DMM Working Group U. Chunduri, Ed.
Internet-Draft Intel Corporation
Intended status: Informational J. Kaippallimalil, Ed.
Expires: 16 May 2025 Futurewei
S. Bhaskaran
Rakuten Symphony
J. Tantsura
Nvidia
L.M. Contreras
Telefonica
12 November 2024
Mobility-aware Transport Network Slicing for 5G
draft-ietf-dmm-tn-aware-mobility-13
Abstract
Network slicing in 5G enables logical networks for communication
services of multiple 5G customers to be multiplexed over the same
infrastructure. While 5G slicing covers logical separation of
various aspects of 5G infrastructure and services, user's data plane
packets over the Radio Access Network (RAN) and Core Network (5GC)
use IP in many segments of an end-to-end 5G slice. When end-to-end
slices in a 5G System use network resources, they are mapped to
corresponding IP transport network slice(s) which in turn provide the
bandwidth, latency, isolation, and other criteria required for the
realization of a 5G slice.
This document describes mapping of 5G slices to transport network
slices using UDP source port number of the GTP-U bearer when the IP
transport network (slice provider) is separated by an "attachment
circuit" from the networks in which the 5G network functions are
deployed, for example, 5G functions that are distributed across data
centers. The slice mapping defined here is supported transparently
when a 5G user device moves across 5G attachment points and session
anchors.
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/.
Chunduri, et al. Expires 16 May 2025 [Page 1]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
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 16 May 2025.
Copyright Notice
Copyright (c) 2024 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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Mapping 3GPP Slice to Transport Network Slices . . . . . . . 4
2.1. Scope of Transport Networks in 5G Network Slicing . . . . 4
2.2. Fronthaul and Mid-Haul Transport Network . . . . . . . . 7
2.3. Backhaul Transport Network . . . . . . . . . . . . . . . 7
2.4. Slice Mapping using UDP Source Port Number . . . . . . . 8
3. Transport Network Underlays . . . . . . . . . . . . . . . . . 12
4. Attachment Circuit as a Service Extensions . . . . . . . . . 14
4.1. Attachment Circuit Extension for GTPU . . . . . . . . . . 14
4.2. ietf-ac-gtpu YANG Module . . . . . . . . . . . . . . . . 16
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. Contributing Authors . . . . . . . . . . . . . . . . . . . . 19
9. Informative References . . . . . . . . . . . . . . . . . . . 19
Appendix A. Abbreviations . . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
Chunduri, et al. Expires 16 May 2025 [Page 2]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
1. Introduction
3GPP architecture for 5G System (5GS) in [TS.23.501-3GPP],
[TS.23.502-3GPP] and [TS.23.503-3GPP] for 5GC (5G Core), and the NG-
RAN architecture defined in [TS.38.300-3GPP] and [TS.38.401-3GPP]
describe slicing as one of the capabilities for the communication
services that 5G systems provide. Slice types defined by the 3GPP
include enhanced mobile broadband (eMBB) communications, ultra-
reliable low latency communications (URLLC), massive internet of
things (MIoT), vehicle-to-X (V2X) and high-performance machine type
communications (HMTC). Other types can be defined in the future to
include new slice types.
5G network slicing is defined by the 3GPP [TS.28.530-3GPP] as an
approach, "where logical networks/partitions are created, with
appropriate isolation, resources, and optimized topology to serve a
purpose or service category (e.g. use case/traffic category, or for
MNO internal reasons) or customers logical system created "on-
demand". A 5G slice instance requested by an end-user is realized by
a 5G network slice subnet (NSS) which is a collection of network
functions across RAN and 5GC that make up the 5G slice. However,
3GPP standards do not specify the capabilities of transport network
(TN) slices or slice characteristics for QoS, hard /soft isolation,
protection and other aspects.
A TN slice across 3GPP interfaces N3, N9 and F1U may use multiple
technologies or network providers. The slice in the 3GPP domain is
mapped to each corresponding TN on the path. 5G system slices for
the distributed infrastructure and NFs that make up the 5GS, and 5G
slices provided to its end users (via UE) are mapped to TN slices
[RFC9543] to provide the corresponding level of bandwidth, isolation,
and other capabilities. A 3GPP F1-U slice subnet instance may be
used to carry all user traffic between a gNB-DU and gNB-CU since the
lower layers of the radio access do not differentiate by user. On
the other hand, an end-user's traffic for eMBB service and assigned
3GPP slice may be mapped to a different TN slice across N3 and N9
segments than traffic for URLLC service. Unlike mapping of a
fronthaul 3GPP slice to a TN slice, the TN slice that F1-U/N3/N9
slice is mapped to is aware of the slice characteristics of the UE
session during initial setup (user initiates 3GPP connectivity
session) and following UE mobility. For example, a UE served by the
3GPP system for high throughput, low latency service and related 3GPP
slice should be mapped to an TN slice that provides the corresponding
characteristics even after handover.
