Layer 2 Virtual Private Network (L2VPN) Operations, Administration, and Maintenance (OAM) Requirements and Framework
draft-ietf-l2vpn-oam-req-frmk-11
The information below is for an old version of the document that is already published as an RFC.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 6136.
|
|
|---|---|---|---|
| Authors | Dinesh Mohan , Ali Sajassi | ||
| Last updated | 2015-10-14 (Latest revision 2010-10-24) | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Informational | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | (None) | |
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 6136 (Informational) | |
| Action Holders |
(None)
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||
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | Stewart Bryant | ||
| Send notices to | (None) |
draft-ietf-l2vpn-oam-req-frmk-11
Internet-Draft A. Sajassi (Editor)
L2VPN Working Group Cisco
Category: Informational
D. Mohan (Editor)
Expires: April 24, 2011 October 24, 2010
L2VPN OAM Requirements and Framework
draft-ietf-l2vpn-oam-req-frmk-11.txt
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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.
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.
When these key words are used in consideration of RFC 2119, these
key words are used in capitalized form as indicated above.
Table of Contents
Conventions used in this document.................................. 2
1. Introduction.................................................... 4
1.1 Relationship with Other OAM Work............................... 5
1.2 Terminology.................................................... 6
2. L2VPN Services & Networks....................................... 6
3. L2VPN OAM Framework............................................. 7
3.1. OAM Layering.................................................. 7
3.2. OAM Domains................................................... 8
3.3. MEPs and MIPs................................................. 9
3.4. MEP and MIP Identifiers...................................... 10
4. OAM Framework for VPLS......................................... 10
4.1. VPLS as Service/Network...................................... 10
4.1.1. VPLS as Bridged LAN Service................................ 10
4.1.2. VPLS as a Network.......................................... 11
4.1.3. VPLS as (V)LAN Emulation................................... 11
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4.2. VPLS OAM..................................................... 11
4.2.1. VPLS OAM Layering.......................................... 12
4.2.2. VPLS OAM Domains........................................... 13
4.2.3. VPLS MEPs & MIPs........................................... 13
4.2.4. VPLS MEP and MIP Identifiers............................... 14
5. OAM Framework for VPWS......................................... 14
5.1. VPWS as Service.............................................. 15
5.2. VPWS OAM..................................................... 15
5.2.1. VPWS OAM Layering.......................................... 16
5.2.2. VPWS OAM Domains........................................... 16
5.2.3. VPWS MEPs & MIPs........................................... 18
5.2.4. VPWS MEP and MIP Identifiers............................... 20
6. VPLS Service OAM Requirements.................................. 20
6.1. Discovery.................................................... 20
6.2. Connectivity Fault Management................................ 20
6.2.1. Connectivity Fault Detection............................... 21
6.2.2. Connectivity Fault Verification............................ 21
6.2.3. Connectivity Fault Localization............................ 21
6.2.4. Connectivity Fault Notification and Alarm Suppression...... 21
6.3. Frame Loss................................................... 21
6.4. Frame Delay.................................................. 22
6.5. Frame Delay Variation........................................ 22
6.6. Availability................................................. 22
6.7. Data Path Forwarding......................................... 23
6.8. Scalability.................................................. 23
6.9. Extensibility................................................ 23
6.10. Security.................................................... 24
6.11. Transport Independence...................................... 24
6.12. Application Independence.................................... 24
7. VPWS OAM Requirements.......................................... 25
7.1. Discovery.................................................... 25
7.2. Connectivity Fault Management................................ 25
7.2.1. Connectivity Fault Detection............................... 25
7.2.2. Connectivity Fault Verification............................ 26
7.2.3. Connectivity Fault Localization............................ 26
7.2.4. Connectivity Fault Notification and Alarm Suppression...... 26
7.3. Frame Loss................................................... 27
7.4. Frame Delay.................................................. 27
7.5. Frame Delay Variation........................................ 27
7.6. Availability................................................. 28
7.7. Data Path Forwarding......................................... 28
7.8. Scalability.................................................. 28
7.9. Extensibility................................................ 28
7.10. Security.................................................... 29
7.11. Transport Independence...................................... 29
7.12. Application Independence.................................... 30
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7.13. Prioritization.............................................. 30
8. VPLS (V)LAN Emulation OAM Requirements......................... 30
8.1. Partial-mesh of PWs.......................................... 30
8.2. PW Fault Recovery............................................ 31
8.3. Connectivity Fault Notification and Alarm Suppression........ 31
9. OAM Operational Scenarios...................................... 31
9.1. VPLS OAM Operational Scenarios............................... 31
10. Acknowledgments............................................... 33
12. IANA Considerations........................................... 33
11. Security Considerations....................................... 33
13. References.................................................... 33
13.1 Normative References......................................... 33
13.2 Informative References....................................... 34
A1. Appendix 1 - Alternate Management Models...................... 34
A1.1. Alternate Model 1 (Minimal OAM)............................. 34
A1.2. Alternate Model 2 (Segment OAM Interworking)................ 35
Authors' Addresses................................................ 36
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 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.
