A Realization of Network Slices for 5G Networks Using Current IP/MPLS Technologies
draft-ietf-teas-5g-ns-ip-mpls-10
| Document | Type | Active Internet-Draft (teas WG) | |
|---|---|---|---|
| Authors | Krzysztof Grzegorz Szarkowicz , Richard Roberts , Julian Lucek , Mohamed Boucadair , Luis M. Contreras | ||
| Last updated | 2024-09-09 | ||
| Replaces | draft-srld-teas-5g-slicing | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Informational | ||
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draft-ietf-teas-5g-ns-ip-mpls-10
TEAS K. G. Szarkowicz, Ed.
Internet-Draft R. Roberts, Ed.
Intended status: Informational J. Lucek
Expires: 13 March 2025 Juniper Networks
M. Boucadair, Ed.
Orange
L. M. Contreras
Telefonica
9 September 2024
A Realization of Network Slices for 5G Networks Using Current IP/MPLS
Technologies
draft-ietf-teas-5g-ns-ip-mpls-10
Abstract
Slicing is a feature that was introduced by the 3rd Generation
Partnership Project (3GPP) in mobile networks. Realization of 5G
slicing implies requirements for all mobile domains, including the
Radio Access Network (RAN), Core Network (CN), and Transport Network
(TN).
This document describes a Network Slice realization model for IP/MPLS
networks with a focus on the Transport Network fulfilling 5G slicing
connectivity service objectives. The realization model reuses many
building blocks currently commonly used in service provider networks.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the Traffic Engineering
Architecture and Signaling Working Group mailing list
(teas@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/teas/.
Source for this draft and an issue tracker can be found at
https://github.com/boucadair/5g-slice-realization.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Internet-Drafts are working documents of the Internet Engineering
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 13 March 2025.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. 5G Network Slicing Integration in Transport Networks . . . . 6
3.1. Scope of the Transport Network . . . . . . . . . . . . . 6
3.2. 5G Network Slicing versus Transport Network Slicing . . . 7
3.3. Transport Network Reference Design . . . . . . . . . . . 8
3.4. Orchestration Overview . . . . . . . . . . . . . . . . . 12
3.5. Mapping 5G Network Slices to Transport Network Slices . . 16
3.6. First 5G Slice versus Subsequent Slices . . . . . . . . . 18
3.7. Overview of the Transport Network Realization Model . . . 21
4. Hand-off Between Domains . . . . . . . . . . . . . . . . . . 23
4.1. VLAN Hand-off . . . . . . . . . . . . . . . . . . . . . . 23
4.2. IP Hand-off . . . . . . . . . . . . . . . . . . . . . . . 24
4.3. MPLS Label Hand-off . . . . . . . . . . . . . . . . . . . 27
5. QoS Mapping Realization Models . . . . . . . . . . . . . . . 32
5.1. QoS Layers . . . . . . . . . . . . . . . . . . . . . . . 32
5.2. QoS Realization Models . . . . . . . . . . . . . . . . . 33
5.3. Transit Resource Control . . . . . . . . . . . . . . . . 48
6. PE Underlay Transport Mapping Models . . . . . . . . . . . . 48
6.1. 5QI-unaware Model . . . . . . . . . . . . . . . . . . . . 50
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6.2. 5QI-aware Model . . . . . . . . . . . . . . . . . . . . . 51
7. Capacity Planning/Management . . . . . . . . . . . . . . . . 52
7.1. Bandwidth Requirements . . . . . . . . . . . . . . . . . 52
7.2. Bandwidth Models . . . . . . . . . . . . . . . . . . . . 55
8. Network Slicing OAM . . . . . . . . . . . . . . . . . . . . . 58
9. Scalability Implications . . . . . . . . . . . . . . . . . . 60
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 60
11. Security Considerations . . . . . . . . . . . . . . . . . . . 60
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 61
12.1. Normative References . . . . . . . . . . . . . . . . . . 62
12.2. Informative References . . . . . . . . . . . . . . . . . 62
Appendix A. Acronyms and Abbreviations . . . . . . . . . . . . . 69
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 71
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 72
1. Introduction
This document focuses on network slicing for 5G networks, covering
the connectivity between Network Functions (NFs) across multiple
domains such as edge clouds, data centers, and the Wide Area Network
(WAN). The document describes a Network Slice realization approach
that fulfills 5G slicing requirements by using existing IP/MPLS
technologies to optimally control connectivity Service Level
Agreements (SLAs) offered for 5G slices. To that aim, this document
describes the scope of the Transport Network in 5G architectures
(Section 3.1), disambiguates 5G Network Slicing versus Transport
Network Slicing (Section 3.2), draws the perimeter of the various
orchestration domains to realize slices (Section 3.4), and identifies
the required coordination between these orchestration domains for
adequate setup of Attachment Circuits (ACs) (Section 3.4.2).
This work is compatible with the framework defined in [RFC9543] which
describes network slicing in the context of networks built from IETF
technologies. Specifically, this document describes an approach to
how RFC 9543 Network Slices are realized within provider networks and
how such slices are stitched to Transport Network resources in a
customer site in the context of Transport Network Slices (Figure 1).
Concretely, the realization of an RFC 9543 Network Slice (i.e.,
connectivity with performance commitments) involves the provider
network and partially the AC (the PE-side of the AC). This document
assumes that the customer site infrastructure is over-provisioned and
involves short distances (low latency) where basic QoS/scheduling
logic is sufficient to comply with the Service Level Objectives
(SLOs).
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|------------------TN Slice------------------|
RFC 9543 Network Slice
+-----SDP Type 3----+
| +- SDP Type 4-+ |
| | | |
v v v v
+------------+ +---------------+ +------------+
| Customer | | Provider | | Customer |
| Site 1 | | Network | | Site 2 |
| | +-+--+ +-+--+ | |
|+---+ +--+-+ AC | | | | AC +-+-+ |
||NF +....+ CE +------+ PE | | PE +----+NF | |
|+---+ +--+-+ | | | | +-+-+ |
| | +-+--+ +-+--+ | |
| | | | | |
+------------+ +---------------+ +------------+
Figure 1: Transport Network Slice & RFC 9543 Network Slice Scopes
The realization approach described in this document is typically
triggered by Network Slice Service requests. How a Network Slice
Service request is placed for realization, including how it is
derived from a 5G Slice Service request, is out of scope. Mapping
considerations between 3GPP and IETF Network Slice Service (e.g.,
mapping of service parameters) are discussed, e.g., in
[I-D.ietf-teas-5g-network-slice-application].
The 5G control plane uses the Single Network Slice Selection
Assistance Information (S-NSSAI) for slice identification
[TS-23.501]. Because S-NSSAIs are not visible to the transport
domain, 5G domains can expose the 5G slices to the transport domain
by mapping to explicit data plane identifiers (e.g., Layer 2, Layer
3, or Layer 4). The realization of the mapping between customer
sites and provider networks is refered to as the "hand-off".
Section 4 lists a set of such hand-off methods.
The realization model described in this document uses a set of
building blocks commonly used in service provider networks.
Concretely, the model uses (1) Layer 2 Virtual Private Network
(L2VPN) [RFC4664] and/or Layer 3 Virtual Private Network (L3VPN)
[RFC4364] service instances for logical separation, (2) fine-grained
resource control at the Provider Edges (PEs), (3) coarse-grained
resource control within the provider network, and (4) capacity
management. More details are provided in Sections 3.7, 5, 6, and 7.
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This realization model uses a single Network Resource Partition (NRP)
(Section 7.1 of [RFC9543]). The applicability to multiple NRPs is
out of scope.
Although this document focuses on 5G, the realizations are not
fundamentally constrained by the 5G use case. The document is not
intended to be a BCP and does not claim to specify mandatory
mechanisms to realize network slices. Rather, a key goal of the
document is to provide pragmatic implementation approaches by
leveraging existing readily-available, widely-deployed techniques.
The document is also intended to align the mobile and the IETF
perspectives of slicing from a realization perspective.
For a definitive description of 3GPP network architectures, the
reader should refer to [TS-23.501]. More details can be found in
[_5G-Book].
2. Definitions
The document uses the terms defined in [RFC9543]. See Section 3.3
for the contextualization of some of these terms.
An extended list of abbreviations used in this document is provided
in Appendix A.
"5G Network Slicing" (or "5G Network Slice") refers to "Network
Slicing" (or "Network Slice") as defined in the 3GPP [TS-28.530].
This document makes use of the following terms:
Customer: An entity that is responsible for managing and
orchestrating the end-to-end 5G Mobile Network, notably the Radio
Access Network (RAN) and Core Network (CN).
This entity is distinct from the customer of a 5G Network Slice
Service.
Customer site: A customer manages and deploys 5G NFs (e.g., gNodeB
(gNB) and 5G Core (5GC)) in customer sites. A customer site can
be either a physical or a virtual location.
Examples of customer sites are a customer private locations (Point
of Presence (PoP), Data Center (DC)), a Virtual Private Cloud
(VPC), or servers hosted within the provider network or colocation
service.
Provider: An entity responsible for interconnecting customer sites.
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A provider orchestrates and manages a provider network.
3. 5G Network Slicing Integration in Transport Networks
3.1. Scope of the Transport Network
The main 5G network building blocks are: the Radio Access Network
(RAN), Core Network (CN), and Transport Network (TN). The Transport
Network is defined by the 3GPP as:
| "part supporting connectivity within and between CN and RAN parts"
| (Section 1 of [TS-28.530]).
As discussed in Section 4.4.1 of [TS-28.530], the 3GPP management
system does not directly control the Transport Network: it is
considered as a non-3GPP managed system.
| "The non-3GPP part includes TN parts. The 3GPP management system
| provides the network slice requirements to the corresponding
| management systems of those non-3GPP parts, e.g. the TN part
| supports connectivity within and between CN and AN parts."
| (Section 4.4.1 of [TS-28.530])
In practice, the TN may not map to a monolithic architecture and
management domain. It is frequently segmented, non-uniform, and
managed by different entities. For example, Figure 2 depicts an NF
instance that is deployed in an edge data center (DC) connected to an
NF located in a Public Cloud via a WAN (e.g., MPLS-VPN service). In
this example, the TN can be seen as an abstraction representing an
end-to-end connectivity based upon three distinct domains: DC, WAN,
and Public Cloud. A model for the Transport Network based on
orchestration domains is introduced in Section 3.4.
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+----------------------------------+
+----+ 5G RAN or Core Network +----+
| +----------------------------------+ |
| |
v v
+--+ +----------------------------------+ +--+
|NF+--+ Transport Network +--+NF|
+--+ +--+---------------+------------+--+ +--+
| | |
v v v
+-- Data Center -+ +-MPLS VPN-+ +-Public-+
| | | Backbone | | Cloud |
|.-----. .-----. | +--+ +--+ +--+ |
|'-----' '-----' | |PE| |PE| |GW| |
|.-. .-. .-. .-. | +--+ +--+ +--+ |
|'-' '-' '-' '-' | | | | |
| | +--+ +--+ | |
| | |PE| |PE| | |
| | +--+ +--+ | |
| | | | | |
+----------------+ +----------+ +--------+
Figure 2: An Example of Transport Network Decomposition
3.2. 5G Network Slicing versus Transport Network Slicing
Network slicing has a different meaning in the 3GPP mobile world and
transport world. This difference can be seen from the descriptions
below that set out the objectives of 5G Network Slicing
(Section 3.2.1) and Transport Network Slicing (Section 3.2.2). These
descriptions are not intended to be exhaustive.