Several network scenarios and mechanisms to map 3GPP and IETF network
slices are found in [I-D.ietf-teas-5g-network-slice-application] and
[I-D.ietf-teas-5g-ns-ip-mpls]. This document defines another
Chunduri, et al. Expires 16 May 2025 [Page 3]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
mechanism where the source UDP port number of a layer 3 GTP bearer is
used to map to the TN slice at the Provider Edge (PE). 3GPP slice
management ([TS.28.541-3GPP]) and Attachment Circuit (AC) in
[I-D.ietf-opsawg-teas-attachment-circuit] provide the basis for the
necessary mapping. Extensions to attachment circuit as a service to
support a layer 3 GTP-U bearer as an attachment curcuit is described
in Section 2.4 and Section 4.
TN slices in this document can be used to realize slices between 3GPP
control plane NFs or for a UE's user plane. For realizing control
plane slicing, the TN slice is deployed along the interface between
two 3GPP NFs. For realizing a 3GPP slice corresponding to a UE PDU
session, the TN slice for each PDU session is mapped to aorresponding
TN slices and is the focus of this document. Since the 3GPP Single
Network Slice Selection Assistance Information (S-NSSAI) is not
visible to TNs, the source UDP port number of the GTP-U bearer is
used to convey a mapping to the TN slices on each 3GPP interface
(i.e., F-U, N3, N9). Following UE handover, the S-NSSAI is mapped
seamlessly to the corresponding GTP-U source port number of the newly
attached network and can be considered to be "mobility aware". Slice
mapping using UDP source port numbers may be used in TN of public or
non public 3GPP networks.
2. Mapping 3GPP Slice to Transport Network Slices
2.1. Scope of Transport Networks in 5G Network Slicing
3GPP [TS.28.530-3GPP] discusses transport network in the context of
network slice subnets, but do not specify further details. The
application of 5GS slices in transport network for backhaul, mid-haul
and front haul are not explicitly covered in 3GPP and is the topic
here. To support specific characteristics in backhaul (N3, N9), mid-
haul (F1) and front haul, it is necessary to provision corresponding
resources in the transport domain and carry a slice identifier that
is understood by both the customer (3GPP network) and the provider
(TN). This section provides an overview and subsequent sections
describe how to provision the mapping information in the TN and apply
it so that user plane packets can be provided the transport resources
(QoS, isolation, protection, etc.) expected by the 5GS slices.
Chunduri, et al. Expires 16 May 2025 [Page 4]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
5G Control and Management Planes
+--------------------------------------------------------------------+
| +----------------------------------------------------------------+ |
| | 5G E2E Network Slice Orchestrator | |
| +---+--------------+-------------+---------------+-----------+---+ |
| | | | | | |
| +---+--+ | F1-C +----+-----+ | N2 +----+---+ |
| | |----------(---------|gNB-CU(CP)|--------(-------| 5GC CP | |
| | | | +----+-----+ | +----+---+ |
+-| |-----------|-------------|---------------|-----------|-----+
| | | | | |
| | +---V---+ | +---V---+ |
| | | IETF | | | IETF | |
|gNB-DU| | NSC | E1 | NSC | |
| | +---+---+ | +---+---+ |
| | | | | |
| | __ V__ | ___V__ |
| | __/ \__ +--+---+ __/ \__ +-+-+
| | / IP/L2 \ | gNB | / IP \ | |
UE-+ +--(PE) Mid-haul (PE)--+CU(UP)+--(PE) Backhaul(PE)--+UPF+--DN
+------+ \__ __/ +------+ \__ __/ +---+
\______/ \______/
|------ F1-U -------| |----- N3 or N9 -----|
Figure 1: Backhaul and Mid-haul Transport Network for 5G
Figure 1 depicts 5GS expanded to show the IP transport and PE
(Provider Edge) providing IP transport service to 5GS user plane
entities 5G-AN (e.g., gNB) and UPF. Each PE hosts the Service
Demarcation Points (SDPs) to the transport network that provides the
slice capabilities. The IETF Network Slice Controller (NSC)
interfaces with the 3GPP network (customer network) that requests for
transport network slices (IETF network slice). The 5G management
plane in turn requests the Network Slice Controller (NSC) to setup
resources and connectivity in the transport network to realize the
particular network slice. 5G E2E network slice orchestration
[TS.28.533-3GPP] is used to manage the life cycle of 5G E2E network
slice across RAN, TN and core network.
The slices provisioned in the TN correspond to 3GPP slices
represented by NSSAI (set of 3GPP slices) available at 3GPP access/
data networks and locations. During 3GPP procedures for session
initialization, the network grants an S-NSSAI (single one out of the
NSSAI) based on the user's session request. The S-NSSAI for the UE's
session is signaled to the user plane nodes (gNB, UPF) during the
session setup and used to associate to the corresponding TN slice.
Chunduri, et al. Expires 16 May 2025 [Page 5]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
The N3, N9 and F1-U user planes use GTP-U [TS.29.281-3GPP] to
transport UE PDUs (IPv4, IPv6, IPv4v6, Ethernet or Unstructured).
