One document matched: draft-ietf-pce-pcecp-interarea-reqs-00.txt
Network Working Group J.-L. Le Roux (Editor)
Internet Draft France Telecom
Category: Informational
Expires: May 2006
December 2005
PCE Communication Protocol (PCECP) specific requirements for Inter-Area
(G)MPLS Traffic Engineering
draft-ietf-pce-pcecp-interarea-reqs-00.txt
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Abstract
For scalability purposes a network may comprise multiple IGP areas.
An inter-area TE-LSP is an LSP that transits through at least two IGP
areas. In a multi-area network, topology visibility remains local to
a given area, and a head-end LSR cannot compute alone an inter-area
shortest constrained path. One key application of the Path
Computation Element (PCE) architecture is the computation of inter-
area TE-LSP paths. In this context, this document lists a detailed
set of PCE Communication Protocol (PCECP) specific requirements for
support of inter-area TE-LSP path computation. It complements generic
requirements for a PCE Communication Protocol.
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119.
Table of Contents
1. Contributors................................................3
2. Terminology.................................................3
3. Introduction................................................4
4. Problem Statement...........................................5
5. Various approaches for PCE-based inter-area path
computation...............................................6
5.1. Single PCE Computation......................................6
5.2. Multiple PCE path computation with inter-PCE
communication.............................................8
6. Considerations on PCE location..............................9
7. Detailed Requirements on PCECP.............................10
7.1. Supported modes for PCE-based inter-area path
computation..............................................10
7.2. Control of area crossing...................................10
7.3. Objective functions........................................11
7.4. TE metric / IGP metric.....................................11
7.5. Recording path attributes..................................11
7.6. Strict Explicit path and Loose Path........................12
7.7. PCE-list enforcement and recording in Multiple PCE
Computation..............................................12
7.8. Inclusion of Area IDs in request...........................13
7.9. Load-Balancing.............................................13
7.10. Diverse Path computation...................................13
7.11. LSP failure handling.......................................14
7.11.1. LSP Rerouting..............................................14
7.11.2. Backup path computation....................................14
7.12. Inter-Area policies........................................15
7.13. Scalability................................................15
8. Manageability consideration................................16
9. Security Considerations....................................16
10. Acknowledgments............................................16
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11. Informative References.....................................16
12. Editor Address:............................................17
13. Contributors' Addresses....................................17
14. Intellectual Property Statement............................18
1. Contributors
The following are the authors that contributed to the present
document:
Jerry Ash (AT&T)
Dean Cheng (Cisco)
Kenji Kumaki (KDDI)
J.L. Le Roux (France Telecom)
Eiji Oki (NTT)
Nabil Bitar (Verizon)
Raymond Zhang (BT Infonet)
2. Terminology
LSR: Label Switching Router
LSP: MPLS Label Switched Path
TE-LSP: Traffic Engineering Label Switched Path
IGP area: OSPF Area or IS-IS level
ABR: IGP Area Border Router, a router that is attached to more
than one IGP areas (ABR in OSPF or L1/L2 router in IS-IS)
Inter-Area TE LSP: TE LSP that traverses more than one IGP area
CSPF: Constraint Shortest Path First
SRLG: Shared Risk Link Group
PCE: Path Computation Element, an entity that can compute path
based on a network graph and applying computational
constraints
PCC: Path Computation Client, any application that request path
computation to be performed by a PCE
PCECP: PCE Communication Protocol, a protocol for communication
between PCCs and PCEs
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3. Introduction
IGP hierarchy consists of separating an IGP domain into multiple IGP
areas, and limiting the topology visibility local to an area. This
mechanism significantly improves IGP scalability.
[RFC4105] lists a set of motivations and requirements for setting up
TE-LSPs across IGP area boundaries. These LSPs are called inter-area
TE-LSPs. These requirements include the computation of inter-
area shortest constrained paths with key guidelines being to respect
the IGP hierarchy concept, and particularly the containment of
topology information. The main challenge with inter-area MPLS-TE
relies actually on path computation. The head-end LSR cannot compute
an end-to-end shortest constrained path, as its topology visibility
is limited to one area. Path computation can rely on loose hops with
ERO expansion on each ABR, but this faces two issues: (1) it does not
guarantee the computation of a shortest path that satisfies the TE-
LSP constraints, and (2) it may result in several signalling
crankback messages before it successfully sets up the path.
