Network Working Group S. Sivabalan, Ed.
Request for Comments: 5455 J. Parker
Category: Standards Track S. Boutros
Cisco Systems, Inc.
KDDI R&D Laboratories, Inc.
March 2009 Diffserv-Aware Class-Type Object for
the Path Computation Element Communication Protocol
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
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This document specifies a CLASSTYPE object to support Diffserv-Aware
Traffic Engineering (DS-TE) where path computation is performed with
the aid of a Path Computation Element (PCE).
Table of Contents
1. Introduction ....................................................21.1. Conventions Used in This Document ..........................32. Terminology .....................................................33. CLASSTYPE Object ................................................33.1. Object Definition ..........................................43.2. Path Computation Request Message with CLASSTYPE Object .....43.3. Processing CLASSTYPE Object ................................53.4. Determination of Traffic Engineering Class (TE-Class) ......63.5. Significance of Class-Type and TE-Class ....................63.6. Error Codes for CLASSTYPE Object ...........................64. Security Considerations .........................................75. IANA Considerations .............................................76. Acknowledgments .................................................77. References ......................................................87.1. Normative References .......................................87.2. Informative References .....................................81. Introduction
[RFC5440] specifies the Path Computation Element Communication
Protocol (PCEP) for communications between a Path Computation Client
(PCC) and a Path Computation Element (PCE), or between two PCEs, in
compliance with [RFC4657].
Diffserv-aware MPLS Traffic Engineering (DS-TE) addresses the
fundamental requirement to be able to enforce different bandwidth
constraints for different classes of traffic. It describes
mechanisms to achieve per-class traffic engineering, rather than on
an aggregate basis across all classes by enforcing Bandwidth
Constraints (BCs) on different classes. Requirements for DS-TE and
the associated protocol extensions are specified in [RFC3564] and
As per [RFC4657], PCEP must support traffic Class-Type as an MPLS-
TE-specific constraint. However, in the present form, PCEP [RFC5440]
does not have the capability to specify the Class-Type in the path
In this document, we define a new PCEP object called CLASSTYPE, which
carries the Class-Type of the TE LSP in the path computation request.
During path computation, a PCE uses the Class-Type to identify the
bandwidth constraint of the TE LSP.
1.1. 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 RFC 2119 [RFC2119].
CT (Class-Type): A set of Traffic Trunks governed by a set of
bandwidth constraints. Used for the purpose of link bandwidth
allocation, constraint-based routing and admission control. A given
Traffic Trunk belongs to the same CT on all links.
DS-TE: Diffserv-Aware Traffic Engineering.
LSR: Label Switching Router.
LSP: Label Switched Path.
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 Peer: an element involved in a PCEP session (i.e., a PCC or the
TE-Class: A pair consisting of a Class-Type and a preemption priority
allowed for that Class-Type. An LSP transporting a Traffic Trunk
from that Class-Type can use that preemption priority as the setup
priority, the holding priority, or both.
TE LSP: Traffic Engineering Label Switched Path.
Traffic Trunk: An aggregation of traffic flows of the same class
(i.e., treated equivalently from the DS-TE perspective), which is
placed inside a TE LSP.
3. CLASSTYPE Object
The CLASSTYPE object is optional and is used to specify the Class-
Type of a TE LSP. This object is meaningful only within the path
computation request, and is ignored in the path reply message. If
the TE LSP for which the path is to be computed belongs to Class 0,
path computation request MUST NOT contain the CLASSTYPE object. This
allows backward compatibility with a PCE that does not support the
3.1. Object Definition
The CLASSTYPE object contains a 32-bit word PCEP common object header
defined in [RFC5440] followed by another 32-bit word object body as
shown in Figure 1.
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
| PCEP common header |
| Reserved | CT |
Figure 1: CLASSTYPE object format
The fields in the common object header are processed as specified in
[RFC5440]. The values of object class and object type are 22 and 1,
respectively. If included, the CLASSTYPE object must be taken into
account by the PCE. As such, the P flag MUST be set. The I flag is
The CLASSTYPE object body contains the following fields:
CT: 3-bit field that indicates the Class-Type. Values allowed are 1,
2, ... , 7. The value of 0 is Reserved.
Reserved: 29-bit reserved field. It MUST be set to zero on
transmission and MUST be ignored on receipt.
