< draft-ietf-pwe3-arch-05.txt   draft-ietf-pwe3-arch-06.txt >
Pseudo-Wire Edge-to-Edge (PWE3) Working Group Stewart Bryant Pseudo-Wire Edge-to-Edge (PWE3) Working Group Stewart Bryant
Internet Draft Cisco Systems Internet Draft Cisco Systems
Document: <draft-ietf-pwe3-arch-05.txt> Document: <draft-ietf-pwe3-arch-06.txt>
Expires: January 2004 Prayson Pate Expires: April 2004 Prayson Pate
Overture Networks, Inc. Overture Networks, Inc.
Editors Editors
August 2003 October 2003
PWE3 Architecture PWE3 Architecture
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. all provisions of section 10 of RFC2026.
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 other Task Force (IETF), its areas, and its working groups. Note that other
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networks (PSNs) using IP or MPLS. It presents the architectural networks (PSNs) using IP or MPLS. It presents the architectural
framework for pseudo wires (PWs), defines terminology, specifies the framework for pseudo wires (PWs), defines terminology, specifies the
various protocol elements and their functions. various protocol elements and their functions.
Co-Authors Co-Authors
The following are co-authors of this document: The following are co-authors of this document:
Thomas K. Johnson Litchfield Communications Thomas K. Johnson Litchfield Communications
Kireeti Kompella Juniper Networks, Inc. Kireeti Kompella Juniper Networks, Inc.
Andrew G. Malis Vivace Networks Andrew G. Malis Tellabs
Thomas D. Nadeau Cisco Systems Thomas D. Nadeau Cisco Systems
Tricci So Caspian Networks Tricci So Caspian Networks
W. Mark Townsley Cisco Systems W. Mark Townsley Cisco Systems
Craig White Level 3 Communications, LLC. Craig White Level 3 Communications, LLC.
Lloyd Wood Cisco Systems Lloyd Wood Cisco Systems
XiPeng Xiao Riverstone Networks XiPeng Xiao Riverstone Networks
Conventions used in this document 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",
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Model................................................ 20 Model................................................ 20
5. PW Encapsulation......................................... 21 5. PW Encapsulation......................................... 21
5.1 Payload Convergence Layer............................ 22 5.1 Payload Convergence Layer............................ 22
5.2 Payload-independent PW Encapsulation Layers.......... 24 5.2 Payload-independent PW Encapsulation Layers.......... 24
5.3 Fragmentation........................................ 27 5.3 Fragmentation........................................ 27
5.4 Instantiation of the Protocol Layers................. 27 5.4 Instantiation of the Protocol Layers................. 27
6. PW Demultiplexer Layer and PSN Requirements.............. 32 6. PW Demultiplexer Layer and PSN Requirements.............. 32
6.1 Multiplexing......................................... 32 6.1 Multiplexing......................................... 32
6.2 Fragmentation........................................ 32 6.2 Fragmentation........................................ 33
6.3 Length and Delivery.................................. 33 6.3 Length and Delivery.................................. 33
6.4 PW-PDU Validation.................................... 33 6.4 PW-PDU Validation.................................... 33
6.5 Congestion Considerations............................ 33 6.5 Congestion Considerations............................ 33
7. Control Plane............................................ 34 7. Control Plane............................................ 34
7.1 Set-up or Teardown of Pseudo-Wires................... 34 7.1 Set-up or Teardown of Pseudo-Wires................... 34
7.2 Status Monitoring.................................... 35 7.2 Status Monitoring.................................... 35
7.3 Notification of Pseudo-wire Status Changes........... 35 7.3 Notification of Pseudo-wire Status Changes........... 35
7.4 Keep-alive........................................... 36 7.4 Keep-alive........................................... 37
7.5 Handling Control Messages of the Native Services..... 37 7.5 Handling Control Messages of the Native Services..... 37
8. Management and Monitoring................................. 37 8. Management and Monitoring................................. 37
8.1 Status and Statistics................................ 37 8.1 Status and Statistics................................ 37
8.2 PW SNMP MIB Architecture............................. 38 8.2 PW SNMP MIB Architecture............................. 38
8.3 Connection Verification and Traceroute................ 41 8.3 Connection Verification and Traceroute................ 41
9. IANA considerations...................................... 41 9. IANA considerations...................................... 41
10. Security Considerations................................. 41 10. Security Considerations................................. 41
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Edge-to-Edge (PWE3) in support of [XIAO]. It discusses the emulation Edge-to-Edge (PWE3) in support of [XIAO]. It discusses the emulation
of services (such as Frame Relay, ATM, Ethernet, TDM and SONET/SDH) of services (such as Frame Relay, ATM, Ethernet, TDM and SONET/SDH)
over packet switched networks (PSNs) using IP or MPLS. It presents over packet switched networks (PSNs) using IP or MPLS. It presents
the architectural framework for pseudo wires (PWs), defines the architectural framework for pseudo wires (PWs), defines
terminology, specifies the various protocol elements and their terminology, specifies the various protocol elements and their
functions. functions.
