One document matched: draft-ietf-pwe3-oam-msg-map-12.xml
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<rfc category='std' ipr='trust200902' docName='draft-ietf-pwe3-oam-msg-map-12.txt'>
<front>
<title abbrev="oam-msg-map">Pseudowire (PW) OAM Message Mapping</title>
<author initials="M" surname="Aissaoui" fullname="Mustapha Aissaoui">
<organization>Alcatel-Lucent</organization>
<address>
<postal>
<street>600 March Rd</street>
<city>Kanata</city>
<region>ON</region>
<code>K2K 2E6</code>
<country>Canada</country>
</postal>
<email>mustapha.aissaoui@alcatel-lucent.com</email>
</address>
</author>
<author initials="P" surname="Busschbach" fullname="Peter Busschbach">
<organization>Alcatel-Lucent</organization>
<address>
<postal>
<street>67 Whippany Rd</street>
<city>Whippany</city>
<region>NJ</region>
<code>07981</code>
<country>USA</country>
</postal>
<email>busschbach@alcatel-lucent.com</email>
</address>
</author>
<author initials="M" surname="Morrow" fullname="Monique Morrow">
<organization>Cisco Systems, Inc.</organization>
<address>
<postal>
<street>Richtistrase 7</street>
<city>CH-8304 Wallisellen</city>
<country>Switzerland</country>
</postal>
<email>mmorrow@cisco.com</email>
</address>
</author>
<author initials="L" surname="Martini" fullname="Luca Martini">
<organization>Cisco Systems, Inc.</organization>
<address>
<postal>
<street>9155 East Nichols Avenue, Suite 400</street>
<city>Englewood</city>
<region>CO</region>
<code>80112</code>
<country>USA</country>
</postal>
<email>lmartini@cisco.com</email>
</address>
</author>
<author initials="Y(J)" surname="Stein" fullname="Yaakov (Jonathan) Stein">
<organization>RAD Data Communications</organization>
<address>
<postal>
<street>24 Raoul Wallenberg St., Bldg C</street>
<city>Tel Aviv</city>
<code>69719</code>
<country>ISRAEL</country>
</postal>
<email>yaakov_s@rad.com</email>
</address>
</author>
<author initials="D" surname="Allan" fullname="Dave Allan">
<organization>Ericsson</organization>
<address>
<email>david.i.allan@ericsson.com</email>
</address>
</author>
<author initials="T" surname="Nadeau" fullname="Thomas Nadeau">
<organization>BT</organization>
<address>
<postal>
<street>BT Centre, 81 Newgate Street</street>
<city>London</city>
<code>EC1A 7AJ</code>
<country>UK</country>
</postal>
<email>tom.nadeau@bt.com</email>
</address>
</author>
<date day="7" month="March" year="2010" />
<area>Internet</area>
<workgroup>PWE3</workgroup>
<keyword>pseudowire</keyword>
<keyword>OAM</keyword>
<abstract>
<t>
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).
</t>
</abstract>
</front>
<middle>
<section title="Acknowledgments">
<t>
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.
</t>
</section>
<section title="Contributors">
<t><list>
<t> Matthew Bocci, matthew.bocci@alcatel-lucent.co.uk
</t>
<t> David Watkinson, david.watkinson@alcatel-lucent.com </t>
<t> Yuichi Ikejiri, y.ikejiri@ntt.com </t>
<t> Kenji Kumaki, kekumaki@kddi.com </t>
<t> Satoru Matsushima, satoru.matsushima@tm.softbank.co.jp </t>
<t> Himanshu Shah, hshah@ciena.com </t>
<t> Simon Delord, Simon.A.DeLord@team.telstra.com </t>
<t> Vasile Radoaca, vasile.radoaca@alcatel-lucent.com </t>
<t> Carlos Pignataro, cpignata@cisco.com </t>
<t> Teruyuki Oya, teruyuki.oya@tm.softbank.co.jp </t>
</list></t>
</section>
<section title="Introduction">
<t> 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. </t>
<t> 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. </t>
<t> 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]. </t>
</section>
<vspace blankLines="99"/>
<section title="Abbreviations and Conventions">
<section title="Abbreviations">
<t><list style="hanging">
<t hangText="AAL5"> ATM Adaptation Layer 5 </t>
<t hangText="AIS "> Alarm Indication Signal </t>
<t hangText="AC "> Attachment Circuit </t>
<t hangText="ATM "> Asynchronous Transfer Mode </t>
<t hangText="AVP "> Attribute Value Pair </t>
<t hangText="BDI "> Backward Defect Indication </t>
<t hangText="BFD "> Bidirectional Forwarding Detection </t>
<t hangText="CC "> Continuity Check </t>
<t hangText="CDN "> Call Disconnect Notify </t>
<t hangText="CE "> Customer Edge </t>
<t hangText="CV "> Connectivity Verification </t>
<t hangText="CPCS"> Common Part Convergence Sub-layer </t>
<t hangText="DBA "> Dynamic Bandwidth Allocation </t>
<t hangText="DLC "> Data Link Connection </t>
<t hangText="FDI "> Forward Defect Indication </t>
<t hangText="FR "> Frame Relay </t>
<t hangText="FRBS"> Frame Relay Bearer Service </t>
<t hangText="ICMP"> Internet Control Message Protocol </t>
<t hangText="IWF "> Interworking Function </t>
<t hangText="LB "> Loopback </t>
<t hangText="LCCE"> L2TP Control Connection Endpoint </t>
<t hangText="LDP "> Label Distribution Protocol </t>
<t hangText="LSP "> label Switched Path </t>
<t hangText="L2TP"> Layer 2 Tunneling Protocol </t>
<t hangText="MPLS"> Multiprotocol Label Switching </t>
<t hangText="NE "> Network Element </t>
<t hangText="NS "> Native Service </t>
<t hangText="OAM "> Operations, Administration and Maintenance </t>
<t hangText="PE "> Provider Edge </t>
<t hangText="PSN "> Packet Switched Network </t>
<t hangText="PW "> Pseudowire </t>
<t hangText="RDI "> Remote Defect Indication </t>
<t hangText="PDU "> Protocol Data Unit </t>
<t hangText="SDU "> Service Data Unit </t>
<t hangText="TLV "> Type Length Value </t>
<t hangText="VCC "> Virtual Channel Connection </t>
<t hangText="VCCV"> Virtual Connection Connectivity Verification </t>
<t hangText="VPC "> Virtual Path Connection </t>
</list></t>
</section>
<section title="Conventions">
<t> 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. </t>
<t> 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.
