Network Working Group Loa Andersson, Ed.
Internet Draft Acreo AB
Intended status: Informational Lou Berger, Ed.
Expires: August 22, 2008 LabN
Luyuan Fang, Ed.
Cisco
Nabil Bitar, Ed.
Verizon
February 22, 2009
MPLS-TP Control Plane Framework
draft-abfb-mpls-tp-control-plane-framework-00.txt
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Abstract
The MPLS Transport Profile (MPLS-TP) supports both static
provisioning of transport paths via an NMS/OSS, and dynamic
provisioning of transport paths via a control plane. This
document provides the framework for MPLS-TP dynamic
provisioning, and covers control plane signaling, routing,
addressing, traffic engineering, path computation, and
recovery in the event of network failures. The document
focuses on the control of Label Switched Paths (LSPs) as the
Pseudowire (PW) control plane is not modified by MPLS-TP.
MPLS-TP uses GMPLS as the control plane for MPLS-TP LSPs.
Backwards compatibility to MPLS is required. Management plane,
manual configuration, the triggering of LSP setup, label
allocation schemes, and hybrid services are out of scope of
this document.
Table of Contents
1. Introduction...............................................3
1.1. Scope.................................................3
1.2. Basic Approach........................................4
1.3. Reference Model.......................................5
2. Control plane requirements.................................7
2.1. Primary Requirements..................................8
2.2. MPLS-TP Framework Derived Requirements...............12
2.3. OAM Framework Derived Requirements...................13
2.4. Security Requirements................................13
3. TE LSPs...................................................14
3.1. General reuse of existing GMPLS control plane
mechanisms................................................14
3.1.1. "In-band" and "out of band".....................14
3.1.2. Addressing......................................15
3.2. Signaling............................................16
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3.3. Routing..............................................17
3.3.1. ISIS-TE/OSPF-TE routing in support of MPLS-TP...17
3.3.1.1. ISIS-TE/OSPF-TE routing for MPLS-TP........18
3.3.1.2. Multiple Switching Capabilities............18
3.3.1.3. Hierarchy..................................18
3.3.2. TE link bundling................................19
3.4. OAM, MEP (hierarchy) configuration & control.........19
3.5. Traffic engineering and constraint-based path
computation...............................................20
3.5.1. Relation to PCE.................................20
3.6. Applicability........................................21
3.7. Recovery.............................................21
3.7.1. E2E, segment....................................21
3.7.2. P2P, P2MP.......................................21
3.8. Diffserv object usage in GMPLS (E-LSPs, L-LSPs)......21
3.9. Management plane support.............................21
3.10. CP reference points (E-NNI, I-NNI, UNI).............21
3.11. MPLS to MPLS-TP interworking........................21
4. Pseudo Wires..............................................21
4.1. General reuse of existing PW control plane mechanisms24
4.2. Signaling............................................24
4.3. Recovery (Redundancy)................................24
5. Security Considerations...................................24
6. IANA Considerations.......................................25
7. Acknowledgments...........................................25
8. References................................................25
Normative References.....................................25
8.1.......................................................25
8.2. Informative References...............................27
9. Authors' Addresses........................................28
1. Introduction
The MPLS Transport Profile (MPLS-TP) is being defined in a joint
effort between the International Telecommunications Union (ITU)
and the IETF. The requirements for MPLS-TP are defined in the
requirements document, see [TP-REQ]. These requirements state
that "A solution MUST be provided to support dynamic
provisioning of MPLS-TP transport paths via a control plane."
This document provides the framework for such dynamic
provisioning.
1.1. Scope
This document covers control plane related topics for MPLS-TP
Label Switched Paths (LSPs) and Pseudowire (PW). The control
plane requirements for MPLS-TP are defined in [TP-REQ]. These
requirements defined the role of the control plane in MPLS-TP.
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In particular, Sections 2.4 and 2.8 of [TP-REQ] provide specific
control plane requirements.
The LSPs provided by MPLS-TP are used as a server layer for IP,
MPLS and PWs, as well as other MPLS-TP LSPs. The PWs are used to
carry client signal other than IP and MPLS. The relationship
between pseudo wires carried and MPLS-TP LSPs is exactly the
same as between pseudo wires and MPLS LSPs in a Packet switched
network (PSN). The PW encapsulation over MPLS-TP LSPs used in
MPLS-TP networks is the same as for PWs over MPLS in an MPLS
network. MPLS-TP also defines protection and restoration (or,
collectively, recovery) functions. The MPLS-TP control plane
provides methods to establish, remove and control MPLS-TP LSP
and PW functions. This includes control of data plane, OAM and
recovery functions.
A general framework for MPLS-TP has been defined in [TP-FWK],
and a survivability framework for MPLS-TP has been defined in
[TP-SURVIVE]. These document scopes the approaches and protocols
that will be used as the foundation for MPLS-TP. Notably,
Section 3.5 of [TP-FWK] scopes the IETF protocols that serve as
the foundation of the MPLS-TP control plane. The PW control
plane is based on the existing PW control plane, see [RFC4447],
and the PW end-to-end (PWE3) architecture, see [RFC3985]. The
LSP control plane is based on Generalized MPLS (GMPLS), see
[RFC3945], which is built on MPLS-TE and its numerous
extensions. [TP-SURVIVE] focuses on LSPs, and the protection
functions that must be supported within MPLS-TP. It does not
specify which control plane mechanisms to be used.
This document discusses the impact of MPLS-TP requirements on
the signaling that is used to provision pseudo wires as
specified in RFC4447. This document also discusses the impact of
the MPLS-TP requirements on the GMPLS signaling and routing
protocols that is used to provision MPLS-TP LSPs.
1.2. Basic Approach
The basic approach taken in defining the MPLS-TP Control Plane
framework is:
1) MPLS technology as defined by the IETF is the foundation for
the MPLS Transport Profile.
2) The data plane for MPLS and MPLS-TP is identical, i.e. any
extensions defined for MPLS-TP is also applicable to MPLS.
And the same encapsulation used for MPLS over any layer 2
network is also used for MPLS-TP.
