dmm S. Homma
Internet-Draft K. Kawakami
Intended status: Standards Track NTT
Expires: September 19, 2018 D. Farinacci
lispers.net
March 18, 2018
Co-existence of 3GPP 5GS and Identifier Locator Separation Solution
draft-homma-dmm-5gs-id-loc-coexistence-00
Abstract
This document describes an approach to introduce Identifier Locator
Separation solution into 3GPP 5GS with low-impact on its
specification, and shows the features and considerations of this
approach.
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 3
2.1. Terms of LISP . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Terms of 5GS . . . . . . . . . . . . . . . . . . . . . . 4
3. Mechanism on Data Plane . . . . . . . . . . . . . . . . . . . 4
4. Mechanisms on Control Plane . . . . . . . . . . . . . . . . . 10
4.1. Pattern 1: Completely Separating . . . . . . . . . . . . 11
4.2. Pattern 2: Interworking with Mapping System as AF . . . . 11
4.3. Pattern 3: Conversing SMF to Mapping System . . . . . . . 11
5. Features Analysis . . . . . . . . . . . . . . . . . . . . . . 11
5.1. Benefits . . . . . . . . . . . . . . . . . . . . . . . . 11
5.2. Issues . . . . . . . . . . . . . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 12
9. Informative References . . . . . . . . . . . . . . . . . . . 12
Appendix A. Case Studies . . . . . . . . . . . . . . . . . . . . 14
A.1. UE-2-UE Communication . . . . . . . . . . . . . . . . . . 14
A.1.1. Case 1: UEs allocated different dUPF . . . . . . . . 14
A.1.2. Case2: UEs allocated the same xTR . . . . . . . . . . 16
A.1.3. Consideration of Case that UE Moves to under Another
xTR . . . . . . . . . . . . . . . . . . . . . . . . . 17
A.2. UE-2-dDN Communication . . . . . . . . . . . . . . . . . 17
A.2.1. Case 3: UE communicates with neighbor dDN . . . . . . 17
A.2.2. Case4: UE communicates with non-neighbor dDN . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
Identifier Locator Separation (ID-LOC) solutions, including LISP,
ILA, ILNP, etc, are technologies that provide new numbering spaces,
identifier of end point and locator for routing, within IP framework
and enables to make management of networks, devices, or sessions be
easier. ID-LOC solutions are also expected to be used for optimizing
user-plane of mobile netowrk
[I-D.bogineni-dmm-optimized-mobile-user-plane], and ways to introduce
ID-LOC systems into the next generation mobile network, especially it
often indicates 3GPP 5GS (5th Generation System), are considered in
the related IETF WGs.
On the other hand, the discussion of the architecture of 5GS Rel.15
including NG-RAN and 5GC (5th Generation Core) was completed on
December 2017, and thus it would be difficult to push an ID-LOC
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solution that requires major changes of the architecture or
specifications. From this reason, an approach that enables to
introduce an ID-LOC mechanism into 5GS without change of its
specifications and to support migration into ID-LOC native network
would be required. Here, ID-LOC native network means a network which
functionalities of ID-LOC mechanism are integrated into as a
fundamental forwarding mechanism.
The goal of this document is providing one of such approaches and
clarifying the features and benefits.
2. Definition of Terms
As a matter of convenience, this document uses the definitions of
LISP (Locator Identifier Separation Protocol) to express
functionalities regarding ID-LOC systems. The detailed
specifications of LISP are described in [RFC6830], [RFC6831],
[RFC6832], [RFC6833], [RFC6836], [RFC7215], [RFC8061], and [RFC8111].
Moreover, definitions and specifications of another approach to
introduce LISP into 3GPP 5GS is described in
[I-D.farinacci-lisp-mobile-network].
This document also referes definitions of 3GPP 5GS [TS.23.501-3GPP].
Some of such terms which are used in this document are listed in this
section.
