PWE3 M. Aissaoui
Internet-Draft P. Busschbach
Intended status: Standards Track Alcatel-Lucent
Expires: September 8, 2010 M. Morrow
L. Martini
Cisco Systems, Inc.
Y(J). Stein
RAD Data Communications
D. Allan
Ericsson
T. Nadeau
BT
March 7, 2010
Pseudowire (PW) OAM Message Mapping
draft-ietf-pwe3-oam-msg-map-12.txt
Abstract
This document specifies the mapping and notification of defect states
between a pseudowire (PW) and the Attachment Circuits (ACs) of the
end-to-end emulated service. It standardizes the behavior of
Provider Edges (PEs) with respect to PW and AC defects. It addresses
ATM, frame relay, TDM, and SONET/SDH PW services, carried over MPLS,
MPLS/IP and L2TPV3/IP Packet Switched Networks (PSNs).
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 8, 2010.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the BSD License.
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Table of Contents
1. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 4
2. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Abbreviations and Conventions . . . . . . . . . . . . . . . . 5
4.1. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 5
4.2. Conventions . . . . . . . . . . . . . . . . . . . . . . . 5
5. Reference Model and Defect Locations . . . . . . . . . . . . . 7
6. Abstract Defect States . . . . . . . . . . . . . . . . . . . . 8
7. OAM Modes . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8. PW Defect States and Defect Notifications . . . . . . . . . . 11
8.1. PW Defect Notification Mechanisms . . . . . . . . . . . . 11
8.1.1. LDP Status TLV . . . . . . . . . . . . . . . . . . . . 12
8.1.2. L2TP Circuit Status AVP . . . . . . . . . . . . . . . 14
8.1.3. BFD Diagnostic Codes . . . . . . . . . . . . . . . . . 15
8.2. PW Defect State Entry/Exit . . . . . . . . . . . . . . . . 17
8.2.1. PW receive defect state entry/exit criteria . . . . . 17
8.2.2. PW transmit defect state entry/exit criteria . . . . . 18
9. Procedures for ATM PW Service . . . . . . . . . . . . . . . . 18
9.1. AC receive defect state entry/exit criteria . . . . . . . 18
9.2. AC transmit defect state entry/exit criteria . . . . . . . 19
9.3. Consequent Actions . . . . . . . . . . . . . . . . . . . . 20
9.3.1. PW receive defect state entry/exit . . . . . . . . . . 20
9.3.2. PW transmit defect state entry/exit . . . . . . . . . 20
9.3.3. PW defect state in ATM Port Mode PW Service . . . . . 20
9.3.4. AC receive defect state entry/exit . . . . . . . . . . 21
9.3.5. AC transmit defect state entry/exit . . . . . . . . . 22
10. Procedures for Frame Relay PW Service . . . . . . . . . . . . 22
10.1. AC receive defect state entry/exit criteria . . . . . . . 22
10.2. AC transmit defect state entry/exit criteria . . . . . . . 22
10.3. Consequent Actions . . . . . . . . . . . . . . . . . . . . 23
10.3.1. PW receive defect state entry/exit . . . . . . . . . . 23
10.3.2. PW transmit defect state entry/exit . . . . . . . . . 23
10.3.3. PW defect state in the FR Port Mode PW Service . . . . 24
10.3.4. AC receive defect state entry/exit . . . . . . . . . . 24
10.3.5. AC transmit defect state entry/exit . . . . . . . . . 24
11. Procedures for TDM PW Service . . . . . . . . . . . . . . . . 24
11.1. AC receive defect state entry/exit criteria . . . . . . . 25
11.2. AC transmit defect state entry/exit criteria . . . . . . . 25
11.3. Consequent Actions . . . . . . . . . . . . . . . . . . . . 25
11.3.1. PW receive defect state entry/exit . . . . . . . . . . 25
11.3.2. PW transmit defect state entry/exit . . . . . . . . . 26
11.3.3. AC receive defect state entry/exit . . . . . . . . . . 26
12. Procedures for CEP PW Service . . . . . . . . . . . . . . . . 26
12.1. Defect states . . . . . . . . . . . . . . . . . . . . . . 27
12.1.1. PW receive defect state entry/exit . . . . . . . . . . 27
12.1.2. PW transmit defect state entry/exit . . . . . . . . . 27
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12.1.3. AC receive defect state entry/exit . . . . . . . . . . 27
12.1.4. AC receive defect state entry/exit . . . . . . . . . . 28
12.2. Consequent Actions . . . . . . . . . . . . . . . . . . . . 28
12.2.1. PW receive defect state entry/exit . . . . . . . . . . 28
12.2.2. PW transmit defect state entry/exit . . . . . . . . . 28
12.2.3. AC receive defect state entry/exit . . . . . . . . . . 28
13. Security Considerations . . . . . . . . . . . . . . . . . . . 29
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
Appendix A. Native Service Management (informative) . . . . . . . 30
A.1. Frame Relay Management . . . . . . . . . . . . . . . . . . 30
A.2. ATM Management . . . . . . . . . . . . . . . . . . . . . . 30
Appendix B. PW Defects and Detection tools . . . . . . . . . . . 32
B.1. PW Defects . . . . . . . . . . . . . . . . . . . . . . . . 32
B.2. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 32
B.3. PW Defect Detection Tools . . . . . . . . . . . . . . . . 32
B.4. PW specific defect detection mechanisms . . . . . . . . . 33
Appendix C. References . . . . . . . . . . . . . . . . . . . . . 34
C.1. Normative References . . . . . . . . . . . . . . . . . . . 34
C.2. Informative References . . . . . . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35
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1. Acknowledgments
The editors would like to acknowledge the important contributions of
Hari Rakotoranto, Eric Rosen, Mark Townsley, Michel Khouderchah,
Bertrand Duvivier, Vanson Lim, Chris Metz, Ben Washam, Tiberiu
Grigoriu, Neil McGill, and Amir Maleki.
2. Contributors
Matthew Bocci, matthew.bocci@alcatel-lucent.co.uk
David Watkinson, david.watkinson@alcatel-lucent.com
Yuichi Ikejiri, y.ikejiri@ntt.com
Kenji Kumaki, kekumaki@kddi.com
Satoru Matsushima, satoru.matsushima@tm.softbank.co.jp
Himanshu Shah, hshah@ciena.com
Simon Delord, Simon.A.DeLord@team.telstra.com
Vasile Radoaca, vasile.radoaca@alcatel-lucent.com
Carlos Pignataro, cpignata@cisco.com
Teruyuki Oya, teruyuki.oya@tm.softbank.co.jp
3. Introduction
This document specifies the mapping and notification of defect states
between a Pseudowire and the Attachment Circuits (AC) of the end-to-
end emulated service. It covers the case whereby the ACs and the PWs
are of the same type in accordance to the PWE3 architecture [RFC3985]
such that a homogeneous PW service can be constructed.
This document is motivated by the requirements put forth in [RFC4377]
and [RFC3916]. Its objective is to standardize the behavior of PEs
with respect to defects on PWs and ACs, so that there is no ambiguity
about the alarms generated and consequent actions undertaken by PEs
in response to specific failure conditions.
This document addresses PWs over MPLS, MPLS/IP and L2TPV3/IP PSNs,
and ATM, frame relay, TDM, and SONET/SDH PW services. Due to its
unique characteristics, the Ethernet PW service is covered in a
separate document [ETH-OAM-IWK].
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4. Abbreviations and Conventions
4.1. Abbreviations
AAL5 ATM Adaptation Layer 5
AIS Alarm Indication Signal
AC Attachment Circuit
ATM Asynchronous Transfer Mode
AVP Attribute Value Pair
BDI Backward Defect Indication
BFD Bidirectional Forwarding Detection
CC Continuity Check
CDN Call Disconnect Notify
CE Customer Edge
CV Connectivity Verification
CPCS Common Part Convergence Sub-layer
DBA Dynamic Bandwidth Allocation
DLC Data Link Connection
FDI Forward Defect Indication
FR Frame Relay
FRBS Frame Relay Bearer Service
ICMP Internet Control Message Protocol
IWF Interworking Function
LB Loopback
LCCE L2TP Control Connection Endpoint
LDP Label Distribution Protocol
LSP label Switched Path
L2TP Layer 2 Tunneling Protocol
MPLS Multiprotocol Label Switching
NE Network Element
NS Native Service
OAM Operations, Administration and Maintenance
PE Provider Edge
PSN Packet Switched Network
PW Pseudowire
RDI Remote Defect Indication
PDU Protocol Data Unit
SDU Service Data Unit
TLV Type Length Value
VCC Virtual Channel Connection
VCCV Virtual Connection Connectivity Verification
VPC Virtual Path Connection
4.2. Conventions
The words "defect" and "fault" are used interchangeably to mean any
condition that obstructs forwarding of user traffic between the CE
endpoints of the PW service.