Fault Management can typically be viewed in terms of the following
categories:
- Fault Detection
- Fault Verification
- Fault Isolation
- Fault Notification & Alarm Suppression
- 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
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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 the level
of 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 devices
upstream and downstream to the fault detection point. For example,
when there is a client/server relationship between two layered
networks, Fault Detection at the server layer may result in the
following Fault Notifications:
- 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 data path using
alternate devices or links (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. 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 metrics 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.
[L2VPN-FRWK] specifies three different types of Layer 2 VPN
services. These are VPWS, VPLS and IPLS.
This document provides a reference model for OAM as it relates to
L2VPN services and their associated Pseudo Wires (PWs) and Public
Switched Network (PSN) tunnels. OAM requirement for L2VPN services
(e.g. VPLS and VPWS) are also identified. Furthermore, if L2VPN
services OAM requirements impose requirements for PW and/or PSN OAM,
those specific PW and/or PSN OAM requirements are also identified.
1.1 Relationship with Other OAM Work
This document leverages protocols, mechanisms and concepts defined
as part of other OAM work. More specifically:
IEEE Std. 802.1ag-2007 [IEEE 802.1ag] specifies the Ethernet
Connectivity Fault Management protocol, which defines the concepts
of Maintenance Domains, Maintenance End-Points and Maintenance
Intermediate Points. This standard also defines mechanisms and
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procedures for proactive fault detection (Continuity Check), fault
notification (Remote Defect Indication - RDI), fault verification
(Loopback) and fault isolation (LinkTrace) in Ethernet networks.
ITU-T Std. Y.1731 [Y.1731] builds upon and extends IEEE 802.1ag in
the following areas: it defines fault notification and alarm
suppression functions for Ethernet (via Alarm Indication Signal -
AIS). It also specifies messages and procedures for Ethernet
performance management, including loss, delay, jitter and throughput
measurement.
1.2 Terminology
This document introduces and uses the following terms. Further, this
document also uses the terms defined in [L2VPN-FRWK] and [L2VPN-
TERM].
AIS Alarm Indication Signal
FM Fault Management
IPLS IP-only LAN Service
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
OAM Domain OAM Domain represents a region over which OAM frames
can operate unobstructed
PM Performance Management
RDI Remote Defect Indication
SLA Service Level Agreement
STP Spanning Tree Protocols
VPLS Virtual Private LAN Service
VPWS Virtual Private Wire Service
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 members 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:
8 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.
8 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. A MEP on a PE receives messages from n-1 other
MEPs (some of them may reside on the same PE) for a given MEG.
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 attached CEs belonging to that service
instance. The reason it is called bridged LAN service is because the
VPLS-capable PE providing this end-to-end virtual LAN service is
performing bridging functions (either full or a subset) as described
in the [L2VPN-FRWK]. This VPLS definition, as specified in [L2VPN-
REQ], includes both bridge module and LAN emulation module (as
specified in [L2VPN-FRWK]).
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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 service instance
and its corresponding provider VLAN in the service provider Ethernet
network. To check the end-to-end service integrity, the OAM
mechanism needs to cover the end-to-end VPLS service as defined in
[L2VPN-REQ] which is from AC to AC including bridge module, VPLS
forwarder, and the associated PWs for this service. This draft
specifies the framework and requirements for such OAM mechanism.
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 (such as OAM for MPLS/IP networks) are needed. The
discussion of network-level OAM is outside of the scope of this
draft.