2.1. Terms of LISP
Ingress/Egress Tunnel Router (xTR): An xTR is a LISP node that has
both Ingress Tunnel Router (ITR) and Egress Tunnel Router (ETR)
functionalities. An ITR is a router which forwards packets to the
ETR, which is assigned the appropriate RLOC, with some
encapsulation (such as LISP header) depending on the result of
EID-to-RLOC mapping. An ETR is a router and it has an RLOC. An
ETR strips the encapsulation attached by an ITR and forwards
packets depending on their EIDs. An xTR has interface to EID-to-
RLOC mapping system.
Endpoint Identifier (EID): An EID is an identifier of end point such
as UE or VM instance. An EID is a 32-bit (for IPv4) or 128-bit
(for IPv6) value used in the source and destination IP address
fields of an IP packet sent from an UE or a VM instance.
Routing Locator (RLOC): An RLOC is an IPv4 or IPv6 address of an xTR
(ETR).
Mapping System: A Mapping System is a system which stores EID-to-
RLOC mapping database. This system uses Map-Register, Map-
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Request, Map-Reply, and Map-Notify messages from xTRs to talk to
Map-Resolvers and Map-Servers that make up the Mapping System.
More details are described in [RFC6833].
EID-to-RLOC Cache: The EID-to-RLOC Cache is a short-lived, ondemand
table in an xTR (ITR) that stores, tracks, and is responsible for
timing out and otherwise validating EID-to-RLOC mappings.
EID-to-RLOC Database: The EID-to-RLOC Database is a global
distributed database that contains all known EID-to-RLOC mappings.
Each xTR (ETR) typically contains a small piece of the database.
In this document, each Mapping System has full of the database.
2.2. Terms of 5GS
User Plane Function (UPF): An UPF handles the user plane paths. An
UPF is connected to SMF with N4 interface. More detailed
information is described in [TS.23.501-3GPP]. This document
defines two types of UPF, Central UPF (cUPF) and Distributed UPF
(dUPF). Their features are described in Section 3
Uplink Classifier (ULCL): An ULCL is an UPF functionality that aims
at diverting Uplink traffic, based on filter rules provided by
SMF, towards Data Network (DN).
Data Network (DN): A DN is a network where network functions and
entities, including operator or 3rd party services, are deployed.
This document defines two types of DN, Central DN (cDN) and
Distributed DN (dDN). Their features are described in Section 3.
Radio Access Network (RAN): A RAN is an access network where radio
baarer sent by UEs traverse. A RAN encupsulate users' packets
with GTP-U.
Session Management Function (SMF): An SMF is a function which
provides control plane functionalities for handling user traffic.
Application Function (AF): An AF is a control plane functionality
and connected to SMF with Naf interfaces.
3. Mechanism on Data Plane
This approach achieves traffic forwarding with optimized path and
session continuity by using ID-LOC and ULCL for particular
communication including UE-2-UE or MEC (Mobile Edge Computing)
communication. ULCL is one of fundamental functions of 5GC Rel.15
and it provides functionalities of packet filtering and divert for
uplink packets sent by UEs.
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The overview of the assumed 5GC architecture of data plane where the
proposal approach works is shown in Figure 1. The details of
numbered interfaces in the figure are described in [TS.23.501-3GPP].
.--.
( )-.
.' cDN/ '
( Internet )
( -'
'-( )
'---'
|N6
+-----+-----+
| cUPF | ===
+-----+-----+ ^
|N9 |
,-----------------------+-----------------------. |
/ \ |
| Transport Network | |
\ / |
`----+---------------------------+--------------'
|N9 |N9 Connected
+-----+-----+ ,-----. +-----+-----+ ,-----. with
| dUPF#1 |N6 / \ | dUPF#2 |N6 / \ GTP-U
| [UL]+---| dDN#A | | [UL]+---| dDN#B |..
| [CL]| \ / | [CL]| \ / |
+-----+-----+ `-----' +-----+-----+ `-----' |
|N3 |N3 |
|
(( o )) (( o )) |
A A v
/-\ RAN /-\ RAN ===
/-|-\ /-|-\
| |
[ UE ] .. [ UE ] ..
