draft-ietf-pce-policy-enabled-path-comp-04.txt   rfc5394.txt 
Internet Draft Igor Bryskin (Adva Optical)
Category: Informational Dimitri Papadimitriou (Alcatel)
Expiration Date: April 31, 2009 Lou Berger (LabN Consulting)
Jerry Ash (AT&T)
October 31, 2008 Network Working Group I. Bryskin
Request for Comments: 5394 Adva Optical
Category: Informational D. Papadimitriou
Alcatel
L. Berger
LabN Consulting
J. Ash
AT&T
December 2008
Policy-Enabled Path Computation Framework Policy-Enabled Path Computation Framework
draft-ietf-pce-policy-enabled-path-comp-04.txt Status of This Memo
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Abstract Abstract
The Path Computation Element (PCE) Architecture introduces the The Path Computation Element (PCE) architecture introduces the
concept of policy in the context of path computation. This document concept of policy in the context of path computation. This document
provides additional details on policy within the PCE Architecture and provides additional details on policy within the PCE architecture and
also provides context for the support of PCE Policy. This document also provides context for the support of PCE Policy. This document
introduces the use of the Policy Core Information Model (PCIM) as a introduces the use of the Policy Core Information Model (PCIM) as a
framework for supporting path computation policy. This document also framework for supporting path computation policy. This document also
provides representative scenarios for the support of PCE Policy. provides representative scenarios for the support of PCE Policy.
Table of Contents Table of Contents
1 Introduction .............................................. 3 1. Introduction ....................................................2
1.1 Terminology ............................................... 4 1.1. Terminology ................................................3
2 Background ................................................ 4 2. Background ......................................................4
2.1 Motivation ................................................ 5 2.1. Motivation .................................................4
2.2 Policy Attributes ......................................... 7 2.2. Policy Attributes ..........................................6
2.3 Representative Policy Scenarios ........................... 8 2.3. Representative Policy Scenarios ............................7
2.3.1 Scenario: Policy Configured Paths ......................... 8 2.3.1. Scenario: Policy Configured Paths ...................7
2.3.2 Scenario: Provider Selection Policy ....................... 11 2.3.2. Scenario: Provider Selection Policy ................10
2.3.3 Scenario: Policy Based Constraints ........................ 12 2.3.3. Scenario: Policy Based Constraints .................12
2.3.4 Scenario: Advanced Load Balancing (ALB) Example .......... 15 2.3.4. Scenario: Advanced Load Balancing (ALB) Example ....14
3 Requirements .............................................. 16 3. Requirements ...................................................16
4 Path Computation Policy Information Model (PCPIM) ......... 18 4. Path Computation Policy Information Model (PCPIM) ..............18
5 Policy-Enabled Path Computation Framework Components ...... 20 5. Policy-Enabled Path Computation Framework Components ...........20
6 Policy Component Configurations ........................... 21 6. Policy Component Configurations ................................21
6.1 PCC-PCE Configurations .................................... 21 6.1. PCC-PCE Configurations ....................................21
6.2 Policy Repositories ....................................... 23 6.2. Policy Repositories .......................................24
6.3 Cooperating PCE Configurations ............................ 25 6.3. Cooperating PCE Configurations ............................25
6.4 Policy Configuration Management ........................... 26 6.4. Policy Configuration Management ...........................27
7 Inter-Component Communication ............................. 26 7. Inter-Component Communication ..................................27
7.1 Policy Communication ..................................... 26 7.1. Policy Communication ......................................27
7.2 PCE Discovery Policy Considerations ....................... 28 7.2. PCE Discovery Policy Considerations .......................29
8 Path Computation Sequence of Events ....................... 29 8. Path Computation Sequence of Events ............................29
8.1 Policy-enabled PCC, Policy-enabled PCE .................... 29 8.1. Policy-Enabled PCC, Policy-Enabled PCE ....................29
8.2 Policy-ignorant PCC, Policy-enabled PCE ................... 30 8.2. Policy-Ignorant PCC, Policy-Enabled PCE ...................31
9 Introduction of New Constraints ........................... 32 9. Introduction of New Constraints ................................32
10 Security Considerations ................................... 32 10. Security Considerations .......................................33
11 Acknowledgments ........................................... 33 11. Acknowledgments ...............................................33
12 IANA Considerations ....................................... 33 12. References ....................................................34
13 References ................................................ 33 12.1. Normative References .....................................34
13.1 Normative References ...................................... 33 12.2. Informative References ...................................34
13.2 Informative References .................................... 34
14 Authors' Addresses ........................................ 35
15 Full Copyright Statement .................................. 36
16 Intellectual Property ..................................... 36
1. Introduction 1. Introduction
The Path Computation Element (PCE) Architecture is introduced in The Path Computation Element (PCE) Architecture is introduced in
[RFC4655]. This document describes the impact of policy-based [RFC4655]. This document describes the impact of policy-based
decision making when incorporated into the PCE architecture and decision making when incorporated into the PCE architecture and
provides additional details on, and context for applying policy provides additional details on, and context for, applying policy
within the PCE Architecture. within the PCE architecture.
Policy-based Management (PBM), see [RFC3198], is a network management Policy-based Management (PBM), see [RFC3198], is a network management
approach that enables a network to automatically perform actions in approach that enables a network to automatically perform actions in
response to network events or conditions based on pre-established response to network events or conditions based on pre-established
rules, also denoted as policies, from a network administrator. PBM rules, also denoted as policies, from a network administrator. PBM
enables network administrators to operate in a high-level manner enables network administrators to operate in a high-level manner
through rule-based strategy (policies can be defined as a set of through rule-based strategy (policies can be defined as a set of
rules and actions); the latter are translated automatically (i.e., rules and actions); the latter are translated automatically (i.e.,
dynamically, without human interference) into individual device dynamically, without human interference) into individual device
configuration directives, aimed at controlling a network as a whole. configuration directives, aimed at controlling a network as a whole.
Two IETF Working Groups have considered policy networking in the Two IETF Working Groups have considered policy networking in the
past: The Resource Allocation Protocol (RAP) working group and the past: The Resource Allocation Protocol (RAP) working group and the
Policy Framework working group. Policy Framework working group.
A framework for policy-based admission control [RFC2753] was defined A framework for policy-based admission control [RFC2753] was defined
and a protocol for use between Policy Enforcement Points (PEP) and and a protocol for use between Policy Enforcement Points (PEP) and
Policy Decision Points (PDP) was specified: Common Open Policy Policy Decision Points (PDP) was specified: Common Open Policy
Service (COPS) [RFC2748]. This document uses the terms PEP and PDP to Service (COPS) [RFC2748]. This document uses the terms PEP and PDP
refer to the functions defined in the COPS context. This document to refer to the functions defined in the COPS context. This document
makes no assumptions nor requires that the actual COPS protocol be makes no assumptions nor does it require that the actual COPS
used. Any suitable policy exchange protocol (for example, SOAP protocol be used. Any suitable policy exchange protocol (for
[W3CSOAP]) may be substituted. example, Simple Object Access Protocol (SOAP) [W3CSOAP]) may be
substituted.
The IETF has also produced a general framework for representing, The IETF has also produced a general framework for representing,
managing, sharing, and reusing policies in a vendor-independent, managing, sharing, and reusing policies in a vendor-independent,
interoperable, and scalable manner. It has also defined an extensible interoperable, and scalable manner. It has also defined an
information model for representing policies, called the Policy Core extensible information model for representing policies, called the
Information Model (PCIM) [RFC3060]; and an extension to this model to Policy Core Information Model (PCIM) [RFC3060], and an extension to
address the need for QoS management, called the QoS Policy this model to address the need for QoS management, called the Quality
Information Model (QPIM) [RFC3644]. However, additional mechanisms of Service (QoS) Policy Information Model (QPIM) [RFC3644]. However,
are needed in order to specify policies related to the path additional mechanisms are needed in order to specify policies related
computation logic as well as its control. to the path computation logic as well as its control.
In Section 2, this document presents policy related background and In Section 2, this document presents policy-related background and
scenarios to provide a context for this work. Section 3 provides scenarios to provide a context for this work. Section 3 provides
requirements that must be addressed by mechanisms and protocols that requirements that must be addressed by mechanisms and protocols that
enable policy-based control over path computation requests and enable policy-based control over path computation requests and
decisions. Section 4 introduces PCIM as a core component in a decisions. Section 4 introduces PCIM as a core component in a
framework for providing policy-enabled path computation. Section 5 framework for providing policy-enabled path computation. Section 5
introduces a set of components that may be used to support policy- introduces a set of components that may be used to support policy-
enabled path computation. Sections 6, 7 and 8 provide details on enabled path computation. Sections 6, 7, and 8 provide details on
possible component configurations, communication and events. Section possible component configurations, communication, and events.
10 discusses the ability to introduce new constraints with minimal Section 10 discusses the ability to introduce new constraints with
impact. It should be noted that this document, in Section 4, only minimal impact. It should be noted that this document, in Section 4,
introduces PCIM, specific PCIM definitions to support path only introduces PCIM; specific PCIM definitions to support path
computation will be discussed in a separate document. computation will be discussed in a separate document.
1.1. Terminology 1.1. Terminology
The reader is assumed to be familiar with the following terms: The reader is assumed to be familiar with the following terms:
BEEP: Blocks Extensible Exchange Protocol, see [RFC3080]. BEEP: Blocks Extensible Exchange Protocol, see [RFC3080].
CIM: Common Information Model, see [DMTF]. CIM: Common Information Model, see [DMTF].
COPS: Common Open Policy Service, see [RFC2748]. COPS: Common Open Policy Service, see [RFC2748].
CSPF: Constraint-based Shortest Path First, see [RFC3630]. CSPF: Constraint-based Shortest Path First, see [RFC3630].
LSP: Label Switched Path, see [RFC3031]. LSP: Label Switched Path, see [RFC3031].
LSR: Label Switching Router, see [RFC3031]. LSR: Label Switching Router, see [RFC3031].
PBM: Policy-based Management, see [RFC3198]. PBM: Policy-Based Management, see [RFC3198].
PC: Path Computation. PC: Path Computation.
PCC: Path Computation Client, see [RFC4655]. PCC: Path Computation Client, see [RFC4655].
PCCIM: Path Computation Core Information Model. PCCIM: Path Computation Core Information Model.
PCE: Path Computation Element, see [RFC4655]. PCE: Path Computation Element, see [RFC4655].
PCEP: Path Computation Element Communication Protocol, PCEP: Path Computation Element Communication Protocol,
see [PCEP]. see [PCEP].
PCIM: Policy Core Information Model, see [RFC3060]. PCIM: Policy Core Information Model, see [RFC3060].
PDP: Policy Decision Points, see [RFC2753]. PDP: Policy Decision Point, see [RFC2753].
PEP: Policy Enforcement Points, see [RFC2753]. PEP: Policy Enforcement Point, see [RFC2753].
QPIM: QoS Policy Information Model, see [RFC3644]. QPIM: QoS Policy Information Model, see [RFC3644].
SLA: Service Level Agreement. SLA: Service Level Agreement.
SOAP: Simple Object Access Protocol, see [W3CSOAP]. SOAP: Simple Object Access Protocol, see [W3CSOAP].
TE: Traffic Engineering, see [RFC3209] and [RFC3473]. TE: Traffic Engineering, see [RFC3209] and [RFC3473].
TED: Traffic Engineering Database, see [RFC3209] and [RFC3473]. TED: Traffic Engineering Database, see [RFC3209] and [RFC3473].
TE LSP: Traffic Engineering MPLS Label Switched Path, see TE LSP: Traffic Engineering MPLS Label Switched Path, see
[RFC3209] and [RFC3473]. [RFC3209] and [RFC3473].
WDM: Wavelength Division Multiplexing
2. Background 2. Background
This section provides some general background on the use of policies This section provides some general background on the use of policies
within the PCE architecture. It presents the rationale behind the use within the PCE architecture. It presents the rationale behind the
of policies in the TE path computation process, as well as use of policies in the TE path computation process, as well as
representative policies usage scenarios. This information is intended representative policies usage scenarios. This information is
to provide context for the presented PCE policy framework. This intended to provide context for the presented PCE policy framework.
section does not attempt to present an exhaustive list of rationales This section does not attempt to present an exhaustive list of
or scenarios. rationales or scenarios.
