can be
can be accordingly extended. accordingly extended.
5. CEM Encapsulation Format 5. CEM Encapsulation Format
In order to transport SONET/SDH SPEs through a packet-oriented In order to transport SONET/SDH SPEs through a packet-oriented
network, the SPE is broken into fragments. A 32-bit CEM Header is network, the SPE is broken into fragments. A 32-bit CEM Header is
pre-pended to each fragment. The Basic CEM packet appears in Figure pre-pended to each fragment. The Basic CEM packet appears in Figure
1. 1.
+-----------------------------------+ +-----------------------------------+
| CEM Header | | CEM Header |
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| | | |
+-----------------------------------+ +-----------------------------------+
Figure 1. Basic CEM Packet Figure 1. Basic CEM Packet
The 32-bit CEM header has the following format: The 32-bit CEM header has the following format:
0 1 2 3 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 2 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 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|D|Resvd| Sequence Num | Structure Pointer |N|P| ECC-6 | |D|R|Rvd| Sequence Num | Structure Pointer |N|P| ECC-6 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2. CEM Header Format Figure 2. CEM Header Format
The above fields are defined as follows: The above fields are defined as follows:
D bit: Signals DBA Mode. MUST be set to zero for Normal Operation. D bit: Signals DBA Mode. MUST be set to zero for Normal Operation.
MUST be set to one if CEM is currently in DBA mode. DBA is an MUST be set to one if CEM is currently in DBA mode. DBA is an
optional mode during which trivial SPEs are not transmitted into the optional mode during which trivial SPEs are not transmitted into the
packet network. See Table 1 and sections 7 and 8 for further packet network. See Table 1 and sections 7 and 8 for further
details. details. Note: for unstructured CEM, the D-bit MUST be set to zero.
Reserved: These bits are reserved for future use, and MUST be set to R bit: CEM-RDI. This bit is set to one to signal to the remote CEM
function that a loss of packet synchronization has occurred.
Rvd: These bits are reserved for future use, and MUST be set to
zero. zero.
Sequence Number: This is a packet sequence number, which MUST Sequence Number: This is a packet sequence number, which MUST
continuously cycle from 0 to 1023. It SHOULD begin at zero when a continuously cycle from 0 to 1023. It SHOULD begin at zero when a
CEM LSP is created. CEM LSP is created.
Structure Pointer: The Structure Pointer MUST contain the offset of Structure Pointer: The Structure Pointer MUST contain the offset of
the J1 byte within the CEM payload. The value is from 0 to 1,022, the J1 byte within the CEM payload. The value is from 0 to 1,022,
where 0 means the first byte after the CEM header. The Structure where 0 means the first byte after the CEM header. The Structure
Pointer MUST be set to 0x3FF (1,023) if a packet does not carry the Pointer MUST be set to 0x3FF (1,023) if a packet does not carry the
J1 byte. See [3], [4] and [6] for more information on the J1 byte J1 byte. See [3], [4] and [6] for more information on the J1 byte
and the SONET/SDH payload pointer. and the SONET/SDH payload pointer. Note: for unstructured CEM, the
Structure Pointer field MUST be set to 0x3FF.
The N and P bits: Indicate negative and positive pointer adjustment The N and P bits: Indicate negative and positive pointer adjustment
events. They are also used to relay SONET/SDH maintenance signals events. They are also used to relay SONET/SDH maintenance signals
such as AIS-P. See Table 1 and sections 7 and 8 for more details. such as AIS-P. See Table 1 and sections 7 and 8 for more details.
Note: for unstructured CEM, the N and P bits MUST both be set to 0.
+---+---+---+----------------------------------------------+ +---+---+---+----------------------------------------------+
| D | N | P | Interpretation | | D | N | P | Interpretation |
+---+---+---+----------------------------------------------+ +---+---+---+----------------------------------------------+
| 0 | 0 | 0 | Normal Mode û No Ptr Adjustment | | 0 | 0 | 0 | Normal Mode “ No Ptr Adjustment |
| 0 | 0 | 1 | Normal Mode û Positive Ptr Adjustment | | 0 | 0 | 1 | Normal Mode “ Positive Ptr Adjustment |
| 0 | 1 | 0 | Normal Mode û Negative Ptr Adjustment | | 0 | 1 | 0 | Normal Mode “ Negative Ptr Adjustment |
| 0 | 1 | 1 | Normal Mode û AIS-P | | 0 | 1 | 1 | Normal Mode “ AIS-P |
| | | | | | | | | |
| 1 | 0 | 0 | DBA Mode û STS SPE Unequipped | | 1 | 0 | 0 | DBA Mode “ STS SPE Unequipped |
| 1 | 0 | 1 | DBA Mode û STS SPE Unequipped Pos Ptr Adj | | 1 | 0 | 1 | DBA Mode “ STS SPE Unequipped Pos Ptr Adj |
| 1 | 1 | 0 | DBA Mode û STS SPE Unequipped Neg Ptr Adj | | 1 | 1 | 0 | DBA Mode “ STS SPE Unequipped Neg Ptr Adj |
| 1 | 1 | 1 | DBA Mode û AIS-P | | 1 | 1 | 1 | DBA Mode “ AIS-P |
+---+---+---+----------------------------------------------+ +---+---+---+----------------------------------------------+
Table 1. Interpretation of D, N, and P bits Table 1. Interpretation of D, N, and P bits
ECC-6: An Error Correction Code to protect the CEM header. This ECC-6: An Error Correction Code to protect the CEM header. This
offers the ability to correct single bit errors and detect up to two offers the ability to correct single bit errors and detect up to two
bit errors. The ECC algorithm is described in Appendix B. bit errors. The ECC algorithm is described in Appendix B. The ECC-
6 can be optionally disabled at provisioning time. If the ECC-6 is
not utilized it MUST be set to zero.
Note: CEM packets are fixed in length for all of the packets of a Note: Normal CEM packets are fixed in length for all of the packets
particular emulated TDM stream. This length is signaled using the of a particular emulated TDM stream. This length is signaled using
CEM Payload Bytes parameter defined in [5], or is statically the CEM Payload Bytes parameter defined in [5], or is statically
provisioned for each TDM stream. Therefore, the length of each CEM provisioned for each TDM stream. Therefore, the length of each CEM
packet does not need to be carried in the CEM header. packet does not need to be carried in the CEM header.
5.1 Transport Encapsulation 5.1 Transport Encapsulation
In principle, CEM packets can be transported over any packet- In principle, CEM packets can be transported over any packet-
oriented network. The following sections describe specifically how oriented network. The following sections describe specifically how
CEM packets MUST be encapsulated for transport over MPLS or IP CEM packets MUST be encapsulated for transport over MPLS or IP
networks. networks.
