RFC 7449
Path Computation Element Communication Protocol (PCEP) Requirements for Wavelength Switched Optical Network (WSON) Routing and Wavelength Assignment
Okay bestie, this one is the RFC for how PCEP (the path computation protocol) should handle RWA in optical networks. It's an Informational document, not a Standards Track spec 🦋. It was published in February 2015 as RFC 7449 (ISSN 2070-1721), and it has no Obsoletes or Updates lines in its title block, so it doesn't replace or change any other RFC 💅.
The authors are the editors Y. Lee (Huawei) and G. Bernstein (Grotto Networking), plus J. Martensson (Acreo), T. Takeda (NTT), T. Tsuritani (KDDI), and O. Gonzalez de Dios (Telefonica) 👑.
Path Computation Element Communication Protocol (PCEP) Requirements for Wavelength Switched Optical Network (WSON) Routing and Wavelength Assignment ✨
Abstract 🌸
Okay so this part sets the scene. The memo lists the application-specific requirements for PCEP when it's used with Wavelength Switched Optical Networks (WSONs) 🧚. Lightpath provisioning in a WSON needs a Routing and Wavelength Assignment (RWA) process. From the path computation point of view, wavelength assignment means working out which wavelength can be used on each hop of a path, and it adds an extra routing constraint to lightpath computation 🌈. The requirements for PCEP extensions that cover optical impairments get their own separate document, so they're not in here 💜.
Status of This Memo 📜
This document is not an Internet Standards Track specification. It's published for informational purposes 🎀.
It's a product of the Internet Engineering Task Force (IETF), it represents the consensus of the IETF community, and it went through public review and was approved for publication by the Internet Engineering Steering Group (IESG). Not every IESG-approved document is a candidate for any level of Internet Standard, so check Section 2 of RFC 5741 for the details 🍓.
For the current status, any errata, and how to give feedback, go to http://www.rfc-editor.org/info/rfc7449 🔥.
Copyright Notice 💖
Copyright (c) 2015 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 publication. Please read these carefully, because they spell out your rights and restrictions for this document 📖. Code Components pulled out of this document must include the Simplified BSD License text, as described in Section 4.e of the Trust Legal Provisions. They're provided without warranty, as the Simplified BSD License describes 💅.
Table of Contents 🗂️
1. Introduction ....................................................3
2. WSON RWA Processes and Architecture .............................4
3. Requirements ....................................................5
3.1. Path Computation Type Option ...............................5
3.2. RWA Processing .............................................6
3.3. Bulk RWA Path Request/Reply ................................6
3.4. RWA Path Reoptimization Request/Reply ......................7
3.5. Wavelength Range Constraint ................................7
3.6. Wavelength Assignment Preference ...........................7
3.7. Signal-Processing Capability Restriction ...................8
4. Manageability Considerations ....................................8
4.1. Control of Function and Policy .............................8
4.2. Information and Data Models (e.g., MIB Module) .............9
4.3. Liveness Detection and Monitoring ..........................9
4.4. Verifying Correct Operation ................................9
4.5. Requirements on Other Protocols and Functional Components ..9
4.6. Impact on Network Operation ................................9
5. Security Considerations .........................................9
6. References .....................................................10
6.1. Normative References ......................................10
6.2. Informative References ....................................10
Acknowledgments....................................................11
Authors' Addresses.................................................111. Introduction 🦋
Okay, first things first: [RFC4655] is the one that defines the PCE-based architecture. It explains how a Path Computation Element (PCE) can compute Label Switched Paths (LSPs) in networks run by Multiprotocol Label Switching Traffic Engineering (MPLS-TE) and Generalized MPLS (GMPLS), whenever a Path Computation Client (PCC) asks for it 💅. A PCC can be any network component that makes that request. For example, it could be an optical switching element inside a Wavelength Division Multiplexing (WDM) network ✨. The PCE can live anywhere in the network. It might sit inside an optical switching element, a Network Management System (NMS), or an Operational Support System (OSS), or it could just be a standalone network server 🌸.
The Path Computation Element Communication Protocol (PCEP) is the protocol used between a PCC and a PCE, and it can also be used between cooperating PCEs 🧚. [RFC4657] lays out the common protocol requirements for PCEP. Any extra application-specific requirements get pushed into separate documents 🍓.
