Network Working Group Yuanlin Bao
Internet-Draft Xihua Fu
Intended status: Informational Gang. Xie
Expires: September 1, 2010 ZTE Corporation
February 28, 2010
The Requirements for Path Computation Element (PCE) Application for
Backup Route
draft-bao-pce-backup-route-computation-reqs-00.txt
Abstract
Backup route is another route for a service which will be used when
working path fails. Traditionally, this route is configured by
operator manually and can't be updated when LSA changes. This
document improves this traditional usage, and PCE (Path Computation
Element) is applied for backup route.
Status of this Memo
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document authors. All rights reserved.
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Table of Contents
1. Conventions used in this document . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Application Model . . . . . . . . . . . . . . . . . . . . . . . 3
4. Architecture Analysis and Requirements . . . . . . . . . . . . 4
4.1. Architecture Analysis . . . . . . . . . . . . . . . . . . . 4
4.2. Requirements to PCC and PCE . . . . . . . . . . . . . . . . 5
4.3. Requirements to PCEP . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
7. Normative References . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
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1. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Introduction
Backup route is a very useful approach to achieve service
restoration. Traditionally, except primary route, operator also sets
a group of routes (usually with priority), i.e. backup route set, for
a service. When the primary route fails, LSR can select a proper
restoration route from backup route set. By this way, faster
restoration can be achieved.
Since backup routes are pre-configured by management plane, it can't
be updated when network state changes dynamically. In some cases,
e.g. a fiber on the backup route is cut, if operator can't update
backup routes in time, the backup routes will become unavailable.
Otherwise, generally the backup routes will be verified whether it is
available before it is used to signal a connection. This is also due
to the problem that backup routes can't be updated timely. And this
will introduce another problem that time delay will affect service
recovery.
This document introduces a PCE-based backup route method, which uses
PCE to update backup route at the policy of network management. This
method helps provider to offer better service for customer and avoids
the unavailablity of backup routes.
3. Application Model
Figure 1 is an application model of pce-based backup route
computation. A user requests ingress LSR (PCC) for a service with
backup route. Then PCC requests PCE to compute a working path and a
backup path. PCE returns the results to PCC, and records that a
backup route service is requested by the PCC. When PCE receives a
LSA change from IGP, it'll check if the backup route computed
previously is affected. If the backup route is affected, it will re-
compute a new backup route, and send it to the PCC.
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+-------------+ +---------+
| | Change | | Change
| PCE |<---------| IGP |<----------
| | of LSA | | of LSA
+-------------+ +---------+
^ |
|Path(W+B) |Path
|Request/ |Refresh
|Response |
V V
+------+ +-------------+ +-------------+
| | Service | LSR | Signaling | |
| USER |--------->| (PCC) |---------->| LSR |
| | Request | | | |
+------+ +-------------+ +-------------+
Figure 1: Backup Route Application Model
4. Architecture Analysis and Requirements
4.1. Architecture Analysis
[RFC4655] introduced 5 PCE models which can be categorized according
to whether PCE functionality is integrated into the network element.
Under this methodology, two groups of PCE model, i.e. composite PCE
and external PCE, is generated.
For composite PCE, due to the resource limitation of the card, the
power of CPU is relatively weak, so the PCE capability is also
limited. However, compared to composite PCE, external PCE has more
resources (i.e. memory and CPU power etc), and it even can be
presented as a dedicated server. Therefore, external PCE is more
powerful than composite PCE. The application of backup route will
increase compuataion burden to PCE. Due to its powerful computation
capability, external PCE is more adequate than composite PCE.
However, if there is not much application of backup route, composite
PCE can also operate well.
[RFC4655] also describes stateful PCE and stateless PCE. For
statefull PCE, there is a strict synchronization between the PCE and
not only the network states (in term of topology and resource
information), but also the set of computed paths and reserved
resources in use in the network. Since stateful PCE can perceive the
network state chang, so it can determine which computed path is
affected. Therefore, it is easier to applying backup route on
stateful PCE.
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Furthermore, considering the PCE failure, if an implementation has a
backup PCE, then the primary and backup PCE MUST keep strict
synchronization. And switching to the backup PCE can't affect the
correctness of path computation
However, the selection of PCE model, stateful PCE or stateless PCE is
out of this document. And the synchronization between primary and
backup PCE is also out of this document, the operator can make a
selection according to the network deployment.
4.2. Requirements to PCC and PCE
In order to support the backup route, PCC SHOULD be able to let PCE
know that it needs backup route service. Thereby, PCE can start
backup service. Otherwise, PCC SHOULD also be able to notify PCE
that backup route service is cancelled, so PCE can stop backup route
services.
As for PCE, it SHOULD record backup route information, and maintain
its state. When network state changes, PCE SHOULD compute the
affected backup routes and send a new route to PCC. However, PCE MAY
also compute backup routes in idle state to obtain the optimized
paths. The policy for PCE to compute backup routes SHOULD be able to
be configured.
4.3. Requirements to PCEP
[RFC4657] gives detailed generic requirements for PCE communication
protocol. However, in order to support backup route, specific
extensions to PCEP is required. For PCReq, it SHOULD be possible for
PCC to request backup route. That is a mechanism is needed to make
PCE know that PCC want a backup route service.
When PCE receives a PCReq message with a backup route serivce
request, it SHOULD perform path computation accroding to the required
policy, e.g. node disjoint, link disjoint and SRLG disjoint etc. And
in the PCRep message, PCE SHOULD able to specify which one is pre-
exsiting route, if PCC requests both primary route and backup route
at the same time. If PCE doesn't support backup route it SHOULD give
a negative response, and the reason of the computation failure. When
network state changes, PCE SHOULD re-compute backup routes according
the configured policy. If a better backup route is found, PCE should
send it to PCC.
When PCC wants to cancel the backup route service, it can send a
notify message to PCE. Since current PCNtf message can't achieve
this function, some extensions is needed.
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5. Security Considerations
This document has no requirement for a change to the security models
within associated protocols.
6. Acknowledgements
The RFC text was produced using Marshall Rose's xml2rfc tool.
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC4657] Ash, J. and J. Le Roux, "Path Computation Element (PCE)
Communication Protocol Generic Requirements", RFC 4657,
September 2006.
[RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element
(PCE) Communication Protocol (PCEP)", RFC 5440,
March 2009.
Authors' Addresses
Yuanlin Bao
ZTE Corporation
5F, R&D Building 3, ZTE Industrial Park, XiLi LiuXian Road
Nanshan District, Shenzhen 518055
P.R.China
Phone: +86 755 26773731
Email: bao.yuanlin@zte.com.cn
URI: http://www.zte.com.cn/
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Xihua Fu
ZTE Corporation
West District,ZTE Plaza,No.10,Tangyan South Road,Gaoxin District
Xi An 710065
P.R.China
Phone: +8613798412242
Email: fu.xihua@zte.com.cn
URI: http://www.zte.com.cn/
Gang Xie
ZTE Corporation
ZTE Plaza, No.19, Huayuan Road East, Haidian District
Bei Jing 100191
P.R.China
Phone: +8613798412242
Email: xie.gang@zte.com.cn
URI: http://www.zte.com.cn/
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