Re: [DMM] Review comments on draft-matsushima-spring-dmm-srv6-mobile-uplane-02

[Satoru Matsushima <[e-mail]>]

Thank you Sri, for your review.

> 1.) It will be useful to identify the key data plane features used today in conjunction with the tunnel based approach and how those features are impacted when using SRv6 user plane. 

Sure. But I’d just cite existing document which well described current approach. It would be sfc for mobile document as one of them:

https://tools.ietf.org/html/draft-ietf-sfc-use-case-mobility

But I couldn’t find tunneled path optimization and service chaining. So it seems to be explained in our I-D, do you think so?


> 2.) There are heartbeat protocols that is used for path check between the access and anchor.

Ok, that would be an OAM feature like ICMPv6 in SRv6. Will try to mention it.


> Assuming those mechanisms are still in use between the access and anchor, I am wondering how these failure events impact the SRv6 states? For exam   
> 3.) Discussion on definition of new SRv6 functions needed to support this architecture will help

Right. Those are End.TM and T.Tmap introduced for stateless interworking between existing user-plane and SRv6 user-plane. Why “statless” is that not to affect existing c-plane and to avoid more mobile state aware entities because one of DMM purposes is to get rid out of mobile state from DPNs as I understand.


> 4.) It will be good if this document sets the overall context, allowing additional drafts to focus on specific aspects.

Yes, while the revise work I found that at least IPv4 support would be good to explain in an additional draft. But in terms of overall context, it would be nice if we can have another document to explain that overall context in addition to this draft because it mentions specific solution already. I think I can help to work on that generic document in case some volunteers we can involve.

I’ll get back to following your comments on specific part of the draft.

