Internet DRAFT - draft-allan-y17iw-overview
draft-allan-y17iw-overview
Internet Draft David Allan
Document: draft-allan-y17iw-overview-00.txt Nortel Networks
Category: Informational June 2003
An overview of Y.17iw
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Copyright Notice
Copyright(C) The Internet Society (2003). All Rights Reserved.
Abstract
This internet draft provides an overview of ITU-T draft
recommendation Y.17iw "OAM functionality for ATM-MPLS
interworking".
Sub-IP ID Summary
[to be removed when published]
WHERE DOES IT FIT IN THE PICTURE OF THE SUB-IP WORK
Fits in the MPLS, and PWE3 boxes.
WHY IS IT TARGETED AT THESE WGs
This draft shows that LSP-PING and Y.1711 can be considered to be
complementary tools in the suite of options to measure and
instrument MPLS.
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Overview of Y.17iw
1. Introduction
Y.17iw is a draft recommendation coming from the collaboration of
ITU-T SG13 Questions 3 and 5.
Y.17iw is focused on fault management interworking between [Y1711]
and [I610] in two scenarios, network interworking (overlay), and
service interworking (peer).
This draft is purely informational.
2. Terminology
The terminology used in the appendices is directly as written in
the ITU-T draft recommendation (for consistency) and borrows from
[Y1711] and [I610]. The relevant terms are:
defect: Interruption of the capability of a transport entity
(e.g. network connection) to transfer user or OAM information.
far end termination - LSP ingress
near end termination - LSP egress
VCLC - virtual channel link connection
VPLC - virtual path link connection
Other definitions are provided with the reference models in
sections 4 and 5.
3. Principles
Y.17iw treats the ATM and MPLS/PW components of the connectivity
between CEs as separate maintenance entities. The maintenance
entities have defect states that act as inputs into either the
client maintenance entity (network interworking or PW scenario) or
peer maintenance entity (service interworking or L2VPN interworking
scenario) and trigger appropriate OAM actions (described in the
appendices). There is no actual interworking or translation of the
OAM protocols per se.
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4. Network Interworking Reference Models
CE1 CE2
| |
| VCLC | F5
|< ======== >|< ======== >|< ======== >| Virtual
/ \ Channel
--------/ \-------- Level
/ \
/ | VPLC | \ F4
|< ======== >|< ======== >|< ======== >| Virtual
| | | | Path
PW | | PW Level
end | | end
service | | service
PE1 PE2
--------/ \--------
/ \
/ \
|< ======== >|< ======== >|< ======== >| PW
/ \ Level
--------/ \--------
/ \
/ \
|< ======== >|< ======== >|< ======== >| PSN
/ \ Tunnel
--------/ \-------- Level
/ \
/ \ F3 etc.
|< ======== >|< ======== >|< ======== >|
Figure 1: Mapping I.610 OAM hierarchy onto PWE
Network Reference Model
Figure 1 illustrates that in the network interworking or overlay
scenario, the PW and PSN layers assume specific position in the
overall hierarchy. W.r.t. to the I.610 model, the PW and PSN layers
are a direct insertion between the F3 and F4 OAM layers.
< --------------------------------------->
IWE ME
< ------ >|< ---------------- >|< ------ >
ATM1 ME | | EATM ME | | ATM2 ME
| | | |
| |-------------- >| |
| | LSP1 ME | |
| |< --------------| |
| | LSP2 ME | |
PE PE
Figure 2: Network Interworking Reference Model
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Figure 2 illustrates the reference model for the network
interworking scenario. The overall e2e ATM connection is uniquely
identified (IEW-ME). The component of the ATM connections extending
across each attachment circuit (ATM1-ME and ATM2-ME) are uniquely
identified. The component of the ATM connection carried by the PW
is uniquely identified (EATM-ME). Each PW LSP has a unique
direction and is a unique maintenance entity (LSP1/2 ME).
5. Service Interworking Reference Model
MPLS/PW ME PE ATM ME
----------------
------ > |--Payload IW--| F4 or F5
|X X| < ------------- > CE
< ------ |---OAM IW-----|
----------------
Figure 3: Service Interworking of a VCC or VPC and a PW/LSP
Figure 3 illustrates that the LSP and the ATM VCC/VPC are peer
maintenance entities. The extraction of 'native service' at the
payload level is a distinct and separate function from the
interworking of the maintenance entity defect states.
6. Applicability
The procedures for the network interworking scenario outlined in
appendix 'A' are applicable to the PWE3 draft [ATM_ENCAP].
The procedures for the service interworking scenario outlined in
appendix 'B' are applicable to [SAJASSI].
