A Realization of IETF Network Slices for 5G Networks Using Current IP/MPLS Technologies
draft-srld-teas-5g-slicing-01
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
|
|
|---|---|---|---|
| Authors | Krzysztof Grzegorz Szarkowicz , Richard Roberts , Julian Lucek , John Drake , Mohamed Boucadair , Luis M. Contreras , Ivan Bykov , Reza Rokui , Luay Jalil , Beny Dwi Setyawan | ||
| Last updated | 2022-10-24 | ||
| Replaced by | draft-ietf-teas-5g-ns-ip-mpls, draft-ietf-teas-5g-ns-ip-mpls, draft-ietf-teas-5g-ns-ip-mpls | ||
| RFC stream | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-srld-teas-5g-slicing-01
TEAS Working Group K. Szarkowicz, Ed.
Internet-Draft R. Roberts
Intended status: Informational J. Lucek
Expires: 27 April 2023 J. Drake
Juniper Networks
M. Boucadair
Orange
LM. Contreras
Telefonica
I. Bykov
Ribbon Communications
R. Rokui
Ciena
L. Jalil
Verizon
B. Setyawan
XL Axiata
24 October 2022
A Realization of IETF Network Slices for 5G Networks Using Current IP/
MPLS Technologies
draft-srld-teas-5g-slicing-01
Abstract
5G slicing is a new feature that was introduced by the 3rd Generation
Partnership Project (3GPP) in mobile networks. It covers slicing
requirements for all mobile domains, including the Radio Access
Network (RAN), Core Network (CN), and Transport Network (TN).
This document describes a basic IETF Network Slice realization model
in IP/MPLS networks with a focus on fulfilling 5G slicing
connectivity requirements. This IETF Network Slice realization model
reuses many building blocks currently commonly used in service
provider networks.
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/.
Szarkowicz, et al. Expires 27 April 2023 [Page 1]
Internet-Draft 5G Transport Slices October 2022
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 27 April 2023.
Copyright Notice
Copyright (c) 2022 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
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. 5G Network Slicing Integration in Transport Networks . . . . 4
2.1. 5G Network Slicing versus Transport Network Slicing . . . 4
2.2. NF to NF Datapath vs Transport Network . . . . . . . . . 5
2.2.1. Segmentation of NF-to-NF Datapath . . . . . . . . . . 5
2.2.2. Orchestration of Local Segment termination at ETN . . 9
2.3. 5G slice to IETF Network Slice mapping . . . . . . . . . 10
2.4. First 5G slice versus subsequent slices . . . . . . . . . 12
3. High-Level Overview of the Realization Model . . . . . . . . 15
3.1. VLAN Hand-off . . . . . . . . . . . . . . . . . . . . . . 16
3.2. IP Hand-off . . . . . . . . . . . . . . . . . . . . . . . 17
3.3. MPLS Label Hand-off . . . . . . . . . . . . . . . . . . . 19
3.3.1. Option B . . . . . . . . . . . . . . . . . . . . . . 20
4. QoS Mapping Models . . . . . . . . . . . . . . . . . . . . . 22
4.1. 5QI-unaware Mode . . . . . . . . . . . . . . . . . . . . 23
4.1.1. Inbound Edge Resource Control . . . . . . . . . . . . 26
4.1.2. Outbound Edge Resource Control . . . . . . . . . . . 29
4.2. 5QI-aware Mode . . . . . . . . . . . . . . . . . . . . . 30
4.2.1. Inbound Edge Resource Control . . . . . . . . . . . . 32
4.2.2. Outbound Edge Resource Control . . . . . . . . . . . 34
4.3. Transit Resource Control . . . . . . . . . . . . . . . . 36
5. Transport Planes Mapping Models . . . . . . . . . . . . . . . 36
5.1. 5QI-unaware Mode . . . . . . . . . . . . . . . . . . . . 37
5.2. 5QI-aware Mode . . . . . . . . . . . . . . . . . . . . . 39
Szarkowicz, et al. Expires 27 April 2023 [Page 2]
Internet-Draft 5G Transport Slices October 2022
6. Capacity Planning/Management . . . . . . . . . . . . . . . . 40
6.1. Bandwidth models . . . . . . . . . . . . . . . . . . . . 43
6.1.1. Scheme 1: Shortest Path Forwarding . . . . . . . . . 43
6.1.2. Scheme 2: TE LSPs with Fixed Bandwidth
Reservations . . . . . . . . . . . . . . . . . . . . 44
6.1.3. Scheme 3: TE LSPs without Bandwidth Reservations . . 45
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 45
8. Security Considerations . . . . . . . . . . . . . . . . . . . 45
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 45
9.1. Normative References . . . . . . . . . . . . . . . . . . 46
9.2. Informative References . . . . . . . . . . . . . . . . . 46
Appendix A. Acronyms and Abbreviations . . . . . . . . . . . . . 49
Appendix B. An overview of 5G Networking . . . . . . . . . . . . 52
B.1. Building Blocks . . . . . . . . . . . . . . . . . . . . . 52
B.2. Core Network . . . . . . . . . . . . . . . . . . . . . . 54
B.3. RAN . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
B.4. Transport Network . . . . . . . . . . . . . . . . . . . . 57
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 59
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 59
1. Introduction
[I-D.ietf-teas-ietf-network-slices] introduces the framework for
network slicing in the context of networks built using IETF
technologies. The IETF network slicing framework introduces the
concept of a Network Resource Partition (NRP), which is simply a
collection of resources identified in the underlay network. There
could be multiple realizations of high-level IETF Network Slice and
NRP concepts, where each realization might be optimized for the
different network slicing use cases that are listed in
[I-D.ietf-teas-ietf-network-slices].
This document describes a basic - using only single NRP - IETF
Network Slice realization model in IP/MPLS networks, with a focus on
fulfilling 5G slicing connectivity requirements. This IETF Network
Slice realization model reuses many building blocks currently
commonly used in communication service provider (CSP) networks.
The reader may refer to [I-D.ietf-teas-ns-ip-mpls] for more advanced
realization models.
Also, the reader may refer to [RFC6459] and [TS-23.501] for more
details about 3GPP network architectures.
Szarkowicz, et al. Expires 27 April 2023 [Page 3]
Internet-Draft 5G Transport Slices October 2022
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. 5G Network Slicing Integration in Transport Networks
2.1. 5G Network Slicing versus Transport Network Slicing
Network Slicing has a different meaning in the mobile and transport
worlds. Hence, for the sake of precision, this section provides a
brief description of the objectives of 5G Network Slicing and
Transport Network Slicing.
* The objective of 5G network slicing is to provide dedicated
resources of the whole 5G infrastructure to certain users,
application, customers or PLMN (e.g., RAN sharing). These
resources are from the Transport Network, RAN and CORE Network
Functions and the underlying infrastructure. [TS-28.530] defines
5G network slicing by introducing the concept of Network Slice
Subnet (NSS) to represent slices within each of these domains:
RAN, CORE and Transport Network (i.e., RAN NSS, CN NSS and TN
NSS). As per 3GPP specifications, NSS can be shared or dedicated
to a single slice.
* The objective of Transport Network slicing is to isolate,
guarantee or prioritize Transport Network resources for slices
such as buffers, link bandwidth or even RIB/FIB. Transport
Network Slicing has two main flavors: Hard and Soft slicing. Hard
slicing provides dedicated network capacity to slices. Soft
Slicing provides shared network capacity with guarantees for each
slice. There are different options to implement TN slices based
on tooling such as VRFs for traffic separation, QoS and TE. Also,
TN slice realization for 5G slices might combine elements of hard
slicing in one part of the transport network, with elements of
soft slicing in other parts of the transport network. An
optimized 5G network slicing architecture should integrate
Transport Network Slicing, however, it is possible to implement 5G
network slicing without Transport Network Slicing, as explained in
the next section.
Szarkowicz, et al. Expires 27 April 2023 [Page 4]
Internet-Draft 5G Transport Slices October 2022
Slicing in the transport network is implemented using IETF
technologies, therefore, inline with
[I-D.ietf-teas-ietf-network-slices], in this document the term
"IETF Network Slice" (IETF NS, or INS in short) is used to
describe the slice in the Transport Network domain of overall 5G
architecture, composed from RAN, TN and CN domains.
2.2. NF to NF Datapath vs Transport Network
The 3GPP specifications loosely define the Transport Network and its
integration in RAN and Core Network domains: the role of the
Transport Network is to interconnect Network Functions. In other
words, it is the end-to-end datapath between two Network Functions.
In practice, this end-to-end datapath is often a non-uniform
architecture made up of several segments potentially managed by
different organizations. In this document, we rather define the
Transport Network with a service provider scope: the TN extends up to
the PE or the CE if it is also managed by the TN Orchestration.
Additionally, we assume that the Transport Network is MPLS or SRv6
capable.
2.2.1. Segmentation of NF-to-NF Datapath
This section introduces a decomposition of the datapath between two
Network Functions (NFs) into two segments based on the Orchestration
domains: TN segments and Local segments.
* TN Segment: the realization of this segment is driven by the IETF
NSC / Transport Network Orchestrator (TNO). Generally speaking, a
TN Segment provides connectivity between two sites.
* Local segment: this segments permits either to connect Network
Functions within a given site or to connect a Network Function to
the Transport Network. The realization of this segment is
directly or indirectly driven by the 5G Orchestration without any
involvement of the Transport Network Orchestration. Generally
speaking, the Local Segment is a datapath local to a site. This
site can be either DC, POP, CO or a virtualized infrastructure in
a Public Cloud.
Note that more complex scenarios are possible, for example with extra
segmentation of TN or Local Segments. Additionally, sites can be of
different types such as Edge, Data Center, or Public Cloud, each with
specific network design, hardware dependencies, management interface
and diverse networking technologies (e.g MPLS, SRv6, VXLAN, L2VPN vs
L3VPN, ...). The objective of this section is to clarify the scope
of the Transport Network rather than to cover any technology or
design combination.
Szarkowicz, et al. Expires 27 April 2023 [Page 5]
Internet-Draft 5G Transport Slices October 2022
The realization of IETF Network Slices (i.e. connectivity with
performance commitments) applies therefore to the TN Segments. We
consider Local Segments as an extension of the connectivity of the
RAN/CORE domain without slice-specific performances requirements by
assuming that the local infrastructure is overprovisioned and
implements traditional QoS/Scheduling logic.
In parallel, since the TN domain can extend either to the CE or to
the PE, we introduce the term Edge Transport Node (ETN) to define
this boundary. The ETN is therefore a Transport Node that stitches
Local segments and TN Segments. Note that depending on the design,
the placement of the SDP as defined in
[I-D.ietf-teas-ietf-network-slices] may or may not be enforced on the
ETN itself. The following figure is a representation of the end-to-
end datapath between Network Functions including Segments and ETN (in
practice PE or a managed CE), where applicable.
SMO / Site TN SMO / Site
Orchestration Orchestration Orchestration
│ │ │
│ │ │
┌ ─ ─ ─ ─ ┼ ┐ ┌ ─ ─ ─│─ ─ ─ ┐ ┌ ┼ ─ ─ ─ ─ ┐
│ │ │
│ ┌──┐ ▼ │ ┌─┴─┐ ▼ ┌─┴─┐ │ ▼ ┌──┐ │
│NF├─────────┤ETN├─────────┤ETN├─────────┤NF│
│ └──┘ │ └─┬─┘Transport└─┬─┘ │ └──┘ │
5G Site 1 Network 5G Site 2
└ ─ ─ ─ ─ ─ ┘ └ ─ ─ ─ ─ ─ ─ ┘ └ ─ ─ ─ ─ ─ ┘
└─────────┘ └─────────┘ └─────────┘
Local TN Local
Segment Segment Segment
■─────────────■
IETF Network Slice
◀─────────────────────────────────────▶
End-to-end datapath between NFs
Figure 1: Segmentation of the NF-NF datapath
NFs may also be placed in the same site and interconnected via a
Local Segment. In this case, there is no TN segment (i.e. no
Transport Network Node is present in the datapath).
Szarkowicz, et al. Expires 27 April 2023 [Page 6]
Internet-Draft 5G Transport Slices October 2022
SMO / Site
Orchestration
│
│
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┼ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐
│
│ ┌──┐ ▼ ┌──┐ │
│NF├─────────────────────────────────────┤NF│
│ └──┘ └──┘ │
5G Site
└ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘
└─────────────────────────────────────┘
Local Segment
◀─────────────────────────────────────▶
End-to-end datapath between NFs
Figure 2: NF-NF datapath within single site
Next, the following picture provides examples of different
realizations of Local and TN segments, as well the Service
Demarcation Points.
* L2 vs L3 Local Segment: the Local Segment can interconnect the NF
and the ETN thanks to a unique vlan/LAN with no intermediate
routing hop (the simplest example is an NF directly connected to a
PE): A1, A2, A3 and A4. Alternatively, the NF interfaces may be
attached in a different LAN/vlan than the ETN interface thanks to
additional local routing between the ETN and the NF (e.g. CE, IP
Fabric...): B1, B2, B3 and B4.
* ETN: the ETN can be either the PE or the CE if it is managed by
the TN Orchestration (A1, A2, B1, B2).
* SDP: the SDP can be located in multiple places as per
[I-D.ietf-teas-ietf-network-slices] section 4.2: A1 + B1 for case
i), A2 + B2 for case i), B3 + A3 for case iii) and B4 + A4 for
case iv)
* Redundancy/Scale-out: no example of redundancy/multihoming/scale-
out is provided for the sake of simplicification. Nonetheless,
each Node/NF can be multiple.
