Internet Draft Document Dinesh Mohan (Editor)
Internet Draft Nortel
Expires: April 2006 Ali Sajassi (Editor)
Cisco Systems
October 2005
L2VPN OAM Requirements and Framework
draft-ietf-l2vpn-oam-req-frmk-04.txt
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Copyright Notice
Copyright (C) The Internet Society (2005). All Rights Reserved.
Abstract
This draft provides framework and requirements for Layer 2 Virtual
Private Networks (L2VPN) Operation, Administration and Maintenance
(OAM). The OAM framework is intended to provide OAM layering across
L2VPN services, Pseudo Wires (PWs) and Packet Switched Network (PSN)
tunnels. The requirements are intended to identify OAM requirement
for L2VPN services (i.e. VPLS, VPWS, and IPLS). Furthermore, if
L2VPN services OAM requirements impose specific requirements on PW
OAM and/or PSN OAM, those specific PW and/or PSN OAM requirements
are also identified.
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Conventions used in this document
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 RFC 2119
Table of Contents
Status of this Memo................................................1
Copyright Notice...................................................1
Abstract...........................................................1
Conventions used in this document..................................2
1. Introduction....................................................3
1.1 Terminology....................................................5
2. L2VPN Services & Networks.......................................5
3. L2VPN OAM Framework.............................................6
3.1. OAM Layering..................................................6
3.2. OAM Domains...................................................7
3.3. MEPs and MIPs.................................................8
3.4. MEP and MIP Identifiers.......................................9
4. OAM Framework for VPLS..........................................9
4.1. VPLS as Service/Network.......................................9
4.1.1. VPLS as Bridged LAN Service.................................9
4.1.2. VPLS as a Network..........................................10
4.1.3. VPLS as (V)LAN Emulation...................................10
4.2. VPLS OAM.....................................................10
4.2.1. VPLS OAM Layering..........................................11
4.2.2. VPLS OAM Domains...........................................11
4.2.3. VPLS MEPs & MIPs...........................................12
4.2.4. VPLS MEP and MIP Identifiers...............................13
5. OAM Framework for VPWS.........................................13
5.1. VPWS as Service..............................................14
5.2. VPWS OAM.....................................................14
5.2.1. VPWS OAM Layering..........................................15
5.2.2. VPWS OAM Domains...........................................16
5.2.3. VPWS MEPs & MIPs...........................................17
5.2.4. VPWS MEP and MIP Identifiers...............................18
6. VPLS Service OAM Requirements..................................19
6.1. Discovery....................................................19
6.2. Connectivity Fault Management................................19
6.3. Connectivity Fault Detection.................................19
6.4. Connectivity Fault Verification..............................19
6.5. Connectivity Fault Localization..............................19
6.6. Connectivity Fault Alarm.....................................20
6.7. Frame Loss...................................................20
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6.8. Frame Delay..................................................20
6.9. Frame Delay Variation........................................21
6.10. Data Path Execution.........................................21
6.11. Scalability.................................................21
6.12. Extensibility...............................................21
6.13. Security....................................................22
6.14. Transport Independence......................................22
6.15. Application Independence....................................22
6.16. Backward Compatibility......................................23
6.17. Availability................................................23
7. VPWS OAM Requirements..........................................23
8. L2VPN Network OAM Requirements.................................23
8.1. VPLS (V)LAN Emulation OAM Requirements.......................23
8.1.1. Partial-mesh of PWs........................................23
8.1.2. PW Fault Recovery..........................................24
8.1.3. Connectivity Fault Notification............................24
9. OAM Operational Scenarios......................................24
9.1. VPLS OAM Operational Scenarios...............................25
9.2. VPWS OAM Operational Scenarios...............................26
10. Acknowledgments...............................................26
11. Security Considerations.......................................26
12. Intellectual Property Considerations..........................26
13. Full Copyright Statement......................................27
14. IPR Notice....................................................27
15. Normative References..........................................27
16. Informative References........................................27
17. Authors' Addresses............................................28
A1. Appendix 1 - Alternate Management Models......................29
A1.1. Alternate Model 1 (Minimal OAM).............................29
A1.2. Alternate Model 2 (Segment OAM Interworking)................30
1. Introduction
This draft provides framework and requirements for Layer 2 Virtual
Private Networks (L2VPN) Operation, Administration and Maintenance
(OAM).
The scope of OAM for any service and/or transport/network
infrastructure technologies can be very broad in nature. OSI has
defined the following five generic functional areas for network
management, commonly abbreviated as "FCAPS" [NM-Standards]: a) Fault
Management, b) Performance Management, c) Configuration Management,
d) Accounting Management, and e) Security Management.
This draft focuses on the Fault and Performance Management aspects.
Other functional aspects of FCAPS are for further study.
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Fault Management can typically be viewed in terms of the following
categories:
- Fault Detection
- Fault Verification
- Fault Isolation
- Fault Notification
- Fault Recovery
Fault Detection deals with mechanism(s) that can detect both hard
failures, such as link and device failures, and soft failures, such
as software failure, memory corruption, mis-configuration, etc.
Typically a lightweight protocol is desirable to detect the fault
and thus it would be prudent to verify the fault via Fault
Verification mechanism before taking additional steps in isolating
the fault. After verifying that a fault has occurred along the data
path, it is important to be able to isolate the fault to a given
device or link. Therefore, a Fault Isolation mechanism is needed in
Fault Management. Fault Notification mechanism can be used in
conjunction with Fault Detection mechanism to notify the upstream
and downstream devices of a fault. For example, when there is a
client/server relationship between two layered networks; Fault
Detection at the server layer will require the following Fault
Notification:
- sending a forward Fault Notification from server layer to the
client layer network(s) using the Fault Notification format
appropriate to the client layer
- sending a backward Fault Notification at server layer, if
applicable, in the reverse direction
- sending a backward Fault Notification at client layer, if
applicable, in the reverse direction
Finally, Fault Recovery deals with recovering from the detected
failure by switching to an alternate available device or link (e.g.,
device redundancy or link redundancy).
Performance Management deals with mechanism(s) that allow
determining and measuring the performance of network/services under
consideration and notification of them. Performance Management can
be used to verify the compliance to both the service and network
level metric objectives/specifications. Performance Management
typically consists of measurement of Performance Parameters e.g.
Frame Loss, Frame Delay, Frame Delay Variation (aka Jitter) etc
across managed entities when the managed entities are in available
state. Performance Management is suspended across unavailable
managed entities. This draft introduces some of these performance
parameters.
[L2VPN-FRWK] specifies three different types of Layer 2 VPN (i.e.
services). These are VPWS, VPLS and IPLS.