2.1. Motivation 2.1. Motivation
The PCE architecture as introduced in [RFC4655] includes policy as an The PCE architecture as introduced in [RFC4655] includes policy as an
integral part of the PCE architecture. This section presents some of integral part of the PCE architecture. This section presents some of
the rationale for this inclusion. the rationale for this inclusion.
Network operators require a certain level of flexibility to shape the Network operators require a certain level of flexibility to shape the
TE path computation process, so that the process can be aligned with TE path computation process, so that the process can be aligned with
their business and operational needs. Many aspects of the path their business and operational needs. Many aspects of the path
computation may be governed by policies. For example, a PCC may use computation may be governed by policies. For example, a PCC may use
policies configured by the operator to decide which optimization policies configured by the operator to decide which optimization
criteria, constraints, diversities and their relaxation strategies to criteria, constraints, diversities and their relaxation strategies to
request while computing path(s) for a particular service. Depending request while computing path(s) for a particular service. Depending
on SLAs, TE and cost/performance ratio goals, path computation on SLAs, TE and cost/performance ratio goals, path computation
requests may be issued differently for different services. A given requests may be issued differently for different services. A given
Service A, for instance, may require two SRLG-disjoint paths for Service A, for instance, may require two Shared Risk Link Group
building end-to-end recovery scheme, while for a Service B link- (SRLG)-disjoint paths for building end-to-end recovery scheme, while
disjoint paths may be sufficient. Service A may need paths with for a Service B link-disjoint paths may be sufficient. Service A may
minimal end-to-end delay, while Service B may be looking for shortest need paths with minimal end-to-end delay, while Service B may be
(minimal-cost) paths. Different constraint relaxation strategies may looking for shortest (minimal-cost) paths. Different constraint
be applied while computing paths for Service A and for Service B, and relaxation strategies may be applied while computing paths for
so forth. So based on distinct service requirements distinct or Service A and for Service B, and so forth. So, based on distinct
similar policies may be adopted when issuing/handling path service requirements, distinct or similar policies may be adopted
computation requests. when issuing/handling path computation requests.
Likewise, a PCE may apply policies to decide which algorithm(s) to Likewise, a PCE may apply policies to decide which algorithm(s) to
use while performing path computations requested from a particular use while performing path computations requested from a particular
PCC or for a particular domain, see [RFC4927]; whether to seek the PCC or for a particular domain, see [RFC4927]; whether to seek the
cooperation of other PCEs to satisfy a particular request or to cooperation of other PCEs to satisfy a particular request or to
handle a request on its own (possibly responding with non explicit handle a request on its own (possibly responding with non-explicit
paths); or how the request should be modified before being sent to paths), or how the request should be modified before being sent to
other member(s) of a group of cooperating PCEs, etc. other member(s) of a group of cooperating PCEs, etc.
Additional motivation for supporting policies within the PCE Additional motivation for supporting policies within the PCE
architecture can be described as follows. Historically, a path architecture can be described as follows. Historically, a path
computation entity was an intrinsic part of an LSR's control plane computation entity was an intrinsic part of an LSR's control plane
and always co-located with the LSR's signaling and routing and always co-located with the LSR's signaling and routing
subsystems. This approach allowed for unlimited flexibility in subsystems. This approach allowed for unlimited flexibility in
providing various path computation enhancements, such as: adding new providing various path computation enhancements, such as: adding new
types of constraints, diversities and their relaxation strategies, types of constraints, diversities and their relaxation strategies,
adopting new objective functions and optimization criteria, etc. All adopting new objective functions and optimization criteria, etc. All
skipping to change at page 6, line 14 skipping to change at page 5, line 45
PCE's new capabilities, new advertising and signaling objects may PCE's new capabilities, new advertising and signaling objects may
need to be standardized, all PCCs may need to be upgraded with new need to be standardized, all PCCs may need to be upgraded with new
software, and new interoperability problems may need to be resolved, software, and new interoperability problems may need to be resolved,
etc. etc.
Within the context of the PCE architecture, it is therefore highly Within the context of the PCE architecture, it is therefore highly
desirable to find a way to introduce new path computation desirable to find a way to introduce new path computation
capabilities without requiring modifying either the capabilities without requiring modifying either the
discovery/communication protocols or the PCC software. One way to discovery/communication protocols or the PCC software. One way to
achieve this objective is to consider path selection constraints, achieve this objective is to consider path selection constraints,
their relaxations and objective functions, as path computation their relaxations, and objective functions, as path computation
request-specific policies. Furthermore, such policies may be request-specific policies. Furthermore, such policies may be
configured and managed by a network operator as any other policies configured and managed by a network operator as any other policies
and may be interpreted in real time by PCCs and PCEs. and may be interpreted in real time by PCCs and PCEs.
There are a number of advantages and useful by-products of such an There are a number of advantages and useful by-products of such an
approach: approach:
- New path computation capabilities may be introduced without - New path computation capabilities may be introduced without
changing PCE-PCC communication and discovery protocols or PCC changing PCE-PCC communication and discovery protocols or PCC
software. Only the PCE module providing the path computation software. Only the PCE module providing the path computation
capabilities (referred to in this document as a path capabilities (referred to in this document as a path computation
computation engine) needs to be updated. engine) needs to be updated.
- Existing constraints, objective functions and their relaxations - Existing constraints, objective functions and their relaxations may
may be aggregated and otherwise associated, thus producing new, be aggregated and otherwise associated, thus producing new, more
more complex objective functions that do not require a change complex objective functions that do not require a change of code
of code even on the PCEs supporting the functions. even on the PCEs supporting the functions.
- Different elements such as conditions, actions, variables, - Different elements such as conditions, actions, variables, etc.,
etc., may be re-used by multiple constraints, diversities, and may be reused by multiple constraints, diversities, and
optimizations. optimizations.
- PCCs and PCEs need to handle other (that is, not request- - PCCs and PCEs need to handle other (that is, not request-specific)
specific) policies. Path computation-related policies of all policies. Path computation-related policies of all types can be
types can be placed within the same policy repositories, can be placed within the same policy repositories, managed by the same
managed by the same policy management tools, and can be policy management tools, and interpreted using the same mechanisms.
interpreted using the same mechanisms. Also policies need to be Also, policies need to be supported by PCCs and PCEs independent of
supported by PCCs and PCEs independent of the peculiarities of a the peculiarities of a specific PCC-PCE communication protocol, see
specific PCC-PCE communication protocol, see [PCEP]. Thus, [PCEP]. Thus, introducing a new (request-specific) type of policy
introducing a new (request-specific) type of policies describing describing constraints and other elements of a path computation
constraints and other elements of a path computation request request will be a natural and relatively inexpensive addition to
will be a natural and relatively inexpensive addition to the the policy-enabled path computation architecture.
policy-enabled path computation architecture.
2.2. Policy Attributes 2.2. Policy Attributes
This section provides a summary listing of the policy attributes that This section provides a summary listing of the policy attributes that
may be included in the policy exchanges described in the scenarios may be included in the policy exchanges described in the scenarios
that follow. This list is provided for guidance and is not intended that follow. This list is provided for guidance and is not intended
to be exclusive. Implementation of this framework might include to be exclusive. Implementation of this framework might include
additional policy attributes not listed here. additional policy attributes not listed here.
Identities Identities
skipping to change at page 7, line 48 skipping to change at page 7, line 32
- holding priority - holding priority
- preexisting LSP route - preexisting LSP route
Requested path computation behavior Requested path computation behavior
- objective function - objective function
- other LSPs to be considered - other LSPs to be considered
Additional policy information Additional policy information
- Transparent policy information as received in RSVP-TE - Transparent policy information as received in Resource
Reservation Protocol (RSVP)-TE
2.3. Representative Policy Scenarios 2.3. Representative Policy Scenarios
This section provides example scenarios of how policies may be This section provides example scenarios of how policies may be
applied using the PCE policy framework within the PCE architecture applied using the PCE policy framework within the PCE architecture
context. Actual networks may deploy one of the scenarios discussed, context. Actual networks may deploy one of the scenarios discussed,
some combination of the presented scenarios, or other scenarios (not some combination of the presented scenarios, or other scenarios (not
discussed). This section should not be viewed as limiting other discussed). This section should not be viewed as limiting other
applications of policies within the PCE architecture. applications of policies within the PCE architecture.
skipping to change at page 8, line 25 skipping to change at page 8, line 7
A very simple usage scenario for PCE policy would be to use PCE to A very simple usage scenario for PCE policy would be to use PCE to
centrally administer configured paths. Configured paths are composed centrally administer configured paths. Configured paths are composed
of strict and loose hops in the form of Explicit Route Objects of strict and loose hops in the form of Explicit Route Objects
(EROs), see [RFC3209], and are used by one or more LSPs. Typically, (EROs), see [RFC3209], and are used by one or more LSPs. Typically,
such paths are configured at the LSP ingress. In the context of such paths are configured at the LSP ingress. In the context of
policy-enabled path computation, an alternate approach is possible. policy-enabled path computation, an alternate approach is possible.
In particular, service-specific policies can be installed that will In particular, service-specific policies can be installed that will
provide configured path(s) for a specific service request. The provide configured path(s) for a specific service request. The
request may be identified based on service parameters such as end- request may be identified based on service parameters such as
points, requested QoS, or even a token that identifies the initiator endpoints, requested QoS, or even a token that identifies the
of a service request. The configured path(s) would then be used as initiator of a service request. The configured path(s) would then be
input to the path computation process, which would return explicit used as input to the path computation process, which would return
routes by expanding of all specified loose hops. explicit routes by expanding of all specified loose hops.
Example of policy: Example of policy:
if(service_destination matches 10.132.12.0/24) if(service_destination matches 10.132.12.0/24)
use path: 10.125.13.1=>10.125.15.1=>10.132.12.1 Use path: 10.125.13.1 => 10.125.15.1 => 10.132.12.1.
else else
compute path dynamically Compute path dynamically.
---------------------- ----------------------
| ----- | | ----- |
| | TED |<-+------------> | | TED |<-+------------>
| ----- | TED synchronization | ----- | TED synchronization
| | | mechanism (e.g., routing protocol) | | | mechanism (e.g., routing protocol)
| | | | | |
| v | | v |
| ------ ----- | Inter-PCE Request/Response | ------ ----- | Inter-PCE Request/Response
| |Policy|<-->| PCE |<.+...........> (when present) | |Policy|<-->| PCE |<.+...........> (when present)
| ------ ----- | | ------ ----- |
skipping to change at page 9, line 28 skipping to change at page 8, line 43
v v
Service ------------- Signaling Service ------------- Signaling
Request |[PCC][Policy]| Protocol Request |[PCC][Policy]| Protocol
<------>| Node |<-------> <------>| Node |<------->
or Signaling ------------- or Signaling -------------
Protocol Protocol
Figure 1: Policy Enabled PCC and PCE Figure 1: Policy Enabled PCC and PCE
Path computation policies may be applied at either a PCC or a PCE, Path computation policies may be applied at either a PCC or a PCE,
see Figure 1. In the PCC case, the configured path would be processed see Figure 1. In the PCC case, the configured path would be
at the PCC and then passed to the PCE along with the PCE request, processed at the PCC and then passed to the PCE along with the PCE
probably in the form of (inclusion) constraints. When applied at the request, probably in the form of (inclusion) constraints. When
PCE, the configured path would be used locally. Both cases require applied at the PCE, the configured path would be used locally. Both
some method to configure and manage policies. In the PCC case, the cases require some method to configure and manage policies. In the
real benefit would come when there is an automated policy PCC case, the real benefit would come when there is an automated
distribution mechanism. policy distribution mechanism.