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3) MPLS PWs are used as-is by MPLS-TP including the use of
targeted-LDP for PW signaling [RFC4447], OSPF-TE, ISIS-TE or
MP-BGP as they apply for (MS)-PW routing. However, the PW can
be encapsulated over an MPLS-TP LSP in (established using
methods and procedures for MPLS-TP LSP establishment) in
addition to the present defined methods of carrying PWs over
packet switched networks (PSNs). That is, the MPLS-TP domain
is a packet switched network from PWE3 architecture aspect
[RFC3985].
4) The MPLS-TP LSP control plane builds on the GMPLS control
plane as defined by the IETF for transport LSPs, the
protocols within scope are RSVP-TE [RFC3473], OSPF-TE
[RFC4203][RFC5392], and ISIS-TE [RFC5307][RFC5316].
5) Existing IETF MPLS and GMPLS RFCs and evolving Working Group
Internet-Drafts should be reused wherever possible.
6) If needed, extensions for the MPLS-TP control plane should
first based on the existing and evolving IETF work, secondly
based on work by other Standard bodies only when IETF decides
that the work is out of IETF scope. New extensions may be
defined otherwise.
7) Extensions to the GMPLS control plane may be required in
order to fully automate MPLS-TP functions.
8) Control-plane software upgrades to existing equipment running
MPLS is acceptable and expected.
9) It is permissible for functions present in the GMPLS control
plane not to be used in MPLS-TP networks, e.g. the
possibility to merge LSPs.
10)
One possible use of the control plane is to configure, enable
and empower OAM functionality; this will require extensions
to existing control plane specifications.
1.3. Reference Model
The control plane reference model is based on the general MPLS-
TP reference model as defined in MPLS-TP framework [TP-FWK]. Per
MPLS-TP framework [TP-FWK], MPLS-TP control plane is based on
GMPLS with RSVP-TE for LSP signaling and LDP for PW signaling.
In both cases, OSPF-TE or ISIS-TE is used for dynamic routing.
From a service perspective, client interfaces are provided for
both the PWs and LSPs. PW client interfaces are defined on an
interface technology basis, e.g., Ethernet over PW [RFC4448]. In
the context of MPLS-TP LSP, the client interface is expected to
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be provided via a UNI, [RFC4208]. As discussed in [TP-FWK],
MPLS-TP also presumes an LSP NNI reference point.
The MPLS-TP end-to-end control plane reference model is shown in
Figure 1. It shows the control plane protocols used by MPLS-TP,
as well as the UNI and NNI reference points.
|< ---- client signal (IP / MPLS / L2 / PW) ------------ >|
|< --------- SP1 ----------- >|< ------- SP2 ------- >|
|< ---------- MPLS-TP End to End PW ------------ >|
|< -------- MPLS-TP End to End LSP --------- >|
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
|CE1|-|-|PE1|--|P1 |--|P2 |--|PE2|-|-|PEa|--|Pa |--|PEb|-|-|CE2|
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
UNI NNI UNI
TE-RTG |< ---------------- >|< --- >|< ---------- >|
RSVP-TE
LDP |< --------------------------------------- >|
Figure 1. End-to-End MPLS-TP Control Plane Reference Model
Legend:
CE: Customer Edge
Client signal: defined in MPLS-TP Requirements
L2: Any layer 2 signal that may be carried
over a PW, e.g. Ethernet.
NNI: Network to Network Interface
PE: Provider Edge
SP: Service Provider
TE-RTG: OSPF-TE or ISIS-TE
Figure 2 adds three hierarchical LSP segments, labeled as "H-
LSPs". These segments are present to support OAM and MEPs within
each provider and across the inter-provider NNI. The MEPs are
used to collect performance information and support OAM
triggered survivability schemes as discussed in [TP-SURVIVE],
and each H-LSP may be protected using any of the schemes
discussed in [TP-SURVIVE].
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|< ------- client signal (IP / MPLS / L2 / PW) ------ >|
|< -------- SP1 ----------- >|< ------- SP2 ----- >|
|< ----------- MPLS-TP End to End PW -------- >|
|< ------- MPLS-TP End to End LSP ------- >|
|< -- H-LSP1 ---- >|<-H-LSP2->|<- H-LSP3 ->|
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
|CE1|-|-|PE1|--|P1 |--|P2 |--|PE2|-|-|PEa|--|Pa |--|PEb|-|-|CE2|
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
UNI NNI UNI
..... ..... ..... ......... ......... ..... .....
|MEP|-|MIP|-|MIP|-|MEP|MEP|-|MEP|MEP|-|MIP|-|MEP|
''''' ''''' ''''' ''''''''' ''''''''' ''''' '''''
TE-RTG |< -- >|< -- >|< -- >||< -- >||< -- >|< -- >|
RSVP-TE (within the MPLS-TP domain)
TE-RTG |< ---------------- >|< ---- >|< --------- >|
RSVP-TE
LDP |< --------------------------------------- >|
Figure 2. MPLS-TP Control Plane Reference Model with OAM
Legend:
CE: Customer Edge
Client signal: defined in MPLS-TP Requirements
L2: Any layer 2 signal that may be carried
over a PW, e.g. Ethernet.
H-LSP: Hierarchical LSP
MEP: Maintenance end points
MIP: Maintenance intermediate points
NNI: Network to Network Interface
PE: Provider Edge
SP: Service Provider
TE-RTG: OSPF-TE or ISIS-TE
While not shown in the Figures above, it is worth noting that
the MPLS-TP control plane must support the addressing separation
and independence between the data, control and management planes
as shown in Figure 3 of [TP-FWK]. Address separation between
the planes is already included in GMPLS.
2. Control plane requirements
The requirements for the MPLS-TP control plane are derived from
the MPLS-TP requirements and framework documents, specifically
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[TP-REQ], [TP-FWK], [TP-OAM], and [TP-SURVIVE]. The
requirements are summarized in this section, but do not replace
those documents. If there are differences between this section
and those documents, those documents shall be considered
authoritative.