Unlike the slice requirements for mid-haul segment (F1-U), the slice
requirements for the backhaul (N3, N9) are setup in the 3GPP network
on a per UE basis. Many UEs traffic (e.g., eMBB) at a location that
have the same requirements from a TN slice are mapped to a single TN
slice. 3GPP network functions (i.e., gNB-DU, gNB-CU and UPF) may
however be distributed (e.g., across multiple data centers) and
therefore require multiple TN slices across the respective
interfaces.
When the gNB functionality is split between a central unit (CU) and a
distributed unit (DU), a mid-haul transport segment provides the
connectivity as shown in Figure 1. Further, the gNB central unit can
be split into the control plane (CP) and user plane (UP) logical
functions as shown in Figure 1. If the RAN uses lower layer split
architecture as specified by O-RAN alliance, then the user plane path
from UE to DN also includes the fronthaul interface. The fronthaul
interface carries the radio frames in the form of In-phase (I) and
Quadrature (Q) samples using eCPRI encapsulation over Ethernet or UDP
over IP. Signaling and data transport over the fronthaul transport
has no notion of an end-user/UE session, but is rather defined by low
latency and other requirements required for processing radio
signaling and data transport between the network entities that
compose gNB. Data of different users between RAN functions have the
same requirements from a TN slice, and can therefore be carried in
the same TN slice. There may however be more than one TN slice
required for RAN based on the distribution of the RAN functions. For
the front-haul described further in Section 2.2, an Ethernet
transport with VLANs can be expected to be the case in many
deployments.
The TN slice may use 5G QoS Indicator (5QI) aware or 5QI unaware
treatment in the provider network. If 5QI aware treatment is
provisioned, packets in the TN slice will additionally be
differentiated by the 5QI value (represented by DSCP in IP header).
If 5QI unaware treatment is provisioned, all packets in the TN slice
regardless of the 5QI (DSCP value) will be treated by TN slice
characteristics. Details of the two layer QoS mechanism are found in
section 5 of [I-D.ietf-teas-5g-ns-ip-mpls].
Mapping a 3GPP slice to a TN slice using GTP-U (UDP) source port
number is described in Section 2.4.
Chunduri, et al. Expires 16 May 2025 [Page 6]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
2.2. Fronthaul and Mid-Haul Transport Network
The O-RAN Alliance defined a lower layer split at the physical layer
of the radio access network whereby the gNB-DU is split into two
entities (O-RU and O-DU) and has specified the fronthaul interface
between the O-RU and the O-DU in [ORAN-WG4.CUS-O-RAN]. The radio
layer information, in the form of In-phase (I) and Quadrature (Q)
samples are transported using enhanced Common Public Radio Interface
(eCPRI) framing over Ethernet or UDP. On an Ethernet based fronthaul
interface, the network slice instance (NSI) information is carried in
the Ethernet header through the VLAN tags and/or PCP marking. The
Ethernet switches in the fronthaul transport network inspects the
slice information (VLAN tag and/or PCP marking) in the Ethernet
header and provide the provisioned capabilities. The mapping of I
and Q samples of different radio resources (radio resource blocks or
carriers) to different slices and to their respective VLAN tags and
or PCP marking on the fronthaul interface is controlled by the O-RAN
fronthaul C-Plane and M-Plane interfaces. The fronthaul transport
network is latency and jitter sensitive. The provisioned slice
capabilities in the fronthaul transport network MUST take care of the
latency and jitter budgets of the specific slice for the fronthaul
interface. The provisioning of the fronthaul transport network is
handled by the NC pertaining to the fronthaul transport. 3GPP
functions gNB-CU (user plane) and gNB-DU may also be distributed and
have a mid-haul transport between the two 3GPP network functions. If
an IP based mid-haul interface is used, the network slice instance
(NSI) information can be MPLS, SRv6 based as defined in
[TS.28.541-3GPP]. However if the 3GPP network function (slice
customer) is physically separated from the slice provider network
(e.g., a gNB-CU (user plane) with baseband units deployed in a data
center), the MPLS, SRv6 information may not be practical to carry
across to the separated IP transport network (slice provider). In
this case, the source UDP port number of the GTP-U can be used to
indicate the slice in the transport network (slice provider).
2.3. Backhaul Transport Network
The backhaul transport over which the protocols for N3 and N9
interfaces run are described in [TS.23.501-3GPP] and
[TS.23.502-3GPP]. The end-user (UE) sessions (IP, Ethernet,
unstructured) are carried over GTP-U transport protocol over the N3
and N9 interfaces. GTP-U between the 3GPP network functions (gNB,
UPF) serves as an overlay protocol across one or more MPLS, SRv6 or
Ethernet transport networks in between. During UE session setup, a
number of parameters for context management are configured in the
gNB, UPF and that includes network slice (S-NSSAI). On an Ethernet
based backhaul interface, the slice information is carried in the
Ethernet header through the VLAN tags. If an IP based backhaul
Chunduri, et al. Expires 16 May 2025 [Page 7]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
interface is used, the network slice instance (NSI) information can
be MPLS, SRv6 based as defined in [TS.28.541-3GPP]. However, if the
3GPP network function (slice customer) is physically separated from
the slice provider network (e.g., a gNB-CU (user plane) or UPF, or
both are deployed in a data center), the MPLS, SRv6 information may
not be practical to carry across to the separated IP transport
network (slice provider). In this case, the source UDP port number
of the GTP-U can be used to indicate the slice in the IP transport
network (slice provider).
