draft-ietf-pce-hierarchy-fwk-00.txt   draft-ietf-pce-hierarchy-fwk-01.txt 
Network Working Group D. King (Ed.) Network Working Group D. King (Ed.)
Internet-Draft Old Dog Consulting Internet-Draft Old Dog Consulting
Intended Status: Informational A. Farrel (Ed.) Intended Status: Informational A. Farrel (Ed.)
Expires: April 4, 2012 Old Dog Consulting Expires: 11 August 2012 Old Dog Consulting
October 4, 2011 11 March 2012
The Application of the Path Computation Element Architecture to the The Application of the Path Computation Element Architecture to the
Determination of a Sequence of Domains in MPLS and GMPLS Determination of a Sequence of Domains in MPLS and GMPLS
draft-ietf-pce-hierarchy-fwk-00.txt draft-ietf-pce-hierarchy-fwk-01.txt
Abstract Abstract
Computing optimum routes for Label Switched Paths (LSPs) across Computing optimum routes for Label Switched Paths (LSPs) across
multiple domains in MPLS Traffic Engineering (MPLS-TE) and GMPLS multiple domains in MPLS Traffic Engineering (MPLS-TE) and GMPLS
networks presents a problem because no single point of path networks presents a problem because no single point of path
computation is aware of all of the links and resources in each computation is aware of all of the links and resources in each
domain. A solution may be achieved using the Path Computation domain. A solution may be achieved using the Path Computation
Element (PCE) architecture. Element (PCE) architecture.
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This Internet-Draft will expire on April 4, 2012. This Internet-Draft will expire on 11 August 2012.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Contents Contents
1. Introduction..................................................3 1. Introduction..................................................3
1.1 Problem Statement.........................................4 1.1 Problem Statement.........................................4
1.2 Definition of a Domain............. ......................5 1.2 Definition of a Domain............. ......................5
1.3 Assumptions and Requirements..............................5 1.3 Assumptions and Requirements..............................5
1.3.1 Metric Objectives...................................6 1.3.1 Metric Objectives...................................6
1.3.2 Domain Diversity....................................6 1.3.2 Domain Diversity....................................7
1.3.3 Existing Traffic Engineering Constraints............7 1.3.3 Existing Traffic Engineering Constraints............7
1.3.4 Commercial Constraints..............................7 1.3.4 Commercial Constraints..............................7
1.3.5 Domain Confidentiality..............................7 1.3.5 Domain Confidentiality..............................7
1.3.6 Limiting Information Aggregation....................7 1.3.6 Limiting Information Aggregation....................7
1.3.7 Domain Interconnection Discovery....................7 1.3.7 Domain Interconnection Discovery....................8
1.4 Terminology...............................................7 1.4 Terminology...............................................8
2. Per Domain Path Computation...................................8 2. Examination of Existing PCE Mechanisms........................9
3. Backward Recursive Path Computation...........................9 2.1 Per Domain Path Computation...............................9
3.1. Applicability of BRPC when the Domain Path is not Known..10 2.2 Backward Recursive Path Computation.......................10
4. Hierarchical PCE..............................................10 2.2.1 Applicability of BRPC when the Domain Path is not
5. Hierarchical PCE Procedures...................................11 Known.................................................10
5.1 Objective Functions and Policy............................11 3. Hierarchical PCE..............................................11
5.2 Maintaining Domain Confidentiality........................12 4. Hierarchical PCE Procedures...................................12
5.3 PCE Discovery.............................................12 4.1 Objective Functions and Policy............................12
5.4 Parent Domain Traffic Engineering Database................13 4.2 Maintaining Domain Confidentiality........................13
5.5 Determination of Destination Domain ......................14 4.3 PCE Discovery.............................................13
5.6 Hierarchical PCE Examples.................................14 4.4 Parent Domain Traffic Engineering Database................14
5.6.1 Hierarchical PCE Initial Information Exchange.......17 4.5 Determination of Destination Domain ......................14
5.6.2 Hierarchical PCE End-to-End Path Computation 4.6 Hierarchical PCE Examples.................................15
4.6.1 Hierarchical PCE Initial Information Exchange.......17
4.6.2 Hierarchical PCE End-to-End Path Computation
Procedure Example.........................................17 Procedure Example.........................................17
5.7 Hierarchical PCE Error Handling...........................17 4.7 Hierarchical PCE Error Handling...........................19
5.8 Hierarchical PCEP Protocol Extensions.....................18 4.8 Hierarchical PCEP Protocol Extensions.....................19
5.8.1 PCEP Request Qualifiers.............................18 4.8.1 PCEP Request Qualifiers.............................19
5.8.2 Indication of H-PCE Capability......................18 4.8.2 Indication of H-PCE Capability......................20
5.8.3 Intention to Utilize Parent PCE Capabilities........19 4.8.3 Intention to Utilize Parent PCE Capabilities........20
5.8.4 Communication of Domain Connectivity Information....19 4.8.4 Communication of Domain Connectivity Information....20
5.8.5 Domain Identifiers..................................19 4.8.5 Domain Identifiers..................................21
6. Hierarchical PCE Applicability................................20 5. Hierarchical PCE Applicability................................21
6.1 Antonymous Systems and Areas..............................20 5.1 Antonymous Systems and Areas..............................21
6.2 ASON architecture (G-7715-2)..............................20 5.2 ASON architecture (G-7715-2)..............................22
6.2.1 Implicit Consistency Between Hierarchical PCE and 5.2.1 Implicit Consistency Between Hierarchical PCE and
G.7715.2..................................................21 G.7715.2..................................................23
6.2.2 Benefits of Hierarchical PCEs in ASON...............23 5.2.2 Benefits of Hierarchical PCEs in ASON...............24
7. Management Considerations ....................................23 6. A Note on BGP-TE..............................................24
7.1 Control of Function and Policy............................23 7. Management Considerations ....................................26
7.1.1 Child PCE...........................................23 7.1 Control of Function and Policy............................26
7.1.2 Parent PCE..........................................23 7.1.1 Child PCE...........................................26
7.1.3 Policy Control......................................24 7.1.2 Parent PCE..........................................26
7.2 Information and Data Models...............................24 7.1.3 Policy Control......................................27
7.3 Liveness Detection and Monitoring.........................24 7.2 Information and Data Models...............................27
7.4 Verifying Correct Operation...............................24 7.3 Liveness Detection and Monitoring.........................27
7.5. Impact on Network Operation..............................25 7.4 Verifying Correct Operation...............................27
8. Security Considerations ......................................25 7.5. Impact on Network Operation..............................28
9. IANA Considerations ..........................................25 8. Security Considerations ......................................28
10. Acknowledgements ............................................25 9. IANA Considerations ..........................................29
11. References ..................................................26 10. Acknowledgements ............................................29
11.1. Normative References....................................26 11. References ..................................................29
11.2. Informative References .................................26 11.1. Normative References....................................29
12. Authors' Addresses ..........................................27 11.2. Informative References .................................20
12. Authors' Addresses ..........................................31
1. Introduction 1. Introduction
The capability to compute the routes of end-to-end inter-domain MPLS The capability to compute the routes of end-to-end inter-domain MPLS
Traffic Engineering (TE) and GMPLS Label Switched Paths (LSPs) may be Traffic Engineering (TE) and GMPLS Label Switched Paths (LSPs) is
provided by a Path Computation Element (PCE). The PCE architecture is expressed as requirements in [RFC4105] and [RFC4216]. This capability
defined in [RFC4655]. The methods for establishing and controlling may be realized by a Path Computation Element (PCE). The PCE
inter-domain MPLS-TE and GMPLS LSPs are documented in [RFC4726]. architecture is defined in [RFC4655]. The methods for establishing
and controlling inter-domain MPLS-TE and GMPLS LSPs are documented in
[RFC4726].
A domain can be defined as a separate administrative, geographic, or In this context, a domain can be defined as a separate
switching environment within the network. A domain may be further administrative, geographic, or switching environment within the
defined as a zone of routing or computational ability. Under these network. A domain may be further defined as a zone of routing or
definitions a domain might be categorized as an Antonymous System computational ability. Under these definitions a domain might be
(AS) or an Interior Gateway Protocol (IGP) area [RFC4726] and categorized as an Antonymous System (AS) or an Interior Gateway
[RFC4655]. Domains are connected through ingress and egress Protocol (IGP) area [RFC4726] and [RFC4655]. Domains are connected
boundary nodes (BNs). A more detailed definition is given in through ingress and egress boundary nodes (BNs). A more detailed
Section 1.2. definition is given in Section 1.2.
In a multi-domain environment, the determination of an end-to-end In a multi-domain environment, the determination of an end-to-end
traffic engineered path is a problem because no single point of path traffic engineered path is a problem because no single point of path
computation is aware of all of the links and resources in each computation is aware of all of the links and resources in each
domain. PCEs can be used to compute end-to-end paths using a per- domain. PCEs can be used to compute end-to-end paths using a per-
domain path computation technique [RFC5152]. Alternatively, the domain path computation technique [RFC5152]. Alternatively, the
backward recursive path computation (BRPC) mechanism [RFC5441] backward recursive path computation (BRPC) mechanism [RFC5441]
allows multiple PCEs to collaborate in order to select an optimal allows multiple PCEs to collaborate in order to select an optimal
end-to-end path that crosses multiple domains. Both mechanisms end-to-end path that crosses multiple domains. Both mechanisms
assume that the sequence of domains to be crossed between ingress assume that the sequence of domains to be crossed between ingress
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to be selected, and the optimum end-to-end path to be derived. to be selected, and the optimum end-to-end path to be derived.