Szarkowicz, et al. Expires 27 April 2023 [Page 7]
Internet-Draft 5G Transport Slices October 2022
Local segment Transport Network
◀───────────────────────────▶◀─────────────────── ─ ─ ─ ─
┌─────────────────────┐ ┌─────────────────── ─ ─ ─ ┐
│ Site Type A1 │ │
│ ┌────┐ │ ┌─■──┐ ┌────┐ . │
│ │ NF ├───────────────────┤ CE ├────┤ PE ├─────╱ ╲
│ └────┘ │ └─┬──┘ └────┘ ; : │
└─────────────────────┘ │ ; :
┌─────────────────────┐ │ ; : │
│ Site Type A2 │ │ │ │
│ ┌────┐ │ ┌────┤ ┌────┐ │ │ │
│ │ NF ├────────────────┤ CE ■───────┤ PE ├───│ │
│ └────┘ │ └────┤ └────┘ ; : │
└─────────────────────┘ │ ; ┌───┐ :
┌─────────────────────┐ │ │ │ P │ │ │
│ Site Type A3 │ │ │ └───┘ │
│ ┌────┐ │ ├────┐ │ │ │
│ │ NF ├─────────────────────■ PE ├──────────│ │
│ └────┘ │ ├────┘ │ │ │
└─────────────────────┘ │ │ │
┌─────────────────────┐ │ │ │ │
│ Site Type A4 │ │ ; :
│ ┌────┐ │ ┌─■──┐ ; : │
│ │ NF ├───────────────────┤ PE ├───────────│ ┌───┐ │
│ └────┘ │ └─┬──┘ │ │ P │ │ │
└─────────────────────┘ │ │ └───┘ │
┌─────────────────────┐ │ │ │ │
│ Site Type B1.───. │ │ │ │
│ ,' `. │ │ │ │ │
│ ; Local :│ │ │ │
│ ┌────┐ │ Routing ││ ┌─■──┐ ┌────┐ │ │ │
│ │ NF ├───┤ managed ├─────┤ CE ├────┤ PE ├─┤ │
│ └────┘ : by SMO ;│ └─┬──┘ └────┘ │ │ │
│ ╲ ╱ │ │ │ │
│ `. ,' │ │ │ ┌───┐ │ │
│ `─' │ │ │ │ P │ │
└─────────────────────┘ │ │ └───┘ │ │
┌─────────────────────┐ │ │ │
│ Site Type B2.───. │ │ │ │ │
│ ,' `. │ │ │ │
│ ; Local :│ │ │ │ │
│ ┌────┐ │ Routing ││ ┌────┤ ┌────┐ │ │
│ │ NF ├───┤ managed ├──┤ CE ■───────┤ PE ├─┤ │ │
│ └────┘ : by SMO ;│ └────┤ └────┘ │ │
│ ╲ ╱ │ │ │ │ │
│ `. ,' │ │ │ ┌───┐ │
│ `─' │ │ │ │ P │ │ │
Szarkowicz, et al. Expires 27 April 2023 [Page 8]
Internet-Draft 5G Transport Slices October 2022
└─────────────────────┘ │ │ └───┘ │
┌─────────────────────┐ │ │ │ │
│ Site Type B3.───. │ │ : ;
│ ,' `. │ │ : ; │
│ ; Local :│ │ │ │
│ ┌────┐ │ Routing ││ ├────┐ │ │ │
│ │ NF ├───┤ managed ├───────■ PE ├──────────│ │
│ └────┘ : by SMO ;│ ├────┘ │ │ │
│ ╲ ╱ │ │ │ │
│ `. ,' │ │ │ ┌───┐ │ │
│ `─' │ │ │ │ P │ │
└─────────────────────┘ │ : └───┘ ; │
┌─────────────────────┐ │ : ;
│ Site Type B4.───. │ │ │ │ │
│ ,' `. │ │ │ │
│ ; Local :│ │ │ │ │
│ ┌────┐ │ Routing ││ ┌─■──┐ : ;
│ │ NF │───┤ managed ├─────┤ PE ├──────────────: ; │
│ └────┘ : by SMO ;│ └─┬──┘ │ │
│ ╲ ╱ │ │ : ; │
│ `. ,' │ │ ╲ ╱
│ `─' │ │ ' │
└─────────────────────┘ └─────────────────── ─ ─ ─ ─
├─────────┤
ETN
■ - Service Demarcation Point
Figure 3: Examples of various combinations of Local Segments, ETN
and SDP
2.2.2. Orchestration of Local Segment termination at ETN
The interconnection between the 5G site and the Transport Network is
made up of shared networking resources. More precisely, the Local
Segment terminates to an interface of the ETN, which must be
configured with consistent dataplane network information (e.g. vlan-
id and IP addresses/subnets). Hence, the realization of this
interconnection requires a coordination between the SMO and the
Transport Orchestration (NSC). In this document, we assume that this
coordination is based on IETF YANG data models and APIs (more details
in further sections). The following diagram is a basic example of a
L3CE-PE realization with shared network resource such as vlan-ID and
IP prefixes, which must be passed between Orchestrators via the
Network Slice Interface.
Szarkowicz, et al. Expires 27 April 2023 [Page 9]
Internet-Draft 5G Transport Slices October 2022
Datapath network resources (i.e., VLAN ID, IP
prefixes) exchanged via SMO-NSC interface (NSI)
┌ ─ ─ ─ ─ ─ ─ ┐ ┌ ─ ─ ─ ─ ─ ─ ┐
TN
│ │ │Orchestration│
SMO / Site IETF APIs/DM
│Orchestration│ ◀────────────▶ │ TSC │
─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ │
│ │
┌ ─ ─ ─ ─ ─ ─ ─ ┼ ┐ ┌ ┼ ─ ─ ─ ─ ─ ─ ─ ┐
▼ ▼
│ ┌──┐ ┌──┐.1│ 192.0.2.0/31 │.0┌──┐ │
│NF├──────┤CE├──────────────────────────┤PE│
│ └──┘ └──┘ │ VLAN 100 │ └──┘ │
Site
│ │ │ TN │
─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
└────────────────────────────────────┘
Local Segment
Figure 4: example
Note that the allocation of these resources (e.g. vlan or IPAM) can
be either managed by the SMO or the Transport Network. In other
words, the initial SMO request for the creation of a new IETF Network
Slice on a given 5G site may or may not include all network
resources. In the latter case, this information is exchanged in a
second step.
2.3. 5G slice to IETF Network Slice mapping
There are multiple options to map 5G network slices to IETF Network
Slices:
* 1 to N: A single 5G Network Slice can map to multiple IETF Network
Slices (1 to N). One example of such a case is the separation of
the 5G Control Plane and User Plane: this use case is represented
in Figure 5 where a slice (EMBB) is deployed with a separation of
User Plane and Control Plane at Transport Network level.
* N to 1: Multiple 5G Network Slices may rely on a same IETF Network
Slice (i.e., in [TS-28.530] semantic, two RAN/CORE NSS rely on a
shared TN NSS). In this case, the SLA differentiation of slices
would be entirely controlled at 5G Control Plane, for example with
appropriate placement strategies: this use case is represented in
Szarkowicz, et al. Expires 27 April 2023 [Page 10]
Internet-Draft 5G Transport Slices October 2022
Figure 6, where a UPF network function for the URLLC slice is
instantiated at the Edge Cloud close the gNB CU-UP User Plane for
better latency/jitter control, while 5G Control Plane and the UPF
for slice EMBB are instantiated in the Regional Cloud.
* N to M: the 5G to IETF Network Slice mapping combines both
approaches with a mix of shared and dedicated associations.
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐
│ 5G Slice eMBB │
│ ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐ │
┌─────┐ N3 ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐ N3 ┌─────┐
│ │CU-UP├─────── IETF Network Slice UP_eMBB ───────┤ UPF │ │
└─────┘ └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘ └─────┘
│ │ │ │
┌─────┐ N2 ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐ N2 ┌─────┐
│ │CU-CP├─────── IETF Network Slice CP ───────┤ AMF │ │
└─────┘ └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘ └─────┘
└ ─ ─ ─ ─ ─ ─│─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─│─ ─ ─ ─ ─ ─ ┘
│ │
Transport Network
│ │
└ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘
Figure 5: 1 (5G slice) to N (IETF Network Slice) mapping
Szarkowicz, et al. Expires 27 April 2023 [Page 11]
Internet-Draft 5G Transport Slices October 2022
┌ ─ ─ ─ ─ ─ ─ ┐
Edge Cloud
│ │
┌─────────┐
│ │UPF_URLLC│ │
└─────┬───┘
└ ─ ─ ─ │ ─ ─ ┘
┌ ─ ─ ─ ─ ─ ─ ─ ┐ ┌ ─ ─ ─ │ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
┌ ─ ─ ┴ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ │ ┌ ─ ─ ─ ─ ─ ─ ─
│ Cell Site │ │ │ │
│ │ │ Regional
│ ┌───────────┐ │ │ │ Cloud │
│CU-UP_URLLC├─────┤ │ │ ┌──────────┐
│ └───────────┘ │ │ IETF Network ├─────┤ 5GC CP │ │
│ Slice ALL │ │ └──────────┘
│ ┌───────────┐ │ │ │ │
│CU-UP_eMBB ├─────┤ │ │ ┌──────────┐
│ └───────────┘ │ │ ├─────┤ UPF_eMBB │ │
─ ─ ─ ─ ─ ─ ─ ─ │ │ │ └──────────┘
│ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘ │
│ └ ─ ─ ─ ─ ─ ─ ─
│ Transport Network
─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘
Figure 6: N (5G slice) to 1 (IETF Network Slice) mapping
Note that the actual realization of the mapping depends on several
factors such as the actual business cases, the VNF vendor
capabilities, the VNF vendor reference designs, as well as service
provider or even legal requirements.
2.4. First 5G slice versus subsequent slices
A 5G Network Slice is fully functional with both 5G Control Plane and
User Plane capabilities (i.e., dedicated NF functions or contexts).
In this regard, the creation of the "first slice" is subject to a
specific logic since it must deploy both CP and UP. This is not the
case for the deployment of subsequent slices because they can share
the CP of the First Slice, while instantiating dedicated UP. An
example of an incremental deployment is depicted in Figure 7
At the time of writing, [NG.113], Section 6.2, specifies that the
eMBB slice (SST=1 and no SD) should be supported globally. This 5G
slice would be the first slice in any 5G deployment.
Szarkowicz, et al. Expires 27 April 2023 [Page 12]
Internet-Draft 5G Transport Slices October 2022
Note that the actual realization of the mapping depends on several
factors such as the actual business cases, the VNF vendor
capabilities, the VNF vendor reference designs, as well as service
providers or even legal requirements.
Szarkowicz, et al. Expires 27 April 2023 [Page 13]
Internet-Draft 5G Transport Slices October 2022
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ 1 ┌─────┐ ┌──────────────────────────┐ │ ┌─────┐ │
s S │NF-CP├──────┤ CP IETF NS (IETF-NS-1) ├──────┤NF-CP│
│ t l └─────┘ └──────────────────────────┘ │ └─────┘ │
i │
│ 5 c ┌─────┐ ┌──────────────────────────┐ │ ┌─────┐ │
G e │NF-UP├──────┤ UP IETF NS (IETF-NS-2) ├──────┤NF-UP│
│ └─────┘ └──────────────────────────┘ │ └─────┘ │
─ ─ ─ ─ ─ ─ ─ ─ ─ ┼ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│
│ Transport Network
│
└ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
Deployment of first 5G slice
│ │
│ │
│ │
─┘ └─
╲ ╱
╲ ╱
V
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ 1 ┌─────┐ ┌──────────────────────────┐ │ ┌─────┐ │
s S │NF-CP├──────┤ CP IETF NS (IETF-NS-1) ├──────┤NF-CP│
│ t l └─────┘ └──────────────────────────┘ │ └─────┘ │
i │
│ 5 c ┌─────┐ ┌──────────────────────────┐ │ ┌─────┐ │
G e │NF-UP├──────┤ UP IETF NS (IETF-NS-2) ├──────┤NF-UP│
│ └─────┘ └──────────────────────────┘ │ └─────┘ │
─ ─ ─ ─ ─ ─ ─ ─ ─ ┼ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─│─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐
2 │
│ n S ┌──────┐ │ ┌──────────────────────────┐ ┌──────┐ │
d l │NF-UP2├─────┤ UP2 IETF NS (IETF-NS-3)├─────┤NF-UP2│
│ i └──────┘ │ └──────────────────────────┘ └──────┘ │
5 c │
│ G e │ │
─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─│─ ─ ─ ─ ─ ─ ─
│
Transport Network │
│
─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘
Deployment of additional 5G slice with shared Control Plane
Figure 7: First and Subsequent Slice Deployment
Szarkowicz, et al. Expires 27 April 2023 [Page 14]
Internet-Draft 5G Transport Slices October 2022
3. High-Level Overview of the Realization Model
[I-D.ietf-teas-ietf-network-slices] introduces the concept of a
Network Resource Partition (NRP), which is defined as a collection of
resources identified in the underlay network. In the basic
realization model described in this document, a single NRP is used
with following characteristics
* L2VPN/L3VPN service instances for logical separation:
This realization model of transport for 5G slices assumes Layer-3
delivery for midhaul and backhaul transport connections, and a
Layer 2 or Layer 3 (eCPRI supports both) delivery model for
fronthaul connections. L2VPN/L3VPN service instances might be
used as basic form of logical slice separation. Further, using
service instances results in additional outer header (as packets
are encapsulated/decapsulated at the nodes performing PE
functions) providing clean discrimantion between 5G QoS and TN
QoS, as explained in Section 4
* Fine-Grained resource control at the edge links of TN domain
(attachment circuits):
This is sometimes called 'admission control' or 'traffic
conditioning'. The main purpose is the enforcement of the
bandwidth contract for the slice right at the edge of the
transport domain where the traffic is handed-off between the
transport domain and the 5G domains (i.e., RAN/Core). The toolset
used here is granular ingress policing (rate limiting) to enforce
contracted bandwidths per slice and, potentially, per traffic
class within the slice. Out-of-contract traffic might be
immediately dropped, or marked as high drop probability traffic,
which is more likely to be dropped somewhere at the transit if
congestion occurs. In the egress direction at the edge of the
transport domain, hierarchical schedulers/shapers can be deployed,
providing guaranteed rates per slice, as well as guarantees per
traffic class within the slice.
* Coarse resource control at the TN transit (non-attachment
circuits) links of the transport domain, using a single Network
Resource Partition (NRP), spanning the entire TN domain
Transit nodes do not maintain any state of individual slices.
Instead, only a flat (non-hierarchical) QoS model is used on
transit links with up to 8 traffic classes. At the transport
domain edge, traffic-flows from multiple slice services are mapped
to the limited number of traffic classes used on transit links.
Szarkowicz, et al. Expires 27 April 2023 [Page 15]
Internet-Draft 5G Transport Slices October 2022
* Capacity planning/management for efficient usage of TN edge and TN
transit resources:
The role of capacity management is to ensure the transport
capacity can be utilized without causing any bottlenecks. The
toolset used here can range from careful network planning, to
ensure more less equal traffic distribution (i.e., equal cost load
balancing), to advanced traffic engineering techniques, with or
without bandwidth reservations, to force more consistent load
distribution even in non-ECMP friendly network topologies.