dUPF: Distributed UPF
cUPF: Central UPF
dDN: Distributed DN
cDN: Central DN
Figure 1: Assumed 5GC Network Architecture
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This network has following features;
o A Central UPF (cUPF) is deployed at a connecting point to Central
DN (cDN). A cUPF becomes anchor point for UEs and it assigns IP
addresses for each UE. The traffic transmitted from UEs are
basically sent to the cUPF.
o Distributed UPFs (dUPFs) and Distributed DNs (dDNs) are deployed
and geographically distributed at user edge side. A unique
address space (it's not necessarily globally unique) is assigned
to dDN. When a dUPF forwards an UE's uplink packet, and if the
subnet of the destination address is the same as the one assigned
to dDN at proximity, then dUPF, with the help of ULCL, may divert
the packet to that dDN. Here, the ULCL identifies each
encapsulated uplink packet to be diverted, by checking if the
destination of the inner packet is one of IP addresses assigned
the dDN. A dUPF removes GTP-U header from the packets, and sends
them to dDN via N6. When dUPF receives packets from dDN, dUPF
encapsulates them with GTP-U header, and merges them into downlink
packets from cUPF. An overview of behaviors of dUPF and ULCL is
shown in Figure 2.
o Network topology between RAN and dUPF/cUPF adopts tree structure
and the section between RAN and dUPF and the section between dUPF
and cUPF are connected with GTP-U.
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GTP-U packets GTP-U packets
from cUPF to cUPF
| ^
| N9 |
| |
+----|------------|-----+
| | dUPF | | ,---------.
| v | | IP packet / \
| o<-----------------------------| |
| | | | | |
| | | | N6 | dDN |
| | +------+ | | |
| | | ULCL |------------->| |
| | +------+ | IP packet | |
| | ^ | \ /
+----|------------|-----+ `---------'
| |
| |
| N3 |
v |
GTP-U packets GTP-U packets
to UE from UE
Figure 2: Behaviors of dUPF and ULCL
In the proposal approach, an xTR is installed between dUPF and dDN.
xTRs are connected with a tunneling protocol (it may be LISP header
or other protocol such as SRv6
[I-D.ietf-6man-segment-routing-header]) and each xTR has connectivity
with one or more Mapping Systems. The overview is shown in Figure 3.
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.--.
( )-.
.' cDN/ '
( Internet )
( -'
'-( )
'---'
|N6 ,---------.
+-----+-----+ | Mapping |
| cUPF | | System |
+-----+-----+ `---------'
|N9 .
,-----------------------+----------------.---------.
/ Transport Network . . . . . . . . . . . . . . . \
| . . |
\ #===========================#=== /
`----+------------#--.-----------+------------#--.-'
|N9 # . |N9 # .
+-----+-----+ +-------+ +-----+-----+ +-------+
| dUPF#1 |N6 | | | dUPF#2 |N6 | |
| [UL]+---+ xTR#1 | | [UL]+---| xTR#2 |..
| [CL]| | | | [CL]| | |
+-----+-----+ +---+---+ +-----+-----+ +---+---+
|N3 | |N3 |
,-----. ,-----.
(( o )) / \ (( o )) / \
A | dDN#A | A | dDN#B |
/-\ RAN \ / /-\ RAN \ /
/-|-\ `-----' /-|-\ `-----'
| |
[ UE ] .. [ UE ] ..
===== : Tunnel connects xTRs
. . . : IF to Mapping System
Figure 3: Proposal Network Architecture
Each dUPF has a filter table of ULCL. Each filter table is
configured to mach addresses assigned within own network domain
(i.e., addresses for UEs assigned by cUPF) or assigned corresponding
with address space of some of dDN. UPFs monitor each uplink GTP-U
packet with its ULCL and divert it to the connected xTR with
decapsulation if the destination address of the inner packet matches
the table. When xTR receives a packet from the dUPF, it obtains RLOC
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which the destination of the packet (EID) belongs to by looking up
its own EID-to-RLOC mapping cache or querying it from the Mapping
System according ID-LOC mechanism. Then it sends the packet to
peered xTR indicated by the RLOC.
The detailed processing flow with LISP below as an example. In this
example, a Mapping System obtains location of each UE from SMF and
keeps its own EID-to-RLOC mapping database up to date. Each xTR
obtains EID-to-RLOC map information which isn't stored in the cache
by sending Map-Request to a Mapping System.