2.1. Primary Requirements
These requirements are based on [TP-REQ]:
1. The MPLS-TP control plane must be able to interoperate
with existing IETF MPLS control planes where appropriate.
2. The MPLS-TP control plane must support a connection-
oriented packet switching model with traffic engineering
capabilities.
3. The MPLS-TP control plane must support traffic engineered
point to point (P2P) and point to multipoint (P2MP)
transport paths.
4. The MPLS-TP control plane must support the logical
separation of the control and management planes from the
data plane.
5. The MPLS-TP control plane must support the physical
separation of the control and management planes from the
data plane.
6. A control plane must be defined for MPLS-TP, but its use
is a network operator's choice.
7. A failure of the control plane must not interfere with the
deliver of service or recovery of established transport
paths.
8. The MPLS-TP control plane must work across domains.
9. The MPLS-TP control plane must not dictate any particular
physical or logical topology, and must include support
ring topologies.
10. The MPLS-TP control plane must not provision transport
paths which contain forwarding loops.
11. The MPLS-TP control plane must support multiple client
layers.
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12. The MPLS-TP control plane must be able to operate
independently over server layer networks.
13. The MPLS-TP control plane must allow a server layer to
hide addressing and topology information form a client
layer.
14. The MPLS-TP control plane must allow for the
identification of a transport path on each link and at the
destination.
15. The MPLS-TP control plane must allow for P2MP capable
server (sub-)layers.
16. The MPLS-TP control plane must support unidirectional,
bidirectional and co-routed bidirectional point-to-point
transport paths.
17. Intermediate nodes must be aware about the pairing
relationship of the forward and the backward directions
belonging to the same bidirectional transport path.
18. The MPLS-TP control plane may support transport paths with
asymmetric bandwidth requirements.
19. The MPLS-TP control plane must support unidirectional
point-to-multipoint transport paths.
20. The MPLS-TP control plane should support bandwidth
modification.
21. The MPLS-TP control plane must support scale gracefully to
support a large number of transport paths, nodes and
links.
22. The MPLS-TP control plane must support configuration of
protection functions and any associated maintenance (OAM)
functions.
23. The MPLS-TP control plane must support the configuration
and modification of OAM maintenance points as well as the
activation/deactivation of OAM when the transport path or
transport service is established or modified.
24. The MPLS-TP control plane must support protection and
restoration mechanisms, i.e., recovery.
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Note that the MPLS-TP Survivability Framework document, [TP-
SURVIVE], provides additional useful information related to
recovery.
25. The MPLS-TP control plane mechanisms used for P2P and P2MP
recovery should identical.
26. The MPLS-TP control plane must support recovery mechanisms
that are applicable at various levels throughout the
network including support for link, path segment and end-
to-end path, and pseudowire segment, and end-to-end
pseudowire recovery.
27. The MPLS-TP control plane must support recovery paths that
meet the SLA protection objectives of the service.
Including:
a. Guarantee 50ms recovery times from the moment of fault
detection in networks with spans less than 1200 km.
b. Protection of 100% of the traffic on the protected
path.
c. Objectives SHOULD be configurable per transport path,
and SHOULD include bandwidth and QoS.
28. The MPLS-TP control plane must support recovery mechanisms
that are applicable to any topology.
29. The MPLS-TP control plane must operate in synergy with
(including coordination of timing) the recovery mechanisms
present in any underlying server transport network (for
example, Ethernet, SDH, OTN, WDM) to avoid race conditions
between the layers.
30. The MPLS-TP control plane must support priority logic to
negotiate and accommodate coexisting requests (i.e.,
multiple requests) for protection switching (e.g.,
administrative requests and requests due to link/node
failures).
31. The MPLS-TP control plane must support recovery and
reversion mechanisms that prevent frequent operation of
recovery in the event of an intermittent defect.
32. The MPLS-TP control plane must support 1+1 protection for
P2P LSPs.
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33. The MPLS-TP control plane must support 1+1 unidirectional
protection for P2MP LSPs.
34. The MPLS-TP control plane must support 1:n protection for
P2P LSPs.
35. The MPLS-TP control plane must support 1:n unidirectional
protection for P2MP LSPs.
36. The MPLS-TP control plane must support the sharing of
resources between a restoration LSP and the LSP being
replaced.
37. The MPLS-TP control plane must support restoration
priority.
38. The MPLS-TP control plane must support preemption
priority.
39. The MPLS-TP control plane should support 1:n (including
1:1) shared mesh restoration.
40. The MPLS-TP control plane must support the definition of
shared protection groups.
41. The MPLS-TP control plane must support sharing of
protection resources.
42. The MPLS-TP control plane must support revertive and non-
revertive protection behavior.
43. The MPLS-TP control plane may support revertive and non-
revertive restoration behavior.
44. The MPLS-TP control plane must support recovery being
triggered by physical (lower) layer fault indication.
45. The MPLS-TP control plane must support recovery being
triggered by OAM.
46. The MPLS-TP control plane must support management plane
recovery triggers (e.g., forced switch, etc.).
47. The MPLS-TP control plane should support control plane
recovery triggers (e.g., forced switch, etc.).
48. The MPLS-TP control plane must support the establishment
and maintenance of all recovery entities and functions.
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49. The MPLS-TP control plane must support signaling of
recovery administrative control.
50. The MPLS-TP control plane must support protection state
coordination (PSC).
51. The MPLS-TP control plane must support transport services
that provide differentiated services and different traffic
types with traffic class separation associated with
different traffic.
52. The MPLS-TP control plane must support the provisioning of
services that provide a guaranteed of Service Level
Specifications (SLS), with support for hard and relative
end-to-end bandwidth guaranteed.
53. The MPLS-TP control plane must support the provisioning of
services which are sensitive to jitter and delay.
2.2. MPLS-TP Framework Derived Requirements
The following additional requirements are based on [TP-FWK]:
54. The address spaces used in the management, control and
data planes are independent.
55. Penultimate hop popping (PHP) is disabled on MPLS-TP LSPs
by default. The applicability of PHP to both MPLS-TP LSPs
and MPLS networks general providing packet transport
services will be clarified in a future version.
