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Segment Routing based Solution for Hierarchical IETF Network Slices
draft-gong-teas-hierarchical-slice-solution-00

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This is an older version of an Internet-Draft whose latest revision state is "Active".
Authors Liyan Gong , Weiqiang Cheng , Changwang Lin , Mengxiao Chen , Jie Dong , Ran Chen , Yanrong Liang
Last updated 2022-07-10
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draft-gong-teas-hierarchical-slice-solution-00
Network Working Group                                           L. Gong    
Internet Draft                                                 W. Cheng
Intended status: Informational                             China Mobile
Expires: January 9, 2023                                         C. Lin
                                                                M. Chen
                                                   New H3C Technologies
                                                                J. Dong
                                                    Huawei Technologies
                                                                R. Chen
                                                        ZTE Corporation
                                                               Y. Liang
                                              Ruijie Networks Co., Ltd.
                                                           July 9, 2022

    Segment Routing based Solution for Hierarchical IETF Network Slices
              draft-gong-teas-hierarchical-slice-solution-00

Abstract

   This document describes a Segment Routing based solution for two-
   level hierarchical IETF network slices. Level-1 network slice is
   realized by associating Flex-Algo with dedicated sub-interfaces, and
   level-2 network slice is realized by using SR Policy with additional
   NRP-ID on data plane.

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
   Task Force (IETF). Note that other groups may also distribute
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on December 9, 2022.

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Copyright Notice

   Copyright (c) 2022 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 of this document. Please review these documents
   carefully, as they describe your rights and restrictions with
   respect to this document. Code Components extracted from this
   document must include Simplified BSD License text as described in
   Section 4.e of the Trust Legal Provisions and are provided without
   warranty as described in the Simplified BSD License.

Table of Contents

   1. Introduction...................................................2
      1.1. Requirements Language.....................................4
   2. Solution based on Segment Routing..............................4
   3. Example........................................................7
   4. Security Considerations.......................................11
   5. IANA Considerations...........................................11
   6. References....................................................11
      6.1. Normative References.....................................11
      6.2. Informative References...................................12
   Authors' Addresses...............................................14

1. Introduction

   Network slicing provides the ability to partition a physical network
   into multiple isolated logical networks of varying sizes,
   structures, and functions so that each slice can be dedicated to
   specific services or customers. [I-D.ietf-teas-ietf-network-slices]
   defines the term "IETF Network Slice" and establishes the general
   principles of network slicing in the IETF context. A Network
   Resource Partition (NRP) is a collection of resources in the
   underlay network. Each NRP is used as the underlay network construct
   to support one or a group of IETF network slice services.

   Hierarchical composition of IETF Network Slice means that a network
   slice can be further sliced into other network slices. Figure 1
   shows the architecture of two-level hierarchical IETF network
   slices. Network resources are partitioned in a hierarchical manner.
   Network resources of the underlay network are partitioned into
   multiple level-1 network slices. Then network resources of a level-1

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   network slice are further partitioned into multiple level-2 network
   slices.

                   +-------------------+
                   |      Underlay     |
                   |      Network      |
                   +---------+---------+
                             |
               +-------------+-------------+
               |                           |
               V                           V
         +-----------+               +-----------+
         |  Level-1  |               |  Level-1  |
         |  Network  |               |  Network  |
         |   Slice   |               |   Slice   |
         |     1     |               |     2     |
         +-----+-----+               +-----+-----+
               |                           |
        +------+------+             +------+------+
        |             |             |             |
        V             V             V             V
   +---------+   +---------+   +---------+   +---------+
   | Level-2 |   | Level-2 |   | Level-2 |   | Level-2 |
   | Network |   | Network |   | Network |   | Network |
   |  Slice  |   |  Slice  |   |  Slice  |   |  Slice  |
   |   1-1   |   |   1-2   |   |   2-1   |   |   2-2   |
   +---------+   +---------+   +---------+   +---------+

   Figure 1: Architecture of Two-level Hierarchical IETF Network Slices

   [I-D.dong-teas-hierarchical-ietf-network-slice] describes several
   possible scenarios of hierarchical IETF network slices. For example,
   level-1 can be industry slices which are used to deliver services
   for different vertical industries, and level-2 can be customer
   slices which are created to meet specific requirements of some or
   all of the customers within the corresponding industry of level-1.