7. References
[ATM ENCAP] Martini et.al., "Encapsulation Methods for Transport of
ATM Cells/Frame Over IP and MPLS Networks", IETF Internet
Draft draft-ietf-pwe3-atm-encap-01.txt, February 2003
[I610] ITU-T Recommendation I.610 (1999), "B-ISDN Operation
and Maintenance Principles and Functions"
[I732] ITU-T Recommendation I.732 (1996), "Functional
Characteristics of ATM equipment"
[SAJASSI] Sajassi et.al., "L2VPN Interworking", IETF Internet Draft
draft-sajassi-l2vpn-interworking-01, March 2003
[Y1711] ITU-T Recommendation Y.1711 (2002), "OAM mechanism for MPLS
networks"
[Y17IW] ITU-T Draft Recommendation Y.17iw, "OAM functionality for
ATM-MPLS interworking", May 2003
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8. Author's Address
David Allan
Nortel Networks Phone: 1-613-763-6362
3500 Carling Ave. Email: dallan@nortelnetworks.com
Ottawa, Ontario, CANADA
9. Full Copyright Statement
"Copyright (C) The Internet Society (2003). Except as set forth
below, authors retain all their rights.
This document and translations of it may be copied and furnished to
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or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
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The limited permissions granted above are perpetual and will not be
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This document and the information contained herein is provided on an
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REPRESENTS (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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Appendix 'A': Procedures for the Network Interworking Scenario
OAM interworking is confined to being an interaction of the near
end defect handling state machine for the MPLS LSP and the
transported ATM VCCs and/or VPCs.
The MPLS LSP defect state acts as an input to the ATM layer
management function (described in [I732]). An MPLS layer defect
acts as a transmission path (TP) failure indicator to the ATM layer
management function.
Note that the possibility of dTTSI_Mismerge/dTTSI_Misbranch MPLS
layer defects means that TP failure can occur without interruption
of F4/F5 flows and user traffic at the ATM layer. This is addressed
by the transition to AIS state.
1) Upon entry of the LSP-ME near end to a defect state.
The egress IWF will instruct the ATM layer management function of
each IWE-ME that is a client of the unavailable LSP-ME to enter e-
t-e-AIS-generation condition and seg-AIS-generation condition with
corresponding suppression of user traffic transiting the EATM-ME.
2) Upon exit of the LSP-ME near end from a defect state.
The egress IWF will instruct the ATM layer management function to
exit end-to-end and seg AIS generation condition and re-enable
transit of IWE traffic across the IWF.
3) ATM LMI
Other ATM Layer Management Interface functions are unaffected.
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Appendix 'B': Procedures for the "Service Interworking" Scenario
1) Transition of MPLS near end termination from defect-free to a
defect state:
The MPLS termination connection point upon transition from defect-
free to a defect state as a result of an MPLS layer defect or
serving layer defect will direct the ATM termination point to
- Enter e-t-e_AIS_cell generation condition
- Enter seg-AIS_cell generation condition
- Suspend e2e CC cell generation, if enabled
- Suspend seg-CC cell generation, if enabled
2) Transition of MPLS near end termination from a defect state to
the defect-free state:
The MPLS near end termination connection point upon transition from
a defect state to the defect-free state as a result of correction
of an MPLS layer defect or serving layer defect will direct the ATM
termination point to:
- release e-t-e-AIS and seg_AIS generation condition,
- resume e2e and seg CC cell generation (if activated)
- and enable forwarding of user traffic.
3) Transition of MPLS far end termination from defect-free to a
defect state:
The MPLS far end termination connection point upon transition from
the defect-free to a defect state as a result of notification of an
MPLS layer defect or serving layer defect will direct the ATM
termination point to enter e-t-e_RDI_cell generation condition.
4) Transition of MPLS far end termination from a defect state to
the defect free state:
The MPLS far end termination connection point upon transition from
a defect state to the defect free state as a result of the absence
of notification of an MPLS layer defect or serving layer defect
will direct the ATM termination point to release e-t-e-RDI
generation condition.
5) Entrance of ATM termination into e2e-AIS-state or seg_AIS_state:
The ATM termination upon entry into the e2e-AIS-state or
seg_AIS_state will direct the MPLS far end termination to initiate
FDI generation and to suspend CV generation. A new defect type is
required and is for further study. The ATM termination MAY enter
the e2e-RDI-generation state.
6) Release of e2e-AIS-state and seg_AIS_state at the ATM
termination:
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The ATM termination upon release of both the e2e-AIS-state and
seg_AIS_state will direct the MPLS far end termination to cease FDI
generation and resume CV generation (if configured to do so).
6) Entrance of ATM termination into e2e-RDI-state or seg_RDI_state:
The ATM termination upon entry into either the e2e-RDI-state or
seg_RDI_state will direct the MPLS far end termination to initiate
BDI generation.
7) Release of e2e-RDI-state and seg_RDI_state:
The ATM termination upon release from both the e2e-RDI-state and
seg_RDI_state will direct the MPLS far end termination to cease BDI
generation.
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