The model described in this document introduces a hierarchical The model described in this document introduces a hierarchical
relationship between domains. It is applicable to environments with relationship between domains. It is applicable to environments with
small groups of domains where visibility from the ingress Label small groups of domains where visibility from the ingress Label
Switching Router (LSR) is limited. Applying the hierarchical PCE Switching Router (LSR) is limited. Applying the hierarchical PCE
model to large groups of domains such as the Internet, is not model to large groups of domains such as the Internet, is not
considered feasible or desirable, and is out of scope for this considered feasible or desirable, and is out of scope for this
document. document.
This document does not specify any protocol extensions or
enhancements. That work is left for future protocol specification
documents. However, some assumptions are made about which protocols
will be used to provide specific functions, and guidelines to
future protocol developers are made in the form of requirements
statements.
1.1 Problem Statement 1.1 Problem Statement
Using a PCE to compute a path between nodes within a single domain is Using a PCE to compute a path between nodes within a single domain is
relatively straightforward. Computing an end-to-end path when the relatively straightforward. Computing an end-to-end path when the
source and destination nodes are located in different domains source and destination nodes are located in different domains
requires co-operation between multiple PCEs, each responsible for requires co-operation between multiple PCEs, each responsible for
its own domain. its own domain.
Techniques for inter-domain path computation described so far Techniques for inter-domain path computation described so far
([RFC5152] and [RFC5441]) assume that the sequence of domains to be ([RFC5152] and [RFC5441]) assume that the sequence of domains to be
crossed from source to destination is well known. No explanation is crossed from source to destination is well known. No explanation is
given (for example, in [RFC4655]) of how this sequence is generated given (for example, in [RFC4655]) of how this sequence is generated
or what criteria may be used for the selection of paths between or what criteria may be used for the selection of paths between
domains. In small clusters of domains, such as simple cooperation domains. In small clusters of domains, such as simple cooperation
between adjacent ISPs, this selection process is not complex. In more between adjacent ISPs, this selection process is not complex. In more
advanced deployments (such as optical networks constructed from advanced deployments (such as optical networks constructed from
multiple sub-domains, or multi-AS environments) the choice of domains multiple sub-domains, or in multi-AS environments) the choice of
in the end-to-end domain sequence can be critical to the domains in the end-to-end domain sequence can be critical to the
determination of an optimum end-to-end path. determination of an optimum end-to-end path.
This document introduces the concept of a hierarchical PCE This document introduces the concept of a hierarchical PCE
architecture and shows how to coordinate PCEs in peer domains in architecture and shows how to coordinate PCEs in peer domains in
order to derive an optimal end-to-end path. order to derive an optimal end-to-end path.
The work is currently scoped to operate with a small group of domains The work is scoped to operate with a small group of domains, and
and there is no intent to apply this model to a large group of there is no intent to apply this model to a large group of domains,
domains, e.g., to the Internet. e.g., to the Internet.
1.2 Definition of a Domain 1.2 Definition of a Domain
A domain is defined in [RFC4726] as any collection of network A domain is defined in [RFC4726] as any collection of network
elements within a common sphere of address management or path elements within a common sphere of address management or path
computational responsibility. Examples of such domains include computational responsibility. Examples of such domains include
IGP areas and Autonomous Systems. Wholly or partially overlapping IGP areas and Autonomous Systems. Wholly or partially overlapping
domains are not within the scope of this document. domains are not within the scope of this document.
In the context of GMPLS, a particularly important example of a domain In the context of GMPLS, a particularly important example of a domain
is the Automatically Switched Optical Network (ASON) subnetwork is the Automatically Switched Optical Network (ASON) subnetwork
[G-8080]. In this case, computation of an end-to-end path requires [G-8080]. In this case, computation of an end-to-end path requires
the selection of nodes and links within a parent domain where some the selection of nodes and links within a parent domain where some
nodes may, in fact, be subnetworks. Furthermore, a domain might be an nodes may, in fact, be subnetworks. Furthermore, a domain might be an
ASON routing area [G-7715]. A PCE may perform the path computation ASON Routing Area [G-7715]. A PCE may perform the path computation
function of an ASON routing controller as described in [G-7715-2]. function of an ASON Routing Controller as described in [G-7715-2].
See Section 6.2 for a further discussion of the applicability to the See Section 6.2 for a further discussion of the applicability to the
ASON architecture. ASON architecture.
This document assumes that the selection of a sequence of domains for This document assumes that the selection of a sequence of domains for
an end-to-end path is in some sense a hierarchical path computation an end-to-end path is in some sense a hierarchical path computation
problem. That is, where one mechanism is used to determine a path problem. That is, where one mechanism is used to determine a path
across a domain, a separate mechanism (or at least a separate set across a domain, a separate mechanism (or at least a separate set
of paradigms) is used to determine the sequence of domains. of paradigms) is used to determine the sequence of domains. The
responsibility for the selection of domain interconnection can belong
to either or both of the mechanisms.
1.3 Assumptions and Requirements 1.3 Assumptions and Requirements
Networks are often constructed from multiple domains. These Networks are often constructed from multiple domains. These
domains are often interconnected via multiple interconnect points. domains are often interconnected via multiple interconnect points.
Its assumed that the sequence of domains for an end-to-end path is Its assumed that the sequence of domains for an end-to-end path is
not always well known; that is, an application requesting end-to-end not always well known; that is, an application requesting end-to-end
connectivity has no preference for, or no ability to specify, the connectivity has no preference for, or no ability to specify, the
sequence of domains to be crossed by the path. sequence of domains to be crossed by the path.
The traffic engineering properties of a domain cannot be seen from The traffic engineering properties of a domain cannot be seen from
outside the domain. Traffic engineering aggregation or abstraction, outside the domain. Traffic engineering aggregation or abstraction,
hides information and can lead to failed path setup or the selection hides information and can lead to failed path setup or the selection
of suboptimal end-to-end paths [RFC4726]. The aggregation process of suboptimal end-to-end paths [RFC4726]. The aggregation process
may also have significant scaling issues for networks with many may also have significant scaling issues for networks with many
possible routes and multiple TE metrics. Flooding TE information possible routes and multiple TE metrics. Flooding TE information
breaks confidentiality and does not scale in the routing protocol. breaks confidentiality and does not scale in the routing protocol.
See Section 7 for a discussion of the concept of inter-domain traffic
engineering information exchange known as BGP-TE.
The primary goal of this document is to define how to derive optimal The primary goal of this document is to define how to derive optimal
end-to-end, multi-domain paths when the sequence of domains is not end-to-end, multi-domain paths when the sequence of domains is not
known in advance. The solution needs to be scalable and to maintain known in advance. The solution needs to be scalable and to maintain
internal domain topology confidentiality while providing the optimal internal domain topology confidentiality while providing the optimal
end-to-end path. It cannot rely on the exchange of TE information end-to-end path. It cannot rely on the exchange of TE information
between domains, and it cannot utilise a computation element that has between domains, and for the confidentiality, scaling, and
universal knowledge of TE properties and topology of all domains. aggregation reasons just cited, it cannot utilise a computation
element that has universal knowledge of TE properties and topology
of all domains.
The sub-sections that follow set out the primary objectives and The sub-sections that follow set out the primary objectives and
requirements to be satisfied by a PCE solution to multi-domain path requirements to be satisfied by a PCE solution to multi-domain path
computation. computation.
1.3.1 Metric Objectives 1.3.1 Metric Objectives
The definition of optimality is dependent on policy, and is based on The definition of optimality is dependent on policy, and is based on
a single objective or a group objectives. An objective is expressed a single objective or a group objectives. An objective is expressed
as an objective function [RFC5541] and may be specified on a path as an objective function [RFC5541] and may be specified on a path
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in this document. They define how the path metrics and TE link in this document. They define how the path metrics and TE link
qualities are manipulated during inter-domain path computation. The qualities are manipulated during inter-domain path computation. The
list is not proscriptive and may be expanded in other documents. list is not proscriptive and may be expanded in other documents.
o Minimize the cost of the path [RFC5541] o Minimize the cost of the path [RFC5541]
o Select a path using links with the minimal load [RFC5541] o Select a path using links with the minimal load [RFC5541]
o Select a path that leaves the maximum residual bandwidth [RFC5541] o Select a path that leaves the maximum residual bandwidth [RFC5541]
o Minimize aggregate bandwidth consumption [RFC5541] o Minimize aggregate bandwidth consumption [RFC5541]
o Minimize the Load of the most loaded Link [RFC5541] o Minimize the Load of the most loaded Link [RFC5541]
o Minimize the Cumulative Cost of a set of paths [RFC5541] o Minimize the Cumulative Cost of a set of paths [RFC5541]
o Minimize the number of boundary nodes used o Minimize or cap the number of domains crossed
o Limit the number of domains crossed
o Disallow domain re-entry o Disallow domain re-entry
See Section 5.1 for further discussion of objective functions. See Section 5.1 for further discussion of objective functions.
1.3.2 Domain Diversity 1.3.2 Domain Diversity
A pair of paths are domain-diverse if they do not transit any of the A pair of paths are domain-diverse if they do not transit any of the
same domains. A pair of paths that share a common ingress and egress same domains. A pair of paths that share a common ingress and egress
are domain-diverse if they only share the same domains at the ingress are domain-diverse if they only share the same domains at the ingress
and egress (the ingress and egress domains). Domain diversity may be and egress (the ingress and egress domains). Domain diversity may be
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relevant constraints such as policy, SLAs, security, peering relevant constraints such as policy, SLAs, security, peering
preferences, and dollar costs. preferences, and dollar costs.
Additionally it may be necessary for the service provider to Additionally it may be necessary for the service provider to
request that specific domains are included or excluded based on request that specific domains are included or excluded based on
commercial relationships, security implications, and reliability. commercial relationships, security implications, and reliability.