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This document provides a description and a reference model for OAM
layering and furthermore emphasizes the importance of proper
independent layering in design and development of OAM functionality
across L2VPN services, Pseudo Wires (PWs) and Public Switched
Network (PSN) tunnels. The requirements are intended to identify OAM
requirement for L2VPN services (e.g. VPLS and VPWS). Furthermore, if
L2VPN services OAM requirements impose specific requirements on PW
OAM and/or PSN OAM, those specific PW and/or PSN OAM requirements
are also identified.
1.1 Terminology
This document introduces and uses the following terms. Further, this
document also uses the terms defined in [L2VPN-ARCH] and [PWE-ARCH].
AIS Alarm Indication Signal
FM Fault Management
OAM Domain OAM Domain represents a region over which OAM frames
can operate unobstructed
ME Maintenance Entity which is defined in a given OAM
domain and represents an entity requiring monitoring
MEG Maintenance Entity Group which represents MEs belonging
to the same service instance. MEG is also called as
Maintenance Association (MA).
MEP Maintenance End Point is responsible for origination
and termination of OAM frames for a given MEG
MIP Maintenance Intermediate Point is located between peer
MEPs and can process OAM frames but does not initiate
or terminate them
PM Performance Management
RDI Remote Defect Indication
SLA Service Level Agreement
STP Spanning Tree Protocols
2. L2VPN Services & Networks
As described in [L2VPN-REQ], following Figure 1 shows a L2VPN
reference model. L2VPN A represents a point-to-point service while
L2VPN B represents a bridged service.
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+-----+ +-----+
+ CE1 +--+ +--| CE2 |
+-----+ | ..................... | +-----+
L2VPN A | +----+ +----+ | L2VPN A
+--| PE |-- Service --| PE |--+
+----+ Provider +----+
/ . Backbone . \ --------_
+-----+ / . | . \ / \ +-----+
+ CE4 +--+ . | . +-\ Access \--| CE5 |
+-----+ . +----+ . | Network | +-----+
L2VPN B ........| PE |....... \ / L2VPN B
+----+ ^ -------
| | logical
| | switching
+-----+ | instance
| CE3 |
+-----+
L2VPN B
Figure 1: L2VPN Reference Model
[L2VPN-FRWK] specifies VPWS, VPLS and IPLS services. VPWS is a
point-to-point service where CEs are presented with point-to-point
virtual circuits. VPLS is a bridged LAN service provided to a set of
CEs that are members of a VPN. CEs that are member of the same
service instance communicate with each other as if they are
connected via a bridged LAN. IPLS is a special VPLS which is used to
carry only IP service packets.
[L2VPN-REQ] assumes the availability of runtime monitoring protocols
while defining requirements for management interfaces. This draft
specifies the requirements and framework for operations,
administration and maintenance (OAM) protocols between network
devices.
3. L2VPN OAM Framework
3.1. OAM Layering
The point-to-point or bridged LAN functionality is emulated by a
network of PEs to which the CEs are connected. This network of PEs
can belong to a single network operator or can span across multiple
network operators. Furthermore, it can belong to a single service
provider or can span across multiple service providers. A service
provider is responsible for providing L2VPN services to its
customers; whereas, a network operator (aka facility provider)
provides the necessary facilities to the service provider(s) in
support of their services. A network operator and a service
provider can be part of same administrative organization or they can
be different administrative organizations.
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Different layers involved in realizing L2VPNs include service layer
and network layers. Network layers can be iterative. In context of
L2VPNs, the service layers consists of VPLS, VPWS (e.g. Ethernet,
ATM, FR, HDLC, SONET, etc. point-to-point emulation), and IPLS.
Similarly in context of L2VPNs, network layers consist of MPLS/IP
networks. The MPLS/IP networks can consist of networks links
realized by different technologies e.g. SONET, Ethernet, ATM etc.
Each layer is responsible for its own OAM. This document provides
the OAM framework and requirements for L2VPN services and networks.
3.2. OAM Domains
When discussing OAM tools for L2VPNs it is important to provide OAM
capabilities and functionality over each domain that a service
provider or a network operator is responsible for. For these
reasons, it is also important that OAM frames are not allowed to
enter/exit other domains. We define an OAM domain as a network
region over which OAM frames operate unobstructed as explained
below.
At the edge of an OAM domain, filtering constructs should prevent
OAM frames from exiting and entering that domain. OAM domains can be
nested but not overlapped. In other words, if there is a hierarchy
of the OAM domains, the OAM frames of a higher-level domain pass
transparently through the lower-level domains but the OAM frames of
a lower-level domain get blocked/filtered at the edge of that
domain.
In order to facilitate the processing of OAM frames, each OAM domain
can be associated with a level at which it operates. Higher level
OAM domains can contain lower level OAM domains but the converse is
not true. It may be noted that the higher level domain does not
necessarily mean a higher numerical value of the level encoding in
the OAM frame.
A PE can be part of several OAM domains with each interface
belonging to the same or a different OAM domain. A PE shall block
outgoing OAM frames and filter out incoming OAM frames whose domain
level is lower or same to the one configured on that interface and
pass through the OAM frames whose domain level is higher than the
one configured on that interface.
Generically, L2VPNs can be viewed as consisting of customer OAM
domain, service provider OAM domain, and network operator OAM domain
as depicted in Figure 2.
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--- ---
/ \ ------ ------- ----- / \
| CE-- / \ / \ / \ --CE |
\ / \ / \ / \ / \ / \ /
--- --PE P P PE-- ---
\ / \ / \ /
\ / \ / \ /
------ ------- -----
Customer OAM Domain
|<-------------------------------------------->|
Service Provider OAM Domain
|<------------------------------>|
Operator Operator Operator
|<-------->|<--------->|<------->|
OAM Domain OAM Domain OAM Domain
Figure 2: OAM Domains
The OAM Domains can be categorized as:
. Hierarchical OAM Domains: Hierarchical OAM Domains result from
OAM Layering and imply a contractual agreement among the OAM
Domain ownerships. In the above example, Customer OAM Domain,
Service Provider OAM Domain and Operator OAM Domains are
hierarchical.
. Adjacent OAM Domains: Adjacent OAM Domains are typically
independent of each other and do not have any relationship
among them. In the above example, the different Operator OAM
Domains are independent of each other.
3.3. MEPs and MIPs
Maintenance End Points (MEPs) are responsible for origination and
termination of OAM frames. MEPs are located at the edge of their
corresponding OAM domains. Maintenance Intermediate Points (MIPs)
are located within their corresponding OAM domains and they normally
pass OAM frames but never initiate them. Since MEPs are located at
the edge of their OAM domains, they are responsible for filtering
outbound OAM frames from leaving the OAM domain or inbound OAM
frames from entering the OAM domain.
