DMM Working Group U. Chunduri, Ed.
Internet-Draft Futurewei
Intended status: Informational L. Contreras
Expires: May 6, 2021 Telefonica
S. Bhaskaran
Altiostar
J. Tantsura
Apstra, Inc.
P. Muley
Nokia
November 2, 2020
Transport aware 5G mobility with PPR
draft-chunduri-dmm-5g-mobility-with-ppr-00
Abstract
This document describes few 5G mobility scenarios and how mobile
network functions map its SST criteria to identifiers in IP packets
that transport segments use to grant transport layer services. This
is based on mapping between mobile and IP transport underlays (IPv6,
MPLS, IPv4) and a new transport network underlay routing mechanism,
Preferred Path Routing (PPR), which brings slice properties and works
with any underlying transport (L2, IPv4, SR and MPLS) is described.
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 RFC2119 [RFC2119].
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 https://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 6, 2021.
Chunduri, et al. Expires May 6, 2021 [Page 1]
Internet-Draft Transport aware 5G mobility with PPR November 2020
Copyright Notice
Copyright (c) 2020 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
(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 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
1.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Transport Network Underlays . . . . . . . . . . . . . . . . . 4
2.1. Using PPR as TN Underlay . . . . . . . . . . . . . . . . 4
2.1.1. PPR on F1-U/N3/N9 Interfaces . . . . . . . . . . . . 5
2.1.2. Path Steering Support to native IP user planes . . . 6
2.1.3. Service Level Guarantee in Underlay . . . . . . . . . 6
3. PPR with various 5G Mobility procedures . . . . . . . . . . . 7
3.1. SSC Mode1 . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. SSC Mode2 . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. SSC Mode3 . . . . . . . . . . . . . . . . . . . . . . . . 9
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Normative References . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
[I-D.clt-dmm-tn-aware-mobility] describes in detail on how TN aware
mobility can be built irrespective of underlying TN technology used.
This document specifies an approach to fulfil the needs of 5GS to
transport user plane traffic from 5G-AN to UPF for all session and
service continuity modes (SSC) [TS.23.501-3GPP] in an optimized
fashion. This is done by, keeping establishment and mobility
procedures aware of underlying transport network along with slicing
requirements using integrated routing and traffic engineering
mechanism, Preferred Path Routing (PPR).
Chunduri, et al. Expires May 6, 2021 [Page 2]
Internet-Draft Transport aware 5G mobility with PPR November 2020
PPR is applicable to any transport network underlay (IPv6, MPLS and
IPv4) is detailed in Section 2.1 used 5G x-haul as described in
[I-D.clt-dmm-tn-aware-mobility] . At the end, Section 3 further
describes the applicability and procedures of PPR with 5G mobility
scenarios in variou mobility scenarios in variouss SSC modes on F1-U,
N3 and N9 interfaces.
1.1. Acronyms
5G-AN - 5G Access Network
BP - Branch Point (5G)
CSR - Cell Site Router
DN - Data Network (5G)
eMBB - enhanced Mobile Broadband (5G)
FRR - Fast ReRoute
gNB - 5G NodeB
GBR - Guaranteed Bit Rate (5G)
GTP-U - GPRS Tunneling Protocol - Userplane (3GPP)
IGP - Interior Gateway Protocols (e.g. IS-IS, OSPFv2, OSPFv3)
mIOT - Massive IOT (5G)
MPLS - Multi Protocol Label Switching
NSSMF - Network Slice Selection Management Function
PPR - Preferred Path Routing
PDU - Protocol Data Unit (5G)
RAN - Radio Access Network
SID - Segment Identifier
SSC - Session and Service Continuity (5G)
SST - Slice and Service Types (5G)
SR - Segment Routing
Chunduri, et al. Expires May 6, 2021 [Page 3]
Internet-Draft Transport aware 5G mobility with PPR November 2020
TE - Traffic Engineering
ULCL - Uplink Classifier (5G)
UP - User Plane(5G)
UPF - User Plane Function (5G)
URLLC - Ultra reliable and low latency communications (5G)
2. Transport Network Underlays
Apart from the various flavors of IETF VPN technologies to share the
transport network resources and capacity, TE capabilities in the
underlay network is an essential component to realize the 5G TN
requirements. This section focuses on PPR and its applicability to
realize Midhaul/Backhaul transport networks. Focus is on the user/
data plane i.e., F1-U/N3/N9 interfaces as laid out in the framework
[I-D.clt-dmm-tn-aware-mobility].