This document gives a set of application-specific PCEP requirements for path computation in Wavelength Switched Optical Networks (WSONs) 🌈. A WSON is a WDM-based optical network where switching is done selectively, based on the wavelength of an optical signal 💜.
The path in a WSON is called a lightpath. A lightpath can span several fiber links, and the path should be assigned a wavelength for each link 🔥.
A transparent optical network is made of optical devices that can switch but can't convert from one wavelength to another 🎀. In a transparent optical network, a lightpath uses the same wavelength across every fiber link it crosses. When that happens, the lightpath is said to satisfy the wavelength-continuity constraint 💖. Two lightpaths that share a fiber link can't be given the same wavelength, because doing so would make both signals interfere with each other 🙈. Polarization-based multiplexing and other extra multiplexing techniques aren't covered here, since the physical-layer aspects aren't standardized yet. So picking the right wavelength for a lightpath is a must-have step in optical path computation 👑.
When a switching node can do wavelength conversion, the wavelength-continuity constraint can be relaxed. A lightpath can then use different wavelengths on different links between origin and destination 🫶. Be aware though, wavelength converters might be limited for cost reasons, and the number of WDM channels a fiber can carry is limited too 💀. A WSON can be a mix of nodes that can't convert wavelengths, nodes with limited conversion, and nodes with full conversion, so wavelength assignment becomes an extra routing constraint that has to be considered in every lightpath computation ⭐.
In this document, we first look at the RWA processes used when wavelength continuity constraints are in play. Then we specify the PCEP requirements that support RWA. Requirements for optical impairments are handled in a separate document 🦋.
The rest of this document uses terminology from [RFC4655] 💜.
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. WSON RWA Processes and Architecture 🌈
In [RFC6163], three alternative process architectures were described for routing and wavelength assignment. They're shown in Figure 1, where R stands for Routing, WA for Wavelength Assignment, and DWA for Distributed Wavelength Assignment 💅.
+-------------------+
| +-------+ +--+ | +-------+ +--+ +-------+ +---+
| | R | |WA| | | R |--->|WA| | R |--->|DWA|
| +-------+ +--+ | +-------+ +--+ +-------+ +---+
| Combined | Separate Processes Separate Processes
| Process | WA performed in a
+-------------------+ distributed manner
(a) (b) (b')
Figure 1: RWA Process AlternativesThese alternatives have the following properties and impact on the PCEP requirements in this document ✨.
(a) Combined Process (R&WA) 💖
Path selection and wavelength assignment happen as a single process. The requirements for PCC-PCE interaction with a PCE that runs such a combined RWA process are covered in this document 🎀.
(b) Routing Separate from Wavelength Assignment (R+WA) 🌸
The routing process hands one or more potential paths to the wavelength assignment process, which then does the final path selection and wavelength assignment 🧚. The requirements for PCE-PCE interaction, where one PCE runs the routing process and another runs the wavelength assignment process, are not addressed in this document 🙈.
(b') Routing and Distributed Wavelength Assignment (R+DWA) 🍓
A standard path computation, which doesn't know the detailed wavelength availability, happens first. After that, wavelength assignment is done along this path in a distributed way, through signaling (RSVP-TE) 🌈. This alternative is a special case of R+WA. It should be covered by GMPLS PCEP extensions, and it doesn't bring any new WSON-specific requirements 💜.
The process architectures for RWA have now been reviewed. Figure 2 shows one typical PCE-based implementation, which is called the Combined Process (R&WA). In this architecture, routing and wavelength assignment are both reached through a single PCE. This is the base architecture that the requirements in this document are written from 🔥.
+----------------------------+
+-----+ | +-------+ +--+ |
| | | |Routing| |WA| |
| PCC |<----->| +-------+ +--+ |
| | | |
+-----+ | PCE |
+----------------------------+
Figure 2: Combined Process (R&WA) Architecture3. Requirements 💅
The requirements for the PCC-to-PCE interface in Figure 2 are specified in this section 👑.