------------------ ------------------- ------------------ -------------------
| | | | | | | |
| PCE | | PCE | | PCE | | PCE |
| | | | | | | |
| ------ ----- | | ----- ------ | | ------ ----- | | ----- ------ |
| |Policy| | TED | | | | TED | |Policy| | | |Policy| | TED | | | | TED | |Policy| |
| ------ ----- | | ----- ------ | | ------ ----- | | ----- ------ |
------------------ ------------------- ------------------ -------------------
^ ^ ^ ^
| Request/ | Request/ | Request/ | Request/
| Response | Response | Response | Response
v v v v
Service -------- Signaling ------------ Signaling ------------ Service -------- Signaling ------------ Signaling ------------
Request|Head-End| Protocol |Intermediate| Protocol |Intermediate| Request|Head-End| Protocol |Intermediate| Protocol |Intermediate|
---->| Node |<--------->| Node |<--------->| Node | ---->| Node |<--------->| Node |<--------->| Node |
-------- ------------ ------------ -------- ------------ ------------
Figure 2. Multiple PCE Path Computation Figure 2: Multiple PCE Path Computation
------------------ ------------------ ------------------ ------------------
| | Inter-PCE Request/Response | | | | Inter-PCE Request/Response | |
| PCE |<-------------------------->| PCE | | PCE |<-------------------------->| PCE |
| | | | | | | |
| ------ ----- | | ------ ----- | | ------ ----- | | ------ ----- |
| |Policy| | TED | | | |Policy| | TED | | | |Policy| | TED | | | |Policy| | TED | |
| ------ ----- | | ------ ----- | | ------ ----- | | ------ ----- |
------------------ ------------------ ------------------ ------------------
^ ^
| Request/ | Request/
| Response | Response
v v
Service ---------- Signaling ---------- Signaling ---------- Service ---------- Signaling ---------- Signaling ----------
Request| Head-End | Protocol | Adjacent | Protocol | Adjacent | Request| Head-End | Protocol | Adjacent | Protocol | Adjacent |
---->| Node |<---------->| Node |<---------->| Node | ---->| Node |<---------->| Node |<---------->| Node |
---------- ---------- ---------- ---------- ---------- ----------
Figure 3. Multiple PCE Path Computation with Inter-PCE Communication Figure 3: Multiple PCE Path Computation with Inter-PCE Communication
Policy-configured paths may also be used in environments with Policy-configured paths may also be used in environments with
multiple (more than one) cooperating PCEs (see Figures 2 and 3). For multiple (more than one) cooperating PCEs (see Figures 2 and 3). For
example, consider the case when there is limited TE visibility and example, consider the case when there is limited TE visibility and
independent PCEs are used to determine path(s) within each area of independent PCEs are used to determine path(s) within each area of
the TE visibility. In such a case, it may not be possible (or the TE visibility. In such a case, it may not be possible (or
desirable) to configure entire explicit path(s) on a single PCE. desirable) to configure entire explicit path(s) on a single PCE.
However, it is possible to configure explicit path(s) for each area However, it is possible to configure explicit path(s) for each area
of the TE visibility and each responsible PCE. One by one, the PCEs of the TE visibility and each responsible PCE. One by one, the PCEs
would then map an incoming signaling request to appropriate would then map an incoming signaling request to appropriate
configured path(s). Note that to make such a scenario work it would configured path(s). Note that to make such a scenario work, it would
likely be necessary to start and finish the configured paths on TE likely be necessary to start and finish the configured paths on TE
domain boundary nodes. Clearly, consistent PCE Policy Repositories domain boundary nodes. Clearly, consistent PCE Policy Repositories
are also critical in this example. are also critical in this example.
2.3.2. Scenario: Provider Selection Policy 2.3.2. Scenario: Provider Selection Policy
A potentially more interesting scenario is applying PC policies in A potentially more interesting scenario is applying PC policies in
multi-provider topologies. There are numerous interesting policy multi-provider topologies. There are numerous interesting policy
applications in such topologies. A rudimentary example is simple applications in such topologies. A rudimentary example is simple
access control, that is, deciding which PCCs are permitted to request access control, that is, deciding which PCCs are permitted to request
inter-domain path computation. inter-domain path computation.
A more complicated example is applying policy to determine which A more complicated example is applying policy to determine which
domain or network provider will be used to support a particular PCE domain or network provider will be used to support a particular PCE
request. Consider the topology presented in Figure 4. In this example request. Consider the topology presented in Figure 4. In this
there are multiple transit domains available to provide a path from a example, there are multiple transit domains available to provide a
source domain to a destination domain. Furthermore, each transit path from a source domain to a destination domain. Furthermore, each
domain may have one or more options for reaching a particular domain. transit domain may have one or more options for reaching a particular
Each domain will need to select which of the multiple available paths domain. Each domain will need to select which of the multiple
will be used to satisfy a particular PCE request. available paths will be used to satisfy a particular PCE request.
In today's typical path computation process, TE reachability, In today's typical path computation process, TE reachability,
availability and metric are the basic criteria for path selection. availability, and metric are the basic criteria for path selection.
However, policies can provide an important added consideration in the However, policies can provide an important added consideration in the
decision process. For example, transit domain A may be more expensive decision process. For example, transit domain A may be more
and provide lower delay or loss than transit domain B. Likewise, a expensive and provide lower delay or loss than transit domain B.
transit domain may wish to treat PCE requests from its own customers Likewise, a transit domain may wish to treat PCE requests from its
differently than requests from other providers. In both cases, own customers differently than requests from other providers. In
computation based on traffic engineering databases will result in both cases, computation based on traffic engineering databases will
multiple transit domain that provide reachability, and policies can result in multiple transit domains that provide reachability, and
be used to govern which PCE requests get better service. policies can be used to govern which PCE requests get better service.
+-------+ +-------+
+----------+Transit+----------+ +----------+Transit+----------+
+---+---+ | Domain| +---+---+ +---+---+ | Domain| +---+---+
|Transit| | C | |Transit| |Transit| | C | |Transit|
+--------+ Domain| +---+---+ | Domain+--------+ +--------+ Domain| +---+---+ | Domain+--------+
| | A +--+ | +--+ F | | | | A +--+ | +--+ F | |
+--+---+ +---+---+ | | | +---+---+ +--+---+ +--+---+ +---+---+ | | | +---+---+ +--+---+
|Source| | | +---+---+ | | |Target| |Source| | | +---+---+ | | |Target|
|Domain| | +---+Transit+---+ | |Domain| |Domain| | +---+Transit+---+ | |Domain|
skipping to change at page 12, line 30 skipping to change at page 11, line 30
| |Transit| | | |Transit| |
+----------+ Domain+----------+ +----------+ Domain+----------+
| E | | E |
+-------+ +-------+
Figure 4: Multi-Domain Network with Multiple Transit Options Figure 4: Multi-Domain Network with Multiple Transit Options
There are multiple options for differentiating which PCE requests use There are multiple options for differentiating which PCE requests use
a particular transit domain and get a particular (better or worse) a particular transit domain and get a particular (better or worse)
level of service. For example, a PCE in the source domain may use level of service. For example, a PCE in the source domain may use
user and request-specific policies to determine the level of service user- and request-specific policies to determine the level of service
to provide. A PCE in the source domain may also use domain-specific to provide. A PCE in the source domain may also use domain-specific
policies to choose which transit domains are acceptable. A PCE in a policies to choose which transit domains are acceptable. A PCE in a
transit domain may use request-specific policies to determine if a transit domain may use request-specific policies to determine if a
request is from a direct customer or another provider, and then use request is from a direct customer or another provider, and then use
domain-specific policies to identify how the request should be domain-specific policies to identify how the request should be
processed. processed.
Example of policy: Example of policy:
if(path computation request issued by a PCC within Source Domain) if(path computation request issued by a PCC within Source Domain)
route the path through Transit Domain A Route the path through Transit Domain A.
else else
route the path through Transit Domain B Route the path through Transit Domain B.
2.3.3. Scenario: Policy Based Constraints 2.3.3. Scenario: Policy Based Constraints
Another usage scenario is the use of policy to provide constraints in Another usage scenario is the use of policy to provide constraints in
a PCE request. Consider an LSR with a policy enabled PCC, as shown in a PCE request. Consider an LSR with a policy enabled PCC, as shown
Figure 1, which receives a service request via signaling, including in Figure 1, which receives a service request via signaling,
over a NNI or UNI reference point, or receives a configuration including over a Network-Network Interface (NNI) or User Network
request over a management interface to establish a service. In either Interface (UNI) reference point, or receives a configuration request
case the path(s) needed to support the service are not explicitly over a management interface to establish a service. In either case,
the path(s) needed to support the service are not explicitly
specified in the message/request, and hence path computation is specified in the message/request, and hence path computation is
needed. needed.
In this case, the PCC may apply user or service-specific policies to In this case, the PCC may apply user- or service-specific policies to
decide how the path selection process should be constrained, that is, decide how the path selection process should be constrained, that is,
which constraints, diversities, optimization criterion and constraint which constraints, diversities, optimization criterion, and
relaxation strategies should be applied in order for the service constraint relaxation strategies should be applied in order for the
LSP(s) to have a likelihood to be successfully established and service LSP(s) to have a likelihood to be successfully established
provide necessary QoS and resilience against network failures. When and provide necessary QoS and resilience against network failures.
deciding on the set of constraints the PCC uses as an input all When deciding on the set of constraints, the PCC uses as an input all
information it knows about the user and service, such as the contents information it knows about the user and service, such as the contents
of the received message, port ID over which message was received, of the received message, port ID over which message was received,
associated VPN ID, signaling/reference point type, request time, etc. associated VPN ID, signaling/reference point type, request time, etc.
Once the constraints and other parameters of the required path Once the constraints and other parameters of the required path
computation are determined, the PCC generates a path computation computation are determined, the PCC generates a path computation
request which includes the request-specific policies that describe request that includes the request-specific policies that describe the
the determined set of constraints, optimizations, and other determined set of constraints, optimizations, and other parameters
parameters that indicate how the request is to be considered in the that indicate how the request is to be considered in the path
path computation process. computation process.
Example of policy: Example of policy:
if(LSP belongs to a WDM layer network) if(LSP belongs to a WDM layer network)
Compute the path with wavelength continuity constraint with the Compute the path with wavelength continuity constraint with the
maximum OSNR at the path end optimization maximum Optical Signal Noise Ratio (OSNR) at the path end
optimization.
else if(LSP belongs to a connection oriented Ethernet layer network) else if(LSP belongs to a connection oriented Ethernet layer network)
Compute the path with minimum end-to-end delay Compute the path with minimum end-to-end delay.
else else
Compute the shortest path Compute the shortest path.
The PCC may also apply server-specific policies in order to select The PCC may also apply server-specific policies in order to select
which PCE to use from the set of known (i.e., discovered or which PCE to use from the set of known (i.e., discovered or
configured) PCEs. The PCC may also use server-specific policies to configured) PCEs. The PCC may also use server-specific policies to
form the request to match the PCE's capabilities so that the request form the request to match the PCE's capabilities so that the request
will not be rejected and has a higher likelihood of being satisfied will not be rejected and has a higher likelihood of being satisfied
in an efficient way. An example of a request modification as the in an efficient way. An example of a request modification as the
result of a server-specific policy is removing a constraint not result of a server-specific policy is removing a constraint not
supported by the PCE. Once the policy processing is completed at the supported by the PCE. Once the policy processing is completed at the
PCC, and the path computation request resulting from the original PCC, and the path computation request resulting from the original
service request is updated by the policy processing, the request is service request is updated by the policy processing, the request is
sent to the PCE. sent to the PCE.
Example of policy: Example of policy:
if(LSP belongs to a WDM layer network) if(LSP belongs to a WDM layer network)
Identify a PCE supporting wavelength continuity and optical Identify a PCE supporting wavelength continuity and optical
impairment constraints; send a request to such PCE, requesting impairment constraints;
path computation with the following constraints: Send a request to such PCE, requesting path computation with the
following constraints:
a) wavelength continuity; a) wavelength continuity;
b) maximum PMD at the path end. b) maximum Polarization Mode Dispersion (PMD) at the path end.
if(the path computation fails) if(the path computation fails) remove the maximum PMD constraint
remove the maximum PMD constraint and try the computation again and try the computation again.
The PCE that receives the request validates and otherwise processes The PCE that receives the request validates and otherwise processes
the request, applying the policies found in the request as well as the request, applying the policies found in the request as well as
any policies that are available at the PCE, e.g., client and domain- any policies that are available at the PCE, e.g., client- and domain-
specific polices. As a result of the policy processing, the PCE may specific policies. As a result of the policy processing, the PCE may
decide to reject the request. decide to reject the request.
Example of policy: Example of policy:
Authenticate the PCC requesting the path computation using the Authenticate the PCC requesting the path computation using the
PCC ID found in the path computation request; PCC ID found in the path computation request;
Reject the request if the authentication fails Reject the request if the authentication fails.
It The PCE also may decide to respond with one or several pre- The PCE also may decide to respond with one or several pre-computed
computed paths if user or client specific polices instruct the PCE to paths if user- or client-specific policies instruct the PCE to do so.
do so. If the PCE decides to satisfy the request by performing a path If the PCE decides to satisfy the request by performing a path
computation, it determines if it needs the cooperation of other PCEs computation, it determines if it needs the cooperation of other PCEs
and defines parameters for path computations to be performed locally and defines parameters for path computations to be performed locally
and remotely. After that, the PCE instructs a co-located path and remotely. After that, the PCE instructs a co-located path
computation engine to perform the local path computation(s) and, if computation engine to perform the local path computation(s) and, if
necessary, sends path computation requests to one or more other PCEs. necessary, sends path computation requests to one or more other PCEs.
