Network Working Group Y. Lee
Internet Draft Huawei
Intended status: Standard Track
Expires: December 2008 G. Bernstein
Grotto Networking
June 27, 2008
PCEP Requirements and Extensions for WSON Routing and Wavelength
Assignment
draft-lee-pce-wson-routing-wavelength-02.txt
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Abstract
This memo provides application-specific requirements and protocol
enhancements for the Path Computation Element communication Protocol
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(PCEP) for the support of Wavelength Switched Optical Networks
(WSON). Lightpath provisioning in WSONs requires a routing and
wavelength assignment (RWA) process. From a path computation
perspective, wavelength assignment is the process of determining
which wavelength can be used on each hop of a path and forms an
additional routing constraint to optical light path computation.
Different computational architectures for the RWA process are given
and the PCEP extensions needed to support these architectures are
defined.
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 0.
Table of Contents
1. Introduction...................................................3
2. Background: RWA Computation Architectures......................4
3. PCECP Requirements.............................................5
3.1. RWA Computation Options...................................5
3.2. Same Wavelength Assignment for Primary and backup paths...6
3.3. Same Wavelength Assignment for Bidirectional LSP..........6
3.4. Wavelength Assignment in PC Reply.........................7
3.5. RWA objective functions...................................7
4. Protocol Extensions for Support of WSON RWA....................7
4.1. RWA Computation Options...................................8
4.2. Lightpath Specific Parameter TLV..........................9
4.3. Objective Functions......................................10
4.4. Error Indicator..........................................11
4.5. NO-PATH Indicator........................................11
5. Manageability Considerations..................................11
5.1. Control of Function and Policy...........................12
5.2. Information and Data Models, e.g. MIB module.............12
5.3. Liveness Detection and Monitoring........................12
5.4. Verifying Correct Operation..............................12
5.5. Requirements on Other Protocols and Functional Components13
5.6. Impact on Network Operation..............................13
6. Security Considerations.......................................13
7. IANA Considerations...........................................13
8. Acknowledgments...............................................13
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9. References....................................................14
9.1. Normative References.....................................14
9.2. Informative References...................................14
Authors' Addresses...............................................15
Intellectual Property Statement..................................15
Disclaimer of Validity...........................................16
1. Introduction
[RFC4655] defines the PCE based Architecture and explains how a Path
Computation Element (PCE) may compute Label Switched Paths (LSP) in
Multiprotocol Label Switching Traffic Engineering (MPLS-TE) and
Generalized MPLS (GMPLS) networks at the request of Path Computation
Clients (PCCs). A PCC is shown to be any network component that
makes such a request and may be for instance an Optical Switching
Element within a Wavelength Division Multiplexing (WDM) network. The
PCE, itself, can be located anywhere within the network, and may be
within an optical switching element, a Network Management System
(NMS) or Operational Support System (OSS), or may be an independent
network server.
The PCE communications Protocol (PCEP) is the communication protocol
used between PCC and PCE, and may also be used between cooperating
PCEs. [RFC4657] sets out the common protocol requirements for PCEP.
Additional application-specific requirements for PCEP are deferred to
separate documents.
This document provides a set of application-specific PCEP
requirements and protocol enhancements for support of path
computation in Wavelength Switched Optical Networks (WSON). WSON
refers to WDM based optical networks in which switching is performed
selectively based on the wavelength of an optical signal.
The path in WSON is referred to as a lightpath. A lightpath may span
multiple fiber links and the path should be assigned a wavelength for
each link. A transparent optical network is made up of optical
devices that can switch but not convert from one wavelength to
another. In a transparent optical network, a lightpath operates on
the same wavelength across all fiber links that it traverses. In such
case, the lightpath is said to satisfy the wavelength-continuity
constraint. Two lightpaths that share a common fiber link can not be
assigned the same wavelength. To do otherwise would result in both
signals interfering with each other. Note that advanced additional
multiplexing techniques such as polarization based multiplexing are
not addressed in this document since the physical layer aspects are
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not currently standardized. Therefore, assigning the proper
wavelength on a lightpath is an essential requirement in the optical
path computation process.
On the other hand, when a switching node has the ability to perform
wavelength conversion the wavelength-continuity constraint can be
relaxed, and a lightpath may use different wavelengths on different
links along its route from origin to destination. It is, however, to
be noted that wavelength converters may be limited due to their
relatively high cost, while the number of WDM channels that can be
supported in a fiber is also limited. As a WSON can be composed of
network nodes that cannot perform wavelength conversion, nodes with
limited wavelength conversion, and nodes with full wavelength
conversion abilities, wavelength assignment is an additional routing
constraint to be considered in all lightpath computation.
