Internet Draft Hang Liu
draft-liu-gmpls-ospf-restoration-00.txt Dimitrios Pendarakis
Expires: April 2003 Bala Rajagopalan
Nooshin Komaee
Tellium, Inc.
October 2002
OSPF-TE Extensions in Support of Shared Mesh Restoration
<draft-liu-gmpls-ospf-restoration-00.txt>
Status of this Memo
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Abstract
This document describes extensions to the OSPF-TE routing
protocol in support of path computation for shared mesh
restoration. New optional sub-TLVs are added to the link TLV
of the Traffic Engineering (TE) LSA so that the sharing
information of the restoration resource on the TE link
reserved for shared mesh restoration is disseminated. The
extensions supports both SRLG-disjoint and node-disjoint
paths.
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1. Introduction
In shared mesh restoration [1,2,3,4], the restoration LSP is
pre-computed and its resource is reserved along the path
through signaling protocols [5, 6, 7]. However no cross-
connections are performed along the restoration path. The
complete establishment of the restoration LSP occurs only
after the working LSP fails, and requires some additional
signaling. The common restoration resource reserved at a node
or on a TE link may be shared by multiple restoration LSPs to
restore multiple working LSPs. In order to avoid contention
for the reserved restoration resource (bandwidth or channel)
during a single SRLG/node failure, two restoration LSPs may
share the common reserved restoration resource only if their
respective working LSPs are mutually SRLG/node disjoint. One
failure then does not disrupt both working LSPs
simultaneously.
Shared mesh restoration achieves efficient utilization of
network resources by sharing the restoration resource. It can
achieve reasonably fast switching time and guarantees
successful recovery from a single SRLG/node failure.
The resource reserved for restoration can even be used by the
other path to carry the extra traffic during normal operation
mode (i.e. while there are no failure on the working LSPs). Of
course, the restoration path needs to be activated when the
working path fails. It may result in a switching time longer
than the dedicated 1+1 protection. Furthermore, since multiple
restoration LSPs may share the common reserved restoration
resource. The contention may occur on the reserved restoration
resource when more than one of the working paths fails
simultaneously due to multiple failures.
This document specifies extensions to OSPF [8] in support of
carrying link state information for the path computation for
shared mesh restoration. It is based on the existing OSPF
routing extensions required to support Traffic Engineering and
GMPLS [9, 10, and 11]. Similar extensions described here can
also be made to IS-IS. These extensions are initially focused
on transport networks; however they are not meant to be
exclusively for the transport networks.
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2. Required Information
In shared mesh restoration, multiple restoration LSPs can
share the same reserved restoration resource on their common
TE links only if the sets of SRLGs and/or nodes traversed by
their respective working LSPs are disjoint in order to
guarantee recovery from a single SRLG failure or a single node
failure. This imposes additional constraints on the path
computation. To compute the restoration LSP for the shared
mesh restoration, the path computation module needs to have
the restoration resource sharing information on the links in
the network. In general, the more detail information is
available, the better results the path computation algorithms
can achieve. On the other hand, in order to reduce the amount
of information handled by OSPF and improve the routing
scalability, it may be desirable to aggregate the information
on a TE link (bundle) [12]. To support path computation for
shared mesh restoration, all or some information below can be
disseminated by routing protocol.
(1) Summarized information about the restoration resource
sharing on a TE link for shared mesh restoration, such as the
total number of restoration LSPs sharing the restoration
resource reserved on the TE link for shared mesh restoration,
the total number of SRLGs recovered by the reserved
restoration resource on the TE link, the total number of nodes
recovered by the reserved restoration resource on the TE link,
the total sharable restoration bandwidth at each priority
level.
(2) The list of SRLGs recovered by the reserved restoration
resource on the TE link and their respective sharable
restoration bandwidth if the SRLG-disjointness is required to
guarantee recovery in the event of a single SRLG failure.
(3) The list of nodes recovered by the reserved restoration
resource on the TE link and their respective sharable
restoration bandwidth if the node-disjointness is also
required to guarantee recovery in the event of a single node
failure. By distinguishing node failure restoration from SRLG
failure restoration, it provides the network operator with
options to offer different levels of services and uses the
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network resource more efficiently as explained later in this
section.