The Path Computation Element (PCE) Architecture, defined in [PCE-
ARCH] can provide a suitable framework for computing an inter-area
shortest path for a TE-LSP.
[PCE-ARCH] defines PCEs as entities that can compute paths based on a
network graph and applying computational constraints. A PCE function
can be located on a LSR or a network server. It defines a Path
Computation Client (PCC) as an application requesting a path
computation to be performed by a PCE. Typically a PCC can be a head-
end LSR, a transit LSR requesting a TE-LSP path computation, or a PCE
requesting a path computation of another PCE, in a collaborative
mode.
One of the key applications of the PCE architecture is inter-domain
path computation, where head-end LSRs have a limited topology view
beyond its own domain. This includes both inter-area and inter-AS
path computation.
Inter-area path computation requirements expressed in [RFC4105] may
be achieved using the services of one or more PCEs.
PCE-based inter-area path computation could rely for instance on a
single multi-area PCE that has the TE database of all the areas in
the IGP domain and can directly compute an end-to-end shortest
constrained path.
Alternatively, PCE-based inter-area path computation could rely on
the cooperation between PCEs whereby each PCE covers one or more IGP
areas and the full set of PCEs covers all areas.
The generic requirements for a PCE Communication Protocol (PCECP),
allowing a PCC to send path computation requests to a PCE and the PCE
to sent path computation response to a PCC are listed in [PCE-COM-
REQ]. The use of a PCE-based approach, for inter-area path
computation implies specific requirements on a PCE Communication
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Protocol, in addition to the generic requirements already listed in
[PCE-COM-REQ].
This document complements these generic requirements by listing a
detailed set of PCECP requirements specific to the PCE-based
computation of inter-area TE-LSPs.
The problem statement is discussed in section 4. Various PCE-based
modes for inter-area path computation are described in section 5.
Considerations for PCE location are provided in section 6. Finally
detailed requirements are listed in section 7.
It is expected that a solution for a PCE Communication Protocol
(PCECP) satisfies these requirements.
Note that PCE-based inter-area path computation may require a
mechanism for an automatic PCE discovery across areas, which is out
of the scope of this document. Detailed requirements for such
mechanism are discussed in [PCE-DISCO-REQ].
4. Problem Statement
In intra-area MPLS-TE, a head-end LSR has complete topology
visibility of the area and can compute an end-to-end shortest
constrained path. IGP hierarchy allows improving IGP scalability,
particularly in large networks with hundreds of nodes and thousands
of links, by dividing the IGP domain into areas and limiting the
flooding scope of topology information to area boundaries. A router
in an area has full topology information for its own area but only
reachability to routes in other areas._ Thus, a head-end LSR cannot
compute an end-to-end constrained path that traverses more than one
IGP area.
A solution for computing inter-area TE-LSP path relies on a per
domain path computation ([PD-COMP]). It is based on loose hop routing
with an ERO expansion on each ABR. This can allow setting up a
constrained path, but faces two major limitations:
-This does not allow computing an optimal constrained path
-This may lead to several signalling crankback messages and
hence delay the LSP setup, and invoke routing activities.
Note that, here, by optimal constrained path we mean the shortest
constrained path across multiple areas, taking into account either
the IGP or TE metric [METRIC]. In other words, such a path is the
path that would have been computed by making use of some CSPF
algorithm in the absence of multiple IGP areas.
The PCE architecture is well suited to inter-area path computation,
as it allows overcoming the path computation limitations resulting
from the limited topology visibility, by introducing path computation
entities with more topology visibility, or by allowing cooperation
between path computation entities in each area.
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Several PCE-based path computation approaches can be used to compute
inter-area optimal constrained paths, they are discussed in next
section.
The use of a PCE-based approach, to perform inter-area path
computation requires specific functions in a PCECP, in addition to
the generic requirements listed in [PCE-COM-REQ]. Detailed
requirements are discussed in section 7.
5. Various approaches for PCE-based inter-area path computation
There are various possible modes for PCE-Based inter-area path
computation.
The computation of an inter-area optimal path could be done by:
- a single PCE, that has enough topology visibility and can
alone compute an end-to-end optimal path,
- multiple PCEs, that have partial topology
visibility and collaborate with each other so as to arrive at
an end-to-end optimal path.
