Internet Engineering Task Force T. Murakami, Ed.
Internet-Draft Arrcus, Inc
Intended status: Informational S. Matsushima
Expires: May 7, 2020 SoftBank
K. Ebisawa
Toyota Motor Corporation
P. Garvia
R. Shekhar
Cisco Systems, Inc.
November 4, 2019
User Plane Message Encoding
draft-murakami-dmm-user-plane-message-encoding-00
Abstract
This document defines the encoding of User Plane messages into
Segment Routing Header (SRH). The SRH carries the User Plane
messages over SRv6 Network.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 2
3. Conventions and Terminology . . . . . . . . . . . . . . . . . 3
4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. User Plane Message encoding into SRH . . . . . . . . . . . . 3
5.1. GTP-U Header format . . . . . . . . . . . . . . . . . . . 3
5.2. Encoding of Tags Field . . . . . . . . . . . . . . . . . 4
5.3. User Plane message Information Element Support . . . . . 5
5.4. Consideration of PSP case . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Consideration . . . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
3GPP defines User Plane messages. The User Plane messages support
in-band signaling for path and tunnel management. Currently, User
Plane messages are defined in TS 29.281 [TS29281].
When applying SRv6 (Segment Routing IPv6) to the user plane of mobile
networks based on draft-ietf-dmm-srv6-mobile-uplane
[I-D.ietf-dmm-srv6-mobile-uplane], User Plane messages must be
carried over SRv6 network. This document defines which User Plane
message must be encoded to SRv6 and also defines how to encode the
User Plane messages into SRH.
In addition, SRH is mandatory at the ultimate segment upon carrying
the User Plane messages because User Plane message is encoded into
SRH. Hence, this document considers how to deal with the encoding of
User Plane messages into SRH when PSP is applied that SRH is popped
out at the penultimate segment.
2. Requirements Language
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 RFC 2119 [RFC2119].
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3. Conventions and Terminology
SRv6: Segment Routing IPv6.
GTP-U: GPRS Tunneling Protocol User Plane.
UPF: User Plane Function.
SRH: IPv6 Segment Routing Header.
PSP: Penultimate Segment POP of the SRH.
USP: Ultimate Segment Pop of the SRH.
4. Motivation
3GPP User Plane needs to support the user plane messages associated
with a GTP-U tunnel defined in [TS29281]. In the case of SRv6 User
Plane [I-D.ietf-dmm-srv6-mobile-uplane], those messages are also
required when the user plane interworks with GTP-U.
Segment Routing Header (SRH) [I-D.ietf-6man-segment-routing-header]
is used for SRv6 User Plane. SRH is able to associate additional
information to the segments. The Tag field of SRH is capable to
indicate different properties within a SID. SRH TLV is capable to
provide meta-data to the endpoint node.
The above capability of SRH motivates us to map the user plane
messages into it because of the same encapsulation with the packets
of carrying client packets. It introduces no additional headers or
extension headers to be chained in the packet just for carrying the
user plane messages.
5. User Plane Message encoding into SRH
This section defines how to encode the User Plane messages into SRH
in order to carry the User Plane messages over SRv6 network.
5.1. GTP-U Header format
3GPP defines GTP-U Header format as shown below.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ver |P|R|E|S|N| Message Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tunnel Endpoint Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number | N-PDU Number | Next-Ext-Hdr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: GTP-U Header format
User Plane message type is encoded in Message Type field of GTP-U
Header. The following User Plane messages must be carried over SRv6
network at least. The value of each User Plane message type is
defined as shown below.
Echo Request: 1
Echo Reply: 2
Error Indication: 26
End Marker: 254
5.2. Encoding of Tags Field
The Segment Routing Header is defined in draft-ietf-6man-segment-
routing-header [I-D.ietf-6man-segment-routing-header]. This draft
defines 16 bits Tag field but does not define the format or use of
this Tag field in the Segment Routing Header.
The User Plane message type encoding is defined in TS 29.281
[TS29281]. Based on this definition, the User Plane message type
must be encoded into the Tag field in the Segment Routing Header in
order to indicate the type of the user plane messages for at least
Echo Request, Echo Reply, Error Indication or End Marker.
Only UPF must process the Tag field where the user plane message is
encoded. In addition, when the user plane message is encoded in the
Tag field, the UPF should not encode any segments in the Segment
Routing Header whose function modifies the Tag field value. Any
other transport router implementing SRv6 must ignore the Tag field
upon processing the Segment Routing Header.
