Mobile User Plane Evolution
draft-zzhang-dmm-mup-evolution-00
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Zhaohui (Jeffrey) Zhang , Keyur Patel | ||
| Last updated | 2022-03-06 | ||
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draft-zzhang-dmm-mup-evolution-00
dmm Z. Zhang
Internet-Draft Juniper Networks
Intended status: Informational K. Patel
Expires: 7 September 2022 Arrcus
6 March 2022
Mobile User Plane Evolution
draft-zzhang-dmm-mup-evolution-00
Abstract
[I-D.zzhang-dmm-5g-distributed-upf] describes evolution of mobile
user plane in 5G, including distributed UPFs and alternative user
plane implementations that some vendors/operators are pushing without
changing 3GPP architecture/signaling. Building on top of that, this
document further discusses potentially integrating UPF and Acess Node
(AN) in a future generation (xG) of mobile network.
This document is not an attempt to do 3GPP work in IETF. Rather, it
discusses potential integration of IETF/wireline and 3GPP/wireless
technologies - first among parties who are familiar with both areas
and friendly with IETF/wireline technologies. If the ideas in this
document are deemed reasonable, feasible and desired among these
parties, they can then be brought to 3GPP for further discussions.
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 7 September 2022.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://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 Revised BSD License text as
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. MUP Evolution in xG . . . . . . . . . . . . . . . . . . . . . 2
1.1. Integrated AN/UP Function . . . . . . . . . . . . . . . . 2
1.2. Separate AN/UP Functions Connected by Pseudo Wires . . . 4
1.2.1. Details on Pseudo Wire . . . . . . . . . . . . . . . 5
2. Security Considerations . . . . . . . . . . . . . . . . . . . 8
3. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
4. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Normative References . . . . . . . . . . . . . . . . . . 8
4.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. MUP Evolution in xG
[I-D.zzhang-dmm-5g-distributed-upf] describes evolution of mobile
user plane in 5G [_3GPP-23.501], including distributed UPFs and
alternative user plane implementations that some vendors/operators
are pushing without changing 3GPP architecture/signaling.
This section discusses potential MUP evolution in a future generation
(referred to as xG) of mobile networks. It does involve changes in
3GPP architecture and signaling, so the purpose of this section is to
share the ideas in IETF community first. If it gains consensus
within IETF community especially among mobile operators, then the
proposal may be brought to 3GPP community for further discussions.
1.1. Integrated AN/UP Function
In the distributed UPF model for 5G [I-D.zzhang-dmm-5g-distributed-
upf], AN and UPF are separate functions connected by N3 tunneling
over a short/internel transport connection. Routing happens on the
UPF between the DN and UEs over the N3 tunnels, and relay happens on
the AN between the N3 tunnels and AN protocol stack.
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With AN and UPF functions more and more disaggregated and virtualized
even in 5G, it is becoming more and more feasible and attractive to
integrate the AN and UPF functions, eliminating the N3 tunneling and
the relay on AN entirely. The combined function is referred to as
ANUP in this document, which does routing between DN and UEs over the
AN protocol stack directly:
N6
UE1 ANUP |
+---------+ |
|App Layer| routing |
+---------+ +--/---+---\-+|
|PDU Layer| | PDU | || PE1
+---------+ +------+IP+L2|| +----+--+
| | | | ||----+VRF1| |
| xG-AN | |xG-AN + or || +----+ |
| | | | || |VRFn| |
| Proto | |Proto +Ether|| +----+--+
| | | | || ( )
| Layers | |Layers+-----+| ( )
| | | | L1 || ( Transport )
+---------+ +------+-----+| ( )
| ( Network ) PE3
| ( +--+----+
UE2 ANUP | ( | |VRF1|
+---------+ | ( | |----+
|App Layer| routing | ( | |VRFn|
+---------+ +--/---+---\-+| ( +--+----+
|PDU Layer| | PDU | || ( )
+---------+ +------+IP+L2|| ( )
| | | | || ( )
| xG-AN | |xG-AN + or || +----+--+
| | | | ||----+VRF1| |
| Proto | |Proto +Ether|| +----+ |
| | | | || |VRFn| |
| Layers | |Layers+-----+| +----+--+
| | | | L1 || PE2
+---------+ +------+-----+|
|
With this architecture, 3GPP and IETF technologies are applied where
they are best applicable: 3GPP technologies responsible for radio
access and IETF technologies for the rest. As IETF technologies
continue to evolve, they can be automatically applied in mobile
networks without any changes in 3GPP architecture/specification.