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐
┌──────────┐ base NRP ┌──────────┐
│ PE│ │ │ │PE │
┌ ┼ ─ ─ ─ ─ ─│─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┼ ─ ─ ─ ─ ─│─
■◀───┐│ │ IETF Network Slice 1 │ │┌────▶■ │
│ │ │ │ ┌─────┐ ┌─────┐ │ │ │
■◀───┤│ │ │ P │ │ P │ │ │├────▶■ │
├ ┼ ─ ─├────▶□◀──────▶□◀───▶□◀──────▶□────▶□◀──────▶□◀───┤─ ─ ─│─
■◀───┤│ │ │ │ │ │ │ │├────▶■ │
│ │ │ │ └─────┘ └─────┘ │ │ │
■◀───┘│ │ IETF Network Slice 2 │ │└────▶■ │
└ ┼ ─ ─ ─ ─ ─│─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┼ ─ ─ ─ ─ ─│─
│ │ │ │ │ │
└──────────┘ └──────────┘
└ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘
■ - SDP, with fine-grained QoS (dedicated resources per IETF NS)
□ - coarse QoS, with resources shared by all IETF NS
Figure 8: Resource allocation in with single NRP slicing model
The 5G control plane relies on S-NSSAI (Single Network Slice
Selection Assistance Information: 32-bit slice identifier) for slice
identification. The S-NSSAI is not visible to the transport domain,
so instead 5G functions can expose the 5G slices to the transport
domain by mapping to explicit L2/L3 identifiers such as VLAN, IP
addresses or DSCP, as documented in
[I-D.geng-teas-network-slice-mapping].
3.1. VLAN Hand-off
In this option, the IETF Network Slice, fulfilling connectivity
requirements between NFs of some 5G slice, is represented at the SDP
by a VLAN, or double VLANs (commonly known as QinQ). Each VLAN can
represent a distinct logical interface on the attachment circuits,
hence it provides the possibility to place these logical interfaces
in distinct L2 or L3 service instances and implement separation
between slices via service instances. Since the 5G interfaces are IP
Szarkowicz, et al. Expires 27 April 2023 [Page 16]
Internet-Draft 5G Transport Slices October 2022
based interfaces (the only exception could be the F2 fronthaul-
interface, where eCPRI with Ethernet encapsulation is used), this
VLAN is typically not transported across the TN domain. Typically,
it has only local significance at a particular SDP. For
simplification it is recommended to rely on a same VLAN identifier
for all ACs, when possible. However, SDPs for a same slice at
different locations may also use different VLAN values. Therefore, a
VLAN to IETF Network Slice mapping table MUST be maintained for each
AC, and the VLAN allocation MUST be coordinated between TN domain and
extended RAN/Core domains. Thus, while VLAN hand-off is simple from
the NF point of view, it adds complexity due to the requirement of
maintaining mapping tables for each SDP.
VLANs representing slices VLANs representing slices
.───────.
│ ,' `. │ │
│ ,' `. │ │
┌──────┐ ▼ ┌─────┐ Transport┌─────┐ ▼ ┌─────┐ ▼ ┌──────┐
│ ●───■───● │ │ ●───■───● ●───────● │
│ NF ●───■───● PE1 │ │ PE2 ●───■───●L2/L3●───────● NF │
│ ●───■───● │ │ ●───■───● ●───────● │
└──────┘ └─────┘ Network └─────┘ └─────┘ └──────┘
`. ,'
`. ,'
`─────'
● – logical interface represented by VLAN on physical interface
■ - Service Demarcation Point
Figure 9: 5G slice with VLAN hand-off
3.2. IP Hand-off
In this option, the slices in the transport domain are instantiated
by IP tunnels (for example, IPsec, GTP-U tunnel) established between
NFs. The transport for a single 5G slice is constructed with
multiple such tunnels, since a typical 5G slice contains many NFs -
especially DUs and CUs. If a shared NF (i.e., an NF that serves
multiple slices, for example a shared DU) is deployed, multiple
tunnels from shared NF are established, each tunnel representing a
single slice. As opposed to the VLAN hand-off case, there is no
logical interface representing slice on the PE, hence all slices are
handled within single service instance. On the other hand, similarly
to the VLAN hand-off case, a mapping table tracking IP to IETF
Network Slice mapping is required.
Szarkowicz, et al. Expires 27 April 2023 [Page 17]
Internet-Draft 5G Transport Slices October 2022
Tunnels representing slices
.───────.
,' `. │
,' `. │
┌──────┐ ┌─────┐ Transport┌─────┐ ┌─────┐ ▼ ┌──────┐
│ ○═════■══════════════════════════════■═══════════════════○ │
│ NF ├───────┤ PE1 │ │ PE2 ├───────┤L2/L3├───────┤ NF │
│ ○═════■══════════════════════════════■═══════════════════○ │
└──────┘ └─────┘ Network └─────┘ └─────┘ └──────┘
`. ,'
`. ,'
`─────'
○ – virtual interface à la loopback (not associated with a VLAN)
for tunnel (IPsec, GTP-U, ...) termination
■ - Service Demarcation Point
Figure 10: 5G slice with IP hand-off
The mapping table can be simplified if, e.g., IPv6 addressing is used
to address NFs. An IPv6 address is a 128-bit long field, while the
S-NSSAI is a 32-bit field: Slice/Service Type (SST): 8 bits, Slice
Differentiator (SD): 24 bits. 32 bits, out of 128 bits of the IPv6
address, MAY be used to encode the S-NSSAI, which makes an IP to
Slice mapping table unnecessary. This is simply an allocation method
to allocate IPv6 addresses to NF loopbacks, without redefining IPv6
semantic. Different IPv6 address allocation schemes following this
concept MAY be used, with one example allocation showed in Figure 11.
This addressing scheme is local to a node; intermediary nodes are not
required to associate any additional semantic with IPv6 address.
NF specific reserved
(not slice specific) for S-NSSAI
◀───────────────────────────▶ ◀───────▶
┌────┬────┬────┬────┬────┬────┬────┬────┐
│2001:0db8:xxxx:xxxx:xxxx:xxxx:ttdd:dddd│
└─────────┴─────────┴─────────┴─────────┘
tt - SST (8 bits)
dddddd - SD (24 bits)
Figure 11: An Example of S-NSSAI embedded into IPv6
Szarkowicz, et al. Expires 27 April 2023 [Page 18]
Internet-Draft 5G Transport Slices October 2022
In the example, the most significant 96 bits of the IPv6 address are
unique to NF, but do not carry any slice specific information, while
the least significant 32 bits are used to embed S-NSSAI information.
The 96-bit part of the address could be further divided, based for
example on geographical location, or DC identification. 128 bits is
wide enough to design an IPv6 addressing scheme, which is most
suitable for particular 5G deployment.
Figure 12 shows an example slicing deployment, where S-NSSAI is
embedded into IPv6 addresses used by NFs. NF-A has a loopback
interface, used to terminate tunnels, with unique per slice IP
addresses allocated from 2001:db8::a:0:0/96 subnet, while NF-B uses
loopback interface with per slice IP addresses allocated from
2001:db8::b:0:0/96. This example shows two slices: eMBB (SST=1) and
MIoT (SST=3). Therefore, for eMBB the tunnel IP addresses are auto-
derived (without the need for a mapping table) as {2001:db8::a:100:0,
2001:db8::b:100:0}, while for MIoT (SST=3) tunnel uses
{2001:db8::a:300:0, 2001:db8::b:300:0}.
2001:db8::a:0:0/96 (NF-A) 2001:db8::b:0:0/96 (NF-B)
.───────.
2001:db8::a:100:0/128 ,' `. 2001:db8::b:100:0/128
│ ,' `. │
┌────▼─┐ eMBB (SST=1) ; Transport : ┌─▼────┐
│ ○════════════════════════════════════════════════════════○ │
│ NF-A │ │ │ │ NF-B │
│ ○════════════════════════════════════════════════════════○ │
└────▲─┘ MIoT (SST=3) ╲ Network ╱ └─▲────┘
│ `. ,' │
2001:db8::a:300:0/128 `. ,' 2001:db8::b:300:0/128
`─────'
Figure 12: Deployment example with S-NSSAI embedded into IPv6
3.3. MPLS Label Hand-off
In this option, the service instances representing different slices
are created directly on the NF, or within the cloud infrastructure
hosting the NF, and attached to the TN domain. Therefore, the packet
is MPLS encapsulated outside the TN domain with native MPLS
encapsulation, or MPLSoUDP encapsulation, depending on the capability
of the NF or cloud infrastructure, with the service label depicting
the slice. There are three major methods (based on [RFC4364],
Section 10) for interconnecting multiple service domains:
* Option A: VRF-to-VRF connections
Szarkowicz, et al. Expires 27 April 2023 [Page 19]
Internet-Draft 5G Transport Slices October 2022
* Option B: redistribution of labeled VPN routes with next-hop
change at domain boundaries
* Option C: redistribution of labeled VPN routes without next-hop
change + redistribution of labeled transport routes with next-hop
change at domain boundaries
MPLS is not used in VRF-to-VRF hand-offs, since services are
terminated at the boundary of each domain, and VLAN hand-off is in
place between the domains. Thus, it is the same as VLAN hand-off,
described in Section 3.1.
3.3.1. Option B
In the Option B scenario, service instances for different IETF
Network Slice services are instantiated outside the TN domain. They
could be instantiated either on the compute, hosting mobile network
functions (Figure 13, left hand side), or within the cloud
infrastructure itself, e.g. on the top of the rack or leaf switch
within cloud IP fabric (Figure 13, right hand side). Between TN
domain and the (extended) RAN/CN domain, packets are MPLS
encapsulated (or MPLSoUDP encapsulated, if cloud or compute
infrastructure doesn't support native MPLS encapsulation), therefore
the PE uses neither a VLAN, nor an IP address for slice
identification at SDP, but instead uses the MPLS label.
Szarkowicz, et al. Expires 27 April 2023 [Page 20]
Internet-Draft 5G Transport Slices October 2022
◁────── ◁────── ◁──────
BGP VPN BGP VPN BGP VPN
COM=1, L=A" COM=1, L=A' COM=1, L=A
COM=2, L=B" COM=2, L=B' COM=2, L=B
COM=3, L=C" COM=3, L=C' COM=3, L=C
◁─────────────▷◁────────────▷◁─────────────▷
nhs nhs nhs nhs
VLANs
service instances service instances representing
representing slices .───────. representing slices slices
│ ,' `. │ │
│ ,' Transport `. │ │
┌────▼─┐ ┌─────┐ ┌─────┐ ┌─▼──────┐ ▼ ┌──────┐
│ ◙ │ │ │ │ │ │ ◙………………●───────● │
│ NF ◙ ├───■───┤ PE1 │ │ PE2 ├───■───┤ ◙………………●───────● NF │
│ ◙ │ │ │ │ │ │ ◙………………●───────● │
└──────┘ └─────┘ └─────┘ └────────┘ └──────┘
`. Network ,' L2/L3
`. ,'
`─────'
● – logical interface represented by VLAN on physical interface
◙ - service instances (with unique MPLS label)
■ - Service Demarcation Point
Figure 13: MPLS Hand-off: Option B
MPLS labels are allocated dynamically, especially in Option B
deployments, where at the domain boundaries service prefixes are
reflected with next-hop self, and new label is dynamically allocated,
as visible in Figure 13. Therefore, for any slice-specific per hop
behavior at the TN domain edge, the PE must be able to determine
which label represents which slice. In the BGP control plane, when
exchanging service prefixes between (extended) RAN/CN domains and TN
domain, each slice might be represented by a unique BGP community, so
tracking label assignment to the slice is possible. For example, in
Figure 13, for the slice identified with COM=1, PE1 advertises a
dynamically allocated label A". Since, based on the community, the
label to slice association is known, PE1 can use this dynamically
allocated label A" to identify incoming packets as belonging to slice
1, and execute appropriate edge per hop behavior.
It is worth noting that slice identification in the BGP control plane
is at the prefix granularity. In extreme case, each prefix can have
different community representing a different slice. Depending on the
business requirements, each slice could be represented by a different
service instance, as outlined in Figure 13. In that case, the route
target extended community might be used as slice differentiator. In
Szarkowicz, et al. Expires 27 April 2023 [Page 21]
Internet-Draft 5G Transport Slices October 2022
another deployment, all prefixes (representing different slices)
might be handled by single 'mobile' service instance, and some other
BGP attribute (e.g., a standard community) might be used for slice
differentiation. Or there could be a deployment that groups multiple
slices together into a single service instance, resulting in a
handful of service instances. In any case, fine-grained per-hop
behavior at the edge of TN domain is possible.
4. QoS Mapping Models
The resources are managed via various QoS policies deployed in the
network. QoS mapping models to support 5G slicing connectivity
implemented over packet switched transport uses two layers of QoS
* 5G QoS
At this layer QoS treatment is indicated by the 5QI (5G QoS
indicator), as defined in [TS-23.501]. A 5QI is an ID that is
used as a reference to 5G QoS characteristics (e.g., scheduling
weights, admission thresholds, queue management thresholds, link
layer protocol configuration, etc.) in the RAN domain. Given the
fact that 5QI applies to the RAN domain, it is not visible to the
TN domain. Therefore, if 5QI-aware treatment is desired in the TN
domain as well, 5G components might set DSCP with a value
representing 5QI, to allow differentiated treatment in TN domain
as well. Based on these DSCP values, at SDP of each TN segment
used to construct transport for given 5G slice, very granular QoS
enforcement might be implemented. The mapping between 5QI and
DSCP is out of scope for this document. Mapping recommendations
are documented in [I-D.henry-tsvwg-diffserv-to-qci]. Each slice
might have flows with multiple 5QIs, thus there could be many
different 5QIs being deployed. 5QIs (or, more precisely,
corresponding DSCP values) are visible to the TN domain at SDP
(i.e., at the edge of the TN domain).
In this document, this layer of QoS will be referred as '5G QoS
Class' ('5G QoS' in short), or '5G DSCP'.
* TN QoS
Szarkowicz, et al. Expires 27 April 2023 [Page 22]
Internet-Draft 5G Transport Slices October 2022
Control of the TN resources on transit links, as well as traffic
scheduling/prioritization on transit links, is based on a flat
(non-hierarchical) QoS model in the IETF Network Slice
realization. That is, IETF Network Slices are assigned dedicated
resources (e.g., QoS queues) at the edge of the TN domain (at
SDP), while all IETF Network Slices are sharing resources (sharing
QoS queues) on the transit links of the TN domain. Typical router
hardware can support up to 8 traffic queues per port, therefore
the architecture assumes 8 traffic queues per port support in
general.
At this layer, QoS treatment is indicated by QoS indicator
specific to the encapsulation used in the TN domain, and it could
be DSCP or MPLS TC. This layer of QoS will be referred as 'TN QoS
Class', or 'TN QoS' for short, in this document.
While 5QI might be exposed to the TN domain, via the DSCP value
(corresponding to specific 5QI value) set in the IP packet generated
by NFs, some 5G deployments might use 5QI in the RAN domain only,
without requesting per 5QI differentiated treatment from the TN
domain. This can be due to an NF limitation (no capability to set
DSCP), or it might simply depend on the overall slicing deployment
model. The O-RAN Alliance, for example, defines a phased approach to
the slicing, with initial phases utilizing only per slice, but not
per 5QI, differentiated treatment in the TN domain
([O-RAN.WG9.XPSAAS], Annex F).