2.1. Using PPR as TN Underlay
In a network implementing source routing, packets may be transported
through the use of Segment Identifiers (SIDs), where a SID uniquely
identifies a segment as defined in [I-D.ietf-spring-segment-routing].
The need for underlay agnostic (L2/IPv4/IPv6/MPLS) TE requirements
are addressed by PPR, of which this section provides an overview.
With PPR, the label/PPR-ID refer not to individual segments of which
the path is composed, but to the identifier of a path that is
deployed on network nodes. The fact that paths and path identifiers
can be computed and controlled by a controller, not a routing
protocol, allows the deployment of any path that network operators
prefer, not just shortest paths. As packets refer to a path towards
a given destination and nodes make their forwarding decision based on
the identifier of a path, not the identifier of a next segment node,
it is no longer necessary to carry a sequence of labels. This
results in multiple benefits including significant reduction in
network layer overhead, increased performance and hardware
compatibility for carrying both path and services along the path.
Details of the IGP extensions for PPR are provided here:
o IS-IS - [I-D.chunduri-lsr-isis-preferred-path-routing]
o OSPF - [I-D.chunduri-lsr-ospf-preferred-path-routing]
o PPR Graph Structure (P2MP) - [I-D.ce-lsr-ppr-graph]
Chunduri, et al. Expires May 6, 2021 [Page 4]
Internet-Draft Transport aware 5G mobility with PPR November 2020
2.1.1. PPR on F1-U/N3/N9 Interfaces
PPR does not remove GTP-U, unlike some other proposals laid out in
[I-D.bogineni-dmm-optimized-mobile-user-plane]. Instead, PPR works
with the existing cellular user plane (GTP-U) for F1-U/N3 and N9
(encapsulation or no-encapsulation). In this scenario, PPR will only
help providing TE benefits needed for 5G slices from transport domain
perspective. It does so for any underlying user/data plane used in
the transport network (L2/IPv4/IPv6/MPLS). This is achieved by:
o For 3 different SSTs, 3 PPR-IDs can be signaled from any node in
the transport network. For Uplink traffic, the 5G-AN will choose
the right PPR-ID based on the S-NSSAI the PDU Session belongs to
and/or the UDP Source port (corresponds to the MTNC-ID
[I-D.clt-dmm-tn-aware-mobility]) of the GTP-U encapsulation
header. Similarly in the Downlink direction matching PPR-ID of
the 5G-AN is chosen based on the S-NSSAI the PDU Session belongs
to. The table below shows a typical mapping:
+----------------+------------+------------------+-----------------+
|GTP/UDP SRC PORT| SST | Transport Path | Transport Path |
| | in S-NSSAI | Info | Characteristics |
+----------------+------------+------------------+-----------------+
| Range Xx - Xy | | | |
| X1, X2(discrete| MIOT | PW ID/VPN info, | GBR (Guaranteed |
| values) | (massive | PPR-ID-A | Bit Rate) |
| | IOT) | | Bandwidth: Bx |
| | | | Delay: Dx |
| | | | Jitter: Jx |
+----------------+------------+------------------+-----------------+
| Range Yx - Yy | | | |
| Y1, Y2(discrete| URLLC | PW ID/VPN info, | GBR with Delay |
| values) | (ultra-low | PPR-ID-B | Req. |
| | latency) | | Bandwidth: By |
| | | | Delay: Dy |
| | | | Jitter: Jy |
+----------------+------------+------------------+-----------------+
| Range Zx - Zy | | | |
| Z1, Z2(discrete| EMBB | PW ID/VPN info, | Non-GBR |
| values) | (broadband)| PPR-ID-C | Bandwidth: Bx |
+----------------+------------+------------------+-----------------+
Figure 1: Mapping of PPR-IDs on N3/N9
Chunduri, et al. Expires May 6, 2021 [Page 5]
Internet-Draft Transport aware 5G mobility with PPR November 2020
o It is possible to have a single PPR-ID for multiple input points
through a PPR tree/graph structure ([I-D.ce-lsr-ppr-graph])
separate in UL and DL direction.