1.3.5 Domain Confidentiality 1.3.5 Domain Confidentiality
A key requirement is the ability to maintain domain confidentiality A key requirement is the ability to maintain domain confidentiality
when computing inter-domain end-to-end paths. When required by local when computing inter-domain end-to-end paths. It should be possible
policy, a PCE should not need to disclose to any other PCE the intra- for local policy to require that a PCE not disclose to any other PCE
domain paths it computes or the internal topology of the domain it the intra-domain paths it computes or the internal topology of the
serves. domain it serves. This requirement should have no impact in the
optimality or quality of the end-to-end path that is derived.
1.3.6 Limiting Information Aggregation 1.3.6 Limiting Information Aggregation
It is important to minimise the amount of aggregation within the In order to reduce processing overhead and to not sacrifice
solution. There should be no associated computation burden or computational detail, there should be no requirement to aggregate or
requirement to aggregate and abstract traffic engineering link abstract traffic engineering link information.
information.
1.3.7 Domain Interconnection Discovery 1.3.7 Domain Interconnection Discovery
To support domain mesh topologies, the solution should allow the To support domain mesh topologies, the solution should allow the
discovery and selection of domain inter-connections. Pre- discovery and selection of domain inter-connections. Pre-
configuration of preferred domain interconnections should also be configuration of preferred domain interconnections should also be
supported for network operators that have bilateral agreement, and supported for network operators that have bilateral agreement, and
preference for the choice of points of interconnection. preference for the choice of points of interconnection.
1.4 Terminology 1.4 Terminology
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Child PCE: A PCE responsible for computing the path across one or Child PCE: A PCE responsible for computing the path across one or
more specific (child) domains. A child PCE maintains a relationship more specific (child) domains. A child PCE maintains a relationship
with at least one parent PCE. with at least one parent PCE.
OF: Objective Function: A set of one or more optimization OF: Objective Function: A set of one or more optimization
criteria used for the computation of a single path (e.g., path cost criteria used for the computation of a single path (e.g., path cost
minimization), or the synchronized computation of a set of paths minimization), or the synchronized computation of a set of paths
(e.g., aggregate bandwidth consumption minimization). See [RFC4655] (e.g., aggregate bandwidth consumption minimization). See [RFC4655]
and [RFC5541]. and [RFC5541].
2. Per-Domain Path Computation 2. Examination of Existing PCE Mechanisms
This section provides a brief overview of two existing PCE
cooperation mechanisms called the per-domain path computation method,
and the backward recursive path computation method. It describes the
applicability of these methods to the multi-domain problem.
2.1 Per-Domain Path Computation
The per-domain path computation method for establishing inter-domain The per-domain path computation method for establishing inter-domain
TE-LSPs [RFC5152] defines a technique whereby the path is computed TE-LSPs [RFC5152] defines a technique whereby the path is computed
during the signalling process on a per-domain basis. The entry BN of during the signalling process on a per-domain basis. The entry BN of
each domain is responsible for performing the path computation for each domain is responsible for performing the path computation for
the section of the LSP that crosses the domain, or for requesting the section of the LSP that crosses the domain, or for requesting
that a PCE for that domain computes that piece of the path. that a PCE for that domain computes that piece of the path.
During per-domain path computation, each computation results in the During per-domain path computation, each computation results in the
best path across the domain to provide connectivity to the next best path across the domain to provide connectivity to the next
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path as advertise by BGP. Note, however, that the existence of an IP path as advertise by BGP. Note, however, that the existence of an IP
forwarding path does guarantee the presence of sufficient bandwidth, forwarding path does guarantee the presence of sufficient bandwidth,
let alone an optimal TE path. Furthermore, in many GMPLS systems let alone an optimal TE path. Furthermore, in many GMPLS systems
inter-domain IP routing will not be present. Thus, per-domain path inter-domain IP routing will not be present. Thus, per-domain path
computation may require a significant number of crankback routing computation may require a significant number of crankback routing
attempts to establish even a sub-optimal path. attempts to establish even a sub-optimal path.
Note also that the PCEs in each domain may have different computation Note also that the PCEs in each domain may have different computation
capabilities, may run different path computation algorithms, and may capabilities, may run different path computation algorithms, and may
apply different sets of constraints and optimization criteria, etc. apply different sets of constraints and optimization criteria, etc.
This can result in the end-to-end path being inconsistent and sub- This can result in the end-to-end path being inconsistent and sub-
optimal. optimal.
Per-domain path computation can suit simply-connected domains where Per-domain path computation can suit simply-connected domains where
the preferred points of interconnection are known. the preferred points of interconnection are known.
3. Backward Recursive Path Computation 2.2 Backward Recursive Path Computation
The Backward Recursive Path Computation (BRPC) [RFC5441] procedure The Backward Recursive Path Computation (BRPC) [RFC5441] procedure
involves cooperation and communication between PCEs in order to involves cooperation and communication between PCEs in order to
compute an optimal end-to-end path across multiple domains. The compute an optimal end-to-end path across multiple domains. The
sequence of domains to be traversed can either be determined before sequence of domains to be traversed can either be determined before
or during the path computation. In the case where the sequence of or during the path computation. In the case where the sequence of
domains is known, the ingress Path Computation Client (PCC) sends a domains is known, the ingress Path Computation Client (PCC) sends a
path computation request to the PCE responsible for the ingress path computation request to the PCE responsible for the ingress
domain. This request is forwarded between PCEs, domain-by-domain, to domain. This request is forwarded between PCEs, domain-by-domain, to
the PCE responsible for the egress domain. The PCE in the egress the PCE responsible for the egress domain. The PCE in the egress
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ingress LSR to connect to the rest of the tree. The ingress PCE then ingress LSR to connect to the rest of the tree. The ingress PCE then
selects the optimal end-to-end path from the tree, and returns the selects the optimal end-to-end path from the tree, and returns the
path to the initiating PCC. path to the initiating PCC.
BRPC may suit environments where multiple connections exist between BRPC may suit environments where multiple connections exist between
domains and there is no preference for the choice of points of domains and there is no preference for the choice of points of
interconnection. It is best suited to scenarios where the domain interconnection. It is best suited to scenarios where the domain
path is known in advance, but can also be used when the domain path path is known in advance, but can also be used when the domain path
is not known. is not known.
3.1. Applicability of BRPC when the Domain Path is Not Known 2.2.1. Applicability of BRPC when the Domain Path is Not Known
As described above BRPC can be used to determine an optimal inter- As described above, BRPC can be used to determine an optimal inter-
domain path when the sequence is known. Even when the sequence of domain path when the domain sequence is known. Even when the sequence
domains is not known BRPC could be used as follows. of domains is not known BRPC could be used as follows.
o The PCC sends a request to the PCE for the ingress domain (the o The PCC sends a request to the PCE for the ingress domain (the
ingress PCE). ingress PCE).
o The ingress PCE sends the path computation request direct to the o The ingress PCE sends the path computation request direct to the
PCE responsible for the domain containing the destination node (the PCE responsible for the domain containing the destination node (the
egress PCE). egress PCE).
o The egress PCE computes an egress VSPT and passes it to a PCE o The egress PCE computes an egress VSPT and passes it to a PCE
responsible for each of the adjacent (potentially upstream) responsible for each of the adjacent (potentially upstream)
skipping to change at page 10, line 44 skipping to change at page 11, line 20
neighboring PCEs. neighboring PCEs.
o When the ingress PCE has received a VSPT from each of its o When the ingress PCE has received a VSPT from each of its
neighboring domains it is able to select the optimum path. neighboring domains it is able to select the optimum path.
Clearly this mechanism (which could be called path computation Clearly this mechanism (which could be called path computation
flooding) has significant scaling issues. It could be improved by flooding) has significant scaling issues. It could be improved by
the application of policy and filtering, but such mechanisms are not the application of policy and filtering, but such mechanisms are not
simple and would still leave scaling concerns. simple and would still leave scaling concerns.
4. Hierarchical PCE 3. Hierarchical PCE
In the hierarchical PCE architecture, a parent PCE maintains a domain In the hierarchical PCE architecture, a parent PCE maintains a domain
topology map that contains the child domains (seen as vertices in the topology map that contains the child domains (seen as vertices in the
topology) and their interconnections (links in the topology). The topology) and their interconnections (links in the topology). The
parent PCE has no information about the content of the child domains; parent PCE has no information about the content of the child domains;
that is, the parent PCE does not know about the resource availability that is, the parent PCE does not know about the resource availability
within the child domains, nor about the availability of connectivity within the child domains, nor about the availability of connectivity
across each domain. The parent PCE is aware of the TE capabilities of across each domain because such knowledge would violate the
the interconnections between child domains as these interconnections confidentiality requirement and would either require flooding of full
are links in its own topology map. information to the parent (scaling issue) or would necessitate some
form of aggregation. The parent PCE is aware of the TE capabilities
of the interconnections between child domains as these
interconnections are links in its own topology map.
Note that in the case that the domains are IGP areas, there is no Note that in the case that the domains are IGP areas, there is no
link between the domains (the ABRs have a presence in both link between the domains (the ABRs have a presence in both
neighboring areas). The parent domain may choose to represent this in neighboring areas). The parent domain may choose to represent this in
its TED as a virtual link that is unconstrained and has zero cost, its TED as a virtual link that is unconstrained and has zero cost,
but this is entirely an implementation issue. but this is entirely an implementation issue.
Each child domain has at least one PCE capable of computing paths Each child domain has at least one PCE capable of computing paths
across the domain. These PCEs are known as child PCEs and have a across the domain. These PCEs are known as child PCEs and have a
relationship with the parent PCE. Each child PCE also knows the relationship with the parent PCE. Each child PCE also knows the
skipping to change at page 11, line 34 skipping to change at page 12, line 15
properties of the domain interconnections. But the parent PCE does properties of the domain interconnections. But the parent PCE does
not know the contents of the child domains. Discovery of the domain not know the contents of the child domains. Discovery of the domain
topology and domain interconnections is discussed further in Section topology and domain interconnections is discussed further in Section
5.3. 5.3.