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The words "defect notification" and "defect indication" are used
interchangeably to mean any OAM message generated by a PE and sent to
other nodes in the network to convey the defect state local to this
PE.
The PW can be carried over three types of Packet Switched Networks
(PSNs). An "MPLS PSN" makes use of MPLS Label Switched Paths [LSPs]
as the tunneling technology to forward the PW packets. An "MPLS/IP
PSN" makes use of MPLS-in-IP tunneling [RFC4023], with an MPLS shim
header used as PW demultiplexer. An "L2TPv3/IP PSN" makes use of
L2TPv3/IP [RFC3931] as the tunneling technology with the L2TPv3/IP
Session ID as the PW demultiplexer.
If LSP-Ping [RFC4379] is run over a PW as described in [RFC4377], it
will be referred to as "VCCV-Ping". If BFD is run over a PW as
described in [RFC4377], it will be referred to as "VCCV-BFD" [VCCV-
BFD].
While PWs are inherently bidirectional entities, defects and OAM
messaging are related to a specific traffic direction. We use the
terms "upstream" and "downstream" to identify PEs in relation to the
traffic direction. A PE is upstream for the traffic it is forwarding
and is downstream for the traffic it is receiving.
We use the terms "local" and "remote" to identify native service
networks and ACs in relation to a specific PE. The local AC is
attached to the PE in question, while the remote AC is attached to
the PE at the other end of the PW.
A "transmit defect" is any defect that impacts traffic that is meant
to be sent or relayed by the observing PE. A "receive defect" is any
defect that impacts traffic that is meant to be received by the
observing PE. Note that a receive defect also impacts traffic meant
to be relayed, and thus can be considered to incorporate two defect
states. Thus when a PE enters both receive and transmit defect
states of a PW service, the receive defect takes precedence over the
transmit defect in terms of the consequent actions.
A "forward defect indication" (FDI) is sent in the same direction as
the user traffic impacted by the defect. A "reverse defect
indication" (RDI) is sent in the direction opposite to that of the
impacted traffic.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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5. Reference Model and Defect Locations
Figure 1 illustrates the PWE3 network reference model with an
indication of the possible defect locations. This model will be
referenced in the remainder of this document for describing the OAM
procedures.
ACs PSN tunnel ACs
+----+ +----+
+----+ | PE1|==================| PE2| +----+
| |---(a)---(b)..(c)......PW1..(d)..(c)..(f)---(e)---| |
| CE1| (N1) | | | | (N2) |CE2 |
| |----------|............PW2.............|----------| |
+----+ | |==================| | +----+
^ +----+ +----+ ^
| Provider Edge 1 Provider Edge 2 |
| |
|<-------------- Emulated Service ---------------->|
Customer Customer
Edge 1 Edge 2
Figure 1: PWE3 Network Defect Locations
The procedures will be described in this document from the viewpoint
of PE1, so that N1 is the local native service network and N2 is the
remote native service network. PE2 will typically implement the same
functionality. Note that PE1 is the upstream PE for traffic
originating in the local NS network N1, while it is the downstream PE
for traffic originating in the remote NS network N2.
The following is a brief description of the defect locations:
a. Defect in NS network N1. This covers any defect in network N1
that impacts all or some ACs attached to PE1, and is thus a local
AC defect. The defect is conveyed to PE1 and to NS network N2
using NS specific OAM defect indications.
b. Defect on a PE1 AC interface (another local AC defect).
c. Defect on a PE1 PSN interface.
d. Defect in the PSN network. This covers any defect in the PSN that
impacts all or some PWs between PE1 and PE2. The defect is
conveyed to the PE using a PSN and/or a PW specific OAM defect
indication. Note that both data plane defects and control plane
defects must be taken into consideration. Although control
messages may follow a different path than PW data plane traffic, a
control plane defect may affect the PW status.
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e. Defect on a PE2 AC interface (a remote AC defect).
f. Defect in NS network N2 (another remote AC defect). This covers
any defect in N2 which impacts all or a subset of ACs attached to
PE2. The defect is conveyed to PE2 and to NS network N1 using the
NS OAM defect indication.
6. Abstract Defect States
PE1 must track four defect states that reflect the observed states of
both directions of the PW service on both the AC and the PW sides.
Defects may impact one or both directions of the PW service.
The observed state is a combination of defects directly detected by
PE1 and defects of which it has been made aware via notifications.
+-----+
----AC receive---->| |-----PW transmit---->
CE1 | PE1 | PE2/CE2
<---AC transmit----| |<----PW receive-----
+-----+
(arrows indicate direction of user traffic impacted by a defect)
Figure 2: Receive and Transmit Defect States
PE1 will directly detect or be notified of AC receive or PW receive
defects as they occur upstream of PE1 and impact traffic being sent
to PE1. As a result, PE1 enters the AC or PW receive defect state.
In Figure 2, PE1 may be notified of a receive defect in the AC by
receiving a Forward Defect indication, e.g., ATM AIS, from CE1 or an
intervening network. This defect notification indicates that user
traffic sent by CE1 may not be received by PE1 due to a defect. PE1
can also directly detect an AC receive defect if it resulted from a
failure of the receive side in the local port or link over which the
AC is configured.
Similarly, PE1 may detect or be notified of a receive defect in the
PW by receiving a Forward Defect indication from PE2. If PW status
is used for fault notification, this message will indicate a Local
PSN-facing PW (egress) Transmit Fault or a Local AC (ingress) Receive
Fault at PE2, as described in Section 8.1.1. This defect
notification indicates that user traffic sent by CE2 may not be
received by PE1 due to a defect. As a result, PE1 enters the PW
receive defect state.
Note that a Forward Defect Indication is sent in the same direction
as the user traffic impacted by the defect.
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Generally, a PE cannot detect transmit defects directly and will
therefore need to be notified of AC transmit or PW transmit defects
by other devices.
In Figure 2, PE1 may be notified of a transmit defect in the AC by
receiving a Reverse Defect indication, e.g., ATM RDI, from CE1. This
defect relates to the traffic sent by PE1 to CE1 on the AC.
Similarly, PE1 may be notified of a transmit defect in the PW by
receiving a Reverse Defect indication from PE2. If PW status is used
for fault notification, this message will indicate a Local PSN-
facing PW (ingress) Receive Fault or a Local Attachment Circuit
(egress) Transmit Fault at PE2, as described in Section 8.1.1. This
defect impacts the traffic sent by PE1 to CE2. As a result, PE1
enters the PW transmit defect state.
Note that a Reverse Defect indication is sent in the reverse
direction to the user traffic impacted by the defect.
The procedures outlined in this document define the entry and exit
criteria for each of the four states with respect to the set of PW
services within the document scope and the consequent actions that
PE1 must perform.
When a PE enters both receive and transmit defect states related to
the same PW service, then the receive defect takes precedence over
transmit defect in terms of the consequent actions.
7. OAM Modes
A homogeneous PW service forwards packets between an AC and a PW of
the same type. It thus implements both NS OAM and PW OAM mechanisms.
PW OAM defect notification messages are described in Section 8.1 NS
OAM messages are described in Appendix A.
This document defines two different OAM modes, the distinction being
the method of mapping between the NS and PW OAM defect notification
messages.
The first mode, illustrated in Figure 3, is called the "single
emulated OAM loop" mode. Here a single end-to-end NS OAM loop is
emulated by transparently passing NS OAM messages over the PW. Note
that the PW OAM is shown outside the PW in Figure 3, as it is
transported in LDP messages or in the associated channel, not inside
the PW itself.