o Same set of PPRs are created uniformly across all needed 5G-ANs
and UPFs to allow various mobility scenarios.
o Any modification of TE parameters of the path, replacement path
and deleted path needed to be updated from TNF to the relevant
ingress points. Same information can be pushed to the NSSF, and/
or SMF as needed.
o PPR can be supported with any native IPv4 and IPv6 data/user
planes (Section 2.1.2) with optional TE features (Section 2.1.3) .
As this is an underlay mechanism it can work with any overlay
encapsulation approach including GTP-U as defined currently for N3
interface.
2.1.2. Path Steering Support to native IP user planes
PPR works in fully compatible way with SR [RFC8402] defined user
planes (SR-MPLS and SRv6) by reducing the path overhead and other
challenges as listed in Section 5.3.7 of
[I-D.bogineni-dmm-optimized-mobile-user-plane]. PPR also expands the
source routing to beyond SR-MPLS and SRv6 i.e., L2, native IPv6 and
IPv4 user planes.
This helps legacy transport networks to get the immediate path
steering benefits and helps in overall migration strategy of the
network to the desired user plane. Some of these benefits with PPR
can be realized with no hardware upgrade except control plane
software for native IPv6 and IPv4 user planes.
2.1.3. Service Level Guarantee in Underlay
PPR optionally allows to allocate resources that are to be reserved
along the preferred path. These resources are required in some cases
(for some 5G SSTs with stringent GBR and latency requirements) not
only for providing committed bandwidth or deterministic latency, but
also for assuring overall service level guarantee in the network.
This approach does not require per-hop provisioning and reduces the
OPEX by minimizing the number of protocols needed and allows dynamism
with Fast-ReRoute (FRR) capabilities.
Chunduri, et al. Expires May 6, 2021 [Page 6]
Internet-Draft Transport aware 5G mobility with PPR November 2020
3. PPR with various 5G Mobility procedures
PPR fulfills the needs of 5GS to transport the user plane traffic
from 5G-AN to UPF in all 3 SSC modes defined [TS.23.501-3GPP]. This
is done in keeping the backhaul network at par with 5G slicing
requirements that are applicable to Radio and virtualized core
network to create a truly end-to-end slice path for 5G traffic. When
UE moves across the 5G-AN (e.g. from one gNB to another gNB), there
is no transport network reconfiguration required with the approach
above.
SSC mode would be specified/defaulted by SMF. No change in the mode
once connection is initiated and this property is not altered here.
3.1. SSC Mode1
+--------------+
+---+----+ |NSSMF +-----+ | +----------------+
| AMF | | | TNF | | | SMF |
+---+--+-+ | +-+-+-+ | +-----+----------+
N1 | +--------+-+---+ |
| | | | |
| | +---+-+--+ |
| | | SDN-C | |
| | +---+-+--+ |
| | | | |
+--------+ N2 +---------+ + ---+ |
| | | | |
+ +---+--+ +--++ +---+ +-+--+ +----+
UE1 |gNB|======|CSR|---N3--------|PE |-|UPF |-N6--| DN |
== +---+ +---+ +---+ +----+ +----+
Figure 2: SSC Mode1 with integrated Transport Slice Function
After UE1 moved to another gNB in the same UPF serving area
Chunduri, et al. Expires May 6, 2021 [Page 7]
Internet-Draft Transport aware 5G mobility with PPR November 2020
+--------------+
+---+----+ |NSSMF +-----+ | +----------------+
| AMF | | | TNF | | | SMF |
+------+-+ | +-+-+-+ | +-----+----------+
| +--------+-+---+ |
| | | |
| +---+-+--+ |
| | SDN-C | |
| +---+-+--+ |
| | | |
N2 +---------+ + ---+ |
| | | |
+---+--+ +--++ +---+ +-+--+ +----+
|gNB|======|CSR|---N3--------|PE |-|UPF |-N6--| DN |
+---+ +---+ +-+-+ +----+ +----+
|
|
|
|
+----+ +---+ |
UE1 |gNB2|======|CSR|------N3-------+
== +----+ +---+
Figure 3: SSC Mode1 with integrated Transport Slice Function
In this mode, IP address at the UE is preserved during mobility
events. This is similar to 4G/LTE mechanism and for respective
slices, corresponding PPR-ID (TE Path) has to be assigned to the
packet at UL and DL direction. During Xn mobility as shown above,
source gNB has to additionally ensure transport path's resources from
TNF are available at the target gNB apart from radio resources check
(at decision and request phase of Xn/N2 mobility scenario).