The list of SRLGs/nodes recovered by the TE link is defined as
the union of SRLGs/nodes traversed by all the working LSPs
whose respective restoration LSPs share the reserved
restoration resource on this TE link. The common reserved
restoration resource (e.g. an OC-48 channel) can be reused by
a restoration LSP to recover a working LSP if no SRLG/node
passed over by its working LSP appears in the list of
SRLGs/nodes already recovered by the restoration resource. The
sharable restoration bandwidth for a SRLG and/or node
indicates the available restoration bandwidth on the TE link
that can be reserved for recovering this SRLG/node failure. If
a working LSP only traverses one SRLG, the available
restoration bandwidth that its restoration LSP can share on
this TE link is the sharable restoration bandwidth for this
SRLG. When a working LSP traverses multiple SRLGs, the
sharable restoration bandwidth available for its restoration
LSP may become smaller on this TE link. It is the same case
for a given node when the node-disjointness is required.
The total sharable restoration bandwidth is the bandwidth
reserved on the TE link for restoration, which is the union of
the sharable restoration bandwidth for all SRLGs and nodes.
A lot of equipment has its own recovery and high availability
requirements. The operator may choose to guarantee recovery
only from a single SRLG failure or from a SRLG/node failure
based on the requirements of the end user applications. For
example, an application requires 99.999% availability. The
node can meet this requirement because it has its own
equipment recovery mechanism. However the fiber links cannot
meet this requirement. In order to meet the application
availability requirements, the shared mesh restored LSP
carrying this application traffic must guarantee recovery from
a single SRLG failure, but it does not have to guarantee
recovery from a single node failure. Then the common
restoration resource can be reserved to restore two working
LSPs that traverse a common node (no node-disjoint constraint);
i.e. less constraints are required to compute the restoration
path.By distinguishing node failure recovery guarantee and SRLG
failure recovery guarantee, the operators can offer different
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levels of services based on performance requirements of the end
user applications and utilize the network resource more
efficiently.
3. OSPF Extensions to Support Path Computation for Shared Mesh
Restoration
It is desirable to carry the sharing information of the
restoration resource on a TE link with the OSPF so that the
information may be used by the path computation algorithm to
compute the restoration path for shared mesh restoration. This
section specifies the extensions to OSPF-TE in support of
shared mesh restoration.
OSPF traffic engineering extensions [9] and GMPLS extensions
[10,11] make use of the Opaque LSA [13]. An Opaque LSA, called
Traffic Engineering LSA is defined to carry the additional
attributes related to traffic engineering and GMPLS links. The
information in the TE LSAs can be used to build an extended TE
link state database just as router LSAs are used to build a
regular link state database. The extensions here are based
upon the OSPF-TE and GMPLS extensions, specifically, we add
the following sub-TLVs to the link TLV of the TE LSA.
3.1 Restoration Information Summary
Restoration Information Summary sub-TLV specifies the sharing
information of the restoration resource reserved for shared
mesh restoration on the TE link. The format of the Restoration
Information Summary sub-TLV is as follows
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type(TBA) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| #Shared Restoration LSPs | #SRLGs recovered |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| #Nodes recovered | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Total Sharable Restoration Bandwidth at priority 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Total Sharable Restoration Bandwidth at priority 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Total Sharable Restoration Bandwidth at priority 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Total Sharable Restoration Bandwidth at priority 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Total Sharable Restoration Bandwidth at priority 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Total Sharable Restoration Bandwidth at priority 5 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Total Sharable Restoration Bandwidth at priority 6 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Total Sharable Restoration Bandwidth at priority 7 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 16 bits
The type of this sub-TLV is TBA.
Length: 16 bits
The length of this sub-TLV is 40 octets.
#Shared Restoration LSPs: 16 bits
This field indicates the number of restoration LSPs
sharing the bandwidth reserved for the mesh restoration
on this TE link.
#SRLGs recovered: 16 bits
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This field indicates the number of SRLGs recovered by
the TE link. The SRLGs here includes all distinct SRLGs
traversed by all the working LSPs whose respective
restoration LSPs shares the reserved restoration
bandwidth on this TE link. Zero means that this
information is not available.
#Nodes recovered: 16 bits
This field indicates the number of nodes recovered by
the TE link. The nodes here include all distinct nodes
traversed by all the working LSPs whose respective
restoration LSPs shares the reserved restoration
bandwidth on this TE link. Zero means that this
information is not available.