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 and its associated VPLS forwarder. Since the emulated LAN
segment is presented as a Virtual LAN (VLAN) to the bridge module of
a VPLS-capable PE, the emulated segment is also referred to as an
emulated VLAN. The OAM mechanisms in this context refer primarily to
integrity check of VPLS forwarders and its associated full-mesh of
PWs and the ability to detect and notify a partial mesh failure.
This draft also covers the OAM framework and requirements for such
OAM mechanism.
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
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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 [L2VPN-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
transparency of OAM mechanisms must be ensured over underlying
transport technologies such as MPLS, IP, etc.
This proposal is aligned with the discussions in other standard
bodies and groups such as ITU-T Q.5/13, IEEE 802.1, and MEF which
address 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 customer sites. 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.
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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 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. The MIP associated with (C) are
expected to be implemented in the bridge module/VPLS forwarder of a
PE device, as per the [L2VPN-FRWK]. (D) represents the MEPs and MIPs
visible within the service provider domain. These MEPs and MIPs are
expected to be implemented in the bridge module/VPLS forwarder of a
PE device, as per the [L2VPN-FRWK]. (E) represents the MEPs and MIPs
visible within each operator domain where MIPs only exist in an
Ethernet access network (e.g., an MPLS access network doesn't have
MIPs at the operator level). 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|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.,
802.1ad 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:
8 VPWS with homogeneous ACs (where both ACs are same type)
8 VPWS with heterogeneous ACs (where the ACs are of different
Layer-2 encapsulation)
Further, the VPWS can itself be classified as:
8 Homogeneous VPWS (when two ACs and PW are of the same type)
8 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 simply be a point-to-point interface such
as Ethernet PHY. The core network connecting PEs can be IP, MPLS,
etc.
Therefore, it is important that the OAM mechanisms can be applied to
different network types some of which are mentioned above. Each such
network may be associated with a separate administrative domain and
also multiple such networks may be associated with a single
administrative domain.
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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 a core network and two types of access network.
In the 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 PWs 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
5.2.2. VPWS OAM Domains
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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 the access network if the ACs are 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 the customer is
responsible for running end-to-end service OAM, if needed. The
service provider is responsible for monitoring the PW ME and the
monitoring of the AC is the shared responsibility of the customer
and the 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 an 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
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
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distinction between Figure 8b-(C) and 8(b)-D) is that in (C), MEs
have MEPs at CEs and at PEs, and have no MIPs. While in (D) MEs have
MEPs at CEs and at PEs and furthermore, MIPs may be present in
between the MEPs; thereby, providing visibility of the network to
the operator.
|<--------------- 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
Note: It may be noted that unlike VPLS OAM Domain in Figure 4, where
multiple operator domains may occur between the U-PE devices, VPWS
OAM domain in Figure 8a and 8b highlight a single Operator domain
between PE devices. This is since unlike the distributed VPLS PE
case (H-VPLS) where VPLS service aware U-PEs and N-PEs may be used
to realize a distributed PE, the VPWS has no such distributed PE
model. If the PSN involves multiple Operator domains, resulting in a
Multi-segment PW [Ms-PW Arch], VPWS OAM Domains remain unchanged
since S-PEs are typically not aware of native service.
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 areas within
the network.
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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 the end-to-end Service Provider
OAM level for VPWS as an end-to-end service as shown in Figure 9
(B1) and (B2). In addition, PE interfaces may support MIPs at end-
to-end Service Provider OAM level when PEs are client service aware,
as shown in Figure 9 (B2). As an example, if one considers an end-
to-end Ethernet line service offered to a subscriber between CE1 and
CE2 which is realized via ATM type AC1 and AC2 and PW which
encapsulates ATM over MPLS, 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 having layered OAM 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.
Although many different OAM layers are possible, as shown in Figure
9, not all may be realized. For example, Figure (B2) and (D) may be
adequate in some cases.
|<--------------- 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
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Figure 9: VPWS MEPs & MIPs
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.
6. VPLS Service OAM Requirements
These requirements are applicable to VPLS PE offering VPLS as an
Ethernet Bridged LAN service, as described in Section 4.1.1.
Further, the performance metrics used in requirements are based on
[MEF10.1] and [RFC2544].
It is noted that OAM solutions that meet the following requirements
may make use of existing OAM mechanisms e.g. Ethernet OAM, VCCV,
etc. however must not break these existing OAM mechanisms. If
extensions are required to existing OAM mechanisms, these should be
coordinated with relevant groups responsible for these OAM
mechanisms.