1.1 Pseudo Wire Definition 1.1 Pseudo Wire Definition
PWE3 is a mechanism that emulates the essential attributes of a PWE3 is a mechanism that emulates the essential attributes of a
service (such as a T1 leased line or Frame Relay) over a PSN. PWE3 is telecommunications service (such as a T1 leased line or Frame Relay)
intended to provide only the minimum necessary functionality to over a PSN. PWE3 is intended to provide only the minimum necessary
emulate the wire with the required degree of faithfulness for the functionality to emulate the wire with the required degree of
given service definition. Any required switching functionality is the faithfulness for the given service definition. Any required switching
responsibility of a forwarder function (FWRD). Any translation or functionality is the responsibility of a forwarder function (FWRD).
other operation needing knowledge of the payload semantics is carried Any translation or other operation needing knowledge of the payload
out by native service processing (NSP) elements. The functional semantics is carried out by native service processing (NSP) elements.
definition of any FWRD or NSP elements is outside the scope of PWE3. The functional definition of any FWRD or NSP elements is outside the
scope of PWE3.
The required functions of PWs include encapsulating service-specific The required functions of PWs include encapsulating service-specific
bit-streams, cells or PDUs arriving at an ingress port, and carrying bit-streams, cells or PDUs arriving at an ingress port, and carrying
them across a IP path or MPLS tunnel. In some cases it is necessary them across a IP path or MPLS tunnel. In some cases it is necessary
to perform other operation such as managing their timing and order, to perform other operation such as managing their timing and order,
to emulate the behavior and characteristics of the service to the to emulate the behavior and characteristics of the service to the
required degree of faithfulness. required degree of faithfulness.
From the perspective of a Customer Edge Equipment (CE), the PW is From the perspective of a Customer Edge Equipment (CE), the PW is
characterised as an unshared link or circuit of the chosen service. characterised as an unshared link or circuit of the chosen service.
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Thus, Ethernet transmission to a "multicast" IEEE-48 address Thus, Ethernet transmission to a "multicast" IEEE-48 address
is in scope, while multicast services like MARS [RFC2022] that is in scope, while multicast services like MARS [RFC2022] that
are implemented on top of the medium are out of scope. are implemented on top of the medium are out of scope.
o Methods to signal or control the underlying PSN. o Methods to signal or control the underlying PSN.
1.4 Terminology 1.4 Terminology
This document uses the following definitions of terms. These terms This document uses the following definitions of terms. These terms
are illustrated in context in Figure 2. are illustrated in context in Figure 2.
Attachment Circuit The circuit or virtual circuit attaching Attachment Circuit The physical or virtual circuit attaching
(AC) a CE to a PE. (AC) a CE to a PE. An attachment Circuit may be
for example a Frame Relay DLCI, an ATM
VPI/VCI, an Ethernet port, a VLAN, a PPP
connection on a physical interface, a
PPP session from an L2TP tunnel, an MPLS
LSP, etc. If both physical and virtual ACs
are of the same technology (e.g., both ATM,
both Ethernet, both Frame Relay) the PW
is said to provide "homogeneous transport";
otherwise it is said to provide
"heterogeneous transport".
CE-bound The traffic direction where PW-PDUs are CE-bound The traffic direction where PW-PDUs are
received on a PW via the PSN, processed received on a PW via the PSN, processed
and then sent to the destination CE. and then sent to the destination CE.
CE Signaling Messages sent and received by the CEs CE Signaling Messages sent and received by the CEs
control plane. It may be desirable or control plane. It may be desirable or
even necessary for the PE to participate even necessary for the PE to participate
in or monitor this signaling in order in or monitor this signaling in order
to effectively emulate the service. to effectively emulate the service.
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PSN Tunnel A tunnel across a PSN inside which one or PSN Tunnel A tunnel across a PSN inside which one or
more PWs can be carried. more PWs can be carried.
