PCE Working Group Young Lee
Internet Draft Samsung
Intended Status: Standard track Haomian Zheng
Expires: September 2020 Huawei
Daniele Ceccarelli
Ericsson
Wei Wang
Beijing Univ. of Posts and Telecom
Peter Park
KT
Bin Young Yoon
ETRI
March 9, 2020
PCEP Extension for Distribution of Link-State and TE information for
Optical Networks
draft-lee-pce-pcep-ls-optical-09
Abstract
In order to compute and provide optimal paths, Path Computation
Elements (PCEs) require an accurate and timely Traffic Engineering
Database (TED). Traditionally this Link State and TE information has
been obtained from a link state routing protocol (supporting traffic
engineering extensions).
This document extends the Path Communication Element Communication
Protocol (PCEP) with Link-State and TE information for optical
networks.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with
the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
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This Internet-Draft will expire on September 9, 2020.
Copyright Notice
Copyright (c) 2020 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
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Table of Contents
1. Introduction ................................................ 3
1.1. Requirements Language .................................. 4
2. Applicability ............................................... 5
3. Requirements for PCEP extension ............................. 6
3.1. Reachable source-destination ........................... 6
3.2. Optical latency......................................... 7
4. PCEP-LS extension for Optical Networks ...................... 7
4.1. Node Attributes TLV .................................... 7
4.2. Link Attributes TLV .................................... 8
4.3. PCEP-LS for Optical Network Extension .................. 9
5. Security Considerations .................................... 10
6. IANA Considerations ........................................ 10
6.1. PCEP-LS Sub-TLV Type Indicators ....................... 10
7. References ................................................. 11
7.1. Normative References .................................. 11
7.2. Informative References ................................ 11
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Appendix A. Contributor Addresses ............................. 13
Author's Addresses ............................................ 13
1. Introduction
In Multiprotocol Label Switching (MPLS) and Generalized MPLS
(GMPLS), a Traffic Engineering Database (TED) is used in computing
paths for connection oriented packet services and for circuits. The
TED contains all relevant information that a Path Computation
Element (PCE) needs to perform its computations. It is important
that the TED should be complete and accurate anytime so that the PCE
can perform path computations.
In MPLS and GMPLS networks, Interior Gateway routing Protocols
(IGPs) have been used to create and maintain a copy of the TED at
each node. One of the benefits of the PCE architecture [RFC4655] is
the use of computationally more sophisticated path computation
algorithms and the realization that these may need enhanced
processing power not necessarily available at each node
participating in an IGP.
Section 4.3 of [RFC4655] describes the potential load of the TED on
a network node and proposes an architecture where the TED is
maintained by the PCE rather than the network nodes. However it does
not describe how a PCE would obtain the information needed to
populate its TED. PCE may construct its TED by participating in the
IGP ([RFC3630] and [RFC5305] for MPLS-TE; [RFC4203] and [RFC5307]
for GMPLS). An alternative is offered by [RFC7752].
[RFC7399] touches upon this issue:"It has also been proposed that
the PCE Communication Protocol (PCEP) [RFC5440] could be extended to
serve as an information collection protocol to supply information
from network devices to a PCE. The logic is that the network devices
may already speak PCEP and so the protocol could easily be used to
report details about the resources and state in the network,
including the LSP state discussed in Sections 14 and 15."
[RFC8231] describes a set of extensions to PCEP to provide stateful
control. A stateful PCE has access to not only the information
carried by the network's Interior Gateway Protocol (IGP), but also
the set of active paths and their reserved resources for its
computations. PCC can delegate the rights to modify the LSP
parameters to an Active Stateful PCE. This requires PCE to quickly
be updated on any changes in the Topology and TEDB, so that PCE can
meet the need for updating LSPs effectively and in a timely manner.
The fastest way for a PCE to be updated on TED changes is via a
direct interface with each network node and with incremental update
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from each network node. [S-PCE-GMPLS] specified the extensions to
apply stateful PCE to GMPLS-based networks.