6.1. Discovery
Discovery allows a VPLS service aware device to learn about other
devices that support the same VPLS service instance within a given
domain.
Discovery also allows a VPLS service aware device to learn
sufficient information (e.g. IP addresses, MAC addressed etc.) from
other VPLS service aware devices such that VPLS OAM frames can be
exchanged among the service aware devices.
(R1) VPLS OAM MUST allow a VPLS service aware device to discover
other devices that share the same VPLS service instance(s) within a
given OAM domain.
6.2. Connectivity Fault Management
VPLS service is realized by exchanging service frames/packets
between devices that support the same VPLS service instance. To
allow the exchange of service frames, connectivity between these
service aware devices is required.
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6.2.1. Connectivity Fault Detection
To ensure service, pro-active connectivity monitoring is required.
Connectivity monitoring facilitates connectivity fault detection.
(R2a) VPLS OAM MUST allow pro-active connectivity monitoring between
two VPLS service aware devices that support the same VPLS service
instance within a given OAM domain.
6.2.2. Connectivity Fault Verification
Once a connectivity fault is detected, connectivity fault
verification may be performed.
(R2b) VPLS OAM MUST allow connectivity fault verification between
two VPLS service aware devices that support the same VPLS service
instance within a given OAM domain.
6.2.3. Connectivity Fault Localization
Further, localization of connectivity fault may be carried out.
(R2c) VPLS OAM MUST allow connectivity fault localization between
two VPLS service aware devices that support the same VPLS service
instance within a given OAM domain.
6.2.4. Connectivity Fault Notification and Alarm Suppression
Typically, when connectivity fault is detected and optionally
verified, VPLS service device may notify the NMS (Network Management
System) via alarms.
However, a single transport/network fault may cause multiple
services to fail simultaneously causing multiple service alarms.
Therefore, VPLS OAM must allow service level fault notification to
be triggered at the client layer as a result of transport/network
faults in the service layer. This fault notification should be used
for the suppression of service level alarms at the client layer.
(R2d) VPLS OAM MUST support fault notification to be triggered as a
result of transport/network faults. This fault notification SHOULD
be used for the suppression of redundant service level alarms.
6.3. Frame Loss
A VPLS service may be considered degraded if service-layer
frames/packets are lost during transit between the VPLS service
aware devices. To determine if a VPLS service is degraded due to
frame/packet loss, measurement of frame/packet loss is required.
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(R3) VPLS OAM MUST support measurement of per-service frame/packet
loss between two VPLS service aware devices that support the same
VPLS service instance within a given OAM domain.
6.4. Frame Delay
A VPLS service may be sensitive to delay experienced by the VPLS
frames/packets during transit between the VPLS service aware
devices. To determine if a VPLS service is degraded due to
frame/packet delay, measurement of frame/packet delay is required.
VPLS 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) VPLS OAM MUST support measurement of per-service two-way
frame/packet delay between two VPLS service aware devices that
support the same VPLS service instance within a given OAM domain.
(R4b) VPLS OAM SHOULD support measurement of per-service one-way
frame/packet delay between two VPLS service aware devices that
support the same VPLS service instance within a given OAM domain.
6.5. Frame Delay Variation
A VPLS service may be sensitive to delay variation experienced by
the VPLS frames/packets during transit between the VPLS service
aware devices. To determine if a VPLS 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) VPLS OAM MUST support measurement of per-service frame/packet
delay variation between two VPLS service aware devices that support
the same VPLS service instance within a given OAM domain.
6.6. Availability
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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.
6.7. Data Path Forwarding
If the VPLS OAM frames flow across a different path than the one
used by VPLS 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 VPLS service frames/packets, must be
used for the VPLS OAM.
(R6) VPLS OAM frames MUST be forwarded along the same path (i.e.
links and nodes) as the VPLS service/data frames.
6.8. Scalability
Mechanisms developed for VPLS OAM need to be such that per-service
OAM can be supported even though the OAM may only be used for
limited VPLS service instances, e.g. premium VPLS service instances,
and may not be used for best-effort VPLS services.
(R7) VPLS OAM MUST be scalable such that a service aware device can
support OAM for each VPLS service that is supported by the device.
6.9. Extensibility
Extensibility is intended to allow introduction of additional OAM
functionality in future such that backward compatibility can be
maintained when interoperating with older version devices. In such a
case, VPLS OAM with reduced functionality should still be possible.