These two modes are referred as to "Single PCE computation" and
"Multiple PCE computation with inter-PCE communication" in [PCE-
ARCH]. Note that these two modes may co-exist in a given multi-area
network.
Note that the per-area path computation mode relying on route
expansion performed directly by ABRs on the path (which function has
composite PCEs) , or on external PCEs contacted by the ABRs on the
path, consists in fact of a simple concatenation of intra area paths.
It actually only implies intra-area path computations and does not
allow computing inter-area optimal paths. Hence this mode is not
discussed in this document.
5.1. Single PCE Computation
In this mode the inter-area path computation is directly performed by
a single PCE that has enough topology information to compute an end-
to-end optimal path.
No inter-PCE communication is required in this mode.
This mode requires that the PCE have at least the TED of all the
crossed areas for a given LSP. The actual distribution of PCEs may
vary, i.e., a PCE may have TE database base from two, three or more
IGP areas. If the head-end and tail-end LSRs are located in two
peripheral areas, the PCE must have the TED of the source, backbone,
and destination areas. In the particular case where the head-
end/tail-End LSR is located in the backbone area and the tail-
end/head-end LSR is located in a peripheral area, the PCE only needs
the TED of the backbone area and the peripheral area to compute the
path.
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Figure 1 below illustrates an example of single PCE inter-area
computation.
------
| PCE0 |
/ ------ \
/ | \
/ | \
/ | \
/ | \
------------------------------------------
| | | |
| ABR2 ABR3 |
R1 area1 | area0 | area2 R2
| ABR1 ABR4 |
| | | |
------------------------------------------
Figure 1: Example of single PCE computation.
In this multi area network PCE0 has topology visibility in area1,
area0 and area2 and can compute and end-to-end path from area 1 to
area 2. To setup an inter-area LSP from R1 in area 1 to R2 in area 2,
R1 has to directly contact PCE0.
Note that this mode may rely on PCEs that have knowledge of topology
in all areas. Such a PCE is called an "all-areas" PCE.
Particular attention should be given on the potential limitations of
this "all-areas" PCE approach, in terms of scalability. Such all-area
PCEs may have to maintain a large topology and this raises
scalability issues both in terms of memory to maintain the TED and
processing to synchronize TED information.
Also such all-area PCEs would potentially serve a large number of
PCCs, and hence may face a huge path computation request overload
during a network event such as link or node failure (that may impact
a large number of TE-LSPs on a large number of head-end LSRs). This
may significantly delay the TE-LSP recovery, and thus may diminish
the benefits of such an approach.
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5.2. Multiple PCE path computation with inter-PCE communication
In this mode the computation of an optimal inter-area TE-LSP path is
distributed across multiple PCEs.
There is at least one PCE per area, and those PCEs do not have enough
topology visibility to compute and inter-area optimal path.
PCEs in each area compute path segments in their respective areas and
collaborate together to arrive at an end-to-end inter-area optimal
path. Such collaboration is ensured thanks to inter-PCE
communication.
The actual distribution of PCEs may vary, i.e. a PCE may have TE
database from one, two, or more IGP areas, and the important thing is
that the collection of topology and TE information maintained by a
set of PCEs collectively must cover all the IGP areas where all
inter-area LSPs traverse.
Figure 2 and 3 below illustrate two examples of multiple PCE inter-
area computation
------ ------ ------
| PCE1 |<------>| PCE0 |<---->| PCE2 |
------ ------ ------
| | |
| | |
--------------------------------------------
| | | |
| ABR2 ABR3 |
R1 area1 | area0 | area2 R2
| ABR1 ABR4 |
| | | |
--------------------------------------------
Figure 2: Cooperation between single-area PCEs
Figure 2 above illustrates a multi-area network with 3 areas. PCE0,
PCE1 and PCE2 are PCEs responsible for path computation respectively
in area 0, 1 and 2. These PCEs have topology visibility limited to
one area and are called single-area PCEs.
To setup an inter-area LSP from R1 in area 1 to R2 in area 2, R1 has
to contact PCE1. PCE1 then collaborates with PCE0, and PCE0 with PCE2
so as to compute an end-to-end shortest constrained path.