3.2. SSC Mode2
In this case, if IP Address is changed during mobility (different UPF
area), then corresponding PDU session is released. No session
continuity from the network is provided and this is designed as an
application offload and application manage the session continuity, if
needed. For PDU Session, Service Request and Mobility cases
mechanism to select the transport resource and the PPR-ID (TE Path)
is similar to SSC Mode1.
Chunduri, et al. Expires May 6, 2021 [Page 8]
Internet-Draft Transport aware 5G mobility with PPR November 2020
3.3. SSC Mode3
In this mode, new IP address may be assigned because of UE moved to
another UPF coverage area. Network ensures UE suffers no loss of
'connectivity'. A connection through new PDU session anchor point is
established before the connection is terminated for better service
continuity. There are two ways in which this happens.
o Change of SSC Mode 3 PDU Session Anchor with multiple PDU
Sessions.
o Change of SSC Mode 3 PDU Session Anchor with IPv6 multi-homed PDU
Session.
In the first mode, from user plane perspective, the two PDU sessions
are independent and the use of PPR-ID by gNB and UPFs is exactly
similar to SSC Mode 1 described above. The following paragraphs
describe the IPv6 multi-homed PDU session case for SSC Mode 3.
+--------------+
+---+----+ |NSSMF +-----+ | +----------------+
| AMF | | | TNF | | | SMF |
+---+--+-+ | +-+-+-+ | +-+-----------+--+
| | +--------+-+---+ | |
N1 | | | | |
| | +---+-+--+ | |
| | | SDN-C | | |
| | +---+-+--+ | |
| | | | | |
to-UE+----+ N2 +-----------+ | N4 N4|
+---+ | | | |
| | | | |
+---+ +---++ +---+ +-------+--+ +---+ +---+
|gNB|===|CSR |---N3---|PE |-| BP UPF |-N9-|PE |-|UPF|-N6->
+---+ +----+ +---+ +-------+--+ +---+ +---+ to DN
| +----+
+-| DN |
N6 +----+
Figure 4: SSC Mode3 and Service Continuity
In the uplink direction for the traffic offloading from the Branching
Point UPF, packet has to reach to the right exit UPF. In this case
packet gets re-encapsulated by the BP UPF (with either GTP-U or the
Chunduri, et al. Expires May 6, 2021 [Page 9]
Internet-Draft Transport aware 5G mobility with PPR November 2020
chosen encapsulation) after bit rate enforcement and LI, towards the
anchor UPF. At this point packet has to be on the appropriate VPN/PW
to the anchor UPF. This mapping is done based on the S-NSSAI the PDU
session belongs to and/or with the UDP source port (corresponds to
the MTNC-ID [I-D.clt-dmm-tn-aware-mobility]) of the GTP-U
encapsulation header to the PPR-ID of the exit node by selecting the
respective TE PPR-ID (PPR path) of the UPF. If it's a non-MPLS
underlay, destination IP address of the encapsulation header would be
the mapped PPR-ID (TE path).