5.1.1 MPLS Transport 5.1.1 MPLS Transport
To transport a CEM packet over an MPLS network, an MPLS label-stack To transport a CEM packet over an MPLS network, an MPLS label-stack
MUST be pushed on top of the CEM packet. MUST be pushed on top of the CEM packet.
The last two labels prior to the CEM header are referred to as the The last two labels prior to the CEM header are referred to as the
Tunnel and VC labels. Tunnel and Virtual Circuit (VC) labels.
The VC label is required, and is the last label prior to the CEM The VC label is required, and is the last label prior to the CEM
Header. The VC label MUST be used to identify the CEM connection Header. The VC label MUST be used to identify the CEM connection
within the MPLS tunnel. within the MPLS tunnel.
The optional tunnel label is immediately above the VC label on the The optional tunnel label is immediately above the VC label on the
label stack. If present, the tunnel label MUST be used to identify label stack. If present, the tunnel label MUST be used to identify
the MPLS LSP used to tunnel the TDM packets through the MPLS network the MPLS LSP used to tunnel the TDM packets through the MPLS network
(the tunnel LSP). (the tunnel LSP).
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+-----------------------------------+ +-----------------------------------+
Figure 4. MPLS Transport Encapsulation Figure 4. MPLS Transport Encapsulation
6. CEM Operation 6. CEM Operation
The following sections describe CEM operation. The following sections describe CEM operation.
6.1 Introduction and Terminology 6.1 Introduction and Terminology
CEM MUST support a normal mode of operation and MAY support an There are two types of CEM: structured and unstructured.
optional extension called Dynamic Bandwidth Allocation (DBA).
During normal operation, SONET/SDH payloads are fragmented, pre- Unstructured CEM packetizes the entire SONET/SDH bit-stream
pended with the CEM Header and the MPLS label-stack, and then (including transport overhead).
transmitted into the packet network. During DBA mode, only the CEM
header and MPLS label stack are transmitted. This is done to Structured CEM terminates the transport overhead and packetizes
conserve bandwidth when meaningful user data is not present in the individual channels (STS-1/Nc) within the SONET/SDH frame. Because
SPE, such as during AIS-P or STS SPE Unequipped. structured CEM terminates the transport overhead, structured CEM
implementations SHOULD meet the generic requirements for SONET/SDH
Line Terminating Equipment as defined in [3], [4], and [6].
Implementations MUST support structured CEM and MAY support
unstructured CEM.
Structured CEM MUST support a normal mode of operation and MAY
support an optional extension called Dynamic Bandwidth Allocation
(DBA). During normal operation, SONET/SDH payloads are fragmented,
pre-pended with the CEM Header, the VC label, and the PSN header,
and then transmitted into the packet network. During DBA mode, only
the CEM header, the VC label, and PSN header are transmitted. This
is done to conserve bandwidth when meaningful user data is not
present in the SPE, such as during AIS-P or STS SPE Unequipped.
6.1.1 CEM Packetizer and De-Packetizer 6.1.1 CEM Packetizer and De-Packetizer
As with all adaptation functions, CEM has two distinct components: As with all adaptation functions, CEM has two distinct components:
adapting TDM SONET/SDH into a CEM packet stream, and converting the adapting TDM SONET/SDH into a CEM packet stream, and converting the
CEM packet stream back into a TDM SONET/SDH. The first function CEM packet stream back into a TDM SONET/SDH. The first function
will be referred to as CEM Packetizer and the second as CEM De- will be referred to as CEM Packetizer and the second as CEM De-
Packetizer. This terminology is illustrated in figure 5. Packetizer. This terminology is illustrated in figure 5.
+------------+ +---------------+ +------------+ +---------------+
| | | | | | | |
SONET --> | CEM | --> MPLS --> | CEM | --> SONET SONET --> | CEM | --> PSN --> | CEM | --> SONET
SDH | Packetizer | | De-Packetizer | SDH SDH | Packetizer | | De-Packetizer | SDH
| | | | | | | |
+------------+ +---------------+ +------------+ +---------------+
Figure 5. CEM Terminology Figure 5. CEM Terminology
Note: the CEM receive function requires a buffering mechanism to Note: the CEM de-packetizer requires a buffering mechanism to
account for delay variation in the CEM packet stream. This account for delay variation in the CEM packet stream. This
buffering mechanism will be generically referred to as the CEM buffering mechanism will be generically referred to as the CEM
jitter buffer. jitter buffer.
6.1.2 CEM DBA 6.1.2 CEM DBA
CEM DBA is an optional mode of operation that only transmits the CEM DBA is an optional mode of operation for structured CEM that only
Header and MPLS Label Stack into the packet network under certain transmits the CEM Header, the VC label, and PSN Header into the
circumstances such as AIS-P or STS Unequipped. packet network under certain circumstances such as AIS-P or STS
Unequipped.
If DBA is supported by a CEM implementation, the user SHOULD be able If DBA is supported by a CEM implementation, the user SHOULD be able
to configure if DBA will be triggered by AIS-P, STS Unequipped, to configure if DBA will be triggered by AIS-P, STS Unequipped,
both, or neither on a per channel basis. both, or neither on a per channel basis.
If DBA is supported, the determination of AIS-P and STS Unequipped If DBA is supported, the determination of AIS-P and STS Unequipped
MUST be based on the state of SONET/SDH Section, Line, and Path MUST be based on the state of SONET/SDH Section, Line, and Path
Overhead bytes. DBA based on pattern detection within the SPE (i.e. Overhead bytes. DBA based on pattern detection within the SPE (i.e.
all zeros, 7Es, or ATM idle cells) is for further study. all zeros, 7Es, or ATM idle cells) is for further study.
During AIS-P, there is no valid payload pointer, so pointer During AIS-P, there is no valid payload pointer, so pointer
adjustments cannot occur. During STS Unequipped, the SONET/SDH adjustments cannot occur. During STS Unequipped, the SONET/SDH
payload pointer is valid, and therefore pointer adjustments MUST be payload pointer is valid, and therefore pointer adjustments MUST be
supported even during DBA. See Table 1 for details. supported even during DBA. See Table 1 for details.