An OAM frame is generally associated with a Maintenance Entity (ME)
or a Maintenance Entity Group (MEG), where a MEG consists of a set
of MEs associated with the same service instance. A ME is a point-
to-point association between a pair of MEPs and represents a
monitored entity. For example, in a VPLS service which involves n
CEs, all the MEs associated with the VPLS service in the customer
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OAM domain (i.e. from CE to CE) can be considered to be part of a
VPLS MEG, where the n-point MEG consists of a maximum of n(n-1)/2
MEs. MEPs and MIPs correspond to a PE or more specifically to an
interface of a PE. For example, an OAM frame can be said to
originate from an ingress PE or more specifically an ingress
interface of that PE.
In Hierarchical OAM Domains, a MEP of lower-level OAM domain can
correspond to a MIP or a MEP of a higher-level OAM domain.
Furthermore, the MIPs of a lower-level OAM domain are always
transparent to the higher-level OAM domain (e.g., OAM frames of a
higher-level OAM domain are not seen by MIPs of a lower-level OAM
domain and get passed through them transparently). Further, the MEs
(or MEGs) are hierarchically organized in hierarchical OAM domains.
For example, in a VPWS service, the VPWS ME in Customer OAM domain
can coincide with the Attachment Circuit (AC) ME, PW ME and another
AC ME in Service Provider OAM Domain. Similarly, the PW ME can
coincide with different ME in Operator OAM Domains.
3.4. MEP and MIP Identifiers
As mentioned previously, OAM at each layer should be independent of
other layers e.g. service layer OAM should be independent of
underlying transport layer. MEPs and MIPs at each layer should be
identified with layer specific identifiers.
4. OAM Framework for VPLS
Virtual Private LAN Service (VPLS) is used in different contexts. In
general, VPLS is used in the following contexts: a) as a bridged LAN
service over networks, some of which are MPLS/IP, b) as an MPLS/IP
network supporting these bridged LAN services, and c) as (V)LAN
emulation.
4.1. VPLS as Service/Network
4.1.1. VPLS as Bridged LAN Service
The most common definition for VPLS is for bridged LAN service over
an MPLS/IP network. The service coverage is considered end-to-end
from UNI to UNI (or AC to AC) among the CE devices and it provides a
virtual LAN service to the attach CEs belonging to that service
instance. The reason it is called bridged LAN service is because the
VPLS-capable PE provide this end-to-end virtual LAN service
performing bridging functions (either full or a subset) as described
in the [L2VPN-FRWK]. A VPLS service instance is also analogous to a
VLAN provided by IEEE 802.1Q networks since each VLAN provides a
Virtual LAN service to its MAC users. Therefore, when a part of the
service provider network is Ethernet based (such as H-VPLS with QinQ
access network), there is a one-to-one correspondence between a VPLS
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service instance and its corresponding provider VLAN in the service
provider Ethernet network. To check the end-to-end service
integrity, service level OAM mechanisms are needed.
4.1.2. VPLS as a Network
Sometimes VPLS is also used to refer to the underlying network that
supports bridged LAN services. This network can be an end-to-end
MPLS/IP network as H-VPLS with MPLS/IP access or can be a hybrid
network consisting of MPLS/IP core and Ethernet access network as in
H-VPLS with QinQ access. In either case, the network consists of a
set of VPLS-capable PE devices capable of performing bridging
functions (either full or a subset). These VPLS-capable PE devices
can be arranged in a certain topology such as hierarchical topology
(H-VPLS) or distributed topology (D-VPLS) or some other topologies
such as multi-tier or star topologies. To check the network
integrity regardless of the network topology, network level OAM
mechanisms are needed for the VPLS networks.
4.1.3. VPLS as (V)LAN Emulation
Sometimes VPLS also refers to (V)LAN emulation. In such context,
VPLS only refers to the full mesh of PWs with split horizon that
emulates a LAN segment over MPLS/IP network for a given service
instance. Since the emulated LAN segment is presented as a Virtual
LAN (VLAN) to the bridge module of a VPLS-capable PE, emulated
segment is also referred to as an emulated VLAN. The OAM mechanisms
in this context refer primarily to integrity check of the full mesh
of PWs and the ability to detect and recover from partial mesh
failure.
4.2. VPLS OAM
When discussing the OAM mechanisms for VPLS, it is important to
consider that the end-to-end service can span across different types
of L2VPN networks. As an example, in case of [VPLS-LDP], the access
network on one side can be bridged network e.g. [IEEE 802.1ad], as
described in section 11 of [VPLS-LDP]. The access network can also
be a [IEEE 802.1ah] based bridged network. The access network on
other side can be MPLS based as described in section 10 of [VPLS-
LDP]; and the core network connecting them can be IP, MPLS, ATM, or
SONET. Similarly, the VPLS service instance can span across [VPLS-
BGP], and distributed VPLS as described in [ROSEN-SIG].
Therefore, it is important that the OAM mechanisms can be applied to
all these network types. Each such network may be associated with a
separate administrative domain and also multiple such networks may
be associated with a single administrative domain. It is important
to ensure that the OAM mechanisms are independent of the underlying
transport mechanisms and solely rely on VPLS service, i.e. the
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transparency of OAM mechanisms must be ensured over underlying
transport technologies such as MPLS, IP, etc.
This proposal is aligned with the current discussions in other
standard bodies and groups such as ITU-T Q.5/13, IEEE 802.1, and MEF
which are addressing Ethernet network and service OAM.
4.2.1. VPLS OAM Layering
Figure 3 shows an example of a VPLS service (with two CE belonging
to customer A) across a service provider network marked by UPE and
NPE devices. More CE devices belonging to the same Customer A can be
connected across different sites of customer. Service provider
network is segmented into core network and two types of access
network. Figure 3(A) shows the bridged access network represented by
its bridge components marked B, and the MPLS access and core network
represented by MPLS components marked P. Figure 3(B) shows the
service/network view at the Ethernet MAC layer marked by E.
--- ---
/ \ ------ ------- ---- / \
| A CE-- / \ / \ / \ --CE A |
\ / \ / \ / \ / \ / \ /
--- --UPE NPE NPE UPE-- ---
\ / \ / \ /
\ / \ / \ /
------ ------- ----
(A) CE----UPE--B--B--NPE---P--P---NPE---P----UPE----CE
(B) E------E---E--E---E------------E----------E-----E
Figure 3: VPLS specific device view
As shown in Figure 3(B), only the devices with Ethernet
functionality are visible to OAM mechanisms operating at Ethernet
MAC layer and the P devices are invisible. Therefore, the OAM along
the path of P devices (e.g., between two PEs) is covered by
transport layer and it is outside the scope of this document.