3.2. Path Computation Request Message with CLASSTYPE Object
[RFC5440] specifies the order in which objects must be inserted in
the PCEP messages. This document specifies that the CLASSTYPE object
be inserted after the END-POINT objects as shown below:
The format of a Path Computation Request (PCReq) message is as
<PCReq Message>::= <Common Header>
Note that an implementation MUST form the PCEP messages using the
object ordering rules specified using Backus-Naur Form. Please refer
to [OBJ-ORD] for more details.
3.3. Processing CLASSTYPE Object
If the LSP is associated with Class-Type N (1 <= N <= 7), the PCC
originating the PCReq MUST include the CLASSTYPE object in the PCReq
message with the Class-Type (CT) field set to N.
If a path computation request contains multiple CLASSTYPE objects,
only the first one is meaningful; subsequent CLASSTYPE object(s) MUST
be ignored and MUST NOT be forwarded.
If the CLASSTYPE object is not present in the path computation
request message, the LSR MUST associate the Class-Type 0 to the LSP.
A path computation reply message MUST NOT include a CLASSTYPE object.
If a PCE needs to forward a path computation request containing the
CLASSTYPE object to another PCE, it MUST store the Class-Type of the
TE LSP in order to complete the path computation when the path
computation reply arrives.
A PCE that does not recognize the CLASSTYPE object MUST reject the
entire PCEP message and MUST send a PCE error message with Error-
Type="Unknown Object" or "Not supported object", defined in
A PCE that recognizes the CLASSTYPE object, but finds that the P flag
is not set in the CLASSTYPE object, MUST send PCE error message
towards the sender with the error type and error value specified in
A PCE that recognizes the CLASSTYPE object, but does not support the
particular Class-Type, MUST send a PCE error message towards the
sender with the error type "Diffserv-aware TE error" and the error
value of "Unsupported Class-Type" (Error-value 1).
A PCE that recognizes the CLASSTYPE object, but determines that the
Class-Type value is not valid (i.e., Class-Type value 0), MUST send a
PCE error towards the sender with the error type "Diffserv-aware TE
error" and an error value of "Invalid Class-Type" (Error-value 2).
3.4. Determination of Traffic Engineering Class (TE-Class)
As specified in RFC 4124, a CT and a preemption priority map to a
Traffic Engineering Class (TE-class), and there can be up to 8
TE-classes. The TE-class value is used to determine the unreserved
bandwidth on the links during path computation. In the case of a
PCE, the CT value carried in the CLASSTYPE object and the setup
priority in the LSP Attribute (LSPA) object are used to determine the
TE-class corresponding to the path computation request. If the LSPA
object is absent, the setup priority is assumed to be 0.
3.5. Significance of Class-Type and TE-Class
To ensure coherent DS-TE operation, a PCE and a PCC should have a
common understanding of a particular DS-TE Class-Type and TE-class.
If a path computation request crosses an Autonomous System (AS)
boundary, these should have global significance in all domains.
Enforcement of this global significance is outside the scope of this
3.6. Error Codes for CLASSTYPE Object
This document defines the following error type and values:
12 Diffserv-aware TE error
Error-value=1: Unsupported Class-Type
Error-value=2: Invalid Class-Type
Error-value=3: Class-Type and setup priority do
not form a configured TE-class
4. Security Considerations
This document does not introduce new security issues. The security
considerations pertaining to PCEP [RFC5440] remain relevant.
5. IANA Considerations
IANA maintains a registry of parameters for PCEP. This contains a
sub-registry for PCEP objects. IANA has made allocations from this
registry as follows:
Object-Class Name Reference
22 CLASSTYPE RFC 5455
1: Class-Type RFC 5455
IANA has allocated error types and values as follows:
Error-Type Meaning Reference
12 Diffserv-aware TE error RFC 5455
Error-value = 1: RFC 5455
Error-value = 2: RFC 5455
Error-value = 3: RFC 5455
Class-Type and setup priority
do not form a configured TE-class
The authors would like to thank Jean Philippe Vasseur, Adrian Farrel,
and Zafar Ali for their valuable comments.
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4124] Le Faucheur, F., Ed., "Protocol Extensions for Support of
Diffserv-aware MPLS Traffic Engineering", RFC 4124, June
[RFC5440] Vasseur, JP., Ed., and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
7.2. Informative References
[RFC4657] Ash, J., Ed., and J. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol Generic Requirements",
RFC 4657, September 2006.
[RFC3564] Le Faucheur, F. and W. Lai, "Requirements for Support of
Differentiated Services-aware MPLS Traffic Engineering",
RFC 3564, July 2003.
[OBJ-ORD] Farrel, A., "Reduced Backus-Naur Form (RBNF) A Syntax Used
in Various Protocol Specifications", Work in Progress,