</t>
<t> 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. </t>
<t> 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]. </t>
<t> 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. </t>
<t> 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. </t>
<t> 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. </t>
<t> 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. </t>
<t> 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]. </t>
</section>
</section>
<section title="Reference Model and Defect Locations">
<t> 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. </t>
<figure align="center">
<artwork><![CDATA[
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
]]></artwork>
<postamble>Figure 1: PWE3 Network Defect Locations</postamble>
</figure>
<t> 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. </t>
<t> The following is a brief description of the defect locations: </t>
<t><list style="hanging">
<t hangText="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. </t>
<t hangText="b."> Defect on a PE1 AC interface (another local AC defect). </t>
<t hangText="c."> Defect on a PE1 PSN interface. </t>
<t hangText="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. </t>
<t hangText="e."> Defect on a PE2 AC interface (a remote AC defect). </t>
<t hangText="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. </t>
</list></t>
</section>
<section title="Abstract Defect States">
<t> 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. </t>
<t> The observed state is a combination of defects directly detected by
PE1 and defects of which it has been made aware via notifications. </t>
<figure align="center">
<artwork><![CDATA[
+-----+
----AC receive---->| |-----PW transmit---->
CE1 | PE1 | PE2/CE2
<---AC transmit----| |<----PW receive-----
+-----+
(arrows indicate direction of user traffic impacted by a defect)
]]></artwork>
<postamble>Figure 2: Receive and Transmit Defect States</postamble>
</figure>
<t> 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. </t>
<t> 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. </t>
<t> 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. </t>
<t> Note that a Forward Defect Indication is sent in the same direction
as the user traffic impacted by the defect. </t>
<t> 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. </t>
<t> 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. </t>
<t> 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. </t>
<t> Note that a Reverse Defect indication is sent in the reverse
direction to the user traffic impacted by the defect. </t>
<t> 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. </t>
<t> 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. </t>
</section>
<section title="OAM Modes">
<t> 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. </t>
<t> This document defines two different OAM modes, the distinction being
the method of mapping between the NS and PW OAM defect notification
messages. </t>
<t> 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. </t>
<figure align="center">
<artwork><![CDATA[
+-----+ +-----+
+-----+ | |=================| | +-----+
| CE1 |-=NS-OAM=>| PE1 |----=NS-OAM=>----| PE2 |-=NS-OAM=>| CE2 |
+-----+ | |=================| | +-----+
+-----+ +-----+
\ /
-------=PW-OAM=>-------
]]></artwork>
<postamble>Figure 3: Single Emulated OAM Loop mode</postamble>
</figure>
<t> The single emulated OAM loop mode implements the following behavior:
</t>
<t><list style="hanging">
<t hangText="a."> The upstream PE (PE1) MUST transparently relay NS OAM
messages over the PW. </t>
<t hangText="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. </t>
<t hangText="c."> The upstream PE MUST signal local defects affecting the PW
using a PW defect notification message. </t>
<t hangText="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. </t>
</list></t>
<t> 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. </t>
<t> 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.</t>
<figure align="center">
<artwork><![CDATA[
+-----+ +-----+
+-----+ | |=================| | +-----+
| CE1 |-=NS-OAM=>| PE1 | | PE2 |-=NS-OAM=>| CE2 |
+-----+ | |=================| | +-----+
+-----+ +-----+
\ /
-------=PW-OAM=>-------
]]></artwork>
<postamble>Figure 4: Coupled OAM Loops mode</postamble>
</figure>
<t> The coupled OAM loops mode implements the following behavior:
</t>
<t><list style="hanging">
<t hangText="a."> The upstream PE (PE1) MUST terminate and translate a received
NS defect notification message into a PW defect notification
message. </t>
<t hangText="b."> The upstream PE MUST signal local failures affecting its
local AC using PW defect notification messages to the
downstream PE. </t>
<t hangText="c."> The upstream PE MUST signal local failures affecting the PW