6.2 Description of Normal CEM Operation 6.2 Description of Normal CEM Operation
During normal operation, the CEM packetizer will receive a fixed During normal operation, the CEM packetizer will receive a fixed
rate byte stream from a SONET/SDH interface. When a packets worth rate byte stream from a SONET/SDH interface. When a packets worth
of data has been received from a SONET/SDH channel, the CEM Header of data has been received from a SONET/SDH channel, the CEM Header,
and MPLS label stack are pre-pended to the SPE fragment and the the VC Label, and PSN Header are pre-pended to the SPE fragment and
resulting CEM packet is transmitted into the MPLS network. Because the resulting CEM packet is transmitted into the packet network.
all CEM packets associated with a specific SONET/SDH channel will Because all normal CEM packets associated with a specific SONET/SDH
have the same length, the transmission of CEM packets for that channel will have the same length, the transmission of CEM packets
channel SHOULD occur at regular intervals. for that channel SHOULD occur at regular intervals.
At the far end of the packet network, the CEM de-packetizer will At the far end of the packet network, the CEM de-packetizer will
receive packets into a jitter buffer and then play out the received receive packets into a jitter buffer and then play out the received
byte stream at a fixed rate onto the corresponding SONET/SDH byte stream at a fixed rate onto the corresponding SONET/SDH
channel. The jitter buffer SHOULD be adjustable in length to channel. The jitter buffer SHOULD be adjustable in length to
account for varying network delay behavior. The receive packet rate account for varying network delay behavior. The receive packet rate
from the packet network should be exactly balanced by the from the packet network should be exactly balanced by the
transmission rate onto the SONET/SDH channel, on average. The time transmission rate onto the SONET/SDH channel, on average. The time
over which this average is taken corresponds to the depth of the over which this average is taken corresponds to the depth of the
jitter buffer for a specific CEM channel. jitter buffer for a specific CEM channel.
The CEM sequence numbers provide a mechanism to detect lost and/or
mis-ordered packets. The CEM de-packetizer MUST detect lost or mis-
ordered packets. The CEM de-packetizer MUST play out a programmable
byte pattern in place of any dropped packets. The CEM de-packetizer
MAY re-order packets received out of order. If the CEM de-
packetizer does not support re-ordering, it MUST drop mis-ordered
packets.
6.3 Description of CEM Operation during DBA 6.3 Description of CEM Operation during DBA
(Note: DBA is only applicable to structured CEM.)
There are several issues that should be addressed by a workable CEM There are several issues that should be addressed by a workable CEM
DBA mechanism. First, when DBA is invoked, there should be a DBA mechanism. First, when DBA is invoked, there should be a
substantial savings in bandwidth utilization in the packet network. substantial savings in bandwidth utilization in the packet network.
The second issue is that the transition in and out of DBA should be The second issue is that the transition in and out of DBA should be
tightly coordinated between the local CEM packetizer and CEM de- tightly coordinated between the local CEM packetizer and CEM de-
packetizer at the far side of the packet network. A third is that packetizer at the far side of the packet network. A third is that
the transition in and out of DBA should be accomplished with minimal the transition in and out of DBA should be accomplished with minimal
disruption to the adapted data stream. disruption to the adapted data stream.
Another goal is that the reduction of CEM traffic due to DBA should Another goal is that the reduction of CEM traffic due to DBA should
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Finally, the implementation of DBA should require minimal Finally, the implementation of DBA should require minimal
modifications beyond what is necessary for the nominal CEM case. modifications beyond what is necessary for the nominal CEM case.
The mechanism described below is a reasonable balance of these The mechanism described below is a reasonable balance of these
goals. goals.
During DBA, packets MUST be emitted at exactly the same rate as they During DBA, packets MUST be emitted at exactly the same rate as they
would be during normal operation. This SHOULD be accomplished by would be during normal operation. This SHOULD be accomplished by
transmitting each DBA packet after a complete packet of data has transmitting each DBA packet after a complete packet of data has
been received from the SONET/SDH channel. The only change from been received from the SONET/SDH channel. The only change from
normal operation is that the CEM packets during DBA MUST only carry normal operation is that the CEM packets during DBA MUST only carry
the CEM header and the MPLS label stack. The D-bit MUST be set to the CEM header, the VC Label, and the PSN Header.
one, to indicate that DBA is active.
Because some links have a minimum supported packet size, the CEM
packetizer MAY append a configurable number of bytes immediately
after the CEM-header to pad out the CEM packet to reach the mimumum
supported packet size. The value of the padding bytes is
implementation specific. The D-bit MUST be set to one, to indicate
that DBA is active.
The CEM de-packetizer MUST assume that each packet received with the The CEM de-packetizer MUST assume that each packet received with the
D-bit set represents a normal-sized packet containing an AIS-P or D-bit set represents a normal-sized packet containing an AIS-P or
SPE Unequipped payload as noted by N and P. See Table 1. SPE Unequipped payload as noted by N and P. See Table 1. The CEM
de-packetizer MUST accept DBA packets with or without padding.
This allows the CEM packetization and de-packetization logic during This allows the CEM packetization and de-packetization logic during
DBA to be virtually identical to the nominal case. It insures that DBA to be similar to the nominal case. It insures that the correct
the correct SONET/SDH indication is reliably transmitted between CEM SONET/SDH indication is reliably transmitted between CEM adaptation
adaptation points. It minimizes the risk of under or over running points. It minimizes the risk of under or over running the jitter
the jitter buffer during the transition in and out of DBA. And, it buffer during the transition in and out of DBA. And, it guarantees
guarantees that faults in the packet network are recognized as that faults in the packet network are recognized as distinctly
distinctly different from line conditioning on the SONET/SDH different from line conditioning on the SONET/SDH interfaces.
interfaces.
6.4 Packet Synchronization
A key component in declaring the state of a CEM service is whether
or not the CEM de-packetizer is in or out of packet synchronization.
The following paragraphs describe how that determination is made.
6.4.1 Acquisition of Packet Synchronization
At startup, a CEM de-packetizer will be out of packet
synchronization by default. To declare packet synchronization at
startup or after a loss of packet synchronization, the CEM de-
packetizer must receive a configurable number of CEM packets with
sequential sequence numbers.
6.4.2 Loss of Packet Synchronization
Once a CEM de-packetizer is in packet sync, it may encounter a set
of events that will cause it to lose packet synchronization.
As discussed in section 6.2, a CEM de-packetizer MAY or MAY NOT
support re-ordering of mis-ordered packets.
If a CEM de-packetizer supports re-ordering, then the determination
that packet synchronization has been lost cannot be made at the time
the packets are received from the PSN. Instead, the determination
MUST be made as the packets are being played out onto the SONET/SDH
interface. This is because it is only at play-out time that the
determination can be made as to whether the entire emulated
SONET/SDH stream was received from the PSN.