1. xTR (source xTR) receives a packet and identify the EID.
2. The source xTR looks up the EID from its own EID-to-RLOC mapping
cache.
3. If there is an entry which matches to the EID, the source xTR
sends the packet to the destination indicated by the RLOC of the
entry.
4. If there are no entries matches to the EID, xTR sends a request
mapping information of the EID (Map-Request) to the Mapping System
depending on its own forwarding table.
5. Mapping System receives the request and detect the RLOC which the
EID is allocated from its own EID-to-RLOC mapping database.
6. Mapping System sends the request to the xTR assigned the RLOC
(peered xTR).
7. The peered xTR recieves the request and registers the EID and
RLOC, and sends a reply (Map-reply) to the source xTR.
8. The source xTR receives the reply and register the opponent xTR
into own EID-to-RLOC mapping cache.
9. If the peered xTR is the same as Source xTR itself, the source xTR
sends the packet to either dDN or dUPF according to the
destination of the packets. Otherwise, the source xTR sends the
packet to the peered xTR with necessary encapsulation.
10. When an xTR receives packets from other xTRs, it sends them with
decapsulation to the appropriate destinations depending on its
forwarding table.
From the above processes, forwarding paths of user traffic diverted
by ULCL from 5GC to xTR are optimized without changing their IP
address (EID).
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Further case studies are described in Appendix A.
4. Mechanisms on Control Plane
For ID-LOC mechanism in mobile networks, a control plane mechanism to
manage location information of UEs is required. There are mainly
three patterns to realize control plane mechanism for ID-LOC as
follows:
Pattern 1: Completely Separating
Pattern 2: Interworking with Mapping System as AF
Pattern 3: Conversing SMF to Mapping System
Some of patterns may require to use 5GS interfaces or add some
functionalities to functions of 5GC. 5GS architecture and the
service-based interfaces are shown in Figure 4. The details of
functions and interfaces are described in [TS.23.501-3GPP].
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+
|NSSF | | NEF | | NRF | | PCF | | UDM | | AF |
+--+--+ +--+--+ +--+--+ +--+--+ +--+--+ +--+--+
Nnssf| Nnef| Nnrf| Npcf| Nudm| |Naf
---+--------+--+-----+--+--------+--+-----+--------+-
Nausf| Namf| Nsmf|
+--+--+ +--+--+ +--+--+
|AUSR | | AMF | | SMF |
+-----+ +--+--+ +-----+
/| |
C-plane N1/ |N2 |N4
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
D-plane / | |
N1 / |N2 |N4
/ | |
+-+-+ +--+--+ N3 +--+--+ N6 +----+
|UE +--+(R)AN+-----+ UPF +-----+ DN |
+---+ +-----+ +-----+ +----+
Figure 4: 5GS Architecture and Service-based Interfaces
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4.1. Pattern 1: Completely Separating
In this pattern, control plane of 5GC and EID-to-RLOC mapping
mechanism are completely separated. Information of an UE and an xTR
which the UE is attached is sent to a Mapping System and registered
in the mapping database only when the xTR receives a packet from the
UE and the UE is not registered yet.
This pattern does not cause any impacts on 5GC architecture.
However, in this pattern, an UE cannot be accessed from other UEs
within the same network domain until a packet from the UE is diverted
to the xTR by the UPF which the UE is located and the EID and RLOC
are registered to the Mapping System.
4.2. Pattern 2: Interworking with Mapping System as AF
In this pattern, a Mapping System interworks with an SMF which
manages sessions of each UE. A scheme to inform, that an UE moves
and is relocated to another UPF, from SMF to AF via Naf interface is
defined in 5GS ([TS.23.502-3GPP])*. A Mapping System is installed as
an AF and obtains mobility information of UEs with the above scheme.
* The stage 3 of discussion of 5GS has not been fixed yet and the
specification may be changed.
This pattern would not cause any impacts on 5GS architecture, and a
Mapping System can always keep the current mobility information of
each UE.
