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PCE                                                              S. Peng
Internet-Draft                                                  Q. Xiong
Intended status: Standards Track                         ZTE Corporation
Expires: March 5, 2021                                            F. Qin
                                                            China Mobile
                                                       September 1, 2020


                 PCE TE Constraints for Network Slicing
                    draft-peng-pce-te-constraints-04

Abstract

   This document proposes a set of extensions for PCEP to support the TE
   constraints of network slicing during path computation, e.g, IGP
   instance, virtual network, specific application, color template and
   FA-id etc.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 5, 2021.

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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   include Simplified BSD License text as described in Section 4.e of




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   3.  PCEP Extensions for TE Constraints in Network Slicing . . . .   3
     3.1.  Source Protocol TLV . . . . . . . . . . . . . . . . . . .   3
     3.2.  Multi-topology TLV  . . . . . . . . . . . . . . . . . . .   4
     3.3.  The AII TLV . . . . . . . . . . . . . . . . . . . . . . .   5
     3.4.  Application Specific TLV  . . . . . . . . . . . . . . . .   6
     3.5.  The Color TLV . . . . . . . . . . . . . . . . . . . . . .   7
     3.6.  The FA-id TLV . . . . . . . . . . . . . . . . . . . . . .   8
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   [RFC5440] describes the Path Computation Element Protocol (PCEP)
   which is used between a Path Computation Element (PCE) and a Path
   Computation Client (PCC) (or other PCE) to enable computation of
   Multi-protocol Label Switching (MPLS) for Traffic Engineering Label
   Switched Path (TE LSP).  PCEP Extensions for the Stateful PCE Model
   [RFC8231] describes a set of extensions to PCEP to enable active
   control of MPLS-TE and Generalized MPLS (GMPLS) tunnels.  As depicted
   in [RFC4655], a PCE MUST be able to compute the path of a TE LSP by
   operating on the TED and considering bandwidth and other constraints
   applicable to the TE LSP service request.  The constraint parameters
   are provided such as metric, bandwidth, delay, affinity, etc.
   However these parameters can't meet the network slicing requirements.

   According to 5G context, network slicing is the collection of a set
   of technologies to support network service differentiation and
   meeting the diversified requirements from vertical industries.  The
   slices may be seen as virtual networks and partition the network
   resources into sub-topologies in transport network.  Multiple
   existing identifiers could be used to identify the virtual network
   resource and viewed as constraints of network slicing when PCE is
   deployed.

   A PCE always perform path computation based on the network topology
   information collected through BGP-LS [RFC7752].  BGP-LS can get



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   multiple link-state data from multiple IGP instance, or multiple
   virtual topologies from a single IGP instance.  It is necessary to
   restrict the PCE to a small topology scope during path computation
   for some special purpose.  BGP-LS can also get application specific
   TE attributes for a link, it is also necessary to restrict PCE to use
   TE attributes of specific application.  The PCE MUST take the
   identifier of slicing into consideration during path computation.

   This document proposes a set of extensions for PCEP to support the TE
   constraints for network slicing during path computation, e.g, IGP
   instance, virtual network, specific application, color template and
   FA-id etc.

2.  Conventions used in this document

2.1.  Terminology

   The terminology is defined as [RFC5440] and [RFC7752].

2.2.  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.

3.  PCEP Extensions for TE Constraints in Network Slicing

   As defined in [RFC5440] , the LSPA object is used to specify the LSP
   attributes to be taken into account by the PCE during path
   computation such as TE constraints.  This document proposes several
   new TLVs for the LSPA object to carry TE constraints in Network
   Slicing.

3.1.  Source Protocol TLV

   The Source Protocol TLV is optional and is defined to carry the
   source protocol constraint.

   In a PCReq message, a PCC MAY insert one Source Protocol TLV to
   indicate the source protocol that MUST be considered by the PCE.  The
   PCE will perform path computation based on the sub-topology
   identified by the specific source protocol.  The absence of the
   Source Protocol TLV MUST be interpreted by the PCE as a path
   computation request for which no constraints need be applied to any
   of the source protocols.




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   In a PCRep/PCInit/PCUpd message, the Source Protocol TLV MAY be
   carried so as to provide the source protocol information for the
   computed path.