Optical impairment constraints are not addressed in this document as
the current scope of the WSON framework [WSON-FRAME] does not include
them.
The remainder of this document uses terminology from [RFC4655].
2. Background: RWA Computation Architectures
The WSON framework [WSON-FRAME] document defines the following RWA
computation architectures.
o Combined RWA --- Both routing and wavelength assignment are
performed at a single computational entity. This choice assumes
that computational entity has sufficient WSON network link/nodal
and topology information to be able to compute RWA.
o Separate Routing and WA --- Separate entities perform routing and
wavelength assignment. The path(s) obtained from the routing
computational entity must be furnished to the entity performing
wavelength assignment.
o Routing with Distributed WA --- Routing is performed at a
computational entity while wavelength assignment is performed in a
distributed fashion across the nodes along the path.
For the Combined RWA architecture, there are two possible computing
entities: (i) the NE is the computational entity -- in this case,
there is no separate PCE as the NE assumes PCE function; (ii) a
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separate PCE is the computational entity. This document is only
concerned with case (ii). In this case, the PCE should perform both
routing (R) and wavelength assignment (WA) upon request of the PCC.
For the Separate Routing and Wavelength architecture, there can be
two variations:
o A separate PCE will perform only wavelength assignment (WA) while
the NE performs the route calculation based on its local
knowledge. In this case, the NE should furnish the route list to
the PCE so that the PCE would be able to assign wavelength to the
route.
o One PCE performs the routing (R) function while another PCE
performs the Wavelength Assignment (WA) function in a tandem
fashion. The fact that two PCEs are involved (one for Routing and
one for Wavelength Assignment (WA)) could be invisible to the
original PCC.
For the Routing with Distributed WA architecture, the PCE is only
responsible for routing (i.e., path computation), not for exact
wavelength assignment. The exact assignment of wavelengths would be
performed at the NEs along the path in a distributed fashion.
3. PCECP Requirements
This section provides the PCECP requirements to support WSON routing
and wavelength assignment (RWA) applications. The requirements
specified in this section are detailed requirements based on high-
level specification in [WSON-FRAME].
3.1. RWA Computation Options
The following RWA computation options should be conveyed in the PC
Request:
o The request is for both Routing and Wavelength Assignment (R+WA).
This case may arise when the NE is not capable of either route
calculation or wavelength assignment at the node level, or when a
more optimal RWA is desired.
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o The request is for Routing (R) only. This case may arise when the
NE is not capable of route calculation at the node level while
wavelength assignment is done at the node level in a distributed
fashion.
o The request is for Wavelength Assignment (WA) only. This case may
arise when the NE is capable of route calculation at the node
level (e.g., via an IGP-TE) but with no wavelength information
is available at the node level, or when two PCEs work in tandem
with one performing the routing (R) function and another
wavelength assignment (WA). In either case, the calculated route
list at one computing entity should be supplied in the request
message to the other computing entity where WA is applied.
The corresponding PC Reply message should include the following
information:
o An indicator that conveys the original request was for (i) Both
Routing and Wavelength Assignment (R+WA); (ii) Wavelength
Assignment (WA) only; (iii) Routing (R) only.
o The route list for all cases above and the recommended wavelengths
to be used for the route for cases (i) and (ii).
o In the case of failure to find a proper route or wavelengths
assigned to the route, proper reasons for the failure should be
conveyed: (i) route not found; (ii) wavelength not found (i.e.,
wavelength blocking); (iii) both route and wavelength not found.
3.2. Same Wavelength Assignment for Primary and backup paths
The PC Request should indicate if the same wavelength assignment for
the primary and backup paths is required or not.
o Same wavelength required
o Different wavelength required
3.3. Same Wavelength Assignment for Bidirectional LSP
When Bidirectional LSP is requested in the PC Request Message, a
further indication should be made if the same wavelength should be
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assigned in both directions in each hop. Note that assigning
different wavelengths for the two directions is assumed as default.
o Same wavelengths required
o Different wavelengths permitted
3.4. Wavelength Assignment in PC Reply
If the original request is either for both Routing and Wavelength
Assignment (R+WA) or for Wavelength Assignment (WA) only, the exact
wavelength assignment result should be conveyed to the PCC using the
ERO object and ERO Label subobject within the ERO. Note that this
requirement is fulfilled by the Label Set mechanism in [RFC3471].
3.5. RWA objective functions
Analogous to [PCE-OF], the RWA computation should support a number of
objective functions in the PC Request Message. The following RWA
objective functions should be supported at a minimum:
o For a sequential request (i.e., one request):
. TBD
o For a concurrent request (i.e., multi-commodity flows):
. Minimize the total number of link-wavelength used
. Minimize the maximum link-wavelength used (load balance)
. Minimize the path length of all flows
The PCRep should indicate which objective function has actually been
applied.