However, VPLS services may impose some specific requirements on PSN
OAM. This document aims to identify such requirements.
4.2.2. VPLS OAM Domains
As described in the previous section, a VPLS service for a given
customer can span across one or more service providers and network
operators.
Figure 4 depicts three OAM domains: (A) customer domain which is
among the CEs of a given customer, (B) service provider domain which
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is among the edge PEs of the given service provider, and (C) network
operator domain which is among the PEs of a given operator.
--- ---
/ \ ------ ------- ---- / \
| CE-- / \ / \ / \ --CE |
\ / \ / \ / \ / \ / \ /
--- --UPE NPE NPE UPE-- ---
\ / \ / \ /
\ / \ / \ /
------ ------- ----
Customer OAM Domain
(A) |<----------------------------------------------->|
Provider OAM Domain
(B) |<---------------------------------->|
Operator Operator Operator
(C) |<--------->|<----------->|<-------->|
OAM Domain OAM Domain OAM Domain
Figure 4: VPLS OAM Domains
4.2.3. VPLS MEPs & MIPs
As shown in Figure 5, (C) represents those MEPs and MIPs that are
visible within the customer domain. (D) represents the MEPs and MIPs
visible within the service provider domain, while (E) represents the
MEPs and MIPs visible within each operator domain. Further, (F)
represents the MEPs and MIPs corresponding to the MPLS layer and may
apply MPLS based mechanisms. The MPLS layer shown in Figure 5 is
just an example and specific OAM mechanisms are outside the scope of
this document.
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--- ---
/ \ ------ ------- ---- / \
| A CE-- / \ / \ / \ --CE A |
\ / \ / \ / \ / \ / \ /
--- --UPE NPE NPE UPE-- ---
\ / \ / \ /
\ / \ / \ /
------ ------- ----
(A) CE----UPE--B-----NPE---P------NPE---P----UPE----CE
(B) E------E---E------E------------E----------E-----E
Customer OAM domain
(C) MEP---MIP--------------------------------MIP---MEP
Provider OAM domain
(D) MEP--------MIP-----------MIP-------MEP
Operator Operator Operator
(E) MEP-MIP--MEP|MEP-------MEP|MEP-----MEP
OAM domain OAM domain OAM domain
MPLS OAM MPLS OAM
(F) MEP--MIP-----MEP--MIP--MEP
domain domain
Figure 5: VPLS OAM Domains, MEPs & MIPs
4.2.4. VPLS MEP and MIP Identifiers
In VPLS, for Ethernet MAC layer, the MEPs and MIPs should be
identified with their Ethernet MAC addresses. As described in [VPLS-
LDP], VPLS instance can be identified in an Ethernet domain (e.g.,
8021.d domain) using VLAN tag (service tag) while in an MPLS/IP
network, PW-ids are used. Both PW-ids and VLAN tags for a given VPLS
instance are associated with a Service Identifier (e.g., VPN
identifier). MEPs and MIPs Identifiers, i.e. MEP Ids and MIP Ids
must be unique within their corresponding Service Identifiers within
the OAM domains.
For Ethernet services e.g. VPLS, Ethernet frames are used for OAM
frames and the source MAC address of the OAM frames represent the
source MEP in that domain. For unicast Ethernet OAM frames, the
destination MAC address represents the destination MEP in that
domain. For multicast Ethernet OAM frames, the destination MAC
addresses corresponds to all MEPs in that domain.
5. OAM Framework for VPWS
Figure 6 shows the VPWS reference model. VPWS is a point-to-point
service where CEs are presented with point-to-point virtual
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circuits. VPWS is realized by combining a pair of Attachment
Circuits between the CEs and PEs and a PW between PEs.
|<------------- VPWS1 <AC11,PW1,AC12> ------------>|
| |
| +----+ +----+ |
+----+ | |==================| | +----+
| |---AC11---|............PW1.............|--AC12----| |
| CE1| |PE1 | | PE2| |CE2 |
| |---AC21---|............PW2.............|--AC22----| |
+----+ | |==================| | +----+
| +----+ PSN Tunnel +----+ |
| |
|<------------- VPWS2 <AC21,PW2,AC22> ------------>|
Figure 6: VPWS Reference Model
5.1. VPWS as Service
VPWS service can be categorized as:
. VPWS with homogeneous ACs (where both ACs are same type)
. VPWS with heterogeneous ACs (where the ACs are of different
types)
Further, the VPWS can itself be classified as:
. Homogeneous VPWS (when two ACs and PW are of the same type)
. Heterogeneous VPWS (when at least one AC or PW is different
type than the others)
Based on the above classifications, the heterogeneous VPWS may have
either homogeneous or heterogeneous ACs. On the other hand,
homogeneous VPWS can have only homogeneous ACs.
5.2. VPWS OAM
When discussing the OAM mechanisms for VPWS, it is important to
consider that the end-to-end service can span across different types
of networks. As an example, the access network between CE and PE on
one side can be Ethernet bridged network, ATM network, etc. In
common scenarios, it could or simply a point-to-point interface of
certain type. The core network connecting PEs can be IP, MPLS, etc.
Therefore, it is important that the OAM mechanisms can be applied to
all these network types. Each such network may be associated with a
separate administrative domain and also multiple such networks may
be associated with a single administrative domain.
This proposal is aligned with the current discussions in other
working groups such as PWE3.
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5.2.1. VPWS OAM Layering
Figure 7 shows an example of a VPWS service (with two CE devices
belonging to customer A) across a service provider network marked by
PE devices. Service provider network can be considered to be
segmented into core network and two types of access network.
In most general case, a PE can be client service aware when it
processes client service PDUs and is responsible for encapsulating
and de-encapsulating client service PDUs onto PW and ACs. This is
particularly relevant for homogeneous VPWS. The service specific
device view for such a deployment is highlighted by Figure 7(A) for
these are the devices that are expected to be involved in end-to-end
VPWS OAM.