Cheers,
--satoru



> 
> Please see inline for additional comments.
> 
> ---------------------------------------------------------
>                Segment Routing IPv6 for Mobile User-Plane
>            draft-matsushima-spring-dmm-srv6-mobile-uplane-02
> 
> Abstract
> 
>    This document discusses the applicability of SRv6 (Segment Routing
>    IPv6) to user-plane of mobile networks that SRv6 source routing
>    capability with its programmability can fulfill the user-plane
>    functions, such as access and anchor functions.  It takes advantage
>    of underlying layer awareness and flexibility to deploy user-plane
>    functions that enables optimizing data-path for applications.
>    Network slicing and an interworking way between SRv6 and existing
>    mobile user-plane are also discussed in this document.
> 
> 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
>    working documents as Internet-Drafts.  The list of current Internet-
>    Drafts is at http://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 May 3, 2018.
> 
> Copyright Notice
> 
>    Copyright (c) 2017 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
> 
> 
> 
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> 
> 
>    (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
>    2.  Conventions and Terminology . . . . . . . . . . . . . . . . .   3
>    3.  Motivations . . . . . . . . . . . . . . . . . . . . . . . . .   3
>    4.  Mobile User-Plane . . . . . . . . . . . . . . . . . . . . . .   3
>    5.  Segment Routing IPv6 for Mobile User-Plane Functions  . . . .   5
>    6.  SRv6 Functions and Behaviors for User-Plane . . . . . . . . .   6
>      6.1.  Per Session Segment for Basic User-Plane  . . . . . . . .   6
>        6.1.1.  Uplink  . . . . . . . . . . . . . . . . . . . . . . .   6
>        6.1.2.  Downlink  . . . . . . . . . . . . . . . . . . . . . .   7
>      6.2.  Aggregated Segment for Basic User-Plane . . . . . . . . .   8
>        6.2.1.  Uplink  . . . . . . . . . . . . . . . . . . . . . . .   8
>        6.2.2.  Downlink  . . . . . . . . . . . . . . . . . . . . . .   8
>      6.3.  Stateless Interworking  . . . . . . . . . . . . . . . . .   9
>      6.4.  Rate Limit Function . . . . . . . . . . . . . . . . . . .  10
>    7.  Network Slicing Considerations  . . . . . . . . . . . . . . .  11
>    8.  Control Plane Considerations  . . . . . . . . . . . . . . . .  11
>    9.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
>    10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
>    11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
>      11.1.  Normative References . . . . . . . . . . . . . . . . . .  12
>      11.2.  Informative References . . . . . . . . . . . . . . . . .  12
>    Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13
> 
> 1.  Introduction
> 
>    In mobile networks, mobility management systems provide connectivity
>    while mobile nodes move around.  While the control-plane of the
>    system signals movements of a mobile node, user-plane establishes
>    tunnel between the mobile node and anchor node over IP based backhaul
>    and core networks.
> 
>    This document discusses the applicability of SRv6 (Segment Routing
>    IPv6) to those mobile networks.  SRv6 provides source routing to
>    networks where operators can explicitly indicate route for the
>    packets from and to the mobile node.  SRv6 endpoint nodes act as
>    roles of anchor of mobile user-plane.
> 
> 
> 
> 
> 
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> 
> 2.  Conventions and Terminology
> 
>    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].
> 
>    All segment routing and SRv6 network programming terms are defined in
>    [I-D.ietf-spring-segment-routing] and
>    "[I-D.filsfils-spring-srv6-network-programming].
> 
> 3.  Motivations
> 
>    Today's and future applications are requiring highly optimized data-
>    path between mobile nodes and the entities of those applications in
>    perspectives of latency, bandwidth, etc,. However current
>    architecture of mobile management is agnostic about underlying
>    topologies of transport layer.  It rigidly fragments the user-plane
>    in radio access, core and service networks and connects them by
>    tunneling techniques through the user-plane functions such as access
>    and anchor nodes.  Those agnostic and rigidness make it difficult for
>    the operator to optimize the data-path.
> 
>    While the mobile network industry has been trying to solve that,
>    applications shift to use IPv6 data-path and network operators adopt
>    it as their IP transport as well.  
> SRv6 integrates both application
>    data-path and underlying transport layer in data-path optimization
>    aspects that does not require any other techniques.
> 
> 
> [Sri] May be worth rephrasing with more details.
> 
>    SRv6 source routing capability with programmable functions
>    [I-D.filsfils-spring-srv6-network-programming] could fulfills the