PSN Tunnel Used to set up, maintain and tear down the PSN Tunnel Used to set up, maintain and tear down the
Signaling underlying PSN tunnel. Signaling underlying PSN tunnel.
PW Demultiplexer Data-plane method of identifying a PW PW Demultiplexer Data-plane method of identifying a PW
terminating at a PE. terminating at a PE.
PW End Service The interface between a PE and a CE. This
(PWES) can be a physical interface like a T1 or
Ethernet, or a virtual interface like a VC
or VLAN.
PWE3 Payload Type A identifier used to distinguish between PWE3 Payload Type A identifier used to distinguish between
Identifier an MPLS IP payload and a CW that is not Identifier an MPLS IP payload and a CW that is not
(PWE3-PID) ECMP safe. (PWE3-PID) ECMP safe.
Time Domain Time Division Multiplexing. Frequently used Time Domain Time Division Multiplexing. Frequently used
Multiplexing (TDM) to refer to the synchronous bit-streams at Multiplexing (TDM) to refer to the synchronous bit-streams at
rates defined by G.702. rates defined by G.702.
Tunnel A method of transparently carrying information Tunnel A method of transparently carrying information
over a network. over a network.
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frame-relay, ATM AAL5 PDU. frame-relay, ATM AAL5 PDU.
Cell ATM. Cell ATM.
Bit-stream Unstructured E1, T1, E3, T3. Bit-stream Unstructured E1, T1, E3, T3.
Structured bit-stream SONET/SDH (e.g. SPE, VT, NxDS0). Structured bit-stream SONET/SDH (e.g. SPE, VT, NxDS0).
3.3.1. Packet Payload 3.3.1. Packet Payload
A packet payload is a variable-size data unit presented to the PE on A packet payload is a variable-size data unit delivered to the PE via
the AC. A packet payload may be large compared to the PSN MTU. The the AC. A packet payload may be large compared to the PSN MTU. The
delineation of the packet boundaries is encapsulation-specific. HDLC delineation of the packet boundaries is encapsulation-specific. HDLC
or Ethernet PDUs can be considered as examples of packet payloads. or Ethernet PDUs can be considered as examples of packet payloads.
Typically a packet will be stripped of transmission overhead such as Typically a packet will be stripped of transmission overhead such as
HDLC flags and stuffing bits before transmission over the PW. HDLC flags and stuffing bits before transmission over the PW.
A packet payload would normally be relayed across the PW as a single A packet payload would normally be relayed across the PW as a single
unit. However, there will be cases where the combined size of the unit. However, there will be cases where the combined size of the
packet payload and its associated PWE3 and PSN headers exceeds the packet payload and its associated PWE3 and PSN headers exceeds the
PSN path MTU. In these cases, some fragmentation methodology needs PSN path MTU. In these cases, some fragmentation methodology needs
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| | | |
native service native service native service native service
Figure 2: PWE3 Network Reference Model Figure 2: PWE3 Network Reference Model
The two PEs (PE1 and PE2) need to provide one or more PWs on behalf The two PEs (PE1 and PE2) need to provide one or more PWs on behalf
of their client CEs (CE1 and CE2) to enable the client CEs to of their client CEs (CE1 and CE2) to enable the client CEs to
communicate over the PSN. A PSN tunnel is established to provide a communicate over the PSN. A PSN tunnel is established to provide a
data path for the PW. The PW traffic is invisible to the core data path for the PW. The PW traffic is invisible to the core
network, and the core network is transparent to the CEs. Native data network, and the core network is transparent to the CEs. Native data
units (bits, cells or packets) presented to the PW End Service (PWES) units (bits, cells or packets) arrive via the AC, are encapsulated in
are encapsulated in a PW-PDU and carried across the underlying a PW-PDU and are carried across the underlying network via the PSN
network via the PSN tunnel. The PEs perform the necessary tunnel. The PEs perform the necessary encapsulation and decapsulation
encapsulation and decapsulation of PW-PDUs, as well as handling any of PW-PDUs, as well as handling any other functions required by the
other functions required by the PW service, such as sequencing or PW service, such as sequencing or timing.
timing. A PE MAY provide multiple PWESs.