56. The MPLS-TP control plane must support both E-LSP and L-
LSP.
57. The MPLS-TP control plane is based on the MPLS control
plane for pseudowires, and more specifically, LDP is used
for PW signaling.
58. Both single-segment and multi-segment PWs shall be
supported by the MPLS-TP control plane. MPLS-TP shall use
the definition of multi-segment PWs that is under
development in the IETF independent from MPLS-TP.
59. The MPLS-TP control plane is based on the GMPLS control
plane for MPLS-TP LSPs. More specifically, GMPLS RSVP-TE
is used for LSP signaling, and GMPLS OSPF-TE and ISIS-TE
are used for routing.
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60. The MPLS-TP LSP control plane must allow for
interoperation with the MPLS-TE LSP control plane.
61. The MPLS-TP control plane must be capable of performing
fast restoration in the event of network failures.
62. The MPLS-TP control plane must ensure its own
survivability and to enable it to recover gracefully from
failures and degradations. These include graceful restart
and hot redundant configurations.
63. The MPLS-TP control plane must support linear, ring and
meshed protection schemes.
2.3. OAM Framework Derived Requirements
The following additional requirements are based on [TP-OAM]:
64. The MPLS-TP control plane must allow for the use of OAM
proactive Continuity Check (CC) and Connectivity
Verification (CV) function.
a. The CC and CV functions operate between MEPs.
b. All OAM packets coming to a MEP source are tunneled
via label stacking, and therefore a MEP may only be
present at an LSP's ingress and egress nodes (and
never at an LSP's transit node).
c. The CC and CV functions may serve as a trigger for
protection switching, see requirement 45 above.
d. This implies that LSP hierarchy must be used in cases
where OAM is used to trigger recovery.
65. The MPLS-TP control plane must support the configuration
of MEPs.
66. The MPLS-TP control plane must support the signaling of
the transmission period and the ME identifier used in CC
and CV.
2.4. Security Requirements
There are no specific MPLS-TP control plane security
requirements. The existing framework for MPLS and GMPLS security
is documented on [MPLS-SEC] and that document applies equally to
MPLS-TP.
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3. TE LSPs
[Editor's note: This section (and the remainder of this
document) is preliminary and will be edited/replaced in future
versions.]
3.1. General reuse of existing GMPLS control plane mechanisms
As described in [RFC3945], Generalized MPLS (GMPLS) extends MPLS
to support additional switching technologies. GMPLS is thus
capable of controlling packet technologies. Most of the initial
efforts on Generalized MPLS (GMPLS) have been related to
delivering circuit connectivity. With the emergence of both
multi-switching environments and the integrated control
paradigm, there is a need to clarify the applicability of GMPLS
to packet switching technologies. In particular, the formal
definition of FAs and hierarchy in [RFC4206] led to the
definition of four regions for PSC (Packet Switching Capable)
interfaces: PSC-1, PSC-2, PSC-3, and PSC-4.
This document describes the GMPLS topics specifically related to
Packet technologies. In particular, it will present how to
signal packet- LSPs and how the four PSC-i regions could be
used.
3.1.1. "In-band" and "out of band"
For an MPLS-TP network, "in-band" is defined such that the
control plane runs over a network set up by that same control
plane.
For an MPLS-TP network, "out of band" is defined such that the
control plane runs over a network that has been established by
other means than the control plane itself.
The term out-of-band is typically refers to the relationship of
the management and control planes relative to the data plane.
It may be used to refer to the management plane independent of
the control plane, or to both of them in concert. There are
multiple uses of the term out-of-band, and it may relate to a
channel, a path or a network. Each of these can be used
independently or in combination. Briefly, the terms are
typically used as follows:
o In-band
This term is used to refer to cases where management and/or
control plane traffic is sent using or embedded in the same
communication channel used to transport the associated data.
IP forwarded, MPLS packet, and Ethernet networks are all
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examples where control traffic is typically sent in-band with
the data traffic.
o Out-of-band, in-fiber
This term is used to refer to cases where management and/or
control plane traffic is sent using a different communication
channel from the associated data traffic, and the
control/management communication channel resides in the same
fiber as the data traffic. Optical transport networks
typically operate in an out-of-band in-fiber configuration.
o Out-of-band, aligned topology
This term is used to refer to the cases where management
and/or control plane traffic is sent using a different
communication channel from the associated data traffic, and
the control/management communication must follow the same
node-to-node path as the data traffic. Such topologies are
usually supported using a parallel fiber or other
configuration where multiple data channels are available and
one is (dynamically) selected as the control channel.
o Out-of-band, independent topology
This term is used to refer to the cases where management
and/or control plane traffic is sent using a different
communication channel from the associated data traffic, and
the control/management communication may follow a path that is
completely independent of the data traffic. Such
configurations don't preclude the use of in-fiber or aligned
topology links, but alignment is not required.
In the context of MPLS-TP, requirement 4 can be met using out-
of-band in-fiber or aligned topology types of control.
Requirement 5 can only be met by using Out-of-band, independent
topology. GMPLS routing and signaling can be used to support
in-band and all of the out-of-band forms of control, see
[RFC3945].
3.1.2. Addressing
MPLS-TP uses the IPv4 and IPv6 address families to identify
MPLS-TP nodes by default for network management and signaling
purpose. The separation of the control and management planes
from the data plane allows each plane to be independently
addressable. Each plane may use addresses that are not mutually
reachable, e.g., it is likely that the data plane will not be
able to reach an address from the management or control planes
and vice versa. Each plane may also use a different address
family. It is even possible to reuse addresses in each plane,
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but this is not recommended as it is likely lead to operational
confusion.
Unnumbered interfaces and links are also permitted and usage is
at the discretion of the network operator.
3.2. Signaling
In this section, we reference the existing MPLS and GMPLS
signaling and routing mechanisms which can be used to support
MPLS-TP LSPs. When controlling a packet-switched data-plane with
GMPLS, the packets have an MPLS (see [RFC3032]) format, with the
so-called "shim header" including a 20-bit label. Unlike MPLS,
GMPLS uses the Generalized Label Object defined in [RFC3471] to
signal such labels.