It then waits for the responses from the local path computation It then waits for the responses from the local path computation
engine and, when used, the remote PCE. It then combines the resulting engine and, when used, the remote PCE. It then combines the
paths and sends the result back to the requesting PCC. The response resulting paths and sends the result back to the requesting PCC. The
may indicate policies describing the resulting paths, their response may indicate policies describing the resulting paths, their
characteristics (summary cost, expected end-to-end delay, etc.). as characteristics (summary cost, expected end-to-end delay, etc.), as
well as additional information related to the request, e.g., which well as additional information related to the request, e.g., which
constraints were honored, which were dismissed, and which were constraints were honored, which were dismissed, and which were
relaxed and in what way. relaxed and in what way.
Example of policy: Example of policy:
if(the path destination belongs to domain A) if(the path destination belongs to domain A)
Instruct local path computation engine to perform the path Instruct local path computation engine to perform the path
computation; computation;
else else
Identify the PCE supporting the destination domain; Identify the PCE supporting the destination domain;
Send path computation request to such PCE; Send path computation request to such PCE;
Wait for and process the response Wait for and process the response.
Send the path computation response to the requesting PCC Send the path computation response to the requesting PCC.
The PCC processes the response and instructs the LSR to encode the The PCC processes the response and instructs the LSR to encode the
received path(s) into the outgoing signaling message(s). received path(s) into the outgoing signaling message(s).
2.3.4. Scenario: Advanced Load Balancing (ALB) Example 2.3.4. Scenario: Advanced Load Balancing (ALB) Example
Figure 5 illustrates a problem that stems from the coupling between Figure 5 illustrates a problem that stems from the coupling between
BGP and IGP in the BGP decision process. If a significant portion of BGP and IGP in the BGP decision process. If a significant portion of
the traffic destined to the data center (or customer network) enters the traffic destined for the data center (or customer network) enters
a PCE-enabled network from AS 1 and all IGP links weights are the a PCE-enabled network from AS 1 and all IGP links' weights are the
same, then both PE3 and PE4 will prefer to reach the data center same, then both PE3 and PE4 will prefer to reach the data center
using the routes advertised by PE2. PE5 will use the router-IDs of using the routes advertised by PE2. PE5 will use the router-IDs of
PE1 and PE2 to break the tie and might therefore also select to use PE1 and PE2 to break the tie and might therefore also select to use
the path through PE2 (if the router ID of PE2 is smaller than that of the path through PE2 (if the router ID of PE2 is smaller than that of
PE1). Either way the net result is that the link between PE2 and CE PE1). Either way, the net result is that the link between PE2 and CE
will carry most of the traffic while the link between PE1 and CE will will carry most of the traffic while the link between PE1 and the
be mostly idle. Customer Edge (CE) will be mostly idle.
.............................. ..............................
. AS 1 . . AS 1 .
. . . .
. +---+ +---+ +----+ . . +---+ +---+ +----+ .
....|PE8|...|PE9|...|PE10|.... ....|PE8|...|PE9|...|PE10|....
+---+ +---+ +----+ +---+ +---+ +----+
| | | | | |
+---+ +---+ +---+ +---+ +---+ +---+
......|PE3|...|PE4|...|PE5|...... ......|PE3|...|PE4|...|PE5|......
skipping to change at page 15, line 47 skipping to change at page 15, line 31
.............. +---+ |P3| | |PCE| . by all .............. +---+ |P3| | |PCE| . by all
. +--+ | x===x . AS0 nodes . +--+ | x===x . AS0 nodes
. AS 0 +---+ . . AS 0 +---+ .
..................|PE7|.......... ..................|PE7|..........
+---+ +---+
Figure 5: Advanced Load Balancing Figure 5: Advanced Load Balancing
This is a common problem for providers and customers alike. Analysis This is a common problem for providers and customers alike. Analysis
of Netflow records, see [IRSCP], for a large ISP network on a typical of Netflow records, see [IRSCP], for a large ISP network on a typical
day has shown that for 71.8% of multi-homed customers there is a day has shown that for 71.8% of multi-homed customers, there is a
complete imbalance, where the most loaded link carries all the complete imbalance, where the most loaded link carries all the
traffic and the least loaded link carries none. traffic and the least loaded link carries none.
PCE policies can address this problem by basing the routing decision PCE policies can address this problem by basing the routing decision
at the ingress routers on the offered load towards the multi-homed at the ingress routers on the offered load towards the multi-homed
customer. For example, in Figure 5 PCE policies could be configured customer. For example, in Figure 5, PCE policies could be configured
such that traffic load is monitored (e.g., based on Netflow data) at such that traffic load is monitored (e.g., based on Netflow data) at
ingress routers PE3 to PE7 towards the data center prefixes served by ingress routers PE3 to PE7 towards the data center prefixes served by
egress routers PE1 and PE2. Using this offered load information, the egress routers PE1 and PE2. Using this offered load information, the
path computations returned by PCE, based on the enabled PCE policies, path computations returned by PCE, based on the enabled PCE policies,
can direct traffic to the appropriate egress router, on a per-ingress can direct traffic to the appropriate egress router, on a per-ingress
router basis. For example, the PCE path computation might direct router basis. For example, the PCE path computation might direct
traffic from both PE4 and PE5 to egress PE1, thus overriding the traffic from both PE4 and PE5 to egress PE1, thus overriding the
default IGP based selection. Alternatively, traffic from each default IGP based selection. Alternatively, traffic from each
ingress router to each egress link could be split 50-50. ingress router to each egress link could be split 50-50.
This scenario is a good example of how a policy governed PCE can This scenario is a good example of how a policy-governed PCE can
account for some information that was not or cannot be advertised as account for some information that was not or cannot be advertised as
TE link/node attributes, and, therefore, cannot be subject for TE link/node attributes, and, therefore, cannot be subject for
explicit path computation constraints. More generally, such explicit path computation constraints. More generally, such
information can be pretty much anything. For example, traffic demand information can be pretty much anything. For example, traffic demand
forecasts, flow monitoring feedback, any administrative policies, forecasts, flow monitoring feedback, any administrative policies,
etc. Further examples are described in [IRSCP] of how PCE policies etc. Further examples are described in [IRSCP] of how PCE policies
might address certain network routing problems, such as selective might address certain network routing problems, such as selective
DDoS blackholing, planned maintenance, and VPN gateway selection. distributed denial-of-service (DDoS) blackholing, planned
maintenance, and VPN gateway selection.
Example of policy: Example of policy:
for(all traffic flows destined to Customer Network) for(all traffic flows destined to Customer Network)
if(flow ingresses on PE3, PE4 or PE5) if(flow ingresses on PE3, PE4, or PE5)
route the flow over PE1 Route the flow over PE1.
else else
route the flow over PE2 Route the flow over PE2.
3. Requirements 3. Requirements
The following requirements must be addressed by mechanisms and The following requirements must be addressed by mechanisms and
protocols that enable policy-based control over path computation protocols that enable policy-based control over path computation
requests and decisions: requests and decisions:
- (G)MPLS path computation-specific - (G)MPLS path computation-specific
The mechanisms must meet the policy-based control requirements The mechanisms must meet the policy-based control requirements
specific to the problem of path computation using RSVP-TE as the specific to the problem of path computation using RSVP-TE as the
signaling protocol on MPLS and GMPLS LSRs. signaling protocol on MPLS and GMPLS LSRs.
- Support for non-(G)MPLS PCCs - Support for non-(G)MPLS PCCs
The mechanisms must be sufficiently generic to support The mechanisms must be sufficiently generic to support non-(G)MPLS
non-(G)MPLS (LSR) clients such as an NMS, or network planner, (LSR) clients such as a Network Management System (NMS), or network
etc. planner, etc.
- Support for many policies - Support for many policies
The mechanisms must include support for many policies and policy The mechanisms must include support for many policies and policy
configurations. In general, the determination and configuration configurations. In general, the determination and configuration of
of viable policies are the responsibility of the service viable policies are the responsibility of the service provider.
provider.
- Provision for monitoring and accounting information - Provision for monitoring and accounting information
The mechanisms must include support for monitoring policy state, The mechanisms must include support for monitoring policy state and
and provide access information. In particular, mechanisms must provide access information. In particular, mechanisms must provide
provide usage and access information that may be used for usage and access information that may be used for accounting
accounting purposes. purposes.
- Fault tolerance and recovery - Fault tolerance and recovery
The mechanisms must include provisions for fault tolerance and The mechanisms must include provisions for fault tolerance and
recovery from failure cases such as failure of PCC/PCE PDPs, recovery from failure cases such as failure of PCC/PCE PDPs,
disruption in communication that separate a PCC/PCE PDP from its disruption in communication that separate a PCC/PCE PDP from its
associated PCC/PCE PEPs. associated PCC/PCE PEPs.
- Support for policy-ignorant nodes - Support for policy-ignorant nodes
The mechanisms should not be mandatory for every node in a The mechanisms should not be mandatory for every node in a network.
network. Policy based path computation control may be enforced at Policy-based path computation control may be enforced at a subset
a subset of nodes, for example, on boundary nodes within an of nodes, for example, on boundary nodes within an administrative
administrative domain. These policy-capable nodes will function domain. These policy-capable nodes will function as trusted nodes
as trusted nodes from the point of view of the policy-ignorant from the point of view of the policy-ignorant nodes in that
nodes in that administrative domain. Alternatively, policy may be administrative domain. Alternatively, policy may be applied solely
applied solely on PCEs with all PCCs being policy-ignorant nodes. on PCEs with all PCCs being policy-ignorant nodes.
- Scalability - Scalability
One of the important requirements for the mechanisms is One of the important requirements for the mechanisms is
scalability. The mechanisms must scale at least to the same scalability. The mechanisms must scale at least to the same extent
extent that RSVP-TE signaling scales in terms of accommodating that RSVP-TE signaling scales in terms of accommodating multiple
multiple LSPs and network nodes in the path of an LSP. There are LSPs and network nodes in the path of an LSP. There are several
several sensitive areas in terms of scalability of policy based sensitive areas in terms of scalability of policy-based path
path computation control. First, not every policy aware node in computation control. First, not every policy-aware node in an
an infrastructure should be expected to contact a remote infrastructure should be expected to contact a remote PDP. This
PDP. This would cause potentially long delays in verifying would cause potentially long delays in verifying requests.
requests. Additionally, the policy control architecture must Additionally, the policy control architecture must scale at least
scale at least as well as RSVP-TE protocol based on factors such as well as RSVP-TE protocol based on factors such as the size of
as the size of RSVP-TE messages, the time required for the RSVP-TE messages, the time required for the network to service an
network to service an RSVP-TE request, local processing time RSVP-TE request, local processing time required per node, and local
required per node, and local memory consumed per node. These memory consumed per node. These scaling considerations are of
scaling considerations are of particular importance during particular importance during re-routing of a set of LSPs.
re-routing of a set of LSPs.
- Security and denial of service considerations - Security and denial-of-service considerations
The policy control architecture, protocols and mechanisms must be The policy control architecture, protocols, and mechanisms must be
secure as far as the following aspects are concerned: secure as far as the following aspects are concerned:
o First, the mechanisms proposed must minimize theft and denial o First, the mechanisms proposed must minimize theft and denial-
of service threats. of-service threats.
o Second, it must be ensured that the entities (such as PEPs o Second, it must be ensured that the entities (such as PEPs and
and PDPs) involved in policy control can verify each other's PDPs) involved in policy control can verify each other's
identity and establish necessary trust before communicating. identity and establish necessary trust before communicating.
- Inter-AS and inter-area requirements - Inter-AS and inter-area requirements
There are several inter-AS policy related requirements discussed There are several inter-AS policy-related requirements discussed in
in [RFC4216] and [INTERAS-PCEP], and inter-area policy related [RFC4216] and [RFC5376], and inter-area policy-related requirements
requirements discussed in [RFC4927]. These requirements discussed in [RFC4927]. These requirements must be addressed by
must be addressed by policy-enabled PCE mechanisms and protocols. policy-enabled PCE mechanisms and protocols.