Therefore, from QoS perspective, the 5G slicing connectivity
realization architecture defines two high-level realization models
for slicing in the transport domain: a 5QI-unaware model and a 5QI-
aware model. Both slicing models in the transport domain could be
used concurrently within the same 5G slice. For example, the TN
segment for 5G midhaul (F2-U interface) might be 5QI-unaware, while
at the same time the TN segment for 5G backhaul (N3 interface) might
follow the 5QI-aware model.
4.1. 5QI-unaware Mode
In 5QI-unaware mode, the DSCP values in the packets received from NF
at SDP are ignored. In the TN domain, there is no QoS
differentiation at the 5G QoS Class level. The entire IETF Network
Slice is mapped to single TN QoS Class, and, therefore, to a single
QoS queue on the routers in the TN domain. With a small number of
deployed 5G slices (for example only two 5G slices: eMBB and MIoT),
it is possible to dedicate a separate QoS queue for each slice on
transit routers. However, with introduction of private/enterprises
slices, as the number of 5G slices (and thus corresponding IETF
Network Slices) increases, a single QoS queue on transit links serves
Szarkowicz, et al. Expires 27 April 2023 [Page 23]
Internet-Draft 5G Transport Slices October 2022
multiple slices with similar characteristics. QoS enforcement on
transit links is fully coarse (single NRP, sharing resources among
all IETF Network Slices), as displayed in Figure 14.
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
┏━━━━━━━━━━━━━━━━━┓ │
┃ Attach. Circuit ┃ PE router
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │
┃ SDP ┃ ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃│ ┌──────────┐ │┃ ┃ Transit link ┃
┃ │IETF NS 1 ├────────────┐ ┃┌────────────────────────┐ ┃
┃│ └──────────┘ │┃ ├─────▶ TN QoS Class 1 │ ┃
┃ ─ ─ ─ ─ ─ ─ ─ ─ ┃ │ ┃└────────────────────────┘ ┃
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │ ┃┌────────────────────────┐ ┃
┃ SDP ┃ │ ┃│ TN QoS Class 2 │ ┃
┃│ ┌──────────┐ │┃ │ ┃└────────────────────────┘ ┃
┃ │IETF NS 2 ├────────┐ │ ┃┌────────────────────────┐ ┃
┃│ └──────────┘ │┃ │ │ ┃│ TN QoS Class 3 │ ┃
┃ ─ ─ ─ ─ ─ ─ ─ ─ ┃ │ │ ┃└────────────────────────┘ ┃
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │ │ ┃┌────────────────────────┐ ┃
┃ SDP ┃ └─────────▶ TN QoS Class 4 │ ┃
┃│ ┌──────────┐ │┃ │ ┃└────────────────────────┘ ┃
┃ │IETF NS 3 ├────────────┘ ┃┌────────────────────────┐ ┃
┃│ └──────────┘ │┃ ┌─────────▶ TN QoS Class 5 │ ┃
┃ ─ ─ ─ ─ ─ ─ ─ ─ ┃ │ ┃└────────────────────────┘ ┃
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │ ┃┌────────────────────────┐ ┃
┃ SDP ┃ │ ┃│ TN QoS Class 6 │ ┃
┃│ ┌──────────┐ │┃ │ ┃└────────────────────────┘ ┃
┃ │IETF NS 4 ├────────┤ ┃┌────────────────────────┐ ┃
┃│ └──────────┘ │┃ │ ┃│ TN QoS Class 7 │ ┃
┃ ─ ─ ─ ─ ─ ─ ─ ─ ┃ │ ┃└────────────────────────┘ ┃
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │ ┃┌────────────────────────┐ ┃
┃ SDP ┃ │ ┃│ TN QoS Class 8 │ ┃
┃│ ┌──────────┐ │┃ │ ┃└────────────────────────┘ ┃
┃ │IETF NS 5 ├────────┘ ┃ Max 8 TN Classes ┃
┃│ └──────────┘ │┃ ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━┫
┃ ─ ─ ─ ─ ─ ─ ─ ─ ┃
┗━━━━━━━━━━━━━━━━━┛ │
└ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
Fine-grained QoS enforcement Coarse QoS enforcement
(dedicated resources per (resources shared by
IETF Network Slice) multiple IETF NSs)
Figure 14: Slice to TN QoS mapping (5QI-unaware model)
When the IP traffic is handed over at the SDP from the extended RAN
or extended Core domains to the TN domain, the PE encapsulates the
traffic into MPLS (if MPLS transport is used in the TN domain), or
Szarkowicz, et al. Expires 27 April 2023 [Page 24]
Internet-Draft 5G Transport Slices October 2022
IPv6 - optionally with some additional headers (if SRv6 transport is
used in the TN domain), and sends out the packets on the TN transit
link.
The original IP header retains the DCSP marking (which is ignored in
5QI-unaware mode), while the new header (MPLS or IPv6) carries QoS
marking (MPLS Traffic Class bits for MPLS encapsulation, or DSCP for
SRv6/IPv6 encapsulation) related to TN CoS. Based on TN QoS Class
marking, per hop behavior for all IETF Network Slices is executed on
TN links. TN domain transit routers do not evaluate the original IP
header for QoS-related decisions. This model is outlined in
Figure 15 for MPLS encapsulation, and in Figure 16 for SRv6
encapsulation.
┌──────────────┐
│ MPLS Header │
├─────┬─────┐ │
│Label│TN TC│ │
┌──────────────┐ ─ ─ ─ ─ ─ ─ ─ ─ ├─────┴─────┴──┤
│ IP Header │ │╲ │ IP Header │
│ ┌───────┤ │ ╲ │ ┌───────┤
│ │5G DSCP│ ────────┘ ╲ │ │5G DSCP│
├──────┴───────┤ ╲ ├──────┴───────┤
│ │ ╲ │ │
│ │ ╲ │ │
│ │ ▏│ │
│ Payload │ ╱ │ Payload │
│(GTP-U/IPsec) │ ╱ │(GTP-U/IPsec) │
│ │ ╱ │ │
│ │ ────────┐ ╱ │ │
│ │ │ ╱ │ │
│ │ │╱ │ │
└──────────────┘ ─ ─ ─ ─ ─ ─ ─ ─ └──────────────┘
Figure 15: QoS with MPLS encapsulation
Szarkowicz, et al. Expires 27 April 2023 [Page 25]
Internet-Draft 5G Transport Slices October 2022
┌──────────────┐
│ IPv6 Header │
│ ┌───────┤
│ │TN DSCP│
├──────┴───────┤
optional
│ IPv6 │
headers
┌──────────────┐ ─ ─ ─ ─ ─ ─ ─ ─ ├──────────────┤
│ IP Header │ │╲ │ IP Header │
│ ┌───────┤ │ ╲ │ ┌───────┤
│ │5G DSCP│ ────────┘ ╲ │ │5G DSCP│
├──────┴───────┤ ╲ ├──────┴───────┤
│ │ ╲ │ │
│ │ ╲ │ │
│ │ ▏│ │
│ Payload │ ╱ │ Payload │
│(GTP-U/IPsec) │ ╱ │(GTP-U/IPsec) │
│ │ ╱ │ │
│ │ ────────┐ ╱ │ │
│ │ │ ╱ │ │
│ │ │╱ │ │
└──────────────┘ ─ ─ ─ ─ ─ ─ ─ ─ └──────────────┘
Figure 16: QoS with IPv6 encapsulation
From the QoS perspective, both options are similar. However, there
is one difference between the two options. The MPLS TC is only 3
bits (8 possible combinations), while DSCP is 6 bits (64 possible
combinations). Hence, SRv6 provides more flexibility for TN CoS
design, especially in combination with soft policing with in-profile/
out-profile, as discussed in Section 4.1.1.
Edge resources are controlled in a very granular, fine-grained
manner, with dedicated resource allocation for each IETF Network
Slice. The resource control/enforcement happens at each SDP in two
directions: inbound and outbound.
4.1.1. Inbound Edge Resource Control
The main aspect of inbound edge resource control is per-slice traffic
capacity enforcement. This kind of enforcement is often called
'admission control' or 'traffic conditioning'. The goal of this
inbound enforcement is to ensure that the traffic above the
contracted rate is dropped or deprioritized, depending on the
business rules, right at the edge of TN domain. This, combined with
appropriate network capacity planning/management, as described in
Section 6, is required to ensure proper isolation between slices in
Szarkowicz, et al. Expires 27 April 2023 [Page 26]
Internet-Draft 5G Transport Slices October 2022
scalable manner. As a result, traffic of one slice has no influence
on the traffic of other slices, even if the slice is misbehaving
(i.e., DDoS attack, equipment failure, etc.) and generates traffic
volumes above the contracted rates.
The slice rates can be characterized with following parameters
[I-D.ietf-teas-ietf-network-slice-nbi-yang]:
* CIR: Committed Information Rate (i.e., guaranteed bandwidth)
* PIR: Peak Information Rate (i.e., maximum bandwidth)
These parameters define the traffic characteristics of the slice and
are part of SLO parameter set provided by the SMO to IETF NSC. Based
on these parameters the inbound policy can be implemented using one
of following options:
* 1r2c (single-rate two-color) rate limiter
This is the most basic rate limiter, which meters at the SDP a
traffic stream of given slice and marks its packets as in-contract
(below contracted CIR) or out-of-contract (above contracted CIR).
In-contract packets are accepted and forwarded. Out-of contract
packets are either dropped right at the SDP (hard rate limiting),
or remarked (with different MPLS TC or DSCP TN markings) to
signify 'this packet should be dropped in the first place, if
there is a congestion' (soft rate limiting), depending on the
business policy of the operator. In the second case, while
packets above CIR are forwarded at the SDP, they are subject to be
dropped during any congestion event at any place in the TN domain.
* 2r3c (two-rate three-color) rate limiter
This was initially defined in [RFC2698], and its improved version
in [RFC4115]. In essence, the traffic is assigned to one of the 3
categories:
- green, for traffic under CIR
- yellow, for traffic between CIR and PIR
- red, for traffic above PIR
Szarkowicz, et al. Expires 27 April 2023 [Page 27]
Internet-Draft 5G Transport Slices October 2022
An inbound 2c3r meter implemented with [RFC4115], compared to
[RFC2698], is more 'customer friendly' as it doesn't impose
outbound peak-rate shaping requirements on customer edge (CE)
devices. 2r3c meters in general give greater flexibility for edge
enforcement regarding accepting the traffic (green), de-
prioritizing and potentially dropping the traffic during
congestion (yellow), or hard dropping the traffic (red).
Inbound edge enforcement mode for 5QI-unaware mode, where all packets
belonging to the slice are treated the same way in the TN domain (no
5Q QoS Class differentiation in the TN domain) is outlined in
Figure 17.
Slice
policer ┌─────────┐
║ ┌───┴──┐ │
║ │ │ │
║ │ S │ │
║ │ l │ │
▼ │ i │ │
──────────────◇────┼──▶ c │ │
│ e │ A │
│ │ t │
│ 1 │ t │
│ │ a │
├──────┤ c │
│ │ h │
│ S │ m │
│ l │ e │
│ i │ n │
──────────────◇────┼──▶ c │ t │
│ e │ │
│ │ C │
│ 2 │ i │
│ │ r │
├──────┤ c │
│ │ u │
│ S │ i │
│ l │ t │
│ i │ │
──────────────◇────┼──▶ c │ │
│ e │ │
│ │ │
│ 3 │ │
│ │ │
└───┬──┘ │
└─────────┘
Szarkowicz, et al. Expires 27 April 2023 [Page 28]
Internet-Draft 5G Transport Slices October 2022
Figure 17: Ingress slice admission control (5QI-unware model)
4.1.2. Outbound Edge Resource Control
While inbound slice admission control at the transport edge is
mandatory in the model, outbound edge resource control might not be
required in all use cases. Use cases that specifically call for
outbound edge resource control are:
* Slices use both CIR and PIR parameters, and transport edge links
(attachment circuits) are dimensioned to fulfil the aggregate of
slice CIRs. If at any given time, some slices send the traffic
above CIR, congestion in outbound direction on the transport edge
link might happen. Therefore, fine-grained resource control to
guarantee at least CIR for each slice is required.
* Any-to-Any (A2A) connectivity constructs are deployed, again
resulting in potential congestion in outbound direction on the
transport edge links, even if only slice CIR parameters are used.
This again requires fine-grained resource control per slice in
outbound direction at transport edge links.
As opposed to inbound edge resource control, typically implemented
with rate-limiters/policers, outbound resource control is typically
implemented with a weighted/priority queuing, potentially combined
with optional shapers (per slice). A detailed analysis of different
queuing mechanisms is out of scope for this document, but is provided
in [RFC7806].
Figure 18 outlines the outbound edge resource control model at the
transport network layer for 5QI-unaware slices. Each slice is
assigned a single egress queue. The sum of slice CIRs, used as the
weight in weighted queueing model, MUST not exceed the physical
capacity of the attachment circuit. Slice requests above this limit
MUST be rejected by the NSC, unless an already established slice with
lower priority, if such exists, is preempted.
Szarkowicz, et al. Expires 27 April 2023 [Page 29]
Internet-Draft 5G Transport Slices October 2022
┌─────────┐ QoS output queues
│ ┌───┴──┐─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ │ S │ ╲│╱
│ │ l │ │
│ │ i │ │
│ A │ c │ │ weight=Slice-1-CIR
│ t │ e ┌─┴──────────────────────────┐ │ shaping=Slice-1-PIR
───┼──t──┼────▶ │ │
│ a │ 1 └─┬──────────────────────────┘ ╱│╲
│ c ├──────┤─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ h │ S │ ╲│╱
│ m │ l │ │
│ e │ i │ │
│ n │ c │ │ weight=Slice-2-CIR
│ t │ e ┌─┴──────────────────────────┐ │ shaping=Slice-2-PIR
───┼─────┼────▶ │ │
│ C │ 2 └─┬──────────────────────────┘ ╱│╲
│ i ├──────┤─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ r │ S │ ╲│╱
│ c │ l │ │
│ u │ i │ │
│ i │ c │ │ weight=Slice-3-CIR
│ t │ e ┌─┴──────────────────────────┐ │ shaping=Slice-3-PIR
───┼─────┼────▶ │ │
│ │ 3 └─┬──────────────────────────┘ ╱│╲
│ └───┬──┘─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
└─────────┘
Figure 18: Egress slice admission control (5QI-unaware model)
4.2. 5QI-aware Mode
In the 5QI-aware model, potentially a large number of 5Q QoS Classes
(the architecture scales to thousands of 5Q slices) is mapped
(multiplexed) to up to 8 TN QoS Classes used in transport transit
equipment, as outlined in Figure 19.