using PW defect notification messages. </t>
<t hangText="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. </t>
</list></t>
<t> 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. </t>
</section>
<section title="PW Defect States and Defect Notifications">
<section title="PW Defect Notification Mechanisms">
<t> 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. </t>
<t> 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
notification. Note that these CV types SHOULD NOT be used when the
PW is established with the LDP control plane. </t>
<t> 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]. </t>
<t> 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. </t>
<t> 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. </t>
<t> The CV types are defined in Section 8.1.3 of this document. </t>
<section title="LDP Status TLV">
<t> [RFC4446] defines the following PW status code points: </t>
<t><list style="hanging">
<t hangText="0x00000000 -"> Pseudowire forwarding (clear all failures) </t>
<t hangText="0x00000001 -"> Pseudowire Not Forwarding </t>
<t hangText="0x00000002 -"> Local Attachment Circuit (ingress) Receive Fault </t>
<t hangText="0x00000004 -"> Local Attachment Circuit (egress) Transmit Fault </t>
<t hangText="0x00000008 -"> Local PSN-facing PW (ingress) Receive Fault </t>
<t hangText="0x00000010 -"> Local PSN-facing PW (egress) Transmit Fault </t>
</list></t>
<t> [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. </t>
<t> 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. </t>
<t> The forward and reverse defect indication definitions used in this
document map to the LDP Status TLV codes as follows: </t>
<t><list style="hanging">
<t hangText=" "> Forward defect indication corresponds to the logical OR of: </t>
<t hangText=" *"> Local Attachment Circuit (ingress) Receive Fault,
</t>
<t hangText=" *"> Local PSN-facing PW (egress) Transmit Fault, and </t>
<t hangText=" *"> PW Not Forwarding. </t>
<t hangText=" "> Reverse defect indication corresponds to the logical OR of: </t>
<t hangText=" *"> Local Attachment Circuit (egress) Transmit Fault and </t>
<t hangText=" *"> Local PSN-facing PW (ingress) Receive Fault. </t>
</list></t>
<t> A PE MUST use PW status notification messages to report all defects
affecting the PW service including, but not restricted, to the
following: </t>
<t><list style="symbols">
<t> defects detected through fault detection mechanisms in
the MPLS and MPLS/IP PSN, </t>
<t> defects detected through VCCV-Ping or VCCV-BFD CV types
0x04 and 0x10 for fault detection only, </t>
<t> defects within the PE that result in an inability to
forward traffic between the AC and the PW, </t>
<t> 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. </t>
</list></t>
<t> 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. </t>
</section>
<section title="L2TP Circuit Status AVP">
<t> [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]. </t>
<t> 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. </t>
<t> 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]. </t>
<t> The forward and reverse defect indication definitions used in this
document map to the L2TP Circuit Status AVP as follows: </t>
<t><list style="hanging">
<t hangText=" "> Forward defect indication corresponds to the logical OR of: </t>
<t hangText=" *"> Local Attachment Circuit (ingress) Receive Fault, </t>
<t hangText=" *"> Local PSN-facing PW (egress) Transmit Fault, and </t>
<t hangText=" *"> PW Not Forwarding. </t>
<t hangText=" "> Reverse defect indication corresponds to the logical OR of: </t>
<t hangText=" *"> Local Attachment Circuit (egress) Transmit Fault and </t>
<t hangText=" *"> Local PSN-facing PW (ingress) Receive Fault. </t>
</list></t>
<t> The status notification conveys defects from the viewpoint of the
originating LCCE (PE). </t>
<t> 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: </t>
<t><list style="symbols">
<t> defects detected through defect detection mechanisms in
the L2TPV3/IP PSN, </t>
<t> 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, </t>
<t> defects within the PE that result in an inability to
forward traffic between the AC and the PW, </t>
<t> 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. </t>
</list></t>
<t> 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: </t>
<t><list style="symbols">
<t> 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. </t>
</list></t>
<t> 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: </t>
<t><list style="symbols">
<t> defects detected through defect detection mechanisms in
the L2TPV3/IP PSN (using StopCCN), </t>
<t> defects detected through VCCV (pseudowire level) (using
CDN), </t>
<t> defects within the PE that result in an inability to
forward traffic between ACs and PW (using CDN).