   For the two-level hierarchical IETF network slices discussed in this
   document, the level-1 and level-2 network slices are both created
   and managed by the same operator, and they are used to provide
   services at different granularity.

   Segment Routing (SR) [RFC8402] is a source routing paradigm that
   explicitly indicates the forwarding path for packets at the ingress
   node. IETF network slices may be realized by using Segment Routing
   technologies.

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   This document proposes a Segment Routing based solution for two-
   level hierarchical IETF network slices. Level-1 network slice is
   realized by associating Flex-Algo with dedicated sub-interfaces, and
   level-2 network slice is realized by using SR Policy with additional
   NRP-ID on data plane.

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.

2. Solution based on Segment Routing

   Flex-Algo is a mechanism that allows IGP to compute the best paths
   along the constrained topology in a distributed manner. [I-D.ietf-
   lsr-flex-algo] specifies the way of using Segment Routing (SR)
   Prefix-SIDs and SRv6 locators to steer packets for Flex-Algo.

   As shown in Figure 2, each NRP for level-1 network slices is
   associated with a Flex-Algo. All the nodes belong to the level-1 NRP
   participate in the associated Flex-Algo. All the links belong to the
   level-1 NRP are included by the Admin Group rules of the associated
   Flex-Algo. Traffics of the level-1 network slices are steered into
   the Flex-Algo paths by using Prefix-SIDs or SRv6 locators, so that
   the corresponding level-1 NRPs will be used for forwarding.

   Segment Routing Policy (SR Policy) is an ordered list of segments
   that represent a source-routed policy [I-D.ietf-spring-segment-
   routing-policy]. The packets steered into an SR Policy carry an
   ordered list of segments associated with that SR Policy.

   In each NRP for level-2 network slices, the connectivity among PEs
   is achieved by SR Policies. The segment lists of these SR Policies
   composed with segments associated with the corresponding Flex-Algo
   of the level-1 NRP. So, the level-2 forwarding paths are restricted
   in the level-1 topology. Traffics of the level-2 network slice are
   steered into the SR Policies, so that the corresponding level-2 NRPs
   will be used for forwarding.

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      ----------------------------------------
     ( |PE|.............|PE|.............|PE| )
     (  --   SR Policy   --   SR Policy   --  )<--+
      ----------------------------------------    |
       Level-2 NRP 1-1                            |
                                                  |
      ----------------------------------------    |
     ( |PE|..............................|PE| )   |
     (  --           SR Policy            --  )<--+
      ----------------------------------------    |
       Level-2 NRP 1-2                            |
                                                  |
      -----------------------------------------   |
     ( |PE|.......|PE|........|PE|.......|PE|  )--+
    (   --:        --         :--         --    )
    (     :         -         :                 )<-------+
     (    :........|P|........:  Flex-Algo 128 )         |
      -----------------------------------------          |
       Level-1 NRP 1                                     |
                                                         |
      -----------------------------------------          |
     ( |PE|..................|PE|              )         |
    (   --:                  :--                )        |
    (    -:                  :-                 )<-------+
     (  |P|..................|P| Flex-Algo 129 )         |
      -----------------------------------------          |
       Level-1 NRP 2                                     |
                                                         |
      ----------------------------------------------     |
     ( |PE|.....-.....|PE|......    |PE|.......|PE| )    |
    (   --     |P|     --      :-...:--     -..:--   )   |
   (    :       -:.............|P|.........|P|        )--+
   (    -......................:-:..-       -         )
    (  |P|.........................|P|......:        )
     (  -                           -               )
      ----------------------------------------------
       Underlay Network

   Figure 2: Framework of Solution

   The network resources for the two-level network slices are also
   partitioned in a hierarchical manner.

