PCE Working Group Q. Wu
Internet-Draft D. Dhody
Intended status: Standards Track Huawei
Expires: April 18, 2014 S. Previdi
Cisco Systems, Inc
October 15, 2013
Extensions to Path Computation Element Communication Protocol (PCEP) for
handling Link Bandwidth Utilization
draft-wu-pce-pcep-link-bw-utilization-00
Abstract
The Path Computation Element Communication Protocol (PCEP) provides
mechanisms for Path Computation Elements (PCEs) to perform path
computations in response to Path Computation Clients (PCCs) requests.
Link bandwidth utilization considering the total bandwidth of a link
in current use for the forwarding is an important factor to consider
during path computation. This document describes extensions to PCEP
to consider them as new constraints during path computation.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on April 18, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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publication of this document. Please review these documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Link Bandwidth Utilization (LBU) . . . . . . . . . . . . . . . 4
4. Link Reserved Bandwidth Utilization (LRBU) . . . . . . . . . . 4
5. PCEP Requirements . . . . . . . . . . . . . . . . . . . . . . 4
6. PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . . 5
6.1. BU Object . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1.1. Elements of Procedure . . . . . . . . . . . . . . . . 6
6.2. New Objective Functions . . . . . . . . . . . . . . . . . 6
6.3. PCEP Message . . . . . . . . . . . . . . . . . . . . . . . 7
7. Other Considerations . . . . . . . . . . . . . . . . . . . . . 9
7.1. Reoptimization Consideration . . . . . . . . . . . . . . . 9
7.2. Inter-domain Consideration . . . . . . . . . . . . . . . . 9
7.3. P2MP Consideration . . . . . . . . . . . . . . . . . . . . 9
7.4. Stateful PCE . . . . . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. Security Considerations . . . . . . . . . . . . . . . . . . . 10
10. Security Considerations . . . . . . . . . . . . . . . . . . . 10
11. Manageability Considerations . . . . . . . . . . . . . . . . . 10
11.1. Control of Function and Policy . . . . . . . . . . . . . . 10
11.2. Information and Data Models . . . . . . . . . . . . . . . 10
11.3. Liveness Detection and Monitoring . . . . . . . . . . . . 10
11.4. Verify Correct Operations . . . . . . . . . . . . . . . . 10
11.5. Requirements On Other Protocols . . . . . . . . . . . . . 10
11.6. Impact On Network Operations . . . . . . . . . . . . . . . 11
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
13.1. Normative References . . . . . . . . . . . . . . . . . . . 11
13.2. Informative References . . . . . . . . . . . . . . . . . . 11
Appendix A. Contributor Addresses . . . . . . . . . . . . . . . . 12
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1. Introduction
Real time link bandwidth utilization is becoming critical in the path
computation in some networks. It is important that link bandwidth
utilization is factored in during path computation. PCC can request
a PCE to provide a path such that it selects under-utilized links.
This document extends PCEP [RFC5440] for this purpose.
Traffic Engineering Database (TED) as populated by Interior Gateway
Protocol (IGP) contains Maximum bandwidth, Maximum reservable
bandwidth and Unreserved bandwidth ([RFC3630] and [RFC3784]).
[OSPF-TE-EXPRESS] and [ISIS-TE-EXPRESS] further populate Residual
bandwidth and Available bandwidth. Further [ISIS-TE-EXPRESS] also
define Bandwidth Utilization.
[Editors Note: [OSPF-TE-EXPRESS] should also be extended in future
version for real time link bandwidth utilization]
The links in the path MAY be monitored for changes in the link
bandwidth utilization, re-optimization of such path MAY be further
requested.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Terminology
The following terminology is used in this document.
IGP: Interior Gateway Protocol. Either of the two routing
protocols, Open Shortest Path First (OSPF) or Intermediate System
to Intermediate System (IS-IS).
PCC: Path Computation Client: any client application requesting a
path computation to be performed by a Path Computation Element.