If a CEM de-packetizer does not support re-ordering, a number of
approaches may be used to minimize the impact of mis-ordered or lost
packets on the final re-assembled SONET/SDH stream. For example,
AAL1 [9] uses a simple state-machine to re-order packets in a sub-
set of possible cases. The algorithm for these state-machines is
outside of the scope of CEM. However, the final determination as to
whether or not to declare loss of packet synchronization MUST be
based on the same criteria as for implementations that do support
re-ordering.
Whether or not a CEM implementation supports re-ordering, the
declaration of loss of packet synchronization MUST be based on the
following criteria.
As packets are played out towards the SONET/SDH interface, the CEM
de-packetizer will encounter Ÿempty÷ packets in the place of packets
that were dropped by the PSN, or effectively dropped due to
limitations of the CEM implementation. If the CEM de-packetizer
encounters more than a configurable number of sequential dropped
packets, the CEM de-packetizer MUST declare loss of packet
synchronization.
7. SONET/SDH Maintenance Signals 7. SONET/SDH Maintenance Signals
There are several issues that must be considered in the mapping of There are several issues that must be considered in the mapping of
maintenance signals between SONET/SDH and MPLS. A description of maintenance signals between SONET/SDH and a PSN. A description of
how these signals and conditions are mapped between the two domains how these signals and conditions are mapped between the two domains
is described below. is described below.
For clarity, the mappings are split into two groups: SONET/SDH to For clarity, the mappings are split into two groups: SONET/SDH to
MPLS, and MPLS to SONET/SDH. PSN, and PSN to SONET/SDH.
7.1 SONET/SDH to MPLS 7.1 SONET/SDH to PSN
The following sections describe how SONET/SDH Maintenance Signals The following sections describe how SONET/SDH Maintenance Signals
and Alarm conditions are mapped into MPLS. and Alarm conditions are mapped into a Packet Switched Network.
7.1.1 AIS-P Indication 7.1.1 AIS-P Indication
In a SONET/SDH network, circuit outages are signaled using In a SONET/SDH network, SONET/SDH Path outages are signaled using
maintenance alarms such as Path AIS (AIS-P). In particular, AIS-P maintenance alarms such as Path AIS (AIS-P). In particular, AIS-P
indicates that the SONET/SDH Path is not currently transmitting indicates that the SONET/SDH Path is not currently transmitting
valid end-user data, and the SPE contains all ones. valid end-user data, and the SPE contains all ones.
It should be noted that nearly every type of service-effecting It should be noted that for structured CEM nearly every type of
section or line defect will result in an AIS-P condition. service-effecting section or line defect will result in an AIS-P
condition.
The SONET/SDH hierarchy is illustrated below. The SONET/SDH hierarchy is illustrated below.
+----------+ +----------+
| PATH | | PATH |
+----------+ +----------+
^ ^
| |
AIS-P AIS-P
| |
| |
skipping to change at page 10, line 31 skipping to change at page 12, line 44
+----------+ +----------+
| SECTION | | SECTION |
+----------+ +----------+
^ ^ ^ ^
| | | |
| | | |
LOS LOF LOS LOF
Figure 6. SONET/SDH Fault Hierarchy. Figure 6. SONET/SDH Fault Hierarchy.
Should the Section Layer detect a Loss of Section (LOS) or Loss of Should the Section Layer detect a Loss of Signal (LOS) or Loss of
Frame (LOF) condition, it sends AIS-L up to the Line Layer. If the Frame (LOF) condition, it sends AIS-L up to the Line Layer. If the
Line Layer detects AIS-L or Loss of Path (LOP), it sends AIS-P to Line Layer detects AIS-L or Loss of Path (LOP), it sends AIS-P to
the Path Layer. the Path Layer.
In normal mode during AIS-P, CEM packets are generated as usual. In normal mode during AIS-P, structured CEM packets are generated as
The N and P bits MUST be set to 11 binary to signal AIS-P explicitly usual. The N and P bits MUST be set to 11 binary to signal AIS-P
through the packet network. The D-bit MUST be set to zero to explicitly through the packet network. The D-bit MUST be set to
indicate that the SPE is being carried through the packet network. zero to indicate that the SPE is being carried through the packet
Normal CEM packets with the SPE fragment, CEM Header, and MPLS label network. Normal CEM packets with the SPE fragment, CEM Header, the
stack MUST be transmitted into the packet network. VC Label, and PSN Header MUST be transmitted into the packet
network.
However, to conserve network bandwidth during AIS-P, DBA MAY be However, to conserve network bandwidth during AIS-P, DBA MAY be
employed. If DBA has been enabled for AIS-P and AIS-P is currently employed. If DBA has been enabled for AIS-P and AIS-P is currently
occurring, the N and P bits MUST be set to 11 binary to signal AIS, occurring, the N and P bits MUST be set to 11 binary to signal AIS,
and the D-bit MUST be set to one to indicate that the SPE is not and the D-bit MUST be set to one to indicate that the SPE is not
being carried through the packet network. Only the CEM header and being carried through the packet network. Only the CEM header, the
the MPLS label stack MUST be transmitted into the packet network. VC Label, and the PSN Header MUST be transmitted into the packet
network.
Also note that this differs from the outage mechanism in [5], which Also note that this differs from the outage mechanism in [5], which
withdraws labels as a result of an endpoint outage. TDM circuit withdraws the VC label as a result of an endpoint outage. TDM
emulation requires the ability to distinguish between the de- circuit emulation requires the ability to distinguish between the
provisioning of a circuit, which would cause the labels to be de-provisioning of a circuit (which causes the VC label to be
withdrawn, and temporary outages, which are signaled using AIS-P. withdrawn), and temporary outages (which are signaled using AIS-P).
7.1.2 STS SPE Unequipped Indication 7.1.2 STS SPE Unequipped Indication
The STS SPE Unequipped Indication is a slightly different case than The STS SPE Unequipped Indication is a slightly different case than
AIS-P. When byte C2 of the Path Overhead (STS path signal label) is AIS-P. When byte C2 of the Path Overhead (STS path signal label) is
00h and Byte B3 (STS Path BIP-8) is valid, it indicates that the SPE 00h and Byte B3 (STS Path BIP-8) is valid, it indicates that the SPE
is unequipped. Note: this is typically signaled by setting the is unequipped. Note: this is typically signaled by setting the
entire SPE to zeros. entire SPE to zeros.
For normal operation during SPE Unequipped, the N and P bits MUST be For normal structured CEM operation during SPE Unequipped, the N and
interpreted as usual. The SPE MUST be transmitted into the packet P bits MUST be interpreted as usual. The SPE MUST be transmitted
network along with the CEM Header and MPLS label stack, and the D- into the packet network along with the CEM Header, the VC Label, and
Bit MUST be set to zero. PSN Header, and the D-Bit MUST be set to zero.