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               Physical Interface 1
   +-------------------------------------------+
   |                                           |
   |  Layer-3 Sub-interface 1-1: NRP-1, 1Gbps  |
   |===========================================|
   |>>>>>> Queue 1-1-1: NRP-1-1, 100Mbps >>>>>>|
   |>>>>>> Queue 1-1-2: NRP-1-2, 200Mbps >>>>>>|
   |>>>>>>              ...              >>>>>>|
   |===========================================|
   |                                           |
   |  Layer-3 Sub-interface 1-2: NRP-2, 2Gbps  |
   |===========================================|
   |>>>>>> Queue 1-2-1: NRP-2-1, 100Mbps >>>>>>|
   |>>>>>> Queue 1-2-2: NRP-2-2, 200Mbps >>>>>>|
   |>>>>>>              ...              >>>>>>|
   |===========================================|
   |                                           |
   +-------------------------------------------+

   Figure 3: Hierarchical Network Resource Partition

   As shown in Figure 3, the bandwidth resource of a physical interface
   is partitioned in two levels.

   The level-1 NRPs are sliced by layer-3 sub-interfaces with dedicated
   bandwidth. The Admin Group of layer-3 sub-interface is included by
   the Flex-Algo which is associated with the level-1 NRP. Meanwhile,
   it is excluded or not included by irrelevant Flex-Algos. So, the
   topology of a level-1 network slice consists of a set of layer-3
   sub-interfaces with dedicated bandwidth of the relevant level-1 NRP.
   When the traffics are forwarded according to Prefix-SIDs or SRv6
   locators of the associated Flex-Algo, the corresponding bandwidth
   resources are used.

   The level-2 NRPs are sliced by HQoS queues with dedicated bandwidth
   under the layer-3 sub-interface of level-1 NRP. Since the Flex-Algo
   associated Prefix-SIDs or SRv6 locators are used as the data plane
   identifier of level-1 NRP, level-2 NRP needs to be identified by
   using an extra dimension. On both MPLS-SR and SRv6 data plane, there
   are several options for realizing level-2 NRP-ID, such as [I-D.ietf-
   6man-enhanced-vpn-vtn-id], [I-D.cheng-spring-srv6-encoding-network-
   sliceid], [I-D.decraene-mpls-slid-encoded-entropy-label-id], and [I-
   D.li-mpls-enhanced-vpn-vtn-id]. As mentioned above, the traffics of
   level-2 network slice are forwarded according to the segment list of
   SR Policy. Firstly, the outgoing interface of the Flex-Algo
   associated segment will be the layer-3 sub-interface of level-1 NRP.
   Then, the HQoS queue will be selected according to the level-2 NRP-

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   ID carried in the packets, and the bandwidth resource of level-2 NRP
   will be used.

   Each NRP can be used to support one or a group of network slice. If
   multiple level-1 network slices need to share the same level-1 NRP,
   those level-1 network slices should be associated to the same Flex-
   Algo, while a single level-1 NRP is still mapped to a single Flex-
   Algo. If multiple level-2 network slices need to share the same
   level-2 NRP, the SR Polices for those level-2 network slices should
   be associated to the same level-2 NRP-ID, and those level-2 network
   slices must belong to the same level-1 network slice, or different
   level-1 network slices which share the same level-1 NRP.

   In the typical per-industrial-per-customer scenario of two-level
   hierarchical network slices, NRP sharing among different slices may
   be unnecessary. One-to-one mapping between network slice and NRP may
   be easier for deployment.

3. Example

   The example network in Figure 4 is used for illustration.

     +---+     +---+     +---+
     |PE1|-----|P1 |-----|PE2|
     +---+     +---+     +---+
       |                   |
       |                   |
       |                   |
     +---+     |---|     +---+
     |P3 |-----|PE3|-----|P2 |
     +---+     |---|     +---+

   Figure 4: Example Network

   There are two level-1 network slices to be deployed, slice 1 for
   education and slice 2 for healthcare. The customers of education
   access from all PEs. The customers of healthcare access from PE1 and
   PE2.