Further, VPLS Service OAM should be defined such that OAM incapable
devices in the middle of the OAM domain should be able to forward
the VPLS OAM frames similar to the regular VPLS service/data
frames/packets.
(R8a) VPLS OAM MUST be extensible such that new functionality and
information elements related to this functionality can be introduced
in future.
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(R8b) VPLS 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 VPLS service/data frames/packets.
6.10. Security
VPLS 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) VPLS OAM frames MUST be prevented from leaking outside their
OAM domain.
(R9b) VPLS 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) VPLS 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.
6.11. Transport Independence
VPLS 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, VPLS OAM must be independently supported as many
different transport/network technologies can be used to carry
service frame/packets.
(R10a) VPLS OAM MUST be independent of the underlying
transport/network technologies and specific transport/network OAM
capabilities.
(R10b) VPLS 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 the VPLS service layer.
6.12. Application Independence
VPLS 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
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used to carry IP traffic; however, VPLS OAM should not assume IP or
rely on the use of IP level OAM functions.
(R11a) VPLS OAM MUST be independent of the application technologies
and specific application OAM capabilities.
7. VPWS OAM Requirements
These requirements are applicable to VPWS PE. The performance
metrics used in requirements are based on [MEF10.1] and [RFC2544],
which are applicable to Ethernet Services.
It is noted that OAM solutions that meet the following requirements
may make use of existing OAM mechanisms e.g. Ethernet OAM, VCCV,
etc. however must not break these existing OAM mechanisms. If
extensions are required to existing OAM mechanisms, these should be
coordinated with relevant groups responsible for these OAM
mechanisms.
7.1. Discovery
Discovery allows a VPWS service aware device to learn about other
devices that support the same VPWS service instance within a given
domain. Discovery also allows a VPWS service aware device to learn
sufficient information (e.g. IP addresses, MAC addresses etc.) from
other VPWS service aware devices such that OAM frames can be
exchanged among the VPWS service aware devices.
(R12) VPWS OAM MUST allow a VPWS service aware device to discover
other devices that share the same VPWS service instance(s) within a
given OAM domain.
7.2. Connectivity Fault Management
VPWS Service is realized by exchanging service frames/packets
between devices that support the same VPWS service instance. To
allow the exchange of service frames, connectivity between these
service aware devices is required.
7.2.1. Connectivity Fault Detection
To ensure service, pro-active connectivity monitoring is required.
Connectivity monitoring facilitates connectivity fault detection.
(R13a) VPWS OAM MUST allow pro-active connectivity monitoring
between two VPWS service aware devices that support the same VPWS
service instance within a given OAM domain.
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(R13b) VPWS OAM mechanism SHOULD allow detection of misbranching or
misconnections.
7.2.2. Connectivity Fault Verification
Once a connectivity fault is detected, connectivity fault
verification may be performed.
(R13c) VPWS OAM MUST allow connectivity fault verification between
two VPWS service aware devices that support the same VPWS service
instance within a given OAM domain.
7.2.3. Connectivity Fault Localization
Further, localization of connectivity fault may be carried out. This
may amount to identifying the specific AC and/or PW that is
resulting in the VPWS connectivity fault.
(R13d) VPWS OAM MUST allow connectivity fault localization between
two VPWS service aware devices that support the same VPWS service
instance within a given OAM domain.
7.2.4. Connectivity Fault Notification and Alarm Suppression
Typically, when connectivity fault is detected and optionally
verified, service device may notify the NMS (Network Management
System) via alarms.
However, a single transport/network fault may cause multiple
services to fail simultaneously causing multiple service alarms.
Therefore, OAM must allow service level fault notification to be
triggered at the client layer as a result of transport/network
faults in the service layer. This fault notification should be used
for the suppression of service level alarms at the client layer.
For example, if an AC fails, both local CE and local PE which are
connected via AC may detect the connectivity failure. The local CE
must notify the remote CE about the failure while the local PE must
notify the remote PE about the failure.
(R13e) VPWS OAM MUST MUST support fault notification to be triggered
as a result of transport/network faults. This fault notification
SHOULD be used for the suppression of redundant service level
alarms.
(R13f) VPWS OAM SHOULD support fault notification in backward
direction, to be triggered as a result of transport/network faults.
This fault notification SHOULD be used for the suppression of
redundant service level alarms.