</t>
</list></t>
<t> 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. </t>
<t> 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). </t>
</section>
<section title="BFD Diagnostic Codes">
<t> [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. </t>
<t> 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
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]. </t>
<t> 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. </t>
<t> 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: </t>
<t><list style="hanging">
<t hangText=" 0 -"> No diagnostic </t>
<t hangText=" 1 -"> Control detection time expired </t>
<t hangText=" 3 -"> Neighbor signaled session down </t>
<t hangText=" 7 -"> Administratively Down </t>
</list></t>
<t> 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. </t>
<t> 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: </t>
<t><list style="hanging">
<t hangText=" 6 -"> Concatenated Path Down </t>
<t hangText=" 8 -"> Reverse Concatenated Path Down </t>
</list></t>
<t> 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 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. </t>
<t> 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. </t>
<t> The forward and reverse defect indications used in this document
map to the following BFD codes: </t>
<t><list style="hanging">
<t hangText=" "> Forward defect indication corresponds to the logical OR of: </t>
<t hangText=" *"> Concatenated Path Down (BFD diagnostic code 06) </t>
<t hangText=" *"> Pseudowire Not Forwarding (PW status code 0x00000001). </t>
<t hangText=" "> Reverse defect indication- corresponds to: </t>
<t hangText=" *"> Reverse Concatenated Path Down (BFD diagnostic code 08). </t>
</list></t>
<t> 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. </t>
</section>
</section>
<section title="PW Defect State Entry/Exit">
<section title="PW receive defect state entry/exit criteria">
<t> PE1, as downstream PE, will enter the PW receive defect state if one
or more of the following occurs: </t>
<t><list style="symbols">
<t> 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. </t>
<t> It detects loss of connectivity on the PSN tunnel
upstream of PE1 which affects the traffic it receives
from PE2. </t>
<t> It detects a loss of PW connectivity through VCCV-BFD or
VCCV-PING which affects the traffic it receives from PE2. </t>
</list></t>
<t> 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 state. </t>
<t> 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. </t>
<t><list style="symbols">
<t> All previously detected defects have disappeared, and </t>
<t> PE2 cleared the FDI, if applicable. </t>
</list></t>
</section>
<section title="PW transmit defect state entry/exit criteria">
<t> PE1, as upstream PE, will enter the PW transmit defect state if the
following conditions occur: </t>
<t><list style="symbols">
<t> 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 </t>
<t> it is not already in the PW receive defect state. </t>
</list></t>
<t> 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. </t>
<t> 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. </t>
</section>
</section>
</section>
<section title="Procedures for ATM PW Service">
<t> Asynchronous Transfer Mode (ATM) Terminology is explained in
Appendix A.2 of this document. </t>
<section title="AC receive defect state entry/exit criteria">
<t> When operating in the coupled OAM loops mode, PE1 enters the AC
receive defect state when any of the following conditions are met: </t>
<t><list style="hanging">
<t hangText="a."> It detects or is notified of a physical layer fault on
the ATM interface. </t>
<t hangText="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. </t>
<t hangText="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. </t>
<t hangText="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. </t>
</list></t>
<t> When operating in the coupled OAM loops mode, PE1 exits the AC
Receive defect state when all previously detected defects have
disappeared. </t>
<t> When operating in the single emulated OAM loop mode, PE1 enters the
AC receive defect state if any of the following conditions are met: </t>
<t><list style="hanging">
<t hangText="a."> It detects or is notified of a physical layer fault on
the ATM interface. </t>
<t hangText="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. </t>
</list></t>
<t> When operating in the single emulated OAM loop mode, PE1 exits the
AC receive defect state when all previously detected defects have
disappeared. </t>
<t> 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]. </t>
</section>
<section title="AC transmit defect state entry/exit criteria">
<t> When operating in the coupled OAM loops mode, PE1 enters the AC
transmit defect state if any of the following conditions are met: </t>
<t><list style="hanging">
<t hangText="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. </t>
<t hangText="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. </t>
</list></t>
<t> 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]. </t>
<t> 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. </t>
</section>
<section title="Consequent Actions">
<t> 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].
</t>
<section title="PW receive defect state entry/exit">
<t> On entry to the PW receive defect state: </t>
<t><list style="hanging">
<t hangText="a."> PE1 MUST commence AIS insertion into the corresponding AC.</t>
<t hangText="b."> PE1 MUST cease generation of CC cells on the
corresponding AC, if applicable. </t>
<t hangText="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. </t>
</list></t>
<t> On exit from the PW receive defect state: </t>
<t><list style="hanging">
<t hangText="a."> PE1 MUST cease AIS insertion into the corresponding
AC. </t>
<t hangText="b."> PE1 MUST resume any CC cell generation on the
corresponding AC, if applicable. </t>
<t hangText="c."> PE1 MUST clear the RDI to PE2, if applicable.