   Under slice 1, two universities require separate slices for
   interconnections among branch campuses. University 1 needs
   interconnection between PE1 and PE2 and interconnection between PE1
   and PE3. University 2 needs interconnection between PE1 and PE2.
   Under slice 2, only one customer requires level-2 network slice.

   Assume that the mapping between network slice and NRP is one to one.
   The topology of NRPs for the above network slices is shown in Figure
   5.

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   Level-1 NRP 1 for Level-1 Network Slice 1:

      PE1-----P1------PE2
       |              |
       |              |
       |              |
      P3------PE3-----P2

   Level-1 NRP 2 for Level-1 Network Slice 2:

      PE1-----P1------PE2

   Level-2 NRP 1-1 for Level-2 Network Slice 1-1:

      PE1<----->PE2
        ^
        |
        +------>PE3

   Level-2 NRP 1-2 for Level-2 Network Slice 1-2:

      PE1<----->PE2

   Level-2 NRP 2-1 for Level-2 Network Slice 2-1:

      PE1<----->PE2

   Figure 5: Topology of NRPs

   The provider assigns Flex-Algo 128 and 129 respectively for the two
   level-1 NRPs. All nodes participate in Flex-Algo 128. Only PE1, P1
   and PE2 participate in Flex-Algo 129. Layer-3 sub-interfaces are set
   up for level-1 NRPs. HQoS queues under the layer-3 sub-interfaces
   are further set up for level-2 NRPs.

   Taking PE1 as an example, the network resource partition of link
   bandwidth is shown in Figure 6.

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   +---+           Physical Interface 1            +---+
   |   |-------------------------------------------|   |
   |   |  Layer-3 Sub-interface 1-1: NRP-1, 1Gbps  |   |
   |   |===========================================|   |
   |   |>>>>>> Queue 1-1-1: NRP-1-1, 100Mbps >>>>>>|   |
   |   |>>>>>> Queue 1-1-2: NRP-1-2, 200Mbps >>>>>>|   |
   |   |===========================================|   |
   |   |                                           |P1 |
   |   |  Layer-3 Sub-interface 1-2: NRP-2, 2Gbps  |   |
   |   |===========================================|   |
   |PE1|>>>>>> Queue 1-2-1: NRP-2-1, 100Mbps >>>>>>|   |
   |   |===========================================|   |
   |   |-------------------------------------------|   |
   |   |                                           +---+
   |   |
   |   |           Physical Interface 2            +---+
   |   |-------------------------------------------|   |
   |   |  Layer-3 Sub-interface 2-1: NRP-1, 1Gbps  |   |
   |   |===========================================|P3 |
   |   |>>>>>> Queue 2-1-1: NRP-1-1, 100Mbps >>>>>>|   |
   |   |===========================================|   |
   |   |-------------------------------------------|   |
   +---+                                           +---+

   Figure 6: Network Resource Partition on PE1

   Physical interface 1 on PE1 corresponds to link PE1-P1, and physical
   interface 2 corresponds to link PE1-P3.

   Under interface 1, there are two layer-3 sub-interfaces 1-1 and 1-2.
   Sub-interfaces 1-1 is used as NRP-1 with dedicated bandwidth for
   level-1 network slice 1. Using Admin Group rules, sub-interfaces 1-1
   is associated with Flex-Algo 128. Traffics of level-1 network slice
   1 are steered into Flex-Algo 128. When the packets are forwarded
   from PE1 to P1, sub-interfaces 1-1 is selected as the outgoing
   interface and associated bandwidth resource will be used. Similarly,
   sub-interface 1-2 is used as NRP-2 for level-1 network slice 2, and
   associated with Flex-Algo 129.