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+-----+ +-----+
+-----+ | |=================| | +-----+
| CE1 |-=NS-OAM=>| PE1 |----=NS-OAM=>----| PE2 |-=NS-OAM=>| CE2 |
+-----+ | |=================| | +-----+
+-----+ +-----+
\ /
-------=PW-OAM=>-------
Figure 3: Single Emulated OAM Loop mode
The single emulated OAM loop mode implements the following behavior:
a. The upstream PE (PE1) MUST transparently relay NS OAM messages
over the PW.
b. The upstream PE MUST signal local defects affecting the AC using a
NS defect notification message sent over the PW. In the case that
it is not possible to generate NS OAM messages (e.g., because the
defect interferes with NS OAM message generation) the PE MUST
signal local defects affecting the AC using a PW defect
notification message.
c. The upstream PE MUST signal local defects affecting the PW using a
PW defect notification message.
d. The downstream PE (PE2) MUST insert NS defect notification
messages into its local AC when it detects or is notified of a
defect in the PW or remote AC. This includes translating received
PW defect notification messages into NS defect notification
messages for defects signaled by the upstream PE.
The single emulated OAM loop mode is suitable for PW services that
have a widely deployed NS OAM mechanism. This document specifies the
use of this mode for ATM PW, TDM PW, and CEP PW services. It is the
default mode of operation for all ATM cell-mode PW services and the
only mode specified for CEP and SAToP/CESoPSN TDM PW services. It is
optional for AAL5 PDU transport and AAL5 SDU transport modes.
The second OAM mode operates three OAM loops joined at the AC/PW
boundaries of the PEs. This is referred to as the "coupled OAM
loops" mode and is illustrated in Figure 4. Note that in contrast to
Figure 3, NS OAM messages are never carried over the PW.
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+-----+ +-----+
+-----+ | |=================| | +-----+
| CE1 |-=NS-OAM=>| PE1 | | PE2 |-=NS-OAM=>| CE2 |
+-----+ | |=================| | +-----+
+-----+ +-----+
\ /
-------=PW-OAM=>-------
Figure 4: Coupled OAM Loops mode
The coupled OAM loops mode implements the following behavior:
a. The upstream PE (PE1) MUST terminate and translate a received NS
defect notification message into a PW defect notification message.
b. The upstream PE MUST signal local failures affecting its local AC
using PW defect notification messages to the downstream PE.
c. The upstream PE MUST signal local failures affecting the PW using
PW defect notification messages.
d. The downstream PE (PE2) MUST insert NS defect notification
messages into the AC when it detects or is notified of defects in
the PW or remote AC. This includes translating received PW defect
notification messages into NS defect notification messages.
This document specifies the coupled OAM loops mode as the default
mode for the frame relay, ATM AAL5 PDU transport, and AAL5 SDU
transport services. It is an optional mode for ATM VCC cell mode
services. This mode is not specified for TDM, CEP, or ATM VPC cell
mode PW services. RFC5087 defines a similar but distinct mode, as
will be explained in Section 11 below. For the ATM VPC cell mode
case a pure coupled OAM loops mode is not possible as a PE MUST
transparently pass VC-level (F5) ATM OAM cells over the PW while
terminating and translating VP-level (F4) OAM cells.
8. PW Defect States and Defect Notifications
8.1. PW Defect Notification Mechanisms
For MPLS and MPLS/IP PSNs, a PE that establishes a PW using Label
Distribution Protocol [LDP] MUST use the LDP status TLV as the
mechanism for AC and PW status and defect notification, as explained
in [RFC4447]. Additionally, a PE MAY use VCCV-BFD Connectivity
Verification (CV) for fault detection only (CV types 0x04 and 0x10
[VCCV-BFD]) but SHOULD notify the remote PE using the LDP Status TLV.
A PE that establishes a PW using means other than LDP, e.g., by
static configuration or by use of BGP, MAY use VCCV-BFD CV (CV types
0x08 and 0x20 [VCCV-BFD]) for AC and PW status and defect
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notification. Note that these CV types SHOULD NOT be used when the
PW is established with the LDP control plane.
For a L2TPV3/IP PSN, a PE SHOULD use the Circuit Status Attribute
Value Pair [AVP] as the mechanism for AC and PW status and defect
notification. In its most basic form, the Circuit Status AVP
[RFC3931] in a Set-Link-Info (SLI) message can signal active/inactive
AC status. The Circuit Status AVP as described in [RFC 5641] is
proposed to be extended to convey status and defects in the AC and
the PSN-facing PW in both ingress and egress directions, i.e., four
independent status bits, without the need to tear down the sessions
or control connection [L2TP-Status].
When a PE does not support the Circuit Status AVP, it MAY use the
Stop-Control-Connection-Notification [StopCCN] and the Call-
Disconnect-Notify [CDN] messages to tear down L2TP sessions in a
fashion similar to LDP's use of Label Withdrawal to tear down a PW.
A PE may use the StopCCN to shutdown the L2TP control connection, and
implicitly all L2TP sessions associated with that control connection,
without any explicit session control messages. This is useful for
the case of a failure which impacts all L2TP sessions (i.e., all PWs)
managed by the control connection. It MAY use the CDN message to
disconnect a specific L2TP session when a failure affects a specific
PW.
Additionally, a PE MAY use VCCV-BFD CV types 0x04 and 0x10 for fault
detection only, but SHOULD notify the remote PE using the Circuit
Status AVP. A PE that establishes a PW using means other than the
L2TP control plane, e.g., by static configuration or by use of BGP,
MAY use VCCV-BFD CV types 0x08 and 0x20 for AC and PW status and
defect notification. These CV types SHOULD NOT be used when the PW
is established via the L2TP control plane.
The CV types are defined in Section 8.1.3 of this document.
8.1.1. LDP Status TLV
[RFC4446] defines the following PW status code points:
0x00000000 - Pseudowire forwarding (clear all failures)
0x00000001 - Pseudowire Not Forwarding
0x00000002 - Local Attachment Circuit (ingress) Receive Fault
0x00000004 - Local Attachment Circuit (egress) Transmit Fault
0x00000008 - Local PSN-facing PW (ingress) Receive Fault
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0x00000010 - Local PSN-facing PW (egress) Transmit Fault
[RFC4447] specifies that "Pseudowire forwarding" code point is used
to clear all faults. It also specifies that "Pseudowire Not
Forwarding" code is used to convey any defect that cannot be
represented by the other code points.
The code points used in the LDP status TLV in a PW status
notification message conveys defects from the viewpoint of the
originating PE. The originating PE conveys this state in the form of
a forward defect or a reverse defect indication.
The forward and reverse defect indication definitions used in this
document map to the LDP Status TLV codes as follows:
Forward defect indication corresponds to the logical OR of:
* Local Attachment Circuit (ingress) Receive Fault,
* Local PSN-facing PW (egress) Transmit Fault, and
* PW Not Forwarding.
Reverse defect indication corresponds to the logical OR of:
* Local Attachment Circuit (egress) Transmit Fault and
* Local PSN-facing PW (ingress) Receive Fault.
A PE MUST use PW status notification messages to report all defects
affecting the PW service including, but not restricted, to the
following:
o defects detected through fault detection mechanisms in the MPLS
and MPLS/IP PSN,
o defects detected through VCCV-Ping or VCCV-BFD CV types 0x04 and
0x10 for fault detection only,
o defects within the PE that result in an inability to forward
traffic between the AC and the PW,
o defects of the AC or in the Layer 2 network affecting the AC as
per the rules detailed in Section 7 for the "single emulated OAM
loop" mode and "coupled OAM loops" modes.
Note that there are two situations that require PW label withdrawal
as opposed to a PW status notification by the PE. The first one is
when the PW is taken down administratively in accordance with
[RFC4447]. The second one is when the Target LDP session established
between the two PEs is lost. In the latter case, the PW labels will
need to be re-signaled when the Targeted LDP session is re-
established.