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------ ------
| PCE1 | <----> | PCE2 |
------ ------
/ \ / \
/ \ / \
--------------------------------------------
| | | |
| ABR2 ABR3 |
R1 area1 | area0 | area2 R2
| ABR1 ABR4 |
| | | |
--------------------------------------------
Figure 3: Cooperation between multi-area PCEs
Figure 3 above illustrates a multi-area network with 3 areas. PCE1,
and PCE2 are PCEs responsible for path computation respectively in
area 0+1 and in area 0+2. This means that PCE1 and PCE2 have topology
visibility in area0+area1 and area0+area2 respectively.
To setup an inter-area LSP from R1 in area 1 to R2 in area 2, R1 has
to contact PCE1. PCE1 then collaborates with PCE2, so as to compute
an end-to-end shortest constrained path.
6. Considerations on PCE location
As explained in [PCE-ARCH] a PCE can be a LSR or a network server.
But note that in the inter-area context, it may be quite efficient
for the ABRs to act as PCEs. Indeed, ABRs have topology information
of the backbone area and at least one peripheral area. An inter-area
TE-LSP optimal path computation could rely on a single ABR, if the
path crosses only two IGP areas, or on collaboration between two ABRs
in case the path crosses three IGP areas.
For instance, in figure 2 above, ABR1 or ABR2 can play PCE1 role, and
similarly ABR3 or ABR4 can play PCE2 role. Note that such ABRs are
not necessarily transit LSRs on the computed inter-area TE LSP.
With such PCE distribution on ABRs, the PCECP would run directly
between LSRs. Note that if N peripheral areas are connected to one
backbone area, with at least N ABRs, inter-area path computation
would potentially require a full mesh of N^2 PCE-PCE communications
between ABRs. This reinforces the requirement for communication
protocol overhead minimization, expressed in [PCE-COM-REQ].
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7. Detailed Requirements on PCECP
This section lists a set of additional requirements for the PCE
Communication Protocol that complement requirements listed in [PCE-
COM-REQ] and are specific to inter-area (G)MPLS TE path computation.
7.1. Supported modes for PCE-based inter-area path computation
The PCECP MUST support the two PCE based inter-area path computation
modes set forth in section 5.
Multiple PCE inter-area path computation requires cooperation between
PCEs. Hence the PCECP MUST support cooperation between PCEs so as to
arrive at an inter-area optimal path. It MUST allow requests and
replies for cooperative inter-area path computation.
A simple cooperation may consists in exchanging intra or inter-area
path Segments, and combine them to build an end-to-end optimal path.
This is a basic cooperation level that allows building an inter-area
optimal path in a recursive manner.
The path segment combination could be done in the backward
direction, in which case an inter-PCE response message includes a set
of computed intra or inter-area path segments from a set of
downstream ABRs to the destination, along with their respective cost.
These path segments have to be completed by upstream PCEs in a
recursive manner so as to build an end-to-end optimal path across
areas. To support this collaboration mode, a response message MUST
allow the inclusion of multiple intra-area or inter-area path
segments from a set of downstream ABRs, to the destination, along
with their respective cost (see also 8.4).
Note that path segment combination in the forward direction is for
further Study.
7.2. Control of area crossing
In addition to the path constraints specified in section 6.1.16 of
[PCE-COM-REQ] the request message MUST allow indicating whether area
crossing is allowed or not.
Indeed, for inter-area TE LSPs whose head-end and tail-end LSRs
reside in the same IGP area, there may be intra-area and inter-area
feasible paths, and, as set forth in [RFC4105], if the shortest path
is an inter-area path, an operator either may want to avoid, as far
as possible, crossing area and thus may prefer selecting a sub-
optimal intra-area path or, conversely, may prefer to use a shortest
path, even if it crosses areas.
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7.3. Objective functions
*Editorial note: This section will be moved to the generic
requirement draft [PCE-COM-REQ] as this requirement applies to
various PCE applications*
As specified in [PCE-COM-REQ] an objective function corresponds to
the optimization criteria used for the computation of one path, or
the synchronized computation of a set of paths. In case of
unsynchronized path computation, this can be, for example, the path
cost or the residual bandwidth on the most loaded path link. In case
of synchronized path computation, this can be, for example, the
global bandwidth consumption or the residual bandwidth on the most
loaded network link.