When a multi-domain path is needed, the ingress PCE sends a request When a multi-domain path is needed, the ingress PCE sends a request
to the parent PCE (using the path computation element protocol, PCEP to the parent PCE (using the path computation element protocol, PCEP
[RFC5440]). The parent PCE selects a set of candidate domain paths [RFC5440]). The parent PCE selects a set of candidate domain paths
based on the domain topology and the state of the inter-domain links. based on the domain topology and the state of the inter-domain links.
It then sends computation requests to the child PCEs responsible for It then sends computation requests to the child PCEs responsible for
each of the domains on the candidate domain paths. each of the domains on the candidate domain paths. These requests may
be sequential or parallel depending on implementation details.
Each child PCE computes a set of candidate path segments across its Each child PCE computes a set of candidate path segments across its
domain and sends the results to the parent PCE. The parent PCE uses domain and sends the results to the parent PCE. The parent PCE uses
this information to select path segments and concatenate them to this information to select path segments and concatenate them to
derive the optimal end-to-end inter-domain path. The end-to-end path derive the optimal end-to-end inter-domain path. The end-to-end path
is then sent to the child PCE which received the initial path request is then sent to the child PCE which received the initial path request
and this passes the path on to the PCC that issues the original and this child PCE passes the path on to the PCC that issued the
request. original request.
5. Hierarchical PCE Procedures 4. Hierarchical PCE Procedures
5.1 Objective Functions and Policy 4.1 Objective Functions and Policy
Deriving the optimal end-to-end domain path sequence is dependent on Deriving the optimal end-to-end domain path sequence is dependent on
the policy applied during domain path computation. An Objective the policy applied during domain path computation. An Objective
Function (OF) [RFC5541], or set of OFs, may be applied to define the Function (OF) [RFC5541], or set of OFs, may be applied to define the
policy being applied to the domain path computation. policy being applied to the domain path computation.
The OF specifies the desired outcome of the computation. It does The OF specifies the desired outcome of the computation. It does
not describe the algorithm to use. When computing end-to-end inter- not describe the algorithm to use. When computing end-to-end inter-
domain paths, required OFs may include (see Section 1.3.1): domain paths, required OFs may include (see Section 1.3.1):
o Minimum cost path o Minimum cost path
o Minimum load path o Minimum load path
o Maximum residual bandwidth path o Maximum residual bandwidth path
o Minimize aggregate bandwidth consumption o Minimize aggregate bandwidth consumption
o Minimize the number of boundary nodes used o Minimize or cap the number of transit domains
o Minimize the number of transit domains
o Disallow domain re-entry o Disallow domain re-entry
The objective function may be requested by the PCC, the ingress The objective function may be requested by the PCC, the ingress
domain PCE (according to local policy), or maybe applied by the domain PCE (according to local policy), or maybe applied by the
parent PCE according to inter-domain policy. parent PCE according to inter-domain policy.
5.2 Maintaining Domain Confidentiality More than one OF (or a composite OF) may be chosen to apply to a
single computation provided they are not contradictory. Composite OFs
may include weightings and preferences for the fulfilment of pieces
of the desired outcome.
4.2 Maintaining Domain Confidentiality
Information about the content of child domains is not shared for Information about the content of child domains is not shared for
scaling and confidentiality reasons. This means that a parent PCE is scaling and confidentiality reasons. This means that a parent PCE is
aware of the domain topology and the nature of the connections aware of the domain topology and the nature of the connections
between domains, but is not aware of the content of the domains. between domains, but is not aware of the content of the domains.
Similarly, a child PCE cannot know the internal topology of another Similarly, a child PCE cannot know the internal topology of another
child domain. Child PCEs also do not know the general domain mesh child domain. Child PCEs also do not know the general domain mesh
connectivity, this information is only known by the parent PCE. connectivity, this information is only known by the parent PCE.
As described in the earlier sections of this document, PCEs can As described in the earlier sections of this document, PCEs can
exchange path information in order to construct an end-to-end inter- exchange path information in order to construct an end-to-end inter-
domain path. Each per-domain path fragment reveals information about domain path. Each per-domain path fragment reveals information about
the topology and resource availability within a domain. Some the topology and resource availability within a domain. Some
management domains or ASes will not want to share this information management domains or ASes will not want to share this information
outside of the domain (even with a trusted parent PCE). In order to outside of the domain (even with a trusted parent PCE). In order to
conceal the information, a PCE may replace a path segment with a conceal the information, a PCE may replace a path segment with a
path-key [RFC5520]. This mechanism effectively hides the content of a path-key [RFC5520]. This mechanism effectively hides the content of a
segment of a path. segment of a path.
5.3 PCE Discovery 4.3 PCE Discovery
It is a simple matter for each child PCE to be configured with the It is a simple matter for each child PCE to be configured with the
address of its parent PCE. Typically, there will only be one or two address of its parent PCE. Typically, there will only be one or two
parents of any child. parents of any child.
The parent PCE also needs to be aware of the child PCEs for all child The parent PCE also needs to be aware of the child PCEs for all child
domains that it can see. This information is most likely to be domains that it can see. This information is most likely to be
configured (as part of the administrative definition of each configured (as part of the administrative definition of each
domain). domain).
Discovery of the relationships between parent PCEs and child PCEs Discovery of the relationships between parent PCEs and child PCEs
does not form part of the H-PCE architecture. Mechanisms that rely on does not form part of the hierarchical PCE architecture. Mechanisms
advertising or querying PCE locations across domain or provider that rely on advertising or querying PCE locations across domain or
boundaries are undesirable for security, scaling, commercial, and provider boundaries are undesirable for security, scaling,
confidentiality reasons. commercial, and confidentiality reasons.
The parent PCE also needs to know the inter-domain connectivity. The parent PCE also needs to know the inter-domain connectivity.
This information could be configured with suitable policy and This information could be configured with suitable policy and
commercial rules, or could be learned from the child PCEs as commercial rules, or could be learned from the child PCEs as
described in Section 4. described in Section 4.
In order for the parent PCE to learn about domain interconnection In order for the parent PCE to learn about domain interconnection
the child PCE will report the identity of its neighbor domains. The the child PCE will report the identity of its neighbor domains. The
IGP in each neighbor domain can advertise its inter-domain TE IGP in each neighbor domain can advertise its inter-domain TE
link capabilities [RFC5316], [RFC5392]. This information can be link capabilities [RFC5316], [RFC5392]. This information can be
collected by the child PCEs and forwarded to the parent PCE, or the collected by the child PCEs and forwarded to the parent PCE, or the
parent PCE could participate in the IGP in the child domains. parent PCE could participate in the IGP in the child domains.
5.4 Parent Domain Traffic Engineering Database 4.4 Parent Domain Traffic Engineering Database
The parent PCE maintains a domain topology map of the child domains The parent PCE maintains a domain topology map of the child domains
and their interconnectivity. Where inter-domain connectivity is and their interconnectivity. Where inter-domain connectivity is
provided by TE links the capabilities of those links must also be provided by TE links the capabilities of those links may also be
known to the parent PCE. Furthermore the parent domain known to the parent PCE. The parent PCE maintains a traffic
may contain nodes and links in its own right. Therefore, the engineering database (TED) for the parent domain in the same way that
parent PCE maintains a traffic engineering database (TED) for any PCE does.
the parent domain in the same way that any PCE does.
The parent domain may just be the collection of child domains and the The parent domain may just be the collection of child domains and
inter-domain links, or it may contain nodes and links in its own their interconnectivity, may include details of the inter-domain TE
right. links, and may contain nodes and links in its own right.
The mechanism for building the parent TED is likely to rely heavily The mechanism for building the parent TED is likely to rely heavily
on administrative configuration and commercial issues because the on administrative configuration and commercial issues because the
network was probably partitioned into domains specifically to address network was probably partitioned into domains specifically to address
these issues. these issues.
In practice, certain information may be passed from the child domains In practice, certain information may be passed from the child domains
to the parent PCE to help build the parent TED. In theory, the parent to the parent PCE to help build the parent TED. In theory, the parent
PCE could listen to the routing protocols in the child domains, but PCE could listen to the routing protocols in the child domains, but
this would violate the confidentiality and scaling issues that may be this would violate the confidentiality and scaling issues that may be
responsible for the partition of the network into domains. So it is responsible for the partition of the network into domains. So it is
much more likely that a suitable solution will involve specific much more likely that a suitable solution will involve specific
communication from an entity in the child domain (such as the child communication from an entity in the child domain (such as the child
PCE) to convey the necessary information. As already mentioned, the PCE) to convey the necessary information. As already mentioned, the
"necessary information" relates to how the child domains are inter- "necessary information" relates to how the child domains are inter-
connected. The topology and available resources within the child connected. The topology and available resources within the child
domain do not need to be communicated to the parent PCE: doing so domain do not need to be communicated to the parent PCE: doing so
would violate the PCE architecture. Mechanisms for reporting this would violate the PCE architecture. Mechanisms for reporting this
information are described in the examples in Section 5.6 in abstract information are described in the examples in Section 4.6 in abstract
terms as "a child PCE reports its neighbor domain connectivity to its terms as "a child PCE reports its neighbor domain connectivity to its
parent PCE"; the specifics of a solution are out of scope of this parent PCE"; the specifics of a solution are out of scope of this
document, but the requirements are indicated in Section 5.8. document, but the requirements are indicated in Section 4.8. See
Section 6 for a brief discussion of BGP-TE.
In models such as ASON (see Section 6.2), it is possible to consider In models such as ASON (see Section 5.2), it is possible to consider
a separate instance of an IGP running within the parent domain where a separate instance of an IGP running within the parent domain where
the participating protocol speakers are the nodes directly present in the participating protocol speakers are the nodes directly present in
that domain and the PCEs (routing controllers) responsible for each that domain and the PCEs (Routing Controllers) responsible for each
of the child domains. of the child domains.