4.2 PWE3 Pre-processing 4.2 PWE3 Pre-processing
In some applications, there is a need to perform operations on the In some applications, there is a need to perform operations on the
native data units received from the CE (including both payload and native data units received from the CE (including both payload and
signaling traffic) before they are transmitted across the PW by the signaling traffic) before they are transmitted across the PW by the
PE. Examples include Ethernet bridging, SONET cross-connect, PE. Examples include Ethernet bridging, SONET cross-connect,
translation of locally-significant identifiers such as VCI/VPI, or translation of locally-significant identifiers such as VCI/VPI, or
translation to another service type. These operations could be translation to another service type. These operations could be
carried out in external equipment, and the processed data sent to the carried out in external equipment, and the processed data sent to the
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functionality is also supported. functionality is also supported.
The required pre-processing can be divided into two components: The required pre-processing can be divided into two components:
o Forwarder (FWRD) o Forwarder (FWRD)
o Native Service Processing (NSP) o Native Service Processing (NSP)
4.2.1. Forwarders 4.2.1. Forwarders
In some applications there is the need to selectively forward payload In some applications there is the need to selectively forward payload
elements from one of more ACs to one or more PWs. In such cases there elements from one or more ACs to one or more PWs. In such cases there
will also be the need to perform the inverse function on PWE3-PDUs will also be the need to perform the inverse function on PWE3-PDUs
received by a PE from the PSN. This is the function of the forwarder. received by a PE from the PSN. This is the function of the forwarder.
The forwarder selects the PW based on, for example: the incoming AC, The forwarder selects the PW based on, for example: the incoming AC,
the contents of the payload, or some statically and/or dynamically the contents of the payload, or some statically and/or dynamically
configured forwarding information. configured forwarding information.
+----------------------------------------+ +----------------------------------------+
| PE Device | | PE Device |
+----------------------------------------+ +----------------------------------------+
Single | | | Single | | |
PWES | | Single | PW Instance AC | | Single | PW Instance
<------>o Forwarder + PW Instance X<===========> <------>o Forwarder + PW Instance X<===========>
| | | | | |
+----------------------------------------+ +----------------------------------------+
Figure 4a: Simple point-to-point service Figure 4a: Simple point-to-point service
+----------------------------------------+ +----------------------------------------+
| PE Device | | PE Device |
+----------------------------------------+ +----------------------------------------+
Multiple| | Single | PW Instance Multiple| | Single | PW Instance
PWES | + PW Instance X<===========> AC | + PW Instance X<===========>
<------>o | | <------>o | |
| |----------------------| | |----------------------|
<------>o | Single | PW Instance <------>o | Single | PW Instance
| Forwarder + PW Instance X<===========> | Forwarder + PW Instance X<===========>
<------>o | | <------>o | |
| |----------------------| | |----------------------|
<------>o | Single | PW Instance <------>o | Single | PW Instance
| + PW Instance X<===========> | + PW Instance X<===========>
<------>o | | <------>o | |
+----------------------------------------+ +----------------------------------------+
Figure 4b: Multiple PWES to Multiple PW Forwarding Figure 4b: Multiple AC to Multiple PW Forwarding
Figure 4a shows a simple forwarder that performs some type of Figure 4a shows a simple forwarder that performs some type of
filtering operation. Because the forwarder has a single input and a filtering operation. Because the forwarder has a single input and a
single output interface, filtering is the only type of forwarding single output interface, filtering is the only type of forwarding
operation that applies. Figure 4b shows a more general forwarding operation that applies. Figure 4b shows a more general forwarding
situation where payloads are extracted from one or more PWESs and situation where payloads are extracted from one or more ACs and
directed to one or more PWs, including, in this instance, a directed to one or more PWs. In this case filtering, direction and
multipoint PW. In this case both filtering and direction operations combination operations MAY be performed on the payloads. For
MAY be performed on the payloads. example, if the AC were frame relay, the forwarder might perform
frame relay switching and the PW instances might be the inter-switch
links.
4.2.2. Native Service Processing 4.2.2. Native Service Processing
In some applications some form of data or address translation, or In some applications some form of data or address translation, or
other operation requiring knowledge of the semantics of the payload, other operation requiring knowledge of the semantics of the payload,
will be required. This is the function of the Native Service will be required. This is the function of the Native Service
Processor (NSP). Processor (NSP).
The use of the NSP approach simplifies the design of the PW by The use of the NSP approach simplifies the design of the PW by
restricting a PW to homogeneous operation. NSP is included in the restricting a PW to homogeneous operation. NSP is included in the
reference model to provide a defined interface to this functionality. reference model to provide a defined interface to this functionality.