In the current RSVP-TE signaling protocol, many objects make use
of the Generalized Label.
According to [RFC3471], a Generalized Label has the following
format: "Generic MPLS labels and Frame Relay labels are encoded
right justified aligned in 32 bits (4 octets). ATM labels are
encoded with the VPI right justified in bits 0-15 and the VCI
right justified in bits 16-31". This is primarily used in RESV
messages to encode the downstream assigned label which shall be
used on a link or FA of an LSP, using the LABEL object (class =
16). When the C-Type is set to 2, this LABEL object is carrying
a Generalized Label encoded as defined in [RFC3471].
When a node wishes to restrict the set of labels possibly
assigned by its downstream neighbour (for the LSP), it can use
the LABEL_SET object in PATH messages: the Label Type must be
set to "Generalized Label" (value=2) and the Sub-Channels must
be such Generalized Labels.
The SUGGESTED_LABEL, RECOVERY_LABEL and UPSTREAM_LABEL objects
(respectively, class = 129, 34, 35; C-Type = 2) of the PATH
messages have an identical format to that of the Generalized
Label Object.
Similarly, the RECORD_ROUTE object of the PATH message can
record the labels which are used along the LSP, using the label
subobject TLV (type = 3). In this subobject, the C-type of the
recorded label is copied (value is therefore 2 in the packet
case), and the Label Object is copied into the appropriate
field.
The Generalized Label Request Object must be used in PATH
messages (C-Type = 4) instead of the simple Label Request
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without range such as defined in [RFC3209] (C-Type = 1). In this
object the Switching Type is then set to PSC-1, PSC-2, PSC-3 or
PSC-4 (respectively values 1 to 4) according to the type of LSP
being opened (see Section 3).
The ACCEPTABLE_LABEL_SET object (Class= 130, C-Type = 1) of the
PathErr message has an identical format to that of the LABEL_SET
object of PATH messages.
An MPLS-TP domain may be a switching point for an LSP that
extends between client network islands. In this case, the MPLS-
TP domain edge that connects to the respective client domain may
have a static switching in the data plane done on the interface
connecting to the respective client node. Alternatively, the LSP
may be signaled between the client network and the MPLS-TP
domain. There are two cases: (1) the client network connects via
a GMPLS UNI to the MPLS-TP domain with knowledge of the remote
MPLS-TP edge node and link that connects to the remote client
node or there is some reachability information exchanged between
the MPLS-TP domain and the client network via dynamic protocol,
or (2) integrated model whereby the client network is an
integrated part of the MPLS-TP domain, less likely option in
some of the operation environments.
3.3. Routing
The major extension in the context of routing PSC-LSPs within
the GMPLS framework is the use of the various PSC-regions
introduced by [RFC3945]. With the introduction of the hierarchy,
formally specified in [RFC4206], it is necessary to use PSC-x as
Switching Capability (SC) and therefore, the nesting process is
modified with regards to the MPLS procedures. In particular, the
policy chosen for announcing the SC associated with a Forwarding
Adjacency has a significant impact. That is an MPLS-TP announced
as an FA in a client network in an integrated model to support
hierarchical MPLS-TP in MPLS-TP domain.
3.3.1. ISIS-TE/OSPF-TE routing in support of MPLS-TP
The major extension in the context of routing PSC-LSPs within
the GMPLS framework is the use of the various PSC-regions
introduced by [RFC3945]. In MPLS, no hierarchy being formally
defined, no limitations were applied on nesting packet LSPs
within other packet LSPs. With the introduction of the
hierarchy, formally specified in [RFC4206], it is necessary to
use PSC-x as Switching Capability (SC) and therefore, the
nesting process is modified with regards to the MPLS procedures.
In particular, the policy chosen for announcing the SC
associated with a Forwarding Adjacency has a significant impact.
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3.3.1.1. ISIS-TE/OSPF-TE routing for MPLS-TP
Per [RFC4203] for OSPF and [RFC5307] for IS-IS, the Interface
Switching Capability Descriptor (ISCD) is a sub-TLV (of type 15)
of the Link TLV, which is used to indicate the Switching
Capability (or Capabilities) of an interface. Per [RFC4203],
this TLV indicates encoding, MTU and bandwidth available at each
priority level. The TLV also carries a Switching Capability
field which indicates the switching hierarchy level:
1: Packet-Switch Capable-1 (PSC-1)
2: Packet-Switch Capable-2 (PSC-2)
3: Packet-Switch Capable-3 (PSC-3)
4: Packet-Switch Capable-4 (PSC-4)
3.3.1.2. Multiple Switching Capabilities
To support interfaces that have more than one ISCD (see Section
"Interface Switching Capability Descriptor" of [RFC4202]), the
ISCD MAY occur more than once within a single routing protocol
link description message. This allows a single packet TE-link or
FA to be announced in multiple PSC regions, both as a PSC-1 and
PSC-2 for instance.
The "regular" packet TE-links (non-FAs) can also be configured
to be used by one or several of the regions. A TE-link set to a
single PSC-x region will be reserved for establishing PSC-x
LSPs, whereas one set to multiple PSC-x, PSC-y and PSC-z regions
will be shared by PSC LSPs of these switching types.
When a TE-link or an FA is shared among regions, it is important
for the nodes receiving traffic over this link/FA to have a
single label- space shared across the regions. This is critical
for the node to guarantee it will receive packets with different
labels in different packet regions, even when they arrive on the
same interface.
The fact that the label-space must be cross-region is
independent from the fact that label-spaces may be per-
interface, per-tunnel, per-upstream neighbor or per-platform.
3.3.1.3. Hierarchy
[RFC4206] defines network regions based on switching
capabilities. The hierarchy of regions is novel in GMPLS and
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this section intends to clarify the hierarchy for PSC nodes, and
the use of the various PSC-regions.