4.3. Pattern 3: Conversing SMF to Mapping System
In this pattern, a Mapping System has functionalities of SMF and acts
as a part of 5GS. In 5GS architecture, an SMF has a role of session
management of UEs, and it updates its own mapping database depending
on movement of an UE.
This approach enables to always keep mapping databases the latest
status, however, it obviously requires extension or replacement of
SMF actually deployed in 5GS network.
5. Features Analysis
5.1. Benefits
o This approach enables to introduce ID-LOC mechanism into 5GC
Rel.15 without any impact, and achieves optimized forwarding with
session continuity in the assumed use cases such as UE-2-UE or UE-
2-dDN communications.
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o Regarding communication to the cDN, this approach can keep
scalability because it does not change the current mechanism of
5GS. (ID-LOC-native network or full-overlay approaches need to
deploy xTR at the cUPF, and thus the EID-to-RLOC mapping cache may
not scale up enough in that cases. Here, a full-overlay approach
means making an ID-LOC system run over the whole 5GC network.)
5.2. Issues
o dUPF and xTR are separated, and thus an extra hop may occur
against the optimized forwarding. However, it can be resolved by
implementing dUPF and xTR within a same box or application.
6. Security Considerations
TBD
7. IANA Considerations
This memo includes no request to IANA.
8. Acknowledgement
The authors would like to thank Ryosuke Kurebayashi, Koji Tsubouchi,
and Toru Okugawa for their kind reviews and technical feedback.
9. Informative References
[I-D.bogineni-dmm-optimized-mobile-user-plane]
Bogineni, K. and A. Rodriguez-Natal, "Optimized Mobile
User Plane Solutions for 5G", draft-bogineni-dmm-
optimized-mobile-user-plane-00 (work in progress), March
2018.
[I-D.farinacci-lisp-mobile-network]
Farinacci, D., Pillay-Esnault, P., and U. Chunduri, "LISP
for the Mobile Network", draft-farinacci-lisp-mobile-
network-02 (work in progress), September 2017.
[]
Previdi, S., Filsfils, C., Raza, K., Dukes, D., Leddy, J.,
Field, B., daniel.voyer@bell.ca, d.,
daniel.bernier@bell.ca, d., Matsushima, S., Leung, I.,
Linkova, J., Aries, E., Kosugi, T., Vyncke, E., Lebrun,
D., Steinberg, D., and R. Raszuk, "IPv6 Segment Routing
Header (SRH)", draft-ietf-6man-segment-routing-header-08
(work in progress), January 2018.
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[I-D.ietf-lisp-eid-mobility]
Portoles-Comeras, M., Ashtaputre, V., Moreno, V., Maino,
F., and D. Farinacci, "LISP L2/L3 EID Mobility Using a
Unified Control Plane", draft-ietf-lisp-eid-mobility-00
(work in progress), May 2017.
[RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
Locator/ID Separation Protocol (LISP)", RFC 6830,
DOI 10.17487/RFC6830, January 2013,
<https://www.rfc-editor.org/info/rfc6830>.
[RFC6831] Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, "The
Locator/ID Separation Protocol (LISP) for Multicast
Environments", RFC 6831, DOI 10.17487/RFC6831, January
2013, <https://www.rfc-editor.org/info/rfc6831>.
[RFC6832] Lewis, D., Meyer, D., Farinacci, D., and V. Fuller,
"Interworking between Locator/ID Separation Protocol
(LISP) and Non-LISP Sites", RFC 6832,
DOI 10.17487/RFC6832, January 2013,
<https://www.rfc-editor.org/info/rfc6832>.
[RFC6833] Fuller, V. and D. Farinacci, "Locator/ID Separation
Protocol (LISP) Map-Server Interface", RFC 6833,
DOI 10.17487/RFC6833, January 2013,
<https://www.rfc-editor.org/info/rfc6833>.
[RFC6836] Fuller, V., Farinacci, D., Meyer, D., and D. Lewis,
"Locator/ID Separation Protocol Alternative Logical
Topology (LISP+ALT)", RFC 6836, DOI 10.17487/RFC6836,
January 2013, <https://www.rfc-editor.org/info/rfc6836>.