It should be noted that this document only outlines the communication It should be noted that this document only outlines the communication
elements and mechanisms needed to allow a wide variety of possible elements and mechanisms needed to allow a wide variety of possible
policies to be applied for path computation control. It does not policies to be applied for path computation control. It does not
include any discussion of any specific policy behavior. Nor does it include any discussion of any specific policy behavior, nor does it
define or require use of specific policies. define or require use of specific policies.
4. Path Computation Policy Information Model (PCPIM) 4. Path Computation Policy Information Model (PCPIM)
The Policy Core Information Model (PCIM) introduced in [RFC3060] and The Policy Core Information Model (PCIM) introduced in [RFC3060] and
expanded in [RFC3460] presents the object-oriented information model expanded in [RFC3460] presents the object-oriented information model
for representing general policy information. for representing general policy information.
This model defines two hierarchies of object classes: This model defines two hierarchies of object classes:
- Structural classes representing policy information and control of - Structural classes representing policy information and control of
policies. policies.
- Association classes that indicate how instances of the structural - Association classes that indicate how instances of the structural
classes are related to each other. classes are related to each other.
These classes can be mapped to various concrete implementations, for These classes can be mapped to various concrete implementations, for
example, to a directory that uses LDAPv3 as its access protocol. example, to a directory that uses Lightweight Directory Access
Protocol version 3 (LDAPv3) as its access protocol.
Figure 6 shows an abstract from the class inheritance hierarchy for Figure 6 shows an abstract from the class inheritance hierarchy for
PCIM. PCIM.
ManagedElement (abstract) ManagedElement (abstract)
| |
+--Policy (abstract) +--Policy (abstract)
| | | |
| +---PolicySet (abstract) | +---PolicySet (abstract)
| | | | | |
skipping to change at page 19, line 51 skipping to change at page 20, line 14
Policy models for application-specific areas such as the Path Policy models for application-specific areas such as the Path
Computation Service may extend the PCIM in several ways. The Computation Service may extend the PCIM in several ways. The
preferred way is to use the PolicyGroup, PolicyRule, and preferred way is to use the PolicyGroup, PolicyRule, and
PolicyTimePeriodCondition classes directly as a foundation for PolicyTimePeriodCondition classes directly as a foundation for
representing and communicating policy information. Then, specific representing and communicating policy information. Then, specific
subclasses derived from PolicyCondition and PolicyAction can capture subclasses derived from PolicyCondition and PolicyAction can capture
application-specific definitions of conditions and actions of application-specific definitions of conditions and actions of
policies. policies.
Policy Quality of Service Information Model [RFC3644] further extends The Policy Quality of Service Information Model [RFC3644] further
the PCIM to represent QoS policy information for large-scale policy extends the PCIM to represent QoS policy information for large-scale
domains. New classes introduced in this document describing QoS and policy domains. New classes introduced in this document describing
RSVP related variables, conditions and actions can be used as a QoS- and RSVP-related variables, conditions, and actions can be used
foundation for the PCPIM. as a foundation for the PCPIM.
Detailed description of the PCPIM will be provided in a separate Detailed description of the PCPIM will be provided in a separate
documents. document.
5. Policy-Enabled Path Computation Framework Components 5. Policy-Enabled Path Computation Framework Components
The following components are defined as part of the framework to The following components are defined as part of the framework to
support policy-enabled path computation: support policy-enabled path computation:
- PCE Policy Repository - PCE Policy Repository
A database from which PCE policies are available in the form of A database from which PCE policies are available in the form of
instances of PCPIM classes. PCE Policies are configured and instances of PCPIM classes. PCE Policies are configured and
managed by PCE Policy Management Tools; managed by PCE Policy Management Tools;
- PCE Policy Decision Point (PCE-PDP) - PCE Policy Decision Point (PCE-PDP)
A logical entity capable of retrieving relevant path computation A logical entity capable of retrieving relevant path computation
policies from one or more Policy Repositories and delivering the policies from one or more Policy Repositories and delivering the
information to associated PCE-PEP(s); information to associated PCE-PEP(s);
- PCE Policy Enforcement Point (PCE-PEP) - PCE Policy Enforcement Point (PCE-PEP)
A logical entity capable of issuing device specific Path A logical entity capable of issuing device-specific Path
Computation Engine configuration requests for the purpose of Computation Engine configuration requests for the purpose of
enforcing the policies; enforcing the policies;
- PCC Policy Decision Point (PCC-PDP) - PCC Policy Decision Point (PCC-PDP)
A logical entity capable of retrieving relevant path computation A logical entity capable of retrieving relevant path computation
policies from one or more Policy Repositories and delivering the policies from one or more Policy Repositories and delivering the
information to associated PCC-PEP(s); information to associated PCC-PEP(s);
- PCC Policy Enforcement Point (PCC-PEP) - PCC Policy Enforcement Point (PCC-PEP)
A logical entity capable of issuing device specific Path A logical entity capable of issuing device-specific Path
Computation Service User configuration requests for the purpose Computation Service User configuration requests for the purpose of
of enforcing the policies. enforcing the policies.
From the policy perspective a PCC is logically decomposed into two From the policy perspective a PCC is logically decomposed into two
parts: PCC-PDP and PCC-PEP. When present, a PCC-PEP is co-located parts: PCC-PDP and PCC-PEP. When present, a PCC-PEP is co-located
with a Path Computation Service User entity that requires remote path with a Path Computation Service User entity that requires remote path
computation (for example, the GMPLS control plane of an LSR). The computation (for example, the GMPLS control plane of an LSR). The
PCC-PEP and PCC-PDP may be physically co-located (as per [RFC2748]) PCC-PEP and PCC-PDP may be physically co-located (as per [RFC2748])
or separated. In the later case they talk to each other via such or separated. In the latter case, they talk to each other via such
protocols as SOAP [W3CSOAP] or BEEP [RFC3080]. protocols as SOAP [W3CSOAP] or BEEP [RFC3080].
Likewise, a PCE is logically decomposed into two parts: PCE-PEP and Likewise, a PCE is logically decomposed into two parts: PCE-PEP and
PCE-PDP. When present, PCE-PEP is co-located with a Path Computation PCE-PDP. When present, PCE-PEP is co-located with a Path Computation
Engine entity that actually provides the Path Computation Service Engine entity that actually provides the Path Computation Service
(that is, runs path computation algorithms). PCE-PEP and PCE-PDP may (that is, runs path computation algorithms). PCE-PEP and PCE-PDP may
be physically co-located or separated. In the later case they be physically co-located or separated. In the later case, they
communicate using such protocols as SOAP and/or BEEP. communicate using such protocols as SOAP and/or BEEP.
PCC-PDP/PCE-PDP may be co-located with, or separated from, an PCC-PDP/PCE-PDP may be co-located with, or separated from, an
associated PCE Policy Repository. In the latter case, the PDPs use associated PCE Policy Repository. In the latter case, the PDPs use
some access protocol (for example, LDAPv3 or SNMP). The task of PDPs some access protocol (for example, LDAPv3 or SNMP). The task of PDPs
is to retrieve policies from the repository(ies) and convey them to is to retrieve policies from the repository (or repositories) and
respective PEPs either in unsolicited way or upon the PEPs requests. convey them to respective PEPs either in an unsolicited way or upon
the PEP's requests.
A PCC-PEP may receive policy information not only from PCC-PDPs(s) A PCC-PEP may receive policy information not only from PCC-PDP(s) but
but also from PCE-PEP(s) via PCC-PCE communication and/or PCE also from PCE-PEP(s) via PCC-PCE communication and/or PCE discovery
discovery protocols. Likewise, a PCE-PEP may receive policy protocols. Likewise, a PCE-PEP may receive policy information not
information not only from PCE-PDPs(s) but also from PCC-PEP(s), via only from PCE-PDP(s) but also from PCC-PEP(s), via the PCC-PCE
the PCC-PCE communication protocol [PCEP]. communication protocol [PCEP].
Any given policy can be interpreted (that is, translated into a Any given policy can be interpreted (that is, translated into a
sequence of concrete device specific configuration requests) either sequence of concrete device specific configuration requests) either
on a PDP or on the associated PEP or partly on the PDP and partly on on a PDP or on the associated PEP or partly on the PDP and partly on
the PEP. the PEP.
Generally speaking, the task of the PCC-PEP is to select the PCE and Generally speaking, the task of the PCC-PEP is to select the PCE and
build path computation requests applying service-specific policies build path computation requests applying service-specific policies
provided by the PCC-PDP. The task of the PCE-PEP is to control path provided by the PCC-PDP. The task of the PCE-PEP is to control path
computations by applying request-specific policies found in the computations by applying request-specific policies found in the
requests as well as client-specific and domain-specific policies requests as well as client-specific and domain-specific policies
supplied by the PCE-PDP. supplied by the PCE-PDP.
6. Policy Component Configurations 6. Policy Component Configurations
6.1. PCC-PCE Configurations 6.1. PCC-PCE Configurations
The PCE policy architecture supports policy being applied at a PCC The PCE policy architecture supports policy being applied at a PCC
and at a PCE. While the architecture supports policy being applied at and at a PCE. While the architecture supports policy being applied
both, there is no requirement for policy to always be applied at at both, there is no requirement for policy to always be applied at
both, or even at either. The use of policy in a network, on PCCs and both, or even at either. The use of policy in a network, on PCCs,
on PCEs, is a specific network design choice. Some networks may and on PCEs, is a specific network design choice. Some networks may
choose to apply policy only at PCCs (Figure 7), some at PCEs (Figure choose to apply policy only at PCCs (Figure 7), some at PCEs (Figure
8), and others at both PCCs and PCEs (Figure 9). Regardless of where 8), and others at both PCCs and PCEs (Figure 9). Regardless of where
policy is applied it must be applied in a consistent fashion in order policy is applied, it must be applied in a consistent fashion in
to achieve the intended results. order to achieve the intended results.
......................... .........................
. . . .
. PCE Policy Management . . PCE Policy Management .
. . . .
......................... .........................
. .
. .
--------- Policy ----------------------- --------- Policy -----------------------
| PCC-PDP |<--------- | PCE Policy Repository | | PCC-PDP |<--------- | PCE Policy Repository |
--------- ----------------------- --------- -----------------------
^ ^
| e.g., SOAP | e.g., SOAP
v v
--------- PCEP --------- --------- PCEP ---------
| PCC-PEP |<------------------------------------------->| PCE | | PCC-PEP |<------------------------------------------->| PCE |
--------- PCC-PCE Communication Protocol --------- --------- PCC-PCE Communication Protocol ---------
Figure 7: Policies Applied On PCC Only Figure 7: Policies Applied on PCC Only
Along with supporting flexibility in where policy may be applied, the Along with supporting flexibility in where policy may be applied, the
PCE architecture is also flexible in terms of where specific types of PCE architecture is also flexible in terms of where specific types of
policies may be applied. Also the PCE architecture allows for the policies may be applied. Also, the PCE architecture allows for the
application of only a subset of policy types. [RFC4655] defines application of only a subset of policy types. [RFC4655] defines
several PC policy types. Each of these may be applied at either a PCC several PC policy types. Each of these may be applied at either a
or a PCE or both. Clearly when policy is only applied at PCCs or at PCC or a PCE or both. Clearly, when policy is only applied at PCCs
PCEs, all PCE policy types used in the network must be applied at or at PCEs, all PCE policy types used in the network must be applied
those locations. at those locations.
......................... .........................
. . . .
. PCE Policy Management . . PCE Policy Management .
. . . .
......................... .........................
. .
. .
----------------------- Policy --------- ----------------------- Policy ---------
| PCE Policy Repository | -------->| PCE-PDP | | PCE Policy Repository | -------->| PCE-PDP |
----------------------- --------- ----------------------- ---------
^ ^
e.g., SOAP | e.g., SOAP |
v v
--------- PCEP --------- --------- PCEP ---------
| PCC |<------------------------------------------->| PCE-PEP | | PCC |<------------------------------------------->| PCE-PEP |
--------- PCC-PCE Communication Protocol --------- --------- PCC-PCE Communication Protocol ---------
Figure 8: Policies Applied On Only Figure 8: Policies Applied on Only
In the case where policy is only applied at a PCE, it is expected In the case where policy is only applied at a PCE, it is expected
that the PCC will pass to the PCE all information about the service that the PCC will pass to the PCE all information about the service
that it can gather in the path computation request (most likely in that it can gather in the path computation request (most likely in
the form of PCPIM policy variables). The PCE is expected to the form of PCPIM policy variables). The PCE is expected to
understand this information and apply appropriate policies while understand this information and apply appropriate policies while
defining the actual parameters of the path computation to be defining the actual parameters of the path computation to be
performed. Note that in this scenario the PCC cannot apply server- performed. Note that in this scenario, the PCC cannot apply server-
specific or any other policies, and PCE selection is static. specific or any other policies, and PCE selection is static.