3.2.1. 5G Network Slicing
5G Network Slicing is defined by the 3GPP [TS-28.530] as an approach:
| "where logical networks/partitions are created, with appropriate
| isolation, resources and optimized topology to serve a purpose or
| service category (e.g. use case/traffic category, or for MNO
| internal reasons) or customers (logical system created "on
| demand")."
These resources are from the TN, RAN, CN domains, and the underlying
infrastructure.
Section 3.1 of [TS-28.530] defines 5G Network Slice as:
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| "a logical network that provides specific network capabilities and
| network characteristics, supporting various service properties for
| network slice customers."
3.2.2. Transport Network Slicing
The term "TN slice" refers to a slice in the Transport Network domain
of the 5G architecture.
The objective of Transport Network Slicing is to isolate, guarantee,
or prioritize Transport Network resources for Slice Services.
Examples of such resources are: buffers, link capacity, or even
Routing Information Base (RIB) and Forwarding Information Base (FIB).
Transport Network Slicing provides various degrees of sharing of
resources between slices. For example, the network capacity can be
shared by all slices, usually with a guaranteed minimum per slice, or
each individual slice can be allocated dedicated network capacity.
Parts of a given network may use the former, while others use the
latter. For example, in order to satisfy local engineering
guidelines and specific service requirements, shared TN resources
could be provided in the backhaul (or midhaul), and dedicated TN
resources could be provided in the midhaul (or backhaul). The
capacity partitioning strategy is deployment specific.
There are different components to implement TN slices based upon
mechanisms such as Virtual Routing and Forwarding instances (VRFs)
for logical separation, Quality of Service (QoS), and Traffic
Engineering (TE). Whether all or a subset of these components are
enabled is a deployment choice.
3.3. Transport Network Reference Design
Figure 3 depicts the reference design used in this document for
modelling the Transport Network based on management perimeters
(Customer vs. Provider).
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Customer Provider Customer
Orchestration Orchestration Orchestration
Domain Domain Domain
+----------------+ +---------------------+ +----------------+
| Customer | | Provider Network | | Customer |
| Site 1 | | | | Site 2 |
| +----+| |+----+ +----+| |+----+ |
|+--+ | || AC || | | || AC || NF | |
||NF|......| CE +--------+ PE | | PE +---------+(CE)| |
|+--+ | || || | | || || | |
| +----+| |+----+ +----+| |+----+ |
| | | | | |
+----------------+ +---------------------+ +----------------+
<-----------------Transport Network--------------->
Figure 3: Reference Design with Customer Site and Provider Network
The description of the main components shown in Figure 3 is provided
in the following subsections.
3.3.1. Customer Site
On top of 5G NFs, a customer may manage additional TN elements (e.g.,
servers, routers, and switches) within a customer site.
NFs may be hosted on a CE, directly connected to a CE, or be located
multiple IP hops from a CE.
The orchestration of the TN within a customer site involves a set of
controllers for automation purposes (e.g., Network Functions
Virtualization Infrastructure (NFVI), Container Network Interface
(CNI), Fabric Managers, or Public Cloud APIs). It is out of scope to
document how these controllers are implemented.
3.3.2. Customer Edge (CE)
A CE is a function that provides logical connectivity of a customer
site (Section 3.3.1) to the provider network (Section 3.3.3). The
logical connectivity is enforced at Layer 2 and/or Layer 3 and is
denominated an Attachment Circuit (AC) (Section 3.3.5). Examples of
CEs include TN components (e.g., router, switch, and firewalls) and
also 5G NFs (i.e., an element of the 5G domain such as Centralized
Unit (CU), Distributed Unit (DU), or User Plane Function (UPF)).
A CE is typically managed by the customer, but it can also be co-
managed with the provider. A co-managed CE is orchestrated by both
the customer and the provider. In this case, the customer and
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provider usually have control on distinct device configuration
perimeters. A co-managed CE has both PE and CE functions and there
is no strict AC connection, although one may consider that the AC
stitching logic happens internally within the CE itself. The
provider manages the AC between the CE and the PE.
This document generalizes the definition of a CE with the
introduction of "Distributed CE"; that is, the logical connectivity
is realized by configuring multiple devices in the customer domain.
The CE function is distributed. An example of distributed CE is the
realization of an interconnection using a L3VPN service based on a
distributed CE composed of a switch (Layer 2) and a router (Layer 3)
(Figure 4). Another example of distributed CE is shown in Figure 5.
+--------------+ +--------------+
| Customer | | Provider |
| Site | | Network |
|................. | |
||+-----+ +----+ | +----+ |
||| | | ================== | |
||| +------------AC---------+ PE | |
||| RTR | | SW ================== | |
||+-----+ +----+ | +----+ |
|'..Distributed..' | |
| CE | | |
+--------------+ +--------------+
Figure 4: Example of Distributed CE
While in most cases CEs connect to PEs using IP (e.g., via Layer 3
VLAN subinterfaces), a CE may also connect to the provider network
using other technologies such as MPLS -potentially over IP tunnels-
or Segment Routing over IPv6 (SRv6) [RFC8986]. The CE has thus
awareness of provider services configuration (e.g., control plane
identifiers such as Route Targets (RTs) and Route Distinguishers
(RDs)). However, the CE is still managed by the customer and the AC
is based on MPLS or SRv6 data plane technologies. The complete
termination of the AC within the provider network may happen on
distinct routers: this is another example of distributed PE.
Service-aware CEs are used, for example, in the deployments discussed
in Sections 4.3.2 and 4.3.3.
3.3.3. Provider Network
A provider uses a provider network to interconnect customer sites.
This document assumes that the provider network is based on IP, MPLS,
or both.
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3.3.4. Provider Edge (PE)
PE is a device managed by a provider that is connected to a CE. The
connectivity between a CE and a PE is achieved using one or multiple
ACs (Section 3.3.5).
This document generalizes the PE definition with the introduction of
"Distributed PE"; that is, the logical connectivity is realized by
configuring multiple devices in the provider network (i.e., provider
orchestration domain). The PE function is distributed.
An example of a distributed PE is the "Managed CE service". For
example, a provider delivers VPN services using CEs and PEs which are
both managed by the provider (case (i) in Figure 5). The managed CE
can also be a Data Center Gateway as depicted in the example (ii) of
Figure 5. A provider-managed CE may attach to CEs of multiple
customers. However, this device is part of the provider network.
+--------------+ +--------------+
| Customer | | Provider |
| Site | | Network |
| | ................. |
| +----+ |+----+ +----+| |
| | ==================Mngd| | || |
| | CE +--------AC------+ CE +---+ PE || |
| | ================== | | || |
| +----+ |+----+ +----+| |
| | '..Distributed..' |
| | | PE |
+--------------+ +--------------+
(i) Distributed PE
+--------------+ +--------------+
| Customer | | Provider |
| Site | | Network |
| .................. .................. |
| | IP Fabric | |+----+ +----+ | |
| |.-----. .-----. ============== DC | | | | |
| |'-----' '-----' +-----AC-----+ GW +---+ PE | | |
| |.-. .-. .-. .-. ============== | | | | |
| |'-' '-' '-' '-' | |+----+ +----+ | |
| '...Distributed..' '...Distributed..' |
| CE | | PE |
| | | |
+--Data Center-+ +--------------+
(ii) Distributed PE and CE
Figure 5: Examples of Distributed PE
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In subsequent sections of this document, the terms CE and PE are used
for both single and distributed devices.
3.3.5. Attachment Circuit (AC)
The AC is the logical connection that attaches a CE (Section 3.3.2)
to a PE (Section 3.3.4). A CE is connected to a PE via one or
multiple ACs.
This document uses the concept of distributed CE and PE (Sections
3.3.2) and (3.3.4) to consolidate a CE/AC/PE definition that is
consistent with the orchestration perimeters (Section 3.4). The CEs
and PEs delimit respectively the customer and provider orchestration
domains, while an AC interconnects these domains.
For consistency with the AC data models terminology (e.g.,
[I-D.ietf-opsawg-teas-attachment-circuit] and
[I-D.ietf-opsawg-ntw-attachment-circuit]), this document assumes that
an AC is configured on a "bearer", which represents the underlying
connectivity. For example, the bearer is illustrated with "===" in
Figures 4 and 5.
An AC is technology-specific. Examples of ACs are Virtual Local Area
Networks (VLANs) (AC) configured on a physical interface (bearer) or
an Overlay VXLAN EVI (AC) configured on an IP underlay (bearer).
Deployment cases where the AC is also managed by the provider are not
discussed in the document because the setup of such an AC does not
require any coordination between the customer and provider
orchestration domains.
| In order to keep the figures simple, only one AC and single-
| homed CEs are represented. Also, the underlying bearers are
| not represented in most of the figures. However, this document
| does not exclude the instantiation of multiple ACs between a CE
| and a PE nor the presence of CEs that are attached to more than
| one PE.
3.4. Orchestration Overview
3.4.1. 5G End-to-End Slice Orchestration Architecture
This section introduces a global framework for the orchestration of a
5G end-to-end slice (a.k.a. 5G Network Slice) with a zoom on TN
parts. This framework helps to delimit the realization scope of RFC
9543 Network Slices and identify interactions that are required for
the realization of such slices.
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This framework is consistent with the management coordination example
shown in Figure 4.7.1 of [TS-28.530].
In reference to Figure 6, a 5G End-to-End Network Slice Orchestrator
(5G NSO) is responsible for orchestrating 5G Network Slices end-to-
end. The details of the 5G NSO are out of the scope of this
document. The realization of the 5G Network Slices spans RAN, CN,
and TN. As mentioned in Section 3.1, the RAN and CN are under the
responsibility of the 3GPP Management System, while the TN is not.
The orchestration of the TN is split into two sub-domains in
conformance with the reference design in Section 3.3:
Provider Network Orchestration domain: As defined in [RFC9543], the
provider relies on a Network Slice Controller (NSC) to manage and
orchestrate RFC 9543 Network Slices in the provider network. This
framework permits to manage connectivity together with SLOs.
Customer Site Orchestration domain: The Orchestration of TN elements
of the customer sites relies upon a variety of controllers (e.g.,
Fabric Manager, Element Management System, or Virtualized
Infrastructure Manager (VIM)).
A TN slice relies upon resources that can involve both the provider
and customer TN domains. More details are provided in Section 3.4.2.
A TN slice might be considered as a variant of horizontal composition
of Network Slices mentioned in Appendix A.6 of [RFC9543].
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+-----------+
| 5G NSO |
+--+---+----+
| |
v |
+---------------+ |
| 3GPP domains | |
+-----------+ Orchestration +-|--------------------------+
| | (RAN and CN) | | |
| +---------------+ | |
| v |
| +-----------------------------------------------+ |
| |TN Orchestration | |
| |+---------------++-----------++---------------+| |
| || Customer Site ||RFC9543 NSC|| Customer Site || |
| || Orchestration || || Orchestration || |
| |+---------------++-----------++---------------+| |
| +---|-------------------|---------------------|-+ |
| | | | |
| | | | |
| v v v |
+-|-----------+ +-----------------+ +------|---+
| | | | Provider | | | |
| v | +----+ Network +----+ +----+ | |
|+--+ +----+ AC | | | | AC | NF |<-+ |
||NF+.....+ CE +------+ PE | | PE +------+(CE)| |
|+--+ +----+ | | | | +----+ |
| | +----+ +----+ | |
| Customer | | | | Customer |
| Site | | | | Site |
+-------------+ +-----------------+ +----------+
RFC 9543
|-----Network Slice---|
|--------------------TN Slice-------------------|
Figure 6: 5G End-to-End Slice Orchestration with TN
The various orchestration depicted in Figure 6 encompass the 3GPP's
Network Slice Subnet Management Function (NSSMF) mentioned, e.g., in
Figure 5 of [I-D.ietf-teas-5g-network-slice-application].