Total Sharable Restoration Bandwidth at priority 0-7: 32 bits
Total Sharable Restoration Bandwidth specifies the
bandwidth that has been allocated for shared mesh
restoration at each of the eight priority levels. The
bandwidth might have been reserved by one or more shared
restoration LSP. It is encoded in the IEEE floating
point format, with 4 octets per priority.
The Restoration Information Summary sub-TLV is optional and if
a LSA doesnÆt carry the Restoration Information Summary sub-
TLV, then it means that the information is unknown.
3.2 SRLG Sharable Restoration Bandwidth
SRLG Sharable Restoration Bandwidth sub-TLV identifies the
sharable restoration bandwidth range for a SRLG on this TE
link. By allowing to specify a range instead of a fixed value,
it may reduce the amount of information handled by the routing
protocol. If the lower bound is equal to the upper bound of
the range, it indicates a fixed value of the sharable
restoration bandwidth. Its format is as follows
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type(TBA) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Priority | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sharable Restoration Bandwidth Lower Bound |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sharable Restoration Bandwidth Upper Bound |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRLG 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRLG N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 16 bits
The type of this sub-TLV is TBA.
Length: 16 bits
The length of this sub-TLV is the length of value field
in octets.
Priority: 8 bits
This field indicates the priority of sharable
restoration bandwidth. The SRLG sharable restoration
bandwidth can be encoded per priority. If the SRLG
sharable restoration bandwidth is not encoded per
priority, the value of the priority field is set to
0xFF, which means the sharable restoration bandwidth is
the same for all priorities.
Sharable Restoration Bandwidth Lower Bound and Upper Bound:
32 bits
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The Sharable Restoration Bandwidth Lower Bound and
Sharable Restoration Bandwidth Upper Bound specify a
range for sharable restoration bandwidth. The sharable
restoration bandwidth for each of SRLG in the following
list falls into this range, i.e. Sharable Restoration
Bandwidth Lower Bound <= sharable restoration bandwidth
for SRLG N < Sharable Restoration Bandwidth Upper
Bound. If the lower bound is equal to the upper bound,
a fixed value of sharable restoration bandwidth is
specified and the sharable restoration bandwidth for
each of SRLGs in the following list is equal to this
value.
SRLG: 32 bits
The value is a list of 32-bit numbers, each of number
identifies a SRLG.
The SRLG Sharable Restoration Bandwidth sub-TLV is optional
and if a LSA doesnÆt carry any SRLG Sharable Restoration
Bandwidth sub-TLV, then it is assumed that the information is
unknown. There may be more than one SRLG Sharable Restoration
Bandwidth sub-TLVs in the LSA. However if there are one or
more SRLG Sharable Restoration Bandwidth sub-TLVs in the LSAs,
the sharable restoration bandwidth for the SRLGs not listed in
these SRLG sharable restoration bandwidth sub-TLVs is assumed
to be equal to the total sharable restoration bandwidth at
that priority on this TE link.
3.3 Node Sharable Restoration Bandwidth
Node Sharable Restoration Bandwidth sub-TLV identifies the
sharable restoration bandwidth range that is reserved on this
TE link for sharing by restoration LSPs to recover a node
failure on their working path. It can be used by the path
computation algorithms to compute the restoration LSP when it
is required that multiple restoration LSP can share the common
restoration resource on their common TE links only if their
respective working LSPs are node disjoint. Its format is as
follows
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type(TBA) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Priority | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sharable Restoration Bandwidth Lower Bound |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sharable Restoration Bandwidth Upper Bound |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Node1 ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NodeN ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 16 bits
The type of this sub-TLV is TBA.
Length: 16 bits
The length of this sub-TLV is the length of value field
in octets.
Priority: 8 bits
This field indicates the priority of sharable
restoration bandwidth. The node sharable restoration
bandwidth can be encoded per priority. If the node
sharable restoration bandwidth is not encoded per
priority, the value of the priority field is set to
0xFF, which means the sharable restoration bandwidth is
the same for all priorities.
Sharable Restoration Bandwidth Lower Bound and Upper Bound:
32 bits
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The Sharable Restoration Bandwidth Lower Bound and
Sharable Restoration Bandwidth Upper Bound specify a
range for sharable restoration bandwidth reserved on a
TE link. The sharable restoration bandwidth for each of
node in the following list falls into this range, i.e.