For the purpose of inter-area path computation the PCECP MUST support
the following "unsynchronized" objective functions:
-Minimum cost path (shortest path)
-Least loaded path (widest path)
-To be completed
Also the PCECP SHOULD support the following "synchronized" objective
functions:
-Minimize aggregate bandwidth consumption on all links
-Maximize the residual bandwidth on the most loaded link.
-Minimize the cumulative cost of a set of diverse paths.
Note that the absence of an objective function in this list does not
mean that it must not be supported. As per the extensibility
requirement expressed in [PCE-COM-REQ], note that new objective
functions can be added to this list without impacting the protocol.
7.4. TE metric / IGP metric
The shortest path selection may rely either on the TE metric or on
the IGP metric (see [METRIC]). Hence the PCECP request message MUST
allow indicating the metric type (IGP or TE) to be used for shortest
path selection.
7.5. Recording path attributes
There are at least three aggregate path attributes defined in
(G)MPLS-TE: the hop-count, the cumulated TE-metric, and the cumulated
IGP-metric. The operator can actually give any semantic to the TE
metric and IGP metric. As suggested in [METRIC], if the TE-metric
encodes the link cost and the IGP metric the link delay, the
cumulated TE-metric indicates the total cost of the LSP and the
cumulated IGP metric the end-to-end propagation delay (provided that
the LSR transit delay is neglected in a first approximation).
A PCC may need to know the aggregate path attributes of an LSR, for
instance to select a preferred path among a set of computed paths.
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In an inter-area context, a PCC may not be able to deduce this
information from the supplied path.
Therefore the PCECP request message MUST allow indicating the set of
aggregate path attributes (hop-count, cumulated TE-metric, cumulated
IGP-Metric) that are required in the reply and the PCECP response
message MUST support the inclusion of a set of aggregate path
attributes.
Note that if new TE link attributes are defined in the future to
encode specific link parameters, and allowing to define specific
aggregate path constraints, such as, e.g. delay, distance or power
loss, the PCEPC will have to be extended to support them.
Note that in case the computed path includes loose hops the PCE may
not be able to give an accurate aggregate path attribute. Hence the
response message MUST allow indicating that an aggregate path
attribute is unknown.
7.6. Strict Explicit path and Loose Path
A Strict Explicit Path is defined as a set of strict hops.
A Loose Path is defined as a set of strict and loose hops.
An inter-area path may be strictly explicit or loose (e.g. a list of
ABRs as loose hops)
It may be useful to indicate to the PCE if a Strict Explicit path is
required or not.
Hence the PCECP request message MUST allow indicating if a Strict
Explicit Path is required/desired.
7.7. PCE-list enforcement and recording in Multiple PCE Computation
In case of multiple-PCE path computation, a PCC may want to indicate
a preferred list of PCEs to be used.
Hence the PCECP request message MUST support the inclusion of a list
of preferred PCEs.
Note that this requires that a PCC in one area have knowledge of PCEs
in other areas. This could rely on configuration or on a PCE
discovery mechanism, allowing discovery across area boundaries (see
[PCE-DISCO-REQ]).
Also it would be useful to know the list of PCEs which effectively
participated in the computation.
Hence the request message MUST support requesting for PCE recording
and the response message MUST support the recording of the set of one
or more PCEs that took part into the computation.
It may also be useful to know the path segments computed by each PCE.
Hence the request message SHOULD allow requesting for the
identification of path segment computed by a PCE, and the response
message SHOULD allow identifying the path segments computed by each
PCE.
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7.8. Inclusion of Area IDs in request
The knowledge of the area in which the source and destination lie
would allow selection of appropriate cooperating PCEs.
A PCE may not be able to determine the location of the source and
destination LSRs. Hence it would be useful that a PCC indicates the
source area ID and destination area IDs.
For that purpose the request message MUST support the inclusion of
source and destination area IDs.
Note that this information could be learned on the PCC by
configuration.
7.9. Load-Balancing
*Editorial note: This section will be moved to the generic
requirement draft [PCE-COM-REQ] as this requirement applies to
various PCE applications*
In some cases a single inter-area path may not fit a TE-LSP bandwidth
constraint. In this case it may be useful to setup a set of paths
whose cumulated residual bandwidth fit the TE-LSP bandwidth request.
This is what we call load balancing.
So as to avoid ending up with a huge number of paths for a given
request, and/or with low bandwidth paths, it is required to control
the number of computed paths and the minimum path bandwidth.