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8.1.2. L2TP Circuit Status AVP
[RFC3931] defines the Circuit Status AVP in the Set-Link-Info (SLI)
message to exchange initial status and status changes in the circuit
to which the pseudowire is bound. [L2TP-Status] defines extensions
to the Circuit Status AVP that are analogous to the PW Status TLV
defined for LDP. Consequently, for L2TPv3/IP the Circuit Status AVP
is used in the same fashion as the PW Status described in the
previous section. Extended circuit status for L2TPv3/IP is described
in [RFC 5641].
If the extended Circuit Status bits are not supported, and instead
only the "A-bit" (Active) is used as described in [RFC3931], a PE MAY
use CDN messages to clear L2TPv3/IP sessions in the presence of
session-level failures detected in the L2TPv3/IP PSN.
A PE MUST set the Active bit in the Circuit Status to clear all
faults, and it MUST clear the Active bit in the Circuit Status to
convey any defect that cannot be represented explicitly with specific
Circuit Status flags from [RFC3931] or [L2TP-Status].
The forward and reverse defect indication definitions used in this
document map to the L2TP Circuit Status AVP as follows:
Forward defect indication corresponds to the logical OR of:
* Local Attachment Circuit (ingress) Receive Fault,
* Local PSN-facing PW (egress) Transmit Fault, and
* PW Not Forwarding.
Reverse defect indication corresponds to the logical OR of:
* Local Attachment Circuit (egress) Transmit Fault and
* Local PSN-facing PW (ingress) Receive Fault.
The status notification conveys defects from the viewpoint of the
originating LCCE (PE).
When the extended Circuit Status definition of [L2TP-Status] is
supported, a PE SHALL use the Circuit Status to report all failures
affecting the PW service including, but not restricted, to the
following:
o defects detected through defect detection mechanisms in the
L2TPV3/IP PSN,
o defects detected through VCCV-Ping or VCCV-BFD CV types 0x04 (BFD
IP/UDP-encapsulated, for PW Fault Detection only) and 0x10 (BFD
PW-ACH-encapsulated (without IP/UDP headers), for PW. Fault
Detection and AC/PW Fault Status Signaling) for fault detection
only which are described in Section 8.1.3 of this document,
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o defects within the PE that result in an inability to forward
traffic between the AC and the PW,
o defects of the AC or in the L2 network affecting the AC as per the
rules detailed in Section 7 for the "single emulated OAM loop"
mode and the "coupled OAM loops" modes.
When the extended Circuit Status definition of [L2TP-Status] is not
supported, a PE SHALL use the A-bit in the Circuit Status AVP in SLI
to report:
o defects of the AC or in the L2 network affecting the AC as per the
rules detailed in Section 7 for the "single emulated OAM loop"
mode and the "coupled OAM loops" modes.
When the extended Circuit Status definition of [L2TP-Status] is not
supported, a PE MAY use the CDN and StopCCN messages in a similar way
to an MPLS PW label withdrawal to report:
o defects detected through defect detection mechanisms in the
L2TPV3/IP PSN (using StopCCN),
o defects detected through VCCV (pseudowire level) (using CDN),
o defects within the PE that result in an inability to forward
traffic between ACs and PW (using CDN).
For ATM L2TPv3/IP pseudowires, in addition to the Circuit Status AVP,
a PE MAY use the ATM Alarm Status AVP [RFC4454] to indicate the
reason for the ATM circuit status and the specific alarm type, if
any. This AVP is sent in the SLI message to indicate additional
information about the ATM circuit status.
L2TP control connections use Hello messages as a keep-alive facility.
It is important to note that if PSN failure is detected by keep-alive
timeout, the control connection is cleared. L2TP Hello messages are
sent in-band so as to follow the data plane with respect to the
source and destination addresses, IP protocol number and UDP port
(when UDP is used).
8.1.3. BFD Diagnostic Codes
[BFD] defines a set of diagnostic codes that partially overlap the
set of defects that can be communicated through LDP Status TLV or
L2TP Circuit Status AVP. This section describes the behavior of the
PEs with respect to using one or both of these methods for detecting
and propagating defect state.
In the case of an PW using LDP signaling, the PEs negotiate the use
of the VCCV capabilities during the label mapping messages exchange
used to establish the two directions of the PW. This is achieved by
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including a capability TLV in the PW FEC interface parameters TLV.
In the L2TPV3/IP case, the PEs negotiate the use of VCCV during the
pseudowire session initialization using the VCCV AVP [RFC5085].
The CV Type Indicators field in the OAM capability TLV or VCCV AVP
defines a bitmask used to indicate the specific OAM capabilities that
the PE can use over the PW being established.
A CV type of 0x04 or 0x10 [VCCV-BFD] indicates that BFD is used for
PW fault detection only. These CV types MAY be used any time the PW
is established using LDP or L2TP control planes. In this mode, only
the following diagnostic (Diag) codes specified in [BFD] will be
used:
0 - No diagnostic
1 - Control detection time expired
3 - Neighbor signaled session down
7 - Administratively Down
A PE MUST use diagnostic code 0 to indicate to its peer PE that is
correctly receiving BFD control messages. It MUST use diagnostic
code 1 to indicate that to its peer it has stopped receiving BFD
control messages and will thus declare the PW to be down in the
receive direction. It MUST use diagnostic code 3 to confirm to its
peer that the BFD session is going down after receiving diagnostic
code 1 from this peer. In this case, it will declare the PW to be
down in the transmit direction. A PE MUST use diagnostic code 7 to
bring down the BFD session when the PW is brought down
administratively. All other defects, such as AC/PW defects and PE
internal failures that prevent it from forwarding traffic, MUST be
communicated through the LDP Status TLV in the case of MPLS PSN or
MPLS/IP PSN, or through the appropriate L2TP codes in the Circuit
Status AVP in the case of L2TPV3/IP PSN.
A CV type of 0x08 or 0x20 in the OAM capabilities TLV indicates that
BFD is used for both PW fault detection and Fault Notification. In
addition to the above diagnostic codes, a PE uses the following codes
to signal AC defects and other defects impacting forwarding over the
PW service:
6 - Concatenated Path Down
8 - Reverse Concatenated Path Down
As specified in [RFC 5085], a PE negotiates the use of VCCV during PW
set-up. When a PW transported over an MPLS-PSN is established using
LDP, the PEs negotiate the use of the VCCV capabilities using the
optional VCCV Capability Advertisement Sub- TLV parameter in the
Interface Parameter Sub-TLV field of the LDP PW ID FEC or using an
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Interface Parameters TLV of the LDP Generalized PW ID FEC. In the
case of L2TPv3/IP PSNs, the PEs negotiate the use of VCCV during the
pseudowire session initialization using VCCV AVP.
Note that a defect that causes the generation of the "PW not
forwarding code" (diagnostic code 6 or 8) does not necessarily result
in the BFD session going down. However, if the BFD session times
out, then diagnostic code 1 must be used since it signals a state
change of the BFD session itself. In general, when a BFD session
changes state, the PEs must use the state change diagnostic codes 0,
1, 3, and 7 in accordance to [BFD] and they MUST override any of the
AC/PW status diagnostic codes (codes 6 or 8) that may have been
signaled prior to the BFD session changing state.
The forward and reverse defect indications used in this document map
to the following BFD codes:
Forward defect indication corresponds to the logical OR of:
* Concatenated Path Down (BFD diagnostic code 06)
* Pseudowire Not Forwarding (PW status code 0x00000001).
Reverse defect indication- corresponds to:
* Reverse Concatenated Path Down (BFD diagnostic code 08).
These diagnostic codes are used to signal forward and reverse defect
states, respectively, when the PEs negotiated the use of BFD as the
mechanism for AC and PW fault detection and status signaling
notification. As stated in Section 8.1, these CV types SHOULD NOT be
used when the PW is established with the LDP or L2TP control plane.
8.2. PW Defect State Entry/Exit
8.2.1. PW receive defect state entry/exit criteria
PE1, as downstream PE, will enter the PW receive defect state if one
or more of the following occurs:
o It receives a Forward Defect Indication (FDI) from PE2 indicating
either a receive defect on the remote AC, or that PE2 detected or
was notified of downstream PW fault.
o It detects loss of connectivity on the PSN tunnel upstream of PE1
which affects the traffic it receives from PE2.
o It detects a loss of PW connectivity through VCCV-BFD or VCCV-PING
which affects the traffic it receives from PE2.