>    user-plane functions of mobility management.  It takes advantage of
>    underlying layer awareness and flexibility to deploy user-plane
>    functions.  Those are the motivations to adopt SRv6 for mobile user-
>    plane.
> 
> 4.  Mobile User-Plane
> 
>    This section describes user-plane using SRv6 for mobile networks.
>    This clarifies mobile user-plane functions to which SRv6 endpoint
>    applied.
> 
>    Figure 1 shows mobile user-plane functions which are connected
>    through IPv6-only networks.  In the Figure 1, an mobile node (MN)
>    connects to an SRv6 endpoint serving access point role for the MN.
>    When the endpoint receives packets from the MN, it pushes SRH to the
>    packets.  The segment list in the SRH indicates the rest of user-
>    plane segments which are L2 and L3 anchors respectively.  Then the
>    endpoint send the packets to the IPv6 network.  In opposite
> 
> 
> 
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> 
>    direction, when an SRv6 endpoint serving L3 anchor role for the MN
>    receives packets to it, the endpoint push SRH consist of the L2
>    anchor and access point segments to the packets.
> 
> [Sri] I realize the control-plane extensions are outside the scope of this work, but might be worth explaining how the CP influences the segment list generation at the endpoint. I am assuming the User Plan Anchor selection, the IP address allocation would influence this segment list selection. May be you want to cover this in Appendix section for PMIP-based and GTP-based control plane as examples. 
> 
> 
> 
>                                 User-plane
>                                 Function
>                                <L2 Anchor>
>                                 O------O
>                                 | SRv6 |
>                                 | End  |
>                                 | Point|
>                                 O------O
>               User-plane           ||           User-plane
>     [MN]      Function        _____||_____      Function
>       |     <Access Point>   /            \    <L3 Anchor>
>    ___v___     O------O     /              \     O------O     ________
>   /  Radio \   | SRv6 |    /                \    | SRv6 |    /        \
>  /  Access  \==| End  |===/     IPv6-Only    \===| End  |===/ Service  \
>  \    NW    /  | Point|   \      Network     /   | Point|   \    NW    /
>   \________/   O------O    \                /    O------O    \________/
>                             \              /
>                              \____________/
> 
> 
>                    Figure 1: Mobile User-plane with SRv6
> 
>    An SRv6 segment represents those each function, such as Access Point,
>    Layer-2 (L2) Anchor and Layer-3 (L3) Anchor.  This makes mobile
>    networks highly flexible to deploy any user-plane functions to which
>    nodes in user flow basis.  
> An SRv6 segment can represent a set of
>    flows in any granularity of aggregation even though it is just for a
>    single flow.
> 
> [Sri] May be some more explanation will greatly help
> 
>    Figure 2 shows that an SRv6 endpoint connects existing IPv4 mobile
>    user-plane, which is defined in [RFC5213] and [TS.29281].  An SRv6
>    segment in the endpoint represents interworking function which
>    enables interworking between existing access point and SRv6 anchor
>    segment, or SRv6 access point segment and existing anchor node.
> 
>    Existing mobile user-plane with IPv6 underlay is expected to be
>    widely deployed.  As IPv6 network should be interoperable with SRv6
>    endpoints can be accommodated on it, interworking with existing IPv6
>    network is out of scope of this document.
> 
> 
> 
> 
> 
> 
> 
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> 
>      ________                                                 _______
>     /        \    O------O                                   /       \
>    / Service  \===|L2/L3 |                                  / Service \
>    \    NW    /   |Anchor|         User-plane               \    NW   /
>     \________/    |Node  |         Function                  \_______/
>                   O------O       <Interworking>                  ||
>                       \\_______     O------O     ________     O------O
>                       /        \    | SRv6 |    /        \    | SRv6 |
>                      / Existing \===| End  |===/ IPv6-Only\===| End  |
>                      \  IPv4 NW /   | Point|   \  Network /   | Point|
>        [MN]           \________/    O------O    \________/    O------O
>         |             //                                         ||
>      ___v____    O------O                                     ___||__
>     / Radio  \   |Access|                                    / Radio  \
>    /  Access  \==|Point |                            [MN]~~~/  Access  \
>    \    NW    /  |Node  |                                   \    NW    /