   Under layer-3 sub-interfaces 1-1, two HQoS queues 1-1-1 and 1-1-2
   are further used as NRP-1-1 and NRP-1-2, with dedicated bandwidth
   for level-2 network slice 1-1 and 1-2. These queues are associated
   with the NRP-ID. When packets are forwarded through sub-interfaces
   1-1, level-2 NRP-ID in the packets will be checked. If level-2 NRP-
   ID exists, the packet will be treated as level-2 network slice
   traffic, and will be forwarded using the associated queue with
   dedicated bandwidth for level-2 network slice. Similarly, HQoS queue
   1-2-1 is used as NRP-2-1 for level-2 network slice 2-1.

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   Under interface 2, only layer-3 sub-interface 2-1 for level-1
   network slice 1 is configured, along with HQoS queue 2-1-1 for
   level-2 network slice 1-1. NRPs for other network slices are not
   necessary, since the link PE1-P3 is not involved in their
   topologies.

   If a packet from university 1 at PE1 needs to be forwarded to
   university 2 at PE2, the level-1 network slice 1 for education will
   be used, as shown in Figure 7. PE1 encapsulates the packet with an
   outer IPv6 header, and the Destination Address in the outer header
   is End SID for PE2 associated with Flex-Algo 128. Along the path
   PE1->P1->PE2, the packet is forwarded through layer-3 sub-interface
   associated with Flex-Algo 128, using dedicated bandwidth for the
   level-1 network slice 1.

   If a packet from a branch campus of university 1 at PE1 needs to be
   forwarded to another branch campus of the same university at PE2,
   the level-2 network slice 1-1 for university 1 will be used, as
   shown in Figure 8. Assume that the level-2 NRP-ID is carried in HBH.
   PE1 encapsulates the packet with an outer IPv6 header, along with
   HBH and SRH. The SRH carries the segment-list of SR Policy to PE2,
   and the SIDs are all associated with Flex-Algo 128. The HBH carries
   the level-2 NRP-ID associated with level-2 network slice 1-1. Along
   the path PE1->P1->PE2, the packet is forwarded through the HQoS
   queue associated with the level-2 NRP-ID, under the layer-3 sub-
   interface associated with Flex-Algo 128. The dedicated bandwidth for
   level-2 network slice 1-1 will be used, other than sharing the
   bandwidth for level-1 network slice 1.

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                 +------------+     +------------+
                 |    IPv6    |     |    IPv6    |
                 | DA=End-PE2 |     | DA=End-PE2 |
                 |   (FA-128) |     |   (FA-128) |
   +-------+     +------------+     +------------+     +-------+
   |Payload| --> |   Payload  | --> |   Payload  | --> |Payload|
   +-------+ PE1 +------------+ P1  +------------+ PE2 +-------+

   Figure 7: Packet Forwarding of Level-1 Network Slice 1

                 +------------+     +------------+
                 |    IPv6    |     |    IPv6    |
                 +------------+     +------------+
                 |     HBH    |     |     HBH    |
                 |   NRP-1-1  |     |   NRP-1-1  |
                 +------------+     +------------+
                 |     SRH    |     |     SRH    |
                 |End.DT      |     |End.DT      |
                 |End.X-P1-PE2|     |End.X-P1-PE2|
                 |End.X-PE1-P1|     |End.X-PE1-P1|
                 |(FA-128)    |     |(FA-128)    |
   +-------+     +------------+     +------------+     +-------+
   |Payload| --> |   Payload  | --> |   Payload  | --> |Payload|
   +-------+ PE1 +------------+ P1  +------------+ PE2 +-------+

   Figure 8: Packet Forwarding of Level-2 Network Slice 1-1

4. Security Considerations

   TBD.

5. IANA Considerations

   This document has no IANA actions.

6. References

6.1. Normative References

   [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>.

   [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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   [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
             Decraene, B., Litkowski, S., and R. Shakir, "Segment
             Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
             July 2018, <https://www.rfc-editor.org/info/rfc8402>.