</t>
</list></t>
</section>
<section title="PW transmit defect state entry/exit">
<t> On entry to the PW Transmit Defect State: </t>
<t><list style="hanging">
<t hangText="a."> PE1 MUST commence RDI insertion into the corresponding AC. </t>
<t hangText="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. </t>
</list></t>
<t> On exit from the PW Transmit Defect State: </t>
<t><list style="hanging">
<t hangText="a."> PE1 MUST cease RDI insertion into the corresponding AC. </t>
<t hangText="b."> PE1 MUST clear the FDI to PE2, if applicable. </t>
</list></t>
</section>
<section title="PW defect state in ATM Port Mode PW Service">
<t> 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 enter the ATM AIS state. </t>
</section>
<section title="AC receive defect state entry/exit">
<t> On entry to the AC receive defect state and when operating in the
coupled OAM loops mode: </t>
<t><list style="hanging">
<t hangText="a."> PE1 MUST send FDI to PE2. </t>
<t hangText="b."> PE1 MUST commence insertion of ATM RDI cells into the
AC towards CE1. </t>
</list></t>
<t> 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: </t>
<t> On entry to the AC receive defect state: </t>
<t><list style="hanging">
<t hangText="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. </t>
<t hangText="b."> If the defect interferes with NS OAM message
generation, PE1 MUST send an FDI indication to PE2. </t>
<t hangText="c."> PE1 MUST cease the generation of CC cells on the
corresponding PW, if applicable. </t>
</list></t>
<t> 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: </t>
<t><list style="hanging">
<t hangText="a."> PE1 MUST transparently relay ATM AIS cells over the
corresponding PW towards CE2. </t>
<t hangText="b."> Upon detection of a defect on the ATM interface on the
PE or in the PE itself, PE1 MUST send FDI to PE2. </t>
<t hangText="c."> PE1 MUST cease generation of CC cells on the
corresponding PW, if applicable. </t>
</list></t>
<t> On exit from the AC receive defect state and when operating in the
coupled OAM loops mode: </t>
<t><list style="hanging">
<t hangText="a."> PE1 MUST clear the FDI to PE2. </t>
<t hangText="b."> PE1 MUST cease insertion of ATM RDI cells into the AC. </t>
</list></t>
<t> On exit from the AC receive defect state and when operating in the
single emulated OAM loop mode: </t>
<t><list style="hanging">
<t hangText="a."> PE1 MUST cease insertion of ATM AIS cells into the
corresponding PW. </t>
<t hangText="b."> PE1 MUST clear the FDI to PE2, if applicable. </t>
<t hangText="c."> PE1 MUST resume any CC cell generation on the
corresponding PW, if applicable. </t>
</list></t>
</section>
<section title="AC transmit defect state entry/exit">
<t> On entry to the AC transmit defect state and when operating in the
coupled OAM loops mode:
</t>
<t><list style="hanging">
<t hangText="* "> PE1 MUST send RDI to PE2. </t>
</list></t>
<t> On exit from the AC transmit defect state and when operating in the
coupled OAM loops mode: </t>
<t><list style="hanging">
<t hangText="* "> PE1 MUST clear the RDI to PE2. </t>
</list></t>
</section>
</section>
</section>
<section title="Procedures for Frame Relay PW Service">
<t> Frame Relay (FR) terminology is explained in Appendix A.1 of this
document. </t>
<section title="AC receive defect state entry/exit criteria">
<t> PE1 enters the AC receive defect state if one or more of the
following conditions are met: </t>
<t><list style="hanging">
<t hangText="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. </t>
<t hangText="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.
</t>
<t hangText="c."> A physical layer alarm is detected on the FR
interface. In this case, this status maps across the
PE to all corresponding PWs. </t>
</list></t>
<t> PE1 exits the AC receive defect state when all previously detected
defects have disappeared. </t>
</section>
<section title="AC transmit defect state entry/exit criteria">
<t> The AC transmit defect state is not valid for a FR AC. </t>
</section>
<section title="Consequent Actions">
<section title="PW receive defect state entry/exit">
<t> The A (Active) bit indicates whether the FR PVC is ACTIVE (1) or
INACTIVE (0) as explained in [RFC 4591]. </t>
<t> On entry to the PW receive defect state: </t>
<t><list style="hanging">
<t hangText="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]. </t>
<t hangText="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. </t>
</list></t>
<t> On exit from the PW receive defect state: </t>
<t><list style="hanging">
<t hangText="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. </t>
<t hangText="b."> PE1 MUST clear the RDI to PE2, if applicable. </t>
</list></t>
</section>
<section title="PW transmit defect state entry/exit">
<t> On entry to the PW transmit defect state:
</t>
<t><list style="hanging">
<t hangText="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. </t>
<t hangText="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. </t>
</list></t>
<t> On exit from the PW transmit defect state: </t>
<t><list style="hanging">
<t hangText="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. </t>
<t hangText="b."> PE1 MUST clear the FDI to PE2, if applicable. </t>
</list></t>
</section>
<section title="PW defect state in the FR Port Mode PW Service">
<t> 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. </t>
</section>
<section title="AC receive defect state entry/exit">
<t> On entry to the AC receive defect state: </t>