2.4. Slice Mapping using UDP Source Port Number
Communication services in 3GPP and the concepts to provision and
manage it are described in [TS.28.530-3GPP]. A brief overview is
given here with the intent to describe how it is related to an IP
transport slice and the mapping between it and the 3GPP slice.
Communication services (e.g., an eMBB service) may be realized in a
3GPP network using one or more slices identified by NSSAI (Network
Slice Selection Assistance Information) in the 3GPP control plane
signaling. In the 3GPP management plane, the network slice
identified by NSSAI is realized in a Network Slice Subnet (NSS). For
example, a slice S-NSSAI is available to a user at different
locations (and even PLMNs) and maybe realized in an NSS at that a
location. An NSS consists of sets of functions from 5GC and RAN that
belong to the NSS. Network interfaces of functions in an NSS may be
associated to one or more slice subnets. These relationships are
illustrated in Figure 2. From the viewpoint of IP transport slicing
and mapping to 3GPP slices, an IP transport network slice is
associated to 3GPP core or RAN network functions in a 3GPP Network
Slice Subnet (NSS). Thus, it can represent a slice of a transport
path for a tenant between two 3GPP user plane functions.
Chunduri, et al. Expires 16 May 2025 [Page 8]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
+-------------------+ +-------------------+ +-------------------+
| Comm. Service A | | Comm. Service B | | Comm. Service C |
+-----+-------------+ +--+-----+----------+ +--------+----------+
| ______________/ | \
| / | \
+-----+---+---+ +-------+-----+ +------+------+
|NSSAI = 000A | |NSSAI = 000B | |NSSAI = 000C |
+-------^-----+ +------^------+ +------^------+
/ / |
______/______ _____/_______ ______|_______
\ Net.Slice \ \ Net.Slice \ | Net.Slice |
\ Subnet-A \ \ Subnet-B \ | Subnet-C |
\ (NSS-A) \ \ (NSS-B) \ | (NSS-C) |
\ \ \ \ | |
\ +--------+\ \ +--------+\ | +--------+ |
\ |NSSI=CN1| \ \ |NSSI=CN1| \ | |NSSI=CN3| |
\+-----\--+ \ \+---\----+ \ | +---|----+ |
\ \ \ \ \ \ | | |
\ +===\====+\ \ +==\=====+ \ | +===|====+ |
\ |NS = TS1| \ \|NS = TS2| \ | |NS = TS3| |
\+====\===+ \ +====\===+ \ | +===|====+ |
\ \ \ \ \ \ | | |
\ +--\-----+\ +--------\-----------+ | |
\ |NSSI=AN1| \ \ \ +--\-----+ \ | |
\+--------+ \ \ \|NSSI=AN2+-----------+ |
\____________\ \ +--------+ \ |
+----\------------\--------------+
+------------+
Figure 2: Slice Configuration
Figure 2 shows the slice hierarchy described in [TS.28.530-3GPP] with
3 communication services enhanced to show the IP transport slice
instances (TS1, TS2, TS3). As an example, when a UE registers with
5GC with NSSAI 000A, OOOB and others, 5GC may select NSSAI 000B in
list of NSSAI allowed for the UE. One of the factors in selecting
the NSSAI is whether the UE may move to another location during the
lifetime of the session. In this case, the NSSAI should be such that
it has a mapping to IP transport network slice during initial attach,
and following handover. For example, a UE that attaches to 5GC with
S-NSSAI = 000B and served by user plane instances CN1 and AN2 uses IP
transport network slice NS = TS2 to provide the resources in the IP
network that corresponds to the UE session. Following handover with
S-NSSAI = 000B, the UE may be served by user plane instances CN1' and
AN2' over an IP slice TS2' in the new location.
Chunduri, et al. Expires 16 May 2025 [Page 9]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
When a 3GPP user plane function (5G-AN, UPF) and IP transport PE are
on different nodes or separated across a network, the PE router needs
to have the means by which to classify the IP packet from 3GPP entity
based on some header information. In [RFC9543] terminology, this is
a scenario where there is an AC between the 3GPP entity (customer
edge) and the SDP (Service Demarcation Point) in the IP transport
network (provider edge). The AC may, for example, be between a UPF
in a data center to a (provider edge) router that serves as the
service demarcation point for the transport network slice. The
identification information is provisioned between the 5G provider and
IP transport network and corresponding information should be carried
in each IP packet on the F1-U, N3, N9 interface. For IP transport
edge nodes to inspect the transport context information efficiently,
it should be carried in an IP header field that is easy to inspect.
It may be noted that the F1-U, N3 and N9 interfaces in 5GS are IP
interfaces. This is illustrated in Figure 3.