>     \________/   O------O                                    \________/
> 
> 
> 
> 
> 
>            Figure 2: Interworking with Existing Mobile Networks
> 
>    The detail of SRv6 segments representing user-plane functions are
>    described in Section 5.
> 
> 5.  Segment Routing IPv6 for Mobile User-Plane Functions
> 
>    This section describes mobile user-plane functions to which SRv6 node
>    can apply SRv6 functions and behaviors so that the nodes configured
>    those segments can fulfills the user-plane functions.  Each function
>    consist of two segments which are uplink (UL) from mobile node to the
>    correspondent node, and downlink (DL) from the correspondent node to
>    mobile node.
> 
>    We support following mobile user-plane functions:
> 
>    Access Point:
> 
>          Access Point function provides SRv6 node the role to which
>          mobile node is connected directly.  eNodeB could be referenced
>          as an entity implementing the access point in 3GPP term.
> 
> 
> [Sri] Should the AP/eNB be impacted for supporting this architecture? Even though the air interface terminates on the AP, for all practical purposes the first-hop router has all the L2 awareness. Unless there is a need to look at the radio parameters/state (Ex: RSSI values ..etc) and if that can impact the SRv6 state machine on the endpoint, I wonder why the AP/eNB should have any SRv6 awareness. Or, may I am missing the point around "SRv6 node the role to which mobile node is connected directly.”. 
>    Layer-2 Anchor:
> 
>          Layer-2 anchor function provides SRv6 node the role to be
>          anchor point while mobile node move around within a serving
>          area which could be assumed as a layer-2 network.  Serving
>          Gateway (SGW) could be referenced as an entity implementing the
>          layer-2 anchor in 3GPP term.
> 
> 
> [Sri] Does micro-mobility (UE movement within the radio network) under the same L2 anchor has any implication on the SRv6 operation ? Can a L2 handoff trigger some change in SRv6 state machine? 
> The key question in my above two comments is where does SRv6 begin, at AP or at First-hope router? 
>    Layer-3 Anchor:
> 
>          Layer-3 anchor function provides SRv6 node the role to be
>          anchor point across a mobile network consists of multiple
>          serving areas.  Packet data network gateway (PGW) could be
>          referenced as an entity implementing the layer-3 anchor.
> 
> 
> 
>    Stateless Interworking:
> 
>          Stateless interworking function provides SRv6 node the role to
>          interworking between existing mobile user-plane and SRv6 mobile
>          user-plane.  It is expected that the endpoint of interworking
>          segment could be unaware from the control-plane of the mobility
>          management.  While there are combinations of interworking
>          either existing or SRv6 network in which user-plane functions
>          accommodate, interworking segment should cover all combinations
>          without mobility state.
> 
> 6.  SRv6 Functions and Behaviors for User-Plane
> 
>    This section describes SRv6 functions and behavior applied to mobile
>    user-plane roles by use cases.  Terminology of SRv6 endpoint
>    functions refers to [I-D.filsfils-spring-srv6-network-programming].
>    In addition to that, new SRv6 functions and behaviors are introduced
>    to cover some user cases.
> 
> 6.1.  Per Session Segment for Basic User-Plane
> 
>    In this use case, we assume that mobile user-plane consists of SRv6
>    segments per session basis.  We expect the user-plane functions as
>    same as existing ones except using SRv6.  That means it just provides
>    fundamental IPv6 connectivity for MNs and no advanced segment routing
>    features introduced to it.
> 
> 
> [Sri] What does per-session mean here? A mobile subscriber session with a specific IP address which is anchored on a UP Anchor?
> Will all IP flows (Ex: TCP/UDP) for a given subscriber and with a specific source IPv6 address, always have the  anchor (L3 endpoint)?
> 
> 6.1.1.  Uplink
> 
>    In uplink, SRv6 node applies following SRv6 end point functions and
>    transit behavior.
> 
>    Access Point:  T.Insert
> 
>    L2-Anchor:  End.B6
> 
>    L3-Anchor:  End.T
> 
> 
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> 
>    When the access point node receives a packet destine to "D::1" from a
>    mobile node "S::1", it does T.Insert process for the receiving
>    packets to push a SRH with SID list (A2::1, D::1) and sets SL=1.  The
>    access point node update DA to "A2::1" which indicates the UL
>    L2-Anchor SID and forward the packet.
> 
> 
> [Sri] Its good explain the above without impacting the AP.
>    The L2-anchor node of "A2::1" segment does End.B6 process for the
>    receiving packet according to the segment.  The node updates DA to
>    next UL L3-anchor segment "A3::1" associated with "A2::1".  In this