<t><list style="hanging">
<t hangText="* "> PE1 MUST send FDI to PE2. </t>
</list></t>
<t> On exit from the AC receive defect state: </t>
<t><list style="hanging">
<t hangText="* "> PE1 MUST clear FDI to PE2. </t>
</list></t>
</section>
<section title="AC transmit defect state entry/exit">
<t> The AC transmit defect state is not valid for a FR AC. </t>
</section>
</section>
</section>
<section title="Procedures for TDM PW Service">
<t> 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. </t>
<t> 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. </t>
<t> 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. </t>
<t> 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. </t>
<t> 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]. </t>
<section title="AC receive defect state entry/exit criteria">
<t> PE1 enters the AC receive defect state if any of the following
conditions are met: </t>
<t><list style="hanging">
<t hangText="a."> It detects a physical layer fault on the TDM interface
(Loss of Signal, Loss of Alignment, etc., as described
in [G.775]). </t>
<t hangText="b."> It is notified of a previous physical layer fault by
detecting AIS. </t>
</list></t>
<t> 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. </t>
</section>
<section title="AC transmit defect state entry/exit criteria">
<t> 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. </t>
</section>
<section title="Consequent Actions">
<section title="PW receive defect state entry/exit">
<t> On entry to the PW receive defect state: </t>
<t><list style="hanging">
<t hangText="a."> PE1 MUST commence AIS insertion into the corresponding
TDM AC. </t>
<t hangText="b."> PE1 MUST set the R bit in all PW packets sent back to
PE2. </t>
</list></t>
<t> On exit from the PW receive defect state: </t>
<t><list style="hanging">
<t hangText="a."> PE1 MUST cease AIS insertion into the corresponding
TDM AC. </t>
<t hangText="b."> PE1 MUST clear the R bit in all PW packets sent back
to PE2. </t>
</list></t>
<t> Note that AIS generation can in general be performed by both
structure-aware and structure-agnostic PEs. </t>
</section>
<section title="PW transmit defect state entry/exit">
<t> On entry to the PW Transmit Defect State: </t>
<t><list style="hanging">
<t hangText="* "> A structure-aware PE1 MUST commence RDI insertion into
the corresponding AC. </t>
</list></t>
<t> On exit from the PW Transmit Defect State: </t>
<t><list style="hanging">
<t hangText="* "> A structure-aware PE1 MUST cease RDI insertion into
the corresponding AC. </t>
</list></t>
<t> Note that structure-agnostic PEs are not capable of injecting RDI
into an AC. </t>
</section>
<section title="AC receive defect state entry/exit">
<t> On entry to the AC receive defect state and when operating in the
single emulated OAM loop mode: </t>
<t><list style="hanging">
<t hangText="a."> PE1 SHOULD overwrite the TDM data with AIS in the PW
packets sent towards PE2. </t>
<t hangText="b."> PE1 MUST set the L bit in these packets. </t>
<t hangText="c."> PE1 MAY omit the payload in order to conserve
bandwidth. </t>
<t hangText="d."> A structure-aware PE1 SHOULD send RDI back towards
CE1. </t>
<t hangText="e."> A structure-aware PE1 that detects a potentially
correctable AC defect MAY use the M field to indicate
this. </t>
</list></t>
<t> On exit from the AC receive defect state and when operating in the
single emulated OAM loop mode: </t>
<t><list style="hanging">
<t hangText="a."> PE1 MUST cease overwriting PW content with AIS and
return to forwarding valid TDM data in PW packets sent
towards PE2. </t>
<t hangText="b."> PE1 MUST clear the L bit in PW packets sent towards
PE2. </t>
<t hangText="c."> A structure-aware PE1 MUST cease sending RDI towards
CE1. </t>
</list></t>
</section>
</section>
</section>
<section title="Procedures for CEP PW Service">
<t> The following procedures apply to SONET/SDH Circuit Emulation
([RFC4842]). They are based on the single emulated OAM loop mode. </t>
<t> 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. </t>
<t> 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. </t>
<t> 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. </t>
<section title="Defect states">
<section title="PW receive defect state entry/exit">
<t> 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: </t>
<t><list style="symbols">
<t> It receives packets with the L bit set. </t>
<t> It receives packets with both the N and P bits set. </t>
<t> It loses packet synchronization. </t>
</list></t>
</section>
<section title="PW transmit defect state entry/exit">
<t> 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. </t>
</section>
<section title="AC receive defect state entry/exit">
<t> PE1 enters the AC receive defect state when any of the following
conditions are met: </t>
<t><list style="hanging">
<t hangText="a."> It detects a physical layer fault on the TDM interface
(Loss of Signal, Loss of Alignment, etc.). </t>
<t hangText="b."> It is notified of a previous physical layer fault by
detecting of AIS. </t>
</list></t>
<t> The exact conditions under which a PE enters and exits the AIS state
are defined in [G.707] and [G.783]. </t>
</section>
<section title="AC receive defect state entry/exit">
<t> The AC transmit defect state is not valid for CEP PWs. RDI signals
are forwarded transparently. </t>
</section>
</section>
<section title="Consequent Actions">
<section title="PW receive defect state entry/exit">
<t> On entry to the PW receive defect state: </t>