Szarkowicz, et al. Expires 27 April 2023 [Page 30]
Internet-Draft 5G Transport Slices October 2022
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
┏━━━━━━━━━━━━━━━━━┓ │
┃ Attach. Circuit ┃ PE router
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │
┃ SDP ┃ ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃│ ┌──────────┐ │┃ ┃ Transit link ┃
┃ │ 5G QoS A ├───────────────┐ ┃┌────────────────────────┐ ┃
I ┃│ └──────────┘ │┃ ├──▶ TN QoS Class 1 │ ┃
E ┃ ┌──────────┐ ┃ │ ┃└────────────────────────┘ ┃
T ┃│ │ 5G QoS B ├───────────┐ │ ┃┌────────────────────────┐ ┃
F ┃ └──────────┘ ┃ │ │ ┃│ TN QoS Class 2 │ ┃
┃│ ┌──────────┐ │┃ │ │ ┃└────────────────────────┘ ┃
N ┃ │ 5G QoS C ├──╋─────┐ │ │ ┃┌────────────────────────┐ ┃
S ┃│ └──────────┘ │┃ │ │ │ ┃│ TN QoS Class 3 │ ┃
┃ ┌──────────┐ ┃ │ │ │ ┃└────────────────────────┘ ┃
1 ┃│ │ 5G QoS D ├─────┐ │ │ │ ┃┌────────────────────────┐ ┃
┃ └──────────┘ ┃ │ │ ├──────▶ TN QoS Class 4 │ ┃
┃└ ─ ─ ─ ─ ─ ─ ─ ┘┃ │ │ │ │ ┃└────────────────────────┘ ┃
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │ │ │ │ ┃┌────────────────────────┐ ┃
┃ ┌──────────┐ ┃ │ ├─────────▶ TN QoS Class 5 │ ┃
┃│ │ 5G QoS A ├─────│──│──│───┘ ┃└────────────────────────┘ ┃
I ┃ └──────────┘ ┃ │ │ │ ┃┌────────────────────────┐ ┃
E ┃│ ┌──────────┐ │┃ │ │ │ ┃│ TN QoS Class 6 │ ┃
T ┃ │ 5G QoS E ├─────│──│──┘ ┃└────────────────────────┘ ┃
F ┃│ └──────────┘ │┃ │ │ ┃┌────────────────────────┐ ┃
┃ ┌──────────┐ ┃ │ │ ┃│ TN QoS Class 7 │ ┃
N ┃│ │ 5G QoS F ├─────│──┘ ┃└────────────────────────┘ ┃
S ┃ └──────────┘ ┃ │ ┃┌────────────────────────┐ ┃
┃│ ┌──────────┐ │┃ ├────────────▶ TN QoS Class 8 │ ┃
2 ┃ │ 5G QoS G ├─────┘ ┃└────────────────────────┘ ┃
┃│ └──────────┘ │┃ ┃ Max 8 TN Classes ┃
┃ SDP ┃ ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━┫
┃└ ─ ─ ─ ─ ─ ─ ─ ┘┃
┗━━━━━━━━━━━━━━━━━┛ │
└ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
Fine-grained QoS enforcement Coarse QoS enforcement
(dedicated resources per (resources shared by
IETF Network Slice) multiple IETF NSs)
Figure 19: Slice 5Q QoS to TN QoS mapping (5QI-aware model)
Given the fact that in large scale deployments (large number of 5G
slices), the number of potential 5G QoS Classes is much higher than
the number of TN QoS Classes, multiple 5G QoS Classes with similar
characteristics - potentially from different IETF Network Slices -
can be mapped to a same TN QoS Class when transported in the TN
domain. That is, common per hop behavior (PHB) is executed on
transit TN routers for all packets grouped together.
Szarkowicz, et al. Expires 27 April 2023 [Page 31]
Internet-Draft 5G Transport Slices October 2022
Like in 5QI-unaware model, the original IP header retains the DCSP
marking corresponding to 5QI (5G QoS Class), while the new header
(MPLS or IPv6) carries QoS marking related to TN QoS Class. Based on
TN QoS Class marking, per hop behavior for all aggregated 5G QoS
Classes from all IETF Network Slices is executed on TN links. TN
domain transit routers do not evaluate original IP header for QoS
related decisions. The original DSCP marking retained in the
original IP header is used at the PE for fine-grained per slice and
per 5G QoS Class inbound/outbound enforcement on AC link.
In 5QI-aware model edge resources are controlled in an even more
granular, fine-grained manner, with dedicated resource allocation for
each IETF Network Slice and dedicated resource allocation for number
of traffic classes (most commonly up 4 or 8 traffic classes,
depending on the HW capability of the equipment) within each IETF
Network Slice.
4.2.1. Inbound Edge Resource Control
Compared to the 5QI-unware model, admission control (traffic
conditioning) in the 5QI-aware model is more granular, as it enforces
not only per slice capacity constraints, but may as well enforce the
constraints per 5G QoS Class within each slice.
5G slice using multiple 5QIs can potentially specify rates in one of
the following ways
* rates per traffic class (CIR, or CIR+PIR), no rate per slice (sum
of rates per class gives the rate per slice)
* rate per slice (CIR, or CIR+PIR), and rates per prioritized
(premium) traffic classes (CIR only). Best effort traffic class
uses the bandwidth (within slice CIR/PIR) not consumed by
prioritized classes
In the first option, the slice admission control is executed with
traffic class granularity, as outlined in Figure 20. In this model,
if a premium class doesn't consume all available class capacity, it
cannot be reused by non-premium (i.e., Best Effort) class.
Szarkowicz, et al. Expires 27 April 2023 [Page 32]
Internet-Draft 5G Transport Slices October 2022
Class ┌─────────┐
policer ┌──┴───┐ │
│ │ │
5Q-QoS-A: CIR-1A ──────◇────────────┼──▶ S │ │
5Q-QoS-B: CIR-1B ──────◇────────────┼──▶ l │ │
5Q-QoS-C: CIR-1C ──────◇────────────┼──▶ i │ │
│ c │ │
│ e │ │
BE CIR/PIR-1D ──────◇────────────┼──▶ │ A │
│ 1 │ t │
│ │ t │
├──────┤ a │
│ │ c │
5Q-QoS-A: CIR-2A ──────◇────────────┼─▶ S │ h │
5Q-QoS-B: CIR-2B ──────◇────────────┼─▶ l │ m │
5Q-QoS-C: CIR-2C ──────◇────────────┼─▶ i │ e │
│ c │ n │
│ e │ t │
BE CIR/PIR-2D ──────◇────────────┼─▶ │ │
│ 2 │ C │
│ │ i │
├──────┤ r │
│ │ c │
5Q-QoS-A: CIR-3A ──────◇────────────┼─▶ S │ u │
5Q-QoS-B: CIR-3B ──────◇────────────┼─▶ l │ i │
5Q-QoS-C: CIR-3C ──────◇────────────┼─▶ i │ t │
│ c │ │
│ e │ │
BE CIR/PIR-3D───────◇────────────┼─▶ │ │
│ 3 │ │
│ │ │
└──┬───┘ │
└─────────┘
Figure 20: Ingress slice admission control (5QI-aware model)
The second model combines the advantages of 5QI-unaware model (per
slice admission control) with the per traffic class admission
control, as outlined in Figure 20. Ingress admission control is at
class granularity for premium classes (CIR only). Non-premium class
(i.e. Best Effort) has no separate class admission control policy,
but is allowed to use entire slice capacity, which is available at
any given moment. I.e., slice capacity, which is not consumed by
premium classes. It is a hierarchical model, as depicted in
Figure 21.
Szarkowicz, et al. Expires 27 April 2023 [Page 33]
Internet-Draft 5G Transport Slices October 2022
Slice
policer ┌─────────┐
Class . ┌──┴───┐ │
policer ; : │ │ │
5Q-QoS-A: CIR-1A ────◇─────────┤─┼──┼──▶ S │ │
5Q-QoS-B: CIR-1B ────◇─────────┤─┼──┼──▶ l │ │
5Q-QoS-C: CIR-1C ────◇─────────┤─┼──┼──▶ i │ │
│ │ │ c │ │
│ │ │ e │ │
BE CIR/PIR-1D ──────────────┤─┼──┼──▶ │ A │
│ │ │ 1 │ t │
: ; │ │ t │
. ├──────┤ a │
; : │ │ c │
5Q-QoS-A: CIR-2A ────◇─────────┤─┼──┼──▶ S │ h │
5Q-QoS-B: CIR-2B ────◇─────────┤─┼──┼──▶ l │ m │
5Q-QoS-C: CIR-2C ────◇─────────┤─┼──┼──▶ i │ e │
│ │ │ c │ n │
│ │ │ e │ t │
BE CIR/PIR-2D ──────────────┤─┼──┼──▶ │ │
│ │ │ 2 │ C │
: ; │ │ i │
. ├──────┤ r │
; : │ │ c │
5Q-QoS-A: CIR-3A ────◇─────────┤─┼──┼──▶ S │ u │
5Q-QoS-B: CIR-3B ────◇─────────┤─┼──┼──▶ l │ i │
5Q-QoS-C: CIR-3C ────◇─────────┤─┼──┼──▶ i │ t │
│ │ │ c │ │
│ │ │ e │ │
BE CIR/PIR-3D ──────────────┤─┼──┼──▶ │ │
│ │ │ 3 │ │
: ; │ │ │
' └──┬───┘ │
└─────────┘
Figure 21: Ingress slice admission control (5QI-aware) - hierarchical
4.2.2. Outbound Edge Resource Control
Figure 22 outlines the outbound edge resource control model at the
transport network layer for 5QI-aware slices. Each slice is assigned
multiple egress queues. The sum of queue weights (equal to 5Q QoS
CIRs within the slice) CIRs MUST not exceed the CIR of the slice
itself. And, similarly to the 5QI-aware model, the sum of slice CIRs
MUST not exceed the physical capacity of the attachment circuit.
Szarkowicz, et al. Expires 27 April 2023 [Page 34]
Internet-Draft 5G Transport Slices October 2022
┌─────────┐ QoS output queues
│ ┌───┴──┐─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ │ ┌─┴──────────────────────────┐ ╲│╱
───┼─────┼────▶ 5Q-QoS-A: w=5Q-QoS-A-CIR │ │
│ │ S └─┬──────────────────────────┘ │
│ │ l ┌─┴──────────────────────────┐ │
───┼─────┼─i──▶ 5Q-QoS-B: w=5Q-QoS-B-CIR │ │
│ │ c └─┬──────────────────────────┘ │ weight=Slice-1-CIR
│ │ e ┌─┴──────────────────────────┐ │ shaping=Slice-1-PIR
───┼─────┼────▶ 5Q-QoS-C: w=5Q-QoS-C-CIR │ │
│ │ 1 └─┬──────────────────────────┘ │
│ │ ┌─┴──────────────────────────┐ │
───┼─────┼────▶ Best Effort (remainder) │ │
│ │ └─┬──────────────────────────┘ ╱│╲
│ A ├──────┤─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ t │ ┌─┴──────────────────────────┐ ╲│╱
│ t │ │ │ │
│ a │ └─┬──────────────────────────┘ │
│ c │ S ┌─┴──────────────────────────┐ │
│ h │ l │ │ │
│ m │ i └─┬──────────────────────────┘ │ weight=Slice-2-CIR
│ e │ c ┌─┴──────────────────────────┐ │ shaping=Slice-2-PIR
│ n │ e │ │ │
│ t │ └─┬──────────────────────────┘ │
│ │ 2 ┌─┴──────────────────────────┐ │
│ C │ │ │ │
│ i │ └─┬──────────────────────────┘ ╱│╲
│ r ├──────┤─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ c │ ┌─┴──────────────────────────┐ ╲│╱
│ u │ │ │ │
│ i │ S └─┬──────────────────────────┘ │
│ t │ l ┌─┴──────────────────────────┐ │
│ │ i │ │ │
│ │ c └─┬──────────────────────────┘ │ weight=Slice-3-CIR
│ │ e ┌─┴──────────────────────────┐ │ shaping=Slice-3-PIR
│ │ │ │ │
│ │ 3 └─┬──────────────────────────┘ │
│ │ ┌─┴──────────────────────────┐ │
│ │ │ │ │
│ │ └─┬──────────────────────────┘ ╱│╲
│ └───┬──┘─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
└─────────┘
Figure 22: Egress slice admission control (5QI-aware)
Szarkowicz, et al. Expires 27 April 2023 [Page 35]
Internet-Draft 5G Transport Slices October 2022
4.3. Transit Resource Control
Transit resource control is much simpler than Edge resource control.
As outlined in Figure 19, at the edge, 5Q QoS Class marking
(represented by DSCP related to 5QI set by mobile components in the
packets handed off to the TN) is mapped to the TN QoS Class. Based
in TN QoS Class, when the packet is encapsulated with outer header
(MPLS or IPv6), TN QoS Class marking (MPLS TC or IPv6 DHCP in outer
header, as depicted in Figure 15 and Figure 16) is set in the outer
header. PHB on transit is based exclusively on that TN QoS Class
marking, i.e., original 5G QoS Class DSCP is not taken into
consideration on transit.
Transit resource control does not use any inbound interface policy,
but only outbound interface policy, which is based on priority queue
combined with weighted or deficit queuing model, without any shaper.
The main purpose of transit resource control is to ensure that during
network congestion events, for example caused by network failures and
temporary rerouting, premium classes are prioritized, and any drops
only occur in non-premium (best-effort) classes. Capacity planning
and management, as described in Section 6, ensures that enough
capacity is available to fulfill all approved slice requests.
5. Transport Planes Mapping Models
A network operator might define various groups of tunnels, where each
tunnel group is created with specific optimization criteria and
constraints. This document refers to such tunnel groups as
'transport planes'. For example, transport plane A might represent
tunnels optimized for latency, transport plane B for high capacity,
transport plane C might represent tunnels using only the "upper half"
of the transport network, and transport plane D might represent
tunnels using only the "lower half" of the transport network.
Figure 23 depicts an example of a simple network with two transport
planes. These transport planes might be realized via various IP/MPLS
techniques, for example Flex-Algo or RSVP/SR traffic engineering
tunnels with or without PCE, and with or without bandwidth
reservations. Section 6 discusses in detail different bandwidth
models that can be deployed in the transport network. However,
discussion about how to realize or orchestrate transport planes is
out of scope for this document.