Part 2 is coming next, bestie, so stay tuned for Section 3 and everything after it 🎀
3.1. Path Computation Type Option 💖
okay so a PCEP request MAY include the path computation type 🎀 and it can be:
- (a) Both RWA, or
- (b) Routing only.
this is needed so we can tell apart the routing with distributed wavelength assignment option we already have and combined RWA ✨. for the distributed option, wavelength assignment happens at each node of the route 🧚
3.2. RWA Processing 🌈
as we talked about in Section 2, a bunch of RWA processing options should be supported in a PCEP request/reply 💅
- (a) When the request is an RWA path computation type, the request MUST further include the wavelength assignment options. at minimum, these should be supported:
- (i) Explicit Label Control (ELC) [RFC3473]
- (ii) A set of recommended labels for each hop. The PCC can select the label based on local policy.
Note that option (ii) may also be used in R+WA or R+DWA.
- (b) In case of an RWA computation type, the response MUST include the wavelength(s) assigned to the path and an indication of which label assignment option has been applied (ELC or label set).
- (c) In the case where a valid path is not found, the response MUST include why the path is not found (e.g., network disconnected, wavelength not found, both, etc.). Note that 'wavelength not found' may include several sub-cases such as wavelength continuity not met, unsupported FEC/Modulation type, etc.
3.3. Bulk RWA Path Request/Reply 🫶
sending simultaneous path requests for "routing only" computation is already supported by the PCEP specification [RFC5440]. to stay consistent, these requirements get added too 💜
- (a) A PCEP request MUST be able to specify an option for bulk RWA path requests. a bulk path request lets you ask for a number of simultaneous RWA path requests at once 🍓
- (b) The PCEP response MUST include the path and the assigned wavelength for each RWA path request specified in the original bulk request.
3.4. RWA Path Reoptimization Request/Reply 🔁
this section has a few requirements for RWA path reoptimization processing in PCEP ✨
- (a) For a reoptimization request, the request MUST provide both the path and current wavelength to be reoptimized and MAY include the following options:
- (i) Reoptimize the path keeping the same wavelength(s)
- (ii) Reoptimize wavelength(s) keeping the same path
- (iii) Reoptimize allowing both the wavelength and the path to change
- (b) The corresponding response to the reoptimized request MUST provide the reoptimized path and wavelengths, even when the request asked for the path or the wavelength to remain unchanged.
- (c) In the case that the new path is not found, the response MUST include why the path is not found (e.g., network disconnected, wavelength not found, both, etc.). Note that 'wavelength not found' may include several sub-cases such as wavelength continuity not met, unsupported FEC/Modulation type, etc.
3.5. Wavelength Range Constraint 🌸
for any RWA computation type request, the requester (PCC) MUST be allowed to specify a restriction on the wavelengths to be used. the requester MAY use this option to restrict the assigned wavelength for explicit labels or label sets. this restriction may, for example, come from the tuning ability of a laser transmitter, any optical element, or a policy-based restriction 🔦
Note that the requester (e.g., PCC) is not required to furnish any range restrictions.
3.6. Wavelength Assignment Preference 🦋
in a network with wavelength conversion capabilities (e.g., sparse 3R regenerators), a request SHOULD be able to indicate whether a single, continuous wavelength should be allocated or not. in other words, the requesting PCC SHOULD be able to specify the precedence of wavelength continuity even if wavelength conversion is available 🙈
- (a) An RWA computation type request MAY include the requester preference for random assignment, descending order, ascending order, etc. A response SHOULD follow the requester preference unless it conflicts with the operator's policy.
- (b) A request for two or more paths MUST allow the requester to include an option constraining the paths to have the same wavelength(s) assigned. This is useful in the case of protection with a single transponder (e.g., 1+1 link disjoint paths). this one is giving protection energy 🛡️
3.7. Signal-Processing Capability Restriction 📡
signal-processing compatibility is a big deal for optical path computation 😭 the signal type for an end-to-end optical path must match at the source and at the destination.
The PCC MUST be allowed to specify the signal type at the endpoints (i.e., at the source and at the destination). at a minimum, these signal-processing capabilities should be supported:
- Modulation Type List
- FEC Type List
The PCC MUST also be allowed to state whether transit modification is acceptable for the above signal-processing capabilities.
4. Manageability Considerations 🛠️
manageability of WSON RWA with PCE must address the following considerations.