4. Protocol Extensions for Support of WSON RWA
This section describes PCEP extension necessary to meet the
requirements set out in the previous section.
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4.1. RWA Computation Options
The PCC has to include the RWA computation option in the PCReq
message in order to convey a particular computation option. To
support such indication a new flag, the RWA Computation (RC) flag, is
defined in the RP (Request Parameter) Object.
The RC flag is defined in the Flags field of the RP (Request
Parameter) object as follows. Bit number assignment to be confirmed
by IANA (see Section 8).
Bit Name Description Reference
10-11 RC-bits Routing Wavelength Computation This document
RC bits (Routing wavelength Computation bits - 2 bits):
o 11: Request is for both R (Routing) and Wavelength Assignment
(WA).
o 01: Request is for Wavelength Assignment (WA) only.
o 10: Request is for Routing (R) only.
When the RC bits are set to 11 in a PCReq message, the requesting PCC
requires the PCE to provide in the PCRep message the assigned
wavelength associated with the computed path. This request is for
both Routing (R) and Wavelength Assignment (WA).
When the RC bits are set to 01 in a PCReq message, the requesting PCC
requires the PCE only to provide wavelength assignment (WA). In such
case, the PCC must provide the already computed route (as indicated
by the ERO and the Bandwidth Object following the RP object) to which
the PCE would assign the wavelengths. Note that this option is to
fulfill one of the RWA computational architectures, namely, the
Separate Routing and WA option.
When the RC bits are set to 11 or 01, then additional parameters
associated with the requested lightpath SHOULD be provided in
optional Lightpath Specific Parameter TLV (as specified in Section
3.4) within the RP object. See Section 4.2 for the encoding of
Lightpath Specific Parameter TLV.
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The RP object in the PCRep message SHOULD properly indicate the
original request for the RWA Computation (RC) bit that has actually
been applied by the PCE. The actual route list and wavelength
assignment is to be found in the ERO within ERO Label subobjects. ERO
Label subobjects can be used to indicate the wavelength to be used on
particular links. Note that GMPLS signaling [RFC3473] supports an
explicit route object (ERO) and with ERO Label subobjects.
4.2. Lightpath Specific Parameter TLV
When the RC bit is set to 11 or 01 and the B bit is set to 1 (which
indicates a bi-directional LSP request) in the RP object in a PCReq
message, then the following Lightpath Specific Parameter TLV SHOULD
be included as part of the RP object within the PCReq message.
The format of the Lightpath Specific Parameter TLV 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be defined by IANA (suggested value = x)
Length 2 bits
Value S bit: 0 or 1
Figure 1 The Lightpath Specific Parameter TLV in the RP object in
the PCReq Message
S bit (Same Wavelength to both directions - 1 bit):
o 0: Request is for the assignment of the same wavelength to
upstream and downstream directions.
o 1: Request is for the assignment of the different wavelength to
upstream and downstream directions.
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4.3. Objective Functions
When the RC (RWA Computation) flags in the RP object of a PCReq
indicate computing wavelength assignment, then the following
Objective Function TLV SHOULD be included in the RP object as an
optional TLV.
The format of the Wavelength Selection Preference TLV 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Objective Function |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be defined by IANA (suggested value = x)
Length 32 bits
Value Objective Function
Figure 2 The Objective Function TLV in the RP object in the PCReq
Message
Three objective functions are defined in this document and their
identifier should be assigned by IANA (suggested value)
Function
Code Description
-------- ------------
1 Minimize the total number of link-wavelength used
2 Minimize the maximum link-wavelength used (load
balance)
3 Minimize the path length of all flows
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4.4. Error Indicator
To indicate errors associated with the RWA request, a new Error-Type
(15) and subsequent error-values are defined as follows for inclusion
in the PCEP-ERROR object.
If a PCE receives a RWA computation request and the PCE is not
capable of RWA, the PCE MUST send a PCErr message with a PCEP ERROR
object (Error-Type=15) and an Error-Value (Error-Value=1). The
corresponding RWA computation request MUST be cancelled.
To indicate an error associated with policy violation, a new error
value "RWA not allowed" is added to the existing error code for
policy violation (Error-Type=6) as defined in [PCEP].
If a PCE receives a RWA computation request which is not compliant
with administrative privileges (i.e., the PCE policy does not support
RWA), the PCE MUST send a PCErr message with a PCEP-ERROR Object
(Error-Type=6) and an Error-Value (Error-Value=3). The corresponding
RWA computation MUST be cancelled.