[RFC7215] Jakab, L., Cabellos-Aparicio, A., Coras, F., Domingo-
Pascual, J., and D. Lewis, "Locator/Identifier Separation
Protocol (LISP) Network Element Deployment
Considerations", RFC 7215, DOI 10.17487/RFC7215, April
2014, <https://www.rfc-editor.org/info/rfc7215>.
[RFC8061] Farinacci, D. and B. Weis, "Locator/ID Separation Protocol
(LISP) Data-Plane Confidentiality", RFC 8061,
DOI 10.17487/RFC8061, February 2017,
<https://www.rfc-editor.org/info/rfc8061>.
[RFC8111] Fuller, V., Lewis, D., Ermagan, V., Jain, A., and A.
Smirnov, "Locator/ID Separation Protocol Delegated
Database Tree (LISP-DDT)", RFC 8111, DOI 10.17487/RFC8111,
May 2017, <https://www.rfc-editor.org/info/rfc8111>.
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[TS.23.501-3GPP]
3rd Generation Partnership Project (3GPP), "3GPP TS
23.501", December 2017,
<http://www.3gpp.org/ftp//Specs/archive/23_series/23.501>.
[TS.23.502-3GPP]
3rd Generation Partnership Project (3GPP), "3GPP TS
23.502", December 2017,
<http://www.3gpp.org/ftp//Specs/archive/23_series/23.502>.
Appendix A. Case Studies
This Appendix describes detailed processes of the proposal approach
in the following types of communications.
1. UE-2-UE Communication
2. UE-2-dDN Communication
A.1. UE-2-UE Communication
In the current architecture, a cUPF becomes an anchor point for UEs,
and all packets between UEs even which are located to the same dUPF
are transferred through the anchor point. This may cause
communication delay and inefficient resource usage. In the proposed
procedure, packets can be transferred without through an anchor
point, and low latency and efficient resource usage can be achieved.
The UE-2-UE communications include communications between UEs located
to different dUPFs (Case 1), and communication between UEs located to
the same dUPF (Case 2). In this section, the detailed procedures of
the cases are described.
Moreover, in a mobile network, an UE may move during communications.
This section describes problems and considerations about UE's
handover in such case.
A.1.1. Case 1: UEs allocated different dUPF
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+-------+
|Mapping|
|System |
+-------+
.
.
.
(3) . #==========================#
. # (4) #
. # V
+-------+ +-------+ +-------+ +-------+
| dUPF#1| | xTR#1 | | dUPF#2| | xTR#2 |
| | | RLOC=X| |+------|<-----| RLOC=Y|
| [UL]| | | || [UL]| (5) | |
| [CL]|------>| | |v [CL]| | |
+-------+ (2) +-------+ +-------+ +-------+
^ |
| (1) |(6)
| v
[UE#1] [UE#2]
EID=a-1 EID=a-2
Figure 5: Procedure in Case 1
(0) Within this network, addresses are assigned to UEs from a
address space [A]. These addresses are described as a-n
(n=1,2,..). EID=a-1 and a-2 are assigned to UE#1 and UE#2.
(1) UE#1 sends packets to UE#2 with setting EID=a-2 as the
destination IP address.
(2) dUPF#1 monitors inner packet of received GTP-U packet and divert
it to xTR#1 with decapsulation if the destination address is one
of address space [A].
(3) xTR#1 updates own EID-to-RLOC mapping chace by interaction with
Mapping System (if needed).
(4) xTR#1 obtains the RLOC(=Y) of EID=a-2 from the EID-to-RLOC
mapping cache, and sends the packets to the xTR#2 with a tunnel
with RLOC=Y as the destination address.
(5) xTR#2 decapsulate the packets, and sends them to dUPF#2.
(6) dUPF#2 encapsulate packets with GTP-U header, and sends them to
UE#2.
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A.1.2. Case2: UEs allocated the same xTR
+-------+
|Mapping|
|System |
+-------+
.
.
.
(3) .
.
.