The user plane messages must be encoded into the Tag filed as shown
below.
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0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| Reserved |B3|B2|B1|B0|
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Figure 2: Tag Field Encoding
Bit 0 [B0]: End Marker
Bit 1 [B1]: Error Indication
Bit 2 [B2]: Echo Request
Bit 3 [B3]: Echo Reply
End Marker, Echo Request and Echo reply messages do not require any
additional information elements. However, Error Indication message
requires the additional information elements like Tunnel Endpoint
Identifier Data IE, GSN Address, etc. These additional information
elements can be encoded into the SRH TLV that is defined in the next
section.
5.3. User Plane message Information Element Support
End Maker, Echo Request and Echo Reply messages do not require any
additional information elements. However, Error Indication message
requires additional 3GPP IEs (Information Element). These additional
information elements must be carried over SRv6 network as well.
However SRv6 SID has limited space only. Hence it cannot carry a lot
of information elements.
In order to carry more information elements, SRH TLV shall be
leveraged. SRH TLV is defined in draft-ietf-6man-segment-routing-
header [I-D.ietf-6man-segment-routing-header] in order to carry the
meta-data for the segment processing. In order to carry 3GPP IEs,
the new type named as "5GS Container" must be defined as the new SRH
TLV. The "5GS Container" can carry multiple 3GPP IEs with 1 TLV.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | 3GPP IE TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// 3GPP IE TLVs //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5GS Container TLV
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Type: to be assigned by IANA
Length: Length of 3GPP IE TLVs
3GPP IE TLVs: Multiple 3GPP IE TLV defined below
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Value //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3GPP IE TLV
Type: 3GPP IE Type defined by 3GPP
Length: Length of Value
Value: 3GPP IE value
5.4. Consideration of PSP case
This section considers PSP case where the SRH is popped out at the
penultimate segment.
In order to carry User Plane message over SRv6 network, SRH must be
sustained over entire SRv6 network because User Plane message type
and required information elements are encoded into SRH. If the
penultimate segment is popping out SRH, i.e., PSP, User Plane message
can not be carried in entire SRv6 network.
In order to avoid this problem, USP must be used in SRv6 network. In
this case, SRH is never popped out and User Plane message can be
sustained over entire SRv6 network. However, if PSP needs to be
enabled in SRv6 network, it is also a possible solution to encap
another SRH which carries User Plane message along with the outer
IPv6 or SRH.
6. Security Considerations
7. IANA Consideration
The type value of SRH TLV for 5GS Container must be assigned by IANA.
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8. Acknowledgements
9. References
9.1. 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>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <https://www.rfc-editor.org/info/rfc2460>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
9.2. Informative References
[]
Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", draft-ietf-6man-segment-routing-header-26 (work in
progress), October 2019.
[I-D.ietf-dmm-srv6-mobile-uplane]
Matsushima, S., Filsfils, C., Kohno, M., Camarillo, P.,
Voyer, D., and C. Perkins, "Segment Routing IPv6 for
Mobile User Plane", draft-ietf-dmm-srv6-mobile-uplane-06
(work in progress), September 2019.
[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
and E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996,
<https://www.rfc-editor.org/info/rfc1918>.
[RFC3513] Hinden, R. and S. Deering, "Internet Protocol Version 6
(IPv6) Addressing Architecture", RFC 3513,
DOI 10.17487/RFC3513, April 2003,
<https://www.rfc-editor.org/info/rfc3513>.
[TS29281] 3GPP, "General Packet Radio System (GPRS) Tunnelling
Protocol User Plane (GTPv1-U)", 2019,
<http://www.3gpp.org/ftp//Specs/
archive/29_series/29.281/29281-f60.zip>.
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Authors' Addresses
Tetsuya Murakami (editor)
Arrcus, Inc
2077 Gateway Place, Suite 400
San Jose
USA
Email: tetsuya@arrcus.com
Satoru Matsushima
SoftBank
1-9-1 Higashi-Shinbashi, Munato-ku
Tokyo
Japan
Email: satoru.matsushima@g.softbank.co.jp
Kentaro Ebisawa
Toyota Motor Corporation
Tokyo
Japan
Email: ebisawa@toyota-tokyo.tech
Pablo Camarillo Garvia
Cisco Systems, Inc.
Spain
Email: pcamaril@cisco.com
Ravi Shekhar
Cisco Systems, Inc.
USA
Email: ravishek@cisco.com
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