>    basic use case, just one UL L3-anchor SID with SL=0 is enough to do
>    it so that there is no need to push another SRH to the packet in that
>    PSP (Penultimate Segment Pop) operation.
> 
>    The L3-anchor node of "A3::1" segment does End.T process for the
>    receiving packet according to the SRH that the node updates DA to
>    D::1, decrement SL and lookup IPv6 table associated with "A3::1".  In
>    this basic use case, decremented SL is 0 so that the node does PSP
>    operation of popped out the SRH from the packet and forward it.
> 
> 6.1.2.  Downlink
> 
>    In downlink, SRv6 node applies following SRv6 end point functions and
>    transit behavior.
> 
>    L3-Anchor:  T.Insert
> 
>    L2-Anchor:  End.B6
> 
>    Access Point:  End.X
> 
>    When the L3-anchor node receives a packet destine to "S::1" from a
>    correspondant node "D::1", it does T.Insert process for the receiving
>    packets to push a SRH with SID list (A2::2, S::1) and sets SL=1.  The
>    access point node update DA to "A2::2" which indicates the DL
>    L2-Anchor SID and forward the packet.
> 
>    The L2-anchor node of "A2::2" segment does End.B6 process for the
>    receiving packet according to the segment.  The node updates DA to
>    next DL access point segment "A1::2" associated with "A2::2".  In
>    this basic use case, just one DL access point SID with SL=0 is enough
>    to do it so that there is no need to push another SRH to the packet
>    in that PSP (Penultimate Segment Pop) operation.
> 
>    The access point node of "A1::2" segment does End.X process for the
>    receiving packet according to the SRH that the node updates DA to
>    S::1, decrement SL and forward the packet to the mobile node through
>    its associated radio channel.  In this basic use case, decremented SL
> 
> 
> 
> 
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> 
>    is 0 so that the node does PSP operation of popped out the SRH from
>    the packet and forward it.
> 
> 6.2.  Aggregated Segment for Basic User-Plane
> 
>    We assume that basic user-plane as well as Section 6.1 here, however
>    this section describes that SRv6 nodes allocate an aggregated segment
>    for multiple sessions, not in per session basis.  Thank to IPv6 GUA,
>    there is no need to employ additional identifier to distinguish each
>    session.  This benefits SRv6 node allows to apply one segment to
>    mobile sessions which belong to same policy.
> 
> 
> [Sri] Some explanations on the assumption around “session" definition will help
> 6.2.1.  Uplink
> 
>    In uplink, SRv6 node applies following SRv6 end point functions and
>    transit behavior.
> 
>    Access Point:  T.Insert
> 
>    L2-Anchor:  End.B6
> 
>    L3-Anchor:  End.T
> 
>    When the access point node receives a packet destine to "D::1" from a
>    mobile node "S::1", it does T.Insert process for the receiving
>    packets to push a SRH with SID list (AG20::, D::1) and sets SL=1.
>    The access point node update DA to "AG20::" which indicates
>    aggregated UL L2-Anchor SID and forward the packet.
> 
>    The aggregated L2-anchor node of "AG20::" segment does End.B6 process
>    for the receiving packet according to the segment.  The node updates
>    DA to aggregated UL L3-anchor segment "AG30::" associated with
>    "AG20::".  In this basic use case, just one UL L3-anchor SID with
>    SL=0 is enough to do it so that there is no need to push another SRH
>    to the packet in that PSP (Penultimate Segment Pop) operation.
> 
>    The aggregated L3-anchor node of "AG30::" segment does End.T process
>    for the receiving packet according to the SRH that the node updates
>    DA to D::1, decrement SL and lookup IPv6 table associated with
>    "AG30::".  In this basic use case, decremented SL is 0 so that the
>    node does PSP operation of popped out the SRH from the packet and
>    forward it.
> 
> 6.2.2.  Downlink
> 
>    In downlink, SRv6 node applies following SRv6 end point functions and
>    transit behavior.
> 
> 
> 
> 
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> 
>    L3-Anchor:  T.Insert
> 
>    L2-Anchor:  End.B6
> 
>    Access Point:  End.X
> 
>    When the L3-anchor node receives a packet destine to "S::1" from a
>    correspondant node "D::1", it does T.Insert process for the receiving
>    packets to push a SRH with SID list (AG21::, S::1) and sets SL=1.
>    The access point node update DA to "AG21::2" which indicates the
>    aggregated DL L2-Anchor SID and forward the packet.
> 
>    The aggregated L2-anchor node of "AG21::" segment does End.B6 process
>    for the receiving packet according to the segment.  The node updates
>    DA to aggregated DL access point segment "AG11::" associated with
>    "AG21::".  In this basic use case, just one aggregated DL access
>    point SID with SL=0 is enough to do it so that there is no need to
>    push another SRH to the packet in that PSP (Penultimate Segment Pop)
>    operation.
> 
>    The aggregated access point node of "AG11::" segment does End.X