According to [RFC4206], there are four PSC regions which are
hierarchically ordered in the following way: PSC-1 < PSC-2 <
PSC-3 < PSC-4, that is PSC-1 is the smallest SC and PSC-4 is the
largest SC. Let us consider two consecutive nodes of an LSP,
such that the first node's SC is PSC-x and the second node's is
PSC-y. The first node is said to be at the border of two packet
regions, with regard to that LSP, if PSC-y is larger than PSC-x
(i.e.: x < y ). Similarly, the second node is said to be at the
border of two packet regions, with regard to that LSP, if x > y.
According to [RFC4202], "a unidirectional LSP must have the same
sets of SCs at both ends". Additionally, such an LSP will only
be routed over TE-links and/or FAs which have (at least) that SC
(since otherwise, the region crossing would trigger the setup of
an FA-LSP, as described in [RFC4206]). This imposes that a PSC-x
LSP be setup using only TE-links and/or FAs which include at
least PSC-x. In the packet-switching context, this means that a
PSC-x cannot directly use links/FAs which do not have a PSC-x
set in their ISCD's Switching Capability Field. Therefore, if
one wants to establish a PSC-x LSP across a PSC-y region, an FA-
LSP must either be available or set-up. It may be announced in
the PSC-x region routing instance (which may be the same as the
PSC-y region routing instance) as a PSC-x TE-link. The SC
associated with an FA is announced using the routing protocol's
Interface Switching Capability Descriptor (ISCD) (see Section
3.1). For instance, if a PSC-1 LSP has to be setup across a PSC-
3 region, the region border node will first have to establish a
PSC-3 LSP in which the PSC-1 LSP will be nested. The PSC-3 LSP
may then be used to announce an FA in the PSC-1 routing
protocol.
In the four packet regions, the switching principles are the
same, which means that a PSC node is most likely to have in fact
all four PSC-1, PSC-2, PSC-3 and PSC-4 switching types. When
using a packet LSP to nest other LSPs, the policy for deciding
which PSCs to announce for the packet FAs and TE-links, and the
policy for cross- region LSP triggering determine the type of
interactions between the PSC-regions. This means there are in
fact multiple ways of using the PSC regions.
3.3.2. TE link bundling
3.4. OAM, MEP (hierarchy) configuration & control
Current MPLS LSP and PW OAM capabilities are not suitable for
transport applications. Hence IETF has started work to define a
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comprehensive set of MPLS-TP OAM functions. Specific OAM
requirements for MPLS-TP are documented in [draft-ietf-mpls-tp-
oam-requirements]. In addition to the actual OAM requirements,
it is also required that the control plane is able to configure
and control OAM entities. This requirement is not yet addressed
by the foreseen MPLS-TP control protocols (i.e, GMPLS for LSPs
and T-LDP for PWs).
To emphasize the importance of OAM establishment via the control
plane it must be noted that for proper OAM; OAM messages and the
actual normal traffic must be congruent: taking the same path
and relying on the same forwarding decisions at intermediate
nodes. Hence, it is desirable that OAM is setup together with
the establishment of the data path (i.e., with the same
signaling). This way OAM setup is bound to connection
establishment signaling, avoiding two separate
management/configuration steps (connection setup followed by OAM
configuration) which would increases delay, processing and more
importantly may be prune to misconfiguration errors.
It must be noted that although the control plane is used to
establish OAM entities, subsequently OAM is executed
independently from the control plane. That is, OAM mechanisms
are responsible for monitoring and initiating recovery actions
(driving switches between primary and backup paths).
GMPLS RSVP-TE based OAM configuration and control should be
general to be applicable to a wide range of data plane
technologies and OAM solution and not be limited to the MPLS
technology and MPLS-TP OAM. On the other hand, GMPLS based OAM
configuration must satisfy all MPLS-TP requirements.
PW OAM establishment is FFS.
3.5. Traffic engineering and constraint-based path computation
Same approach as MPLS. Specific algorithms out of scope.
Similar to MPLS, but adds bidirectional and recovery path
computation.
3.5.1. Relation to PCE
Path Computation Element (PCE) may be used for path computation
of a GMPLS LSP across domains and in a single domain. A Network
Management System (NMS) may be used to trigger path computation
for a GMPLS LSP and configure the cross-connects along the
computed path. Alternatively, the path computation may be
triggered by a network node via PCE Communication Protocol
(PCECP) and the LSP signaled using GMPLS.
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3.6. Applicability
3.7. Recovery
3.7.1. E2E, segment
3.7.2. P2P, P2MP
3.8. Diffserv object usage in GMPLS (E-LSPs, L-LSPs)
3.9. Management plane support
3.10. CP reference points (E-NNI, I-NNI, UNI)
3.11. MPLS to MPLS-TP interworking
- Leverage current MPLS and GMPLS development
- Backward compatibility
4. Pseudo Wires
[Editor's note: This section is preliminary and will be
edited/replaced in future versions.]
MPLS Pseudo Wires, as defined in [RFC3985], provide for emulated
services over an MPLS Packet Switched Network (PSN). There are
several types of pseudowires: (1) Ethernet PWs providing for
Ethernet port or Ethernet VLAN over MPLS [RFC4448], (2) HDLC/PPP
Pseudowire providing for HDLCP/PPP leased line transport of
MPLS[RFC4618], (3) ATM PWs [RFC4816], (4) Frame Relay PWs
[RFC4619], and (5) circulation Emulation PWs [RFC4553].
Today's transport networks based on PDH, WDM, or SONET/SDH
provide transport for PDH or SONET (e.g., ATM over SONET or
Packet PPP over SONET) client signals with no payload awareness.
Implementing PW capability allows the use of an existing
technology to substitute the TDM transport with Packet-aware
transport, using well-defined pseudowire encapsulation methods
for carrying various packet services over MPLS, and providing
for potentially better bandwidth utilization.
There are two types of pseudowires: (1) Single-Segment
pseudowires (SS-PW), and (2) Multi-segment pseudowires (MS-PW).
An MPLS-TP domain may transport a PW with endpoints within a
client network transparently. Alternatively, an MPLS-TP edge
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node may be the Terminating PE (T-PE) for a PW, performing
adaptation from the native attachment circuit technology (e.g.