+-------+ +-------+ +-------+ +-------+
| dUPF#1| | xTR#1 | | dUPF#2| | xTR#2 |
|+------|<----- | RLOC=X| | | | RLOC=Y|
|| [UL]| (4) | | | [UL]| | |
|v [CL]|------>| | | [CL]| | |
+-------+ (2) +-------+ +-------+ +-------+
| ^
(5) | | (1)
v |
[UE#2] [UE#1]
EID=a-2 EID=a-1
Figure 6: Procedure in Case 2
(0) Within this network, addresses are assigned to UEs from a
address space [A] These addresses are described as a-n (n=1,2,..).
EID=a-1 and a-2 are assigned to UE#1 and UE#2.
(1) UE#1 sends packets to UE#2 with setting EID=a-2 as the
destination IP address.
(2) dUPF#1 monitors inner packets of recieved GTP-U traffic and
divert it to xTR#1 with decapsulation if the destination address
is one of address space [A].
(3) xTR#1 updates own EID-to-RLOC mapping cache by interaction with
Mapping System (if needed).
(4) xTR#1 obtains the RLOC(=X) from the EID-to-RLOC mapping cache.
Since RLOC=X indicates itself, xTR#1 sends the packets back to
dUPF#1.
(5) dUPF#2 encapsulate packets with GTP-U, and sends them to UE#2.
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A.1.3. Consideration of Case that UE Moves to under Another xTR
When an UE moves to a serving area of another dUPF during
communication with another UE, EID-to-RLOC mapping database of a
Mapping System and the tables of the xTR and the peered xTR must be
updated. The xTRs can't send packets to the appropriate xTR during
the updating, and thus packet drop or stalling may occur.
To mitigate this problem, further consideration is needed. For
example, a mechanism that immediately advertise the update of
location of UEs to Mapping System and the appropriate xTRs depending
on movement of each UE might be required.
A.2. UE-2-dDN Communication
The UE-2-dDN communications basically correspond the communication
between an UE and neighbor dDN (Case3). On the other hand, if an UE
moved under another dUPF during usage of a statefull application, or
the application is not uniformly deployed in every dDN, the UE needs
to continue to communicate with the previous dDN (Case4).
In such cases, in the current architecture, all packets are needed to
go through the anchor point or dynamic GTP tunnel reconfiguration
between dUPF is required. The former solution causes additional
communication delay and inefficient resource usage. The latter
solution increase the cost of 5GS control plane to dynamically update
the GTP tunnel with multiple UPFs and their ULCL filter tables along
with the movement of the UE. The propal approach achieves
appropriate packet transfer in such cases.
In this section, the detailed procedures of communications between an
UE and neighbor dDN and communications between an UE and non-neighbor
dDN
A.2.1. Case 3: UE communicates with neighbor dDN
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+-------+
|Mapping|
|System |
+-------+
.
.
.
(3) .
.
.
+-------+ +-------+ +-------+ +-------+
| dUPF#1| | xTR#1 | | dUPF#2| | xTR#2 |
|+------|<----- | RLOC=X| | | | RLOC=Y|
|| [UL]| (6) | | | [UL]| | |
|v [CL]|------>| | | [CL]| | |
+-------+ (2) +-------+ +-------+ +-------+
| ^ | ^
(7) | | (1) (4)| | (5)
v | v |
,-------.
[UE#1] / dDN#B \
EID=a1 | | ^ |
| v | |
| [APL#1] |
\ EID=b-1 /
`-------'
Figure 7: Procedure in Case 3
(0) Within this network, UEs are assigned their addresses from an
address space [A]. These addresses are described as a-n
(n=1,2,...). Also, applications in dDN#B are assigned their
addresses from a address space [B]. These addresses are described
as b-n (n=1,2,..). EID=a-1 and b-1 assigned to UE#1 and APL#1
which is located in dDN#B.
[Uplink Processes]
(1) UE#1 sends packets to dDN#B with setting EID=b-1 as the
destination IP address.
(2) dUPF#1 monitors inner of recieved GTP-U packets and divert it to
xTR#1 with decapsulation if the destination IP address is one of
address space [B].