The specification of the various types of NSP is outside the scope of The specification of the various types of NSP is outside the scope of
PWE3. PWE3.
+----------------------------------------+ +----------------------------------------+
| PE Device | | PE Device |
Multiple+----------------------------------------+ Multiple+----------------------------------------+
PWES | | | Single | PW Instance AC | | | Single | PW Instance
<------>o NSP # + PW Instance X<===========> <------>o NSP # + PW Instance X<===========>
| | | | | | | |
|------| |----------------------| |------| |----------------------|
| | | Single | PW Instance | | | Single | PW Instance
<------>o NSP #Forwarder + PW Instance X<===========> <------>o NSP #Forwarder + PW Instance X<===========>
| | | | | | | |
|------| |----------------------| |------| |----------------------|
| | | Single | PW Instance | | | Single | PW Instance
<------>o NSP # + PW Instance X<===========> <------>o NSP # + PW Instance X<===========>
| | | | | | | |
+----------------------------------------+ +----------------------------------------+
Figure 5: NSP in a Multiple PWEs to Multiple Figure 5: NSP in a Multiple AC to Multiple
PW Forwarding PE PW Forwarding PE
Figure 5 illustrates the relationship between NSP, forwarder and PWs Figure 5 illustrates the relationship between NSP, forwarder and PWs
in a PE. The NSP function MAY apply any transformation operation in a PE. The NSP function MAY apply any transformation operation
(modification, injection, etc.) on the payloads as they pass between (modification, injection, etc.) on the payloads as they pass between
the physical interface to the CE and the virtual interface to the the physical interface to the CE and the virtual interface to the
forwarder. A PE device MAY contain more than one forwarder. forwarder. These transformation operations will of course be limited
to those that have been implemented in the data path, and which are
enabled by the PE configuration. A PE device MAY contain more than
one forwarder.
This model also supports the operation of a system in which the NSP This model also supports the operation of a system in which the NSP
functionality includes terminating the data-link, and applying functionality includes terminating the data-link, and applying
Network Layer processing to the payload is also supported. Network Layer processing to the payload is also supported.
4.3 Maintenance Reference Model 4.3 Maintenance Reference Model
Figure 6 illustrates the maintenance reference model for PWs. Figure 6 illustrates the maintenance reference model for PWs.
|<------- CE (end-to-end) Signaling ------>| |<------- CE (end-to-end) Signaling ------>|
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suitable for transmission of the PW, the PE MAY fall back to either a suitable for transmission of the PW, the PE MAY fall back to either a
generic PW fragmentation method, or, if available the fragmentation generic PW fragmentation method, or, if available the fragmentation
service of the underlying PSN. service of the underlying PSN.
It is acceptable for a PE implementation not to support It is acceptable for a PE implementation not to support
fragmentation. A PE that does not support fragmentation will drop fragmentation. A PE that does not support fragmentation will drop
packets that exceed the PSN MTU, and the management plane of the packets that exceed the PSN MTU, and the management plane of the
encapsulating PE MAY be notified. encapsulating PE MAY be notified.
If the length of a L2/L1 frame, restored from a PW PDU, exceeds the If the length of a L2/L1 frame, restored from a PW PDU, exceeds the
MTU of the destination PWES, it MUST be dropped. In this case, the MTU of the destination AC, it MUST be dropped. In this case, the
management plane of the destination PE MAY be notified. management plane of the destination PE MAY be notified.
5.4 Instantiation of the Protocol Layers 5.4 Instantiation of the Protocol Layers
This document does not address the detailed mapping of the Protocol This document does not address the detailed mapping of the Protocol
Layering model to existing or future IETF standards. The Layering model to existing or future IETF standards. The
instantiation of the logical Protocol Layering model is shown in instantiation of the logical Protocol Layering model is shown in
Figure 9. Figure 9.
5.4.1. PWE3 over an IP PSN 5.4.1. PWE3 over an IP PSN
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the Payload Convergence Layer provided when needed. (It is accepted the Payload Convergence Layer provided when needed. (It is accepted
that there MAY sometimes be good reason not to follow this rule, but that there MAY sometimes be good reason not to follow this rule, but
the exceptional circumstances need to be documented in the the exceptional circumstances need to be documented in the
Encapsulation Layer definition for that payload type). Encapsulation Layer definition for that payload type).