4.5. NO-PATH Indicator
To communicate the reason(s) for not being able to find RWA
computation, the NO-PATH object MAY be used in the PCRep message. The
NO-PATH object is defined in [PCEP].
As defined in [PCEP], the NO-PATH object carries the NO-PATH_VECTOR
TLV which has a flags field. One new bit flag is defined in this
document to indicate RWA-specific computation failures as follows:
0x10: when set, the PCE indicates that no wavelength was found
associated with RWA computation in the PCRep message.
5. Manageability Considerations
Manageability of WSON Routing and Wavelength Assignment (RWA) with
PCE must address the following considerations:
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5.1. Control of Function and Policy
In addition to the parameters already listed in Section 8.1 of
[PCEP], a PCEP implementation SHOULD allow configuring the following
PCEP session parameters on a PCC:
o The ability to send a WSON RWA request.
In addition to the parameters already listed in Section 8.1 of
[PCEP], a PCEP implementation SHOULD allow configuring the following
PCEP session parameters on a PCE:
o The support for WSON RWA.
o The maximum number of synchronized path requests associated with
WSON RWA per request message.
o A set of WSON RWA specific policies (authorized sender, request
rate limiter, etc).
These parameters may be configured as default parameters for any PCEP
session the PCEP speaker participates in, or may apply to a specific
session with a given PCEP peer or a specific group of sessions with a
specific group of PCEP peers.
5.2. Information and Data Models, e.g. MIB module
Extensions to the PCEP MIB module defined in [PCEP-MIB] should be
defined, so as to cover the WSON RWA information introduced in this
document. A future revision of this document will list the
information that should be added to the MIB module.
5.3. 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 section 8.3 of [PCEP].
5.4. Verifying Correct Operation
Mechanisms defined in this document do not imply any new verification
requirements in addition to those already listed in section 8.4 of
[PCEP]
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5.5. Requirements on Other Protocols and Functional Components
The PCE Discovery mechanisms ([ISIS PCED] and [OSPF PCED]) may be
used to advertise WSON RWA path computation capabilities to PCCs.
5.6. Impact on Network Operation
Mechanisms defined in this document do not imply any new network
operation requirements in addition to those already listed in section
8.6 of [PCEP].
6. Security Considerations
This document has no requirement for a change to the security models
within PCEP [PCEP]. However the additional information distributed in
order to address the RWA problem represents a disclosure of network
capabilities that an operator may wish to keep private. Consideration
should be given to securing this information.
7. IANA Considerations
A future revision of this document will present requests to IANA for
codepoint allocation.
8. Acknowledgments
The authors would like to thank Adrian Farrel for many helpful
comments that greatly improved the contents of this draft.
This document was prepared using 2-Word-v2.0.template.dot.
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9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3471] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Functional Description", RFC 3471,
January 2003.
[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
January 2003.
[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.
[PCEP] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) communication Protocol (PCEP) - Version 1",
draft-ietf-pce-pcep, work in progress.
9.2. Informative References
[PCE-OF] Le Roux, JL., Vasseur, JP., and Y. Lee, "Objective Function
encoding in Path Computation Element communication and
discovery protocols", draft-ietf-pce-pce-of, work in
progress.
[PCE-GCO] Y. Lee, J.L. Le Roux, D. King, and E. Oki, "Path
Computation Element Communication Protocol (PCECP)
Requirements and Protocol Extensions In Support of Global
Concurrent Optimization", draft-ietf-pce-global-concurrent-
optimization, work in progress.
[WSON-FRAME] Bernstein, G. and Lee, Y. (Editors), and W. Imajuku,
"Framework for GMPLS and PCE Control of Wavelength Switched
Optical Networks", draft-bernstein-ccamp-wavelength-
switched, work in progress.
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[ISIS-PCED] Le Roux, J. and JP. Vasseur, "IS-IS protocol extensions
for Path Computation Element (PCE) Discovery", draft-ietf-
pce-disco-proto-isis, work in progress.
[OSPF-PCED] Le Roux, J. and JP. Vasseur, "OSPF protocol extensions
for Path Computation Element (PCE) Discovery", draft-ietf-
pce-disco-proto-ospf, work in progress.
Authors' Addresses
Young Lee (Ed.)
Huawei Technologies
1700 Alma Drive, Suite 100
Plano, TX 75075, USA
Phone: (972) 509-5599 (x2240)
Email: ylee@huawei.com
Greg Bernstein (Ed.)
Grotto Networking
Fremont, CA, USA
Phone: (510) 573-2237
Email: gregb@grotto-networking.com
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