If DBA has been enabled for STS SPE Unequipped and the Unequipped is If DBA has been enabled for STS SPE Unequipped and the Unequipped
occurring on the SONET/SDH channel, the D-bit MUST be set to one to condition is occurring on the SONET/SDH channel, the D-bit MUST be
indicate DBA is active. Only the CEM Header and MPLS Label Stack set to one to indicate DBA is active. Only the CEM Header, the VC
must be transmitted into the packet network. The N and P bits MUST Label, and PSN Header MUST be transmitted into the packet network.
be used to signal pointer adjustments as normal. See Table 1 and The N and P bits MUST be used to signal pointer adjustments as
section 8 for details. normal. See Table 1 and section 8 for details.
7.1.3 RDI-P Indication 7.1.3 CEM-RDI
The CEM function MUST send RDI-P towards the packet network under a The CEM function MUST send CEM-RDI towards the packet network during
variety of network errors such as loss of packet synchronization. loss of packet synchronization. This MUST be accomplished by
This MUST be accomplished by modifying the SONET/SDH Path Overhead setting the R bit to one in the CEM header. This applies for both
within the CEM packets. Specifically the G1 byte must be updated to structured and unstructured CEM.
signal RDI-P and the B3 (Path BIP-8) must be re-computed. See [3],
[4], and [6] for details.
7.2 MPLS to SONET/SDH 7.2 PSN to SONET/SDH
The following sections discuss how the various conditions on the The following sections discuss how the various conditions on the
packet network are converted into SONET/SDH indications. packet network are converted into SONET/SDH indications.
7.2.1 AIS-P Indication 7.2.1 AIS-P Indication
There are several conditions in the packet network that will cause There are several conditions in the packet network that will cause
the CEM de-packetization function to send an AIS-P indication onto a the structured CEM de-packetization function to send an AIS-P
SONET/SDH channel. indication onto a SONET/SDH channel.
The first of these is the receipt of CEM packets with the N and P The first of these is the receipt of structured CEM packets with the
bits set to one, and the D-bit set to zero. This is an explicit N and P bits set to one, and the D-bit set to zero. This is an
indication of AIS-P being received at the far-end of the packet explicit indication of AIS-P being received at the far-end of the
network, with DBA disabled for AIS-P. The CEM de-packetizer MUST packet network, with DBA disabled for AIS-P. The CEM de-packetizer
play out the received SPE fragment (which will incidentally be MUST play out the received SPE fragment (which will incidentally be
carrying all ones), and MUST configure the SONET/SDH Overhead to carrying all ones), and MUST configure the SONET/SDH Overhead to
signal AIS-P as defined in [3], [4], and [6]. signal AIS-P as defined in [3], [4], and [6].
The second case is the receipt of CEM packets with the N and P bits The second case is the receipt of structured CEM packets with the N
set to one, and the D-bit set to one. This is an explicit and P bits set to one, and the D-bit set to one. This is an
indication of AIS-P being received at the far-end of the packet explicit indication of AIS-P being received at the far-end of the
network, with DBA enabled for AIS-P. The CEM de-packetizer MUST packet network, with DBA enabled for AIS-P. The CEM de-packetizer
play out one packetÆs worth of all ones for each packet received, MUST play out one packetËs worth of all ones for each packet
and MUST configure the SONET/SDH Overhead to signal AIS-P as defined received, and MUST configure the SONET/SDH Overhead to signal AIS-P
in [3], [4], and [6]. as defined in [3], [4], and [6].
Additional conditions that SHOULD trigger the transmission of AIS-P A third case that will cause a structured CEM de-packetization
onto a SONET/SDH channel include loss of packet synchronization and function to send an AIS-P indication onto a SONET/SDH channel is
jitter buffer under-run. The definition of these conditions are loss of packet synchronization.
under investigation and will be clarified in a subsequent revision
of this draft.
7.2.2 STS SPE Unequipped Indication 7.2.2 STS SPE Unequipped Indication
There are two conditions in the packet network that will cause the There are three conditions in the packet network that will cause the
CEM function to transmit STS SPE Unequipped indications onto the CEM function to transmit STS SPE Unequipped indications onto the
SONET/SDH channel. SONET/SDH channel.
The first, which is transparent to CEM, is the receipt of regular The first, which is transparent to CEM, is the receipt of regular
CEM packets that happen to be carrying an SPE that contains the CEM packets that happen to be carrying an SPE that contains the
appropriate Path overhead to signal STS SPE unequipped. This case appropriate Path overhead to signal STS SPE unequipped. This case
does not require any special processing on the part of the CEM de- does not require any special processing on the part of the CEM de-
packetizer. packetizer.
The second case is the receipt of CEM packets that have the D-bit The second case is the receipt of structured CEM packets that have
set to one to indicate DBA active and the N and P bits set to 00 the D-bit set to one to indicate DBA active and the N and P bits set
binary, 01 binary, or 10 binary to indicate SPE Unequipped with or to 00 binary, 01 binary, or 10 binary to indicate SPE Unequipped
without pointer adjustments. The CEM de-packetizer MUST use this with or without pointer adjustments. The CEM de-packetizer MUST use
information to transmit a packet of all zeros onto the SONET/SDH this information to transmit a packet of all zeros onto the
interface, and adjust the payload pointer as necessary. SONET/SDH interface, and adjust the payload pointer as necessary.
7.2.3 RDI-P Indication
The CEM function MUST send an RDI-P towards a SONET/SDH channel The third case when a structured CEM de-packetizer MUST send an STS
under the conditions defined for SONET/SDH Line Terminating SPE Unequipped Indication towards the SONET/SDH interface is when
equipment in [3], [4], and [6]. the VC-label has been withdrawn due to de-provisioning of the
circuit.
8. Clocking Modes 8. Clocking Modes
It is necessary to be able to regenerate the input service clock at It is necessary to be able to regenerate the input service clock at
the output interface. Two clocking modes are supported: synchronous the output interface. Two clocking modes are supported: synchronous
and asynchronous. and asynchronous. Selection of the clocking mode is made as part of
service provisioning. Both ends of the emulated circuit must be
configured with the same clocking mode.
8.1 Synchronous 8.1 Synchronous
When synchronous SONET/SDH timing is available at both ends of the When synchronous SONET/SDH timing is available at both ends of the
circuit, the N and P bits are used to signal negative or positive circuit, the issue of clock recovery becomes much simpler.
pointer justification events.
8.1.1 Synchronous Unstructured CEM
For unstructured CEM, the external clock is used to clock each bit
onto the optical carrier.