5.5 Determination of Destination Domain 4.5 Determination of Destination Domain
The PCC asking for an inter-domain path computation is aware of the The PCC asking for an inter-domain path computation is aware of the
identity of the destination node by definition. If it knows the identity of the destination node by definition. If it knows the
egress domain it can supply this information as part of the path egress domain it can supply this information as part of the path
computation request. However, if it does not know the egress domain computation request. However, if it does not know the egress domain
this information must be determined by the parent PCE. this information must be known by the child PCE or known/determined
by the parent PCE.
In some specialist topologies the parent PCE could determine the In some specialist topologies the parent PCE could determine the
destination domain based on the destination address, for example from destination domain based on the destination address, for example from
configuration. However, this is not appropriate for many multi-domain configuration. However, this is not appropriate for many multi-domain
addressing scenarios. In IP-based multi-domain networks the addressing scenarios. In IP-based multi-domain networks the
parent PCE may be able to determine the destination domain by parent PCE may be able to determine the destination domain by
participating in inter-domain routing. Finally, the parent PCE could participating in inter-domain routing. Finally, the parent PCE could
issue specific requests to the child PCEs to discover if they contain issue specific requests to the child PCEs to discover if they contain
the destination node, but this has scaling implications. the destination node, but this has scaling implications.
5.6 Hierarchical PCE Examples For the purposes of this document, the precise mechanism of the
discovery of the destination domain is left out of scope. Suffice to
say that for each multi-domain path computation some mechanism will
be required to determine the location of the destination.
The following example describes the hierarchical domain topology. 4.6 Hierarchical PCE Examples
Figure 1 (sample hierarchical domain topology) demonstrates four
interconnected domains within a fifth parent domain. Each domain The following example describes the generic hierarchical domain
contains a single PCE: topology. Figure 1 demonstrates four interconnected domains within a
fifth, parent domain. Each domain contains a single PCE:
o Domain 1 is the ingress domain and child PCE 1 is able to compute o Domain 1 is the ingress domain and child PCE 1 is able to compute
paths within the domain. Its neighbors are Domain 2 and Domain 4. paths within the domain. Its neighbors are Domain 2 and Domain 4.
The domain also contains the source LSR (S) and three egress The domain also contains the source LSR (S) and three egress
boundary nodes (BN11, BN12, and BN13). boundary nodes (BN11, BN12, and BN13).
o Domain 2 is served by child PCE 2. Its neighbors are Domain 1 and o Domain 2 is served by child PCE 2. Its neighbors are Domain 1 and
Domain 3. The domain also contains four boundary nodes (BN21, BN22, Domain 3. The domain also contains four boundary nodes (BN21, BN22,
BN23, and BN24). BN23, and BN24).
o Domain 3 is the egress domain and is served by child PCE 3. Its o Domain 3 is the egress domain and is served by child PCE 3. Its
neighbors are Domain 2 and Domain 4. The domain also contains the neighbors are Domain 2 and Domain 4. The domain also contains the
destination LSR (D) and three ingress boundary nodes (BN31, BN32, destination LSR (D) and three ingress boundary nodes (BN31, BN32,
and BN33). and BN33).
o Domain 4 is served by child PCE 4. Its neighbors are Domain 2 and o Domain 4 is served by child PCE 4. Its neighbors are Domain 2 and
Domain 3. The domain also contains two boundary nodes (BN41 and Domain 3. The domain also contains two boundary nodes (BN41 and
BN42). BN42).
All of these domains are encompassed within Domain 5 which is served All of these domains are contained within Domain 5 which is served
by the parent PCE (PCE 5). by the parent PCE (PCE 5).
----------------------------------------------------------------- -----------------------------------------------------------------
| Domain 5 | | Domain 5 |
| ----- | | ----- |
| |PCE 5| | | |PCE 5| |
| ----- | | ----- |
| | | |
| ---------------- ---------------- ---------------- | | ---------------- ---------------- ---------------- |
| | Domain 1 | | Domain 2 | | Domain 3 | | | | Domain 1 | | Domain 2 | | Domain 3 | |
skipping to change at page 16, line 26 skipping to change at page 17, line 26
| \ ---- / | | \ ---- / |
| \ | | / | | \ | | / |
| ----| D4 |---- | | ----| D4 |---- |
| | | | | | | |
| ---- | | ---- |
| | | |
---------------------------- ----------------------------
Figure 2 : Abstract Domain Topology as Seen by the Parent PCE Figure 2 : Abstract Domain Topology as Seen by the Parent PCE
5.6.1 Hierarchical PCE Initial Information Exchange 4.6.1 Hierarchical PCE Initial Information Exchange
Based on the Figure 1 topology, the following is an illustration of Based on the Figure 1 topology, the following is an illustration of
the initial hierarchical PCE information exchange. the initial hierarchical PCE information exchange.
1. Child PCE 1, the PCE responsible for Domain 1, is configured 1. Child PCE 1, the PCE responsible for Domain 1, is configured
with the location of its parent PCE (PCE5). with the location of its parent PCE (PCE5).
2. Child PCE 1 establishes contact with its parent PCE. The parent 2. Child PCE 1 establishes contact with its parent PCE. The parent
applies policy to ensure that communication with PCE 1 is allowed. applies policy to ensure that communication with PCE 1 is allowed.
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4. Child PCE 1 reports its neighbor domain connectivity to its parent 4. Child PCE 1 reports its neighbor domain connectivity to its parent
PCE. PCE.
5. Child PCE 1 reports any change in the resource availability on its 5. Child PCE 1 reports any change in the resource availability on its
inter-domain links to its parent PCE. inter-domain links to its parent PCE.
Each child PCE performs steps 1 through 5 so that the parent PCE can Each child PCE performs steps 1 through 5 so that the parent PCE can
create a domain topology view as shown in Figure 2. create a domain topology view as shown in Figure 2.
5.6.2 Hierarchical PCE End-to-End Path Computation Procedure 4.6.2 Hierarchical PCE End-to-End Path Computation Procedure
The procedure below is an example of a source PCC requesting an The procedure below is an example of a source PCC requesting an
end-to-end path in a multi-domain environment. The topology is end-to-end path in a multi-domain environment. The topology is
represented in Figure 1. It is assumed that the each child PCE has represented in Figure 1. It is assumed that the each child PCE has
connected to its parent PCE and exchanged the initial information connected to its parent PCE and exchanged the initial information
required for the parent PCE to create its domain topology view as required for the parent PCE to create its domain topology view as
described in Section 5.6.1. described in Section 5.6.1.
1. The source PCC (the ingress LSR in our example), sends a request 1. The source PCC (the ingress LSR in our example), sends a request
to the PCE responsible for its domain (PCE1) for a path to the to the PCE responsible for its domain (PCE 1) for a path to the
destination LSR. destination LSR (D).
2. PCE 1 determines the destination, is not in domain 1. 2. PCE 1 determines the destination is not in domain 1.
3. PCE 1 sends a computation request to its parent PCE (PCE 5). 3. PCE 1 sends a computation request to its parent PCE (PCE 5).
4. The parent PCE determines that the destination is in Domain 3. 4. The parent PCE determines that the destination is in Domain 3.
(See Section 5.5). (See Section 5.5).
5. PCE 5 determines the likely domain paths according to the domain 5. PCE 5 determines the likely domain paths according to the domain
interconnectivity and TE capabilities between the domains. For interconnectivity and TE capabilities between the domains. For
example, three domain paths (S-BN11-BN21-D2-BN23-BN31-D, S-BN11- example, assuming that the link BN12-BN22 is not suitable for the
BN21-D2-BN24-BN32-D, and S-BN13-BN41-D4-BN42-BN33-D) are requested path, three domain paths are determined:
determined (assuming the link BN12-BN22 is not suitable for the
requested path). S-BN11-BN21-D2-BN23-BN31-D
S-BN11-BN21-D2-BN24-BN32-D
S-BN13-BN41-D4-BN42-BN33-D
6. PCE 5 sends edge-to-edge path computation requests to PCE 2 6. PCE 5 sends edge-to-edge path computation requests to PCE 2
which is responsible for Domain 2 (e.g., BN21-BN23 and BN21-BN24) which is responsible for Domain 2 (i.e., BN21-to-BN23 and BN21-
and to PCE 4 for Domain 4 (e.g., BN41-BN42). to-BN24), and to PCE 4 for Domain 4 (i.e., BN41-to-BN42).
7. PCE 5 sends source-to-edge path computation requests to PCE 1 7. PCE 5 sends source-to-edge path computation requests to PCE 1
which is responsible for Domain 1 (e.g., S-BN11 and S-BN13). which is responsible for Domain 1 (i.e., S-to-BN11 and S-to-
BN13).
8. PCE 5 sends edge-to-egress path computation requests to PCE3 8. PCE 5 sends edge-to-egress path computation requests to PCE3
which is responsible for Domain 3 (e.g., BN31-D, BN32-D, and which is responsible for Domain 3 (i.e., BN31-to-D, BN32-to-D,
BN33-D). and BN33-to-D).
9. PCE 5 correlates all the computation responses from each child 9. PCE 5 correlates all the computation responses from each child
PCE, adds in the information about the inter-domain links, and PCE, adds in the information about the inter-domain links, and
applies any requested and locally configured policies. applies any requested and locally configured policies.
10. PCE 5 then selects the optimal end-to-end multi-domain path 10. PCE 5 then selects the optimal end-to-end multi-domain path
that meets the policies and objective functions, and supplies the that meets the policies and objective functions, and supplies the
resulting path to PCE 1. resulting path to PCE 1.
11. PCE 1 forwards the path to the PCC (the ingress LSR). 11. PCE 1 forwards the path to the PCC (the ingress LSR).
5.7 Hierarchical PCE Error Handling Note that there is no requirement for steps 6, 7, and 8 to be carried
out in parallel or in series. Indeed, they could be overlapped with
step 5. This is an implementation issue.