   The format of the Source Protocol TLV is shown as 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Type=TBD1             |            Length=12          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Protocol-ID  |                  Reserved                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          Identifier                           |
       |                           (64 bits)                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                       Figure 1: Source Protocol TLV

   The code point for the TLV type is TBD1.  The TLV length is 12
   octets.

   Protocol-ID (8 bits): defined in [RFC7752] section 3.2.

   Reserved (24 bits): This field MUST be set to zero on transmission
   and MUST be ignored on receipt.

   Identifier (64 bits): defined in [RFC7752] section 3.2.

3.2.  Multi-topology TLV

   The Multi-topology TLV is optional and is defined to carry the multi-
   topology protocol constraint.

   In a PCReq message, a PCC MAY insert one Multi-topology TLV to
   indicate the sub-topology of an IGP instance that MUST be considered
   by the PCE.  The PCE will perform path computation based on the sub-
   topology identified by the specific Multi-Topology ID within a source
   protocol.  The absence of the Multi-topology TLV MUST be interpreted
   by the PCE as a path computation request for which no constraints
   need be applied to any of the multi-topologies.

   In a PCRep/PCInit/PCUpd message, the Multi-topology TLV MAY be
   carried so as to provide the Multi-topology information for the
   computed path.




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   The Multi-topology TLV MUST be carried after a Source Protocol TLV,
   if not it MUST be ignored.

   The format of the Multi-topology TLV is shown as Figure 2:


       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=TBD2             |            Length=4           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |R R R R|   Multi-Topology ID   |          Reserved             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                       Figure 2: Multi-topology TLV

   The code point for the TLV type is TBD2.  The TLV length is 4 octets.

   Multi-Topology ID (12 bits): Semantics of the IS-IS MT-ID are defined
   in Section 7.2 of [RFC5120].  Semantics of the OSPF MT-ID are defined
   in Section 3.7 of [RFC4915].  If the value is derived from OSPF, then
   the upper 9 bits MUST be set to 0.  Bits R are reserved and SHOULD be
   set to 0 when originated and ignored on receipt.

   Reserved (16 bits): This field MUST be set to zero on transmission
   and MUST be ignored on receipt.

3.3.  The AII TLV

   Administrative Instance Identifier (AII) is provided to specify the
   TE purpose within a virtual network as per
   [I-D.peng-lsr-network-slicing].  The AII TLV is optional and is
   defined to carry the AII constraint.

   In a PCReq message, a PCC MAY insert one AII TLV to indicate the
   global virtual network that MUST be considered by the PCE.  The PCE
   will perform path computation based on the intra-domain or inter-
   domain sub-topology identified by the specific AII, which is
   independent of routing protocols such as IGP/BGP.  The absence of the
   AII TLV MUST be interpreted by the PCE as a path computation request
   for which no constraints need be applied to any of the virtual
   network, i.e, a default AII (0) will be applied.

   In a PCRep/PCInit/PCUpd message, the AII TLV MAY be carried so as to
   provide the network slicing information for the computed path.

   The format of the AII TLV is shown as Figure 3:



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       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=TBD3             |            Length=4           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           AII                                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                             Figure 3: AII TLV

   The code point for the TLV type is TBD3.  The TLV length is 4 octets.

   AII (32 bits): indicate the AII information as defined in
   [I-D.peng-lsr-network-slicing].

3.4.  Application Specific TLV

   The Application Specific TLV is optional and is defined to carry the
   application specific constraints.

   In a PCReq message, a PCC MAY insert one Application Specific TLV to
   indicate the application that MUST be considered by the PCE.  The PCE
   will perform path computation using the specific application
   attributes.  The absence of the Application Specific TLV MUST be
   interpreted by the PCE as a path computation request for which no
   constraints need be applied to any of the Application Specific
   attributes.

   In a PCRep/PCInit/PCUpd message, the Application Specific TLV MAY be
   inserted so as to provide the Application Specific information for
   the computed path.

   The format of the Application Specific TLV is shown as Figure 4:

       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=TBD4             |            Length=8           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Standard Application ID                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |               User Defined Application ID                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                    Figure 4: Application Specific TLV




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   The code point for the TLV type is TBD4.  The TLV length is 8 octets.