Where appropriate, timing is provided by RTP [RFC3550], which when Where appropriate, timing is provided by RTP [RFC3550], which when
used also provides a sequencing service. PW Demultiplexing may be used also provides a sequencing service. PW Demultiplexing may be
provided by a number of existing IETF tunnel protocols. Some of provided by a number of existing IETF tunnel protocols. Some of
these tunnel protocols provide an optional sequencing service. these tunnel protocols provide an optional sequencing service.
(Sequencing is provided either by RTP, or by the PW Demultiplexer (Sequencing is provided either by RTP, or by the PW Demultiplexer
Layer, but not both). A PSN Convergence Layer is not needed, because Layer, but not both).
all the tunnel protocols shown above are designed to operate directly
over an IP PSN. RTP is normally carried over UDP, however the tunnel protcols that
are capable of carrying a PW, provide sufficient functionality to
carry RTP without an intervening transport layer. UDP MAY therefore
be omitted from the protocol stack.
A PSN Convergence Layer is not needed, because all the tunnel
protocols shown above are designed to operate directly over an IP
PSN.
As a special case, if the PW Demultiplexer is an MPLS label, the As a special case, if the PW Demultiplexer is an MPLS label, the
protocol architecture of section 5.4.2 can be used instead of the protocol architecture of section 5.4.2 can be used instead of the
protocol architecture of this section. protocol architecture of this section.
5.4.2. PWE3 over an MPLS PSN 5.4.2. PWE3 over an MPLS PSN
The MPLS ethos places importance on wire efficiency. By using a The MPLS ethos places importance on wire efficiency. By using a
control word, some components of the PWE3 protocol layers can be control word, some components of the PWE3 protocol layers can be
compressed to increase this efficiency. compressed to increase this efficiency.
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This section describes PWE3 control plane services. This section describes PWE3 control plane services.
7.1 Set-up or Teardown of Pseudo-Wires 7.1 Set-up or Teardown of Pseudo-Wires
A PW MUST be set up before an emulated service can be established, A PW MUST be set up before an emulated service can be established,
and MUST be torn down when an emulated service is no longer needed. and MUST be torn down when an emulated service is no longer needed.
Set up or teardown of a PW can be triggered by an operator command, Set up or teardown of a PW can be triggered by an operator command,
from the management plane of a PE, by signaling (i.e., set-up or from the management plane of a PE, by signaling (i.e., set-up or
teardown) of a PWES, e.g., an ATM SVC, or by an auto-discovery teardown) of an AC, e.g., an ATM SVC, or by an auto-discovery
mechanism. mechanism.
During the set-up process, the PEs need to exchange some information During the set-up process, the PEs need to exchange some information
(e.g. learn each other's capabilities). The tunnel signaling (e.g. learn each other's capabilities). The tunnel signaling
protocol MAY be extended to provide mechanisms to enable the PEs to protocol MAY be extended to provide mechanisms to enable the PEs to
exchange all necessary information on behalf of the PW. exchange all necessary information on behalf of the PW.
Manual configuration of PWs can be considered a special kind of Manual configuration of PWs can be considered a special kind of
signaling, and is allowed. signaling, and is allowed.
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7.3.2. Misconnection and Payload Type Mismatch 7.3.2. Misconnection and Payload Type Mismatch
With PWE3, misconnection and payload type mismatch can occur. If a With PWE3, misconnection and payload type mismatch can occur. If a
misconnection occurs it can breach the integrity of the system. If a misconnection occurs it can breach the integrity of the system. If a
payload mismatch occurs it can disrupt the customer network. In both payload mismatch occurs it can disrupt the customer network. In both
instances, there are security and operational concerns. instances, there are security and operational concerns.
The services of the underlying tunneling mechanism, and its The services of the underlying tunneling mechanism, and its
associated control protocol, can be used to mitigate this. As part associated control protocol, can be used to mitigate this. As part
of the PW set-up a PW-TYPE identifier is exchanged. This is then used of the PW set-up a PW-TYPE identifier is exchanged. This is then used
by the forwarder and the NSP to verify the compatibility of the by the forwarder and the NSP to verify the compatibility of the ACs.
PWESs.