[RFC8281] describes the setup, maintenance and teardown of PCE-
initiated LSPs under the stateful PCE model, without the need for
local configuration on the PCC, thus allowing for a dynamic network
that is centrally controlled and deployed. This model requires
timely topology and TED update at the PCE.
[PCEP-LS-Arch] proposes alternative architecture approaches for
learning and maintaining the Link State (and TE) information
directly on a PCE from network nodes as an alternative to IGPs and
BGP transport and investigate the impact from the PCE, routing
protocol, and network node perspectives.
[RFC6805] describes a Hierarchical PCE (H-PCE) architecture which
can be used for computing end-to-end paths for inter-domain MPLS
Traffic Engineering (TE) and GMPLS Label Switched Paths (LSPs).
Within the Hierarchical PCE (H-PCE) architecture [RFC6805], the
Parent PCE (P-PCE) is used to compute a multi-domain path based on
the domain connectivity information. A Child PCE (C-PCE) may be
responsible for a single domain or multiple domains, it is used to
compute the intra-domain path based on its domain topology
information.
[Stateful H-PCE] presents general considerations for stateful PCE(s)
in hierarchical PCE architecture. In particular, the behavior
changes and additions to the existing stateful PCE mechanisms
(including PCE-initiated LSP setup and active PCE usage) in the
context of networks using the H-PCE architecture.
[PCEP-LS] describes a mechanism by which Link State and TE
information can be collected from packet networks and shared with
PCE with the PCEP itself. This is achieved using a new PCEP message
format.
This draft describes an optical extension of [PCEP-LS] and explains
how encodings suggested by [PCEP-LS] can be used in the optical
network contexts.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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2. Applicability
There are three main applicability of this alternative proposed by
this draft:
- Case 1: Where there is IGP running in optical network but
there is a need for a faster link-state and TE resource
collection at the PCE directly from an optical node (PCC) via
a PCC-PCE interface.
o A PCE may receive an incremental update (as opposed to
the entire TE information of the node/link).
Note: A PCE may receive full information from IGP using
existing mechanism. In some cases, the convergence of full
link-state and TE resource information of the entire network
may not be appropriate for certain applications. Incremental
update capability will enhance the accuracy of the TE
information at a given time.
- Case 2: Where there is no IGP running in the optical network
and there is a need for link-state and TE resource collections
at the PCE directly from an optical node (PCC) via a PCC-PCE
interface.
- Case 3: Where there is a need for transporting abstract
optical link-state and TE information from child PCE and to a
parent PCE in H-PCE [RFC6805] and [Stateful H-PCE] as well as
for Physical Network Controller (PNC) to Multi-Domain Service
Coordinator (MDSC) in Abstraction and Control of TE Networks
(ACTN) [RFC8453].
Note: The applicability for Case 3 may arise as a consequence
of Case 1 and Case 2. When TE information changes occur in the
optical network, this may also affect abstracted TE
information and thus needs to be updated to Parent PCE/MSDC
from each child PCE/PNC.
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3. Requirements for PCEP extension
The key requirements associated with link-state (and TE)
distribution are identified for PCEP and listed in Section 4 of
[PCEP-LS]. These new functions required in PCEP to support
distribution of link-state (and TE) information are described in
Section 5 of [PCEP-LS]. Details of PCEP messages and related
Objects/TLVs are specified in Sections 8 and 9 of [PCEP-LS]. The key
requirements and new functions specified in [PCEP-LS] are equally
applicable to optical networks.
Besides the generic requirements specified in [PCEP-LS], optical
specific features also need to be considered in this document. As
connection-based network, there are specific parameters such as
reachable table, optical latency, wavelength consistency and some
other parameters that need to be included during the topology
collection. Without these restrictions, the path computation may be
inaccurate or infeasible for deployment, therefore these information
MUST be included in the PCEP.