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3.4.2. Transport Network Segments and Network Slice Instantiation
This document focuses on deployments where the Service Demarcation
Points (SDPs) are located per Types 3 and 4 of Figure 1 of [RFC9543].
The concept of distributed PE (Section 3.3.4) assimilates CE-based
SDPs defined in Section 5.2 of [RFC9543] (i.e., Types 1 and 2) as SDP
Type 3 or 4 in this document.
In reference to the architecture depicted in Section 3.4.1, the
connectivity between NFs can be decomposed into three main segment
types that are as follows:
Customer Site: Either connects NFs located in the same customer site
or connects an NF to a CE.
This segment may not be present if the NF is the CE. In this case
the AC connects the NF to a PE.
The realization of this segment is driven by the 5G Network
Orchestration (e.g., NFs instantiation) and the Customer Site
Orchestration for the TN part.
Provider Network: Represents the connectivity between two PEs. The
realization of this segment is controlled by an NSC (Section 6.3
of [RFC9543]).
Attachment Circuit: The orchestration of this segment relies
partially upon an NSC for the configuration of the AC on the PE
customer-facing interfaces and the Customer Site Orchestration for
the configuration of the AC on the CE.
PEs and CEs that are connected via an AC need to be provisioned
with consistent data plane and control plane information (VLAN-
IDs, IP addresses/subnets, BGP Autonomous System (AS) Number,
etc.). Hence, the realization of this interconnection is
technology-specific and requires coordination between the Customer
Site Orchestration and an NSC. Automating the provisioning and
management of the AC is thus key to automate the overall service
provisioning. Aligned with [RFC8969], this document assumes that
this coordination is based upon standard YANG data models and
APIs.
The provisioning of a Network Slice may rely on new or existing
ACs.
Figure 7 is a basic example of a Layer 3 CE-PE link realization
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with shared network resources (such as VLAN-IDs and IP prefixes)
which are passed between Orchestrators via a dedicated interface,
e.g., the Network Slice Service Model (NSSM)
[I-D.ietf-teas-ietf-network-slice-nbi-yang] or the Attachment
Circuit-as-a-Service (ACaaS)
[I-D.ietf-opsawg-teas-attachment-circuit].
+---------------+ +------------------+
| | | RFC9543 NSC |
| Customer Site | | |
| Orchestration | IETF APIs/DM |(Provider Network |
| |<----------------->| Orchestration) |
+---------------+ +------------------+
| |
| |
+---------------|-+ +-|---------------+
| v | | v |
| +--+ +--+.1| 192.0.2.0/31 |.0+--+ |
| |NF+......+CE+--------------------------+PE| |
| +--+ +--+ | VLAN 100 | +--+ |
| Customer | | Provider |
| Site | | Network |
+-----------------+ +-----------------+
|----------- AC -----------|
Figure 7: Coordination of Transport Network Resources for the AC
Provisioning
3.5. Mapping 5G Network Slices to Transport Network Slices
There are multiple options for mapping 5G Network Slices to TN
slices:
* 1 to N: A single 5G Network Slice can be mapped to multiple TN
slices (1 to N). For instance, consider the scenario depicted in
Figure 8, illustrating the separation of the 5G control plane and
user plane in TN slices for a single 5G Enhanced Mobile Broadband
(eMBB) network slice. It is important to note that this mapping
can serve as an interim step to M to N mapping. Further details
about this scheme are described in Section 3.6.
* M to 1: Multiple 5G Network Slices may rely upon the same TN
slice. In such a case, the Service Level Agreement (SLA)
differentiation of slices would be entirely controlled at the 5G
control plane, for example, with appropriate placement strategies:
this use case is represented in Figure 9, where a User Plane
Function (UPF) for the Ultra Reliable Low Latency Communication
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(URLLC) slice is instantiated at the edge cloud close to the gNB
Centralized Unit User Plane (CU-UP) for better latency/jitter
control, while the 5G control plane and the UPF for eMBB slice are
instantiated in the regional cloud.
* M to N: The 5G to TN slice mapping combines both approaches with a
mix of shared and dedicated associations.
In this scenario, a subset of the TN slices can be intended for
sharing by multiple 5G Network Slices (e.g., the control plane TN
slice is shared by multiple 5G network Slices).
In practice, for operational and scaling reasons, typically M to N
would be used, with M >> N.
+---------------------------------------------------------------+
| 5G Slice eMBB |
| +------------------------------------+ |
| +-----+ N3 | +---------------------------------+| N3 +-----+ |
| |CU-UP+------+ RFC 9543 Network Slice UP_eMBB +------+ UPF | |
| +-----+ | +---------------------------------+| +-----+ |
| | | |
| +-----+ N2 | +---------------------------------+| N2 +-----+ |
| |CU-CP+------+ RFC 9543 Network Slice CP +------+ AMF | |
| +-----+ | +---------------------------------+| +-----+ |
+------------|------------------------------------|-------------+
| |
| Transport Network |
+------------------------------------+
Figure 8: 1 (5G Slice) to N (RFC 9543 Network Slice) Mapping
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+-------------+
| Edge Cloud |
| |
| +---------+ |
| |UPF_URLLC| |
| +-----+---+ |
+-------|-----+
+---------------+ +-------|----------------------+
| Cell Site | | +-----+--------------------+ | +--------------+
| | | | | | Regional |
| +-----------+ | | | | | | Cloud |
| |CU-UP_URLLC+-----+ | | | +-----------+|
| +-----------+ | | | RFC 9543 Network +-----+ 5GC CP | |
| | | | Slice ALL | | | +-----------+|
| +-----------+ | | | | | | |
| |CU-UP_eMBB +-----+ | | | +-----------+
| +-----------+ | | | +-----+ UPF_eMBB | |
+---------------+ | | | | | +-----------+|
| +--------------------------+ | | |
| | +--------------+
| Transport Network |
+------------------------------+
Figure 9: N (5G Slice) to 1 (RFC 9543 Network Slice) Mapping
Note that the actual realization of the mapping depends on several
factors, such as the actual business cases, the NF vendor
capabilities, the NF vendor reference designs, as well as service
provider or even legal requirements.
Mapping approaches that preserve the 5G slice identification in the
TN (e.g., Section 4.2) may simplify required operations to map back
TN slices to 5G slices. However, such considerations are not
detailed in this document because these are under the responsibility
of the 3GPP orchestration domain.
3.6. First 5G Slice versus Subsequent Slices
An operational 5G Network Slice incorporates both 5G control plane
and user plane capabilities. For instance, consider a slice based on
split-CU in the RAN, both CU-UP and Centralized Unit Control Plane
(CU-CP) need to be deployed along with the associated interfaces E1,
F1-c, F1-u, N2, and N3 which are conveyed in the TN. In this regard,
the creation of the "first slice" can be subject to a specific logic
that does not apply to subsequent slices. Let us consider the
example depicted in Figure 10 to illustrate this deployment. In this
example, the first 5G slice relies on the deployment of NF-CP and NF-
UP functions together with two TN slices for control and user planes
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(INS-CP and INS-UP1). Next, the deployment of a second slice relies
solely on the instantiation of a UPF (NF-UP2) together with a
dedicated user plane TN slice (INS-UP2). In this example, the
control plane of the first 5G slice is also updated to integrate the
second slice: the TN slice (INS-CP) and Network Functions (NF-CP) are
shared.
At the time of writing (2024), Section 6.1.2 of [NG.113] specifies
that the eMBB slice (SST-1 and no Slice Differentiator (SD)) should
be supported globally. This 5G slice would be the first slice in any
5G deployment.
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+---------------------------------------------------------------+
| +------------------------------+ |
| 1 +-----+ | +--------------------------+ | +-----+ |
| s S |NF-CP+------+ CP TN Slice (TNS-CP) +------+NF-CP| |
| t l +-----+ | +--------------------------+ | +-----+ |
| i | | |
| 5 c +-----+ | +--------------------------+ | +-----+ |
| G e |NF-UP+------+ UP TN Slice (TNS-UP1) +------+NF-UP| |
| +-----+ | +--------------------------+ | +-----+ |
+------------------|------------------------------|-------------+
| |
| Transport Network |
+------------------------------+
Deployment of first 5G slice
| |
| |
--+ +--
\ /
\ /
+---------------------------------------------------------------+
| +------------------------------+ |
| 1 +-----+ | +--------------------------+ | +-----+ |
| s S |NF-CP+------+ CP TN Slice (TNS-CP) +------+NF-CP| |
| t l +-----+ | +--------------------------+ | +-----+ |
| i | | |
| 5 c +-----+ | +--------------------------+ | +-----+ |
| G e |NF-UP+------+ UP TN Slice (TNS-UP1) +------+NF-UP| |
| +-----+ | +--------------------------+ | +-----+ |
+------------------|------------------------------|-------------+
| |
+------------------|------------------------------|-------------+
| 2 | | |
| n S +------+ | +--------------------------+ | +------+ |
| d l |NF-UP2+-----+ UP TN Slice (TNS-UP2) +-----+NF-UP2| |
| i +------+ | +--------------------------+ | +------+ |
| 5 c | | |
| G e | | |
+------------------|------------------------------|-------------+
| |
| Transport Network |
+------------------------------+
Deployment of additional 5G slice with shared Control Plane
Figure 10: First and Subsequent Slice Deployment
Overall, policies might be provided by an operator (e.g., to Network
Slice Controllers) to indicate whether the same or dedicated CP NFs
are allowed when processing a new slice creation request. Providing
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such a policy is meant to better automate the realization of 5G
slices and minimize the realization delay that might be induced by
extra cycles to seek for operator validation.
3.7. Overview of the Transport Network Realization Model
The realization model described in this document is depicted in
Figure 11. The following building blocks are used:
* L2VPN [RFC4664] and/or L3VPN [RFC4364] 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 delivery for fronthaul connections. Enhanced
Common Public Radio Interface (eCPRI) [ECPRI] supports both
delivery models. L2VPN/L3VPN service instances might be used as a
basic form of logical slice separation. Furthermore, using
service instances results in an additional outer header (as
packets are encapsulated/decapsulated at the nodes hosting service
instances) providing clean discrimination between 5G QoS and TN
QoS, as explained in Section 5.
The use of VPNs for realizing Network Slices is briefly described
in Appendix A.4 of [RFC9543].
* Fine-grained resource control at the PE:
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 provider
network where the traffic is handed-off between the customer site
and the provider network.
The method used here is granular ingress policing (rate limiting)
to enforce contracted bandwidths per slice and, potentially, per
traffic class within the slice. Traffic above the enforced rate
might be immediately dropped, or marked as high drop-probability
traffic, which is more likely to be dropped somewhere inside the
provider network if congestion occurs. In the egress direction at
the PE node, hierarchical schedulers/shapers can be deployed,
providing guaranteed rates per slice, as well as guarantees per
traffic class within each slice.