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7.3. Frame Loss
A VPWS service may be considered degraded if service-layer
frames/packets are lost during transit between the VPWS service
aware devices. To determine if a VPWS service is degraded due to
frame/packet loss, measurement of frame/packet loss is required.
(R14) VPWS OAM MUST support measurement of per-service frame/packet
loss between two VPWS service aware devices that support the same
VPWS service instance within a given OAM domain.
7.4. Frame Delay
A VPWS service may be sensitive to delay experienced by the VPWS
service frames/packets during transit between the VPWS service aware
devices. To determine if a VPWS service is degraded due to
frame/packet delay, measurement of frame/packet delay is required.
VPWS 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.
(R15a) VPWS OAM MUST support measurement of per-service two-way
frame/packet delay between two VPWS service aware devices that
support the same VPWS service instance within a given OAM domain.
(R15b) VPWS OAM SHOULD support measurement of per-service one-way
frame/packet delay between two VPWS service aware devices that
support the same VPWS service instance within a given OAM domain.
7.5. Frame Delay Variation
A VPWS service may be sensitive to delay variation experienced by
the VPWS frames/packets during transit between the VPWS service
aware devices. To determine if a VPWS 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.
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(R16) VPWS OAM MUST support measurement of per-service frame/packet
delay variation between two VPWS service aware devices that support
the same VPWS service instance within a given OAM domain.
7.6. 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.
7.7. Data Path Forwarding
If the VPWS OAM frames flow across a different path than the one
used by VPWS 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 VPWS service frames/packets, must be
used for the VPWS OAM.
(R17a) VPWS OAM frames MUST be forwarded along the same path as the
VPWS service/data frames.
(R17b) VPWS OAM MUST be forwarded using the transfer plane (data
plane) as regular VPWS service/data frames/packets and must not rely
on control plane messages.
7.8. Scalability
Mechanisms developed for VPWS OAM need to be such that per-service
OAM can be supported even though the OAM may only be used for
limited VPWS service instances, e.g. premium VPWS service instance,
and may not be used for best-effort services.
(R18) VPWS OAM MUST be scalable such that a service aware device can
support OAM for each VPWS service that is supported by the device.
7.9. Extensibility
Extensibility is intended to allow introduction of additional OAM
functionality in future such that backward compatibility can be
maintained when interoperating with older version devices. In such a
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case, VPWS service OAM with reduced functionality should still be
possible. Further, VPWS service OAM should be such that OAM
incapable devices in the middle of the OAM domain should be able to
forward the VPWS OAM frames similar to the regular VPWS service/data
frames/packets.
(R19a) VPWS OAM MUST be extensible such that new functionality and
information elements related to this functionality can be introduced
in future.
(R19b) VPWS OAM MUST be defined such that devices not supporting the
OAM are able to forward the VPWS OAM frames in a similar fashion as
the regular VPWS service/data frames/packets.
7.10. Security
VPWS 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 VPWS
OAM frames are prevented from leaking outside their domain. Also,
VPWS 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).
(R20a) VPWS OAM frames MUST be prevented from leaking outside their
OAM domain.
(R20b) VPWS 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.
(R20c) VPWS 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.
7.11. Transport Independence
VPWS 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, VPWS OAM must be independently supported as many
different transport/network technologies can be used to carry
service frame/packets.
(R21a) VPWS OAM MUST be independent of the underlying
transport/network technologies and specific transport/network OAM
capabilities.
(R21b) VPWS OAM MAY allow adaptation/interworking with specific
transport/network OAM functions. For example, this would be useful
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to allow Fault Notifications from transport/network layer(s) to be
sent to the VPWS service layer.
7.12. Application Independence
VPWS service itself may be used to carry application frame/packets.
The application may use its own OAM; VPWS OAM must not be dependent
on application OAM. As an example, a VPWS service may be used to
carry IP traffic; however, VPWS OAM should not assume IP or rely on
the use of IP level OAM functions.
(R22a) OAM MUST be independent of the application technologies and
specific application OAM capabilities.
7.13. Prioritization
VPWS service could be composed of several data flows each related to
a given usage/application with specific requirements in term of
connectivity and/or performances. Dedicated VPWS OAM should be
applicable to these flows.
(R23) VPWS OAM SHOULD support configurable prioritization for OAM
packet/frames to be compatible with associated VPWS service
packets/frames.