Some advantages of this new architecture include:
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* Any kind of tunnels can be used for the DN VPN, whether it is MPLS
or SRv6, w/o the overhead of UDP/GTP encapsulation compared to GTP
tunneling. Network slicing function is still supported (even with
current GTP tunneling the transport network need to instantiate
slices for N3/N9 tunnels as well).
* 5G-LAN and MEC become native applications (PDU sessions terminate
into the closest ANUP and routed/switched to various DNs).
* MBS becomes very simple - the ANUP gets the multicast traffic from
the DN and then use either shared radio bearer or individual
bearers to send to interested UEs.
Because the ANUP already implement the routing/switching functions,
even the PE functions (for the DN VPN) could be optionally integrated
into it, further streamlining end-to-end communication by reducing
NFs and connections between them.
1.2. Separate AN/UP Functions Connected by Pseudo Wires
There are still cases where separate AN/UP functions are desired/
required:
* An MNO may want to deploy one UPF for a cluster of ANs in
proximity in some scenarios/locations
* An MNO may support MVNOs who have their own UP functions but make
use of the hosting MNO's ANs
* Home Routed roaming requires separate HPLMN UPs and VPLMN ANs
All these still require tunneling between ANs and UPs, but the
tunneling can be achieved via IETF's Pseudo Wire technology [RFC3985]
as shown in the following diagram. Note that, using PW is just an
option - GTP can still be used if that is desired.
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UE1 AN
+---------+
|App Layer|
+---------+
|PDU Layer| relay
+---------+ +--/---+--\---+ Pseudo Wire
| | | | |--------------------------------+
| xG-AN | |xG-AN | PW | \
| | | | | \
| Proto | |Proto |Proto | +----+--+ \
| | | | | ( ) \
| Layers | |Layers|Layers| ( ) \
| | | | | ( Transport ) UP \
+---------+ +------+------+ ( ) | +
( Network ) PE3 | routing |
N6 ( +--+----+|+--/--+---\--+ |
UE2 ANUP | ( | |VRF1||| | PDU | |
+---------+ | ( | |----+||IP+L2+------+ |
|App Layer| routing | ( | |VRFn||| | | |
+---------+ +--/---+---\-+ | ( +--+----+|| or | PW +-+
|PDU Layer| | PDU | | | ( ) || | |
+---------+ +------+IP+L2| | ( ) ||Ether|Proto |
| | | | | | ( ) || | |
| xG-AN | |xG-AN + or | | +----+--+ ||-----|Layers|
| | | | +-+---+VRF1| | || L1 | |
| Proto | |Proto +Ether| | +----+ | |+-----+------+
| | | | | | |VRFn| | |
| Layers | |Layers+-----+ | +----+--+ N6
| | | | L1 | | PE2
+---------+ +------+-----+ |
|
On the AN, relay happens between the AN protocol stack and PW
protocol stack. On the UP (at the right side of the above diagram),
routing happens at PDU layer (over the PW that is stitched to the AN
protocol stack on the AN) between UE1 and N6 connection to VRF1 on
PE3. The UP is either one in HPLMN in Home Routed Roaming case (and
the AN is in the VPLMN), or one in VMNO (and the AN is in the hosting
MNO), or one for a cluster of ANs.
1.2.1. Details on Pseudo Wire
This section provides some details on how PWs are used for the AN-UP
tunneling.