PCE: Path Computation Element. An entity (component, application,
or network node) that is capable of computing a network path or
route based on a network graph and applying computational
constraints.
PCEP: Path Computation Element Protocol.
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RSVP: Resource Reservation Protocol
TE LSP: Traffic Engineering Label Switched Path.
3. Link Bandwidth Utilization (LBU)
The bandwidth utilization on a link, forwarding adjacency, or bundled
link is populated in the TED (Bandwidth Utilization in
[ISIS-TE-EXPRESS]). For a link or forwarding adjacency, bandwidth
utilization represent the actual utilization of the link (i.e.: as
measured in the router). For a bundled link, bandwidth utilization
is defined to be the sum of the component link bandwidth utilization.
This includes traffic for both RSVP and non-RSVP.
LBU Percentage is described as the (LBU / Maximum bandwidth) * 100.
4. Link Reserved Bandwidth Utilization (LRBU)
The reserved bandwidth utilization on a link, forwarding adjacency,
or bundled link can be calculated from the TED. This includes
traffic for only RSVP-TE LSPs.
LRBU can be calculated by using the Residual bandwidth, available
bandwidth and LBU. The actual bandwidth by non-RSVP TE traffic can
be calculated by subtracting Available Bandwidth from Residual
Bandwidth. Once we have the actual bandwidth for non-RSVP TE
traffic, subtracting this from LBU would result in LRBU.
LRBU Percentage is described as the (LRBU / (current reserved
bandwidth)) * 100; where the current reserved bandwidth can be
calculated by subtracting Residual bandwidth from Maximum bandwidth.
5. PCEP Requirements
Following requirements associated with bandwidth utilization are
identified for PCEP:
1. PCE supporting this draft MUST have the capability to compute
end-to-end path with bandwidth utilization constraints. It MUST
also support the combination of bandwidth utilization constraint
with existing constraints (cost, hop-limit...).
2. PCC MUST be able to request for bandwidth utilization constraint
in PCReq message as the boundary condition that should not be
crossed for each link in the path.
3. PCC MUST be able to request for bandwidth utilization constraint
in PCReq message as an Objective function (OF) [RFC5541] to be
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optimized.
4. PCEs are not required to support bandwidth utilization
constraint. Therefore, it MUST be possible for a PCE to reject a
PCReq message with a reason code that indicates no support for
bandwidth utilization constraint.
5. PCEP SHOULD provide mechanism to handle bandwidth utilization
constraint in multi-domain (e.g., Inter-AS, Inter-Area or Multi-
Layer) environment.
6. PCEP Extensions
This section defines extensions to PCEP [RFC5440] for requirements
outlined in Section 5. The proposed solution is used to consider
bandwidth utilization during path computation.
6.1. BU Object
The BU (Bandwidth Utilization) is used to indicate the upper limit of
the acceptable link bandwidth utilization percentage.
The BU object may be carried within the PCReq message and PCRep
messages.
BU Object-Class is TBD.
Two Object-Type values are defined for the BU object:
o Link Bandwidth Utilization (LBU): BU Object-Type is 1.
o Link Reserved Bandwidth Utilization (LRBU): BU Object-Type is 2.
The format of the BU object body is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth Utilization |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
BU Object Body Format
Bandwidth utilization (32 bits): Represents the bandwidth
utilization quantified as a percentage (as described in Section 3
and Section 4). The basic unit is 0.000000023%, with the maximum
value 4,294,967,295 representing 98.784247785% (4,294,967,295 *
0.000000023%). This value is the maximum Bandwidth utilization
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percentage that can be expressed.
The BU object body has a fixed length of 4 bytes.
6.1.1. Elements of Procedure
PCC SHOULD request the PCE to factor in the bandwidth utilization
during path computation by including a BU object in the PCReq
message.
Multiple BU objects MAY be inserted in a PCReq or a PCRep message for
a given request but there MUST be at most one instance of the BU
object for each object type. If, for a given request, two or more
instances of a BU object with the same object type are present, only
the first instance MUST be considered and other instances MUST be
ignored.