The procedure on how the optical parameters are used is described in
following sections.
3.1. Reachable source-destination
The reachable source-destination node pair indicates that there are
a few number of OCh paths between two nodes. The reachability is
restricted by impairment, wavelength consistency and so on. This
information is necessary at PCE to promise the path computed between
source node and destination node is reachable. In this scenario, the
PCE should be responsible to compute how many OCh paths are
available to set up connections between source and destination node.
Moreover, if a set of optical wavelength is indicated in the path
computation request, the PCE should also determine whether a
wavelength of the set of preselected optical wavelength is available
for the source-destination pair connection.
To enable PCE to complete the above functions, the reachable
relationship and OMS link information need to be reported to PCE.
Once PCE detect that any wavelength is available, the corresponding
OMS link should be included in a lambda plane. Then this link can be
used for path computation in future.
Moreover, in a hierarchical PCE architecture, the information above
need to be reported from child PCE to parent PCE, who acts as a
service coordinator.
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3.2. Optical latency
It is a usual case that the PCC indicates the latency when
requesting the path computation. In optical networks the latency is
a very sensitive parameter and there is stricter requirement on
latency. Given the maximal number of OCh paths between source-
destination nodes, the PCE also need to determine how many OCh path
satisfies the indicated latency threshold.
There is usually high-performance algorithm running on the PCE to
guarantee the performance of the computed path. During the
computation, the delay factor may be converted into a kind of link
weight. After the algorithm provides a few candidate paths between
the source and destination nodes, the PCE SHOULD be capable to
selecting one shortest path by computing the total path propagation
delay.
Optical PCEs are embedded with optimization algorithm, e.g.,
shortest path algorithm, to improve the performance of computed
path.
4. PCEP-LS extension for Optical Networks
This section provides additional PCEP-LS extension necessary to
support optical networks. All Objects/TLVs defined in [PCEP-LS] are
applicable to optical networks.
4.1. Node Attributes TLV
Node-Attributed TLV is defined in Section 9.2.10.1 in [PCEP-LS] as
follows. This TLV is applicable for LS Node Object-Type as defined
in [PCEP-LS].
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Node Attributes Sub-TLVs (variable) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The following 'Node Attribute' sub-TLVs are valid for optical
networks:
+-----------+------------------+--------------+-------------------+
| Sub-TLV | Description | TLV/Sub-TLV | Length |Reference|
+-----------+------------------+--------------+---------+---------+
| TBD | Connectivity | 5/14 | variable|[RFC7579]|
| | Matrix | | |[RFC7580]|
| TBD | Resource Block | 6/1 | variable|[RFC7688]|
| | Information | | | |
| TBD | Resource Block | 6/2 | variable|[RFC7688]|
| | Accessibility | | | |
| TBD | Resource Block | 6/3 | variable|[RFC7688]|
| | Wavelength Const | | | |
| TBD | Resource Block | 6/4 | variable|[RFC7688]|
| | Pool State | | | |
| TBD | Resource Block | 6/5 | variable|[RFC7688]|
| | Shared Access | | | |
| | Wavelength Avail.| | | |
+------------------------------------------------------=----------+
4.2. Link Attributes TLV
Link-Attributes TLV is defined in Section 9.2.10.2 in [PCEP-LS] as
follows. This TLV is applicable for LS Link Object-Type as defined
in [PCEP-LS].