The request message MUST allow indicating if load-balancing is
allowed or not. It MUST also include the number of paths in a load-
balancing path group, and the minimum path bandwidth in a load-
balancing path group. The response MUST support the inclusion of the
set of computed paths of a load-balancing path group, as well as
their respective bandwidth.
7.10. Diverse Path computation
For various reasons including protection and load balancing, the
computation of diverse inter-area paths may be required.
There are various levels of diversity in an inter-area context:
-Per area diversity (intra-area path segments are link, node or
SRLG disjoint)
-Inter-Area diversity (end-to-end inter-area paths are link,
node or SRLG disjoint)
Note that two paths may be disjoint in the backbone area but shared
in peripheral areas. Also two paths may be node disjoints within
areas but may share ABRs.
The request message MUST allow requesting the computation of a set of
diverse paths between a same couple of nodes or distinct couples of
nodes. It MUST allow indicating the required level of intra-area
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diversity (link, node, SRLG) on a per area basis, as well as the
level of inter-area diversity (shared ABRs or ABR disjointness).
The response message MUST allow indicating the level of diversity of
a set of computed loose paths.
Note that specific objective function may be requested for diverse
path computation, such as to minimize the cumulated cost of a set of
diverse paths (see also 7.3).
7.11. LSP failure handling
7.11.1. LSP Rerouting
*Editorial note: This section will be moved to the generic
requirement draft [PCE-COM-REQ] as this requirement applies to
various PCE applications*
Upon LSP failure, due to link, node or SRLG failure, a head-end LSR
may send a request to the PCE so as to reroute the LSP over an
alternate path. So as to ease the computation such request should
include the previous path and the failed element (if it can be
identified).
Hence the request message MUST allow indicating if the computation is
for an LSP restoration, and MUST support the inclusion of the
previously computed path as well as the failed element.
Note that the old path is actually useful only if the old LSP is not
torn down yet. This is up to the PCC to decide if it includes the old
path or not.
Note that a network failure may impact a large number of LSPs. A
potentially large number of PCCs, are going to simultaneously send a
request to the PCE. Some jittering may be used on PCCs so as to delay
a request to the PCE, under network failure condition.
The PCECP MAY support the inclusion, in a response message to a PCC,
of an upper bound of the jitter to be used for further requests to
the PCE (e.g. the PCC will wait for a random value between 0 and the
upper bound before sending another request). This upper bound would
depend on the level of congestion of the PCE.
7.11.2. Backup path computation
ABRs can be protected using Fast Reroute (FRR) node protection [MPLS-
FRR]. This requires setting up inter-area FRR backup LSPs (bypass or
detour).
The PCECP SHOULD support the computation of inter-area FRR backup
LSPs (detour or bypass). Note that the objective function may be to
minimize overhaul backup bandwidth consumption, by maximizing
bandwidth sharing among backup LSPs protecting independent elements.
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Detailed requirements for intra and inter-area PCE-based backup path
computation are for further study and will be addressed in a separate
document.
7.12. Inter-Area policies
As already defined in Section 8.2 a request message MUST allow
indicating whether area crossing is allowed or not.
A PCE may want to apply policies based on the initiating PCC.
In a multiple-PCE computation the address of the initiating PCC may
no longer be part of the request messages sent between PCEs.
Hence, the request message MUST support the inclusion of the address
of the originator PCC.
Note that in some case this is important to contain an inter-area
path within a single AS. Hence the request message MUST allow
indicating that AS crossing is not authorized.
7.13. Scalability
As already pointed out in [PCE-COM-REQ] the PCECP MUST scale well, at
least as good as linearly, with an increase of any of the following
parameters:
- number of PCCs communicating with a single PCE
- number of PCEs communicated to by a single PCC
- number of PCEs communicated to by another PCE
- number of request per PCE per second in steady state
- number of requests per PCE per second under emergency condition
Note that these numbers will depend on the level of PCE distribution
and on the PCE approach used (Single PCE computation, Multiple PCEs
computation…)
For instance in a network that comprises I IGP areas, with P PCCs
per area and A ABRs per area boundary then
-For single PCE computation with an all-areas PCE Server:
-Number of PCCs communicating with a single PCE=I*P
-Number of PCEs communicated to by a single PCC=1
-Number of PCEs communicated to by another PCE=0
-For multiple PCE computation with ABRs acting as PCEs:
-Number of PCCs communicating with a single PCE=P
-Number of PCE communicated to by a single PCC=I*A
-Number of PCEs communicated to by another PCE=I*A
Typical values for a large inter-area network can be: I=50, P=100,
and A=2.