Ethernet 802.1q) to an MPLS PW for transport over an MPLS-TP
domain, with a GMPLS LSP or a hierarchy of LSPs transporting the
PW between the T-PEs. In this way, the PW is analogous to a
transport channel in a TDM network and the LSP is equivalent to
a container of multiple non-concatenated channels, albeit they
are packet containers. The MPLS-TP domain may also contain
Switching PEs (S-PEs) for a multi-segment PW whereby the T-PEs
may be at the edge of the MPLS-TP domain or in a client network.
In this latter case, a T-PE in a client network is a T-PE
performing the adaptation of the native service to MPLS and the
MPLS-TP domain performs Pseudo-wire switching.
SS-PW signaling control plane is based on LDP with specific
procedures defined in [RFC4447]. [Segmented-PW] and [MS-PW]
allow for static switching of multi-segment pseudowires in data
and control plane and for dynamic routing and placement of an
MS-PW whereby signaling is still based on Targeted LDP (T-LDP).
The MPLS-TP domain shall use the same PW signaling protocols and
procedures for placing SS-PWs and MS-PWs. This will leverage
existing technology as well as facilitate interoperability with
client networks with native attachment circuits or PW segment
that is switched across the MPLS-TP domain.
The same control protocol and procedures are reused as much as
possible. However, when using PWs in MPLS-TP, a set of new
requirements are defined which may require extensions of the
existing control mechanisms. This section identifies areas where
extensions are needed based on the PW Control Plane related
requirements documented in [draft-ietf-mpls-tp-requirements].
The baseline requirement for extensions to support transport
applications is that any new mechanisms and capabilities must be
able to interoperate with existing IETF MPLS [RFC3031] and IETF
PWE3 [RFC3985] control and data planes where appropriate. Hence,
extensions of the PW Control Plane must be in-line with the
procedures defined in [RFC4447].
For MPLS-TP, it is required that the data and control planes are
both logically and physically separated. That is, the PW Control
Plane must be able to operate out-of-band (OOB). This ensures
that in the case of control plane failures the data plane is not
affected and can continue to operate normally. This was not a
design requirement for the current PW Control Plane. However,
due to the PW concept, i.e., PWs are connecting logical entities
('forwarders'), and the operation of the PW control protocol,
i.e., only edge PE nodes (T-PE, S-PE) take part in the signaling
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exchanges: moving T-LDP out-of-band seems to be, theoretically,
a straightforward exercise.
More precisely, if IP addressing is used in the MPLS-TP control
plane then T-LDP addressing can be maintained, although all
addresses will refer to control plane entities. Both, the PWid
FEC and Generalized PWid FEC Elements can possibly be used in an
OOB case as well (Detailed evaluation is FFS). The PW Label
allocation and exchange mechanisms can be possibly reused
unchanged (Detailed evaluation is FFS). Binding a PW to an LSP,
or PW segments to LSPs can be left to networks elements acting
as T-PEs and S-PEs or a control plane entity that may be the
same one signaling the PW. If the control plane is physically
separated from the forwarder, the control plane must be able to
program the forwarders with necessary information.
For transport applications, it is mandatory that bidirectional
traffic is following congruent paths. Today, each direction of a
PW or a PW segment is bound to a unidirectional LSP that extends
between two T-PEs, S-PEs, or a T-PE and an S-PE. The
unidirectional LSPs in both directions are not required to
following congruent paths, and therefore both directions of a PW
may not follow congruent paths. The only requirement today is
that a PW or a PW segment shares the same T-PEs in both
directions, and same S-PEs in both directions. This poses a new
requirement on the PW Control Plane, namely to ensure that both
ends map the PW to the same transport path. When a bidirectional
LSP is selected on one end to transport the PW, a mechanism is
needed that signals to the remote end which LSP has been
selected locally to transport the PW. This likely can be
accomplished by adding a new TLV to PW signaling. This coincides
with the gap identified for OOB support: a new mechanism may be
needed to explicitly bind PWs to the supporting transport LSP.
Alternatively, two unidirectional LSPs may be used to support
the PW. However, to meet the congruency requirement, the LSPs
must be placed so that they are forced to follow the same path
(switches and links). This maybe accomplished by placing one
unidirectional TE-LSP in one direction at one endpoint, and
forcing the other endpoint to setup a TE-LSP with an ERO that
has the nodes/links in the reverse order from the RRO seen in
the path message of the LSP in the reverse direction. In this
case, when one endpoint selects an LSP to bind the PW to, it
must identify to the remote end which LSP to bind the other
direction of the PW to.
Transport applications require resource guarantees. In the case
of transport LSPs, resource reservation mechanisms are provided
via RSVP-TE and the use of DiffServ. If multiple PWs are
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multiplexed into the same transport LSP resources, contention
may occur. However, local policy at PEs may ensure proper
resource sharing among PWs mapped into a resource guaranteed
LSP. On the other hand, it is limited if any guarantees can be
provided to PWs if the LSPs used to support MPLS-TP PWs do not
support resource guarantees.
The PW control plane must be able to establish and configure all
of the available features manageable for the PW, including
protection and OAM entities and mechanisms. There is ongoing
work on PW protection and MPLS-TP OAM.
To summarize, the main areas identified for potential PW Control
Plane extensions to support MPLS-TP are the following.
o Move PW Control Plane out-of-band
o Explicit control of PW to LSP binding
o PW QoS and congestion control
o PW protection
o PW OAM configuration and control
4.1. General reuse of existing PW control plane mechanisms
4.2. Signaling
4.3. Recovery (Redundancy)
5. Security Considerations
[Editor's note: This section is preliminary and will be
edited/replaced in future versions.]
This document is a framework document and does not describe bits
on the wire and have a very small impact on MPLS/GMPLS security
issues. However it gives guidelines for future extension to
existing MPLS and GMPLS protocols, it is understood that the
documents that specify these extensions will address the
security issues that relates to the extensions.