Szarkowicz, et al. Expires 27 April 2023 [Page 36]
Internet-Draft 5G Transport Slices October 2022
┌───────────────┐ ┌──────┐
│ Head-End PE │ ╔═══════════════════════════════▶│ PE-A │
│ │ ║ ╔═══════════════════════════▷│ │
│ ┌ ─ ─ ─ ─ ┐ │ ║ ╚═════════════════════╗ └──────┘
│ ●══════╝ ╔═════════════════════╝
│ │Transport●════════════════════════════════╗ ┌──────┐
│ Plane A ●═════════════╗ ╚═════▶│ PE-B │
│ │ ●═══════╗ ║ ║ ╔═══╗ ╔═══╗ ╔═════▷│ │
│ ─ ─ ─ ─ ─ │ ║ ║ ║ ║ ║ ║ ║ ║ └──────┘
│ │ ║ ║ ║ ║ ╚═══╝ ╚═══╝
│ ┌ ─ ─ ─ ─ ┐ │ ║ ║ ║ ║ ┌──────┐
│ ○═══════║══╝ ╚════════════════════════▶│ PE-C │
│ │Transport○═══════║════════╝ ╔═════▷│ │
│ Plane B ○═══════║═════════════════╗ ║ └──────┘
│ │ ○═════╗ ╚═══════════════╗ ║ ║
│ ─ ─ ─ ─ ─ │ ║ ╔═╗ ╔═╗ ╔═╗ ╔═╗ ║ ╚══════╝ ┌──────┐
│ │ ║ ║ ║ ║ ║ ║ ║ ║ ║ ╚══════════════▶│ PE-D │
└───────────────┘ ╚═╝ ╚═╝ ╚═╝ ╚═╝ ╚════════════════▷│ │
└──────┘
●════════▶ Tunnels of Transport Plane A
○════════▷ Tunnels of Transport Plane B
Figure 23: Transport Planes
Similar to the QoS mapping models discussed in Section 4, for mapping
to transport planes at the ingress PE, both 5QI-unaware and 5QI-aware
modes are defined. In essence, entire slices can be mapped to
transport planes without 5G QoS consideration (5QI-unaware mode), or
flows with different 5G QoS Classes, even if they are from the same
slice, might be mapped to different transport planes (5QI-aware
mode).
5.1. 5QI-unaware Mode
As discussed in Section 4.1, in the 5QI-unware model, the TN domain
doesn't take into account 5G QoS during execution of per-hop
behavior. The entire slice is mapped to single TN QoS Class,
therefore the entire slice is subject to the same per-hop behavior.
Similarly, in 5QI-unaware transport plane mapping mode, the entire
slice is mapped to a single transport plane, as depicted in
Figure 24.
Szarkowicz, et al. Expires 27 April 2023 [Page 37]
Internet-Draft 5G Transport Slices October 2022
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
┏━━━━━━━━━━━━━━━━━┓ │
┃ Attach. Circuit ┃ PE router
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │
┃ SDP ┃
┃│ ┌──────────┐ │┃ │
┃ │IETF NS 1 ├──────────┐
┃│ └──────────┘ │┃ │ │
┃ ─ ─ ─ ─ ─ ─ ─ ─ ┃ │
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │ ┌─────────┐ │
┃ SDP ┃ │ │ │
┃│ ┌──────────┐ │┃ │ │Transport│ │
┃ │IETF NS 2 ├──────┐ ├───▶ Plane │
┃│ └──────────┘ │┃ │ │ │ A │ │
┃ ─ ─ ─ ─ ─ ─ ─ ─ ┃ │ │ │ │
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │ │ └─────────┘ │
┃ SDP ┃ │ │
┃│ ┌──────────┐ │┃ │ │ │
┃ │IETF NS 3 ├──────┤ │
┃│ └──────────┘ │┃ │ │ ┌─────────┐ │
┃ ─ ─ ─ ─ ─ ─ ─ ─ ┃ │ │ │ │
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │ │ │Transport│ │
┃ SDP ┃ ├───│───▶ Plane │
┃│ ┌──────────┐ │┃ │ │ │ B │ │
┃ │IETF NS 4 ├──────┘ │ │ │
┃│ └──────────┘ │┃ │ └─────────┘ │
┃ ─ ─ ─ ─ ─ ─ ─ ─ ┃ │
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │ │
┃ SDP ┃ │
┃│ ┌──────────┐ │┃ │ │
┃ │IETF NS 5 ├──────────┘
┃│ └──────────┘ │┃ │
┃ ─ ─ ─ ─ ─ ─ ─ ─ ┃
┗━━━━━━━━━━━━━━━━━┛ │
└ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
Figure 24: Slice to Transport Plane mapping (5QI-unaware model)
It is worth noting that there is no strict correlation between TN QoS
Classes and Transport Planes. The TN domain can be operated with
e.g., 8 TN QoS Classes (representing 8 hardware queues in the
routers), and 2 Transport Classes (e.g., latency optimized transport
plane using link latency metrics for path calculation, and transport
plane following IGP metrics). TN QoS Class determines the per-hop
behavior when the packets are transiting through the TN domain, while
Transport Plane determines the path, optimized or constrained based
on operator's business criteria, that the packets use to transit
through the TN domain.
Szarkowicz, et al. Expires 27 April 2023 [Page 38]
Internet-Draft 5G Transport Slices October 2022
5.2. 5QI-aware Mode
In 5QI-aware mode, the traffic can be mapped to transport planes at
the granularity of 5G QoS Class. Given that the potential number of
transport planes is limited, packets from multiple 5G QoS Classes
with similar characteristics are mapped to a common transport class,
as depicted in Figure 25.
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐
┏━━━━━━━━━━━━━━━━━┓
┃ Attach. Circuit ┃ │
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ PE router
┃ SDP ┃ │
┃│ ┌──────────┐ │┃
┃ │ 5G QoS A ├──────┐ │
I ┃│ └──────────┘ │┃ │
E ┃ ┌──────────┐ ┃ │ │
T ┃│ │ 5G QoS B ├──────┤
F ┃ └──────────┘ ┃ │ ┌─────────┐ │
┃│ ┌──────────┐ │┃ │ │ │
N ┃ │ 5G QoS C ├───────────┐ │Transport│ │
S ┃│ └──────────┘ │┃ ├────│────▶ Plane │
┃ ┌──────────┐ ┃ │ │ │ A │ │
1 ┃│ │ 5G QoS D ├───────────┤ │ │
┃ └──────────┘ ┃ │ │ └─────────┘ │
┃└ ─ ─ ─ ─ ─ ─ ─ ┘┃ │ │
┃┌ ─ ─ ─ ─ ─ ─ ─ ┐┃ │ │ │
┃ ┌──────────┐ ┃ │ │
┃│ │ 5G QoS A ├──────┤ │ ┌─────────┐ │
I ┃ └──────────┘ ┃ │ │ │ │
E ┃│ ┌──────────┐ │┃ │ │ │Transport│ │
T ┃ │ 5G QoS E ├──────┘ ├────▶ Plane │
F ┃│ └──────────┘ │┃ │ │ B │ │
┃ ┌──────────┐ ┃ │ │ │
N ┃│ │ 5G QoS F ├───────────┤ └─────────┘ │
S ┃ └──────────┘ ┃ │
┃│ ┌──────────┐ │┃ │ │
2 ┃ │ 5G QoS G ├───────────┘
┃│ └──────────┘ │┃ │
┃ SDP ┃
┃└ ─ ─ ─ ─ ─ ─ ─ ┘┃ │
┗━━━━━━━━━━━━━━━━━┛
└ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘
Figure 25: Slice to Transport Plane mapping (5QI-aware model)
Szarkowicz, et al. Expires 27 April 2023 [Page 39]
Internet-Draft 5G Transport Slices October 2022
6. Capacity Planning/Management
This section describes the information conveyed by the SMO to the
transport controller with respect to slice bandwidth requirements.
Figure 26 shows three DCs that contain instances of network
functions. Also shown are PEs that have links to the DCs. The PEs
belong to the transport network. Other details of the transport
network, such as P-routers and transit links are not shown. Also
details of the DC infrastructure such as switches and routers are not
shown.
The SMO is aware of the existence of the network functions and their
locations. However, it is not aware of the details of the transport
network. The transport controller has the opposite view - it is
aware of the transport infrastructure and the links between the PEs
and the DCs, but is not aware of the individual network functions.
.───.
,' `.
┌ ─ ─ ─ ─ DC 1─ ─ ─ ─ ╱ ╲ ┌ ─ ─ ─ ─ DC 2─ ─ ─ ─
┌──────┐ │ ┌────┐ ┌────┐ ┌──────┐ │
│ │ NF1A │ ■──┤PE1A│ │PE2A├──■ │ NF2A │
└──────┘ │ └────┘ └────┘ └──────┘ │
│ ┌──────┐ ; : │ ┌──────┐
│ NF1B │ │ │ │ │ NF2B │ │
│ └──────┘ ; : │ └──────┘
┌──────┐ │ ┌────┐ ┌────┐ ┌──────┐ │
│ │ NF1C │ ■──┤PE1B│ │PE2B├──■ │ NF2C │
└──────┘ │ └┬───┘ └───┬┘ └──────┘ │
└ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ │ Transport │ └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ │
│ Network │ ┌ ─ ─ ─ ─ DC 3─ ─ ─ ─
│ ┌───┴┐ ┌──────┐ │
: │PE3A├──■ │ NF3A │
: └────┘ └──────┘ │
│ │ │ ┌──────┐
: ; │ NF3B │ │
: ; │ └──────┘
: ┌────┐ ┌──────┐ │
╲ │PE3B├──■ │ NF3C │
╲ └────┘ └──────┘ │
╲ ╱ └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
`. ,'
`─'
■ - SDP, with fine-grained QoS (dedicated resources per IETF NS)
Figure 26: Multi-DC architecture
Szarkowicz, et al. Expires 27 April 2023 [Page 40]
Internet-Draft 5G Transport Slices October 2022
Let us consider 5G Slice X that uses some of the network functions in
the three DCs. If the slice has latency requirements, the SMO will
have taken those into account when deciding which network functions
in which DC would participate in the slice. As a result of that
placement decision, the three DCs shown are involved in 5G Slice X,
rather than other DCs. In order to make this determination, the SMO
needs information from the NSC about the latency between DCs.
Preferably, the NSC would present the topology in an abstracted form,
consisting of point-to-point abstracted links between pairs of DCs
and associated latency and optionally delay variation and link loss
values. It would be valuable to have a mechanism for the SMO to
inform the NSC which DC-pairs are of interest for these metrics -
there may be of order thousands of DCs, but the SMO will only be
interested in these metrics for a small fraction of all the possible
DC-pairs, i.e. those in the same region of the network. The
mechanism for conveying the information will be discussed in a future
version of this document.
Figure 27 shows the matrix of bandwidth demands for 5G slice X.
Within the slice, multiple network function instances might be
sending traffic from DCi to DCj. However, the SMO sums the
associated demands into one value. For example, NF1A and NF1B in DC1
might be sending traffic to multiple NFs in DC2, but this is
expressed as one value in the traffic matrix: the total bandwidth
required for 5G Slice X from DC1 to DC2 (8 units). Each row in the
right-most column in the traffic matrix shows the total amount of
traffic going from a given DC into the transport network, regardless
of the destination DC. Note that this number can be less than the
sum of DC-to-DC demands in the same row, on the basis that not all
the network functions are likely to be sending at their maximum rate
simultaneously. For example, the total traffic from DC1 for Slice X
is 11 units, which is less than the sum of the DC-to-DC demands in
the same row (13 units). Note, as described in Section 4, a slice
may have per-QoS class bandwidth requirements, and may have CIR and
PIR limits. This is not included in the example, but the same
principles apply in such cases.
Szarkowicz, et al. Expires 27 April 2023 [Page 41]
Internet-Draft 5G Transport Slices October 2022
To┌──────┬──────┬──────┬──────────────┐
From │ DC 1 │ DC 2 │ DC 3 │Total from DC │
┌──────┼──────┼──────┼──────┼──────────────┤
│ DC 1 │ n/a │ 8 │ 5 │ 11.0 │
├──────┼──────┼──────┼──────┼──────────────┤
│ DC 2 │ 1 │ n/a │ 2 │ 2.5 │
├──────┼──────┼──────┼──────┼──────────────┤
│ DC 3 │ 4 │ 7 │ n/a │ 10.0 │
└──────┴──────┴──────┴──────┴──────────────┘
Slice X
To┌──────┬──────┬──────┬──────────────┐
From │ DC 1 │ DC 2 │ DC 3 │Total from DC │
┌──────┼──────┼──────┼──────┼──────────────┤
│ DC 1 │ n/a │ 4 │ 2.5 │ 6.0 │
├──────┼──────┼──────┼──────┼──────────────┤
│ DC 2 │ 0.5 │ n/a │ 0.8 │ 1.0 │
├──────┼──────┼──────┼──────┼──────────────┤
│ DC 3 │ 2.6 │ 3 │ n/a │ 5.1 │
└──────┴──────┴──────┴──────┴──────────────┘
Slice Y
Figure 27: Inter-DC traffic demand matrix
[I-D.ietf-teas-ietf-network-slice-nbi-yang] can be used to convey all
of the information in the traffic matrix to the IETF NSC. The IETF
NSC applies policers corresponding to the last column in the traffic
matrix to the appropriate PE routers, in order to enforce the
bandwidth contract. For example, it applies a policer of 11 units to
PE1A and PE1B that face DC1, as this is the total bandwidth that DC1
sends into the transport network corresponding to Slice X. Also, the
controller may apply shapers in the direction from the TN to the DC,
if otherwise there is the possibility of a link in the DC being
oversubscribed. Note that a peer NF endpoint of an AC can be
identified using 'peer-sap-id' as defined in [I-D.ietf-opsawg-sap].
Depending on the bandwidth model used in the network (Section 6.1),
the other values in the matrix, i.e., the DC-to-DC demands, may not
be directly applied to the transport network. Even so, the
information may be useful to the IETF NSC for capacity planning and
failure simulation purposes. If, on the other hand, the DC-to-DC
demand information is not used by the IETF NSC, the IETF YANG Data
Model for L3VPN Service Delivery [RFC8299] or the IETF YANG Data
Model for L2VPN Service Delivery [RFC8466] could be used instead of
[I-D.ietf-teas-ietf-network-slice-nbi-yang], as they support
conveying the bandwidth information in the right-most column of the
traffic matrix.
Szarkowicz, et al. Expires 27 April 2023 [Page 42]
Internet-Draft 5G Transport Slices October 2022
The transport network may be implemented in such a way that it has
various types of paths, for example low-latency traffic might be
mapped onto a different transport path to other traffic (for example
a particular flex-algo or a particular set of TE LSPs), as discussed
in Section 5. The SMO can use
[I-D.ietf-teas-ietf-network-slice-nbi-yang] to request low-latency
transport for a given slice if required. However, [RFC8299] or
[RFC8466] do not support requesting a particular transport-type,
e.g., low-latency. One option is to augment these models to convey
this information. This can be achieved by reusing the underlay-
transport construct used in [RFC9182] and [RFC9291].
6.1. Bandwidth models
This section describes three bandwidth management schemes that could
be employed in the transport network. Many variations are possible,
but each example describes the salient points of the corresponding
scheme. Schemes 2 and 3 use TE, other variations on TE are possible
as described in [I-D.ietf-teas-rfc3272bis].