Note that if the PW control session (LDP session, the L2TP session,
or the L2TP control connection) between the PEs fails, the PW is torn
down and needs to be re-established. However, the consequent actions
towards the ACs are the same as if the PW entered the receive defect
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state.
PE1 will exit the PW receive defect state when the following
conditions are met. Note that this may result in a transition to the
PW operational state or the PW transmit defect state.
o All previously detected defects have disappeared, and
o PE2 cleared the FDI, if applicable.
8.2.2. PW transmit defect state entry/exit criteria
PE1, as upstream PE, will enter the PW transmit defect state if the
following conditions occur:
o It receives a Reverse Defect Indication (RDI) from PE2 indicating
either a transmit fault on the remote AC, or that PE2 detected or
was notified of a upstream PW fault, and
o it is not already in the PW receive defect state.
PE1 will exit the transmit defect state if it receives an OAM message
from PE2 clearing the RDI, or it has entered the PW receive defect
state.
For a PWE3 over a L2TPV3/IP PSN using the basic Circuit Status AVP
[RFC3931], the PW transmit defect state is not valid and a PE can
only enter the PW receive defect state.
9. Procedures for ATM PW Service
Asynchronous Transfer Mode (ATM) Terminology is explained in Appendix
A.2 of this document.
9.1. AC receive defect state entry/exit criteria
When operating in the coupled OAM loops mode, PE1 enters the AC
receive defect state when any of the following conditions are met:
a. It detects or is notified of a physical layer fault on the ATM
interface.
b. It receives an end-to-end Flow 4 OAM [F4] Alarm Indication Signal
[AIS] AIS OAM flow on a Virtual Path [VP] AC, or an end-to-end
Flow 5 [F5] AIS OAM flow on a Virtual Circuit [VC] as per ITU-T
Recommendation I.610 [I.610 AC, indicating that the ATM VPC or VCC
is down in the adjacent Layer 2 ATM network.
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c. It receives a segment F4 AIS OAM flow on a Virtual Path[VP] AC, or
a segment F5 AIS OAM flow on a VC AC, provided that the operator
has provisioned segment OAM and the PE is not a segment end-point.
d. It detects loss of connectivity on the ATM VPC/VCC while
terminating segment or end-to-end ATM continuity check (ATM CC)
cells with the local ATM network and CE.
When operating in the coupled OAM loops mode, PE1 exits the AC
Receive defect state when all previously detected defects have
disappeared.
When operating in the single emulated OAM loop mode, PE1 enters the
AC receive defect state if any of the following conditions are met:
a. It detects or is notified of a physical layer fault on the ATM
interface.
b. It detects loss of connectivity on the ATM VPC/VCC while
terminating segment ATM continuity check (ATM CC) cells with the
local ATM network and CE.
When operating in the single emulated OAM loop mode, PE1 exits the AC
receive defect state when all previously detected defects have
disappeared.
The exact conditions under which a PE enters and exits the AIS state,
or declares that connectivity is restored via ATM CC, are defined in
Section 9.2 of ITU-T Recommendation I.610 [I.610].
9.2. AC transmit defect state entry/exit criteria
When operating in the coupled OAM loops mode, PE1 enters the AC
transmit defect state if any of the following conditions are met:
a. It terminates an end-to-end F4 RDI OAM flow, in the case of a VPC,
or an end-to-end F5 RDI OAM flow, in the case of a VCC, indicating
that the ATM VPC or VCC is down in the adjacent L2 ATM.
b. It receives a segment F4 RDI OAM flow on a VP AC, or a segment F5
RDI OAM flow on a VC AC, provided that the operator has
provisioned segment OAM and the PE is not a segment end-point.
PE1 exits the AC transmit defect state if the AC state transitions to
working or to the AC receive defect state. The exact conditions for
exiting the RDI state are described in Section 9.2 of ITU-T
Recommendation I.610 [I.610].
Note that the AC transmit defect state is not valid when operating in
the single emulated OAM loop mode, as PE1 transparently forwards the
received RDI cells as user cells over the ATM PW to the remote CE.
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9.3. Consequent Actions
In the remainder of this section, the text refers to AIS, RDI and CC
without specifying whether there is an F4 (VP-level) flow or an F5
(VC- level) flow, or whether it is an end-to-end or a segment flow.
Precise ATM OAM procedures for each type of flow are specified in
Section 9.2 of ITU-T Recommendation I.610 [I.610].
9.3.1. PW receive defect state entry/exit
On entry to the PW receive defect state:
a. PE1 MUST commence AIS insertion into the corresponding AC.
b. PE1 MUST cease generation of CC cells on the corresponding AC, if
applicable.
c. If the PW defect was detected by PE1 without receiving FDI from
PE2, PE1 MUST assume PE2 has no knowledge of the defect and MUST
notify PE2 by sending RDI.
On exit from the PW receive defect state:
a. PE1 MUST cease AIS insertion into the corresponding AC.
b. PE1 MUST resume any CC cell generation on the corresponding AC, if
applicable.
c. PE1 MUST clear the RDI to PE2, if applicable.
9.3.2. PW transmit defect state entry/exit
On entry to the PW Transmit Defect State:
a. PE1 MUST commence RDI insertion into the corresponding AC.
b. If the PW failure was detected by PE1 without receiving an RDI
from PE2, PE1 MUST assume PE2 has no knowledge of the defect and
MUST notify PE2 by sending FDI.
On exit from the PW Transmit Defect State:
a. PE1 MUST cease RDI insertion into the corresponding AC.
b. PE1 MUST clear the FDI to PE2, if applicable.
9.3.3. PW defect state in ATM Port Mode PW Service
In case of transparent cell transport PW service, i.e., "port mode",
where the PE does not keep track of the status of individual ATM VPCs
or VCCs, a PE cannot relay PW defect state over these VCCs and VPCs.
If ATM CC is run on the VCCs and VPCs end-to-end (CE1 to CE2), or on
a segment originating and terminating in the ATM network and spanning
the PSN network, it will timeout and cause the CE or ATM switch to
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enter the ATM AIS state.
9.3.4. AC receive defect state entry/exit
On entry to the AC receive defect state and when operating in the
coupled OAM loops mode:
a. PE1 MUST send FDI to PE2.
b. PE1 MUST commence insertion of ATM RDI cells into the AC towards
CE1.
When operating in the single emulated OAM loop mode, PE1 must be able
to support two options, subject to the operator's preference. The
default option is the following:
On entry to the AC receive defect state:
a. PE1 MUST transparently relay ATM AIS cells, or, in the case of a
local AC defect, commence insertion of ATM AIS cells into the
corresponding PW towards CE2.
b. If the defect interferes with NS OAM message generation, PE1 MUST
send an FDI indication to PE2.
c. PE1 MUST cease the generation of CC cells on the corresponding PW,
if applicable.
In certain operational models, for example in the case that the ATM
access network is owned by a different provider than the PW, an
operator may want to distinguish between defects detected in the ATM
access network and defects detected on the AC directly adjacent to
the PE. Therefore, the following option MUST also be supported:
a. PE1 MUST transparently relay ATM AIS cells over the corresponding
PW towards CE2.
b. Upon detection of a defect on the ATM interface on the PE or in
the PE itself, PE1 MUST send FDI to PE2.
c. PE1 MUST cease generation of CC cells on the corresponding PW, if
applicable.
On exit from the AC receive defect state and when operating in the
coupled OAM loops mode:
a. PE1 MUST clear the FDI to PE2.
b. PE1 MUST cease insertion of ATM RDI cells into the AC.
On exit from the AC receive defect state and when operating in the
single emulated OAM loop mode:
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a. PE1 MUST cease insertion of ATM AIS cells into the corresponding
PW.
b. PE1 MUST clear the FDI to PE2, if applicable.
c. PE1 MUST resume any CC cell generation on the corresponding PW, if
applicable.
9.3.5. AC transmit defect state entry/exit
On entry to the AC transmit defect state and when operating in the
coupled OAM loops mode:
* PE1 MUST send RDI to PE2.