For managed CEs, edge admission control can be distributed between
CEs and PEs, where a part of the admission control is implemented
on the CE and other part of the admission control is implemented
on the PE.
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* Coarse-grained resource control at the transit (non-attachment
circuits) links in the provider network, using a single NRP
(called "base NRP" in Figure 11), spanning the entire provider
network. Transit nodes in the provider network do not maintain
any state of individual slices. Instead, only a flat (non-
hierarchical) QoS model is used on transit links in the provider
network, with up to 8 traffic classes. At the PE, traffic-flows
from multiple slice services are mapped to the limited number of
traffic classes used on provider network transit links.
* Capacity planning/management for efficient usage of provider
network resources:
The role of capacity management is to ensure the provider network
capacity can be utilized without causing any bottlenecks. The
methods used here can range from careful network planning, to
ensure a more or less equal traffic distribution (i.e., equal cost
load balancing), to advanced TE techniques, with or without
bandwidth reservations, to force more consistent load distribution
even in non-ECMP friendly network topologies. See also Section 8
of [RFC9522]).
..............................................
: Base NRP :
+-----:----+ +----:-----+
| PE : | | : PE |
-- -- |- -- -- --| - -- -- -- -- -- -- -- -- -- -- -- | -- -- -- |
N *<---+ | | +--->*
S | | | +-----+ +-----+ | | |
# *<---+ | | P | | P | | +--->*
1 | | | | | | | | | |
== == | +---->o<----->o<--->o<------>o---->o<----->o<----| |
N | | | | | | | | | |
S *<---+ | | | | | | +--->*
# | | | +-----+ +-----+ | | |
2 *<---+ | | +--->*
-- -- |- -- -- --|-- -- -- -- -- -- -- -- -- -- -- -- | -- -- -- |
| : | | : |
+-----:----+ +----:-----+
: :
'..............................................'
* SDP, with fine-grained QoS (dedicated resources per Network Slice)
o Coarse-grained QoS, with resources shared by all Network Slices
... Base NRP
-- -- Network Slice
Figure 11: Resource Allocation Slicing Model with a Single NRP
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P nodes shown in Figure 11 are routers that do no interface with
customer devices. See Section 5.3.1 of [RFC4026].
This document does not describe in detail how to manage an L2VPN or
L3VPN, as this is already well-documented. For example, the reader
may refer to [RFC4176] and [RFC6136] for such details.
4. Hand-off Between Domains
The 5G control plane relies upon 32-bit S-NSSAIs for slice
identification. The S-NSSAI is not visible to the transport domain.
So instead, 5G network functions can expose the 5G slices to the
transport domain by mapping to explicit Layer 2 or Layer 3
identifiers, such as VLAN-IDs, IP addresses, or Differentiated
Services Code Point (DSCP) values. These section lists few hand-off
methods for slice mapping between customer sites and provider
networks.
More details about the mapping between 3GPP and RFC 9543 Network
Slices is provided in [I-D.ietf-teas-5g-network-slice-application].
4.1. VLAN Hand-off
In this option, the RFC 9543 Network Slice, fulfilling connectivity
requirements between NFs that belong to a 5G slice, is represented at
an SDP by a VLAN ID (or double VLAN IDs, commonly known as QinQ), as
depicted in Figure 12.
VLANs representing slices VLANs representing slices
| +------------------+ | |
| | | | |
+------+ v +-+---+ Provider +---+-+ v +-----+ v +------+
| +-------+* | | *+-------+ +.......+ |
| NF +-------+* PE | | PE *+-------+L2/L3+.......+ NF |
| +-------+* | | *+-------+ +.......+ |
+------+ AC +-+---+ Network +---+-+ AC +-----+ +------+
| |
+------------------+
+ Logical interface represented by a VLAN on a physical interface
* SDP
Figure 12: Example of 5G Slice with VLAN Hand-off Providing End-
to-End Connectivity
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Each VLAN represents a distinct logical interface on the ACs; hence
it provides the possibility to place these logical interfaces in
distinct Layer 2 or Layer 3 service instances and implement
separation between slices via service instances. Since the 5G
interfaces are IP-based interfaces (with an exception of the F2
fronthaul-interface, where eCPRI with Ethernet encapsulation is
used), this VLAN is typically not transported across the provider
network. Typically, it has only local significance at a particular
SDP. For simplification, a deployment may rely on the same VLAN
identifier for all ACs. However, that may not be always possible.
As such, SDPs for a same slice at different locations may use
different VLAN values. Therefore, a VLAN to RFC 9543 Network Slice
mapping table is maintained for each AC, and the VLAN allocation is
coordinated between customer orchestration and provider
orchestration.
While VLAN hand-off is simple for NFs, it adds complexity at the
provider network because of the requirement of maintaining mapping
tables for each SDP and performing a configuration task for new VLANs
and IP subnet for every slice on every AC.
4.2. IP Hand-off
In this option, an explicit mapping between source/destination IP
addresses and slice's specific S-NSSAI is used. The mapping can have
either local (e.g., pertaining to single NF attachment) or global TN
significance. The mapping can be realized in multiple ways,
including (but not limited to):
* S-NSSAI to a dedicated IP address for each NF
* S-NSSAI to a pool of IP addresses for global TN deployment
* S-NSSAI to a subset of bits of an IP address
* S-NSSAI to a DSCP value
* Use a deterministic algorithm to map S-NSAAI to an IP subnet,
prefix, or pools. For example, adaptations to the algorithm
defined in [RFC7422] may be considered.
Mapping S-NSSAIs to IP addresses makes IP addresses an identifier for
slice-related policy enfocement in the Transport Network (e.g.,
Differentiated Services, traffic steering, bandwidth allocation,
security policies, or monitoring).
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One example of the IP hand-off realization is the arrangement, where
the slices in the TN domain are instantiated using IP tunnels (e.g.,
IPsec or GTP-U tunnels) established between NFs, as depicted in
Figure 13. The transport for a single 5G slice might be 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.
Tunnels representing slices
+------------------+ |
| | |
+------+ +--+--+ Provider +---+-+ +-----+ v +------+
| o============*================*==========================o |
| NF +-------+ PE | | PE +-------+L2/L3+.......+ NF |
| o============*================*==========================o |
+------+ AC +-+---+ Network +---+-+ AC +-----+ +------+
| |
+------------------+
o Tunnel (IPsec, GTP-U, ...) termination point
* SDP
Figure 13: Example of 5G Slice with IP Hand-off Providing End-to-End
Connectivity
As opposed to the VLAN hand-off case (Section 4.1), there is no
logical interface representing a slice on the PE, hence all slices
are handled within a single service instance. The IP and VLAN hand-
offs are not mutually exclusive, but instead could be used
concurrently. Since the TN doesn't recognize S-NSSAIs, a mapping
table similar to the VLAN Hand-off solution is needed (Section 4.1).
The mapping table can be simplified if, for example, 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.
The S-NSSAI/IPv6 mapping is a local IPv6 address allocation method to
NFs not disclosed to on-path nodes. IP forwarding is not altered by
this method and is still achieved following BCP 198 [RFC7608].
Concretely, intermediary TN nodes are not required to associate any
additional semantic with IPv6 address.
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However, operators using such mapping methods should be aware of the
implications of any change of S-NSSAI on the IPv6 addressing plans.
For example, modifications of the S-NSSAIs in-use will require
updating the IP addresses used by NFs involved in the associated
slices.
4.2.1. An Example of Local IPv6 Addressing Plan for Network Functions
Different IPv6 address allocation schemes following the above
approach may be used, with one example allocation shown in Figure 14.
NF-specific Reserved
(not slice specific) for S-NSSAI
<----------------------------><--------->
+----+----+----+----+----+----+----+----+
|xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:ttdd:dddd|
+----+----+----+----+----+----+----+----+
<------------------128 bits------------->
tt - SST (8 bits)
dddddd - SD (24 bits)
Figure 14: An Example of S-NSSAI Embedded into an IPv6 Address
In reference to Figure 14, the most significant 96 bits of the IPv6
address are unique to the NF, but do not carry any slice-specific
information. The S-NSSAI information is embedded in the least
significant 32 bits. The 96-bit part of the address may be
structured by the provider, for example, on the geographical location
or the DC identification. Refer to Section 2.1. of [RFC9099] for a
discussion on the benefits of structuring an address plan around both
services and geographic locations for more structured security
policies in a network.
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Figure 15 uses the example from Figure 14 to demonstrate a slicing
deployment, where the entire S-NSSAI is embedded into IPv6 addresses
used by NFs. Let us consider that "NF-A" has a set of tunnel
termination points with unique per-slice IP addresses allocated from
2001:db8:a:0::/96, while "NF-B" uses a set of tunnel termination
points with per-slice IP addresses allocated from 2001:db8:b:0::/96.
This example shows two slices: "customer A eMBB" (SST-01, SD-00001)
and "customer B Massive Internet of Things (MIoT)" (SST-03, SD-
00003). For "customer A eMBB" slice, the tunnel IP addresses are
auto-derived as the IP addresses {2001:db8:a::100:1,
2001:db8:b::100:1}, where {:0100:0001} is used as the last two
octets. "customer B MIoT" slice (SST-3, SD-00003) tunnel uses the IP
addresses {2001:db8:a::300:3, 2001:db8:b::300:3} and simply adds
{:0300:0003} as the last two octets. Leading zeros are not
represented in the resulting IPv6 addresses as per [RFC5952].
2001:db8:a::/96 (NF-A) 2001:db8:b::/96 (NF-B)
2001:db8:a::100:1/128 2001:db8:b::100:1/128
| |
| + - - - - - - - - + eMBB (SST=1) |
| | | | |
+----v-+ +--+--+ Provider +---+-+ v +-----+ +-v----+
| o============*================*==========================o |
| NF +-------+ PE | | PE +-------+L2/L3+.......+ NF |
| o============*================*==========================o |
+----^-+ +--+--+ Network +---+-+ ^ +-----+ +-^----+
| | | | |
| + - - - - - - - - + MIoT (SST=3) |
| |
2001:db8:a::300:3/128 2001:db8:b::300:3/128
o Tunnel (IPsec, GTP-U, etc) termination point
* SDP
Figure 15: Deployment Example with S-NSSAI Embedded into IPv6
Addresses
4.3. MPLS Label Hand-off
In this option, the service instances representing different slices
are created directly on the NF, or within the customer site hosting
the NF, and attached to the provider network. Therefore, the packet
is encapsulated outside the provider network with MPLS encapsulation
or MPLS-in-UDP encapsulation [RFC7510], depending on the capability
of the customer site, with the service label depicting the slice.
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There are three major methods (based upon Section 10 of [RFC4364])
for interconnecting MPLS services over multiple service domains:
Option A (Section 4.3.1): VRF-to-VRF connections.
Option B (Section 4.3.2): redistribution of labeled VPN routes with
next-hop change at domain boundaries.
Option C (Section 4.3.3): redistribution of labeled VPN routes
without next-hop change and redistribution of labeled transport
routes with next-hop change at domain boundaries.
Figure 16 illustrates the use of service-aware CE (Section 3.3.2) for
the deployment discussed in Sections 4.3.2 and 4.3.3.