When applying policy at both PCC and PCE, it is necessary to select When applying policy at both the PCC and PCE, it is necessary to
which types of policies are applied at each. In such configurations, select which types of policies are applied at each. In such
it is likely that the application of policy types will be distributed configurations, it is likely that the application of policy types
across PCC and PCE rather than applying all of them at both. For will be distributed across the PCC and PCE rather than applying all
example, user-specific and server-specific policies may be applied at of them at both. For example, user-specific and server-specific
a PCC, request and client specific policies may be applied at a PCE, policies may be applied at a PCC, request- and client-specific
while domain-specific policies may be applied at both the PCC and policies may be applied at a PCE, while domain-specific policies may
PCE. be applied at both the PCC and PCE.
In the case when policy is only applied at a PCC, the PCC must apply In the case when policy is only applied at a PCC, the PCC must apply
all the types of required policies, for example user, service, server all the types of required policies, for example user-, service-,
and domain-specific policies. The PCC uses the policies to construct server-, and domain-specific policies. The PCC uses the policies to
a path computation request that appropriately represents the applied construct a path computation request that appropriately represents
policies. The request will necessarily be limited to the set of the applied policies. The request will necessarily be limited to the
"basic" (that is, non-policy capable) constraints explicitly defined set of "basic" (that is, non-policy capable) constraints explicitly
by the PCC-PCE communication protocol. defined by the PCC-PCE communication protocol.
6.2. Policy Repositories 6.2. Policy Repositories
Within the policy-enabled path computation framework policy Within the policy-enabled path computation framework policy
repositories may be used in a single or multiple PCE policy repositories may be used in a single or multiple PCE policy
repository configuration: repository configuration:
o) Single PCE Policy Repository o) Single PCE Policy Repository
In this configuration there is a single PCE Policy Repository shared In this configuration, there is a single PCE Policy Repository shared
between PCCs and PCEs. between PCCs and PCEs.
......................... .........................
. . . .
. PCE Policy Management . . PCE Policy Management .
. . . .
......................... .........................
. .
. .
--------- Policy a ----------------------- Policy b --------- --------- Policy a ----------------------- Policy b ---------
skipping to change at page 25, line 13 skipping to change at page 25, line 33
Figure 10: Multiple PCE/PCC Policy Repositories Figure 10: Multiple PCE/PCC Policy Repositories
6.3. Cooperating PCE Configurations 6.3. Cooperating PCE Configurations
The previous section shows the relationship between PCCs and PCEs. A The previous section shows the relationship between PCCs and PCEs. A
parallel relationship exists between cooperating PCEs, and, in fact, parallel relationship exists between cooperating PCEs, and, in fact,
this relationship can be viewed as the same as the relationship this relationship can be viewed as the same as the relationship
between PCCs and PCEs. The one notable difference is that there will between PCCs and PCEs. The one notable difference is that there will
be cases where having a shared PCE Policy Repository will not be be cases where having a shared PCE Policy Repository will not be
desirable, for example, when the PCEs are managed by different desirable, for example, when the PCEs are managed by different
entities. Note that in this case it still remains necessary for the entities. Note that in this case, it still remains necessary for the
policies to be consistent across the domains in order to identify policies to be consistent across the domains in order to identify
usable paths. The other notable difference is that a PCE, while usable paths. The other notable difference is that a PCE, while
processing a path computation request, may need to apply requester- processing a path computation request, may need to apply requester-
specific (that is, client-specific) policies in order to modify the specific (that is, client-specific) policies in order to modify the
request before sending it to other cooperating PCE(s). This request before sending it to other cooperating PCE(s). This
relationship is particularly important as the PCE Architecture allows relationship is particularly important as the PCE architecture allows
for configuration where all PCCs are not policy-enabled. for configuration where all PCCs are not policy-enabled.
The following are example configurations. These examples do not The following are example configurations. These examples do not
represent an exhaustive list and other configurations are expected. represent an exhaustive list and other configurations are expected.
o) Single Policy Repository o) Single Policy Repository
In this configuration there is a single PCE Policy repository shared In this configuration, there is a single PCE Policy Repository shared
between PCEs. This configuration is likely to be useful within a between PCEs. This configuration is likely to be useful within a
single administrative domain where multiple PCEs are provided for single administrative domain where multiple PCEs are provided for
redundancy or load distribution purposes. redundancy or load distribution purposes.
......................... .........................
. . . .
. PCE Policy Management . . PCE Policy Management .
. . . .
......................... .........................
. .
skipping to change at page 26, line 4 skipping to change at page 26, line 25
^ ^ ^ ^
| e.g., SOAP e.g., SOAP | | e.g., SOAP e.g., SOAP |
v v v v
--------- --------- --------- ---------
| PCE-PEP |<------------------------------------------->| PCE-PEP | | PCE-PEP |<------------------------------------------->| PCE-PEP |
--------- PCE-PCE Communication Protocol --------- --------- PCE-PCE Communication Protocol ---------
Figure 11: Single PCC Policy Repository Figure 11: Single PCC Policy Repository
o) Multiple Policy Repositories o) Multiple Policy Repositories
The repositories in this case may be fully or partially synchronized The repositories in this case may be fully or partially synchronized
by some discovery/synchronization management protocol(s) or may be by some discovery/synchronization management protocol(s) or may be
completely independent. In the multi-domain case it is expected that completely independent. In the multi-domain case, it is expected
the repositories will be distinct, providing, however. consistent that the repositories will be distinct, providing, however,
policies. consistent policies.
-------------- -------------- -------------- --------------
| PCE Policy | | PCE Policy | | PCE Policy | | PCE Policy |
---| Repository A | | Repository B |--- ---| Repository A | | Repository B |---
| -------------- -------------- | | -------------- -------------- |
| | | |
| Policy a Policy b | | Policy a Policy b |
| | | |
v v v v
--------- --------- --------- ---------
skipping to change at page 26, line 34 skipping to change at page 27, line 9
--------- PCEP --------- --------- PCEP ---------
| PCE-PEP |<------------------------------------------->| PCE-PEP | | PCE-PEP |<------------------------------------------->| PCE-PEP |
--------- PCC-PCE Communication Protocol --------- --------- PCC-PCE Communication Protocol ---------
Figure 12: Multiple PCC Policy Repositories Figure 12: Multiple PCC Policy Repositories
6.4. Policy Configuration Management 6.4. Policy Configuration Management
The management of path computation policy information used by PCCs The management of path computation policy information used by PCCs
and PCEs is largely out of scope of the described framework. The and PCEs is largely out of scope of the described framework. The
framework assumes that such information is installed, removed and framework assumes that such information is installed, removed, and
otherwise managed using typical policy management techniques. Policy otherwise managed using typical policy management techniques. Policy
Repositories may be populated and managed via static configuration, Repositories may be populated and managed via static configuration,
standard and proprietary policy management tools, or even dynamically standard and proprietary policy management tools, or even dynamically
via policy management/discovery protocols and applications. via policy management/discovery protocols and applications.
7. Inter-Component Communication 7. Inter-Component Communication
7.1. Policy Communication 7.1. Policy Communication
Flexibility in the application of policy types is imperative from the Flexibility in the application of policy types is imperative from the
architecture perspective. However, this commodity implies added architecture perspective. However, this commodity implies added
complexity on the part of the PCE related communication protocols. complexity on the part of the PCE-related communication protocols.
One added complexity is that PCE communication protocols must carry One added complexity is that PCE communication protocols must carry
certain information to support various policy types that may be certain information to support various policy types that may be
applied. For example, in the case where policy is only applied at a applied. For example, in the case where policy is only applied at a
PCE, a PCC-PCE request must carry sufficient information for the PCE PCE, a PCC-PCE request must carry sufficient information for the PCE
to apply service or user-specific policies. This does imply that a to apply service- or user-specific policies. This does imply that a
PCC must have sufficient understanding of what policies can be PCC must have sufficient understanding of what policies can be
applied at the PCE. Such information may be obtained via local applied at the PCE. Such information may be obtained via local
configuration, static coding or even via a PCE discovery mechanism. configuration, static coding, or even via a PCE discovery mechanism.
The PCC must also have sufficient understanding to properly encode The PCC must also have sufficient understanding to properly encode
the required information for each policy type. the required information for each policy type.
Another added complexity is that PCE communication protocols must Another added complexity is that PCE communication protocols must
also be able to carry information that may result from a policy also be able to carry information that may result from a policy
decision. For example, user or service-specific policy applied at a decision. For example, user- or service-specific policy applied at a
PCC may result in policy related information that must be carried PCC may result in policy-related information that must be carried
along with the request for use by a PCE. This complexity is along with the request for use by a PCE. This complexity is
particularly important as it may be used to introduce new path particularly important as it may be used to introduce new path
computation parameters (e.g., constraints, objection functions, etc.) computation parameters (e.g., constraints, objection functions, etc.)
without modification of the core PCC and PCE. This communication will without modification of the core PCC and PCE. This communication
likely simply require the PCE communication protocols to support will likely simply require the PCE communication protocols to support
opaque policy related information elements. opaque policy-related information elements.
A final added complexity is that PCE communication protocols must A final added complexity is that PCE communication protocols must
also be able to support updated or unsolicited responses from a PCE. also be able to support updated or unsolicited responses from a PCE.
For example, changes in PCE policy may force a change to a previously For example, changes in PCE policy may force a change to a previously
provided path. Such updated or unsolicited responses may contain provided path. Such updated or unsolicited responses may contain
information that the PCC must act on, and may contain policy information that the PCC must act on, and may contain policy
information that must be provided to a PCC. information that must be provided to a PCC.
PCC-PEP and PCE-PEP or a pair of PCE-PEPs communicate via a request- PCC-PEP and PCE-PEP or a pair of PCE-PEPs communicate via a request-
response type PCC-PCE Communication Protocol, i.e., [PCEP]. This response type PCC-PCE Communication Protocol, i.e., [PCEP]. This
skipping to change at page 27, line 40 skipping to change at page 28, line 14
PCC-PEP and PCE-PEP or a pair of PCE-PEPs communicate via a request- PCC-PEP and PCE-PEP or a pair of PCE-PEPs communicate via a request-
response type PCC-PCE Communication Protocol, i.e., [PCEP]. This response type PCC-PCE Communication Protocol, i.e., [PCEP]. This
document makes no assumptions as to what exact protocol is used to document makes no assumptions as to what exact protocol is used to
support this communication. This document does assume that the support this communication. This document does assume that the
semantics of a path computation request are sufficiently abstract and semantics of a path computation request are sufficiently abstract and
general, and support both PCE-PCC and PCE-PCE communication. general, and support both PCE-PCC and PCE-PCE communication.
From a policy perspective, a path computation request should include From a policy perspective, a path computation request should include
at a minimum: at a minimum:
o One or more source addresses; o One or more source addresses;
o One or more destination addresses; o One or more destination addresses;
o Computation type (P2P, P2MP, MP2P, etc.); o Computation type (P2P (point to point), P2MP (point to multipoint),
MP2P (multipoint to point), etc.);
o Number of required paths; o Number of required paths;
o Zero or more policy descriptors in the following format: o Zero or more policy descriptors in the following format:
<policy name>, <policy name>,
<policy variable1 name>, <param11>, <param12>,...,<param1N> <policy variable1 name>, <param11>, <param12>,...,<param1N>
<policy variable2 name>, <param21>, <param12>,...,<param2N> <policy variable2 name>, <param21>, <param12>,...,<param2N>
... ...
<policy variableM name>, <paramM1>, <paramM2>,...,<paramMN> <policy variableM name>, <paramM1>, <paramM2>,...,<paramMN>
A successful path computation response, at minimum, should include A successful path computation response, at minimum, should include
the list of computed paths and may include policies (in the form of the list of computed paths and may include policies (in the form of
skipping to change at page 28, line 17 skipping to change at page 28, line 41
PCC-PCE Communication Protocol provides transport for policy PCC-PCE Communication Protocol provides transport for policy
information and should not understand nor make any assumptions about information and should not understand nor make any assumptions about
the semantics of policies specified in path computation requests and the semantics of policies specified in path computation requests and
responses. responses.