8.1.2 Synchronous Structured CEM
For structured CEM, the external clock is used to clock the
SONET/SDH carrier. The N and P bits are used to signal negative or
positive pointer justification events between structured CEM end-
points.
If there is a frequency offset between the frame rate of the If there is a frequency offset between the frame rate of the
transport overhead and that of the SONET/SDH SPE, then the alignment transport overhead and that of the SONET/SDH SPE, then the alignment
of the SPE shall periodically slip back or advance in time through of the SPE shall periodically slip back or advance in time through
positive or negative stuffing. The N and P bits are used to replay positive or negative stuffing. The N and P bits are used to replay
the stuff indicators and eliminate transport jitter. the pointer adjustment events and eliminate transport jitter.
During a negative pointer adjustment event, the H3 byte from the
SONET/SDH stream is incorporated into the CEM packet payload in
order with the rest of the SPE. During a positive pointer
adjustment event, the stuff byte is not included in the CEM packet
payload.
The pointer adjustment event MUST be transmitted in three The pointer adjustment event MUST be transmitted in three
consecutive packets by the packetizer. The de-packetizer MUST play consecutive packets by the packetizer. The de-packetizer MUST play
out the pointer adjustment event when any one packet with N/P bit out the pointer adjustment event when the first packet of the three
set is received. with N/P bit set is received.
Furthermore, it is possible for pointer adjustments to occur in back
to back SONET/SDH frames. In order to support this possibility, the
packet size for a particular circuit MUST be no larger than
(783*N)/3. Where N is the STS-Nc multiplier.
Since the minimum value of N is one, all CEM implementations MUST
support a minimum payload length of 783/3 or 261 bytes. Smaller
payload lengths MAY be supported as an option.
The CEM de-packetizer MUST utilize the CEM sequence numbers to The CEM de-packetizer MUST utilize the CEM sequence numbers to
insure that SONET/SDH pointer adjustment events are not played any insure that SONET/SDH pointer adjustment events are not played any
more frequently than once per every three CEM packets transmitted by more frequently than once per every three CEM packets transmitted by
the remote CEM packetizer. the remote CEM packetizer.
If both bits are set, then an AIS-P event has occurred (this is References [3],[4],and [6] specify that pointer adjustment events
further discussed in section 7). MUST be separated by three SONET/SDH frames without a pointer
adjustment event. In order to relay all legal pointer adjustment
events, the packet size for a specific circuit MUST be no larger
than (783 * 4 * N)/3, where N is the STS-Nc multiplier.
When DBA is invoked (i.e. the D-bit = 1), N and P have additional However, some SONET/SDH equipment allows pointer adjustments to
meanings. See Table 1 and section 7. occur in back to back SONET/SDH frames. In order to support this
possibility, the packet size for a particular circuit SHOULD be no
larger than (783*N)/3. Where N is the STS-Nc multiplier.
Since the minimum value of N is one, CEM implementations SHOULD
support a minimum payload length of 783/3 or 261 bytes. Smaller
payload lengths MAY be supported as an option.
8.2 Asynchronous 8.2 Asynchronous
If synchronous timing is not available, the N and P bits are not If synchronous timing is not available, other methods MAY be
used for frequency justification and adaptive methods are used to employed to regenerate the circuit timing.
recover the timing. The N and P bits are only used for the
occurrence of a path AIS event. An example adaptive method can be For structured CEM, the CEM packetizer SHOULD generate the N and P
found in section 3.4.2 of [9]. bits as usual. However, without external synchronization, this
information is not sufficient to reliably justify the SPE within the
SONET/SDH transport framing at the CEM de-packetizer. The de-
packetizer MAY employ an adaptive algorithm to introduce pointer
adjustment events to map the CEM SPE to the SONET/SDH transport
framing. Regardless of whether the N and P bits are used by the de-
packetizer as part of the adaptive clock recovery algorithm, they
MUST still be used in conjunction with the D-bit to signal AIS-P,
SPE Unequipped, and DBA.
For unstructured CEM, the CEM de-packetizer MAY use an adaptive
clock recovery technique to regenerate the SONET/SDH transport
clock.
An example adaptive clock recovery method can be found in section
3.4.2 of [10].
9. CEM LSP Signaling 9. CEM LSP Signaling
For maximum network scaling, CEM LSP signaling may be performed For maximum network scaling in MPLS applications, CEM LSP signaling
using the LDP Extended Discovery mechanism as augmented by the VC may be performed using the LDP Extended Discovery mechanism as
FEC Element defined in [5]. MPLS traffic tunnels may be dedicated augmented by the VC FEC Element defined in [5]. MPLS traffic
to CEM, or shared with other MPLS-based services. The value 8008 is tunnels may be dedicated to CEM, or shared with other MPLS-based
used for the VC Type in the VC FEC Element in order to signify that services. The value 8008 is used for the VC Type in the VC FEC
the LSP being signaled is to carry CEM. Note that the generic Element in order to signify that the LSP being signaled is to carry
control word defined in [6] is not used, as its functionality is CEM. Note that the generic control word defined in [6] is not used,
included in the CEM encapsulation header. as its functionality is included in the CEM encapsulation header.
Alternatively, static label assignment may be used, or a dedicated Alternatively, static label assignment may be used, or a dedicated
traffic engineered LSP may be used for each CEM circuit. traffic engineered LSP may be used for each CEM service.
CEM packets are fixed in length for all of the packets of a Normal CEM packets are fixed in length for all of the packets of a
particular emulated TDM stream. This length is signaled using the particular emulated TDM stream. This length is signaled using the
CEM Payload Bytes parameter defined in [5], or is statically CEM Payload Bytes parameter defined in [5], or is statically
provisioned for each TDM stream. provisioned for each CEM service.
The use of DBA is signaled by the use of the CEM Options parameter At this time, other aspects of the CEM service MUST be statically
defined in [5], or is statically provisioned for each TDM stream. provisioned. The CEM-MIB [11] provides a method for statically
provisioning CEM services.
In [5], Parameter ID 0x05 is allocated for †CEM OptionsË. At this
time, the CEM Options parameter is reserved and MUST be set to zero.
The use of the CEM Options parameter is for future consideration.
10. Open Issues 10. Open Issues
Future revisions of this document may discuss the following items. Future revisions of this document may discuss the following items.
Underlying MPLS QoS requirements are not covered by this revision of Underlying MPLS QoS requirements are not covered by this revision of
the draft. Future revisions may discuss underlying QoS the draft. Future revisions may discuss underlying QoS
requirements. requirements.
Support for VT and lower speed non-SONET/SDH services are not Support for VT and lower speed non-SONET/SDH services are not
covered in this revision of the draft. Future revisions may address covered in this revision of the draft. Future revisions may address
VT and non-SONET/SDH TDM services. VT and non-SONET/SDH TDM services.