+--------------+ +--------------+
| Customer | | Provider |
| Site | | Network |
| | | |
| | | |
| | <------MP-BGP-----> | |
| +--+-+ +-+--+ |
| | | MPLS-based AC | | |
| | CE +------------------+ PE | |
| +--+----+--+ | | |
| | VRF foo | +-+--+ |
+--------+----------+ +--------------+
Figure 16: Example of MPLS-based Attachment Circuit
4.3.1. Option A
This option is not based on MPLS label hand-off, but VLAN hand-off,
described in Section 4.1.
4.3.2. Option B
In this option, L3VPN service instances are instantiated outside the
provider network. These L3VPN service instances are instantiated in
the customer site which could be, for example, either on the compute
that hosts mobile NFs (Figure 17, left hand side) or within the DC/
cloud infrastructure itself (e.g., on the top of the rack or leaf
switch within cloud IP fabric (Figure 17, right hand side)). On the
AC connected to a PE, packets are already MPLS encapsulated (or MPLS-
in-UDP/MPLS-in-IP encapsulated, if cloud or compute infrastructure
don't support MPLS encapsulation). Therefore, the PE uses neither a
VLAN nor an IP address for slice identification at the SDP, but
instead uses the MPLS label.
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<------ <------ <------
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
| | |
+---+ | +--------------+ +|---------|----------+
| | | | Provider | || | |
|+--+-v-+ +-+---+ +--+--+ +-+v----+ v +------+|
|| # | |* | | *| | #<><>x.......x ||
|| NF # +-------+* PE | | PE *+------+ #<><>x.......x NF ||
|| # | AC |* | | *| AC | #<><>x.......x ||
|+---+--+ +-+---+ +---+-+ +-+-----+ +------+|
| CS1| | Network | | L2/L3 CS2 |
+----+ +---------------+ +---------------------+
x Logical interface represented by a VLAN on a physical interface
# Service instances (with unique MPLS labels)
* SDP
Figure 17: Example of MPLS Hand-off with Option B
MPLS labels are allocated dynamically in Option B deployments, where
at the domain boundaries service prefixes are reflected with next-hop
self, and a new label is dynamically allocated, as visible in
Figure 17 (e.g., labels A, A', and A" for the first depicted slice).
Therefore, for any slice-specific per-hop behavior at the provider
network edge, the PE needs to determine which label represents which
slice. In the BGP control plane, when exchanging service prefixes
over an AC, each slice might be represented by a unique BGP
community, so tracking label assignment to the slice might be
possible. For example, in Figure 17, for the slice identified with
COM-1, the PE advertises a dynamically allocated label A". Since,
based on the community, the label to slice association is known, the
PE 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
might be with per-prefix granularity. In the 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 17.
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In that case, the route target extended community (Section 4 of
[RFC4360]) might be used as slice differentiator. In other
deployments, all prefixes (representing different slices) might be
handled by a single 'mobile' service instance, and some other BGP
attribute (e.g., a standard community [RFC1997]) might be used for
slice differentiation. There could be also a deployment option 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 provider network is possible.
4.3.3. Option C
Option B relies upon exchanging service prefixes between customer
sites and the provider network. This may lead to scaling challenges
in large scale 5G deployments as the PE node needs to carry all
service prefixes. To alleviate this scaling challenge, in Option C,
service prefixes are exchanged between customer sites only. In doing
so, the provider network is offloaded from carrying, propagating, and
programing appropriate forwarding entries for service prefixes.
Option C relies upon exchanging service prefixes via multi-hop BGP
sessions between customer sites, without changing the NEXT_HOP BGP
attribute. Additionally, IPv4/IPv6 labeled unicast (SAFI-4) host
routes, used as NEXT_HOP for service prefixes, are exchanged via
direct single-hop BGP sessions between adjacent nodes in a customer
site and a provider network, as depicted in Figure 18. As a result,
a node in a customer site performs hierarchical next-hop resolution.
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<-------------------------------------------
BGP VPN
COM=1, L=A, NEXT_HOP=CS2
COM=2, L=B, NEXT_HOP=CS2
COM=3, L=C, NEXT_HOP=CS2
<------------------------------------------>
<------ <------ <------
BGP LU BGP LU BGP LU
CS2, L=X" CS2, L=X' CS2, L=X
<-------------><------------><------------->
nhs nhs nhs nhs
VLANs
service instances service instances representing
representing slices representing slices slices
| | |
+---+ | +--------------+ +|---------|----------+
| | | | Provider | || | |
|+--+-v-+ +-+---+ +--+--+ +-+v----+ v +------+|
|| # | |* | | *| | #<><>x.......x ||
|| NF # +-------+* PE | | PE *+------+ #<><>x.......x NF ||
|| # | AC |* | | *| AC | #<><>x.......x ||
|+---+--+ +-+---+ +---+-+ +-+-----+ +------+|
| CS1| | Network | | L2/L3 CS2 |
+----+ +---------------+ +---------------------+
x Logical interface represented by a VLAN on s physical interface
# Service instances (with unique MPLS label)
* SDP
Figure 18: MPLS Hand-off with Option C
This architecture requires an end-to-end Label Switched Path (LSP)
leading from a packet's ingress node inside one customer site to its
egress inside another customer site, through a provider network.
Hence, at the domain (customer site, provider network) boundaries
NEXT_HOP attribute for IPv4/IPv6 labeled unicast needs to be modified
to "next-hop self" (nhs), which results in new IPv4/IPv6 labeled
unicast label allocation. Appropriate label swap forwarding entries
for IPv4/IPv6 labeled unicast labels are programmed in the data
plane. On the AC there is no additional 'labeled transport' protocol
(i.e., no LDP, RSVP, SR, ...).
Packets are transmitted over the AC with the IPv4/IPv6 labeled
unicast as the top label, with service label deeper in the label
stack. In Option C, the service label is not used for forwarding
lookup on the PE. This significantly lowers the scaling pressure on
PEs, as PEs need to program forwarding entries only for IPv4/IPv6
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labeled unicast host routes, used as NEXT_HOP for service prefixes.
Also, since one IPv4/IPv6 labeled unicast host route represent one
customer site, regardless of the number of slices in the customer
site, the number of forwarding entries on a PE is considerably
reduced.
For any slice-specific per-hop behavior at the provider network edge,
as described in details in Section 3.7, the PE need to determine
which label in the packet represents which slice. This can be
achieved, for example, by allocating non-overlapping service label
ranges for each slice, and use these ranges for slice identification
purposes on PE.
5. QoS Mapping Realization Models
5.1. QoS Layers
The resources are managed via various QoS policies deployed in the
network. QoS mapping models to support 5G slicing connectivity
implemented over packet switched provider network uses two layers of
QoS that are discussed in Section 5.1.
5.1.1. 5G QoS Layer
QoS treatment is indicated in the 5G QoS layer by the 5G QoS
Indicator (5QI), as defined in [TS-23.501]. A 5QI is an identifier
that is used as a reference to 5G QoS characteristics (e.g.,
scheduling weights, admission thresholds, queue management
thresholds, and link layer protocol configuration) in the RAN domain.
Given that 5QI applies to the RAN domain, it is not visible to the
provider network. Therefore, if 5QI-aware treatment is desired in
the provider network as well, 5G network functions might set DSCP
with a value representing 5QI so that differentiated treatment can
implemented in the provider network as well. Based on these DSCP
values, at SDP of each provider network segment used to construct
transport for given 5G slice, very granular QoS enforcement might be
implemented.
The exact mapping between 5QI and DSCP is out of scope for this
document. Mapping recommendations are documented, e.g., in
[I-D.cbs-teas-5qi-to-dscp-mapping].
Each slice service might have flows with multiple 5QIs. 5QIs (or,
more precisely, corresponding DSCP values) are visible to the
provider network at SDPs (i.e., at the edge of the provider network).
In this document, this layer of QoS is referred to as '5G QoS Class'
('5G QoS' in short) or '5G DSCP'.
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5.1.2. TN QoS Layer
Control of the TN resources on provider network transit links, as
well as traffic scheduling/prioritization on provider network transit
links, is based on a flat (non-hierarchical) QoS model in this
Network Slice realization. That is, RFC 9543 Network Slices are
assigned dedicated resources (e.g., QoS queues) at the edge of the
provider network (at SDPs), while all RFC 9543 Network Slices are
sharing resources (sharing QoS queues) on the transit links of the
provider network. Typical router hardware can support up to 8
traffic queues per port, therefore the document assumes 8 traffic
queues per port support in general.
At this layer, QoS treatment is indicated by a QoS indicator specific
to the encapsulation used in the provider network. Such an indicator
may be DSCP or MPLS Traffic Class (TC). This layer of QoS is
referred to as 'TN QoS Class', or 'TN QoS' for short, in this
document.
5.2. QoS Realization Models
While 5QI might be exposed to the provider network 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 provider
network. This might be due to an NF limitation (e.g., 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
(Annex F of [O-RAN.WG9.XPSAAS]).
Therefore, from a QoS perspective, the 5G slicing connectivity
realization defines two high-level realization models for slicing in
the TN domain: a 5QI-unaware model and a 5QI- aware model. Both
slicing models in the TN domain could be used concurrently within the
same 5G slice. For example, the TN segment for 5G midhaul (F1-U
interface) might be 5QI-aware, while at the same time the TN segment
for 5G backhaul (N3 interface) might follow the 5QI-unaware model.
These models are further elaborated in the following two subsections.
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5.2.1. 5QI-unaware Model
In 5QI-unaware mode, the DSCP values in the packets received from NF
at SDP are ignored. In the provider network, there is no QoS
differentiation at the 5G QoS Class level. The entire RFC 9543
Network Slice is mapped to a single TN QoS Class, and, therefore, to
a single QoS queue on the routers in the provider network. 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 in the provider network. However, with
the introduction of private/enterprises slices, as the number of 5G
slices (and thus corresponding RFC 9543 Network Slices) increases, a
single QoS queue on transit links in the provider network serves
multiple slices with similar characteristics. QoS enforcement on
transit links is fully coarse-grained (single NRP, sharing resources
among all RFC 9543 Network Slices), as displayed in Figure 19.
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+------------------------------------------------------------+
+-----------------+ PE |
|+ - - - - - - - +| |
|| SDP || +---------------------------+
|| +----------+ || | Transit link |
|| | NS 1 +------------+ |+------------------------+ |
|| +----------+ || |-----> TN QoS Class 1 | |
|+ - - - - - - - +| | |+------------------------+ |
|+ - - - - - - - +| | |+------------------------+ |
|| SDP || | || TN QoS Class 2 | |
|| +----------+ || | |+------------------------+ |
| | NS 2 +--------+ | |+------------------------+ |
|| +----------+ || | | || TN QoS Class 3 | |
|+ - - - - - - - +| | | |+------------------------+ |
|+ - - - - - - - +| | | |+------------------------+ |
|| SDP || +---------> TN QoS Class 4 | |
|| +----------+ || | |+------------------------+ |
|| | NS 3 +------------+ |+------------------------+ |
|| +----------+ || +---------> TN QoS Class 5 | |
|+ - - - - - - - +| | |+------------------------+ |
|+ - - - - - - - +| | |+------------------------+ |
|| SDP || | || TN QoS Class 6 | |
|| +----------+ || | |+------------------------+ |
|| | NS 4 +--------+ |+------------------------+ |
|| +----------+ || | || TN QoS Class 7 | |
|+ - - - - - - - +| | |+------------------------+ |
|+ - - - - - - - +| | |+------------------------+ |
|| SDP || | || TN QoS Class 8 | |
|| +----------+ || | |+------------------------+ |
|| | NS 5 +--------+ | Max 8 TN Classes |
|| +----------+ || +---------------------------+
|+ - - - - - - - +| |
+-----------------+ |
+------------------------------------------------------------+
Fine-grained QoS enforcement Coarse-grained QoS enforcement
(dedicated resources per (resources shared by multiple
RFC 9543 Network Slice) RFC 9543 Network Slices)
Figure 19: Slice to TN QoS Mapping (5QI-unaware Model)
When the IP traffic is handed over at the SDP from the AC to the
provider network, the PE encapsulates the traffic into MPLS (if MPLS
transport is used in the provider network), or IPv6 - optionally with
some additional headers (if SRv6 transport is used in the provider
network), and sends out the packets on the provider network transit
link.