On exit from the AC transmit defect state and when operating in the
coupled OAM loops mode:
* PE1 MUST clear the RDI to PE2.
10. Procedures for Frame Relay PW Service
Frame Relay (FR) terminology is explained in Appendix A.1 of this
document.
10.1. AC receive defect state entry/exit criteria
PE1 enters the AC receive defect state if one or more of the
following conditions are met:
a. A Permanent Virtual Circuit (PVC) is not deleted from the FR
network and the FR network explicitly indicates in a full status
report (and optionally by the asynchronous status message) that
this PVC is inactive [Q.933]. In this case, this status maps
across the PE to the corresponding PW only.
b. The Link Integrity Verification (LIV) indicates that the link from
the PE to the Frame Relay network is down [Q.933]. In this case,
the link down indication maps across the PE to all corresponding
PWs.
c. A physical layer alarm is detected on the FR interface. In this
case, this status maps across the PE to all corresponding PWs.
PE1 exits the AC receive defect state when all previously detected
defects have disappeared.
10.2. AC transmit defect state entry/exit criteria
The AC transmit defect state is not valid for a FR AC.
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10.3. Consequent Actions
10.3.1. PW receive defect state entry/exit
The A (Active) bit indicates whether the FR PVC is ACTIVE (1) or
INACTIVE (0) as explained in [RFC 4591].
On entry to the PW receive defect state:
a. PE1 MUST clear the Active bit for the corresponding FR AC in a
full status report, and optionally in an asynchronous status
message, as per Q.933 Annex A [Q.933].
b. If the PW failure was detected by PE1 without receiving FDI from
PE2, PE1 MUST assume PE2 has no knowledge of the defect and MUST
notify PE2 by sending RDI.
On exit from the PW receive defect state:
a. PE1 MUST set the Active bit for the corresponding FR AC in a full
status report, and optionally in an asynchronous status message,
as per Q.933 annex A. PE1 does not apply this procedure on a
transition from the PW receive defect state to the PW transmit
defect state.
b. PE1 MUST clear the RDI to PE2, if applicable.
10.3.2. PW transmit defect state entry/exit
On entry to the PW transmit defect state:
a. PE1 MUST clear the Active bit for the corresponding FR AC in a
full status report, and optionally in an asynchronous status
message, as per Q.933 Annex A.
b. If the PW failure was detected by PE1 without RDI from PE2, PE1
MUST assume PE2 has no knowledge of the defect and MUST notify PE2
by sending FDI.
On exit from the PW transmit defect state:
a. PE1 MUST set the Active bit for the corresponding FR AC in a full
status report, and optionally in an asynchronous status message,
as per Q.933 annex A. PE1 does not apply this procedure on a
transition from the PW transmit defect state to the PW receive
defect state.
b. PE1 MUST clear the FDI to PE2, if applicable.
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10.3.3. PW defect state in the FR Port Mode PW Service
In case of port mode PW service, STATUS ENQUIRY and STATUS messages
are transported transparently over the PW. A PW Failure will
therefore result in timeouts of the Q.933 link and PVC management
protocol at the Frame Relay devices at one or both sites of the
emulated interface.
10.3.4. AC receive defect state entry/exit
On entry to the AC receive defect state:
* PE1 MUST send FDI to PE2.
On exit from the AC receive defect state:
* PE1 MUST clear FDI to PE2.
10.3.5. AC transmit defect state entry/exit
The AC transmit defect state is not valid for a FR AC.
11. Procedures for TDM PW Service
The following procedures apply to SAToP ([RFC4553]), CESoPSN
([RFC5086]) and TDMoIP ([RFC5087]). These technologies utilize the
single emulated OAM loop mode. RFC 5087 distinguishes between trail-
extended and trail-terminated scenarios; the former is essentially
the single emulated loop model. The latter applies to cases where
the NS networks are run by different operators and defect
notifications are not propagated across the PW.
Since TDM is inherently real-time in nature, many OAM indications
must be generated or forwarded with minimal delay. This requirement
rules out the use of messaging protocols, such as PW status messages.
Thus, for TDM PWs, alternate mechanisms are employed.
The fact that TDM PW packets are sent at a known constant rate can be
exploited as an OAM mechanism. Thus, a PE enters the PW receive
defect state whenever a preconfigured number of TDM PW packets do not
arrive in a timely fashion. It exits this state when packets once
again arrive at their proper rate.
Native TDM carries OAM indications in overhead fields that travel
along with the data. TDM PWs emulate this behavior by sending urgent
OAM messages in the PWE control word.
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The TDM PWE3 control word contains a set of flags used to indicate PW
and AC defect conditions. The L bit is an AC forward defect
indication used by the upstream PE to signal NS network defects to
the downstream PE. The M field may be used to modify the meaning of
receive defects. The R bit is a PW reverse defect indication used by
the PE to signal PSN failures to the remote PE. Upon reception of
packets with the R bit set, a PE enters the PW transmit defect state.
L bits and R bits are further described in [RFC5087].
11.1. AC receive defect state entry/exit criteria
PE1 enters the AC receive defect state if any of the following
conditions are met:
a. It detects a physical layer fault on the TDM interface (Loss of
Signal, Loss of Alignment, etc., as described in [G.775]).
b. It is notified of a previous physical layer fault by detecting
AIS.
The exact conditions under which a PE enters and exits the AIS state
are defined in [G.775]. Note that Loss of Signal and AIS detection
can be performed by PEs for both structure-agnostic and structure-
aware TDM PW types. Note that PEs implementing structure- agnostic
PWs can not detect Loss of Alignment.
11.2. AC transmit defect state entry/exit criteria
PE1 enters the AC transmit defect state when it detects RDI according
to the criteria in [G.775]. Note that PEs implementing structure-
agnostic PWs can not detect RDI.
11.3. Consequent Actions
11.3.1. PW receive defect state entry/exit
On entry to the PW receive defect state:
a. PE1 MUST commence AIS insertion into the corresponding TDM AC.
b. PE1 MUST set the R bit in all PW packets sent back to PE2.
On exit from the PW receive defect state:
a. PE1 MUST cease AIS insertion into the corresponding TDM AC.
b. PE1 MUST clear the R bit in all PW packets sent back to PE2.
Note that AIS generation can in general be performed by both
structure-aware and structure-agnostic PEs.
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11.3.2. PW transmit defect state entry/exit
On entry to the PW Transmit Defect State:
* A structure-aware PE1 MUST commence RDI insertion into the
corresponding AC.
On exit from the PW Transmit Defect State:
* A structure-aware PE1 MUST cease RDI insertion into the
corresponding AC.
Note that structure-agnostic PEs are not capable of injecting RDI
into an AC.
11.3.3. AC receive defect state entry/exit
On entry to the AC receive defect state and when operating in the
single emulated OAM loop mode:
a. PE1 SHOULD overwrite the TDM data with AIS in the PW packets sent
towards PE2.
b. PE1 MUST set the L bit in these packets.
c. PE1 MAY omit the payload in order to conserve bandwidth.
d. A structure-aware PE1 SHOULD send RDI back towards CE1.
e. A structure-aware PE1 that detects a potentially correctable AC
defect MAY use the M field to indicate this.
On exit from the AC receive defect state and when operating in the
single emulated OAM loop mode:
a. PE1 MUST cease overwriting PW content with AIS and return to
forwarding valid TDM data in PW packets sent towards PE2.
b. PE1 MUST clear the L bit in PW packets sent towards PE2.
c. A structure-aware PE1 MUST cease sending RDI towards CE1.
12. Procedures for CEP PW Service
The following procedures apply to SONET/SDH Circuit Emulation
([RFC4842]). They are based on the single emulated OAM loop mode.
Since SONET and SDH are inherently real-time in nature, many OAM
indications must be generated or forwarded with minimal delay. This
requirement rules out the use of messaging protocols, such as PW
status messages. Thus, for CEP PWs alternate mechanisms are
employed.
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The CEP PWE3 control word contains a set of flags used to indicate PW
and AC defect conditions. The L bit is a forward defect indication
used by the upstream PE to signal to the downstream PE a defect in
its local attachment circuit. The R bit is a PW reverse defect
indication used by the PE to signal PSN failures to the remote PE.