Chunduri, et al. Expires 16 May 2025 [Page 10]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
upstream GTP-U packet
=====================================>
customer edge attachment slice provider customer edge
circuit "ac1" ______
+-------------+ ______ __/ \__ +-----------+
| gNB-CU | __/ \__ / IP \ | UPF |
|N3 IP i/f = +--/ Data Center\---(PE) Backhaul (PE)--+N3 IP i/f =|
| gNB-AN2-if | \__ Network__/ \__ __/ |UPF-CN1-if |
+-------\-----+ \______/ \___\__/ +-----------+
\ \
\ \+--------------------+
+--------------\----------------+ | Slice Mapping: |
|+--------------------------+ | |Match: |
||3GPP CP Config: | | | vlan-id = 100 |
||NSSI = AN2 | | | src-port = 5678 |
|+--------------------------+ | |Action: |
|+-----------------------------+| | select NS = TS2 |
||Slice Mapping to UPF-CN1-if: || +--------------------+
|| EP_Transport S-NSSAI=000B ||
|| ipAddress = UPF-CN1-if ||
|| connectionPointIDType = ||
|| "ATTACHMENT_CIRCUIT" ||
|| connectionPointId = "ac1" ---------+
|+-----------------------------+| |
+-------------------------------+ |
V
+-----------------------------------------------+
| * "ac1" properties: |
| - vlan-id: 100 |
| - src-port = 5678 |
| - CE address (gNB-CU): gNB-AN2-if |
| - PE address: 192.0.2.2/30 |
| - Routing: static 198.51.100.0/24 via |
| 192.9.2.1 tag primary_UP_slice |
+-----------------------------------------------+
Figure 3: Slice Mapping using UDP source port
Figure 3 shows the configuration and mapping applied to network
instances in a 3GPP network slice subnet and corresponding IP
transport network instances for sending an upstream GTP packet from
gNB-CU (user plane) to UPF. The gNB-CU (user plane) function is in a
data center (site 1) and separated from the IP transport slice
provider by an AC ("ac1" in Figure 3). The AC ("ac1") is for an
EP_Transport configured as specified in [TS.28.541-3GPP] and realized
using [I-D.ietf-opsawg-teas-attachment-circuit] and related
extensions for GTP in Section 4.
Chunduri, et al. Expires 16 May 2025 [Page 11]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
In this example, a GTP-U packet at gNB-CU (user plane) is from a UE
session with S-NSSAI = 000B (and thus associated to 3GPP and IP
transport network instances in the figure for providing slice
resources). Since the GTP-U packet belongs to a session with S-NSSAI
= 000B, the gNB-CU (UP) maps it to UDP port 5678 in the GTP-U header
(outer encapsulation source port) and uses VLAN ID 100 based on the
slice mapping to EP_Transport and "ac1" as shown in the figure. The
slice mapping proposed in this document does not depend on VLANs,
however, this example is to illustrate that the UDP mapping can be
used in conjunction with other AC properties. The GTP-U packet is
forwarded by the data center network to the PE router at IP backhaul
network. The PE matches on VLAN ID of GTP-U packet and IP source
port to select the provisioned slice (NS = TS2). The GTP-U packet is
then forwarded to the UPF. For a downstream GTP-U packet, the UPF
customer edge may similarly be attached to a PE and have similar
slice configuration and mapping (details are not shown in the
figure).
PEs can thus be provisioned with a policy based on the source UDP
port number (and other identifiers like VLAN) to the underlying
transport path and then deliver the QoS/slice resource provisioned in
the transport network. The source UDP port number that is encoded is
the outer IP (corresponding to GTP-U header) while the inner IP
packet (UE payload) is unaltered. The source UDP port number is
encoded by the node that creates the GTP-U encapsulation and
therefore, this mechanism has no impact on UDP checksum calculations.
3GPP network operators may use IPsec gateways (SEG) to secure packets
between two sites - for example over an F1-U, N3 or N9 segment. The
IP network slice identifier in the GTP-U packet should be in the
outer IP source port number even after IPSec encryption for PE
transport routers to inspect and provide the level of service
provisioned. Tunnel mode - which is the case for SEG/IPSec gateways
- adds an outer IP header in both AH (Authenticated Header) and ESP
(Encapsulated Security Payload) modes. Mechanisms described in
[I-D.xu-ipsecme-esp-in-udp-lb] may be used to encapsulate the ESP
packet in UDP for better load balancing and this can also be used to
preserve the UDP source port of GTP-U packet.
3. Transport Network Underlays
Traffic engineered underlay networks are an essential component to
realize the slicing defined in this document. Transport networks
should be able to realize midhaul, backhaul and control plane slices
shown in Figure 1. This section outlines how GTP/UDP source ports
are used to map to slice types. [RFC9543] (section 7) describes in
more detail how a network slice can be realized over different
transport network technologies including enhanced VPN, IP/MPLS and
Chunduri, et al. Expires 16 May 2025 [Page 12]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
SR-TE.