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The original IP header retains the DCSP marking (which is ignored in
5QI-unaware model), 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 Class of Service (CoS). Based
on TN CoS marking, per-hop behavior for all RFC 9543 Network Slices
is executed on provider network transit links. Provider network
transit routers do not evaluate the original IP header for QoS-
related decisions. This model is outlined in Figure 20 for MPLS
encapsulation, and in Figure 21 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 20: QoS with MPLS Encapsulation
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+--------------+
| IPv6 Header |
| +-------+
| |TN DSCP|
+------+-------+
: Optional :
: IPv6 :
: Headers :
+--------------+ - - - - - - - - +-----+-----+--+
| IP Header | |\ | IP Header |
| +-------+ | \ | +-------+
| |5G DSCP|---------+ \ | |5G DSCP|
+------+-------+ \ +------+-------+
| | \ | |
| | \ | |
| | | |
| Payload | / | Payload |
|(GTP-U/IPsec) | / |(GTP-U/IPsec) |
| | / | |
| |---------+ / | |
| | | / | |
| | |/ | |
+--------------+ - - - - - - - - +--------------+
Figure 21: QoS with IPv6 Encapsulation
From a 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 traffic, as discussed in Section 5.2.1.1.
Provider network edge resources are controlled in a granular, fine-
grained manner, with dedicated resource allocation for each RFC 9543
Network Slice. The resource control/enforcement happens at each SDP
in two directions: inbound and outbound.
5.2.1.1. Inbound Edge Resource Control
The main aspect of inbound provider network edge resource control is
per-slice traffic volume 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 provider network. This,
combined with appropriate network capacity planning/management
(Section 7) is required to ensure proper isolation between slices in
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a scalable manner. As a result, traffic of one slice has no
influence on the traffic of other slices, even if the slice is
misbehaving (e.g., Distributed Denial-of-Service (DDoS) attacks or
node/link failures) 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 5G NSO to an NSC.
Based on these parameters, the provider network's inbound policy can
be implemented using one of following options:
* 1r2c (single-rate two-color) rate limiter
This is the most basic rate limiter, described in Section 2.3 of
[RFC2475]. It meters at the SDP a traffic stream of given slice
and marks its packets as in-profile (below CIR being enforced) or
out-of-profile (above CIR being enforced). In-profile packets are
accepted and forwarded. Out-of profile 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 provider
network. In the second case, while packets above CIR are
forwarded at the SDP, they are subject to being dropped during any
congestion event at any place in the provider network.
* 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
these three categories:
- Green, for traffic under CIR
- Yellow, for traffic between CIR and PIR
- Red, for traffic above PIR
An inbound 2r3c 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)
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devices. 2r3c meters in general give greater flexibility for
provider network edge enforcement regarding accepting the traffic
(green), de- prioritizing and potentially dropping the traffic on
transit during congestion (yellow), or hard dropping the traffic
(red).
Inbound provider network edge enforcement model for 5QI-unaware
model, where all packets belonging to the slice are treated the same
way in the provider network (no 5Q QoS Class differentiation in the
provider) is outlined in Figure 22.
Slice
policer +---------+
| +---|--+ |
| | | |
| | S | |
| | l | |
v | 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 | |
| | |
+---|--+ |
+---------+
Figure 22: Ingress Slice Admission Control (5QI-unware Model)
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5.2.1.2. Outbound Edge Resource Control
While inbound slice admission control at the provider network edge is
mandatory in the architecture described in this document, outbound
provider network edge resource control might not be required in all
use cases. Use cases that specifically call for outbound provider
network edge resource control are:
* Slices use both CIR and PIR parameters, and provider network edge
links (ACs) 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 provider network edge link
(AC) 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
provider network edge links, even if only slice CIR parameters are
used. This again requires fine-grained resource control per slice
in outbound direction at the provider network edge links.
As opposed to inbound provider network 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 23 outlines the outbound provider network edge resource
control model 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, should not exceed the physical capacity of
the AC. Slice requests above this limit should be rejected by the
NSC, unless an already established slice with lower priority, if such
exists, is preempted.
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+---------+ 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 23: Ingress Slice Admission control (5QI-unaware Model)
5.2.2. 5QI-aware Model
In the 5QI-aware model, potentially a large number of 5G QoS Classes,
represented via the DSCP set by NFs (the architecture scales to
thousands of 5G slices) is mapped (multiplexed) to up to 8 TN QoS
Classes used in a provider network transit equipment, as outlined in
Figure 24.
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+------------------------------------------------------------+
+-----------------+ PE |
|+ - - - - - - - +| |
R || SDP || +---------------------------+
F || +----------+ || | Transit link |
C || |5G DSCP A +---------------+ |+------------------------+ |
9 || +----------+ || +--> TN QoS Class 1 | |
5 || +----------+ || | |+------------------------+ |
4 || |5G DSCP B +-----------+ | |+------------------------+ |
3 || +----------+ || | | || TN QoS Class 2 | |
|| +----------+ || | | |+------------------------+ |
N || |5G DSCP C +--------+ | | |+------------------------+ |
S || +----------+ || | | | || TN QoS Class 3 | |
|| +----------+ | | | | |+------------------------+ |
1 || |5G DSCP D +-----+ | | | |+------------------------+ |
|| +----------+ | | | +------> TN QoS Class 4 | |
|+ - - - - - - - +| | | | | |+------------------------+ |
R |+ - - - - - - - +| | | | | |+------------------------+ |
F || +----------+ | | +---------> TN QoS Class 5 | |
C || |5G DSCP A +-----|--|--|---+ |+------------------------+ |
9 || +----------+ || | | | |+------------------------+ |
5 || +----------+ || | | | || TN QoS Class 6 | |
4 || |5G DSCP E +-----|--|--+ |+------------------------+ |
3 || +----------+ || | | |+------------------------+ |
|| +----------+ || | | || TN QoS Class 7 | |
N || |5G DSCP F +-----|--+ |+------------------------+ |
S || +----------+ || | |+------------------------+ |
|| +----------+ || +------------> TN QoS Class 8 | |
2 || |5G DSCP G +-----+ |+------------------------+ |
|| +----------+ || | Max 8 TN Classes |
|| SDP || +---------------------------+
|+ - - - - - - - +| |
+-----------------+ |
+------------------------------------------------------------+
Fine-grained QoS enforcement Coarse-grained QoS enforcement
(dedicated resources per (resources shared by multiple
RFC 9543 Network Slice) RFC 9543 Network Slices)
Figure 24: Slice 5Q QoS to TN QoS Mapping (5QI-aware Model)
Given that in deployments with a 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 slices - would be grouped with common
operator-defined TN logic and mapped to a same TN QoS Class when
transported in the provider network. That is, common Per-hop
Behavior (PHB) [RFC2474] is executed on transit provider network
routers for all packets grouped together. An example of this
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approach is outlined in Figure 25. A provider may decide to
implement Diffserv-Intercon PHBs at the boundaries of its network
domain [RFC8100].
Note: The numbers indicated in Figure 25 (S-NSSAI, 5QI, DSCP, queue,
etc.) are provided for illustration purposes only and should not
be considered as deployment guidance.
+------------- PE -----------------+
+------ NF-A ------+ | |
| | | + - - - - + |
| 3GPP S-NSSAI 100 | | | SDP | |
|.------. .-------.| | |.-------.| |
||5QI=1 +->DSCP=46+------>DSCP=46+---+ |
|'------' '-------'| | |'-------'| | |
|.------. .-------.| | |.-------.| | |
||5QI=65+->DSCP=46+------>DSCP=46+|--+ |
|'------' '-------'| | |'-------'| | |
|.------. .-------.| | |.-------.| | |
||5QI=7 +->DSCP=10+------>DSCP=10------+ .--------------. |
|'------' '-------'| | |'-------'| | | |TN QoS Class 5| |
+------------------+ | +- - - - -+ +-|--> Queue 5 | |
| | | '--------------' |
+------ NF-B ------+ | | | |
| | | + - - - - + | | |
| 3GPP S-NSSAI 200 | | | SDP | | | |
|.------. .-------.| | |.-------.| | | |
||5QI=1 +->DSCP=46+------>DSCP=46+---+ | .--------------. |
|'------' '-------'| | |'-------'| | | |TN QoS Class 1| |
|.------. .-------.| | |.-------.| | +--> Queue 1 | |
||5QI=65+->DSCP=46+------>DSCP=46+|--+ | '--------------' |
|'------' '-------'| | |'-------'| | |
|.------. .-------.| | |.-------.| | |
||5QI=7 +->DSCP=10+------>DSCP=10+-----+ |
|'------' '-------'| | |'-------'| |
+------------------+ | +- - - - -+ |
+------------------------------------+
Figure 25: Example of 3GPP QoS Mapped to TN QoS
In current SDO progress of 3GPP (Release 17) and O-RAN, the mapping
of 5QI to DSCP is not expected to be in a per-slice fashion, where
5QI to DSCP mapping may vary from 3GPP slice to 3GPP slice, hence the
mapping of 5G QoS DSCP values to TN QoS Classes may be rather common.
Like in the 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.
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Based on TN QoS Class marking, per-hop behavior for all aggregated 5G
QoS Classes from all RFC 9543 Network Slices is executed on the
provider network transit links. Provider network transit routers do
not evaluate the 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 the AC.
In the 5QI-aware model, compared to the 5QI-unware model, provider
network edge resources are controlled in an even more granular, fine-
grained manner, with dedicated resource allocation for each RFC 9543
Network Slice and dedicated resource allocation for number of traffic
classes (most commonly up 4 or 8 traffic classes, depending on the
Hardware capability of the equipment) within each RFC 9543 Network
Slice.
5.2.2.1. 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.
A 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 26. 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.
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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 26: 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 26. 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 it is allowed to use the 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 27.
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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 27: Ingress Slice Admission Control (5QI-aware) - Hierarchical
5.2.2.2. Outbound Edge Resource Control
Figure 28 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, which are 5Q QoS
queue CIRs within the slice, should not exceed the CIR of the slice
itself. And, similarly to the 5QI-aware model, the sum of slice CIRs
should not exceed the physical capacity of the AC.