<t><list style="hanging">
<t hangText="a."> PE1 MUST commence AIS-P/V insertion into the
corresponding AC. See [RFC4842]. </t>
<t hangText="b."> PE1 MUST set the R bit in all PW packets sent back to
PE2. </t>
</list></t>
<t> On exit from the PW receive defect state: </t>
<t><list style="hanging">
<t hangText="a."> PE1 MUST cease AIS-P/V insertion into the
corresponding AC. </t>
<t hangText="b."> PE1 MUST clear the R bit in all PW packets sent back
to PE2. </t>
</list></t>
<t> See [RFC4842] for further details. </t>
</section>
<section title="PW transmit defect state entry/exit">
<t> On entry to the PW Transmit Defect State: </t>
<t><list style="hanging">
<t hangText="a."> A structure-aware PE1 MUST commence RDI insertion into
the corresponding AC. </t>
</list></t>
<t> On exit from the PW Transmit Defect State: </t>
<t><list style="hanging">
<t hangText="a."> A structure-aware PE1 MUST cease RDI insertion into
the corresponding AC. </t>
</list></t>
</section>
<section title="AC receive defect state entry/exit">
<t> On entry to the AC receive defect state: </t>
<t><list style="hanging">
<t hangText="a."> PE1 MUST set the L bit in these packets. </t>
<t hangText="b."> If Dynamic Bandwidth Allocation (DBA) has been
enabled, PE1 MAY omit the payload in order to conserve
bandwidth. </t>
<t hangText="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. </t>
</list></t>
<t> On exit from the AC receive defect state: </t>
<t><list style="hanging">
<t hangText="a."> PE1 MUST cease overwriting PW content with AIS-P/V and
return to forwarding valid data in PW packets sent
towards PE2. </t>
<t hangText="b."> PE1 MUST clear the L bit in PW packets sent towards
PE2. </t>
</list></t>
<t> See [RFC4842] for further details. </t>
</section>
</section>
</section>
<section title="Security Considerations">
<t> 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. </t>
<t> 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. </t>
</section>
<section title="IANA Considerations">
<t> This document requires no IANA actions.</t>
</section>
</middle>
<back>
<vspace blankLines="99"/>
<section title="Native Service Management (informative)">
<section title="Frame Relay Management">
<t> The management of Frame Relay Bearer Service (FRBS) connections can
be accomplished through two distinct methodologies: </t>
<t><list style="hanging">
<t hangText="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]. </t>
<t hangText="b."> Based on FRBS LMI, and similar to ATM ILMI where LMI is
common in private Frame Relay networks. </t>
</list></t>
<t> In addition, ITU-T I.620 addresses Frame Relay loopback, but the
deployment of this standard is relatively limited [I.620]. </t>
<t> 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. </t>
<t> The status of any provisioned Frame Relay PVC may be updated
through: </t>
<t><list style="hanging">
<t hangText="a."> Frame Relay STATUS messages in response to Frame Relay STATUS
ENQUIRY messages; these are mandatory. </t>
<t hangText="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. </t>
</list></t>
<t> 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. </t>
<t> 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. </t>
</section>
<section title="ATM Management">
<t> 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
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: </t>
<t><list style="hanging">
<t hangText="a."> Alarm indication signal (AIS). </t>
<t hangText="b."> Remote Defect indication (RDI). </t>
<t hangText="c."> Continuity Check (CC). </t>
<t hangText="d."> Loopback (LB). </t>
</list></t>
<t> 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. </t>
<t> 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. </t>
<t> 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. </t>
</section>
</section>
<vspace blankLines="99"/>
<section title="PW Defects and Detection tools">
<section title="PW Defects">
<t> Possible defects that impact PWs are the following: </t>
<t><list style="hanging">
<t hangText="a."> Physical layer defect in the PSN interface. </t>
<t hangText="b."> PSN tunnel failure which results in a loss of connectivity
between ingress and egress PE. </t>
<t hangText="c."> Control session failures between ingress and egress PE. </t>
</list></t>
<t> In case of an MPLS PSN and an MPLS/IP PSN there are additional
defects:
</t> <t><list style="hanging">
<t hangText="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. </t>
<t hangText="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. </t>
<t hangText="c."> Unintended self-replication; e.g., due to loops or denial-
of-service attacks. </t>
</list></t>
</section>
<section title="Packet Loss">
<t> Persistent congestion in the PSN or in a PE could impact the proper
operation of the emulated service. </t>
<t> 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. </t>
<t> 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. </t>
</section>
<section title="PW Defect Detection Tools">
<t> To detect the defects listed above, Service Providers have a variety
of options available. </t>
<t> Physical Layer defect detection and notification mechanisms include
SONET/SDH Los of Signal (LOS), Loss of Alignment (LOA), and AIS/RDI.</t>
<t> PSN defect detection mechanisms vary according to the PSN type. </t>
<t> 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. </t>
<t> For PWE3 over an MPLS PSN and an MPLS/IP PSN, several tools can be
used. </t>