In other instances, a PE can be client service unaware when it does
not process native service PDUs but instead encapsulates access
technology PDUs over PWs. This may be relevant for VPWS with
heterogeneous ACs. For example, if the service is Ethernet VPWS
which is offered across an ATM AC, ATM PW and Ethernet AC. In this
case, the PE which is attached to ATM AC and ATM PW may be
transparent to the client Ethernet service PDUs. On the other hand,
the PE which is attached to ATM PW and Ethernet AC is expected to be
client Ethernet service aware. The service specific device view for
such a deployment is highlighted by Figure 7(B) for these are the
devices that are expected to be involved in end-to-end VPWS OAM,
where PE1 is expected to be client service unaware.
|<--------------- VPWS <AC1,PW,AC2> -------------->|
| |
| +----+ +----+ |
+----+ | |==================| | +----+
| |---AC1----|............PW..............|--AC2-----| |
| CE1| |PE1 | | PE2| |CE2 |
+----+ | |==================| | +----+
+----+ PSN Tunnel +----+
access core access
|<---------.|<----------------------.|<---------.|
(A).CE----------PE-----------------------PE-------------CE
(B).CE-----------------------------------PE-------------CE
Figure 7: VPWS specific device view
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5.2.2. VPWS OAM Domains
As described in the previous section, a VPWS service for a given
customer can span across one or more network operators.
Figure 8a and 8b depicts three OAM domains: (A) customer domain
which is among the CEs of a given customer, (B) service provider
domain which depends on the management model, and (C) network
operator domain which is among the PEs of a given operator and could
also be present in access if the access is provided by a different
network operator. The core network operator may be responsible for
managing the PSN Tunnel in these examples.
For the first management model, as shown in Figure 8a, the CEs are
expected to be managed by the customer and customer is responsible
for running end-to-end service OAM, if needed. The service provider
is responsible to monitor the PW ME and the monitoring of the AC is
responsibility shared between the customer and service provider. In
most simple cases, when the AC is realized across a physical
interface that connects the CE to PE, the monitoring requirements
across the AC ME are minimal.
|<--------------- VPWS <AC1,PW,AC2> -------------->|
| |
| +----+ +----+ |
+----+ | |==================| | +----+
| |---AC1----|............PW..............|--AC2-----| |
| CE1| |PE1 | | PE2| |CE2 |
+----+ | |==================| | +----+
+----+ PSN Tunnel +----+
Customer OAM Domain
(A).|<------------------------------------------------.|
Service Provider OAM Domain
(B) |<--------------------------.|
Operator OAM Domain
(C) |<---------------.|
Figure 8a: VPWS OAM Domains - Management Model 1
Figure 8b highlights another management model, where the CEs are
managed by the Service Provider and where CEs and PEs are connected
via access network. The access network between the CEs and PEs may
or may not be provided by a distinct network operator. In this
model, the VPWS service ME spans between the CEs in the Service
Provider OAM Domain, as shown by Figure 8b(B). The Service Provider
OAM Domain may additionally monitor the AC MEs and PW MEs
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individually, as shown by Figure 8b(C). The network operators may be
responsible for managing the access service MEs (e.g. access
tunnels) and core PSN Tunnel MEs, as shown by Figure 8b(D). The
distinction between Figure 8b (C) and (D) is that (C) MEs have MEPs
at CE and PEs and have no MIPs while (D) MEs have MEPs at CEs and
PEs and likely MIPs in between, thereby having a visibility to
Operator network.
|<--------------- VPWS <AC1,PW,AC2> -------------->|
| |
| +----+ +----+ |
+----+ | |==================| | +----+
| |---AC1----|............PW..............|--AC2-----| |
| CE1| |PE1 | | PE2| |CE2 |
+----+ | |==================| | +----+
+----+ PSN Tunnel +----+
Customer OAM Domain
(A).|<--------------------------------------------------.|
Service Provider (SP) OAM Domain
(B). |<------------------------------------------------.|
SP OAM SP OAM SP OAM
(C) |<---------.|<----------------------.|<---------.|
Domain Domain Domain
Operator Operator Operator
(D) |<---------.|<----------------------.|<---------.|
OAM Domain OAM Domain OAM Domain
Figure 8b: VPWS OAM Domains - Management Model 2
5.2.3. VPWS MEPs & MIPs
The location of MEPs and MIPs can be based upon the management model
used in the VPWS scenarios. The interest remains in being able to
monitor end-to-end service and also support segment monitoring in
the network to allow isolation of faults to specific
responsibilities within the network.
The end-to-end service monitoring is provided by end-to-end ME and
additional segment OAM monitoring is provided by segment MEs, all in
the Service Provider OAM Domain. The end-to-end MEs and segment MEs
are hierarchically organized as mentioned earlier for hierarchical
OAM domains. This is shown in Figure 8b (B) and (C).
The CE interfaces support MEPs at end-to-end Service Provider OAM
level for VPWS end-to-end service as shown in Figure 9 (B1) and
(B2). In addition, PE interfaces may support MIPs at end-to-end
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Service Provider OAM level when PEs are client service aware, shown
in Figure 9 (B2). As an example, if one considers an enc-to-end
Ethernet line service offered to subscriber between CE1 and CE2
which is realized via ATM type AC1 and AC2 and PW which encapsulates
ATM over MPSL, the PEs can be considered as Ethernet service
unaware, and therefore cannot support any Ethernet MIPs. Figure 9
(B1) represents this particular situation. Of course, another view
of the end-to-end service can be ATM, in which case PE1 and PE2 can
be considered to be service aware, and therefore support ATM MIPs.
Figure 9 (B2) represents this particular situation.
In addition, CEs and PE interfaces support MEPs at a segment (lower
level) Service Provider OAM level for AC and PW MEs and no MIPs are
involved at this segment Service Provider OAM Level, as shown in
Figure 9 (C). Operators may also run segment OAM by having MEPs at
Network Operator OAM level, as shown in Figure 9 (D).
The advantage of this option is that end-to-end and segment OAM can
be carried out in an independent manner. It is also possible to
carry out some optimizations, e.g. when proactive segment OAM
monitoring is performed, proactive end-to-end monitoring may not be
needed since client layer end-to-end ME could simply use fault
notifications from the server layer segment MEs.
|<--------------- VPWS <AC1,PW,AC2> -------------->|
| |
| +----+ +----+ |
+----+ | |==================| | +----+
| |---AC1----|............PW..............|--AC2-----| |
| CE1| |PE1 | | PE2| |CE2 |
+----+ | |==================| | +----+
+----+ PSN Tunnel +----+
(B1) MEP-----------------------------------------------MEP
(B2) MEP----------MIP---------------------MIP----------MEP
(C) MEP-------MEP|MEP------------------MEP|MEP--------MEP
(D) MEP-------MEP|MEP------------------MEP|MEP--------MEP
Figure 9: VPWS MEPs & MIPs
Though, different possible OAM layers have been shown in the Figure
9, not all may be realized. For example, Figure (B2) and (D) may be
adequate in some cases.