The combination of N and P bits is used by the local PE to signal
loss of pointer to the remote PE.
The fact that CEP PW packets are sent at a known constant rate can be
exploited as an OAM mechanism. Thus, a PE enters the PW receive
defect state when it loses packet synchronization. It exits this
state when it regains packet synchronization. See [RFC4842] for
further details.
12.1. Defect states
12.1.1. PW receive defect state entry/exit
In addition to the conditions specified in Section 8.2.1, PE1 will
enter the PW receive defect state when one of the following becomes
true:
o It receives packets with the L bit set.
o It receives packets with both the N and P bits set.
o It loses packet synchronization.
12.1.2. PW transmit defect state entry/exit
In addition to the conditions specified in Section 8.2.2 PE1 will
enter the PW transmit defect state if it receives packets with the R
bit set.
12.1.3. AC receive defect state entry/exit
PE1 enters the AC receive defect state when any of the following
conditions are met:
a. It detects a physical layer fault on the TDM interface (Loss of
Signal, Loss of Alignment, etc.).
b. It is notified of a previous physical layer fault by detecting of
AIS.
The exact conditions under which a PE enters and exits the AIS state
are defined in [G.707] and [G.783].
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12.1.4. AC receive defect state entry/exit
The AC transmit defect state is not valid for CEP PWs. RDI signals
are forwarded transparently.
12.2. Consequent Actions
12.2.1. PW receive defect state entry/exit
On entry to the PW receive defect state:
a. PE1 MUST commence AIS-P/V insertion into the corresponding AC.
See [RFC4842].
b. PE1 MUST set the R bit in all PW packets sent back to PE2.
On exit from the PW receive defect state:
a. PE1 MUST cease AIS-P/V insertion into the corresponding AC.
b. PE1 MUST clear the R bit in all PW packets sent back to PE2.
See [RFC4842] for further details.
12.2.2. PW transmit defect state entry/exit
On entry to the PW Transmit Defect State:
a. A structure-aware PE1 MUST commence RDI insertion into the
corresponding AC.
On exit from the PW Transmit Defect State:
a. A structure-aware PE1 MUST cease RDI insertion into the
corresponding AC.
12.2.3. AC receive defect state entry/exit
On entry to the AC receive defect state:
a. PE1 MUST set the L bit in these packets.
b. If Dynamic Bandwidth Allocation (DBA) has been enabled, PE1 MAY
omit the payload in order to conserve bandwidth.
c. If Dynamic Bandwidth Allocation (DBA) is not enabled PE1 SHOULD
insert AIS-V/P in the SDH/SONET client layer in the PW packets
sent towards PE2.
On exit from the AC receive defect state:
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a. PE1 MUST cease overwriting PW content with AIS-P/V and return to
forwarding valid data in PW packets sent towards PE2.
b. PE1 MUST clear the L bit in PW packets sent towards PE2.
See [RFC4842] for further details.
13. Security Considerations
The mapping messages described in this document do not change the
security functions inherent in the actual messages. All generic
security considerations applicable to PW traffic specified in Section
10 of RFC 3985 are applicable to NS OAM messages transferred inside
the PW.
Security considerations in Section 10 of RFC 5085 for VCCV apply to
the OAM messages thus transferred. Security considerations
applicable to the PWE3 control protocol of RFC 4447 Section 8.2 apply
to OAM indications transferred using the LDP status message.
14. IANA Considerations
This document requires no IANA actions.
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Appendix A. Native Service Management (informative)
A.1. Frame Relay Management
The management of Frame Relay Bearer Service (FRBS) connections can
be accomplished through two distinct methodologies:
a. Based on ITU-T Q.933 Annex A, Link Integrity Verification
procedure, where STATUS and STATUS ENQUIRY signaling messages are
sent using DLCI=0 over a given UNI and NNI physical link [Q.933].
b. Based on FRBS LMI, and similar to ATM ILMI where LMI is common in
private Frame Relay networks.
In addition, ITU-T I.620 addresses Frame Relay loopback, but the
deployment of this standard is relatively limited [I.620].
It is possible to use either, or both, of the above options to manage
Frame Relay interfaces. This document will refer exclusively to
Q.933 messages.
The status of any provisioned Frame Relay PVC may be updated through:
a. Frame Relay STATUS messages in response to Frame Relay STATUS
ENQUIRY messages; these are mandatory.
b. Optional unsolicited STATUS updates independent of STATUS ENQUIRY
(typically under the control of management system, these updates
can be sent periodically (continuous monitoring) or only upon
detection of specific defects based on configuration.
In Frame Relay, a Data Link Connection [DLC] is either up or down.
There is no distinction between different directions. To achieve
commonality with other technologies, down is represented as a receive
defect.
Frame relay connection management is not implemented over the PW
using either of the techniques native to FR, therefore PW mechanisms
are used to synchronize the view each PE has of the remote Native
Service/Attachment Circuit [NS/AC]. A PE will treat a remote NS/AC
failure in the same way it would treat a PW or PSN failure; that is
using AC facing FR connection management to notify the CE that FR is
down.
A.2. ATM Management
ATM management and OAM mechanisms are much more evolved than those of
Frame Relay. There are five broad management-related categories,
including fault management (FT), Performance management (PM),
configuration management (CM), Accounting management (AC), and
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Security management (SM). [I.610] describes the functions for the
operation and maintenance of the physical layer and the ATM layer,
that is, management at the bit and cell levels [I.610]. Because of
its scope, this document will concentrate on ATM fault management
functions. Fault management functions include the following:
a. Alarm indication signal (AIS).
b. Remote Defect indication (RDI).
c. Continuity Check (CC).
d. Loopback (LB).
Some of the basic ATM fault management functions are described as
follows: Alarm indication signal (AIS) sends a message in the same
direction as that of the signal, to the effect that an error has been
detected.
Remote defect indication (RDI) sends a message to the transmitting
terminal that an error has been detected. Alarms related to the
physical layer are indicated using path AIS/RDI. Virtual path AIS/
RDI and virtual channel AIS/RDI are also generated for the ATM layer.
OAM cells (F4 and F5 cells) are used to instrument virtual paths and
virtual channels respectively with regard to their performance and
availability. OAM cells in the F4 and F5 flows are used for
monitoring a segment of the network and end-to-end monitoring. OAM
cells in F4 flows have the same VPI as that of the connection being
monitored. OAM cells in F5 flows have the same VPI and VCI as that
of the connection being monitored. The AIS and RDI messages of the
F4 and F5 flows are sent to the other network nodes via the VPC or
the VCC to which the message refers. The type of error and its
location can be indicated in the OAM cells. Continuity check is
another fault management function. To check whether a VCC that has
been idle for a period of time is still functioning, the network
elements can send continuity-check cells along that VCC.
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Appendix B. PW Defects and Detection tools
B.1. PW Defects
Possible defects that impact PWs are the following:
a. Physical layer defect in the PSN interface.
b. PSN tunnel failure which results in a loss of connectivity between
ingress and egress PE.
c. Control session failures between ingress and egress PE.
In case of an MPLS PSN and an MPLS/IP PSN there are additional
defects:
a. PW labeling error, which is due to a defect in the ingress PE, or
to an over-writing of the PW label value somewhere along the LSP
path.
b. LSP tunnel Label swapping errors or LSP tunnel label merging
errors in the MPLS network. This could result in the termination
of a PW at the wrong egress PE.
c. Unintended self-replication; e.g., due to loops or denial- of-
service attacks.
B.2. Packet Loss
Persistent congestion in the PSN or in a PE could impact the proper
operation of the emulated service.
A PE can detect packet loss resulting from congestion through several
methods. If a PE uses the sequence number field in the PWE3 Control
Word for a specific Pseudowire [RFC3985] and [RFC4385], it has the
ability to detect packet loss. Translation of congestion detection
to PW defect states is outside the scope of this specification.
There are congestion alarms that are raised in the node and to the
management system when congestion occurs. The decision to declare
the PW Down and to select another path is usually at the discretion
of the network operator.
B.3. PW Defect Detection Tools
To detect the defects listed above, Service Providers have a variety
of options available.
