Segment Routing IPv6 for Mobile User-Plane
draft-matsushima-spring-dmm-srv6-mobile-uplane-02
The information below is for an old version of the document.
| Document | Type |
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|---|---|---|---|
| Authors | Satoru Matsushima , Clarence Filsfils , Miya Kohno , Daniel Voyer | ||
| Last updated | 2017-10-30 | ||
| Replaced by | draft-ietf-dmm-srv6-mobile-uplane, RFC 9433 | ||
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draft-matsushima-spring-dmm-srv6-mobile-uplane-02
SPRING and DMM S. Matsushima
Internet-Draft SoftBank
Intended status: Standards Track C. Filsfils
Expires: May 3, 2018 M. Kohno
Cisco Systems, Inc.
D. Voyer
Bell Canada
October 30, 2017
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.
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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
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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.
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.
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.
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.
Layer-2 Anchor:
Layer-2 anchor function provides SRv6 node the role to be
anchor point while mobile node move around within a serving
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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.
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.
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.
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.
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.
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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.
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.
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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., daniel.voyer@bell.ca, d.,
daniel.bernier@bell.ca, 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.
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[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: satoru.matsushima@g.softbank.co.jp
Clarence Filsfils
Cisco Systems, Inc.
Belgium
Email: cf@cisco.com
Miya Kohno
Cisco Systems, Inc.
Japan
Email: mkohno@cisco.com
Daniel Voyer
Bell Canada
Canada
Email: daniel.voyer@bell.ca
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