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Link Attributes Sub-TLVs (variable) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The following 'Link Attribute' sub-TLVs are valid for optical
networks:
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+-----------+-----------------+--------------+--------+----------+
| Sub-TLV | Description | TLV/Sub-TLV | Length |Reference |
| | | | | |
+-----------+-----------------+--------------+--------+----------+
| TBD | ISCD | 15 |Variable|[RFC4203] |
| | | | | |
| TBD | OTN-TDM SCSI | 15/1,2 |Variable|[RFC4203] |
| | | | |[RFC7138] |
| TBD | WSON-LSC SCSI | 15/1,2 |Variable|[RFC4203] |
| | | | |[RFC7688] |
| TBD | Flexi-grid SCSI | 15/1 |Variable|[RFC8363] |
| | | | | |
| TBD | Port Label | 34 |Variable|[RFC7579] |
| | Restriction | | |[RFC7580] |
| | | | |[RFC8363] |
+-----------+-----------------+--------------+--------+----------+
4.3. PCEP-LS for Optical Network Extension
This section provides additional PCEP-LS extension necessary to
support optical networks parameters discussed in Sections 3.1 and
3.2.
The link state information collection is usually done before the
path computation processing. The procedure can be divided into 1)
link state collection by receiving the corresponding topology
information in a periodical style; 2) path computation on PCE,
triggered by receiving the path computation request message from
PCC, and completed by transmitting a path computation reply with the
path computation result, per [RFC4655].
For OTN networks, max bandwidth available may be per ODU 0/1/2/3
switching level or aggregated across all ODU switching levels (i.e.,
ODUj/k).
For WSON networks, RWA information collected from NEs would be
utilized to compute light paths. The list of information can be
found in [RFC7688]. More specifically, the max bandwidth available
may be per lambda/frequency level (OCh) or aggregated across all
lambda/frequency level. Per OCh level abstraction gives more
detailed data to the P-PCE at the expense of more information
processing. Either the OCh-level or the aggregated level abstraction
in the RWA constraint (i.e., wavelength continuity) needs to be
taken into account by the PCE during path computation. Resource
Block Accessibility (i.e., wavelength conversion information) in
[RFC7688] needs to be taken into account in order to guarantee the
reliability for optical path computation.
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[Editor's Note: Encoding will be provided in the revision, including
RFC7688 RWA information]
5. Security Considerations
This document extends PCEP for LS (and TE) distribution including a
set of TLVs. Procedures and protocol extensions defined in this
document do not affect the overall PCEP security model. See
[RFC5440], [RFC8253]. The PCE implementation SHOULD provide
mechanisms to prevent strains created by network flaps and amount of
LS (and TE) information. Thus it is suggested that any mechanism
used for securing the transmission of other PCEP message be applied
here as well. As a general precaution, it is RECOMMENDED that these
PCEP extensions only be activated on authenticated and encrypted
sessions belonging to the same administrative authority.
6. IANA Considerations
This document requests IANA actions to allocate code points for the
protocol elements defined in this document.
6.1. PCEP-LS Sub-TLV Type Indicators
This document specifies a set of PCEP-LS Sub-TLVs. IANA is requested
to create a "PCEP-LS Sub-TLV Types" sub-registry in the "PCEP TLV
Type Indicators" for the sub-TLVs carried in the PCEP-LS TLV (Node
Attributes TLV and Link Attributes TLV).
+-----------+------------------+--------------+----------+
| Sub-TLV | Description | Ref Sub-TLV | Reference|
+-----------+------------------+--------------+----------+
| TBD | Connectivity | 5/14 | [RFC7579]|
| | Matrix | | [RFC7580]|
| TBD | Resource Block | 6/1 | [RFC7688]|
| | Information | | |
| TBD | Resource Block | 6/2 | [RFC7688]|
| | Accessibility | | |
| TBD | Resource Block | 6/3 | [RFC7688]|
| | Wavelength Const | | |
| TBD | Resource Block | 6/4 | [RFC7688]|
| | Pool State | | |
| TBD | Resource Block | 6/5 | [RFC7688]|
| | Shared Access | | |
| | Wavelength Avail.| | |
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| TBD | ISCD | 15 |[RFC4203] |
| | | | |
| TBD | OTN-TDM SCSI | 15/1,2 |[RFC4203] |
| | | |[RFC7138] |
| TBD | WSON-LSC SCSI | 15/1,2 |[RFC4203] |
| | | |[RFC7688] |
| TBD | Flexi-grid SCSI | 15/1 |[RFC8363] |
| | | | |
| TBD | Port Label | 34 |[RFC7579] |
| | Restriction | |[RFC7580] |
| | | |[RFC8363] |
+-----------+------------------+--------------+----------+
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.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, October 2008.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
March 2009.