8. VPLS (V)LAN Emulation OAM Requirements
8.1. 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 PWs should be
shutdown such that the remaining PWs have full connectivity among
them, when partial VPLS service is acceptable.
(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 MUST 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.
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Note: Shutdown action in R13b and R13c may not necessarily involve
withdrawal of labels etc.
8.2. 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.
8.3. Connectivity Fault Notification and Alarm Suppression
When connectivity fault is detected in (V)LAN emulation, PE devices
may notify the NMS (Network Management System) via alarms. 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 NMS. To prevent multiple alarms for the same
fault, (V)LAN emulation OAM must 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 trigger fault notification and
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.
9.1. VPLS OAM Operational Scenarios
--- ---
/ \ ------ ------- ---- / \
| A CE-- / \ / \ / \ --CE A |
\ / \ / \ / \ / \ / \ /
--- --UPE NPE NPE UPE-- ---
\ / \ / \ /
\ / \ / \ /
------ ------- ----
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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 [Y.1731] 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.1731] 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.1731] capabilities are not available across the PE devices, the
fault management option using segment OAM introduced in Section
5.2.3 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, or 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, 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.1731]
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
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mechanisms e.g. VCCV or BFD across Figure 10 (F) MEs for additional
monitoring or as an alternative to monitoring across Figure 10 (E)
MEs.
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.
12. IANA Considerations
This document has no actions for IANA.
11. Security Considerations
This document takes into account the security considerations and
imposes requirements on solutions to prevent OAM messages from
leaking outside an OAM domain and for OAM domains to be transparent
to OAM frames from higher OAM domains, as specified in Section 6.10
and 7.10.
For additional levels of security, the solutions may be required to
encrypt and/or authenticate OAM frames inside an OAM domain however
solutions are out of the scope of this draft.
13. References
13.1 Normative References
[IEEE 802.1ad] "IEEE Standard for Local and metropolitan area
networks - virtual Bridged Local Area Networks, Amendment 4:
Provider Bridges", 2005
[IEEE 802.1ag] "IEEE Standard for Local and metropolitan area
networks - virtual Bridged Local Area Networks, Amendment 5:
Connectivity Fault Management", 2007
[IEEE 802.1ah] "IEEE Standard for Local and metropolitan area
networks - virtual Bridged Local Area Networks, Amendment 6:
Provider Backbone Bridges", 2008
[Y.1731] "ITU-T Recommendation Y.1731 (02/08) - OAM functions and
mechanisms for Ethernet based networks", February 2008
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[L2VPN-FRWK] "Framework for Layer 2 Virtual Private Networks
(L2VPNs)", RFC 4664
[L2VPN-REQ] "Service Requirements for Layer-2 Provider Provisioned
Virtual Private Networks", RFC 4665
[L2VPN-TERM] "Provider Provisioned Virtual Private Network (VPN)
Terminology", RFC 4026
[MEF10.1] "Ethernet Services Attributes: Phase 2", MEF 10.1, 2006
[NM-Standards] "TMN Management Functions", M.3400, February 2000
[VPLS-BGP] "Virtual Private LAN Service", RFC 4761, Jan 2007
[VPLS-LDP] "Virtual Private LAN Services over MPLS", RFC 4762, Jan
2007
13.2 Informative References
[BRIDGE-INTEROP] "VPLS Interoperability with CE Bridges", draft-
ietf-l2vpn-vpls-bridge-interop-05.txt, Work in progress, March 2010
[L2VPN-SIG] "Provisioning, Autodiscovery, and Signaling in L2VPNs",
draft-ietf-l2vpn-signaling-08.txt, Work in progress, May 2006
[MS-PW Arch] "An Architecture for Multi-segment Pseudowire Emulation
Edge-to-Edge", draft-ietf-pwe3-ms-pw-arch-04.txt, Work in progress,
June 2008
[RFC2544] "Benchmarking Methodology for Network Interconnect
Devices", RFC 2544, 1999
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.
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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
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.
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|<--------------- 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
Authors' Addresses
Ali Sajassi
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
Email: sajassi@cisco.com
Dinesh Mohan
Nortel
3500 Carling Ave
Ottawa, ON K2H8E9
Email: mohand@nortel.com
Simon Delord
Uecomm
658 Church St
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
Samer Salam
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
Email: ssalam@cisco.com
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