6.1.1. Scheme 1: Shortest Path Forwarding
Shortest path forwarding is used according to the IGP metric. Given
that some slices are likely to have latency SLOs, the IGP metric on
each link can be set to be in proportion to the latency of the link.
In this way, all traffic follows the minimum latency path between
endpoints.
In Scheme 1, although the operator provides bandwidth guarantees to
the slice customers, there is no explicit end-to-end underpinning of
the bandwidth SLO, in the form of bandwidth reservations across the
transport network. Rather, the expected performance is achieved via
capacity planning, based on traffic growth trends and anticipated
future demands, in order to ensure that network links are not over-
subscribed. This scheme is analogous to that used in many existing
business VPN deployments, in that bandwidth guarantees are provided
to the customers but are not explicitly underpinned end to end across
the transport network.
A variation on the scheme is that Flex-Algo, defined in
[I-D.ietf-lsr-flex-algo], is used, for example one Flex-Algo could
use latency-based metrics and another Flex-Algo could use the IGP
metric. There would be a many-to-one mapping of slices to Flex-
Algos.
Szarkowicz, et al. Expires 27 April 2023 [Page 43]
Internet-Draft 5G Transport Slices October 2022
While Scheme 1 is technically feasible, it is vulnerable to
unexpected changes in traffic patterns and/or network element
failures resulting in congestion. This is because, unlike Schemes 2
and 3 that employ TE, traffic cannot be diverted from the shortest
path.
6.1.2. Scheme 2: TE LSPs with Fixed Bandwidth Reservations
Scheme 2 uses RSVP-TE or SR-TE LSPs with fixed bandwidth
reservations. By "fixed", we mean a value that stays constant over
time, unless the SMO communicates a change in slice bandwidth
requirements, due to the creation or modification of a slice. Note
that the "reservations" would be in the mind of the transport
controller - it is not necessary (or indeed possible for SR-TE) to
reserve bandwidth at the network layer. The bandwidth requirement
acts as a constraint whenever the controller (re)computes the path of
an LSP. There could be a single mesh of LSPs between endpoints that
carry all of the traffic types, or there could be a small handful of
meshes, for example one mesh for low-latency traffic that follows the
minimum latency path and another mesh for the other traffic that
follows the minimum IGP metric path, as described in Section 5.
There would be a many-to-one mapping of slices to LSPs.
The bandwidth requirement from DCi to DCj is the sum of the DCi-DCj
demands of the individual slices. For example, if only Slice X and
Slice Y are present, then the bandwidth requirement from DC1 to DC2
is 12 units (8 units for Slice X and 4 units for Slice Y). When the
SMO requests a new slice, the transport controller, in its mind,
increments the bandwidth requirement according to the requirements of
the new slice. For example, in Figure 26, suppose a new slice is
instantiated that needs 0.8 Gbps from DC1 to DC2. The transport
controller would increase its notion of the bandwidth requirement
from DC1 to DC2 from 12 Gbps to 12.8 Gbps to accommodate the
additional expected traffic.
In the example, each DC has two PEs facing it for reasons of
resilience. The transport controller needs to determine how to map
the DC1 to DC2 bandwidth requirement to bandwidth reservations of TE
LSPs from DC1 to DC2. For example, if the routing configuration is
arranged such that in the absence of any network failure, traffic
from DC1 to DC2 always enters PE1A and goes to PE2A, the controller
reserves 12.8 Gbps of bandwidth on the LSP from PE1A to PE2A. If, on
the other hand, the routing configuration is arranged such that in
the absence of any network failure, traffic from DC1 to DC2 always
enters PE1A and is load-balanced across PE2A and PE2B, the controller
reserves 6.4 Gbps of bandwidth on the LSP from PE1A to PE2A and 6.4
Gbps of bandwidth on the LSP from PE1A to PE2B. It might be tricky
for the transport controller to be aware of all conditions that
Szarkowicz, et al. Expires 27 April 2023 [Page 44]
Internet-Draft 5G Transport Slices October 2022
change the way traffic lands on the various PEs, and therefore know
that it needs to change bandwidth reservations of LSPs accordingly.
For example, there might be an internal failure within DC1 that
causes traffic from DC1 to land on PE1B, rather than PE1A. The
transport controller may not be aware of the failure and therefore
may not know that it now needs to apply bandwidth reservations to
LSPs from PE1B to PE2A/PE2B.
6.1.3. Scheme 3: TE LSPs without Bandwidth Reservations
Like Scheme 2, Scheme 3 uses RSVP-TE or SR-TE LSPs. There could be a
single mesh of LSPs between endpoints that carry all of the traffic
types, or there could be a small handful of meshes, for example one
mesh for low-latency traffic that follows the minimum latency path
and another mesh for the other traffic that follows the minimum IGP
metric path, as described in Section 5. There would be a many-to-one
mapping of slices to LSPs.
The difference between Scheme 2 and Scheme 3 is that Scheme 3 does
not have fixed bandwidth reservations for the LSPs. Instead, actual
measured data-plane traffic volumes are used to influence the
placement of TE LSPs. One way of achieving this is to use
distributed RSVP-TE with auto-bandwidth. Alternatively, the
transport controller can use telemetry-driven automatic congestion
avoidance. In this approach, when the actual traffic volume in the
data plane on given link exceeds a threshold, the controller, knowing
how much actual data plane traffic is currently travelling along each
RSVP or SR-TE LSP, can tune the paths of one or more LSPs using the
link such that they avoid that link.
It would be undesirable to move a minimum-latency LSP rather than
another type of LSP in order to ease the congestion, as the new path
will typically have a higher latency, if the minimum-latency LSP is
currently following the minimum-latency path. This can be avoided by
designing the algorithms described in the previous paragraph such
that they avoid moving minimum-latency LSPs unless there is no
alternative.
7. IANA Considerations
This memo includes no request to IANA.
8. Security Considerations
IETF Network Slices considerations are discussed in Section 6 of
[I-D.ietf-teas-ietf-network-slices]. TBC.
9. References
Szarkowicz, et al. Expires 27 April 2023 [Page 45]
Internet-Draft 5G Transport Slices October 2022
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8299] Wu, Q., Ed., Litkowski, S., Tomotaki, L., and K. Ogaki,
"YANG Data Model for L3VPN Service Delivery", RFC 8299,
DOI 10.17487/RFC8299, January 2018,
<https://www.rfc-editor.org/info/rfc8299>.
[RFC8466] Wen, B., Fioccola, G., Ed., Xie, C., and L. Jalil, "A YANG
Data Model for Layer 2 Virtual Private Network (L2VPN)
Service Delivery", RFC 8466, DOI 10.17487/RFC8466, October
2018, <https://www.rfc-editor.org/info/rfc8466>.
9.2. Informative References
[RFC2698] Heinanen, J. and R. Guerin, "A Two Rate Three Color
Marker", RFC 2698, DOI 10.17487/RFC2698, September 1999,
<https://www.rfc-editor.org/info/rfc2698>.
[RFC4115] Aboul-Magd, O. and S. Rabie, "A Differentiated Service
Two-Rate, Three-Color Marker with Efficient Handling of
in-Profile Traffic", RFC 4115, DOI 10.17487/RFC4115, July
2005, <https://www.rfc-editor.org/info/rfc4115>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC6459] Korhonen, J., Ed., Soininen, J., Patil, B., Savolainen,
T., Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation
Partnership Project (3GPP) Evolved Packet System (EPS)",
RFC 6459, DOI 10.17487/RFC6459, January 2012,
<https://www.rfc-editor.org/info/rfc6459>.
[RFC7806] Baker, F. and R. Pan, "On Queuing, Marking, and Dropping",
RFC 7806, DOI 10.17487/RFC7806, April 2016,
<https://www.rfc-editor.org/info/rfc7806>.
Szarkowicz, et al. Expires 27 April 2023 [Page 46]
Internet-Draft 5G Transport Slices October 2022
[RFC9182] Barguil, S., Gonzalez de Dios, O., Ed., Boucadair, M.,
Ed., Munoz, L., and A. Aguado, "A YANG Network Data Model
for Layer 3 VPNs", RFC 9182, DOI 10.17487/RFC9182,
February 2022, <https://www.rfc-editor.org/info/rfc9182>.
[RFC9291] Boucadair, M., Ed., Gonzalez de Dios, O., Ed., Barguil,
S., and L. Munoz, "A YANG Network Data Model for Layer 2
VPNs", RFC 9291, DOI 10.17487/RFC9291, September 2022,
<https://www.rfc-editor.org/info/rfc9291>.
[I-D.ietf-lsr-flex-algo]
Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
A. Gulko, "IGP Flexible Algorithm", Work in Progress,
Internet-Draft, draft-ietf-lsr-flex-algo-26, 17 October
2022, <https://www.ietf.org/archive/id/draft-ietf-lsr-
flex-algo-26.txt>.
[I-D.ietf-opsawg-sap]
Boucadair, M., de Dios, O. G., Barguil, S., Wu, Q., and V.
Lopez, "A YANG Network Model for Service Attachment Points
(SAPs)", Work in Progress, Internet-Draft, draft-ietf-
opsawg-sap-10, 4 October 2022,
<https://www.ietf.org/archive/id/draft-ietf-opsawg-sap-
10.txt>.
[I-D.ietf-teas-ietf-network-slices]
Farrel, A., Drake, J., Rokui, R., Homma, S., Makhijani,
K., Contreras, L. M., and J. Tantsura, "Framework for IETF
Network Slices", Work in Progress, Internet-Draft, draft-
ietf-teas-ietf-network-slices-15, 21 October 2022,
<https://www.ietf.org/archive/id/draft-ietf-teas-ietf-
network-slices-15.txt>.
[I-D.ietf-teas-ietf-network-slice-nbi-yang]
Wu, B., Dhody, D., Rokui, R., Saad, T., Han, L., and J.
Mullooly, "IETF Network Slice Service YANG Model", Work in
Progress, Internet-Draft, draft-ietf-teas-ietf-network-
slice-nbi-yang-03, 24 October 2022,
<https://datatracker.ietf.org/api/v1/doc/document/draft-
ietf-teas-ietf-network-slice-nbi-yang/>.
Szarkowicz, et al. Expires 27 April 2023 [Page 47]
Internet-Draft 5G Transport Slices October 2022
[I-D.ietf-teas-ns-ip-mpls]
Saad, T., Beeram, V. P., Dong, J., Wen, B., Ceccarelli,
D., Halpern, J., Peng, S., Chen, R., Liu, X., Luis
Contreras, M., Rokui, R., and L. Jalil, "Realizing Network
Slices in IP/MPLS Networks", Work in Progress, Internet-
Draft, draft-ietf-teas-ns-ip-mpls-00, 16 June 2022,
<https://www.ietf.org/archive/id/draft-ietf-teas-ns-ip-
mpls-00.txt>.
[I-D.ietf-teas-rfc3272bis]
Farrel, A., "Overview and Principles of Internet Traffic
Engineering", Work in Progress, Internet-Draft, draft-
ietf-teas-rfc3272bis-21, 11 September 2022,
<https://www.ietf.org/archive/id/draft-ietf-teas-
rfc3272bis-21.txt>.
[I-D.geng-teas-network-slice-mapping]
Geng, X., Dong, J., Pang, R., Han, L., Rokui, R., Jin, J.,
and J. Tantsura, "5G End-to-end Network Slice Mapping from
the view of Transport Network", Work in Progress,
Internet-Draft, draft-geng-teas-network-slice-mapping-05,
7 March 2022, <https://www.ietf.org/archive/id/draft-geng-
teas-network-slice-mapping-05.txt>.
[I-D.henry-tsvwg-diffserv-to-qci]
Henry, J., Szigeti, T., and L. M. C. Murillo, "Diffserv to
QCI Mapping", Work in Progress, Internet-Draft, draft-
henry-tsvwg-diffserv-to-qci-04, 13 April 2020,
<https://www.ietf.org/archive/id/draft-henry-tsvwg-
diffserv-to-qci-04.txt>.
[TR-GSTR-TN5G]
ITU-T, "Technical Report GSTR-TN5G", 9 February 2018,
<https://www.itu.int/dms_pub/itu-t/opb/tut/T-TUT-HOME-
2018-PDF-E.pdf>.
[TS-23.501]
3GPP, "TS 23.501: System architecture for the 5G System
(5GS)", 2021,
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3144>.
[TS-28.530]
3GPP, "TS 23.530: Management and orchestration; Concepts,
use cases and requirements)", 2021,
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3273>.
Szarkowicz, et al. Expires 27 April 2023 [Page 48]
Internet-Draft 5G Transport Slices October 2022
[O-RAN.WG9.XPSAAS]
O-RAN Alliance, "O-RAN.WG9.XPSAAS: O-RAN WG9 Xhaul Packet
Switched Architectures and Solutions Version 02.00", 1
July 2021, <https://www.o-ran.org/specifications>.
[NG.113] GSMA, "NG.113: 5GS Roaming Guidelines Version 4.0", 28 May
2021, <https://www.gsma.com/newsroom/wp-content/
uploads//NG.113-v4.0.pdf>.
Appendix A. Acronyms and Abbreviations
3GPP: 3rd Generation Partnership Project
5GC: 5G Core
5QI: 5G QoS Indicator
A2A: Any-to-Any
AC: Attachment Circuit
AMF: Access and Mobility Management Function
AUSF: Authentication Server Function
BBU: Baseband Unit
BH: Backhaul
BS: Base Station
CE: Customer Edge
CIR: Committed Information Rate
CN: Core Network
CoS: Class of Service
CP: Control Plane
CSP: Communication Service Provider
CU: Centralized Unit
CU-CP: Centralized Unit Control Plane
CU-UP: Centralized Unit User Plane
Szarkowicz, et al. Expires 27 April 2023 [Page 49]
Internet-Draft 5G Transport Slices October 2022
DC: Data Center
DDoS: Distributed Denial of Services
DN: Data Network
DSCP: Differentiated Services Code Point
DU: Distributed Unit
eCPRI: enhanced Common Public Radio Interface
FH: Fronthaul
FIB: Forwarding Information Base
GPRS: Generic Packet Radio Service
gNB: gNodeB
GTP: GPRS Tunneling Protocol
GTP-U: GPRS Tunneling Protocol User plane
HW: Hardware
ID: Identifier
IGP: Interior Gateway Protocol
IP: Internet Protocol
L2VPN: Layer 2 Virtual Private Network
L3VPN: Layer 3 Virtual Private Network
LSP: Label Switched Path
MH: Midhaul
MIoT: Massive Internet of Things
MPLS: Multiprotocol Label Switching
NF: Network Function
NR: New Radio
Szarkowicz, et al. Expires 27 April 2023 [Page 50]
Internet-Draft 5G Transport Slices October 2022
NRF: Network Function Repository
NRP: Network Resource Partition
NSC: Network Slice Controller
NSS: Network Slice Subnet
PE: Provider Edge
PIR: Peak Information Rate
PLMN: Public Land Mobile Network
PSTN: Public Switched Telephony Network
QoS: Quality of Service
RAN: Radio Access Network
RF: Radio Frequency
RIB: Routing Information Base
RSVP: Resource Reservation Protocol
RU: Radio Unit
SD: Slice Differentiator
SDP: Service Demarcation Point
SLA: Service Level Agreement
SLO: Service Level Objective
SMF: Session Management Function
SMO: Service Management and Orchestration
S-NSSAI: Single Network Slice Selection Assistance Information
SST: Slice/Service Type
SR: Segment Routing
SRv6: Segment Routing version 6
Szarkowicz, et al. Expires 27 April 2023 [Page 51]
Internet-Draft 5G Transport Slices October 2022
TC: Traffic Class
TE: Traffic Engineering
TN: Transport Network
TS: Technical Specification
UDM: Unified Data Management
UE: User Equipment
UP: User Plane
UPF: User Plane Function
URLLC: Ultra Reliable Low Latency Communication
VLAN: Virtual Local Area Network
VNF: Virtual Network Function
VPN: Virtual Private Network
VRF: Virtual Routing and Forwarding
VXLAN: Virtual Extensible Local Area Network
Appendix B. An overview of 5G Networking
This section provides a brief introduction to 5G mobile networking
with a perspective on the Transport Network. This section does not
intend to replace or define 3GPP architecure, it just provides a
brief overview for readers that do not have a mobile background. For
more comprehensive information, refer to [TS-23.501].