5.2.4. VPWS MEP and MIP Identifiers
In VPWS, the MEPs and MIPs should be identified with their native
addressing schemes. MEPs and MIPs Identifiers, i.e. MEP Ids and MIP
Ids must be unique within their corresponding OAM domains and must
also be unique to the VPWS service instance.
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6. VPLS Service OAM Requirements
6.1. Discovery
Discovery allows a service aware device to learn about other devices
that support the same service instance within a given domain.
Discovery also allows a service aware device to learn sufficient
information (e.g. IP addresses, MAC addressed etc.) from other
service aware devices such that OAM frames can be exchanged among
the service aware devices.
(R1) OAM MUST allow a service aware device to discover other devices
that share the same service instance(s) within a given OAM domain.
6.2. Connectivity Fault Management
Service is realized by exchanging service frames/packets between
devices that support the service instance. To allow the exchange of
service frames, connectivity between these service aware devices is
required.
6.3. Connectivity Fault Detection
To ensure service, pro-active connectivity monitoring is required.
Connectivity monitoring facilitates connectivity fault detection.
(R2a) OAM MUST allow pro-active connectivity monitoring between two
service aware devices that support the same service instance within
a given OAM domain.
6.4. Connectivity Fault Verification
Once a connectivity fault is detected, connectivity fault
verification may be performed.
(R2b) OAM MUST allow connectivity fault verification between two
service aware devices that support the same service instance within
a given OAM domain.
6.5. Connectivity Fault Localization
Further, localization of connectivity fault may be carried out.
(R2c) OAM MUST allow connectivity fault localization between two
service aware devices that support the same service instance within
a given OAM domain.
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6.6. Connectivity Fault Alarm
Typically, when connectivity fault is detected and optionally
verified, service device may notify the EMS/NMS (Element Management
System/Network Management System).
However, a single transport/network fault may cause multiple
services to fail causing multiple connectivity faults. Therefore,
OAM must allow alarm notification to allow suppression of service
connectivity fault notifications.
(R2d) OAM MUST allow forwarding of transport/network fault
indications to those service aware devices that support service
instance affected by the fault.
6.7. Frame Loss
A service may be considered degraded if it is sensitive to service
frames/packets loss during transit between the service aware
devices. To determine if a service is degraded due to frame/packet
loss, measurement of frame/packet loss is required.
(R3) OAM MUST support measurement of per-service frame/packet loss
between two service aware devices that support the same service
instance within a given OAM domain.
6.8. Frame Delay
A service may be sensitive to delay experienced by the service
frames/packets during transit between the service aware devices. To
determine if a service is degraded due to frame/packet delay,
measurement of frame/packet delay is required.
Frame/packet delay measurement can be of two types:
One-way delay
One-way delay is used to characterize certain applications like
multicast and broadcast applications. The measurement for one-way
delay usually requires clock synchronization between two devices in
question.
Two-way delay
Two-way delay or round-trip delay does not require clock
synchronization between two devices involved in measurement and is
usually sufficient to determine the frame/packet delay being
experienced.
(R4a) OAM MUST support measurement of per-service two-way
frame/packet delay between two service aware devices that support
the same service instance within a given OAM domain.
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(R4b) OAM SHOULD support measurement of per-service one-way
frame/packet delay between two service aware devices that support
the same service instance within a given OAM domain.
6.9. Frame Delay Variation
A service may be sensitive to delay variation experienced by the
service frames/packets during transit between the service aware
devices. To determine if a service is degraded due to frame/packet
delay variation, measurement of frame/packet delay variation is
required. For frame/packet delay variation measurements, one-way
mechanisms are considered to be sufficient.
(R5) OAM MUST support measurement of per-service frame/packet delay
variation between two service aware devices that support the same
service instance within a given OAM domain.
6.10. Data Path Execution
If the OAM frames flow across a different path than the one used by
service frames/packets, accurate measurement and/or determination of
service state may not be made. Therefore data path, i.e. the one
being taken by service frames/packets, must be used for the service
OAM.
(R6) OAM frames MUST be forwarded along the same path as the
service/data frames.
6.11. Scalability
Mechanisms developed for OAM need to be such that per-service OAM
can be supported even though the OAM may only be used for limited
services e.g. premium services and may not be used for best effort
services.
Note: The specific numbers or range of services should align with
the [L2VPN-FRWK]
(R7) OAM MUST be scalable such that a service device can support OAM
for each service that is supported by the device.
6.12. Extensibility
Extensibility is intended to allow introduction of additional
functionality in future such that backward compatibility can be
maintained i.e. when working with older version devices, service OAM
with reduced functionality is still possible.
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(R8) OAM MUST be extensible such that new functionality and
information elements related to this functionality can be introduced
in future.
6.13. Security
OAM frames belonging to an OAM domain originate and terminate within
that OAM domain. Security implies that an OAM domain must be capable
of filtering OAM frames. The filtering is such that the OAM frames
are prevented from leaking outside their domain. Also, OAM frames
from outside the OAM domains should be either discarded (when such
OAM frames belong to same or lower-level OAM domain) or
transparently passed (when such OAM frames belong to a higher-level
OAM domain).
(R9a) OAM frames MUST be prevented from leaking outside their OAM
domain.
(R9b) OAM frames from outside an OAM domain MUST be prevented from
entering the OAM domain when such OAM frames belong to the same
level or lower-level OAM domain.
(R9c) OAM frames from outside an OAM domain MUST be transported
transparently inside the OAM domain when such OAM frames belong to
the higher-level OAM domain.
6.14. Transport Independence
Service frame/packets delivery is carried out across transport
infrastructure, also called network infrastructure. Though specific
transport/network technologies may provide their own OAM
capabilities, Service OAM must be independently supported as many
different transport/network technologies can be used to carry
service frame/packets.
(R10a) OAM MUST be independent of the underlying transport/network
technologies and specific transport/network OAM capabilities.
(R10b) OAM MAY allow adaptation/interworking with specific
transport/network OAM functions. For example, this would be useful
to allow Fault Notifications from transport/network layer(s) to be
sent to service layer.
6.15. Application Independence
Service itself may be used to carry application frame/packets. The
application may use its own OAM; service OAM must not be dependent
on application OAM. As an example, a VPLS service may be used to
carry IP traffic; however, VPLS OAM should not assume IP or rely on
the use of IP level OAM functions.
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(R11a) OAM MUST be independent of the application technologies and
specific application OAM capabilities.
6.16. Backward Compatibility
Service OAM should be such that non-service aware and/or OAM
incapable devices in the middle of the OAM domain should be able to
forward the OAM frames similar to the regular service/data
frames/packets.