Sharable Restoration Bandwidth Lower Bound <= sharable
restoration bandwidth for Node N < Sharable Restoration
Bandwidth Upper Bound. If the lower bound is equal to
the upper bound, a fixed value of sharable restoration
bandwidth is specified and the sharable restoration
bandwidth for each of nodes in the following list is
equal to this value.
Node ID: 32 bits
The value is a list of 32-bit numbers, each of number
identifies a node.
The Node Sharable Restoration Bandwidth sub-TLV is optional
and if a LSA doesnÆt carry any Node Sharable Restoration
Bandwidth sub-TLV, then it is assumed that the information is
unknown. There may be more than one Node Sharable Restoration
Bandwidth sub-TLVs in the LSA. However if there are one or
more Node Sharable Restoration Bandwidth sub-TLVs in the LSAs,
the sharable restoration bandwidth for the nodes not listed in
these Node sharable restoration bandwidth sub-TLVs is assumed
to be equal to the total sharable restoration bandwidth at
that priority on this TE link.
4. Acknowledgments
The authors would like to thank Ramu Ramamurthy, Eric
Bouillet, Ahmet Akyamac, Jean-Francois Labourdette, and Sid
Chaudhuri for extremely valuable discussions on path
computation algorithms and useful input that they have provided
in this work.
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5. References
1. D. Papadimitriou, et al., "Analysis Grid for GMPLS-based
Recovery Mechanisms," Internet Draft, work in progress,
draft-papadimitriou-ccamp-gmpls-recovery-analysis-00.txt,
April 2002.
2. E. Mannie, et al., "Recovery (Protection and Restoration)
Terminology for GMPLS," Internet Draft, work in progress,
draft-mannie-gmpls-recovery-terminology-00.txt, February
2002.
3. J. P. Lang, B. Rajagopalan, et al., "Generalized MPLS
Recovery Functional Specification," Internet Draft, work in
progress, draft-bala-gmpls-recovery-functional-00.txt,
August, 2002.
4. G. Li, et al., "RSVP-TE Extensions for Shared-Mesh
Restoration in Transport Networks," Internet Draft, work in
progress, draft-li-shared-mesh-restoration-01.txt, November
2001.
5. P. Ashwood-Smith, et al, "Generalized MPLS - Signaling
Functional Description," Internet Draft, work in progress,
draft-ietf-mpls-generalized-signaling-08.txt, April 2002.
6. P. Ashwood-Smith, et al., "Generalized MPLS û RSVP-TE
Extensions," Internet Draft, work in progress, draft-ietf-
mpls-generalized-rsvp-te-07.txt, April 2002.
7. P. Ashwood-Smith, et al., "Generalized MPLS Signaling - CR-
LDP Extensions," Internet Draft, work in progress, draft-
ietf-mpls-generalized-cr-ldp-06.txt, April 2002.
8. J. Moy, "OSPF Version 2", RFC 2328, April 1998.
9. D. Katz, et al., "Traffic Engineering Extensions to OSPF",
Internet Draft, work in progress, draft-katz-yeung-ospf-
traffic-06.txt, October 2001.
10. K. Kompella, et al., "Routing Extensions in Support of
Generalized MPLS," Internet Draft, work in progress, draft-
ietf-ccamp-gmpls-routing-04.txt, April 2002.
11. K. Kompella, et al., "OSPF Extensions in Support of
Generalized MPLS", Internet Draft, work in progress, draft-
ietf-ccamp-ospf-gmpls-extensions-05.txt, April 2002.
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12. K. Kompella, et al., "Link Bundling in MPLS Traffic
Engineering," Internet Draft, work in progress, draft-
kompella-mpls-bundle-05.txt, February 2001.
13. Coltun, R., "The OSPF Opaque LSA Option," RFC 2370,
July 1998.
6. Authors' Addresses
Hang Liu
Dimitrios Pendarakis
Bala Rajagopalan
Nooshin Komaee
Tellium, Inc.
2 Crescent Place
Oceanport, NJ 07757
USA
Phone: +1 732 923 4100
Email: {hliu, dpendarakis, braja, nkomaee}@tellium.com
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