   Standard Application ID: Represents a bit-position value for a single
   STANDARD application that is defined in the IANA "IGP Parameters"
   registries under the "Link Attribute Applications" registry
   [I-D.ietf-isis-te-app].

   User Defined Application ID: Represents a single user defined
   application which is a specific implementation.

3.5.  The Color TLV

   The Color TLV is optional and is defined to carry the color
   constraints.

   In a PCReq message, a PCC MAY insert one Color TLV to indicate the
   traffic engineering purpose that is recognized by both PCE and PCC
   with no conflict meaning.  The PCE will perform path computation
   based on the color template.  The same color template may be also
   defined at PCC and the existing constraints (i.e, metric, bandwidth,
   delay, etc) carried in the message MUST be ignored.  The absence of
   the Color TLV MUST be interpreted by the PCE as a path computation
   request for which traditional constraints that are contained in
   message need be applied.

   In a PCRep/PCInit/PCUpd message, the Color TLV MAY be inserted so as
   to provide the TE purpose information for the computed path, the PCC
   recognize the color value that match a local color-template.

   The format of the Color TLV is shown as Figure 5:


       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=TBD5             |            Length=4           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Color                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                            Figure 5: Color TLV

   The code point for the TLV type is TBD5.  The TLV length is 4 octets.

   Color (32 bits): indicate a TE template, 0 is invalid value.  It is
   consistent with the Color Extended Community defined in




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   [I-D.ietf-idr-tunnel-encaps], and color of SR policy defined in
   [I-D.ietf-spring-segment-routing-policy].

   Note that Color TLV defined in this document is used to represent a
   TE template, it can be suitable for any TE instance such as RSVP-TE,
   SR-TE, SR-policy.  [I-D.ietf-pce-segment-routing-policy-cp] has
   proposed the SR policy KEY (that also includes a color information)
   as an association group KEY to associate many candidate paths,
   however it is only for association purpose but not constraint purpose
   for path computation.

   A color template can be defined to contain existing constraints such
   as metric, bandwidth, delay, affinity parameters, and the sub-
   topology constraints above defined in this document.

3.6.  The FA-id TLV

   FA-id defined in [I-D.ietf-lsr-flex-algo] is a short mapping of SR
   policy color to optimize segment stack depth for the IGP area partial
   of the entire SR policy.  The overlay service that want to be carried
   over a particular SR-FA path must firstly let the SR policy supplier
   know that requirement.  There are two possible ways to map a color to
   an FA-id.  One is explicit mapping configuration within color
   template, the other is dynamicly replacing a long segment list to
   short FA segment by headend or controller once the constraints
   contained in the color-template equal to that contained in FAD.

   In addition to the above mapping behavior, it is also possible to
   merge the constraints contained in the color-template and constraints
   contained in FAD.  The merging behavior can be used to compute SR-TE
   path within a Flex-algo plane.

   In a PCReq message, a PCC MAY insert one FA-id TLV to indicate the
   above explicit FA-id mapping or merging.

   For mapping case, the PCE will perform path computation based on the
   FA-id.  In detailed, The PCE will check if there are connectivity
   within the corresponding Flex-algo plane to the destination.  If yes,
   the path computation result will be represented as segment list with
   a single prefix-SID@FA for intra-domain case, or several prefix-
   SID@FA for inter-domain case.

   For merging case, the PCE will perform path computation based on the
   total constraints combinded with the ones contained in FAD identified
   by FA-id and other ones contained in PCReq message.  The later
   constraints can get from color template or directly represent by a
   color.  In this case the computed path will be limited in the
   specific Flex-algo plane determined by link resource Including/



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   Excluding rules of FAD, and at the same time the path will also meet
   other constraints for the TE purpose within the Flex-algo plane.  The
   PCE can optimize the strictly path to a loosely path when a part of
   the strictly path is consistent with the algorithm based path, i.e,
   some consecutive adjacency SIDs can be replaced with a single
   algorithm based prefix Sid.

   In a PCRep/PCInit/PCUpd message, the FA-id TLV MAY be inserted so as
   to provide the FA plane information for the computed path.