<t><list style="hanging">
<t hangText="a."> LSP-Ping and LSP-Traceroute [RFC4379] for LSP tunnel
connectivity verification. </t>
<t hangText="b."> LSP-Ping with Bi-directional Forwarding Detection [VCCV-BFD]
for LSP tunnel continuity checking. </t>
<t hangText="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. </t>
</list></t>
</section>
<section title="PW specific defect detection mechanisms">
<t> [RFC4377] describes how LSP-Ping and BFD can be used over individual
PWs for connectivity verification and continuity checking
respectively. </t>
<t> 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: </t>
<t><list style="hanging">
<t hangText="a."> Egress PE detection of failure (e.g., BFD). </t>
<t hangText="b."> Ingress PE detection of failure (e.g., LSP-PING). </t>
<t hangText="c."> Ingress PE notification of failure (e.g. RSVP Path-err). </t>
</list></t>
</section>
</section>
<vspace blankLines="99"/>
<section title="References" >
<section title='Normative References'>
<t><list style="hanging">
<t hangText="[BFD]"> Katz, D., Ward, D., "Bidirectional Forwarding Detection",
draft-ietf-bfd-base-11.txt, work in progress, January 2010. </t>
<t hangText="[FRF.19]"> Frame Relay Forum, "Frame Relay Operations, Administration,
and Maintenance Implementation Agreement", March 2001. </t>
<t hangText="[ICMP]"> Postel, J. "Internet Control Message Protocol" RFC 792. </t>
<t hangText="[G.707]"> ITU-T Recommendation G.707 "Network Node Interface For The
Synchronous Digital Hierarchy", December 2003. </t>
<t hangText="[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. </t>
<t hangText="[G.783]"> ITU-T Recommendation G.783 "Characteristics of synchronous
digital hierarchy (SDH) equipment functional blocks ", March 2006. </t>
<t hangText="[I.610]"> ITU-T Recommendation I.610 "B-ISDN operation and maintenance
principles and functions", February 1999. </t>
<t hangText="[I.620]"> ITU-T Recommendation I.620 "Frame relay operation and
maintenance principles and functions", October 1996. </t>
<t hangText="[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. </t>
<t hangText="[RFC2119]"> Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. </t>
<t hangText="[RFC3931]"> Lau, J., et. al. "Layer Two Tunneling Protocol (Version 3",
RFC 3931, March 2005. </t>
<t hangText="[RFC4023]"> Worster. T., et al., "Encapsulating MPLS in IP or Generic
Routing Encapsulation (GRE)", RFC 4023, March 2005. </t>
<t hangText="[RFC4379]"> Kompella, K., et. al., "Detecting MPLS Data Plane
Failures", RFC4379, February 2006. </t>
<t hangText="[RFC4446]"> Martini, L., et al., "IANA Allocations for pseudo
Wire Edge to Edge Emulation (PWE3)", RFC4446, April 2006. </t>
<t hangText="[RFC4447]"> Martini, L., Rosen, E., Smith, T., "Pseudowire Setup and
Maintenance using LDP", RFC4447, April 2006. </t>
<t hangText="[RFC4842]"> Malis, A., et. al., "SONET/SDH Circuit Emulation over
Packet (CEP)", RFC 4842, April 2007. </t>
<t hangText="[RFC5085]"> Nadeau, T., et al., "Pseudowire Virtual Circuit Connection
Verification (VCCV)", RFC 5085, December 2007. </t>
<t hangText="[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. </t>
</list></t>
</section>
<vspace blankLines="99"/>
<section title='Informative References'>
<t><list style="hanging">
<t hangText="[CONGESTION]"> Rosen, E., Bryant, S., Davie, B., "PWE3 Congestion
Control Framework", draft-ietf-pwe3-congestion-frmwk-02.txt,
work in progress, June 2009. </t>
<t hangText="[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. </t>
<t hangText="[L2TP-Status]"> McGill, N. Pignataro, C., "L2TPv3/IP Extended Circuit
Status Values", draft-ietf-l2tpext-circuit-status-extensions-04,
work in progress, April 2009. </t>
<t hangText="[RFC3916]"> Xiao, X., McPherson, D., Pate, P., "Requirements for
Pseudowire Emulation Edge to-Edge (PWE3)", RFC 3916, September 2004. </t>
<t hangText="[RFC3985]"> Bryant, S., Pate, P., "PWE3 Architecture", RFC 3985, March
2005. </t>
<t hangText="[RFC4377]"> Nadeau, T. et.al., "OAM Requirements for MPLS Networks",
RFC4377, February 2006. </t>
<t hangText="[RFC4385]"> Bryant, S. et al., "Pseudowire Emulation Edge-to-Edge
(PWE3) Control Word for Use over an MPLS PSN," RFC 4385, February 2006. </t>
<t hangText="[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. </t>
<t hangText="[RFC4553]"> Vainshtein, A. et al., "Structure-Agnostic Time Division
Multiplexing (TDM) over Packet (SAToP)", RFC 4553, June 2006. </t>
<t hangText="[RFC4591]"> Townsley, Market al.,"Frame Relay over Layer 2 Tunnelling
Protocol Version 3 (L2TPv3/IP)", RFC 4591, July 2006. </t>
<t hangText="[RFC4717]"> Martini, L., et al., "Encapsulation Methods for Transport
of ATM Cells/Frame Over IP and MPLS Networks", RFC4717, December 2006. </t>
<t hangText="[RFC5085]"> Nadeau,T et al., "Pseudowire Virtual Circuit Connectivity
Verification: A Control Channel for Pseudowires",(VCCV), RFC 5085,December 2007. </t>
<t hangText="[RFC5086]"> Vainshtein ,A..,et al., "Structure-Aware Time Division
Multiplexed (TDM) Circuit Emulation Service over Packet Switched Network (CESoPSN)",
RFC 5086, December 2007. </t>
<t hangText="[RFC5087]"> Y.(J) Stein et al., "Time Division Multiplexing over IP
(TDMoIP)", RFC 5087, December 2007. </t>
<t hangText="[RFC5641]"> McGill,N., et al., "Layer 2 Tunnelling Protocol Version 3
(L2TPv3) Extended Circuit Status Values," RFC 5641, August 2009. </t>
</list></t>
</section>
</section>
</back>
</rfc>
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