Note: This document explicitly allows for (but does not require) the Note: This document explicitly allows for (but does not require) the
PCC to decide that all necessary constraints, objective functions, PCC to decide that all necessary constraints, objective functions,
etc. pertinent to the computation of paths for the service in etc. pertinent to the computation of paths for the service in
question are to be determined by the PCE performing the computation. question are to be determined by the PCE performing the computation.
In this case the PCC will use a set of policies (more precisely, In this case, the PCC will use a set of policies (more precisely,
PCPIM policy variables) describing the service-specific information. PCPIM policy variables) describing the service-specific information.
These policies may be placed within the path computation request and These policies may be placed within the path computation request and
delivered to the PCE via a PCC-PCE communication protocol such as delivered to the PCE via a PCC-PCE communication protocol such as
[PCEP]. The PCE (more precisely, PCE-PEP) is expected to understand [PCEP]. The PCE (more precisely, PCE-PEP) is expected to understand
this information and use it to determine the constraints and this information and use it to determine the constraints and
optimization functions applying local policies (that is, policies optimization functions applying local policies (that is, policies
locally configured or provided by the associated PCE-PDP(s)). locally configured or provided by the associated PCE-PDP(s)).
7.2. PCE Discovery Policy Considerations 7.2. PCE Discovery Policy Considerations
Dynamic PCE discovery allows for PCCs and PCEs to automatically Dynamic PCE discovery allows for PCCs and PCEs to automatically
discover a set of PCEs (including information required for the PCE discover a set of PCEs (including information required for the PCE
selection). It also allows for PCCs and PCEs to dynamically detect selection). It also allows for PCCs and PCEs to dynamically detect
new PCEs or any modification of PCEs status. Policy can be applied in new PCEs or any modification of PCEs status. Policy can be applied
two ways in this context: in two ways in this context:
1. Restricting the scope of information distribution for the 1. Restricting the scope of information distribution for the
mandatory set of information (in particular the PCE presence mandatory set of information (in particular the PCE presence and
and location). location).
2. Restricting the type and nature of the optional information 2. Restricting the type and nature of the optional information
distributed by the discovery protocol. The latter is also distributed by the discovery protocol. The latter is also subject
subject to policy since the PCE architecture allows for to policy since the PCE architecture allows for distributing this
distributing this information using either PCE discovery information using either PCE discovery protocol(s) or PCC-PCE
protocol(s) or PCC-PCE communication protocol(s). One important communication protocol(s). One important policy decision in this
policy decision in this context is the nature of the information context is the nature of the information to be distributed,
to be distributed, especially, when this information is not especially, when this information is not strictly speaking
strictly speaking a "discovery" information, rather, the PCE "discovery" information, rather, the PCE state changes. Client-
state changes. Client-specific and domain-specific policies may specific and domain-specific policies may be applied when deciding
be applied when deciding whether this information should be whether this information should be distributed and to which
distributed and to which clients of the path computation service clients of the path computation service (that is, which PCCs
(that is, which PCCs and/or PCEs) and/or PCEs).
Another place where policy applies is at the administrative Another place where policy applies is at the administrative
boundaries. In multi-domain networks multiple PCEs will communicate boundaries. In multi-domain networks, multiple PCEs will communicate
with each other and across administrative boundaries. In such cases, with each other and across administrative boundaries. In such cases,
domain-specific polices would be applied to 1) filter the information domain-specific policies would be applied to 1) filter the
exchanged between peering PCEs during the discovery process (to the information exchanged between peering PCEs during the discovery
bare minimum in most cases if at all allowed by the security policy) process (to the bare minimum in most cases if at all allowed by the
and 2) limit the content of information being passed in path security policy) and 2) limit the content of information being passed
computation request and responses. in path computation request and responses.
8. Path Computation Sequence of Events 8. Path Computation Sequence of Events
This section presents a non-exhaustive list of representative This section presents a non-exhaustive list of representative
scenarios. scenarios.
8.1. Policy-enabled PCC, Policy-enabled PCE 8.1. Policy-Enabled PCC, Policy-Enabled PCE
When a GMPLS LSR receives a Setup (RSVP Path) message from an When a GMPLS LSR receives a Setup (RSVP Path) message from an
upstream LSR, the LSR may decide to use a remote Path Computation upstream LSR, the LSR may decide to use a remote Path Computation
Entity. The following sequence of events occurs in this case: Entity. The following sequence of events occurs in this case:
- A PCC-PEP co-located with the LSR applies the service-specific - A PCC-PEP co-located with the LSR applies the service-specific
policies to select a PCE for the service path computation as policies to select a PCE for the service path computation as well
well as to build the path computation request (that is, to as to build the path computation request (that is, to select a list
select a list of policies, their variables, conditions and of policies, their variables, conditions and actions expressing
actions expressing constraints, diversities, objective functions constraints, diversities, objective functions and relaxation
and relaxation strategies appropriate for the service path strategies appropriate for the service path computation). The
computation). The policies may be: policies may be:
a) Statically configured on the PCC-PEP; a) Statically configured on the PCC-PEP;
b) Communicated to the PCC-PEP by a remote or local PCC-PDP b) Communicated to the PCC-PEP by a remote or local PCC-PDP via
via protocol such as SOAP either pro-actively (most of the protocol such as SOAP either proactively (most of the cases) or
cases) or upon an explicit request by the PCC-PEP in case when upon an explicit request by the PCC-PEP in cases when some
some specifics of the new service have not been covered yet by specifics of the new service have not been covered yet by the
the policies so far known to the PCC-PEP) policies so far known to the PCC-PEP).
The input for the decision process on the PCC-PEP is the The input for the decision process on the PCC-PEP is the
information found in the signaling message as well as any other information found in the signaling message as well as any other
service-specific information such as port ID over which the message service-specific information such as port ID over which the message
was received, associated VPN ID, the reference point type (UNI, E- was received, associated VPN ID, the reference point type (UNI,
NNI, etc.) and so forth. After the path computation request is E-NNI, etc.) and so forth. After the path computation request is
built it is sent directly to the PCE-PEP using the PCC-PCE built, it is sent directly to the PCE-PEP using the PCC-PCE
Communication Protocol, e.g., [PCEP]. Communication Protocol, e.g., [PCEP].
- PCE-PEP validates and otherwise processes the request applying - PCE-PEP validates and otherwise processes the request applying the
the policies found in the request as well as client and domain policies found in the request- as well as client- and domain-
specific polices. The latter, again, may be either statically specific policies. The latter, again, may be either statically
configured on the PCE-PEP or provided by the associated local or configured on the PCE-PEP or provided by the associated local or
remote PCE-PDP via a protocol such as SOAP. The outcome of the remote PCE-PDP via a protocol such as SOAP. The outcome of the
decision process is the following information: decision process is the following information:
a) Whether the request should be satisfied, rejected or a) Whether the request should be satisfied, rejected, or dismissed.
dismissed.
b) The sets of sources and destinations for which paths should b) The sets of sources and destinations for which paths should be
be locally computed. locally computed.
c) The set of constraints, diversities, optimization functions c) The set of constraints, diversities, optimization functions, and
and relaxations to be considered in each of locally performed relaxations to be considered in each of locally performed path
path computation. computation.
d) The address of the next-in-chain PCE. d) The address of the next-in-chain PCE.
e) The path computation request to be sent to the e) The path computation request to be sent to the next-in-chain
next-in-chain PCE. PCE.
The PCE-PEP instructs a co-located path computation engine to The PCE-PEP instructs a co-located path computation engine to
perform the local path computation(s) and, if necessary, sends the perform the local path computation(s) and, if necessary, sends the
path computation request to the next-in-chain PCE using a PCC-PCE path computation request to the next-in-chain PCE using a PCC-PCE
Communication Protocol. Then it waits for the responses from the Communication Protocol. Then, it waits for the responses from the
local path computation engine and the remote PCE, combines the local path computation engine and the remote PCE, combines the
resulting paths and sends them back to the PCC-PEP using the PCC- resulting paths, and sends them back to the PCC-PEP using the PCC-
PCE Communication Protocol. The response contains the resulting PCE Communication Protocol. The response contains the resulting
paths as well as policies describing some additional information paths as well as policies describing some additional information
(for example, which of constraints were honored, which were (for example, which of constraints were honored, which were
dismissed and which were relaxed and in what way) dismissed, and which were relaxed and in what way).
- PCC-PEP instructs the signaling sub-system of the GMPLS LSR to - PCC-PEP instructs the signaling subsystem of the GMPLS LSR to
encode the received path(s) into the outgoing Setup message(s). encode the received path(s) into the outgoing Setup message(s).
8.2. Policy-ignorant PCC, Policy-enabled PCE 8.2. Policy-Ignorant PCC, Policy-Enabled PCE
This case parallels the previous example, but the user and service- This case parallels the previous example, but the user- and service-
specific policies should be applied at the PCE as the PCC is policy specific policies should be applied at the PCE as the PCC is policy
ignorant. Again, when a GMPLS LSR has received a Setup (RSVP Path) ignorant. Again, when a GMPLS LSR has received a Setup (RSVP Path)
message from an upstream LSR, the LSR may decide to use a non co- message from an upstream LSR, the LSR may decide to use a non-co-
located Path Computation Entity. The following sequence of events located Path Computation Entity. The following sequence of events
occurs in this case: occurs in this case:
- The PCC constructs a PCE request using information found in the - The PCC constructs a PCE request using information found in the
signaling/provisioning message as well as any other service signaling/provisioning message as well as any other service-
specific information such as port ID over which the message was specific information such as port ID over which the message was
received, associated VPN ID, the reference point type (UNI, E- received, associated VPN ID, the reference point type (UNI, E-NNI,
NNI, etc.) and so forth. This information is encoded in the etc.) and so forth. This information is encoded in the request in
request in the form of policy variables. After the request is the form of policy variables. After the request is built, it is
built it is sent directly to the PCE-PEP using a PCC-PCE sent directly to the PCE-PEP using a PCC-PCE Communication
Communication Protocol. Protocol.
- PCE-PEP validates and otherwise processes the request - PCE-PEP validates and otherwise processes the request interpreting
interpreting the policy variables found in the request and the policy variables found in the request and applying user-,
applying user, service- and also client- and domain- specific service-, client-, and domain-specific policies to build the actual
polices to build the actual path computation request. The path computation request. The policies, again, may be either
policies, again, may be either statically configured on the statically configured on the PCE-PEP or provided by the associated
PCE-PEP or provided by the associated local or remote PCE-PDP via local or remote PCE-PDP via a protocol such as SOAP. The outcome
a protocol such as SOAP. The outcome of the decision process is of the decision process is the following information:
the following information:
a) Whether the request should be satisfied, rejected or a) Whether the request should be satisfied, rejected, or dismissed.
dismissed.
b) The sets of sources and destinations for which paths should b) The sets of sources and destinations for which paths should be
be locally computed. locally computed.
c) The set of constraints, diversities, optimization functions c) The set of constraints, diversities, optimization functions, and
and relaxations to be considered in each of locally performed relaxations to be considered in each of locally performed path
path computation. computation.
d) The address of the next-in-chain PCE. d) The address of the next-in-chain PCE.
e) The path computation request to be sent to the next-in- e) The path computation request to be sent to the next-in-chain
chain PCE. PCE.
The PCE-PEP instructs a co-located path computation engine to The PCE-PEP instructs a co-located path computation engine to
perform the local path computation(s) and, if necessary, sends the perform the local path computation(s) and, if necessary, sends the
path computation request to the next-in-chain PCE using the PCC-PCE path computation request to the next-in-chain PCE using the PCC-PCE
Communication Protocol. Then it waits for the responses from the Communication Protocol. Then, it waits for the responses from the
local path computation engine and the remote PCE, combines the local path computation engine and the remote PCE, combines the
resulting paths and sends them back to the PCC-PEP using the PCC- resulting paths, and sends them back to the PCC-PEP using the PCC-
PCE Communication Protocol. The response contains the resulting PCE Communication Protocol. The response contains the resulting
paths as well as policies describing some additional information paths as well as policies describing some additional information
(for example, which of constraints were honored, which were (for example, which of constraints were honored, which were
dismissed and which were relaxed and in what way) dismissed, and which were relaxed and in what way)
- PCC-PEP instructs the signaling sub-system of the GMPLS LSR to - PCC-PEP instructs the signaling sub-system of the GMPLS LSR to
encode the received path(s) into the outgoing Setup message(s). encode the received path(s) into the outgoing Setup message(s).