An example with different user plane slice types and transport paths
is shown in the figure. In this case with 3 different 3GPP Slice and
Service Types (SSTs), 3 transport TE paths are setup. For uplink
traffic, an underlying TE transport path may be from a gNB-CU to a
UPF for example. A similar downlink path and underlying transport
from UPF to gNB-CU is configured. The figure shows UDP port ranges,
SST, transport path (in this example pseudowire/VPN) and transport
path characteristics.
+----------------+------------+------------------+-----------------+
|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 | TE-PATH-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 | TE-PATH-B | Req. |
| | latency) | | Bandwidth: By |
| | | | Delay: Dy |
| | | | Jitter: Jy |
+----------------+------------+------------------+-----------------+
| Range Zx - Zy | | | |
| Z1, Z2(discrete| EMBB | PW ID/VPN info, | Non-GBR |
| values) | (broadband)| TE-PATH-C | Bandwidth: Bx |
+----------------+------------+------------------+-----------------+
Figure 4: Mapping of Transport Paths on F1-U/N3/N9
In some E2E scenarios, security is desired granularly in the
underlying transport network. In such cases, there would be a need
to have separate sub-ranges under each SST to provide the TE path in
preserving the security characteristics. The UDP source port range
captured in Figure 4 would be sub-divided to maintain the TE path for
the current SSTs with the security. The current solution doesn't
provide any mandate on the UE traffic in selecting the type of
security.
Chunduri, et al. Expires 16 May 2025 [Page 13]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
There are many possible transport network technologies that may be
used to realize these slices. These are described in [RFC9543].
4. Attachment Circuit as a Service Extensions
4.1. Attachment Circuit Extension for GTPU
Section 2.4 provided a description of how a GTP-U connection AC can
be mapped using source address and port number to an IETF transport
slice. To facilitate slice capabilities within a provider network,
the AC is a means to bind the slice service that is previously agreed
between the customer (i.e., 3GPP network) and provider (i.e., IP
network provider). This section uses provisioning of attachment
circuits described in [I-D.ietf-opsawg-teas-attachment-circuit] and
extends it to support GTP and encapsulated GTP.
The overall tree structure of the AC service in
[I-D.ietf-opsawg-teas-attachment-circuit] is extended to support
attachment circuits that are encapsulated layer 3 such as GTP and
GTPU in ESP-UDP encapsulation (IPSec (ESP) UDP encapsulation as in
[I-D.xu-ipsecme-esp-in-udp-lb]).
Chunduri, et al. Expires 16 May 2025 [Page 14]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
+--rw specific-provisioning-profiles
| ...
+--rw service-provisioning-profiles
| ...
+--rw attachment-circuits
+--rw ac-group-profile* [name]
| ...
+--rw placement-constraints
| ...
+--rw ac* [name]
...
+--rw l2-connection {ac-common:layer2-ac}?
| ...
+--rw ip-connection {ac-common:layer3-ac}?
| +--rw ipv4 {vpn-common:ipv4}?
| | ...
| +--rw ipv6 {vpn-common:ipv6}?
| | ...
| +--rw (l3-service)?
| +--:(l3-tunnel-service)
| +--rw l3-tunnel-service
| +--rw type? identityref
| +--rw (ietf-ac-gtpu)?
| ...
+--rw routing-protocols
| ...
+--rw oam
| ...
+--rw security
| ...
+--rw service
...
Figure 5: Extended AC Service Tree with UDP Tunnel
The 'l3-service' and 'l3-tunnel-service' in the attachment circuits
structure in [I-D.ietf-opsawg-teas-attachment-circuit] is used to
configure the relevant layer 3 tunnel properties of a GTP-U AC. IPv4
and IPv6 properties of the GTP-U bearer are provided in "ip-
connection" and the extension below adds source port number and range
for the GTP-U connection.
Chunduri, et al. Expires 16 May 2025 [Page 15]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
module: ietf-ac-gtpu
augment /ac-svc:attachment-circuits/ac-svc:ac/ac-svc:ip-connection
/ac-svc:l3-service/ac-svc:l3-tunnel-service
/ac-svc:l3-tunnel-service:
+--rw (udp-port)?
+--:(port-range-or-operator)
+--rw source-port-range-or-operator
+--rw (port-range-or-operator)?
+--:(range)
| +--rw lower-port inet:port-number
| +--rw upper-port inet:port-number
+--:(operator)
+--rw operator? operator
+--rw port inet:port-number
Figure 6: GTPU Yang Module
'l3-tunnel-service' in [I-D.ietf-opsawg-teas-attachment-circuit] is
extended in this document to carry UDP source port number/range.
For encapsulations other than UDP, the underlying transports may use
mappngs using the relevant constructs native to the respective
technology (e.g., MPLS, SR-MPLS and SRv6). This is not covered in
this document.