In the event that a child PCE in a domain cannot find a suitible 4.7 Hierarchical PCE Error Handling
path to the egress. The child PCE should return the relevent
error notifying the parent PCE. Depending on the error response the In the event that a child PCE in a domain cannot find a suitable
path to the egress. The child PCE should return the relevant
error to notify the parent PCE. Depending on the error response the
parent PCE can elect to: parent PCE can elect to:
o Cancel the request and send the relevent response back to the o Cancel the request and send the relevant response back to the
intial child PCE requesting an end-to-end path. initial child PCE that requested an end-to-end path;
o Relax the contraints associated with the intial path request; o Relax the constraints associated with the initial path request;
o Select another candidate domain and send the path request to the o Select another candidate domain and send the path request to the
child PCE responsible for the domain. child PCE responsible for the domain.
If the parent PCE does not recieve a response from a child PCE within If the parent PCE does not receive a response from a child PCE within
an alloted time period. The parent PCE can either: an allotted time period. The parent PCE can either:
o Send the path request to another child PCE in the same domain, if a o Send the path request to another child PCE in the same domain, if a
secoundary child PCE exists; secondary child PCE exists;
o Select another candidate domain and send the path request to the o Select another candidate domain and send the path request to the
child PCE responsible for that domain. child PCE responsible for that domain.
5.8 Requirements for Hierarchical PCEP Protocol Extensions 4.8 Requirements for Hierarchical PCEP Protocol Extensions
This section lists the high-level requirements for extensions to the This section lists the high-level requirements for extensions to the
PCEP to support the hierachical PCE model. PCEP to support the hierarchical PCE model. It is provided to offer
guidance to PCEP protocol developers in designing a solution suitable
[Editors Note: This section may be expanded as work progresses.] for use in a hierarchical PCE framework.
5.8.1 PCEP Request Qualifiers 4.8.1 PCEP Request Qualifiers
PCEP request (PCReq) messages are used by a PCC or a PCE to make a PCEP request (PCReq) messages are used by a PCC or a PCE to make a
computation request or enquiry to a PCE. The requests are qualified computation request or enquiry to a PCE. The requests are qualified
so that the PCE knows what type of action is required. so that the PCE knows what type of action is required.
Support of the H-PCE architecture will introduce two new Support of the hierarchical PCE architecture will introduce two new
qualifications as follows: qualifications as follows:
o It must be possible for a child PCE to indicate that the request it o It must be possible for a child PCE to indicate that the response
sends to a parent PCE shold be satisfied by a domain sequence only, it receives from the parent PCE should consist of a domain sequence
that is, not by a full end-to-end path. This allows the child PCE only (i.e., not a fully-specified end-to-end path). This allows the
to initiate per-domain or backward recursive path computation. child PCE to initiate per-domain or backward recursive path
computation.
o A parent PCE needs to be able to ask a child PCE whether a o A parent PCE may need to be able to ask a child PCE whether a
particular node address (the destination of an end-to-end path) is particular node address (the destination of an end-to-end path) is
present in the domain that the child PCE serves. present in the domain that the child PCE serves.
In PCEP, such request qualifications are carried as bit-flags in the In PCEP, such request qualifications are carried as bit-flags in the
RP object carried within the PCReq message. RP object carried within the PCReq message.
5.8.2 Indication of H-PCE Capability 4.8.2 Indication of Hierarchical PCE Capability
Although parent/child PCE relationships are likely configured, it Although parent/child PCE relationships are likely configured, it
assist network operations if the parent PCE is able to indicate to will assist network operations if the parent PCE is able to indicate
the child that it really is capable of acting as a parent PCE. This to the child that it really is capable of acting as a parent PCE.
will help to trap misconfigurations. This will help to trap misconfigurations.
A parent PCE needs a way to indicate that is capable of acting as a In PCEP, such capabilities are carried in the Open Object within the
parent PCE, and should also be able to indicate the identity of the Open message.
parent domain. This informaiton is most obviously carried in the Open
Object within the Open message.
5.8.3 Intention to Utilize Parent PCE Capabilities 4.8.3 Intention to Utilize Parent PCE Capabilities
A PCE that is capable of acting as a parent PCE might not be A PCE that is capable of acting as a parent PCE might not be
configured or willing to act as the parent for a specific child PCE. configured or willing to act as the parent for a specific child PCE.
This fact could be determined when the child sends a PCReq that This fact could be determined when the child sends a PCReq that
requires parental activity (such as querying other child PCEs), and requires parental activity (such as querying other child PCEs), and
could result in a negative response in a PCEP Error (PCErr) message. could result in a negative response in a PCEP Error (PCErr) message.
However, the expense of a poorly targetted PCReq can be avoided if However, the expense of a poorly targeted PCReq can be avoided if
the child PCE indicates that it might wish to use the parent as a the child PCE indicates that it might wish to use the parent as a
parent (for example, on the Open message), and if the parent parent (for example, on the Open message), and if the parent
determines at that time whether it is willing to act as a parent to determines at that time whether it is willing to act as a parent to
this child. this child.
5.8.4 Communication of Domain Connectivity Information 4.8.4 Communication of Domain Connectivity Information
Section 5.4 describes how the parent PCE needs a parent TED and Section 5.4 describes how the parent PCE needs a parent TED and
indicates that the information might be supplied from the child PCEs indicates that the information might be supplied from the child PCEs
in each domain. This requires a mechanism whereby information about in each domain. This requires a mechanism whereby information about
inter-domain links can be supplied by a child PCE to a parent PCE, inter-domain links can be supplied by a child PCE to a parent PCE,
for example on a PCEP Notify (PCNtf) message. for example on a PCEP Notify (PCNtf) message.
The information that would be exchanged includes: The information that would be exchanged includes:
o Identifier of advertising child PCE o Identifier of advertising child PCE
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o TE properties of the link (metrics, bandwidth) o TE properties of the link (metrics, bandwidth)
o Other properties of the link (technology-specific) o Other properties of the link (technology-specific)
o Identifier of link end-points o Identifier of link end-points
o Identifier of adjacent domain o Identifier of adjacent domain
It may be desirable for this information to be periodically updated, It may be desirable for this information to be periodically updated,
for example, when available bandwidth changes. In this case, the for example, when available bandwidth changes. In this case, the
parent PCE might be given the ability to configure thresholds in the parent PCE might be given the ability to configure thresholds in the
child PCE to prevent flapping of information. child PCE to prevent flapping of information.
5.8.5 Domain Identifiers 4.8.5 Domain Identifiers
Domain identifiers are already needed to allow a PCE to indicate Domain identifiers are already present in PCEP to allow a PCE to
which domains it serves, and to allow the representation of domains indicate which domains it serves, and to allow the representation of
as abstract nodes in paths. The wider use of domains in the context domains as abstract nodes in paths. The wider use of domains in the
of this work on H-PCE will require that domains can be identified in context of this work on hierarchical PCE will require that domains
more places within objects in PCEP messages. This should pose no can be identified in more places within objects in PCEP messages.
problems. This should pose no problems.
However, more attention may need to be applied to the precision of However, more attention may need to be applied to the precision of
domian identifier definitions. domain identifier definitions to ensure that it is always possible to
unambiguously identify a domain from its identifier. This work will
be necessary in configuration, and also in protocol specifications
(for example, an OSPF area identifier is sufficient within an
Autonomous System, but becomes ambiguous in a path that crosses
multiple Autonomous Systems).
6. Hierarchical PCE Applicability 5. Hierarchical PCE Applicability
As per [RFC4655], PCE can inherently support inter-domain path As per [RFC4655], PCE can inherently support inter-domain path
computation for any definition of a domain as set out in Section 1.2. computation for any definition of a domain as set out in Section 1.2
of this document.
Hierarchical PCE can be applied to inter-domain environments, Hierarchical PCE can be applied to inter-domain environments,
including Antonymous Systems and IGP areas. The hierarchical PCE including Antonymous Systems and IGP areas. The hierarchical PCE
procedures make no distinction between, Antonymous Systems and IGP procedures make no distinction between, Antonymous Systems and IGP
area applications, although it should be noted that the TED area applications, although it should be noted that the TED
maintained by a parent PCE must be able to support the concept of maintained by a parent PCE must be able to support the concept of
child domains connected by inter-domain links or directly connected child domains connected by inter-domain links or directly connected
at boundary nodes (see Section 4). at boundary nodes (see Section 4).
This section sets out the applicability of hierarchical PCE to three This section sets out the applicability of hierarchical PCE to three
environments: environments:
o MPLS traffic engineering across multiple Autonomous Systems o MPLS traffic engineering across multiple Autonomous Systems
o MPLS traffic engineering across multiple IGP areas o MPLS traffic engineering across multiple IGP areas
o GMPLS traffic engineering in the ASON architecture o GMPLS traffic engineering in the ASON architecture
6.1 Antonymous Systems and Areas 5.1 Antonymous Systems and Areas
Networks are comprised of domains. A domain can be considered to be Networks are comprised of domains. A domain can be considered to be
a collection of network elements within an AS or area that has a a collection of network elements within an AS or area that has a
common sphere of address management or path computational common sphere of address management or path computational
responsibility. responsibility.
As networks increase in size and complexity it may be required to As networks increase in size and complexity it may be required to
introduce scaling methods to reduce the amount information flooded introduce scaling methods to reduce the amount information flooded
within the network and make the network more manageable. An IGP within the network and make the network more manageable. An IGP
hierarchy is designed to improve IGP scalability by dividing the hierarchy is designed to improve IGP scalability by dividing the
IGP domain into areas and limiting the flooding scope of topology IGP domain into areas and limiting the flooding scope of topology
information to within area boundaries. This restricts visibility of information to within area boundaries. This restricts a router's
the area to routers in a single area. If a router needs to compute a visibility to information about links and other routers within the
route to destination located in another AS or area a method is single area. If a router needs to compute a route to destination
required to compute a path across teh AS and area boundaries. located in another area, a method is required to compute a path
across the area boundary.
