Network Working Group Y. Lee
Internet Draft Huawei
Intended status: Standard Track
Expires: June 2010 G. Bernstein
Grotto Networking
Jonas Martensson
Acreo
T. Takeda
NTT
T. Tsuritani
KDDI
December 15, 2009
PCEP Requirements for WSON Impairments
draft-lee-pce-wson-impairments-01.txt
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Abstract
This memo provides application-specific requirements for the Path
Computation Element communication Protocol (PCEP) for the support of
Impairments in Wavelength Switched Optical Networks (WSON). From a
path computation perspective, optical impairments are additional
constraints on the process of determining an optical light path.
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
1.1. WSON RWA Processes (no impairments).......................5
1.2. WSON IA-RWA Processes.....................................5
2. WSON PCE Architectures and Requirements........................7
2.1. RWA PCC to PCE Interface..................................8
2.1.1. A new RWA path request...............................8
2.1.2. An RWA path re-optimization request..................8
2.2. RWA-PCE to IV-PCE Interface...............................9
3. Manageability Considerations..................................10
3.1. Control of Function and Policy...........................10
3.2. Information and Data Models, e.g. MIB module.............11
3.3. Liveness Detection and Monitoring........................11
3.4. Verifying Correct Operation..............................11
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3.5. Requirements on Other Protocols and Functional Components11
3.6. Impact on Network Operation..............................11
4. Security Considerations.......................................12
5. IANA Considerations...........................................12
6. Acknowledgments...............................................12
7. References....................................................12
7.1. Normative References.....................................12
7.2. Informative References...................................13
Authors' Addresses...............................................14
Intellectual Property Statement..................................14
Disclaimer of Validity...........................................15
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 communication 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 for support of path computation in Wavelength Switched
Optical Networks (WSON) with impairments. 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
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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
not currently standardized. Therefore, assigning the proper
wavelength on a lightpath is an essential requirement in the optical
path computation process.
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.
One of the most basic questions in communications is whether one can
successfully transmit information from a transmitter to a receiver
within a prescribed error tolerance, usually specified as a maximum
permissible bit error ratio (BER). This generally depends on the
nature of the signal transmitted between the sender and receiver and
the nature of the communications channel between the sender and
receiver. The optical path utilized (along with the wavelength)
determines the communications channel.
The optical impairments incurred by the signal along the fiber and at
each optical network element along the path determine whether the BER
performance or any other measure of signal quality can be met for
this particular signal on this particular path. Given the existing
standards covering optical characteristics (impairments) and the
knowledge of how the impact of impairments may be estimated along a
path, [WSON-IMP] provides a framework for impairment aware path
computation and establishment utilizing GMPLS protocols and the PCE
architecture.
Some transparent optical subnetworks are designed such that over any
path the degradation to an optical signal due to impairments never
exceeds prescribed bounds. This may be due to the limited geographic
extent of the network, the network topology, and/or the quality of
the fiber and devices employed. In such networks the path selection
problem reduces to determining a continuous wavelength from source
to destination (the Routing and Wavelength Assignment problem).
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These networks are discussed in [WSON-Frame]. In other optical
networks, impairments are important and the path selection process
must be impairment-aware.
In this document we first review the processes for routing and
wavelength assignment (RWA) used when wavelength continuity
constraints are present. We then review the processes for optical
impairment aware RWA (IA-RWA). Based on selected process models we
then specify requirements for PCEP to support IA-RWA. Note that
requirements for PCEP to support RWA are specified in a separate
document [PCEP-RWA].
The remainder of this document uses terminology from [RFC4655].
1.1. WSON RWA Processes (no impairments)
In [WSON-Frame] three alternative process architectures were given
for performing routing and wavelength assignment. These are shown
schematically in Figure 1.
+-------------------+
| +-------+ +--+ | +-------+ +--+ +-------+ +---+
| |Routing| |WA| | |Routing|--->|WA| |Routing|--->|DWA|
| +-------+ +--+ | +-------+ +--+ +-------+ +---+
| Combined | Separate Processes Separate Processes
| Processes | WA performed in a
+-------------------+ Distributed manner
(a) (b) (c)
Figure 1 RWA process alternatives.
Detail description of each alternative can be found in [WSON-FRAME].
1.2. WSON IA-RWA Processes
In [WSON-IMP] impairments were addressed by adding an "impairment
validation" (IV) process. For approximate impairment validation three
process alternatives were given in [WSON-IMP] and are shown in Figure
2. Since there are many possible alternative combinations, these are
just three examples. Please note that the requirements for all
possible architectures can be reduced to the cases in Figure 3 in
section 2.