BU object MAY be carried in a PCRep message in case of unsuccessful
path computation along with a NO-PATH object to indicate the
constraints that could not be satisfied.
If the P bit is clear in the object header and PCE does not
understand or does not support bandwidth utilization during path
computation it SHOULD simply ignore BU object.
If the P Bit is set in the object header and PCE receives BU object
in path request and it understands the BU object, but the PCE is not
capable of bandwidth utilization check during path computation, the
PCE MUST send a PCErr message with a PCEP-ERROR Object Error-Type = 4
(Not supported object) [RFC5440]. The path computation request MUST
then be cancelled.
If the PCE does not understand the BU object, then the PCE MUST send
a PCErr message with a PCEP-ERROR Object Error-Type = 3 (Unknown
object) [RFC5440].
6.2. New Objective Functions
This document defines two additional objective functions -- namely,
MUP (Maximum Under-Utilized Path) and MRUP (Maximum Reserved Under-
Utilized Path. Hence two new objective function codes have to be
defined.
Objective functions are formulated using the following terminology:
o A network comprises a set of N links {Li, (i=1...N)}.
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o A path P is a list of K links {Lpi,(i=1...K)}.
o Bandwidth Utilization on link L is denoted u(L).
o Reserved Bandwidth Utilization on link L is denoted ru(L).
o Maximum bandwidth on link L is denoted M(L).
o Current Reserved bandwidth on link L is denoted c(L).
The description of the two new objective functions is as follows.
Objective Function Code: TBD
Name: Maximum Under-Utilized Path (MUP)
Description: Find a path P such that (Min {(M(Lpi)- u(Lpi)) /
M(Lpi), i=1...K } ) is maximized.
Objective Function Code: TBD
Name: Maximum Reserved Under-Utilized Path (MRUP)
Description: Find a path P such that (Min {(c(Lpi)- ru(Lpi)) /
c(Lpi), i=1...K } ) is maximized.
These new objective function are used to optimize paths based on
bandwidth utilization as the optimization criteria.
If the objective function defined in this document are unknown/
unsupported, the procedure as defined in [RFC5541] is followed.
6.3. PCEP Message
The new optional BU objects MAY be specified in the PCReq message.
As per [RFC5541], an OF object specifying a new objective function
MAY also be specified.
The format of the PCReq message (with [RFC5541] as a base) is updated
as follows:
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<PCReq Message> ::= <Common Header>
[<svec-list>]
<request-list>
where:
<svec-list> ::= <SVEC>
[<OF>]
[<metric-list>]
[<svec-list>]
<request-list> ::= <request> [<request-list>]
<request> ::= <RP>
<END-POINTS>
[<LSPA>]
[<BANDWIDTH>]
[<bu-list>]
[<metric-list>]
[<OF>]
[<RRO>[<BANDWIDTH>]]
[<IRO>]
[<LOAD-BALANCING>]
and where:
<bu-list>::=<BU>[<bu-list>]
<metric-list> ::= <METRIC>[<metric-list>]
The BU objects MAY be specified in the PCRep message, in case of an
unsuccessful path computation to indicate the bandwidth utilization
as a reason for failure. The OF object MAY be carried within a PCRep
message to indicate the objective function used by the PCE during
path computation.
The format of the PCRep message (with [RFC5541] as a base) is updated
as follows:
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<PCRep Message> ::= <Common Header>
[<svec-list>]
<response-list>
where:
<svec-list> ::= <SVEC>
[<OF>]
[<metric-list>]
[<svec-list>]
<response-list> ::= <response> [<response-list>]
<response> ::= <RP>
[<NO-PATH>]
[<attribute-list>]
[<path-list>]
<path-list> ::= <path> [<path-list>]
<path> ::= <ERO>
<attribute-list>
and where:
<attribute-list> ::= [<OF>]
[<LSPA>]
[<BANDWIDTH>]
[<bu-list>]
[<metric-list>]
[<IRO>]
<bu-list>::=<BU>[<bu-list>]
<metric-list> ::= <METRIC> [<metric-list>]
7. Other Considerations
7.1. Reoptimization Consideration
PCC can monitor the link bandwidth utilization of the setup LSPs and
in case of drastic change, it MAY ask PCE for reoptimization as per
[RFC5440].