(R12) OAM MUST be defined such that devices not supporting the OAM
are able to forward the OAM frames in a similar fashion as the
regular service/data frames/packets.
6.17. Availability
A service may be considered unavailable if the service
frames/packets do not reach their intended destination (e.g.
connectivity is down or frame/packet loss is occurring) or the
service is degraded (e.g. frame/packet delay and/or delay variation
threshold is exceeded).
Entry and exit conditions may be defined for unavailable state.
Availability itself may be defined in context of service type.
Since availability measurement may be associated with connectivity,
frame/packet loss, frame/packet delay and frame/packet delay
variation measurements, no additional requirements are specified
currently.
7. VPWS OAM Requirements
TBD
8. L2VPN Network OAM Requirements
8.1. VPLS (V)LAN Emulation OAM Requirements
8.1.1. Partial-mesh of PWs
As indicated in [BRIDGE-INTEROP], VPLS service OAM relies upon
bidirectional Ethernet links or (V)LAN segments and failure in one
direction or link results in failure of the whole link or (V)LAN
segment. Therefore, when partial-mesh failure occurs in (V)LAN
emulation, either the entire PW mesh should be shutdown when only an
entire VPLS service is acceptable or a subset of PW with full PW
mesh should be realized when partial VPLS service is acceptable.
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(R13a) PW OAM for PWs related to a (V)LAN emulation MUST allow
detection of partial-mesh failure condition.
(R13b) PW OAM for PWs related to a (V)LAN emulation MUST allow the
entire mesh of PWs to be shutdown upon detection of a partial-mesh
failure condition.
(R13c) PW OAM for PWs related to a (V)LAN emulation MAY allow the
subset of PWs to be shutdown upon detection of a partial-mesh
failure condition in a manner such that full mesh is present across
the remaining subset.
8.1.2. PW Fault Recovery
As indicated in [BRIDGE-INTEROP], VPLS service OAM fault detection
and recovery relies upon (V)LAN emulation recovery such that fault
detection and recovery time in (V)LAN emulation should be less than
the VPLS service fault detection and recovery time to prevent
unnecessary switch-over and temporary flooding/loop within customer
OAM domain that is dual-homed to provider OAM domain.
(R14a) PW OAM for PWs related to a (V)LAN emulation MUST support a
fault detection time in the provider OAM domain faster than the VPLS
fault detection time in the customer OAM domain.
(R14b) PW OAM for PWs related to a (V)LAN emulation MUST support a
fault recovery time in the provider OAM domain faster than the VPLS
fault recovery time in the customer OAM domain.
8.1.3. Connectivity Fault Notification
When connectivity fault is detected in (V)LAN emulation, PE devices
may notify the EMS/NMS (Element Management System/Network Management
System). However, a single (V)LAN emulation fault may result in CE
devices or U-PE devices detecting connectivity fault in VPLS service
and therefore also notifying the EMS/NMS. To prevent multiple
notifications for the same fault, (V)LAN emulation OAM should
provide alarm suppression capability in the VPLS service OAM.
(R15) PW OAM for PWs related to a (V)LAN emulation MUST support
interworking with VPLS service OAM to allow alarm suppression in the
VPLS service upon fault detection in (V)LAN emulation.
9. OAM Operational Scenarios
This section highlights how the different OAM mechanisms can be
applied as per the OAM framework for different L2VPN services.
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9.1. VPLS OAM Operational Scenarios
--- ---
/ \ ------ ------- ---- / \
| A CE-- / \ / \ / \ --CE A |
\ / \ / \ / \ / \ / \ /
--- --UPE NPE NPE UPE-- ---
\ / \ / \ /
\ / \ / \ /
------ ------- ----
Customer OAM domain
(C) MEP---MIP--------------------------------MIP---MEP
Service Provider(SP) OAM domain
(D) MEP--------MIP-----------MIP-------MEP
SP OAM SP OAM SP OAM
(D1) MEP-MIP--MEP|MEP-------MEP|MEP-----MEP
domain domain domain
Operator Operator Operator
(E) MEP-MIP--MEP|MEP-------MEP|MEP-----MEP
OAM domain OAM domain OAM domain
MPLS OAM MPLS OAM
(F) MEP--MIP-----MEP--MIP--MEP
domain domain
Figure 10: VPLS OAM Domains, MEPs & MIPs
Among the different MEs identified in Figure 5, for VPLS OAM in
Customer OAM domain, [IEEE 802.1ag] and [ITU-T Y.17ethoam] Ethernet
OAM mechanisms can be applied, to meet various requirements
identified in Section 6. The mechanisms can be applied across Figure
10 (C) MEs.
Similarly, inside the Service Provider OAM domain, [IEEE 802.1ag]
and [Y.17ethoam] Ethernet OAM mechanisms can be applied across
Figure 10 (D) MEs to meet functional requirements identified in
Section 6.
It may be noted that in the interim, when [IEEE 802.1ag] and
[Y.17ethoam] capabilities are not available across the PE devices,
the management option introduced in Section 5.2.3.2 can be applied,
with the limitations cited below. In this option, the Service
Provider can run segment OAM across the Figure 10 (D1) MEs. The OAM
mechanisms across the Figure 10 (D1) MEs can be non-Ethernet e.g.
[VCCV]/[BFD] when network technology is MPLS. The Service Provider
can monitor each sub-network segment ME using the native technology
OAM and by performing interworking across the segment MEs e.g. [OAM-
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MSG-MAP]/[OAM-INTERWORKING], attempt to realize end-to-end
monitoring between a pair of VPLS end-points. However, such
mechanisms do not fully utilize the data plane forwarding as
experienced by native (i.e. Ethernet) service PDUs and therefore
monitoring is severely limited in the sense that monitoring at
Figure 10 (D1) and interworking across them could lead to an
indication that the ME between VPLS end-points is functional while
the customer may be experiencing end-to-end connectivity issues in
the data plane.
Inside the Network Operator OAM domain, [IEEE 802.1ag] and
[Y.17ethoam] Ethernet OAM mechanisms can also be applied across
Figure 10 (E) MEs to meet functional requirements identified in
Section 6. In addition, the network operator could decide to use
native OAM mechanisms e.g. [VCCV]/[BFD] across Figure 10 (F) MEs for
additional monitoring or as an alternative to monitoring across
Figure 10 (E) MEs.
9.2. VPWS OAM Operational Scenarios
TBD
10. Acknowledgments
The authors would like to thank Deborah Brungard, Vasile Radoaca,
Lei Zhu, Yuichi Ikejiri, Yuichiro Wada, and Kenji Kumaki for their
reviews and comments.