Note also that the memory and CPU consumed to maintain and
synchronize the TED on a PCE will directly depend on the number of
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areas under control of the PCE. This may diminish the benefits of
"all area" PCEs, but this is beyond the scope of this document.
8. Manageability consideration
Manageability of inter-area PCEs must address the following
consideration for section 7:
- need for a MIB module for control plane and monitoring
- need for built-in diagnostic tools
- configuration implications for the protocol
9. Security Considerations
IGP areas are administrated by the same entity. Hence the inter-area
application does not imply new trust model, or new security issues
beyond those already defined in [PCE-COM-REQ].
10. Acknowledgments
We would also like to thank Adrian Farrel, Jean-Philippe Vasseur,
Bruno Decraene and Yannick Le Louedec for their useful comments and
suggestions.
11. Informative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3667] Bradner, S., "IETF Rights in Contributions", BCP 78, RFC
3667, February 2004.
[BCP79] Bradner, S., "Intellectual Property Rights in IETF
Technology", RFC 3979, March 2005.
[RFC4105] Le Roux J.L., Vasseur J.P., Boyle, J., et al. "Requirements
for inter-area MPLS-TE" RFC 4105, June 2005.
[PCE-ARCH] A. Farrel, JP. Vasseur and J. Ash, “Path Computation
Element (PCE) Architecture”, draft-ietf-pce-architecture (work in
progress).
[PCE-COM-REQ] J. Ash, J.L Le Roux et al., “PCE Communication Protocol
Generic Requirements”, draft-ietf-pce-comm-protocol-gen-reqs (work in
progress).
[PCE-DISC-REQ] J.L. Le Roux et al., “Requirements for Path
Computation Element (PCE) Discovery”, draft-ietf-pce-discovery-reqs
(work in progress).
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[PD-COMP] Vasseur, J.P., Ayyangar, A., Zhang, R., " A Per-domain path
computation method for computing Inter-domain Traffic Engineering
(TE) Label Switched Path (LSP)", draft-ietf-ccamp-inter-domain-pd-
path-comp, work in progress
[METRIC] Le Faucheur, F., Uppili, R., Vedrenne, A., Merckx, P.,
and T. Telkamp, "Use of Interior Gateway Protocol(IGP) Metric as a
second MPLS Traffic Engineering (TE) Metric", BCP 87, RFC 3785, May
2004.
[ID-RSVP] Ayyangar, A., Vasseur, J.P., "Inter domain GMPLS Traffic
Engineering - RSVP-TE extensions", draft-ietf-ccamp-inter-domain-
rsvp-te, work in progress.
12. Editor Address:
Jean-Louis Le Roux
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex
FRANCE
Email: jeanlouis.leroux@francetelecom.com
13. Contributors' Addresses
Jerry Ash
AT&T
Room MT D5-2A01
200 Laurel Avenue
Middletown, NJ 07748, USA
Phone: +1-(732)-420-4578
Email: gash@att.com
Nabil Bitar
Verizon
40 Sylvan Road
Waltham, MA 02145
Email: nabil.bitar@verizon.com
Dean Cheng
Cisco Systems Inc.
3700 Cisco Way
San Jose CA 95134 USA
Phone: +1 408 527 0677
Email: dcheng@cisco.com
Kenji Kumaki
KDDI Corporation
Garden Air Tower
Iidabashi, Chiyoda-ku,
Tokyo 102-8460, JAPAN
Le Roux et al. [Page 17]
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Phone: +81-3-6678-3103
Email: ke-kumaki@kddi.com
Eiji Oki
NTT
Midori-cho 3-9-11
Musashino-shi, Tokyo 180-8585, JAPAN
Email: oki.eiji@lab.ntt.co.jp
Raymond Zhang
BT INFONET Services Corporation
2160 E. Grand Ave.
El Segundo, CA 90245 USA
Email: Raymond_zhang@bt.infonet.com
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Copyright Statement
Le Roux et al. [Page 18]
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Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Le Roux et al. [Page 19]
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