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(3) xTR#1 updates own EID-to-RLOC mapping cache by interaction with
Mapping System (if needed). Or xTR#1 may update its own cache by
a Map-Notify message when an APL is deployed or deleted in dDB#B.
(4) xTR#1 obtains RLOC(=X) of EID=b-1 from the EID-to-RLOC mapping
cache. Since RLOC=X indicates itself and EID=b-1 is within [B],
xTR#1 sends the packets to the dDN#B.
[Downlink Processes]
(5) APL#1 in dDN#B sends packets to UE#1 with setting EID=a-1 as the
destination IP address.
(6) xTR#1 obtains RLOC of EID=a-1 (i.e., RLOC=X) from the EID-to-
RLOC mapping cache. Since RLOC=X indicates xTR#1 itself, xTR#1
sends packets to dUPF#1.
(7) dUPF#2 encapsulates packets with GTP-U, and sends them to UE#1.
A.2.2. Case4: UE communicates with non-neighbor dDN
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+-------+
|Mapping|
|System |
+-------+
.
. (7)
. #==============================#
(3) . # #==========================# #
. # # (4) # #
. V # V #
+-------+ +-------+ +-------+ +-------+
| dUPF#1| (8) | xTR#1 | | dUPF#2| | xTR#2 |
|+------|<------| RLOC=X| | | (0) | RLOC=Y|
|| [UL]| | | | [UL]|<---->| |
|v [CL]|------>| | | [CL]| | |
+-------+ (2) +-------+ +-------+ +-------+
| ^ ^ | ^
(9) | | (1) | (0) (5)| | (6)
v | | v |
(0) v ,-------.
[UE#1] <= = = = = = = = = = = =[UE#1] / dDN#C \
EID=a-1 UE#1 moves to the serving area of | | ^ |
dUPF#1 from the serving area of UPF#2 | v | |
| [APL#2] |
\ EID=c-1 /
`-------'
Figure 8: Procedure in Case 4
(0) Within this network, UEs are assigned their addresses from an
address space [A]. These addresses are described as a-n
(n=1,2,..). And applications in dDN#C are assigned their
addresses from an address space [C]. These addresses are
described as c-n (n=1,2,..). EID=a-1 and c-1 assigned to UE#1 and
APL#2 which is located in dDN#C. UE#1 has movedto the serving
area of dUPF#1 from the serving area of UPF#2 while communicating
to APL#2.
[Uplink Processes]
(1) UE#1 sends packets to APL#2 with setting EID=c-1 as the
destination IP address.
(2) dUPF#1 monitors each inner packet of received GTP-U traffic and
divert it to xTR#1 with decapsulation if the destination addressis
one of address space [C].
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(3) xTR#1 updates own EID-to-RLOC mapping cache by interaction with
Mapping System (if needed).
(4) xTR#1 obtains RLOC(=Y) of EID=c-1 from the EID-to-RLOC mapping
cache, and sends the packet to the xTR#2 with a tunnel with RLOC=Y
as the destination address.
(5) xTR#2 decapsulates the packets received from xTR#1, and sends
them to dDN#C depending on its forwarding table.
[Downlink Processes]
(6) APL#2 sends packets to UE#1 with setting EID=a-1 as the
destination IP address.
(7) xTR#2 obtains RLOC(=X) of EID=a-1 from the EID-to-RLOC mapping
cache, and sends the packets to the xTR#1 with a tunnel with
RLOC=X as the destination address.
(8) xTR#1 decapsulates the packets received from xTR#2m and sends
them to the dUPF#1 depending on its forwarding table.
(9) dUPF#1 encapsulates the packets with GTP-U and sends packets to
UE#1.
Authors' Addresses
Shunsuke Homma
NTT, Corp.
3-9-11, Midori-cho
Musashino-shi, Tokyo 180-8585
Japan
Email: homma.shunsuke@lab.ntt.co.jp
Kenta Kawakami
NTT, Corp.
3-9-11, Midori-cho
Musashino-shi, Tokyo 180-8585
Japan
Email: kawakami.kenta@lab.ntt.co.jp
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Dino Farinacci
lispers.net
San Jose, CA
USA
Email: farinacci@gmail.com
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