>    process for the receiving packet according to the SRH that the node
>    updates DA to S::1, decrement SL and forward the packet to the mobile
>    node through its associated radio channel.  In this basic use case,
>    decremented SL is 0 so that the node does PSP operation of popped out
>    the SRH from the packet and forward it.
> 
> 6.3.  Stateless Interworking
> 
>    SRv6 SID for stateless interworking function is encoding identifiers
>    of corresponding tunnel in existing network as argument of the SID.
>    This document define an SRv6 end function, "End.TM", and a transit
>    behavior "T.Tmap" using following SID encoding:
> 
> 
>                 +----------------------+------+-------+-------+
>                 |Locater of interwork  |  DA  |  SA   | Tun-ID|
>                 +----------------------+------+-------+-------+
>                         128-a-b-c          a      b       c
> 
> 
>                Figure 3: Stateless Interworking SID Encoding
> 
>    In SRv6 to existing network direction, an endpoint of interworking
>    allocates End.TM function to a SID prefix, say "T0::".  When the
>    endpoint receives packet and the active segment of the packet
>    indicates that SID prefix, the endpoint does End.TM process that pops
>    the SRH of the SID, and then the endpoint encaps the payload with the
> 
> 
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> 
>    encoded information in the SID which are tunnel identifier of tunnel
>    header, source and destination IPv4 address of IPv4 header described
>    in Figure 3.  Then the endpoint send out the packet to the existing
>    network along with its routing policy.
> 
>    In existing network to SRv6 network direction, existing network
>    allocates IPv4 address spaces routed to interworking SRv6 network.
>    SRv6 network allocates a domain-wise SID prefix for interworking
>    segments, say "T1::".  When a SRv6 endpoint connects to existing
>    network receives packet destined to the allocated IPv4 address, the
>    endpoint does T.Tmap behavior that decaps outer IPv4 and tunnel
>    header, and then pushs an SRH with the SID which consists of the
>    allocated SID prefix "T1::", source and destination addresses, and
>    tunnel identifier as described in Figure 3.  Then the endpoint send
>    out the packet to the SRv6 network along with its routing policy.
> 
>    In case of IPv4 flow packet over the user-plane, the endpoint does
>    IPv6 header encaps and decaps instead of SRH insert and pop process.
>    The IPv6 header includes interworking segment SID in the SRH.
> 
>    Noted that to make sure stateless interworking, entities of control-
>    plane in mobile management should cooperate with SRv6 user-plane
>    settings.  Further control-plane consideration is discussed in
>    Section 8.
> 
> 6.4.  Rate Limit Function
> 
>    Mobile user-plane requires rate-limit feature.  SID is able to encode
>    limiting rate as an argument in SID.  Multiple flows of packets
>    should have same group identifier in SID when those flows are in an
>    same AMBR group.  This helps to keep user-plane stateless.  That
>    enables SRv6 endpoint nodes which are unaware from the mobile
>    control-plane information.  Encoding format of rate limit segment SID
>    is following:
> 
> 
>                 +----------------------+----------+-----------+
>                 | Locater of rate-limit| group-id | limit-rate|
>                 +----------------------+----------+-----------+
>                           128-i-j            i          j
> 
> 
>                Figure 4: Stateless Interworking SID Encoding
> 
>    In case of j bit length is zero in SID, the node should not do rate
>    limiting unless static configuration or control-plane sets the limit
>    rate associated to the SID.
> 
> 
> [Sri] In addition to Rate Limiting, probably few other QoS elements have to supported here.
> 
> 
> 
> 
> Matsushima, et al.         Expires May 3, 2018                 [Page 10]
> Internet-Draft             SRv6-mobile-uplane               October 2017
> 
> 
> 7.  Network Slicing Considerations
> 
>    Mobile network may be required to create a network slicing that
>    represent a set of network resources and isolate those resource from
>    other slices.  User-plane functions represented as SRv6 segments
>    would be part of a slice.
> 
>    To represent a set of user-plane function segments for a slice,
>    sharing same prefix through those SIDs within the slice could be a
>    straightforward way.  SIDs in a network slice may include other type
>    of functions in addition to the mobile user-plane functions described
>    in this document, and underlay integration to meet SLA and quality
>    requirements.
> 
>    While network slicing has been discussed in the IETF and other
>    standardization bodies, what functionalities are required for network
>    slicing in mobile user-plane is further study item and to be