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+---------+ 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 28: Egress Slice Admission Control (5QI-aware)
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5.3. Transit Resource Control
Transit resource control is much simpler than Edge resource control
in the provider network. As outlined in Figure 24, at the provider
network edge, 5Q QoS Class marking (represented by DSCP related to
5QI set by mobile network functions in the packets handed off to the
TN) is mapped to the TN QoS Class. Based on TN QoS Class, when the
packet is encapsulated with outer header (MPLS or IPv6), TN QoS Class
marking (MPLS TC or IPv6 DSCP in outer header, as depicted in Figures
20 and 21) is set in the outer header. PHB in provider network
transit routers is based exclusively on that TN QoS Class marking,
i.e., original 5G QoS Class DSCP is not taken into consideration on
transit.
Provider network 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 traffic that was de-
prioritized by ingress admission control Section 5.2.1.1 or in non-
premium (best-effort) classes. Capacity planning and management, as
described in Section 7, ensures that enough capacity is available to
fulfill all approved slice requests.
6. PE Underlay Transport Mapping Models
The PE underlay transport (underlay transport, for short) refers to a
specific path forwarding behavior between PEs in order to provide
packet delivery that is consistent with the corresponding SLOs. This
realization step focuses on controlling the paths that will be used
for packet delivery between PEs, independent of the underlying
network resource partitioning.
It is worth noting that TN QoS Classes and underlay transport are
each related to different engineering objectives. The TN domain can
be operated with, e.g., 8 TN QoS Classes (representing 8 hardware
queues in the routers), and two underlay transports (e.g., latency
optimized underlay transport using link latency metrics for path
calculation, and underlay transport following Interior Gateway
Protocol (IGP) metrics). TN QoS Class determines the per-hop
behavior when the packets are transiting through the provider
network, while underlay transport determines the paths for packets
through provider network based on the operator's requirements. This
path can be optimized or constrained.
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A network operator can define multiple underlay transports within a
single NRP. An underlay transport may be realized in multiple ways
such as (but not limited to):
* A mesh of RSVP-TE [RFC3209] or SR-TE [RFC9256] tunnels created
with specific optimization criteria and constraints. For example,
mesh "A" might represent tunnels optimized for latency, and mesh
"B" might represent tunnels optimized for high capacity.
* A Flex-Algorithm [RFC9350] with a particular metric-type (e.g.,
latency), or one that only uses links with particular properties
(e.g., MACsec link [IEEE802.1AE]), or excludes links that are
within a particular geography.
These protocols can be controlled, e.g., by tuning the protocol list
under the "underlay-transport" data node defined in the L3VPN Network
Model (L3NM) [RFC9182] and the L2VPN Network Model (L2NM) [RFC9291].
Also, underlay transports may be realized using separate NRPs.
However, such an approach is left out of the scope given the current
state of the technology (2024).
Similar to the QoS mapping models discussed in Section 5, for mapping
to underlay transports at the ingress PE, both 5QI-unaware and 5QI-
aware models are defined. Essentially, entire slices can be mapped
to underlay transports without 5G QoS consideration (5QI-unaware
model). For example, flows with different 5G QoS Classes, even from
same slice, can be mapped to different underlay transports (5QI-aware
model).
Figure 29 depicts an example of a simple network with two underlay
transports, each using a mesh of TE tunnels with or without Path
Computation Element (PCE) [RFC5440], and with or without bandwidth
reservations. Section 7 discusses in detail different bandwidth
models that can be deployed in the provider network. However,
discussion about how to realize or orchestrate underlay transports is
out of scope for this document.
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+---------------+ +------+
| Ingress PE | .------------------------------->| PE-A |
| | | .-------------------------->>| |
| +---------+ | | '---------------------. +------+
| | x------' .---------------------'
| |Underlay x--------------------------------. +------+
| |Transportx-------------. '----->| PE-B |
| | A x-------. | | .---. .---. .---->>| |
| +---------+ | | | | | | | | | +------+
| | | | | | '---' '---'
| +---------+ | | | | | +------+
| | o-------|--' '------------------------>| PE-C |
| |Underlay o-------|--------' .---->>| |
| |Transporto-------|-----------------. | +------+
| | B o-----. '---------------. | |
| +---------+ | | .-. .-. .-. .-. | '------' +------+
| | | | | | | | | | | '-------------->| PE-D |
+---------------+ '-' '-' '-' '-' '--------------->>| |
+------+
x-----> Tunnels of Underlay Transport A
o---->> Tunnels of Underlay Transport B
Figure 29: Example of Underlay Transport Relying on TE Tunnels
For illustration purposes, Figure 29 shows only single tunnels per
underlay transport for (ingress PE, egress PE) pair. However, there
might be multiple tunnels within a single underlay transport between
any pair of PEs.
6.1. 5QI-unaware Model
As discussed in Section 5.2.1, in the 5QI-unware model, the provider
network 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 PE underlay transport mapping model, the
entire slice is mapped to a single underlay transport, as depicted in
Figure 30.
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+-----------------------------------------+
|.. .. .. .. .. .. |
: AC : PE |
:+---------------+: |
:| SDP |: |
:| +----------+ |: |
:| | NS 1 +----------+ |
:| +----------+ |: | |
:+---------------+: | |
:+---------------+: | +---------+ |
:| SDP |: | | | |
:| +----------+ |: | |Underlay | |
:| | NS 2 +------+ +--->Transport| |
:| +----------+ |: | | | A | |
:+---------------+: | | | | |
:+---------------+: | | +---------+ |
:| SDP |: | | |
:| +----------+ |: | | |
:| | NS 3 +-----+ | |
:| +----------+ |: | | +---------+ |
:+---------------+: | | | | |
:+---------------+: | | |Underlay | |
:| SDP |: +------->Transport| |
:| +----------+ |: | | | B | |
:| | NS 4 +------+ | | | |
:| +----------+ |: | +---------+ |
:+---------------+: | |
:+---------------+: | |
:| SDP |: | |
:| +----------+ |: | |
:| | NS 5 +----------+ |
:| +----------+ |: |
:+---------------+: |
'.. .. .. .. .. .. |
+-----------------------------------------+
Figure 30: Network Slice to PEs Underlay Transport Mapping (5QI-
unaware Model)
6.2. 5QI-aware Model
In 5QI-aware model, the traffic can be mapped to underlay transports
at the granularity of 5G QoS Class. Given that the potential number
of underlay transports is limited, packets from multiple 5G QoS
Classes with similar characteristics are mapped to a common underlay
transport, as depicted in Figure 31.
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+-------------------------------------------+
|.. .. .. .. .. .. |
: AC : PE |
:+---------------+: |
R :| SDP |: |
F :| +----------+ |: |
C :| | 5G QoS A +------+ |
9 :| +----------+ |: | |
5 :| +----------+ |: | |
4 :| | 5G QoS B +------+ |
3 :| +----------+ |: | +---------+ |
:| +----------+ |: | | | |
N :| | 5G QoS C +-----------+ |Underlay | |
S :| +----------+ |: +--------->Transport| |
:| +----------+ |: | | | A | |
1 :| | 5G QoS D +-----------+ | | |
:| +----------+ |: | | +---------+ |
:+---------------+: | | |
R :+---------------+: | | |
F :| +----------+ |: | | |
C :| | 5G QoS A +------+ | +---------+ |
9 :| +----------+ |: | | | | |
5 :| +----------+ |: | | |Underlay | |
4 :| | 5G QoS E +------+ +---->Transport| |
3 :| +----------+ |: | | B | |
:| +----------+ |: | | | |
N :| | 5G QoS F +-----------+ +---------+ |
S :| +----------+ |: | |
:| +----------+ |: | |
2 :| | 5G QoS G +-----------+ |
:| +----------+ |: |
:| SDP |: |
:+---------------+: |
'.. .. .. .. .. .. |
+-------------------------------------------+
Figure 31: Network Slice to Underlay Transport Mapping (5QI-aware
Model)
7. Capacity Planning/Management
7.1. Bandwidth Requirements
This section describes the information conveyed by the 5G NSO to the
NSC with respect to slice bandwidth requirements.
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Figure 32 shows three DCs that contain instances of network
functions. Also shown are PEs that have links to the DCs. The PEs
belong to the provider network. Other details of the provider
network, such as P-routers and transit links are not shown. Also
details of the DC infrastructure in customer sites, such as switches
and routers, are not shown.
The 5G NSO is aware of the existence of the network functions and
their locations. However, it is not aware of the details of the
provider network. The NSC has the opposite view - it is aware of the
provider network infrastructure and the links between the PEs and the
DCs, but is not aware of the individual network functions at customer
sites.
+ - - - - DC 1- - - -+ + - - - - - - - - + + - - - - DC 2- - - -+
| +------+ | +----+ +----+ | +------+ |
| | NF1A | +--*PE1A| |PE2A*--+ | NF2A | |
| +------+ | +----+ +----+ | +------+ |
| +------+ | | | | +------+ |
| | NF1B | | | | | | NF2B | |
| +------+ | | | | +------+ |
| +------+ | +----+ +----+ | +------+ |
| | NF1C | +--*PE1B| |PE2B*--+ | NF2C | |
| +------+ | +----+ +----+ | +------+ |
+ - - - - - - - - - -+ | Provider | + - - - - - - - - - -+
| |
| Network | + - - - - DC 3- - - -+
| +----+ | +------+ |
| |PE3A*--+ | NF3A | |
| +----+ | +------+ |
| | | +------+ |
| | | | NF3B | |
| | | +------+ |
| +----+ | +------+ |
| |PE3B*--+ | NF3C | |
| +----+ | +------+ |
+ - - - - - - - - + + - - - - - - - - - -+
* SDP, with fine-grained QoS (dedicated resources per RFC 9543 NS)
Figure 32: An Example of Multi-DC Architecture
Let us consider 5G slice "X" that uses some of the network functions
in the three DCs. If this slice has latency requirements, the 5G NSO
will have taken those into account when deciding which NF instances
in which DC are to be invoked for this slice. As a result of such a
placement decision, the three DCs shown are involved in 5G slice "X",
rather than other DCs. For its decision-making, the 5G NSO needs
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information from the NSC about the observed 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 5G NSO to
inform the NSC which DC-pairs are of interest for these metrics -
there may be of order thousands of DCs, but the 5G NSO 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 provider network. The
mechanism for conveying the information is out of scope for this
document.
Table 1 shows the matrix of bandwidth demands for 5G slice "X".
Within the slice, multiple NF instances might be sending traffic from
DCi to DCj. However, the 5G NSO 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 NFs 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 5, 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.
+=========+======+======+======+===============+
| From/To | 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 |
+---------+------+------+------+---------------+
Table 1: Inter-DC Traffic Demand Matrix
(Slice X)
[I-D.ietf-teas-ietf-network-slice-nbi-yang] can be used to convey all
of the information in the traffic matrix to an NSC. The 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
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PE1B that face DC1, as this is the total bandwidth that DC1 sends
into the provider 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 [RFC9408].
Depending on the bandwidth model used in the provider network
(Section 7.2), the other values in the matrix, i.e., the DC-to-DC
demands, may not be directly applied to the provider network. Even
so, the information may be useful to the NSC for capacity planning
and failure simulation purposes. If, on the other hand, the DC-to-DC
demand information is not used by the 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.
The provider 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-Algorithm, a particular set of TE paths, or a
specific queue [RFC9330]), as discussed in Section 5. The 5G NSO 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 defined in [RFC9182] and [RFC9291].
7.2. Bandwidth Models
This section describes three bandwidth management schemes that could
be employed in the provider 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 [RFC9522].