The current draft only considers DBA based on SONET/SDH Overhead. Use of the CEM Options parameter in [5] is currently undefined.
It would be very desirable to extending DBA to include pattern-based Future revision of this draft will determine how the CEM Options
suppression such as long runs of HDLC flags (i.e. 0x7E). One issue word will be used.
that complicates pattern-based DBA is that the path overhead appears
every Nx87 bytes within the SPE. One solution may be to have a
special mode of DBA, where the Path Overhead is explicitly
transported within the packet along with the specific pattern (e.g.
7E).
This revision of the draft does not provide a definition for æloss The CEM-MIB[11] calls out a number of CEM performance parameters
of packet synchronizationÆ or æjitter buffer under-runÆ. Details such as Errored Seconds, Severely Errored Seconds, and Unavailable
for declaring these conditions at the de-packetizer will be Seconds. These terms are currently not defined in this draft. The
addressed in future revisions. definition of these terms is for future consideration.
The current draft only considers DBA based on SONET/SDH Overhead.
It may be desirable to extending DBA to include pattern-based
suppression such as long runs of HDLC flags (i.e. 0x7E).
11. Security Considerations 11. Security Considerations
As with [5], this document does not affect the underlying security As with [5], this document does not affect the underlying security
issues of MPLS. issues of MPLS.
12. Intellectual Property Disclaimer 12. Intellectual Property Disclaimer
This document is being submitted for use in IETF standards This document is being submitted for use in IETF standards
discussions. Vivace Networks, Inc. has filed one or more patent discussions. Vivace Networks, Inc. has filed one or more patent
skipping to change at page 15, line 29 skipping to change at page 18, line 29
Levels", BCP 14, RFC 2119, March 1997 Levels", BCP 14, RFC 2119, March 1997
[3] American National Standards Institute, "Synchronous Optical [3] American National Standards Institute, "Synchronous Optical
Network (SONET) - Basic Description including Multiplex Network (SONET) - Basic Description including Multiplex
Structure, Rates and Formats," ANSI T1.105-1995. Structure, Rates and Formats," ANSI T1.105-1995.
[4] ITU Recommendation G.707, "Network Node Interface For The [4] ITU Recommendation G.707, "Network Node Interface For The
Synchronous Digital Hierarchy", 1996. Synchronous Digital Hierarchy", 1996.
[5] Martini et al, "Transport of Layer 2 Frames Over MPLS", draft- [5] Martini et al, "Transport of Layer 2 Frames Over MPLS", draft-
martini-l2circuit-trans-mpls-05.txt, work in progress, February martini-l2circuit-trans-mpls-06.txt, work in progress, July
2001. 2001.
[6] Telcordia Technologies, ôSynchronous Optical Network (SONET) [6] Telcordia Technologies, ŸSynchronous Optical Network (SONET)
Transport Systems: Common Generic Criteriaö, GR-253-CORE, Issue Transport Systems: Common Generic Criteria÷, GR-253-CORE, Issue
3, September 2000. 3, September 2000.
[7] Martini et al, "Encapsulation Methods for Transport of Layer 2 [7] Martini et al, "Encapsulation Methods for Transport of Layer 2
Frames Over MPLS", draft-martini-l2circuit-encap-mpls-01.txt, Frames Over MPLS", draft-martini-l2circuit-encap-mpls-02.txt,
work in progress, February 2001. work in progress, July 2001.
[8] Worster, ôMPLS Label Stack Encapsulation in IPö, draft-worster- [8] Worster, ŸMPLS Label Stack Encapsulation in IP÷, draft-worster-
mpls-in-ip-04, work in progress, Expires August 2001. mpls-in-ip-05, work in progress, July 2001.
[9] ATM Forum, "Circuit Emulation Service Interoperability [9] ITU-T, ŸRecommendation I.363.1, B-ISDN Adaptation Layer
Specification: Type AAL1÷, Appendix III, August 1996.
[10] ATM Forum, "Circuit Emulation Service Interoperability
Specification Version 2.0", af-vtoa-0078.000, January 1997. Specification Version 2.0", af-vtoa-0078.000, January 1997.
13. Acknowledgments [11] Danenberg et al, "SONET/SDH Circuit Emulation Service Over MPLS
(CEM) Management Information Base Using SMIv2", draft-
danenberg-pw-cem-mib-01.txt, work in progress, July 2001.
14. Acknowledgments
The authors would like to thank Mitri Halabi and Bob Colvin, both of The authors would like to thank Mitri Halabi and Bob Colvin, both of
Vivace Networks, for their comments and suggestions. Vivace Networks, for their comments and suggestions.
14. Authors' Addresses 15. Authors' Addresses
Andrew G. Malis Andrew G. Malis
Vivace Networks, Inc. Vivace Networks, Inc.
2730 Orchard Parkway 2730 Orchard Parkway
San Jose, CA 95134 San Jose, CA 95134
Email: Andy.Malis@vivacenetworks.com Email: Andy.Malis@vivacenetworks.com
Ken Hsu Ken Hsu
Vivace Networks, Inc. Vivace Networks, Inc.
2730 Orchard Parkway 2730 Orchard Parkway
San Jose, CA 95134 San Jose, CA 95134
Email: Ken.Hsu@vivacenetworks.com Email: Ken.Hsu@vivacenetworks.com
skipping to change at page 16, line 40 skipping to change at page 19, line 46
Sewickley, PA 15143 Sewickley, PA 15143
Email: jshirron@laurelnetworks.com Email: jshirron@laurelnetworks.com
Luca Martini Luca Martini
Level 3 Communications, LLC. Level 3 Communications, LLC.
1025 Eldorado Blvd. 1025 Eldorado Blvd.
Broomfield, CO 80021 Broomfield, CO 80021
Email: luca@level3.net Email: luca@level3.net
Thomas K. Johnson Thomas K. Johnson
Litchfield Communications Litchfield Communications, Inc.
76 Westbury Park Rd. 76 Westbury Park Rd.
Watertown, CT 06795 Watertown, CT 06795
Email: tom_johnson@litchfieldcomm.com Email: tom_johnson@litchfieldcomm.com
Ed Hallman Ed Hallman
Litchfield Communications Litchfield Communications, Inc.
76 Westbury Park Rd. 76 Westbury Park Rd.
Watertown, CT 06795 Watertown, CT 06795
Email: ed_hallman@litchfieldcomm.com Email: ed_hallman@litchfieldcomm.com
Marlene Drost Marlene Drost
Litchfield Communications Litchfield Communications, Inc.