When an LSR within an AS or area needs to compute a path across an When an LSR within an AS or area needs to compute a path across an
area or AS boundary it must also use an inter-AS computation area or AS boundary it must also use an inter-AS computation
technique. Hierachical PCE is equally applicable to computing technique. Hierarchical PCE is equally applicable to computing
inter-area and inter-AS MPLS and GMPLS paths across domain inter-area and inter-AS MPLS and GMPLS paths across domain
boundaries. boundaries.
6.2 ASON Architecture 5.2 ASON Architecture
The International Telecommunications Union (ITU) defines the ASON The International Telecommunications Union (ITU) defines the ASON
architecture in [G-8080]. [G-7715] defines the routing architecture architecture in [G-8080]. [G-7715] defines the routing architecture
for ASON and introduces a hierarchical architecture. In this for ASON and introduces a hierarchical architecture. In this
architecture, the Routing Areas (RAs) have a hierarchical architecture, the Routing Areas (RAs) have a hierarchical
relationship between different routing levels, which means a parent relationship between different routing levels, which means a parent
(or higher level) RA can contain multiple child RAs. The (or higher level) RA can contain multiple child RAs. The
interconnectivity of the lower RAs is visible to the higher level RA. interconnectivity of the lower RAs is visible to the higher level RA.
Note that the RA hierarchy can be recursive. Note that the RA hierarchy can be recursive.
In the ASON framework, a path computation request is termed a Route In the ASON framework, a path computation request is termed a Route
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It can be seen that the hierarchical PCE architecture fits the It can be seen that the hierarchical PCE architecture fits the
hierarchical ASON routing architecture well. It can be used to hierarchical ASON routing architecture well. It can be used to
provide paths across subnetworks, and to determine end-to-end paths provide paths across subnetworks, and to determine end-to-end paths
in networks constructed from multiple subnetworks or RAs. in networks constructed from multiple subnetworks or RAs.
When hierarchical PCE is applied to implement hierarchical remote When hierarchical PCE is applied to implement hierarchical remote
path computation in [G-7715-2], it is very important for operators to path computation in [G-7715-2], it is very important for operators to
understand the different terminology and implicit consistency understand the different terminology and implicit consistency
between hierarchical PCE and [G-7715-2]. between hierarchical PCE and [G-7715-2].
6.2.1 Implicit Consistency Between Hierarchical PCE and G.7715.2 5.2.1 Implicit Consistency Between Hierarchical PCE and G.7715.2
This section highlights the correspondence between features of the This section highlights the correspondence between features of the
hierarchical PCE architecture and the ASON routing architecture. hierarchical PCE architecture and the ASON routing architecture.
(1) RC (Routing Controller) and PCE (Path Computation Element) (1) RC (Routing Controller) and PCE (Path Computation Element)
[G-8080] describes the Routing Controller Component as an [G-8080] describes the Routing Controller component as an
abstract entity, which is responsible for responding to requests abstract entity, which is responsible for responding to requests
for path (route) information and topology information. It can be for path (route) information and topology information. It can be
implemented as a single entity, or as a distributed set of implemented as a single entity, or as a distributed set of
entities that make up a cooperative federation. entities that make up a cooperative federation.
[RFC4655] describes PCE (Path Computation Element) is an entity [RFC4655] describes PCE (Path Computation Element) is an entity
(component, application, or network node) that is capable of (component, application, or network node) that is capable of
computing a network path or route based on a network graph and computing a network path or route based on a network graph and
applying computational constraints. applying computational constraints.
Therefore, in the ASON architecture, a PCE can be regarded as a Therefore, in the ASON architecture, a PCE can be regarded as a
realizations of the RC. realizations of the RC.
(2) Route Query Requester/Route Query Responder and PCC/PCE (2) Route Query Requester/Route Query Responder and PCC/PCE
[G-7715-2] describes the Route Query Requester as a Connection [G-7715-2] describes the Route Query Requester as a Connection
Controller or Routing Controller that sends a route query message Controller or Routing Controller that sends a route query message
to a Routing Controller requesting for one or more paths that to a Routing Controller requesting one or more paths that
satisfy a set of routing constraints. The Route Query Responder satisfy a set of routing constraints. The Route Query Responder
is a Routing Controller that performs path computation upon is a Routing Controller that performs path computation upon
receipt of a route query message from a Route Query Requester, receipt of a route query message from a Route Query Requester,
sending a response back at the end of the path computation. sending a response back at the end of the path computation.
In the context of ASON, a signaling controller initiates and In the context of ASON, a Signaling Controller initiates and
processes signaling messages and closely coupled to a signaling processes signaling messages and is closely coupled to a
protocol speaker. A routing controller makes routing decisions Signaling Protocol Speaker. A Routing Controller makes routing
and is usually coupled to configuration entities and/or routing a decisions and is usually coupled to configuration entities
protocol speaker. and/or a Routing Protocol Speaker.
It can be seen that a PCC corresponds to a Route Query Requester, It can be seen that a PCC corresponds to a Route Query Requester,
and a PCE corresponds to a Route Query Responder. A PCE/RC can and a PCE corresponds to a Route Query Responder. A PCE/RC can
also act as a Route Query Requester sending requests to another also act as a Route Query Requester sending requests to another
Route Query Responder. Route Query Responder.
The PCEP path computation request (PCReq) and path computation The PCEP path computation request (PCReq) and path computation
reply (PCRep) messages between PCC and PCE correspond to the reply (PCRep) messages between PCC and PCE correspond to the
RI_QUERY and RI_UPDATE messages in [G-7715-2]. RI_QUERY and RI_UPDATE messages in [G-7715-2].
(3) Routing Area Hierarchy and Hierarchical Domain (3) Routing Area Hierarchy and Hierarchical Domain
The ASON routing hierarchy model is shown in Figure 6 of The ASON routing hierarchy model is shown in Figure 6 of
[G-7715] through an example that illustrates routing area levels. [G-7715] through an example that illustrates routing area levels.
If the hierarchical remote path computation mechanism of If the hierarchical remote path computation mechanism of
[G-7715-2] is applied in this scenario, each routing area should [G-7715-2] is applied in this scenario, each routing area should
have at least one RC for route query function and there is a have at least one RC for route query function and there is a
parent RC for the child RCs in each routing area. parent RC for the child RCs in each routing area.
According to [G-8080], the parent RC has visibility of the According to [G-8080], the parent RC has visibility of the
structure of the lower level, so it knows the interconnectivity structure of the lower level, so it knows the interconnectivity
of the RAs in the lower level. Each child RC can compute edge-to- of the RAs in the lower level. Each child RC can compute edge-to-
edge paths across its own child RA. edge paths across its own child RA.
Thus, an RA corresponds to a domain, and the hierarchical Thus, an RA corresponds to a domain in the PCE architecture, and
relationship between RAs corresponds to the hierarchical the hierarchical relationship between RAs corresponds to the
relationship between domains. Furthermore, a parent PCE in a hierarchical relationship between domains in the hierarchical PCE
parent domain can be regarded as parent RC in a higher routing architecture. Furthermore, a parent PCE in a parent domain can be
level, and a child PCE in a child domain can be regarded as child regarded as parent RC in a higher routing level, and a child PCE
RC in a lower routing level. in a child domain can be regarded as child RC in a lower routing
level.
6.2.2 Benefits of Hierarchical PCEs in ASON 5.2.2 Benefits of Hierarchical PCEs in ASON
RCs in an ASON environment can use the hierarchical PCE model to RCs in an ASON environment can use the hierarchical PCE model to
fully match the ASON hierarchical routing model, so the hierarchical fully match the ASON hierarchical routing model, so the hierarchical
PCE mechanisms can be applied to fully satisfy the architecture and PCE mechanisms can be applied to fully satisfy the architecture and
requirements of [G-7715-2] without any changes. If the hierarchical requirements of [G-7715-2] without any changes. If the hierarchical
PCE mechanism is applied in ASON, it can be used to determine end-to- PCE mechanism is applied in ASON, it can be used to determine end-to-
end optimized paths across sub-networks and RAs before initiating end optimized paths across sub-networks and RAs before initiating
signaling to create the connection. It can also improve the signaling to create the connection. It can also improve the
efficiency of connection setup to avoid crankback. efficiency of connection setup to avoid crankback.
6. A Note on BGP-TE
The concept of exchange of TE information between Autonomous Systems
(ASes) is discussed in [BGP-TE]. The information exchanged in this
way could be the full TE information from the AS, an aggregation of
that information, or a representation of the potential connectivity
across the AS. Furthermore, that information could be updated
frequently (for example, for every new LSP that is set up across the
AS) or only at threshold-crossing events.
There are a number of discussion points associated with the use of
[BGP-TE] concerning the volume of information, the rate of churn of
information, the confidentiality of information, the accuracy of
aggregated or potential-connectivity information, and the processing
required to generate aggregated information. The PCE architecture and
the architecture enabled by [BGP-TE] make different assumptions about
the operational objectives of the networks, and this document does
not attempt to make one of the approaches "right" and the other
"wrong". Instead, this work assumes that a decision has been made to
utilize the PCE architecture.
Indeed, [BGP-TE] may have some uses within the PCE model. For
example, [BGP-TE] could be used as a "northbound" TE advertisement
such that a PCE does not need to listen to an IGP in its domain, but
has its TED populated by messages received (for example) from a
Route Reflector. Furthermore, the inter-domain connectivity and
connectivity capabilities that is required information for a parent
PCE could be obtained as a filtered subset of the information
available in [BGP-TE].