4.1. Control of Function and Policy 🎛️
in addition to the parameters already listed in Section 8.1 of [RFC5440], a PCEP implementation SHOULD allow configuring the following PCEP session parameters on a PCC:
- The ability to send a WSON RWA request.
in addition to the parameters already listed in Section 8.1 of [RFC5440], a PCEP implementation SHOULD allow configuring the following PCEP session parameters on a PCE:
- The support for WSON RWA.
- The maximum number of bulk path requests associated with WSON RWA per request message.
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.
4.2. Information and Data Models 🗂️
as this document only concerns the requirements to support WSON RWA, no additional MIB module is defined in this document. however, the corresponding solution document will list the information that should be added to the PCE MIB module defined in [RFC7420].
4.3. Liveness Detection and Monitoring 💓
This document does not define any new mechanisms that imply any new liveness detection and monitoring requirements in addition to those already listed in Section 8.3 of [RFC5440].
4.4. Verifying Correct Operation ✅
This document does not define any new mechanisms that imply any new verification requirements in addition to those already listed in Section 8.4 of [RFC5440]
4.5. Requirements on Other Protocols and Functional Components 🧩
if PCE discovery mechanisms ([RFC5089] and [RFC5088]) were to be extended for technology-specific capabilities, advertising WSON RWA path computation capability should be considered.
4.6. Impact on Network Operation 🌐
This document does not define any new mechanisms that imply any new network operation requirements in addition to those already listed in Section 8.6 of [RFC5440].
5. Security Considerations 🔐
⚠️ this part is seriously important, bestie. please read it all 🥺
This document has no requirement for a change to the security models within PCEP [RFC5440]. 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.
solutions that address the requirements in this document need to verify that existing PCEP security mechanisms adequately protect the additional network capabilities and must include new mechanisms as necessary 🚨
6. References 📚
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
August 2006, <http://www.rfc-editor.org/info/rfc4655>.
[RFC5440] Vasseur, JP., Ed., and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
March 2009, <http://www.rfc-editor.org/info/rfc5440>.6.2. Informative References
[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
January 2003, <http://www.rfc-editor.org/info/rfc3473>.
[RFC4657] Ash, J., Ed., and J. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol Generic
Requirements", RFC 4657, September 2006,
<http://www.rfc-editor.org/info/rfc4657>.
[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,
<http://www.rfc-editor.org/info/rfc5088>.
[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,
<http://www.rfc-editor.org/info/rfc5089>.
[RFC6163] Lee, Y., Ed., Bernstein, G., Ed., and W. Imajuku,
"Framework for GMPLS and Path Computation Element (PCE)
Control of Wavelength Switched Optical Networks (WSONs)",
RFC 6163, April 2011,
<http://www.rfc-editor.org/info/rfc6163>.
[RFC7420] Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
Hardwick, "Path Computation Element Communication Protocol
(PCEP) Management Information Base (MIB) Module", RFC
7420, December 2014,
<http://www.rfc-editor.org/info/rfc7420>.Acknowledgments 🙏
the authors would like to thank Adrian Farrel, Cycil Margaria, and Ramon Casellas for many helpful comments that greatly improved the content of this document 💖
Authors' Addresses 💌
Young Lee (editor)
Huawei Technologies
5340 Legacy Drive, Building 3
Plano, TX 75245
United States
Phone: (469) 277-5838
EMail: leeyoung@huawei.com
Greg Bernstein (editor)
Grotto Networking
Fremont, CA
United States
Phone: (510) 573-2237
EMail: gregb@grotto-networking.com
Jonas Martensson
Acreo
Isafjordsgatan 22
164 40 Kista
Sweden
EMail: Jonas.Martensson@acreo.se
Tomonori Takeda
NTT Corporation
3-9-11, Midori-Cho
Musashino-Shi, Tokyo 180-8585
Japan
EMail: tomonori.takeda@ntt.com
Takehiro Tsuritani
KDDI R&D Laboratories, Inc.
2-1-15 Ohara Kamifukuoka Saitama, 356-8502
Japan
Phone: +81-49-278-7806
EMail: tsuri@kddilabs.jp
Oscar Gonzalez de Dios
Telefonica
Distrito Telefonica, ed. Sur 3, Pta 3, Ronda de la Comunicacion
Madrid, 28050
Spain
Phone: +34 913129647
EMail: oscar.gonzalezdedios@telefonica.comthat's the whole thing, bestie 🌈🎉👑
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