B.1. Building Blocks
[TS-23.501] defines the Network Functions (UPF, AMF, etc.) that
compose the 5G System (5GS) Architecture together with related
interfaces (e.g., N1, N2...). This architecture has native Control
and User Plane separation, and the Control Plane leverages a service-
based architecture. Figure 28 outlines an example 5GS architecture
with a subset of possible network functions and network interfaces.
Szarkowicz, et al. Expires 27 April 2023 [Page 52]
Internet-Draft 5G Transport Slices October 2022
┌─────┐ ┌─────┐ ┌─────┐ ┌─────┐ ┌─────┐ ┌─────┐
│NSSF │ │ NEF │ │ NRF │ │ PCF │ │ UDM │ │ AF │
└──┬──┘ └──┬──┘ └──┬──┘ └──┬──┘ └──┬──┘ └──┬──┘
Nnssf│ Nnef│ Nnrf│ Npcf│ Nudm│ │Naf
───┴────────┴──┬─────┴──┬───────┴───┬────┴────────┴────
Nausf│ Namf│ Nsmf│
┌──┴──┐ ┌──┴──┐ ┌──┴──────┐
│AUSR │ │ AMF │ │ SMF │
└─────┘ └──┬──┘ └──┬──────┘
╱ │ │ ╲
Control Plane N1 ╱ │N2 │N4 ╲N4
════════════════════════════════════════════════════════════
User Plane ╱ │ │ ╲
┌───┐ ┌──┴──┐ N3 ┌──┴──┐ N9 ┌─────┐ N6 .───.
│UE ├──┤(R)AN├─────┤ UPF ├────┤ UPF ├────( DN )
└───┘ └─────┘ └─────┘ └─────┘ `───'
Figure 28: 5GS Architecture and Service-based Interfaces
Similar to previous versions [RFC6459], a 5G mobile network is split
into 4 major domains:
* UE, MS, MN, and Mobile
The terms UE (User Equipment), MS (Mobile Station), MN (Mobile
Node), and mobile refer to the devices that are hosts with the
ability to obtain Internet connectivity via a 3GPP network. An MS
is comprised of the Terminal Equipment (TE) and a Mobile Terminal
(MT). The terms UE, MS, MN, and mobile are used interchangeably
within this document.
* Radio Access Network (RAN)
Provides wireless connectivity to the UE devices via radio. It is
made up of the Antenna that transmits and receives signals to the
UE and the Base Station that digitizes the signal and converts the
RF data stream to IP packets.
* Core Network (CN)
Controls the CP of the RAN and provides connectivity to the Data
Network (e.g., the Internet or a private VPN). The Core Network
hosts dozens of services such as authentication, phone registry,
charging, access to PSTN and handover.
* Transport Network (TN)
Szarkowicz, et al. Expires 27 April 2023 [Page 53]
Internet-Draft 5G Transport Slices October 2022
Provides connectivity between sites where 5G Network Functions are
located. The TN may connect sites from the RAN to the Core
Network, as well as sites within the RAN or within the CN. This
connectivity is achieved by IP Networking.
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│
│ ┌────────────┐ ┌────────────┐
│ │ │ │ │
│ ┌────┐ │ │ │ │ .───────.
│ UE ├──────┤ RAN │ │ CN ├────( DN )
│ └────┘ │ │ │ │ `───────'
│ │ │ │ │
│ └──────┬─────┘ └──────┬─────┘
│ │ │
│ │ │
│ │ │
│ ┌─────┴─────────────────┴────┐
│ │ │
│ │ │
│ Transport Network │ │
│ │ │
│ │ │
│ └────────────────────────────┘
│
│ 5G System
│
└ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
Figure 29: Building blocks of 5G architecture (high-level
representation)
B.2. Core Network
The 5G Core Network (5GC) is made up of a set of Network Functions
(NFs) which fall into two main categories:
* 5GC User Plane: the User Plane Function (UPF) is the interconnect
point between the mobile infrastructure and the Data Network (DN).
It interfaces with the RAN via the N3 interface by encapsulating/
decapsulating the User Plane Traffic in GTP Tunnels (aka GTP-U or
Mobile User Plane).
* 5GC Control Plane: the 5G Control Plane is made up of a
comprehensive set of Network Functions. An exhaustive list and
description of these entities is out of the scope of this
document. The following NFs and interfaces are worth mentioning,
since their connectivity may rely on the Transport Network:
Szarkowicz, et al. Expires 27 April 2023 [Page 54]
Internet-Draft 5G Transport Slices October 2022
- the AMF (Access and Mobility Function) connects with the RAN
control plane over the N2 interface
- the SMF controls the 5GC UPF via the N4 interface
┌ ─ ─ ─ ─ ┐ ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐
RAN 5G Core (5GC)
│ │ │ │
│ │ │ [AUSF] [NRF] [UDM] etc. │
│ │ │ (Service Based) │
( Architecture)
│ │ │ │
N2 ┌─────┐ N11 ┌─────┐
│ CP ───────────┤ AMF ├─────┤ SMF │ │
└─────┘ └──┬──┘
│ │ │ │ │
│ Control Plane
═══════════════════════════════════════════════════════════
│ User Plane
│ │ │ │ N4 │
N3 ┌──┴──┐ N6 .───────.
│ UP ───────────────────────┤ UPF ├───────▶( DN )
└─────┘ `───────'
│ │ │ │
─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
Figure 30: 5G Core Network (CN)
B.3. RAN
The radio access network (RAN) connects cellular wireless devices to
a mobile Core Network. The RAN network is made up of 3 components,
which form the Radio Base Station:
* The Baseband Unit (BBU) provides the interface between the Core
Network and the Radio Network. It connects to the Radio Unit and
is responsible for the baseband signal processing to packet.
* The Radio Unit (RU) is located close to the Antenna and controlled
by the BBU. It converts the Baseband signal received from the BBU
to a Radio frequency signal.
* The Antenna converts the electric signal received from the RU to
radio waves
Szarkowicz, et al. Expires 27 April 2023 [Page 55]
Internet-Draft 5G Transport Slices October 2022
The 5G RAN Base Station is called a gNodeB (gNB). It connects to the
Core Network via the N3 (user plane) and N2 (control plane)
interfaces.
The 5G RAN architecture supports RAN disaggregation in various ways.
Notably, the BBU can be split into a DU (Distributed Unit) for
digital signal processing and a CU (Centralized Unit) for RAN Layer 3
processing. Furthermore, the CU can be itself split into Control
Plane (CU-CP) and User Plane (CU-UP).
Figure 31 depicts a disaggregated RAN with NFs and interfaces.
Szarkowicz, et al. Expires 27 April 2023 [Page 56]
Internet-Draft 5G Transport Slices October 2022
┌─────────────────────────────────┐ ┌ ─ ─ ─ ─ ─ ┐
│ │ N3
┌────┐ NR │ ├────┤ 5G Core │
│ UE ├──────┤ gNodeB │
└────┘ │ ├────┤ (5GC) │
│ │ N2
└─────────────────────────────────┘ └ ─ ─ ─ ─ ─ ┘
│ │
│ │
│ │
─┘ └─
╲ ╱
╲ ╱
V
┌─────────────────────────────────┐ ┌ ─ ─ ─ ─ ─ ┐
│ ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐ │
│ │ │ │
┌────┐ NR │ ┌────┐ F2 │┌────┐ F1-U ┌─────┐│ │ N3 ┌─────┐
│ UE ├────────┤ RU ├─────┤ DU ├──────┤CU-UP├──────────┤ UPF │ │
└────┘ │ └────┘ │└────┘ └──┬──┘│ │ └─────┘
│ ╲ │ │ │ │
│ │ ╲ │ │ │
│ ╲ │ │ │ │
│ │ ╲ │E1 │ │
│ F1-C ╲ │ │ │ │
│ │ ╲ │ │ │
│ ╲ │ │ │ │
│ │ ╲ │ │ │
│ ┌──┴──┐ │ N2 │ ┌─────┐ │
│ │ │CU-CP├──────────┤ AMF │
│ └─────┘ │ │ └─────┘ │
│ │ │ │
│ BBU split │ │ 5G Core │
│ └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘ │
│ │ │ (5GC) │
│ disaggregated gNodeB │
└─────────────────────────────────┘ └ ─ ─ ─ ─ ─ ┘
Figure 31: RAN Disaggregation
B.4. Transport Network
5G TN segments
The 5G transport architecture defines three main segments for the
Transport Network, which are commonly referred to as Fronthaul (FH),
Midhaul (MH), and Backhaul (BH) ([TR-GSTR-TN5G]).
Szarkowicz, et al. Expires 27 April 2023 [Page 57]
Internet-Draft 5G Transport Slices October 2022
* Fronthaul happens before the BBU processing. In 5G, this
interface is based on eCPRI (Enhanced CPRI) with native Ethernet
or IP encapsulation.
* Midhaul is optional: this segment is introduced in the BBU split
presented in Appendix B.3, where Midhaul network refers to the DU-
CU interconnection (i.e., F1 interface). At this level, all
traffic is encapsulated in IP (signaling and user plane).
* Backhaul happens after BBU processing. Therefore, it maps to the
interconnection between the RAN and the Core Network. All traffic
is also encapsulated in IP.
Figure 32 illustrates the different segments of the Transport Network
with the relevant Network Functions.
┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐
│ Transport Network │
│ │
TN Segment 1 TN Segment 2 TN Segment 3
│ (Fronthaul) (Midhaul) (Backhaul) │
┌───────────┐ ┌────────────┐ ┌───────────┐
│ │ │ │ │ │ │ │
─ ┼ ─ ─ ─ ─ ─ ┼ ┼ ─ ─ ─ ─ ─ ─│─│─ ─ ─ ─ ─ ─│─ ─ ─ ─ ─ ─ ─
┌─┴──┐ ┌─┴─┴┐ ┌─┴─┴┐ ┌──┴──┐ .───.
│ RU │ │ DU │ │ CU │ │ UPF ├────( DN )
└────┘ └────┘ └────┘ └─────┘ `───'
Figure 32: 5G Transport Segments
It is worth mentioning that a given part of the transport network can
carry several 5G transport segments concurrently, as outlined in
Figure 33. This is because different types of 5G network functions
might be placed in the same location (e.g., the UPF from one slice
might be placed in the same location as the CU-UP from another
slice).
Szarkowicz, et al. Expires 27 April 2023 [Page 58]
Internet-Draft 5G Transport Slices October 2022
┌ ─ ─ ─ ─ ┐
┌────┐ Colocated
││RU-1│ │ RU/DU
└─┬──┘
│ │ FH-1 │
┌─┴──┐
││DU-1│ │ ┌────┐ ┌─────┐ .───.
└─┬──┘ │CU-1│ │UPF-1├────────( DN )
└ ─│─ ─ ─ ┘ └─┬─┬┘ └─┬───┘ `───'
┌ ─│─ ─ ─ ─ ─ ─│─│─ ─ ─ ─ ─ ─ ┼ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
│ MH-1 │ │ BH-1 │ Transport Network │
│ └───────────┘ └────────────┘
┌───────────┐ ┌────────────┐ ┌───────────┐ │
│ │ FH-2 │ │ MH-2 │ │ BH-2 │
─ ┼ ─ ─ ─ ─ ─ ┼ ┼ ─ ─ ─ ─ ─ ─│─│─ ─ ─ ─ ─ ─│─ ─ ─ ─ ─ ─ ─ ┘
┌─┴──┐ ┌─┴─┴┐ ┌─┴─┴┐ ┌─┴───┐ .───.
│RU-2│ │DU-2│ │CU-2│ │UPF-2├────( DN )
└────┘ └────┘ └────┘ └─────┘ `───'
Figure 33: Concurrent 5G Transport Segments
Acknowledgements
The authors would like to thank Adrian Farrel, Joel Halpern and Tarek
Saad for their reviews of this document and for providing valuable
feedback on it.
Contributors
To be added later
Authors' Addresses
Krzysztof G. Szarkowicz (editor)
Juniper Networks
Wien
Austria
Email: kszarkowicz@juniper.net
Richard Roberts
Juniper Networks
Rennes
France
Email: rroberts@juniper.net
Szarkowicz, et al. Expires 27 April 2023 [Page 59]
Internet-Draft 5G Transport Slices October 2022
Julian Lucek
Juniper Networks
London
United Kingdom
Email: jlucek@juniper.net
John E. Drake
Juniper Networks
Sunnyvale, CA
United States of America
Email: jdrake@juniper.net
Mohamed Boucadair
Orange
Rennes
France
Email: mohamed.boucadair@orange.com
Luis M. Contreras
Telefonica
Ronda de la Comunicacion, s/n
28050 Madrid
Spain
Email: luismiguel.contrerasmurillo@telefonica.com
URI: http://lmcontreras.com/
Ivan Bykov
Ribbon Communications
Tel Aviv
Israel
Email: ivan.bykov@rbbn.com
Reza Rokui
Ciena
Ottawa
Canada
Email: rrokui@ciena.com
Luay Jalil
Verizon
Dallas, TX
United States of America
Szarkowicz, et al. Expires 27 April 2023 [Page 60]
Internet-Draft 5G Transport Slices October 2022
Email: luay.jalil@verizon.com
Beny Dwi Setyawan
XL Axiata
Jakarta
Indonesia
Email: benyds@xl.co.id
Szarkowicz, et al. Expires 27 April 2023 [Page 61]