In the downlink direction for the incoming packet, UPF has to
encapsulate the packet (with either GTP-U or the chosen
encapsulation) to reach the BP UPF. Here mapping is done based on
the S-NSSAI the PDU session belongs, to the PPR-ID (TE Path) of the
BP UPF. If it's a non-MPLS underlay, destination IP address of the
encapsulation header would be the mapped PPR-ID (TE path). In
summary:
o Respective PPR-ID on N3 and N9 has to be selected with correct
transport characteristics from TNF.
o For N2 based mobility SMF has to ensure transport resources are
available for N3 Interface to new BP UPF and from there the
original anchor point UPF.
o For Service continuity with multi-homed PDU session same transport
network characteristics of the original PDU session (both on N3
and N9) need to be observed for the newly configured IPv6
prefixes.
4. Acknowledgements
TBD.
5. IANA Considerations
This document has no requests for any IANA code point allocations.
6. Security Considerations
This document does not introduce any new security issues.
7. References
Chunduri, et al. Expires May 6, 2021 [Page 10]
Internet-Draft Transport aware 5G mobility with PPR November 2020
7.1. 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>.
7.2. Informative References
[I-D.bogineni-dmm-optimized-mobile-user-plane]
Bogineni, K., Akhavain, A., Herbert, T., Farinacci, D.,
Rodriguez-Natal, A., Carofiglio, G., Auge, J.,
Muscariello, L., Camarillo, P., and S. Homma, "Optimized
Mobile User Plane Solutions for 5G", draft-bogineni-dmm-
optimized-mobile-user-plane-01 (work in progress), June
2018.
[I-D.ce-lsr-ppr-graph]
Chunduri, U. and T. Eckert, "Preferred Path Route Graph
Structure", draft-ce-lsr-ppr-graph-04 (work in progress),
September 2020.
[I-D.chunduri-lsr-isis-preferred-path-routing]
Chunduri, U., Li, R., White, R., Tantsura, J., Contreras,
L., and Y. Qu, "Preferred Path Routing (PPR) in IS-IS",
draft-chunduri-lsr-isis-preferred-path-routing-06 (work in
progress), September 2020.
[I-D.chunduri-lsr-ospf-preferred-path-routing]
Chunduri, U., Qu, Y., White, R., Tantsura, J., and L.
Contreras, "Preferred Path Routing (PPR) in OSPF", draft-
chunduri-lsr-ospf-preferred-path-routing-04 (work in
progress), March 2020.
[I-D.clt-dmm-tn-aware-mobility]
Chunduri, U., Li, R., Bhaskaran, S., Kaippallimalil, J.,
Tantsura, J., Contreras, L., and P. Muley, "Transport
Network aware Mobility for 5G", draft-clt-dmm-tn-aware-
mobility-07 (work in progress), September 2020.
[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-09
(work in progress), July 2020.
Chunduri, et al. Expires May 6, 2021 [Page 11]
Internet-Draft Transport aware 5G mobility with PPR November 2020
[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-15 (work
in progress), January 2018.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[TS.23.501-3GPP]
3rd Generation Partnership Project (3GPP), "System
Architecture for 5G System; Stage 2, 3GPP TS 23.501
v2.0.1", December 2017.
Authors' Addresses
Uma Chunduri (editor)
Futurewei
2330 Central Expressway
Santa Clara, CA 95050
USA
Email: umac.ietf@gmail.com
Luis M. Contreras
Telefonica
Sur-3 building, 3rd floor
Madrid 28050
Spain
Email: luismiguel.contrerasmurillo@telefonica.com
Sridhar Bhaskaran
Altiostar
Email: sridharb@altiostar.com
Jeff Tantsura
Apstra, Inc.
Email: jefftant.ietf@gmail.com
Chunduri, et al. Expires May 6, 2021 [Page 12]
Internet-Draft Transport aware 5G mobility with PPR November 2020
Praveen Muley
Nokia
440 North Bernardo Ave
Mountain View, CA 94043
USA
Email: praveen.muley@nokia.com
Chunduri, et al. Expires May 6, 2021 [Page 13]