   [I-D.ietf-teas-ietf-network-slices] Farrel, A., Drake, J., Rokui,
             R., Homma, S., Makhijani, K., Contreras, L. M., and J.
             Tantsura, "Framework for IETF Network Slices", Work in
             Progress, Internet-Draft, draft-ietf-teas-ietf-network-
             slices-12, 30 June 2022,
             <https://www.ietf.org/archive/id/draft-ietf-teas-ietf-
             network-slices-12.txt>.

   [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-20 (work in progress), May 2022.

   [I-D.ietf-spring-segment-routing-policy] Filsfils, C., Talaulikar,
             K., Voyer, D., Bogdanov, A., and P. Mattes, "Segment
             Routing Policy Architecture", Work in Progress, Internet-
             Draft, draft-ietf-spring-segment-routing-policy-22, 22
             March 2022, <http://www.ietf.org/internet-drafts/draft-
             ietf-spring-segment-routing-policy-22.txt>.

6.2. Informative References

   [I-D.dong-teas-hierarchical-ietf-network-slice] Dong, J., and Z. Li,
             "Considerations about Hierarchical IETF Network Slices",
             Work in Progress, Internet-Draft, draft-dong-teas-
             hierarchical-ietf-network-slice-01, 7 March 2022,
             <http://www.ietf.org/internet-drafts/draft-dong-teas-
             hierarchical-ietf-network-slice-01.txt>.

   [I-D.ietf-6man-enhanced-vpn-vtn-id] Dong, J., Li, Z., Xie, C., Ma,
             C., and G. Mishra, "Carrying Virtual Transport Network
             (VTN) Identifier in IPv6 Extension Header", Work in
             Progress, Internet-Draft, draft-ietf-6man-enhanced-vpn-
             vtn-id-00, 5 March 2022, <http://www.ietf.org/internet-
             drafts/draft-ietf-6man-enhanced-vpn-vtn-id-00.txt>.

   [I-D.cheng-spring-srv6-encoding-network-sliceid] Cheng, W., Lin, C.,
             Gong, L., Zadok, S., and X. Wang, "Encoding Network Slice
             Identification for SRv6", Work in Progress, Internet-
             Draft, draft-cheng-spring-srv6-encoding-network-sliceid-
             04, 8 July 2022, <http://www.ietf.org/internet-
             drafts/draft-cheng-spring-srv6-encoding-network-sliceid-
             04.txt>.

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   [I-D.decraene-mpls-slid-encoded-entropy-label-id] Decraene B.,
             Filsfils, C., Henderickx W., Saad T., Beeram V., "Using
             Entropy Label for Network Slice Identification in MPLS
             networks", Work in Progress, Internet-Draft, draft-
             decraene-mpls-slid-encoded-entropy-label-id-04, 14 June
             2022, <http://www.ietf.org/internet-drafts/draft-decraene-
             mpls-slid-encoded-entropy-label-id-04.txt>.

   [I-D.li-mpls-enhanced-vpn-vtn-id] Li, Z. and J. Dong, "Carrying
             Virtual Transport Network Identifier in MPLS Packet", Work
             in Progress, Internet-Draft, draft-li-mpls-enhanced-vpn-
             vtn-id-02, 7 March 2022, <http://www.ietf.org/internet-
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Internet-Draft     Hierarchical Network Slice SR Solution     July 2022

Authors' Addresses

   Liyan Gong
   China Mobile
   Email: gongliyan@chinamobile.com
   
   Weiqiang Cheng
   China Mobile
   Email: chengweiqiang@chinamobile.com

   Changwang Lin
   New H3C Technologies
   Email: linchangwang.04414@h3c.com

   Mengxiao Chen
   New H3C Technologies
   Email: chen.mengxiao@h3c.com

   Jie Dong
   Huawei Technologies
   Email: jie.dong@huawei.com

   Ran Chen
   ZTE Corporation
   Email: chen.ran@zte.com.cn

   Yanrong Liang
   Ruijie Networks Co., Ltd.
   Email: liangyanrong@ruijie.com.cn

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