4.2. ietf-ac-gtpu YANG Module
The "ietf-ac-gtpu" module uses definitions in
[I-D.ietf-opsawg-teas-attachment-circuit] and [RFC8519].
module ietf-ac-gtpu {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-ac-gtpu";
prefix ac-gtpu;
import ietf-ac-common {
prefix ac-common;
reference
"RFC SSSS: YANG Data Models for Bearers and 'Attachment
Circuits'-as-a-Service (ACaaS)";
}
import ietf-ac-svc {
prefix ac-svc;
reference
Chunduri, et al. Expires 16 May 2025 [Page 16]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
"RFC SSSS: YANG Data Models for Bearers and 'Attachment
Circuits'-as-a-Service (ACaaS)";
}
import ietf-packet-fields {
prefix packet-fields;
reference
"RFC 8519: YANG Data Model for Network Access
Control Lists (ACLs), Section 4.2";
}
organization
"IETF DMM (Distributed Mobility Management)";
contact
"WG Web:
WG List:
Author: Mohamed Boucadair
";
description
"This YANG module defines a YANG model for augmenting the ACaaS
service model with GTP-U as Layer 3 tunnel service.
Copyright (c) 2024 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Revised BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; see the
RFC itself for full legal notices.";
revision 2023-11-13 {
description
"Initial revision.";
reference
"RFC XXXX: Mobility-aware Transport Network Slicing for 5G";
}
identity gtp-u {
base ac-common:l3-tunnel-type;
description
"GPRS Tunneling Protocol - User plane.";
}
Chunduri, et al. Expires 16 May 2025 [Page 17]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
augment "/ac-svc:attachment-circuits/ac-svc:ac"
+ "/ac-svc:ip-connection/ac-svc:l3-service"
+ "/ac-svc:l3-tunnel-service/ac-svc:l3-tunnel-service" {
when "derived-from-or-self(./type, 'gtpu')" {
description
"Only applicable if l3 service type is GTP-U.";
}
description
"Augments Layer 3 AC service with required data nodes for
GTP-U support.";
choice udp-port {
description
"Choice of specifying the source port number or referring
to a group of port numbers.";
container source-port-range-or-operator {
description
"Indicates a set of source ports numbers.";
uses packet-fields:port-range-or-operator;
}
}
}
}
Figure 7: GTPU YANG Module
5. Acknowledgements
Thanks to Young Lee for discussions on this document including 3GPP
and IETF slice orchestration in the early discussions. Thanks to Sri
Gundavelli, Kausik Majumdar, Hannu Flinck, Joel Halpern, Satoru
Matsushima and Tianji Jiang who provided detailed feedback on this
document. Mohamed Boucadair provided detailed Yang structures for
the ietf-ac-gtpu attachment circuit to make it flexible for use in
this document and for future services.
6. IANA Considerations
This document has no requests for IANA code point allocations.
7. Security Considerations
Section 10 of [RFC9543] discusses security considerations that are
applicable to network slicing and apply in this document.
Provisioning the TN slice using an IETF Network Slice Controller
should ensure the authentication of entities, privacy of information
exchanged and secure transport between components as identified in
[I-D.ietf-teas-ns-controller-models]. YANG extensions and its
Chunduri, et al. Expires 16 May 2025 [Page 18]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
transport should conform to the security considerations in
[I-D.ietf-opsawg-teas-attachment-circuit].
8. Contributing Authors
The following people contributed substantially to the content of this
document and should be considered co-authors.
Praveen Muley
Nokia
440 North Bernardo Ave
Mountain View CA 94043
USA
Email: praveen.muley@nokia.com
Richard Li
Independent
Email: richard.li@seu.edu.cn
Xavier De Foy
InterDigital Communications, LLC
1000 Sherbrooke West
Montreal
Canada
Email: Xavier.Defoy@InterDigital.com
Reza Rokui
Ciena
Email: rrokui@ciena.com
9. Informative References
[I-D.ietf-opsawg-teas-attachment-circuit]
Boucadair, M., Roberts, R., de Dios, O. G., Barguil, S.,
and B. Wu, "YANG Data Models for Bearers and 'Attachment
Circuits'-as-a-Service (ACaaS)", Work in Progress,
Internet-Draft, draft-ietf-opsawg-teas-attachment-circuit-
18, 7 November 2024,
.
Chunduri, et al. Expires 16 May 2025 [Page 19]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
[I-D.ietf-teas-5g-network-slice-application]
Geng, X., Contreras, L. M., Rokui, R., Dong, J., and I.
Bykov, "IETF Network Slice Application in 3GPP 5G End-to-
End Network Slice", Work in Progress, Internet-Draft,
draft-ietf-teas-5g-network-slice-application-03, 10 June
2024, .
[I-D.ietf-teas-5g-ns-ip-mpls]
Szarkowicz, K. G., Roberts, R., Lucek, J., Boucadair, M.,
and L. M. Contreras, "A Realization of Network Slices for
5G Networks Using Current IP/MPLS Technologies", Work in
Progress, Internet-Draft, draft-ietf-teas-5g-ns-ip-mpls-
13, 11 October 2024,
.
[I-D.ietf-teas-ns-controller-models]
Contreras, L. M., Rokui, R., Tantsura, J., Wu, B., and X.
Liu, "IETF Network Slice Controller and its Associated
Data Models", Work in Progress, Internet-Draft, draft-
ietf-teas-ns-controller-models-03, 21 October 2024,
.