Physical Layer defect detection and notification mechanisms include
SONET/SDH Los of Signal (LOS), Loss of Alignment (LOA), and AIS/RDI.
PSN defect detection mechanisms vary according to the PSN type.
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For PWE3 over an L2TPV3/IP PSN, with L2TP as encapsulation protocol,
the defect detection mechanisms described in [RFC3931] apply. This
includes, for example, the keep-alive mechanism performed with Hello
messages for detection of loss of connectivity between a pair of
LCCEs (i.e., dead PE peer and path detection). Furthermore, the
tools Ping and Traceroute, based on ICMP Echo Messages [RFC792] apply
and can be used to detect defects on the IP PSN. Additionally, VCCV-
Ping [RFC5085] and VCCV-BFD [VCCV-BFD] can also be used to detect
defects at the individual pseudowire level.
For PWE3 over an MPLS PSN and an MPLS/IP PSN, several tools can be
used.
a. LSP-Ping and LSP-Traceroute [RFC4379] for LSP tunnel connectivity
verification.
b. LSP-Ping with Bi-directional Forwarding Detection [VCCV-BFD] for
LSP tunnel continuity checking.
c. Furthermore, if RSVP-TE is used to setup the PSN Tunnels between
ingress and egress PE, the hello protocol can be used to detect
loss of connectivity [RFC3209], but only at the control plane.
B.4. PW specific defect detection mechanisms
[RFC4377] describes how LSP-Ping and BFD can be used over individual
PWs for connectivity verification and continuity checking
respectively.
Furthermore, the detection of a fault could occur at different points
in the network and there are several ways the observing PE determines
a fault exists:
a. Egress PE detection of failure (e.g., BFD).
b. Ingress PE detection of failure (e.g., LSP-PING).
c. Ingress PE notification of failure (e.g. RSVP Path-err).
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Appendix C. References
C.1. Normative References
[BFD] Katz, D., Ward, D., "Bidirectional Forwarding Detection",
draft-ietf-bfd-base-11.txt, work in progress, January 2010.
[FRF.19] Frame Relay Forum, "Frame Relay Operations, Administration,
and Maintenance Implementation Agreement", March 2001.
[ICMP] Postel, J. "Internet Control Message Protocol" RFC 792.
[G.707] ITU-T Recommendation G.707 "Network Node Interface For The
Synchronous Digital Hierarchy", December 2003.
[G.775] ITU-T Recommendation G.775 "Loss of Signal (LOS), Alarm
Indication Signal(AIS) and Remote Defect Indication (RDI) defect
detection and clearance criteria for PDH signals", October 1998.
[G.783] ITU-T Recommendation G.783 "Characteristics of synchronous
digital hierarchy (SDH) equipment functional blocks ", March 2006.
[I.610] ITU-T Recommendation I.610 "B-ISDN operation and maintenance
principles and functions", February 1999.
[I.620] ITU-T Recommendation I.620 "Frame relay operation and
maintenance principles and functions", October 1996.
[Q.933] ITU-T Recommendation Q.933 "ISDN Digital Subscriber
Signalling System No. 1 (DSS1) Signalling specifications for frame
mode switched and permanent virtual connection control and status
monitoring", February 2003.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3931] Lau, J., et. al. "Layer Two Tunneling Protocol (Version
3", RFC 3931, March 2005.
[RFC4023] Worster. T., et al., "Encapsulating MPLS in IP or Generic
Routing Encapsulation (GRE)", RFC 4023, March 2005.
[RFC4379] Kompella, K., et. al., "Detecting MPLS Data Plane
Failures", RFC4379, February 2006.
[RFC4446] Martini, L., et al., "IANA Allocations for pseudo Wire
Edge to Edge Emulation (PWE3)", RFC4446, April 2006.
[RFC4447] Martini, L., Rosen, E., Smith, T., "Pseudowire Setup and
Maintenance using LDP", RFC4447, April 2006.
[RFC4842] Malis, A., et. al., "SONET/SDH Circuit Emulation over
Packet (CEP)", RFC 4842, April 2007.
[RFC5085] Nadeau, T., et al., "Pseudowire Virtual Circuit Connection
Verification (VCCV)", RFC 5085, December 2007.
[VCCV-BFD] Nadeau, T., Pignataro, C., "Bidirectional Forwarding
Detection (BFD) for the Pseudowire Virtual Circuit Connectivity
Verification (VCCV)", draft-ietf-pwe3-vccv-bfd-07, July 2009.
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C.2. Informative References
[CONGESTION] Rosen, E., Bryant, S., Davie, B., "PWE3 Congestion
Control Framework", draft-ietf-pwe3-congestion-frmwk-02.txt, work
in progress, June 2009.
[ETH-OAM-IWK] Mohan, D., et al., "MPLS and Ethernet OAM
Interworking", draft-ietf-pwe3-mpls-eth-oam-iwk-01, work in
progress, October 2009.
[L2TP-Status] McGill, N. Pignataro, C., "L2TPv3/IP Extended Circuit
Status Values", draft-ietf-l2tpext-circuit-status-extensions-04,
work in progress, April 2009.
[RFC3916] Xiao, X., McPherson, D., Pate, P., "Requirements for
Pseudowire Emulation Edge to-Edge (PWE3)", RFC 3916, September
2004.
[RFC3985] Bryant, S., Pate, P., "PWE3 Architecture", RFC 3985, March
2005.
[RFC4377] Nadeau, T. et.al., "OAM Requirements for MPLS Networks",
RFC4377, February 2006.
[RFC4385] Bryant, S. et al., "Pseudowire Emulation Edge-to-Edge
(PWE3) Control Word for Use over an MPLS PSN," RFC 4385, February
2006.
[RFC4454] Singh, S., Townsley, M., and C. Pignataro, "Asynchronous
Transfer Mode (ATM) over Layer 2 Tunneling Protocol Version 3
(L2TPv3/IP)", RFC 4454, May 2006.
[RFC4553] Vainshtein, A. et al., "Structure-Agnostic Time Division
Multiplexing (TDM) over Packet (SAToP)", RFC 4553, June 2006.
[RFC4591] Townsley, Market al.,"Frame Relay over Layer 2 Tunnelling
Protocol Version 3 (L2TPv3/IP)", RFC 4591, July 2006.
[RFC4717] Martini, L., et al., "Encapsulation Methods for Transport
of ATM Cells/Frame Over IP and MPLS Networks", RFC4717, December
2006.
[RFC5085] Nadeau,T et al., "Pseudowire Virtual Circuit Connectivity
Verification: A Control Channel for Pseudowires",(VCCV), RFC
5085,December 2007.
[RFC5086] Vainshtein ,A..,et al., "Structure-Aware Time Division
Multiplexed (TDM) Circuit Emulation Service over Packet Switched
Network (CESoPSN)", RFC 5086, December 2007.
[RFC5087] Y.(J) Stein et al., "Time Division Multiplexing over IP
(TDMoIP)", RFC 5087, December 2007.
[RFC5641] McGill,N., et al., "Layer 2 Tunnelling Protocol Version 3
(L2TPv3) Extended Circuit Status Values," RFC 5641, August 2009.
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Authors' Addresses
Mustapha Aissaoui
Alcatel-Lucent
600 March Rd
Kanata, ON K2K 2E6
Canada
Email: mustapha.aissaoui@alcatel-lucent.com
Peter Busschbach
Alcatel-Lucent
67 Whippany Rd
Whippany, NJ 07981
USA
Email: busschbach@alcatel-lucent.com
Monique Morrow
Cisco Systems, Inc.
Richtistrase 7
CH-8304 Wallisellen
Switzerland
Email: mmorrow@cisco.com
Luca Martini
Cisco Systems, Inc.
9155 East Nichols Avenue, Suite 400
Englewood, CO 80112
USA
Email: lmartini@cisco.com
Yaakov (Jonathan) Stein
RAD Data Communications
24 Raoul Wallenberg St., Bldg C
Tel Aviv 69719
ISRAEL
Email: yaakov_s@rad.com
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Dave Allan
Ericsson
Email: david.i.allan@ericsson.com
Thomas Nadeau
BT
BT Centre, 81 Newgate Street
London EC1A 7AJ
UK
Email: tom.nadeau@bt.com
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