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+-----------------------------------+
| +--+ +-------+ +--+ |
| |IV| |Routing| |WA| |
| +--+ +-------+ +--+ |
| |
| Combined Processes |
+-----------------------------------+
(a)
+--------------+ +----------------------+
| +----------+ | | +-------+ +--+ |
| | IV | | | |Routing| |WA| |
| |candidates| |----->| +-------+ +--+ |
| +----------+ | | Combined Processes |
+--------------+ +----------------------+
(b)
+-----------+ +----------------------+
| +-------+ | | +--+ +--+ |
| |Routing| |------->| |WA| |IV| |
| +-------+ | | +--+ +--+ |
+-----------+ | Distributed Processes|
+----------------------+
(c)
Figure 2 Process flows for the three main approximate impairment
architectural alternatives.
These alternatives have the following properties and impact on PCEP
requirements in this document.
1. Combined IV and RWA Process - Here the processes of impairment
validation, routing and wavelength assignment are aggregated into
a single PCE. The requirements for PCC-PCE interaction with such a
combined IV-RWA process PCE is addressed in this document.
2. IV-Candidates + RWA Process - As explained in [WSON-IMP]
separating the impairment validation process from the RWA process
maybe necessary to deal with impairment sharing constraints. In
this architecture one PCE computes impairment candidates and
another PCE uses this information while performing RWA. The
requirements for PCE-to-PCE interaction of this architecture will
be addressed in this document.
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3. Routing + Distributed WA and IV - Here a standard path computation
(unaware of detailed wavelength availability or optical
impairments) takes place, then wavelength assignment and
impairment validation is performed along this path in a
distributed manner via signaling (RSVP-TE). This alternative
should be covered by existing or emerging GMPLS PCEP extensions
and does not present new WSON specific requirements.
2. WSON PCE Architectures and Requirements
In the previous section we reviewed various process architectures for
implementing RWA with and without regard for optical impairment. In
Figure 3 we reduce these alternatives to two PCE based
implementations. In Figure 3(a) we show the three processes of
routing, wavelength assignment and impairment validation accessed via
a single PCE. The implementation details of the interactions of the
processes are not subject to standardization in this case only the
PCC to PCE communications.
In Figure 3(b) the impairment validation process is implemented in a
separate PCE. Here the RWA-PCE acts as a coordinator and the PCC to
RWA-PCE interface will be the same as in Figure 3(a), however in this
case we have additional requirements for the RWA-PCE to IV-PCE
interface.
+-----------------------------------+
+-----+ | +--+ +-------+ +--+ |
| | | |IV| |Routing| |WA| |
| PCC |<----->| +--+ +-------+ +--+ |
| | | |
+-----+ | PCE |
+-----------------------------------+
(a)
+----------------------+ +--------------+
+-----+ | +-------+ +--+ | | |
| | | |Routing| |WA| | | IV |
| PCC |<----->| +-------+ +--+ |<--->| candidates |
| | | | | |
+-----+ | RWA-PCE (coordinator)| | IV-PCE |
+----------------------+ +--------------+
(b)
Figure 3 PCE architectures for RWA.
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2.1. RWA PCC to PCE Interface
The PCC to PCE interface of Figure 3(a) and the PCC to RWA-PCE
(coordinator) interface of Figure 3(b) are the same and we will cover
both in this section. The following requirements for these interfaces
are arranged by use cases:
2.1.1. A new RWA path request/reply
1. The PCReq Message MAY include some specific measure of optical
signal quality to which all feasible paths should conform:
o The BER limit
o Q factor
o OSNR + Margin
o PMD
If the PCReq Message does not include the BER limit and no default
BER limit is provisioned at the PCE then the PCE will return an error
specifying that a BER limit must be provided.
Margin" means "insurance" (e.g. 3~6dB) for suppliers and operators
against unpredictable degradation and unestimatable degradation due
to fiber nonlinearity and mismatched wavelength along the path.
2. The PCRep Message MUST include the route, wavelengths assigned to
the route and an indicator that says if the path conforms to the
required quality or not. In the case where a valid path is not
found, the PCRep Message MUST include why the path is not found
(e.g., no route, wavelength not found, BER failure, etc.)
2.1.2. An RWA path re-optimization request/reply
1. If a BER limit was required in the original path request then a
BER limit MUST be furnished in the re-optimization request.
Otherwise, furnishing a BER limit is optional. In the case where a
valid path is not found, the PCRep Message MUST include why the
path is not found (e.g., no route, wavelength not found, BER
failure, etc.)