7.3.3. Packet Loss, Corruption, and Out-of-order Delivery 7.3.3. Packet Loss, Corruption, and Out-of-order Delivery
A PW can incur packet loss, corruption, and out-of-order delivery on A PW can incur packet loss, corruption, and out-of-order delivery on
the PSN path between the PEs. This can impact the working condition the PSN path between the PEs. This can impact the working condition
of an emulated service. For some payload types, packet loss, of an emulated service. For some payload types, packet loss,
corruption, and out-of-order delivery can be mapped to either a bit corruption, and out-of-order delivery can be mapped to either a bit
error burst, or loss of carrier on the PW. If a native service has error burst, or loss of carrier on the PW. If a native service has
some mechanism to deal with bit error, the corresponding PWE3 service some mechanism to deal with bit error, the corresponding PWE3 service
should provide a similar mechanism. should provide a similar mechanism.
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connection status method. connection status method.
For troubleshooting purposes, it is sometimes desirable to know the For troubleshooting purposes, it is sometimes desirable to know the
exact functional path of a PW between PEs. This is provided by the exact functional path of a PW between PEs. This is provided by the
traceroute service of the underlying PSN. The opaque nature of the traceroute service of the underlying PSN. The opaque nature of the
PW means that this traceroute information is only available within PW means that this traceroute information is only available within
the provider network, e.g., at the PEs. the provider network, e.g., at the PEs.
9. IANA considerations 9. IANA considerations
The control word PID bits need to be assigned by IANA. Sections 5.4.3 and 5.4.4 discuss the issue of aliasing between PW and
IP packets on an MPLS PSN. This aliasing is resolved by using two
historic IP version numbers to indicate that the payload is an MPLS
preferred control word, or a PWE3 PID. The IP version number
registry needs to be updated to allocate IP version number 0
(currently reserved) to MPLS preferred control word, and IP version
number 1 (currently unassigned) to PWE3 PID.
10. Security Considerations 10. Security Considerations
PWE3 provides no means of protecting the integrity, confidentiality PWE3 provides no means of protecting the integrity, confidentiality
or delivery of the native data units. The use of PWE3 can therefore or delivery of the native data units. The use of PWE3 can therefore
expose a particular environment to additional security threats. expose a particular environment to additional security threats.
Assumptions that might be appropriate when all communicating systems Assumptions that might be appropriate when all communicating systems
are interconnected via a point to point or circuit-switched network are interconnected via a point to point or circuit-switched network
may no longer hold when they are interconnected using an emulated may no longer hold when they are interconnected using an emulated
wire carried over some types of PSN. It is outside the scope of this wire carried over some types of PSN. It is outside the scope of this
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Based on the type of data being transferred, the PW MAY indicate to Based on the type of data being transferred, the PW MAY indicate to
the PW Demultiplexer Layer that enhanced security services are the PW Demultiplexer Layer that enhanced security services are
required. The PW Demultiplexer Layer MAY define multiple protection required. The PW Demultiplexer Layer MAY define multiple protection
profiles based on the requirements of the PW emulated service. CE- profiles based on the requirements of the PW emulated service. CE-
to-CE signaling and control events emulated by the PW and some data to-CE signaling and control events emulated by the PW and some data
types may require additional protection mechanisms. Alternatively, types may require additional protection mechanisms. Alternatively,
the PW Demultiplexer Layer may use peer authentication for every PSN the PW Demultiplexer Layer may use peer authentication for every PSN
packet to prevent spoofed native data units from being sent to the packet to prevent spoofed native data units from being sent to the
destination CE. destination CE.
The unlimited transformation capability of the NSP may be perceived
as a security risk. In practise the type of operation that the NSP
may perform will be limited to those that have been implemented in
the data path. The access controls that are in place in the PE to
protect and validate its configuration will be sufficient to ensure
that the NSP performs as expected.
Acknowledgments Acknowledgments
We thank: Sasha Vainshtein for his work on Native Service Processing We thank: Sasha Vainshtein for his work on Native Service Processing
and advice on bit-stream over PW services. Thomas K. Johnson for his and advice on bit-stream over PW services. Thomas K. Johnson for his
work on the background and motivation for PWs. work on the background and motivation for PWs.
We also thank: Ron Bonica, Stephen Casner, Durai Chinnaiah, Jayakumar We also thank: Ron Bonica, Stephen Casner, Durai Chinnaiah, Jayakumar
Jayakumar, Ghassem Koleyni, Danny McPherson, Eric Rosen, John Jayakumar, Ghassem Koleyni, Danny McPherson, Eric Rosen, John
Rutemiller, Scott Wainner and David Zelig for their comments and Rutemiller, Scott Wainner and David Zelig for their comments and
contributions. contributions.
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