>    discussed.
> 
> 
> [Sri] I am not sure if slicing discussion is relevant here
> 
> 8.  Control Plane Considerations
> 
>    Mobile control-plane entities must allocate SIDs to user-plane
>    function segments in case of those entities are distributed to
>    accommodate in the SRv6 nodes, or those are separated from the
>    endpoint but each of them corresponds to each SRv6 node.  In latter
>    case, control-plane entity must advertise allocated SID to the
>    endpoint through some means which are out of scope of this document.
> 
>    Noted that in the case of aggregated segments for mobile user-plane
>    functions, allocated SIDs for the segments can be pre-configured to
>    SRv6 nodes.  The control-plane should utilize those SIDs to manage
>    mobility sessions especially when increasing number of sessions is
>    expected to hit the upper-limit of the user-plane nodes.
> 
>    When a centralized controller interfaces to mobile control-planes is
>    capable to allocate SIDs to the controlling SRv6 endpoints, the
>    mobile control-planes just need to indicate the endpoint nodes and
>    their user-plane functions to the controller.  In this case, the
>    controller must allocate appropriate SIDs for the user-plane roles to
>    the indicated SRv6 endpoints.  The controller must advertise
>    allocated SIDs to the endpoints.  To build centralized controller for
>    mobile user-plane is out of scope of this document.
> 
>    However, to indicate endpoints and their user-plane functions from
>    mobile control-plane to user-plane, the endpoint or the controller
>    could take advantage of [I-D.ietf-dmm-fpc-cpdp].  It provides
>    interface to the control-plane to manage the user-plane of mobile
>    networks.
> 
> 
> 
> Matsushima, et al.         Expires May 3, 2018                 [Page 11]
> Internet-Draft             SRv6-mobile-uplane               October 2017
> 
> 
>    In case of stateless interworking, SID allocating entity needs to be
>    aware SID prefix which interworking SRv6 endpoint and SRv6 domain
>    allocate discussed in Section 6.3.  The mobile control-plane also
>    need to allocate tunnel endpoint IPv4 address to which corresponding
>    interworking segment destined from existing user-plane that is also
>    discussed in Section 6.3.
> 
> 9.  Security Considerations
> 
>    TBD
> 
> 10.  IANA Considerations
> 
>    This document has no actions for IANA.
> 
> 11.  References
> 
> 11.1.  Normative References
> 
>    [I-D.filsfils-spring-srv6-network-programming]
>               Filsfils, C., Leddy, J., [e-mail], d.,
>               [e-mail], d., Steinberg, D., Raszuk, R.,
>               Matsushima, S., Lebrun, D., Decraene, B., Peirens, B.,
>               Salsano, S., Naik, G., Elmalky, H., Jonnalagadda, P.,
>               Sharif, M., Ayyangar, A., Mynam, S., Henderickx, W.,
>               Bashandy, A., Raza, K., Dukes, D., Clad, F., and P.
>               Camarillo, "SRv6 Network Programming", draft-filsfils-
>               spring-srv6-network-programming-02 (work in progress),
>               October 2017.
> 
>    [I-D.ietf-spring-segment-routing]
>               Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B.,
>               Litkowski, S., and R. Shakir, "Segment Routing
>               Architecture", draft-ietf-spring-segment-routing-13 (work
>               in progress), October 2017.
> 
>    [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>.
> 
> 11.2.  Informative References
> 
>    [I-D.ietf-dmm-fpc-cpdp]
>               Matsushima, S., Bertz, L., Liebsch, M., Gundavelli, S.,
>               Moses, D., and C. Perkins, "Protocol for Forwarding Policy
>               Configuration (FPC) in DMM", draft-ietf-dmm-fpc-cpdp-09
>               (work in progress), October 2017.
> 
> 
> 
> Matsushima, et al.         Expires May 3, 2018                 [Page 12]
> Internet-Draft             SRv6-mobile-uplane               October 2017
> 
> 
>    [RFC5213]  Gundavelli, S., Ed., Leung, K., Devarapalli, V.,
>               Chowdhury, K., and B. Patil, "Proxy Mobile IPv6",
>               RFC 5213, DOI 10.17487/RFC5213, August 2008,
>               <https://www.rfc-editor.org/info/rfc5213>.
> 
>    [TS.29281]
>               3GPP, , "General Packet Radio System (GPRS) Tunnelling
>               Protocol User Plane (GTPv1-U)", 3GPP TS 29.281 10.3.0,
>               September 2011.
> 
> Authors' Addresses
> 
>    Satoru Matsushima
>    SoftBank
>    Tokyo
>    Japan
> 
>    Email: [e-mail]
> 
> 
>    Clarence Filsfils
>    Cisco Systems, Inc.
>    Belgium
> 
>    Email: [e-mail]
> 
> 
>    Miya Kohno
>    Cisco Systems, Inc.
>    Japan
> 
>    Email: [e-mail]
> 
> 
>    Daniel Voyer
>    Bell Canada
>    Canada
> 
>    Email: [e-mail]
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Matsushima, et al.         Expires May 3, 2018                 [Page 13]
> 
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