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2.2. RWA-PCE to IV-PCE Interface
In [WSON-IMP] a sequence diagram for the interaction of the PCC, RWA-
PCE and IV-PCE of Figure 3(b) was given and is repeated here in
Figure 4. The interface between the PCC and the RWA-PCE (acting as
the coordinator) was covered in section 2.1.
+---+ +-------------+ +-----------------+
|PCC| |RWA-Coord-PCE| |IV-Candidates-PCE|
+-+-+ +------+------+ +---------+-------+
...___ (a) | |
| ````---...____ | |
| ```-->| |
| | |
| |--..___ (b) |
| | ```---...___ |
| | ```---->|
| | |
| | |
| | (c) ___...|
| | ___....---'''' |
| |<--'''' |
| | |
| | |
| (d) ___...| |
| ___....---''' | |
|<--''' | |
| | |
| | |
Figure 4 Sequence diagram for the interactions between PCC, RWA-
Coordinating-PCE and the IV-Candidates-PCE.
The interface between the RWA-Coord-PCE and the IV-Candidates-PCE is
specified by the following requirements:
1. The PCReq Message from the RWA-Coord-PCE to the IV-PCE MUST
include an indicator that more than one (candidate) path between
source and destination is desired.
2. The PCReq message from the RWA-Coord-PCE to the IV-Candidates-PCE
MUST include a limit on the number of optical impairment qualified
paths to be returned by the IV-PCE.
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3. The PCReq message from the RWA-Coord-PCE to the IV-Candidates-PCE
MAY include wavelength constraints. Note that optical impairments
are wavelength sensitive and hence specifying a wavelength
constraint may help limit the search for valid paths. This
requirement has been already covered in [PCEP-RWA] and is
presented here for an illustration purpose.
4. The PCRep Message from the IV-Candidates-PCE to RWA-Coord-PCE MUST
include a set of optical impairment qualified paths along with any
wavelength constraints on those paths.
5. The PCRep Message from the IV-Candidates-PCE to RWA-Coord-PCE MUST
indicate "no path found" in case where a valid path is not found.
6. The PCReq Message from the RWA-PCE to the IV-PCE MAY include one
or more specified paths and wavelengths that is to be verified by
the IV-PCE. This requirement is necessary when the IV-PCE is
allowed to verify specific paths.
Note that once the Combined RWA Process PCE receives the resulting
paths from the IV Candidates PCE, then the Combined RWA PCE computes
RWA for the IV qualified candidate paths and sends the result back to
the PCC.
3. Manageability Considerations
Manageability of WSON Routing and Wavelength Assignment (RWA) with
PCE must address the following considerations:
3.1. 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.
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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.
3.2. 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.
3.3. 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].
3.4. 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]
3.5. Requirements on Other Protocols and Functional Components
The PCE Discovery mechanisms ([RFC5089] and [RFC5088]) may be used to
advertise WSON RWA path computation capabilities to PCCs.
3.6. 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].
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4. 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.
5. IANA Considerations
A future revision of this document will present requests to IANA for
codepoint allocation.
6. 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.
7. References
7.1. 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.
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[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.
7.2. Informative References
[WSON-Frame] Bernstein, G. and Lee, Y. (Editors), and W. Imajuku, "A
Framework for the Control and Measurement of Wavelength
Switched Optical Networks (WSON) with Impairments
draft-bernstein-ccamp-wson-impairments-02.txt, work in
progress.
[WSON-IMP] Bernstein, G. and Lee, Y. (Editors), and D. Li, "Framework
for GMPLS and PCE Control of Wavelength Switched Optical
Networks", draft-bernstein-ccamp-wavelength-switched, work
in progress.
[PCEP-RWA] Y. Lee, G. Bernstein, J. Martensson, T. Takeda and T.
Otani, "PCEP Requirements for WSON Routing and Wavelength
Assignment", draft-lee-pce-wson-routing-wavelength, work in
progress.
[RFC5088] Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
Zhang, "OSPF Protocol Extensions for Path Computation
Element (PCE) Discovery", RFC 5088, January 2008.
[RFC5089] Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
Zhang, "IS-IS Protocol Extensions for Path Computation
Element (PCE) Discovery", RFC 5089, January 2008.
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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
Jonas Martensson
Acreo
Email:Jonas.Martensson@acreo.se
Tomonori Takeda
NTT Corporation
3-9-11, Midori-Cho
Musashino-Shi, Tokyo 180-8585, Japan
Email: takeda.tomonori@lab.ntt.co.jp
Takehiro Tsuritani
2-1-15 Ohara, Fujimino, Saitama, 356-8502, JAPAN
KDDI R&D Laboratories Inc.
Phone: +81-49-278-7806
Email: tsuri@kddilabs.jp
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