[I-D.xu-ipsecme-esp-in-udp-lb]
Xu, X., Hegde, S., Pismenny, B., Zhang, D., Xia, L., and
M. Puttaswamy, "Encapsulating IPsec ESP in UDP for Load-
balancing", Work in Progress, Internet-Draft, draft-xu-
ipsecme-esp-in-udp-lb-13, 7 October 2024,
.
[ORAN-WG4.CUS-O-RAN]
O-RAN Alliance (O-RAN), "O-RAN Fronthaul Working Group;
Control, User and Synchronization Plane Specification;
v2.0.0", August 2019.
[RFC8519] Jethanandani, M., Agarwal, S., Huang, L., and D. Blair,
"YANG Data Model for Network Access Control Lists (ACLs)",
RFC 8519, DOI 10.17487/RFC8519, March 2019,
.
[RFC9543] Farrel, A., Ed., Drake, J., Ed., Rokui, R., Homma, S.,
Makhijani, K., Contreras, L., and J. Tantsura, "A
Framework for Network Slices in Networks Built from IETF
Technologies", RFC 9543, DOI 10.17487/RFC9543, March 2024,
.
Chunduri, et al. Expires 16 May 2025 [Page 20]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
[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.
[TS.23.502-3GPP]
3rd Generation Partnership Project (3GPP), "Procedures for
5G System; Stage 2, 3GPP TS 23.502, v2.0.0", December
2017.
[TS.23.503-3GPP]
3rd Generation Partnership Project (3GPP), "Policy and
Charging Control System for 5G Framework; Stage 2, 3GPP TS
23.503 v1.0.0", December 2017.
[TS.28.530-3GPP]
3rd Generation Partnership Project (3GPP), "Aspects;
Management and Orchestration; Concepts, use cases and
requirements (Release 17)", June 2022.
[TS.28.533-3GPP]
3rd Generation Partnership Project (3GPP), "Management and
Orchestration Architecture Framework (Release 15)", June
2018.
[TS.28.541-3GPP]
3rd Generation Partnership Project (3GPP), "Management and
orchestration; 5G Network Resource Model (NRM); Stage 2
and stage 3 (Release 19)", July 2024.
[TS.29.281-3GPP]
3rd Generation Partnership Project (3GPP), "GPRS Tunneling
Protocol User Plane (GTPv1-U), 3GPP TS 29.281 v15.1.0",
December 2018.
[TS.38.300-3GPP]
3rd Generation Partnership Project (3GPP), "NR; NR and NG-
RAN Overall Description; Stage 2; v15.7.0", September
2019.
[TS.38.401-3GPP]
3rd Generation Partnership Project (3GPP), "NG-RAN;
Architecture description; v15.7.0", September 2019.
Appendix A. Abbreviations
5G-AN – 5G Access Network
Chunduri, et al. Expires 16 May 2025 [Page 21]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
5GS – 5G System
AC – Attachment Circuit
CSR – Cell Site Router
CP – Control Plane (5G)
CU – Centralized Unit (5G, gNB)
DN – Data Network (5G)
DU – Distributed Unit (5G, gNB)
eMBB – enhanced Mobile Broadband (5G)
gNB – Next Generation Node B
GBR – Guaranteed Bit Rate (5G)
GTP-U – GPRS Tunneling Protocol - User plane (3GPP)
MIoT – Massive IoT (5G)
MPLS – Multi Protocol Label Switching
NG-RAN – Next Generation Radio Access Network (i.e., gNB, NG-eNB -
RAN functions which connect to 5GC)
NSC – Network Slice Controller
NSS – Network Slice Subnet
NSSAI – Network Slice Selection Assistance Information
NSSI – Network Slice Subnet Identifier
NSSF – Network Slice Selection Function
PDU – Protocol Data Unit (5G)
PW – Pseudo Wire
SDP – Service Demarcation Point
S-NSSAI – Single Network Slice Selection Assistance Information
SST – Slice and Service Types (5G)
Chunduri, et al. Expires 16 May 2025 [Page 22]
Internet-Draft Mobility-aware Transport Network Slicing November 2024
SR – Segment Routing
TE – Traffic Engineering
UP – User Plane(5G)
UPF – User Plane Function (5G)
URLLC – Ultra reliable and low latency communications (5G)
Authors' Addresses
Uma Chunduri (editor)
Intel Corporation
2191 Laurelwood Rd
Santa Clara, CA 95054
United States of America
Email: umac.ietf@gmail.com
John Kaippallimalil (editor)
Futurewei
United States of America
Email: john.kaippallimalil@futurewei.com
Sridhar Bhaskaran
Rakuten Symphony
Email: sridhar.bhaskaran@rakuten.com
Jeff Tantsura
Nvidia
Email: jefftant.ietf@gmail.com
Luis M. Contreras
Telefonica
Telefonica Sur-3 building, 3rd floor
28050 Madrid
Spain
Email: luismiguel.contrerasmurillo@telefonica.com
Chunduri, et al. Expires 16 May 2025 [Page 23]