76 Westbury Park Rd. 76 Westbury Park Rd.
Watertown, CT 06795 Watertown, CT 06795
Email: marlene_drost@litchfieldcomm.com Email: marlene_drost@litchfieldcomm.com
Appendix A. SONET/SDH Rates and Formats Appendix A. SONET/SDH Rates and Formats
For simplicity, the discussion in this section uses SONET For simplicity, the discussion in this section uses SONET
terminology, but it applies equally to SDH as well. SDH-equivalent terminology, but it applies equally to SDH as well. SDH-equivalent
terminology is shown in the tables. terminology is shown in the tables.
The basic SONET modular signal is the synchronous transport signal- The basic SONET modular signal is the synchronous transport signal-
skipping to change at page 17, line 23 skipping to change at page 21, line 23
(SPEs). The optical counterpart of the STS-N is the Optical Carrier- (SPEs). The optical counterpart of the STS-N is the Optical Carrier-
level N, or OC-N. Table 2 lists standard SONET line rates discussed level N, or OC-N. Table 2 lists standard SONET line rates discussed
in this document. in this document.
OC Level OC-1 OC-3 OC-12 OC-48 OC-192 OC Level OC-1 OC-3 OC-12 OC-48 OC-192
SDH Term - STM-1 STM-4 STM-16 STM-64 SDH Term - STM-1 STM-4 STM-16 STM-64
Line Rate(Mb/s) 51.840 155.520 622.080 2,488.320 9,953.280 Line Rate(Mb/s) 51.840 155.520 622.080 2,488.320 9,953.280
Table 2. Standard SONET Line Rates Table 2. Standard SONET Line Rates
Each SONET frame is 125 ´s and consists of nine rows. An STS-N frame Each SONET frame is 125 ³s and consists of nine rows. An STS-N frame
has nine rows and N*90 columns. Of the N*90 columns, the first N*3 has nine rows and N*90 columns. Of the N*90 columns, the first N*3
columns are transport overhead and the other N*87 columns are SPEs. columns are transport overhead and the other N*87 columns are SPEs.
A number of STS-1s may also be linked together to form a super-rate A number of STS-1s may also be linked together to form a super-rate
signal with only one SPE. The optical super-rate signal is denoted signal with only one SPE. The optical super-rate signal is denoted
as OC-Nc, which has a higher payload capacity than OC-N. as OC-Nc, which has a higher payload capacity than OC-N.
The first 9-byte column of each SPE is the path overhead (POH) and The first 9-byte column of each SPE is the path overhead (POH) and
the remaining columns form the payload capacity with fixed stuff the remaining columns form the payload capacity with fixed stuff
(STS-Nc only). The fixed stuff, which is purely overhead, is N/3-1 (STS-Nc only). The fixed stuff, which is purely overhead, is N/3-1
columns for STS-Nc. Thus, STS-1 and STS-3c do not have any fixed columns for STS-Nc. Thus, STS-1 and STS-3c do not have any fixed
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SDH VC Level - VC-4 VC-4-4c VC-4-16c VC-4-64c SDH VC Level - VC-4 VC-4-4c VC-4-16c VC-4-64c
Payload Size(Bytes) 774 2,340 9,360 37,440 149,760 Payload Size(Bytes) 774 2,340 9,360 37,440 149,760
Payload Rate(Mb/s) 49.536 149.760 599.040 2,396.160 9,584.640 Payload Rate(Mb/s) 49.536 149.760 599.040 2,396.160 9,584.640
SPE Size(Bytes) 783 2,349 9,396 37,584 150,336 SPE Size(Bytes) 783 2,349 9,396 37,584 150,336
SPE Rate(Mb/s) 50.112 150.336 601.344 2,405.376 9,621.504 SPE Rate(Mb/s) 50.112 150.336 601.344 2,405.376 9,621.504
Table 2. Payload Size and Rate Table 2. Payload Size and Rate
To support circuit emulation, the entire SPE of a SONET STS or SDH To support circuit emulation, the entire SPE of a SONET STS or SDH
VC level is encapsulated into packets, using the encapsulation VC level is encapsulated into packets, using the encapsulation
defined in section 5, for carriage across MPLS networks. defined in section 5, for carriage across packet-switched networks.
Appendix B. ECC-6 Definition Appendix B. ECC-6 Definition
ECC-6 is an Error Correction Code to protect the CEM header. This ECC-6 is an Error Correction Code to protect the CEM header. This
provides single bit correction and the ability to detect up to two provides single bit correction and the ability to detect up to two
bit errors. bit errors.
Error Correction Code: Error Correction Code:
|---------------Header bits 0-25 -------------------| ECC-6 code| |---------------Header bits 0-25 -------------------| ECC-6 code|
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} }
} }
In other words, for each CEM header bit (i) set to 1, set the In other words, for each CEM header bit (i) set to 1, set the
resulting matrix column Y[i] according to Figure 7. resulting matrix column Y[i] according to Figure 7.
The final ECC-6 code is calculated as even parity of each row in Y The final ECC-6 code is calculated as even parity of each row in Y
(i.e. ECC[k]=CEM[25+k]=even parity of row k). (i.e. ECC[k]=CEM[25+k]=even parity of row k).
The receiver also uses matrix X to calculate an intermediate matrix The receiver also uses matrix X to calculate an intermediate matrix
YÆ based on all 32 bits of the CEM header. Therefore YÆ is 32 YË based on all 32 bits of the CEM header. Therefore YË is 32
columns wide and includes the ECC-6 code. columns wide and includes the ECC-6 code.
for i = 0 to 31 { for i = 0 to 31 {
if CEM[i] = 0 { if CEM[i] = 0 {
YÆ[i] = 0; YË[i] = 0;
} else { } else {
YÆ[i] = X[i]; YË[i] = X[i];
} }
} }
The receiver then appends the incoming ECC-6 code to Y as column 32 The receiver then appends the incoming ECC-6 code to Y as column 32
(ECC[0] should align with row 0) and calculates even parity for each (ECC[0] should align with row 0) and calculates even parity for each
row. The result is a single 6 bit column Z. If all 6 bits are 0, row. The result is a single 6 bit column Z. If all 6 bits are 0,
there are no bit errors (or at least no detectable errors). there are no bit errors (or at least no detectable errors).
Otherwise, it uses Z to perform a reverse lookup on X[] from Figure Otherwise, it uses Z to perform a reverse lookup on X[] from Figure
7. If Z matches column X[i], then there is a single bit error. The 7. If Z matches column X[i], then there is a single bit error. The
receiver should invert bit CEM[i] to correct the header. If Z fails receiver should invert bit CEM[i] to correct the header. If Z fails
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