9. Introduction of New Constraints 9. Introduction of New Constraints
An important aspect of the policy-enable path computation framework An important aspect of the policy-enabled path computation framework
discussed above is the ability to introduce new constraints with discussed above is the ability to introduce new constraints with
minimal impact. In particular, only those components and mechanisms minimal impact. In particular, only those components and mechanisms
that will use a new constraint need to be updated in order to support that will use a new constraint need to be updated in order to support
the new constraint. Importantly, those components and mechanisms that the new constraint. Importantly, those components and mechanisms
will not use the new constraint, must not require any change in order that will not use the new constraint must not require any change in
for the new constraint to be utilized. For example, the PCE order for the new constraint to be utilized. For example, the PCE
communication protocols must not require any changes to support new communication protocols must not require any changes to support new
constraints. Likewise, PCC and PCEs that will not process new constraints. Likewise, PCC and PCEs that will not process new
constraints must not require any modification. constraints must not require any modification.
Consider the case where a PCE has been upgraded with software Consider the case where a PCE has been upgraded with software
supporting optical physical impairment constraint, such as supporting optical physical impairment constraint, such as
Polarization Mode Dispersion (PMD), that previously was not supported Polarization Mode Dispersion (PMD), that previously was not supported
in the domain. In this case, one or more new policies will be in the domain. In this case, one or more new policies will be
installed in the PCE Policy Repository (associated with the PCE) installed in the PCE Policy Repository (associated with the PCE)
defining the constraint (rules that determine application criteria, defining the constraint (rules that determine application criteria,
set of policy variables, conditions, actions, etc.) and its set of policy variables, conditions, actions, etc.) and its
relaxation strategy(ies). The new policies will be also propagated relaxation strategy (or strategies). The new policies will be also
into other PCE Policy Repositories within the domain via discovery propagated into other PCE Policy Repositories within the domain via
and synchronization protocols or via local configuration. PCE-PDPs discovery and synchronization protocols or via local configuration.
and PCC-PDPs will then retrieve the corresponding policies from the PCE-PDPs and PCC-PDPs will then retrieve the corresponding policies
repository(ies). From then on PCC-PDPs will instruct associated PCC- from the repository (or repositories). From then on, PCC-PDPs will
PEPs to add the new policy information into path computation requests instruct associated PCC-PEPs to add the new policy information into
for services with certain parameters (for example, for services path computation requests for services with certain parameters (for
provisioned in the OCh layer). example, for services provisioned in the optical channel (OCh)
layer).
It is important to note that policy-enabled path computation model It is important to note that policy-enabled path computation model
naturally solves the PCE capability discovery issues. Suppose a PCE naturally solves the PCE capability discovery issues. Suppose a PCE
working in a single PCE Policy Repository configuration starts to working in a single PCE Policy Repository configuration starts to
support a new constraint. Once a corresponding policy installed in support a new constraint. Once a corresponding policy installed in
the repository, it automatically becomes available for all repository the repository, it automatically becomes available for all repository
users, that is, PCCs. In the multi-repository case some policy users, that is, PCCs. In the multi-repository case some policy
synchronization must be provided, however, this problem is one of the synchronization must be provided; however, this problem is one of the
management plane which is solved already. management plane which is solved already.
10. Security Considerations 10. Security Considerations
This document adds to the policy security considerations mentioned in This document adds to the policy security considerations mentioned in
[RFC4655]. In particular it is now necessary to consider the security [RFC4655]. In particular, it is now necessary to consider the
issues related to policy information maintained in PCE Policy security issues related to policy information maintained in PCE
Repositories and policy related transactions. The most notable Policy Repositories and policy-related transactions. The most
issues, some of which are also listed in [RFC4655], are: notable issues, some of which are also listed in [RFC4655], are:
- Unauthorized access to the PCE Policy Repositories; - Unauthorized access to the PCE Policy Repositories;
- Interception of policy information when it is retrieved from
the repositories and/or transported from PDPs to PEPs;
- Interception of policy related information in path computation - Interception of policy information when it is retrieved from the
repositories and/or transported from PDPs to PEPs;
- Interception of policy-related information in path computation
requests and responses; requests and responses;
o Impersonation of user and client identities; o Impersonation of user and client identities;
o Falsification of policy information and/or PCE capabilities; o Falsification of policy information and/or PCE capabilities;
o Denial of service attacks on policy related communication o Denial-of-service attacks on policy-related communication
mechanisms. mechanisms.
As with [RFC4655], it is expected that PCE solutions will address the As with [RFC4655], it is expected that PCE solutions will address the
PCE aspects of these issues in detail. PCE aspects of these issues in detail.
11. Acknowledgments 11. Acknowledgments
Adrian Farrel contributed significantly to this document. We would Adrian Farrel contributed significantly to this document. We would
like to thank Bela Berde for fruitful discussions on PBM and Policy- like to thank Bela Berde for fruitful discussions on PBM and policy-
driven path computation. We would also like to thank Kobus Van der driven path computation. We would also like to thank Kobus Van der
Merwe for providing insights and examples regarding PCE policy Merwe for providing insights and examples regarding PCE policy
applications. applications.
12. IANA Considerations 12. References
None.
13. References
13.1. Normative References 12.1. Normative References
[RFC2753] R. Yavatkar, D. Pendarakis, R. Guerin, A Framework for [RFC2753] Yavatkar, R., Pendarakis, D., and R. Guerin, "A Framework
Policy Based Admission Control, RFC 2753, January 2000. for Policy-based Admission Control", RFC 2753, January
2000.
[RFC3060] B. Moore, et al., Policy Core Information Model -- [RFC3060] Moore, B., Ellesson, E., Strassner, J., and A. Westerinen,
Version 1 Specification, RFC 3060, February 2001. "Policy Core Information Model -- Version 1
Specification", RFC 3060, February 2001.
[RFC3209] Awduche, D., et al., "Extensions to RSVP for LSP [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001. Tunnels", RFC 3209, December 2001.
[RFC3460] Moore, B. Ed., "Policy Core Information Model (PCIM) [RFC3460] Moore, B., Ed., "Policy Core Information Model (PCIM)
Extensions", RFC 3460, January 2003. Extensions", RFC 3460, January 2003.
[RFC3473] Berger, L., et al., "Generalized Multi-Protocol Label [RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Switching (GMPLS) Signaling Resource ReserVation
Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC
3473, January 2003. 3473, January 2003.
[RFC3644] Y. Snir, et al., Policy Quality of Service (QoS) [RFC3644] Snir, Y., Ramberg, Y., Strassner, J., Cohen, R., and B.
Information Model, RFC 3644, November 2003. Moore, "Policy Quality of Service (QoS) Information
Model", RFC 3644, November 2003.
[RFC4216] Zhang, R., Vasseur, J-P., Eds., "MPLS Inter-Autonomous [RFC4216] Zhang, R., Ed., and J.-P. Vasseur, Ed., "MPLS Inter-
System (AS) Traffic Engineering (TE) Requirements", Autonomous System (AS) Traffic Engineering (TE)
RFC4216, November 2005. Requirements", RFC 4216, November 2005.
[RFC4655] Farrel, A., Vasseur, JP., Ash, J., "Path Computation [RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Element (PCE) Architecture", RFC 4655, August 2006. Computation Element (PCE)-Based Architecture", RFC 4655,
August 2006.
[RFC4927] Le Roux, J-L., Ed., "PCE Communication Protocol [RFC4927] Le Roux, J.-L., Ed., "Path Computation Element
(PCECP) Specific Requirements for Inter-Area Communication Protocol (PCECP) Specific Requirements for
MPLS and GMPLS Traffic Engineering", June 2007. Inter-Area MPLS and GMPLS Traffic Engineering", RFC 4927,
June 2007.
13.2. Informative References 12.2. Informative References
[DMTF] Common Information Model (CIM) Schema, version 2.x. [DMTF] Common Information Model (CIM) Schema, version 2.x.
Distributed Management Task Force, Inc. The components Distributed Management Task Force, Inc. The components of
of the CIM v2.x schema are available via links on the the CIM v2.x schema are available via links on the
following DMTF web page: following DMTF web page:
http://www.dmtf.org/standards/standard_cim.php. http://www.dmtf.org/standards/standard_cim.php.
[IRSCP] Van der Merwe, J., et al., "Dynamic Connectivity [IRSCP] Van der Merwe, J., et al., "Dynamic Connectivity
Management with an Intelligent Route Service Control Management with an Intelligent Route Service Control
Point," ACM SIGCOMM Workshop on Internet Network Point," ACM SIGCOMM Workshop on Internet Network
Management (INM), Pisa, Italy, September 11, 2006. Management (INM), Pisa, Italy, September 11, 2006.
[PCEP] Vasseur, J., Le Roux, J., Eds., "Path Computation Element [PCEP] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
(PCE) Communication Protocol (PCEP)", Work in Progress, Element (PCE) Communication Protocol (PCEP)", Work in
draft-ietf-pce-pcep-16.txt, October 14, 2008. Progress, November 2008.
[RFC2748] D. Durham, et al., The COPS (Common Open Policy Service) [RFC2748] Durham, D., Ed., Boyle, J., Cohen, R., Herzog, S., Rajan,
protocol, RFC 2748, IETF, January 2000. R., and A. Sastry, "The COPS (Common Open Policy Service)
Protocol", RFC 2748, January 2000.
[RFC3031] Rosen, E,. Viswanathan, V. Callon, R., "Multiprotocol [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001. Label Switching Architecture", RFC 3031, January 2001.
[RFC3080] Rose, M., "The Blocks Extensible Exchange Protocol [RFC3080] Rose, M., "The Blocks Extensible Exchange Protocol Core",
Core", RFC 3080, March 2001. RFC 3080, March 2001.
[RFC3198] Westerinen, A., et al., "Terminology for Policy-Based [RFC3198] Westerinen, A., Schnizlein, J., Strassner, J., Scherling,
M., Quinn, B., Herzog, S., Huynh, A., Carlson, M., Perry,
J., and S. Waldbusser, "Terminology for Policy-Based
Management", RFC 3198, November 2001. Management", RFC 3198, November 2001.
[RFC3630] Katz, D., Kompella, K., Yeung., D., "Traffic Engineering [RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630, September (TE) Extensions to OSPF Version 2", RFC 3630, September
2003. 2003.
[INTERAS-PCEP] Bitar, N., Zhang, R., Kumaki, K., Eds., "Inter-AS [RFC5376] Bitar, N., Zhang, R., and K. Kumaki, "Inter-AS
Requirements for the Path Computation Element Requirements for the Path Computation Element
Communication Protocol (PCECP)", February 2006. Communication Protocol (PCECP)", RFC 5376, November 2008.
[W3CSOAP] Hadley, M., Mendelsohn, N., Moreau, J., Nielsen, H., [W3CSOAP] Hadley, M., Mendelsohn, N., Moreau, J., Nielsen, H., and
and Gudgin, M., "SOAP Version 1.2 Part 1: Messaging Gudgin, M., "SOAP Version 1.2 Part 1: Messaging
Framework", W3C REC REC-soap12-part1-20030624, June Framework", W3C REC REC-soap12-part1-20030624, June 2003.
2003.
14. Authors' Addresses Authors' Addresses
Igor Bryskin Igor Bryskin
ADVA Optical ADVA Optical
7926 Jones Branch Drive 7926 Jones Branch Drive
Suite 615 Suite 615
McLean, VA 22102 McLean, VA 22102
Email: ibryskin@advaoptical.com EMail: ibryskin@advaoptical.com
Dimitri Papadimitriou (Alcatel) Dimitri Papadimitriou
Alcatel
Fr. Wellesplein 1, Fr. Wellesplein 1,
B-2018 Antwerpen, Belgium B-2018 Antwerpen, Belgium
Phone: +32 3 240-8491 Phone: +32 3 240-8491
Email: dimitri.papadimitriou@alcatel.be EMail: dimitri.papadimitriou@alcatel.be
Lou Berger Lou Berger
LabN Consulting, LLC LabN Consulting, LLC
Phone: +1 301 468 9228 Phone: +1 301 468 9228
Email: lberger@labn.net EMail: lberger@labn.net
Jerry Ash Jerry Ash
AT&T AT&T
Email: gash5107@yahoo.com EMail: gash5107@yahoo.com
15. Full Copyright Statement
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contained in BCP 78, and except as set forth therein, the authors
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