From [RFC3985]:
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---------------------------------------------------------------------
This document an architecture for Pseudo Wire Emulation
Edge-to-Edge (PWE3) in support of [RFC3916]. It discusses the
emulation of services such as Frame Relay, ATM, Ethernet, TDM, and
SONET/SDH over packet switched networks (PSNs) using IP or MPLS. It
presents the architectural framework for pseudo wires (PWs), defines
terminology, and specifies the various protocol elements and their
functions.
…
PWs provide the following functions in order to emulate the behavior
and characteristics of the native service.
o Encapsulation of service-specific PDUs or circuit data arriving
at the PE-bound port (logical or physical).
o Carriage of the encapsulated data across a PSN tunnel.
o Establishment of the PW, including the exchange and/or
distribution of the PW identifiers used by the PSN tunnel
endpoints.
…
The payload is classified into the following generic types of native
data units:
o Packet
o Cell
o Bit stream
o Structured bit stream
---------------------------------------------------------------------
When applied to tunneling between AN and UP, the PW payload type is
"Packet" - IP packet or Ethernet frame (that is the over the SDAP
layer between UE and AN) for IP or Ethernet PDU session respectively.
In case of Unstructured PDU session type, the PW payload type would
be "Bit stream" or "Structured bit stream".
Also from [RFC3985]:
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---------------------------------------------------------------------
Figure 2 illustrates the network reference model for point-to-point
PWs.
|<-------------- Emulated Service ---------------->|
| |<------- Pseudo Wire ------>| |
| | |<-- PSN Tunnel -->| | |
| V V V V |
V AC +----+ +----+ AC V
+-----+ | | PE1|==================| PE2| | +-----+
| |----------|............PW1.............|----------| |
| CE1 | | | | | | | | CE2 |
| |----------|............PW2.............|----------| |
+-----+ ^ | | |==================| | | ^ +-----+
^ | +----+ +----+ | | ^
| | Provider Edge 1 Provider Edge 2 | |
| | | |
Customer | | Customer
Edge 1 | | Edge 2
| |
| |
Native service Native service
---------------------------------------------------------------------
The following explains the mapping to AN-UP tunneling:
* CE1 corresponds to a UE and PE1 corresponds to the AN
* The radio link between CE1/UE and PE1/AN is the AC in PW
architecture. PDU session is the Emulated Service. Pseudo Wire
corresponds to the AN-UP tunnel. TSN tunnel corresponds to the
UDP tunnel that transports N3/N9 in 5G.
* PE2 and CE2 together correspond to the UP. It could be viewed
that the PE2 provides AN function (with the PW corresponding to
the radio link) and CE2 provides the UP function.
* PE1 takes the PDU packet from UE (after decapsulate the SDAP
stack), which is treated as PW payload, and sends to PE2 over the
PW. PE2 decapsulates the PW encapsulation and exposes the PDU
(like that a gNB decapsulates the SDAP stack), which is then
terminated by CE2 (though PE2 and CE2 are integrated into a single
UP).
In 5G Home Routed roaming architecture, there is a pair of I-UPFs
between the two PLMNs - the N3 tunnel does not extend directly from a
VPLMN's AN to a HPLMN's UPF. The same concept also exists in VPN/PW
technology - the I-UPFs are comparable to a pair of ASBRs that
provide Option-B inter-AS VPN/PW services.
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2. Security Considerations
To be provided.
3. Acknowledgements
The authors thank Arda Akamn, Constantine Polychronopoulos, Sandeep
Patel and Shraman Adhikary for their review, comments and suggestions
to make this document and solution more complete.
4. References
4.1. Normative References
[RFC3985] Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
Edge-to-Edge (PWE3) Architecture", RFC 3985,
DOI 10.17487/RFC3985, March 2005,
<https://www.rfc-editor.org/info/rfc3985>.
4.2. Informative References
[_3GPP-23.501]
"System architecture for the 5G System (5GS), V17.3.0",
December 2021.
Authors' Addresses
Zhaohui Zhang
Juniper Networks
Email: zzhang@juniper.net
Keyur Patel
Arrcus
Email: keyur@arrcus.com
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