7.2. Inter-domain Consideration
7.3. P2MP Consideration
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7.4. Stateful PCE
8. IANA Considerations
TBD
9. Security Considerations
TBD
10. Security Considerations
This document defines a new BU object and OF codes which does not add
any new security concerns beyond those discussed in [RFC5440].
11. Manageability Considerations
11.1. Control of Function and Policy
The only configurable item is the support of the new constraints on a
PCE which MAY be controlled by a policy module. If the new
constraints are not supported/allowed on a PCE, it MUST send a PCErr
message as specified in Section 6.1.1.
11.2. Information and Data Models
[PCEP-MIB] describes the PCEP MIB, there are no new MIB Objects for
this document.
11.3. Liveness Detection and Monitoring
Mechanisms defined in this document do not imply any new liveness
detection and monitoring requirements in addition to those already
listed in [RFC5440].
11.4. Verify Correct Operations
Mechanisms defined in this document do not imply any new operation
verification requirements in addition to those already listed in
[RFC5440].
11.5. Requirements On Other Protocols
PCE requires the TED to be populated with the bandwidth utilization.
This mechanism is described in [OSPF-TE-EXPRESS] or
[ISIS-TE-EXPRESS].
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11.6. Impact On Network Operations
Mechanisms defined in this document do not have any impact on network
operations in addition to those already listed in [RFC5440].
12. Acknowledgments
We would like to thank Alia Atlas, John E Drake, David Ward for their
useful comments and suggestions.
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, RFC 2119,
March 1997.
13.2. Informative References
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic
Engineering (TE) Extensions to OSPF Version 2",
RFC 3630, September 2003.
[RFC3784] Smit, H. and T. Li, "Intermediate System to
Intermediate System (IS-IS) Extensions for Traffic
Engineering (TE)", RFC 3784, June 2004.
[RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation
Element (PCE) Communication Protocol (PCEP)",
RFC 5440, March 2009.
[RFC5541] Le Roux, JL., Vasseur, JP., and Y. Lee, "Encoding
of Objective Functions in the Path Computation
Element Communication Protocol (PCEP)", RFC 5541,
June 2009.
[OSPF-TE-EXPRESS] Giacalone, S., Ward, D., Drake, J., Atlas, A., and
S. Previdi, "OSPF Traffic Engineering (TE) Metric
Extensions
[draft-ietf-ospf-te-metric-extensions]",
June 2013.
[ISIS-TE-EXPRESS] Previdi, S., Giacalone, S., Ward, D., Drake, J.,
Atlas, A., Filsfils, C., and W. Qin, "IS-IS
Traffic Engineering (TE) Metric Extensions
[draft-ietf-isis-te-metric-extensions-01]",
October 2013.
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[PCEP-MIB] Kiran Koushik, A S., Stephan, E., Zhao, Q., King,
D., and J. Hardwick, "PCE communication
protocol(PCEP) Management Information Base
[draft-ietf-pce-pcep-mib]", Feb 2013.
Appendix A. Contributor Addresses
Udayasree Palle
Huawei Technologies
Leela Palace
Bangalore, Karnataka 560008
INDIA
EMail: udayasree.palle@huawei.com
Authors' Addresses
Qin Wu
Huawei Technologies
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
EMail: sunseawq@huawei.com
Dhruv Dhody
Huawei Technologies
Leela Palace
Bangalore, Karnataka 560008
INDIA
EMail: dhruv.ietf@gmail.com
Stefano Previdi
Cisco Systems, Inc
Via Del Serafico 200
Rome 00191
IT
EMail: sprevidi@cisco.com
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