   In general, the FA-id TLV is only meaningful for the domain (ingress
   domain) that headend node belongs to.  For inter-domain case,
   operator SHOULD ensure the FA-id configuration of different domain
   are same for an E2E slice, when he want to explicitly indicate FA-id
   in PCEP message, otherwise the PCE has to choose different FA-id for
   other domain as long as the contents of FAD is consistent with the
   one of ingress domain.

   The format of the FA-id TLV is shown as Figure 6:


       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=TBD6             |            Length=4           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    FA-id      |M|   Flags     |           Reserved            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                            Figure 6: FA-id TLV

   The code point for the TLV type is TBD6.  The TLV length is 4 octets.

   FA-id (8 bits): indicate an explicit FA-id information.

   Flags (8 bits): Currently only one flag, Flag-M, is defined.

   Flag-M: Indicate mapping behavior when unset, and merging behavior
   when set.

4.  Security Considerations

   TBA







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5.  Acknowledgements

   TBA

6.  IANA Considerations

   IANA is requested to make allocations from the registry, as follows:

         +-------+---------------------------+------------------+
         | Type  | TLV                       | Reference        |
         +-------+---------------------------+------------------+
         | TBD1  | Source Protocol TLV       | [this document]  |
         | TBD2  | Multi-topology TLV        | [this document]  |
         | TBD3  | AII TLV                   | [this document]  |
         | TBD4  | Application Specific TLV  | [this document]  |
         | TBD5  | Color TLV                 | [this document]  |
         | TBD6  | FA-id TLV                 | [this document]  |
         +-------+---------------------------+------------------+

                                  Table 1

7.  Normative References

   [I-D.ietf-idr-tunnel-encaps]
              Patel, K., Velde, G., Sangli, S., and J. Scudder, "The BGP
              Tunnel Encapsulation Attribute", draft-ietf-idr-tunnel-
              encaps-17 (work in progress), July 2020.

   [I-D.ietf-isis-te-app]
              Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and
              J. Drake, "IS-IS Application-Specific Link Attributes",
              draft-ietf-isis-te-app-19 (work in progress), June 2020.

   [I-D.ietf-lsr-flex-algo]
              Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
              A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex-
              algo-10 (work in progress), August 2020.

   [I-D.ietf-pce-segment-routing-policy-cp]
              Koldychev, M., Sivabalan, S., Barth, C., Peng, S., and H.
              Bidgoli, "PCEP extension to support Segment Routing Policy
              Candidate Paths", draft-ietf-pce-segment-routing-policy-
              cp-00 (work in progress), June 2020.








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   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture", draft-
              ietf-spring-segment-routing-policy-08 (work in progress),
              July 2020.

   [I-D.peng-lsr-network-slicing]
              Peng, S., Chen, R., and G. Mirsky, "Packet Network Slicing
              using Segment Routing", draft-peng-lsr-network-slicing-00
              (work in progress), February 2019.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <https://www.rfc-editor.org/info/rfc4655>.

   [RFC4915]  Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
              Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
              RFC 4915, DOI 10.17487/RFC4915, June 2007,
              <https://www.rfc-editor.org/info/rfc4915>.

   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120,
              DOI 10.17487/RFC5120, February 2008,
              <https://www.rfc-editor.org/info/rfc5120>.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <https://www.rfc-editor.org/info/rfc5440>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,
              <https://www.rfc-editor.org/info/rfc7752>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.





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   [RFC8231]  Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for Stateful PCE", RFC 8231,
              DOI 10.17487/RFC8231, September 2017,
              <https://www.rfc-editor.org/info/rfc8231>.

Authors' Addresses

   Shaofu Peng
   ZTE Corporation
   No.50 Software Avenue
   Nanjing, Jiangsu  210012
   China

   Email: peng.shaofu@zte.com.cn


   Quan Xiong
   ZTE Corporation
   No.6 Huashi Park Rd
   Wuhan, Hubei  430223
   China

   Email: xiong.quan@zte.com.cn


   Fengwei Qin
   China Mobile
   Beijing
   China

   Email: qinfengwei@chinamobile.com



















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