It is also understood that that the MPLS/GMPLS security
framework [MPLS-SEC] is applicable to both this document and the
documents that will be written as a result of the output of this
document.
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6. IANA Considerations
7. Acknowledgments
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
The authors would like to acknowledge the contributions of
Yannick Brehon to this work.
8. References
8.1. Normative References
[RFC3031] Rosen, E., Viswanathan, A., Callon, R.,
"Multiprotocol Label Switching Architecture", RFC
3031, January 2001.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and Conta, A. "MPLS Label
Stack Encoding", RFC 3032, January 2001.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan,
V., and G. Swallow, "RSVP-TE: Extensions to RSVP for
LSP Tunnels", RFC 3209, December 2001.
[RFC3471] Berger, L., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Functional Description",
RFC 3471, January 2003.
[RFC3473] Berger, L. Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation
Protocol-Traffic Engineering (RSVP-TE) Extensions",
January 2003.
[RFC3945] Mannie, E., "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", RFC 3945, October
2004.
[RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-
to-Edge (PWE3) Architecture", RFC 3985, March 2005.
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[RFC4202] Kompella, K. and Y. Rekhter, "Routing Extensions in
Support of Generalized Multi-Protocol Label
Switching(GMPLS)", RFC 4202, October 2005.
[RFC4203] Kompella, K. and Y. Rekhter, "OSPF Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, October 2005.
[RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths
(LSP) Hierarchy with Generalized Multi-Protocol Label
Switching (GMPLS) Traffic Engineering (TE)", RFC
4206, October 2005.
[RFC4208] Swallow, G., Drake, J., Ishimatsu, H., and Rekhter,
Y., "Generalized Multi-Protocol Label Switching
(GMPLS) User-Network Interface (UNI): Resource
ReserVation Protocol-Traffic Engineering (RSVP-TE)
Support for the Overlay Model", RFC 4206, October
2005.
[RFC4447] Martini, L., Ed., "Pseudowire Setup and Maintenance
Using the Label Distribution Protocol (LDP)", RFC
4447, April 2006.
[RFC4448] Martini, L., Ed., "Encapsulation Methods for
Transport Ethernet over MPLS Network", RFC 4448,
April 2006.
[RFC4553] Vainshtein, A., Ed., and Stein, YJ., Ed.,"Structure-
Agnostic Time Division Multiplexing (TDM) over Packet
(SAToP)", RFC 4553, June 2006.
[RFC4618] Martini, L., Rosen, E., Heron, G., and Malis, A.,
"Encapsulation Methods for Transport of PPP/High-
Level Data Link Control (HDLC) over MPLS Networks",
RFC 4618, September 2006.
[RFC4619] Martini, L., Ed., Kawa, C., Ed., and Malis, A., Ed.,
"Encapsulation Methods for Transport of Frame Relay
over Multiprotocol Label Switching (MPLS) Networks",
September 2006.
[RFC4816] Malis, A., Martini, L., Brayley, J., and Walsh, T.,
"Pseudowire Emulation Edge-to-Edge (PWE3)
Asynchronous Transfer Mode (ATM) Transparent Cell
Transport Service", RFC 4816, February 2007.
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[RFC5307] Kompella, K. and Rekhter, Y., "IS-IS Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 5307, October 2008.
[RFC5316] Chen, M., Zhang, R., and Duan, X., "ISIS Extensions
in Support of Inter-Autonomous System (AS) MPLS and
GMPLS Traffic Engineering", RFC 5392, December 2008.
[RFC5392] Chen, M., Zhang, R., and Duan, X., "OSPF Extensions
in Support of Inter-Autonomous System (AS) MPLS and
GMPLS Traffic Engineering", RFC 5392, January 2009.
8.2. Informative References
[MPLS-SEC] Fang, L., et al, "Security Framework for MPLS and
GMPLS Networks", work in Progress, draft-ietf-mpls-
mpls-and-gmpls-security-framework-04.txt, November
2008.
[Segmented-PW] Martini, L., Nadeau, T., and Duckett M., "
Segmented Pseaudowire", work in Progress, draft-ietf-
pwe3-segmented-pw-11.txt, February 2009.
[MS-PW] Bocci, M., and Bryant, B., "An Architecture for
Multi-Segment Pseudowire Emulation Edge-to-Edge",
work in Progress, draft-ietf-pwe3-ms-pw-arch-05.txt,
September 2008.
[TP-FWK] Bocci, M., Ed., Et al, "A Framework for MPLS in
Transport Networks", work in Progress, draft-ietf-
mpls-tp-framework-00, November 2008.
[TP-OAM] Busi, I., Ed., Niven-Jenkins, B., Ed., "MPLS-TP OAM
Framework and Overview", work in Progress, draft-
busi-mpls-tp-oam-framework-00, October 2008.
[TP-SURVIVE] Sprecher, N., et al., "Multiprotocol Label
Switching Transport Profile Survivability Framework",
work in Progress, draft-sprecher-mpls-tp-survive-fwk-
00.txt, July 2008.
[TP-REQ] Niven-Jenkins, B., Et al, "MPLS-TP Requirements",
work in Progress, draft-ietf-mpls-tp-requirements-04,
February 2009.
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9. Authors' Addresses
Loa Andersson (editor)
Redback Networks
Phone: +46 8 632 77 14
Email: loa@pi.nu
Lou Berger (editor)
LabN Consulting, L.L.C.
Phone: +1-301-468-9228
Email: lberger@labn.net
Luyuan Fang (editor)
Cisco Systems, Inc.
300 Beaver Brook Road
Boxborough, MA 01719
USA
Email: lufang@cisco.com
Nabil Bitar (editor)
Verizon,
40 Sylvan Rd.,
Waltham, MA 02451
Email: nabil.n.bitar@verizon.com
Attila Takacs
Ericsson
1. Laborc u.
Budapest, HUNGARY 1037
Email: attila.takacs@ericsson.com
Martin Vigoureux
Alcatel-Lucent
Email: martin.vigoureux@alcatel-lucent.fr
Andersson, et al. Expires August 22, 2009 [Page 28]