Authors would also like to thank Shahram Davari, Norm Finn, Dave
Allan, Thomas Nadeau, Monique Morrow, Yoav Cohen, Marc Holness,
Malcolm Betts, Paul Bottorff, Hamid-ould Brahim, Lior Shabtay, and
Dan Cauchy for their feedback.
11. Security Considerations
Security issues resulting from this draft will be discussed in
greater depth at a later point. It is recommended in [RFC3036] that
LDP security (authentication) methods be applied. This would
prevent unauthorized participation by a PE in a VPLS. Traffic
separation for a VPLS is effected by using VC labels. However, for
additional levels of security, the customer MAY deploy end-to-end
security, which is out of the scope of this draft. In addition, the
L2FRAME] document describes security issues in greater depth.
12. Intellectual Property Considerations
This document is being submitted for use in IETF standards
discussions.
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13. Full Copyright Statement
Copyright (C) The Internet Society (2005).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (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.
14. IPR Notice
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
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rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
15. Normative References
[NM-Standards] "TMN Management Functions", M.3400, February 2000.
[RFC3036] "LDP Specification", RFC 3036, January 2001.
16. Informative References
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[PWE3-ETHERNET] "Encapsulation Methods for Transport of Ethernet
Frames Over IP/MPLS Networks", draft-ietf-pwe3-ethernet-encap-
08.txt, Work in progress, September 2004.
[L2VPN-REQ] "Service Requirements for Layer-2 Provider Provisioned
Virtual Private Networks", draft-ietf-l2vpn-requirements-02.txt,
Work in progress, September 2004.
[L2VPN-FRWK] "Framework for Layer 2 Virtual Private Networks
(L2VPNs)", draft-ietf-l2vpn-l2-framework-05.txt, Work in Progress,
June 2004.
[IEEE 802.1ad] "IEEE standard for Provider Bridges", Work in
Progress, July 2005.
[IEEE 802.1ah] "IEEE standard for Provider Backbone Bridges", Work
in Progress, July 2005.
[ROSEN-SIG] "Provisioning Models and Endpoint Identifiers in L2VPN
Signaling", draft-ietf-l2vpn-signaling-02.txt, Work in progress,
September 2004.
[VPLS-LDP] "Virtual Private LAN Services over MPLS",
draft-ietf-l2vpn-vpls-ldp-05.txt, Work in progress, September 2004.
[VPLS-BGP] "Virtual Private LAN Service",
draft-ietf-l2vpn-vpls-bgp-02.txt, Work in progress, May 2004.
[BRIDGE-INTEROP] "VPLS Interoperability with CE Bridges", draft-
sajassi-l2vpn-vpls-bridge-interop-01.txt, Work in progress, July
2005.
[PWE3-OAM] "PWE3 Applications and OAM Scenarios", draft-delord-pwe2-
oam-applications-01.txt, Work in progress, May 2005.
17. Authors' Addresses
Dinesh Mohan
Nortel
3500 Carling Ave
Ottawa, ON K2H8E9
Email: mohand@nortel.com
Ali Sajassi
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
Email: sajassi@cisco.com
Simon Delord
Uecomm
658 Church St
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Richmond, VIC, 3121, Australia
E-mail: sdelord@uecomm.com.au
Philippe Niger
France Telecom
2 av. Pierre Marzin
22300 LANNION, France
E-mail: philippe.niger@francetelecom.com
A1. Appendix 1 - Alternate Management Models
In consideration of the management models that can be deployed
besides the hierarchical models elaborated in this document, this
section highlights some alternate models that are not recommended
due to their limitations, as pointed out below. These alternatives
have been highlighted as potential interim models while the network
equipments are upgraded to support full functionality and meet the
requirements set forward by this document.
A1.1. Alternate Model 1 (Minimal OAM)
In this model, the end-to-end service monitoring is provided by
applying CE to CE ME in the Service Provider OAM Domain.
A MEP is located at each CE interface that is part of the VPWS
service, as shown in Figure A1.1 (B). The network operators can
carry out segment (e.g. PSN Tunnel ME, etc.) monitoring independent
of the VPWS end-to-end service monitoring, as shown in Figure A1.1
(D).
The advantage of this option is that VPWS service monitoring is
limited to CEs. The limitation of this option is that the
localization of faults at the VPWS Service level.
|<--------------- VPWS <AC1,PW,AC2> -------------->|
| |
| +----+ +----+ |
+----+ | |==================| | +----+
| |---AC1----|............PW..............|--AC2-----| |
| CE1| |PE1 | | PE2| |CE2 |
+----+ | |==================| | +----+
+----+ PSN Tunnel +----+
(B) MEP-----------------------------------------------MEP
(D) MEP-------MEP|MEP------------------MEP|MEP--------MEP
Figure A1.1: VPWS MEPs & MIPs - Minimal OAM
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A1.2. Alternate Model 2 (Segment OAM Interworking)
In this model, the end-to-end service monitoring is provided by
interworking OAM across each segment. Typical segments involved in
this case include two AC MEs and PW ME, as shown in Figure A1.2 (C).
These segments are expected in the Service Provider OAM Domain. An
interworking function is required to transfer the OAM information
flows across the OAM segments for the purposes of end-to-end
monitoring. Depending on whether homogenous VPWS is deployed or
heterogeneous VPWS is deployed, the interworking function could be
straightforward or more involved.
In this option, the CE and PE interfaces support MEPs for AC and PW
MEs and no MIPs are involved at the Service Provider OAM Level, as
shown in Figure A1.2 (C). The network operators may run segment OAM
by having MEPs at Network Operator OAM level, as shown in Figure
A1.2 (D).
The limitations of this model are that it requires interworking
across the OAM segments and does not conform to the OAM layering
principles, where each OAM layer ought to be independent of the
other. For end-to-end OAM determinations, the end-to-end service
frame path is not necessarily exercised. Further, it requires
interworking function implementation for all possible technologies
across access and core that may be used to realize end-to-end
services.
|<--------------- VPWS <AC1,PW,AC2> -------------->|
| |
| +----+ +----+ |
+----+ | |==================| | +----+
| |---AC1----|............PW..............|--AC2-----| |
| CE1| |PE1 | | PE2| |CE2 |
+----+ | |==================| | +----+
+----+ PSN Tunnel +----+
(C) MEP-------MEP|MEP------------------MEP|MEP--------MEP
(D) MEP-------MEP|MEP------------------MEP|MEP--------MEP
Figure A1.2: VPWS MEPs & MIPs - Segment OAM Interworking