7. Management Considerations 7. Management Considerations
General PCE management considerations are discussed in [RFC4655]. In General PCE management considerations are discussed in [RFC4655]. In
the case of the hierarchical PCE architecture, there are additional the case of the hierarchical PCE architecture, there are additional
management considerations. management considerations.
The administrative entity responsible for the management of the The administrative entity responsible for the management of the
parent PCEs must be determined. In the case of multi-domains (e.g., parent PCEs must be determined. In the case of multi-domains (e.g.,
IGP areas or multiple ASes) within a single service provider IGP areas or multiple ASes) within a single service provider
network, the management responsibility for the parent PCE would most network, the management responsibility for the parent PCE would most
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The hierarchical procedure requires interaction with multiple PCEs. The hierarchical procedure requires interaction with multiple PCEs.
Once a child PCE requests an end-to-end path, a sequence of events Once a child PCE requests an end-to-end path, a sequence of events
occurs that requires interaction between the parent PCE and each occurs that requires interaction between the parent PCE and each
child PCE. If a child PCE is not operational, and an alternate child PCE. If a child PCE is not operational, and an alternate
transit domain is not available, then a failure must be reported. transit domain is not available, then a failure must be reported.
7.4 Verifying Correct Operation 7.4 Verifying Correct Operation
Verifying the correct operation of a parent PCE can be performed by Verifying the correct operation of a parent PCE can be performed by
monitoring a set of parameters. The parent PCE implementation should monitoring a set of parameters. The parent PCE implementation should
provide the following parameters: provide the following parameters monitored by the parent PCE:
Parameters monitored by the parent PCE:
o Number of child PCE requests. o Number of child PCE requests.
o Number of successful hierarchical PCE procedures completions on a o Number of successful hierarchical PCE procedures completions on a
per-PCE-peer basis. per-PCE-peer basis.
o Number of hierarchical PCE procedure completion failures on a per- o Number of hierarchical PCE procedure completion failures on a per-
PCE-peer basis. PCE-peer basis.
o Number of hierarchical PCE procedure requests from unauthorized o Number of hierarchical PCE procedure requests from unauthorized
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7.5. Impact on Network Operation 7.5. Impact on Network Operation
The hierarchical PCE procedure is a multiple-PCE path computation The hierarchical PCE procedure is a multiple-PCE path computation
scheme. Subsequent requests to and from the child and parent PCEs do scheme. Subsequent requests to and from the child and parent PCEs do
not differ from other path computation requests and should not have not differ from other path computation requests and should not have
any significant impact on network operations. any significant impact on network operations.
8. Security Considerations 8. Security Considerations
The hierarchical PCE procedure relies on PCEP and inherits the The hierarchical PCE procedure relies on PCEP and inherits the
security requirements defined [RFC5440]. Any multi-domain security requirements defined [RFC5440]. As noted in Section 7,
operation necessarily involves the exchange of information across there is a security relationship between child and parent PCEs.
domain boundaries. This is bound to represent a significant This relationship, like any PCEP relationship assumes
security and confidentiality risk especially when the child preconfiguration of identities, authority, and keys, or can
domains are controlled by different commercial concerns. operate through any key distribution mechanism outside the scope of
PCEP. As PCEP operates over TCP, it may make use of any TCP security
mechanism.
The hierarchical PCE architecture makes use of PCE policy The hierarchical PCE architecture makes use of PCE policy
[RFC5394] and the security aspects of the PCE communication protocol [RFC5394] and the security aspects of the PCE communication protocol
documented in [RFC5440]. It is expected that the parent PCE will documented in [RFC5440]. It is expected that the parent PCE will
require all child PCEs to use full security when communicating with require all child PCEs to use full security when communicating with
the parent and that security will be maintained by not supporting the the parent and that security will be maintained by not supporting the
discovery by a parent of child PCEs. discovery by a parent of child PCEs.
Confidentiality may be enhanced by the use of Path Keys [RFC5520]. PCE operation also relies on information used to build the TED.
Attacks on a PCE system may be achieved by falsifying or impeding
this flow of information. The child PCE TEDs are constructed as
described in [RFC4655] and are unchanged in this document: if the PCE
listens to the IGP for this information, then normal IGP security
measures may be applied, and it should be noted that an IGP routing
system is generally assumed to be a trusted domain such that router
subversion is not a risk. The parent PCE TED is constructed as
described in this document and may involve:
- multiple parent-child relationships using PCEP (as already
described)
- the parent PCE listening to child domain IGPs (with the same
security features as a child PCE listening to its IGP)
- an external mechanism (such as [BGP-TE]) which will need to be
authorized and secured.
Any multi-domain operation necessarily involves the exchange of
information across domain boundaries. This is bound to represent a
significant security and confidentiality risk especially when the
child domains are controlled by different commercial concerns. PCEP
allows individual PCEs to maintain confidentiality of their domain
path information using Path Keys [RFC5520], and the hierarchical
PCE architecture is specifically designed to enable as much isolation
of domain topology and capabilities information as is possible.
Further considerations of the security issues related to inter-AS Further considerations of the security issues related to inter-AS
path computation see [RFC5376]. path computation see [RFC5376].
9. IANA Considerations 9. IANA Considerations
This document makes no requests for IANA action. This document makes no requests for IANA action.
10. Acknowledgements 10. Acknowledgements
The authors would like to thank David Amzallag, Oscar Gonzalez de The authors would like to thank David Amzallag, Oscar Gonzalez de
Diosm and Franz Rambach for their comments and suggestions. Diosm, Franz Rambach, Ramon Casellas, Olivier Dugeon, Filippo Cugini,
and Dhruv Dhody for their comments and suggestions.
11. References 11. References
11.1 Normative References 11.1 Normative References
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006. Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC5152] Vasseur, JP., Ayyangar, A., and R. Zhang, "A Per-Domain [RFC5152] Vasseur, JP., Ayyangar, A., and R. Zhang, "A Per-Domain
Path Computation Method for Establishing Inter-Domain Path Computation Method for Establishing Inter-Domain
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[G-7715] ITU-T Recommendation G.7715 (2002), Architecture [G-7715] ITU-T Recommendation G.7715 (2002), Architecture
and Requirements for the Automatically and Requirements for the Automatically
Switched Optical Network (ASON). Switched Optical Network (ASON).
[G-7715-2] ITU-T Recommendation G.7715.2 (2007), ASON [G-7715-2] ITU-T Recommendation G.7715.2 (2007), ASON
routing architecture and requirements for remote route routing architecture and requirements for remote route
query. query.
11.2. Informative References 11.2. Informative References
[RFC4105] Le Roux, J.-L., Vasseur, J.-P, and Boyle, J.,
"Requirements for Inter-Area MPLS Traffic Engineering",
RFC 4105, June 2005.
[RFC4216] Zhang, R., and Vasseur, J.-P., "MPLS Inter-Autonomous
System (AS) Traffic Engineering (TE) Requirements", RFC
4216, November 2005.
[RFC4726] Farrel, A., Vasseur, J., and A. Ayyangar, "A Framework [RFC4726] Farrel, A., Vasseur, J., and A. Ayyangar, "A Framework
for Inter-Domain Multiprotocol Label Switching Traffic for Inter-Domain Multiprotocol Label Switching Traffic
Engineering", RFC 4726, November 2006. Engineering", RFC 4726, November 2006.
[RFC4875] Aggarwal, R., Papadimitriou, D., and Yasukawa, S., [RFC4875] Aggarwal, R., Papadimitriou, D., and Yasukawa, S.,
"Extensions to Resource Reservation Protocol - Traffic "Extensions to Resource Reservation Protocol - Traffic
Engineering (RSVP-TE) for Point-to-Multipoint TE Label Engineering (RSVP-TE) for Point-to-Multipoint TE Label
Switched Paths (LSPs)", RFC 4875, May 2007. Switched Paths (LSPs)", RFC 4875, May 2007.
[RFC5152] Vasseur, JP., Ayyangar, A., and R. Zhang, "A Per-Domain [RFC5152] Vasseur, JP., Ayyangar, A., and R. Zhang, "A Per-Domain
skipping to change at page 27, line 32 skipping to change at page 31, line 24
[RFC5392] Chen, M., Zhang, R., and X. Duan, "OSPF Extensions in [RFC5392] Chen, M., Zhang, R., and X. Duan, "OSPF Extensions in
Support of Inter-Autonomous System (AS) MPLS and GMPLS Support of Inter-Autonomous System (AS) MPLS and GMPLS
Traffic Engineering", RFC 5392, January 2009. Traffic Engineering", RFC 5392, January 2009.
[RFC5541] Roux, J., Vasseur, J., and Y. Lee, "Encoding [RFC5541] Roux, J., Vasseur, J., and Y. Lee, "Encoding
of Objective Functions in the Path of Objective Functions in the Path
Computation Element Communication Computation Element Communication
Protocol (PCEP)", RFC5541, December 2008. Protocol (PCEP)", RFC5541, December 2008.
[PCEP-MIB] Stephan, E., K. Koushik, Q. Zhao, and D. King, "PCE [BGP-TE] Gredler, H., Medved, J, Farrel, A. and Previdi, S.,
communication protocol (PCEP) Management Information "North-Bound Distribution of Link-State and TE
Base", Work in Progress, June 2010 Information using BGP", draft-gredler-idr-ls-distribution,
work in progress.
[PCEP-MIB] Stephan, E., Koushik, K., Zhao, Q., and King, D., "PCE
Communication Protocol (PCEP) Management Information
Base", work in progress.
12. Authors' Addresses 12. Authors' Addresses
Daniel King Daniel King
Old Dog Consulting Old Dog Consulting
Email: daniel@olddog.co.uk Email: daniel@olddog.co.uk
Adrian Farrel Adrian Farrel
Old Dog Consulting Old Dog Consulting
Email: adrian@olddog.co.uk Email: adrian@olddog.co.uk
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