[RFC7688] Lee, Y., Ed., and G. Bernstein, Ed., "GMPLS OSPF
Enhancement for Signal and Network Element Compatibility
for Wavelength Switched Optical Networks", RFC 7688,
November 2015.
[RFC8174] B. Leiba, "Ambiguity of Uppercase vs Lowercase in RFC 2119
Key Words", RFC 8174, May 2017.
7.2. Informative References
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630, September
2003.
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[RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, October 2005.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC5307] Kompella, K., Ed., and Y. Rekhter, Ed., "IS-IS Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 5307, October 2008.
[RFC7752] Gredler, H., Medved, J., Previdi, S., Farrel, A., and
S.Ray, "North-Bound Distribution of Link-State and TE
information using BGP", RFC 7752, March 2016.
[S-PCE-GMPLS] X. Zhang, et. al, "Path Computation Element (PCE)
Protocol Extensions for Stateful PCE Usage in GMPLS-
controlled Networks", draft-ietf-pce-pcep-stateful-pce-
gmpls, work in progress.
[RFC7399] A. Farrel and D. king, "Unanswered Questions in the Path
Computation Element Architecture", RFC 7399, October 2015.
[RFC8453] D.Ceccarelli, and Y. Lee (Editors), "Framework for
Abstraction and Control of TE Networks", RFC453, August,
2018.
[RFC6805] A. Farrel and D. King, "The Application of the Path
Computation Element Architecture to the Determination of a
Sequence of Domains in MPLS and GMPLS", RFC 6805, November
2012.
[PCEP-LS-Arch] Y. Lee, D. Dhody and D. Ceccarelli, "Architecture and
Requirement for Distribution of Link-State and TE
Information via PCEP", draft-leedhody-teas-pcep-ls, work
in progress.
[PCEP-LS] D. Dhody, Y. Lee and D. Ceccarelli "PCEP Extension for
Distribution of Link-State and TE Information.", work in
progress, September 21, 2015
[RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "PCEP
Extensions for Stateful PCE", RFC8231, September 2017.
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[RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., Dhody, D.,
"PCEPS: Usage of TLS to Provide a Secure Transport for the
Path Computation Element Communication Protocol (PCEP)",
RFC8253, October 2017.
[RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "PCEP
Extensions for PCE-initiated LSP Setup in a Stateful PCE
Model", RFC8281, December 2017.
[Stateful H-PCE] D. Dhody, Y. Lee and D. Ceccarelli, "Hierarchical
Stateful Path Computation Element (PCE)", draft-ietf-pce-
stateful-hpce, work-in-progress.
[RFC8363] X. Zhang, H. Zheng, R. Casellas, O. Gonzalez de Dios, D.
Ceccarelli, "GMPLS OSPF Extensions in support of Flexi-
grid DWDM networks", RFC8363, May 2018.
Appendix A. Contributor Addresses
Dhruv Dhody
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
Email: dhruv.ietf@gmail.com
Author's Addresses
Young Lee
Samsung
Email: younglee.tx@gmail.com
Haomian Zheng
Huawei Technologies Co., Ltd.
Email: zhenghaomian@huawei.com
Daniele Ceccarelli
Ericsson
Torshamnsgatan,48
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Stockholm
Sweden
EMail: daniele.ceccarelli@ericsson.com
Wei Wang
Beijing University of Posts and Telecom
No. 10, Xitucheng Rd. Haidian District, Beijing 100876, P.R.China
Email: weiw@bupt.edu.cn
Peter Park
KT
Email: peter.park@kt.com
Bin Yeong Yoon
ETRI
Email: byyun@etri.re.kr
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