7.2.1. Scheme 1: Shortest Path Forwarding (SPF)
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.
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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
provider 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 provider network.
A variation on the scheme is that Flex-Algorithm [RFC9350] is used.
For example, one Flex-Algorithm could use latency-based metrics and
another Flex-Algorithm could use the IGP metric. There would be a
many-to-one mapping of Network Slices to Flex-Algorithms.
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 which employ TE, traffic cannot be diverted from the shortest
path.
7.2.2. Scheme 2: TE Paths with Fixed Bandwidth Reservations
Scheme 2 uses RSVP-TE [RFC3209] or SR-TE paths [RFC9256] with fixed
bandwidth reservations. By "fixed", we mean a value that stays
constant over time, unless the 5G NSO communicates a change in slice
bandwidth requirements, due to the creation or modification of a
slice. Note that the "reservations" may be maintained by 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
a path. There could be a single mesh of paths 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 paths.
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The bandwidth requirement from DCi to DCj is the sum of the DCi-DCj
demands of the individual slices. For example, if only slices "X"
and "Y" are present, then the bandwidth requirement from "DC1" to
"DC2" is 12 units (8 units for slice "X" (Table 1) and 4 units for
slice "Y" (Table 2)). When the 5G NSO requests a new slice, the NSC,
increments the bandwidth requirement according to the requirements of
the new slice. For example, in Figure 32, 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.
+=========+======+======+======+===============+
| From/To | 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 |
+---------+------+------+------+---------------+
Table 2: Inter-DC Traffic Demand Matrix
(Slice Y)
In the example, each DC has two PEs facing it for reasons of
resilience. The NSC 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 path 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 path
from "PE1A" to "PE2A" and 6.4 Gbps of bandwidth on the path from
"PE1A" to "PE2B". It might be tricky for the NSC to be aware of all
conditions that change the way traffic lands on the various PEs, and
therefore know that it needs to change bandwidth reservations of
paths accordingly. For example, there might be an internal failure
within "DC1" that causes traffic from "DC1" to land on "PE1B", rather
than "PE1A". The NSC may not be aware of the failure and therefore
may not know that it now needs to apply bandwidth reservations to
paths from "PE1B" to "PE2A" / "PE2B".
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7.2.3. Scheme 3: TE Paths without Bandwidth Reservation
Like Scheme 2, Scheme 3 uses RSVP-TE or SR-TE paths. There could be
a single mesh of paths 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 paths.
The difference between Scheme 2 and Scheme 3 is that Scheme 3 does
not have fixed bandwidth reservations for the paths. Instead, actual
measured data-plane traffic volumes are used to influence the
placement of TE paths. One way of achieving this is to use
distributed RSVP-TE with auto-bandwidth. Alternatively, the NSC 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
path, can tune the paths of one or more paths using the link such
that they avoid that link. This approach is similar to that
described in Section 4.3.1 of [RFC9522].
It would be undesirable to move a path that has latency as its cost
function, rather than another type of path, in order to ease the
congestion, as the altered path will typically have a higher latency.
This can be avoided by designing the algorithms described in the
previous paragraph such that they avoid moving minimum-latency paths
unless there is no alternative.
8. Network Slicing OAM
The deployment and maintenance of slices within a network imply that
a set of OAM functions ([RFC6291]) need to be deployed by the
providers, e.g.:
* Providers should be able to execute OAM tasks on a per Network
Slice basis. These tasks can cover the "full" slice within a
domain or a portion of that slice (for troubleshooting purposes,
for example).
For example, per-slice OAM tasks can consist of (but not limited
to):
- tracing resources that are bound to a given Network Slice,
- tracing resources that are invoked when forwarding a given flow
bound to a given Network Slice,
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- assessing whether flow isolation characteristics are in
conformance with the Network Slice Service requirements, or
- assessing the compliance of the allocated Network Slice
resources against flow/ customer service requirements.
[RFC7276] provides an overview of available OAM tools. These
technology-specific tools can be reused in the context of network
slicing. Providers that deploy network slicing capabilities
should be able to select whatever OAM technology or specific
feature that would address their needs.
* Providers may want to enable differentiated failure detect and
repair features for a subset of network slices. For example, a
given Network Slice may require fast detect and repair mechanisms,
while others may not be engineered with such means. The provider
can use techniques such as [RFC5286], [RFC5714], or [RFC8355].
* Providers may deploy means to dynamically discover the set of
Network Slices that are enabled within its network. Such dynamic
discovery capability facilitates the detection of any mismatch
between the view maintained by the control/management plane and
the actual network configuration. When mismatches are detected,
corrective actions should be undertaken accordingly. For example,
a provider may rely upon the L3NM [RFC9182] or the L2NM [RFC9291]
to maintain the full set of L3VPN/L2VPNs that are used to deliver
Network Slice Services. The correlation between an LxVPN instance
and a Network Slice Service is maintained using "parent-service-
id" attribute (Section 7.3 of [RFC9182]).
* Means to report a set of network performance metrics to assess
whether the agreed slice service objectives are honored. These
means are used for SLO monitoring and violation detect purposes.
For example, [RFC9375] can be used to report links' one-way delay,
one-way delay variation, etc. Both conventional active/passive
measurement methods [RFC7799] and more recent telemetry methods
(e.g., YANG Push [RFC8641]) can be used.
* Means to report and expose observed performance metrics and other
OAM state to customer. For example,
[I-D.ietf-teas-ietf-network-slice-nbi-yang] exposes a set of
statistics per SDP, connectivity construct, and connection group.
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9. Scalability Implications
The mapping between 5G slice to TN slices (see Section 3.5) is a
design choice of service operators that may be a function of, e.g.,
the number of instantiated slices, requested services, or local
engineering capabilities and guidelines. However, operators should
carefully consider means to ease slice migration strategies. For
example, a provider may initially adopt a 1-to-1 mapping if it has to
instantiate just a few Network Slices and accommodate the need of
only a few customers. That provider may decide to move to a N-to-1
mapping for aggregation/scalability purposes if sustained increased
slice demand is observed.
Putting in place adequate automation means to realize Network Slices
(including the adjustment of Slice Services to Network Slices
mapping) would ease slice migration operations.
The realization model described in the document inherits the
scalability properties of the underlying L2VPN and L3VPN technologies
(Section 3.7). Readers may refer, for example, to Section 13 of
[RFC4365] or Section 1.2.5 of [RFC6624] for a scalability assessment
of some of these technologies. Providers may adjust the mapping
model to better handle local scalability constraints.
10. IANA Considerations
This document does not make any IANA request.
11. Security Considerations
Section 10 of [RFC9543] discusses generic security considerations
that are applicable to network slicing, with a focus on the following
considerations:
* Conformance to security constraints:
Specific security requests, such as not routing traffic through a
particular geographical region can be met by mapping the traffic
to an underlay transport that avoids that region.
* IETF NSC authentication:
This is out of the scope for this document. It should be
addressed in documents that describe IETF NSC realization (e.g.,
[I-D.ietf-teas-ns-controller-models]).
* Specific isolation criteria:
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Adequate admission control policies, for example policers as
described in Section 5.2.1.1, should be configured in the edge of
the provider network to control access to specific slice
resources. This prevents the possibility of one slice consuming
resources at the expense of other slices. Likewise, access to
classification and mapping tables have to be controlled to prevent
misbehaviors (an unauthorized entity may modify the table to bind
traffic to a random slice, redirect the traffic, etc.). Network
devices have to check that a required access privilege is provided
before granting access to specific data or performing specific
actions.
* Data Confidentiality and Integrity of an IETF Network Slice:
As described in Section 5.1.2.1 of [RFC9543], the customer might
request an SLE that mandates encryption. As described in
Section 6, this can be achieved, e.g., by mapping the traffic to
an underlay transport that uses only MACsec-encrypted links.
Many of the YANG modules cited in this document define schema for
data that is designed to be accessed via network management protocols
such as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF
layer is the secure transport layer, and the mandatory-to-implement
secure transport is Secure Shell (SSH) [RFC6242]. The lowest
RESTCONF layer is HTTPS, and the mandatory-to-implement secure
transport is TLS [RFC8446].
The NETCONF access control model [RFC8341] provides the means to
restrict access for particular NETCONF or RESTCONF users to a
preconfigured subset of all available NETCONF or RESTCONF protocol
operations and content.
In order to avoid the need for a mapping table to associate source/
destination IP addresses and slices' specific S-NSSAIs, Section 4.2
describes an approach where some or all S-NSSAI bits are embedded in
an IPv6 address using an algorithm approach. An attacker from within
the transport network who has access to the mapping configuration may
infer the slices to which belong a packet. It may also alter these
bits which may lead to steering the packet via a distinct network
slice, and thus lead to service disruption. Note that such an on-
path attacker may make more damage (e.g., randomly drop packets).
Security considerations specific to each of the technologies and
protocols listed in the document are discussed in the specification
documents of each of these protocols.
12. References
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12.1. Normative References
[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/rfc/rfc4364>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/rfc/rfc6241>.
[RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure
Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
<https://www.rfc-editor.org/rfc/rfc6242>.
[RFC7608] Boucadair, M., Petrescu, A., and F. Baker, "IPv6 Prefix
Length Recommendation for Forwarding", BCP 198, RFC 7608,
DOI 10.17487/RFC7608, July 2015,
<https://www.rfc-editor.org/rfc/rfc7608>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/rfc/rfc8040>.
[RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration
Access Control Model", STD 91, RFC 8341,
DOI 10.17487/RFC8341, March 2018,
<https://www.rfc-editor.org/rfc/rfc8341>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>.
[RFC9543] Farrel, A., Ed., Drake, J., Ed., Rokui, R., Homma, S.,
Makhijani, K., Contreras, L., and J. Tantsura, "A
Framework for Network Slices in Networks Built from IETF
Technologies", RFC 9543, DOI 10.17487/RFC9543, March 2024,
<https://www.rfc-editor.org/rfc/rfc9543>.
12.2. Informative References
[ECPRI] Common Public Radio Interface, "Common Public Radio
Interface: eCPRI Interface Specification", n.d.,
<http://www.cpri.info/downloads/
eCPRI_v_2.0_2019_05_10c.pdf>.
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[I-D.cbs-teas-5qi-to-dscp-mapping]
Contreras, L. M., Bykov, I., and K. G. Szarkowicz, "5QI to
DiffServ DSCP Mapping Example for Enforcement of 5G End-
to-End Network Slice QoS", Work in Progress, Internet-
Draft, draft-cbs-teas-5qi-to-dscp-mapping-02, 8 July 2024,
<https://datatracker.ietf.org/doc/html/draft-cbs-teas-5qi-
to-dscp-mapping-02>.
[I-D.ietf-opsawg-ntw-attachment-circuit]
Boucadair, M., Roberts, R., de Dios, O. G., Barguil, S.,
and B. Wu, "A Network YANG Data Model for Attachment
Circuits", Work in Progress, Internet-Draft, draft-ietf-
opsawg-ntw-attachment-circuit-13, 5 September 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-opsawg-
ntw-attachment-circuit-13>.
[I-D.ietf-opsawg-teas-attachment-circuit]
Boucadair, M., Roberts, R., de Dios, O. G., Barguil, S.,
and B. Wu, "YANG Data Models for Bearers and 'Attachment
Circuits'-as-a-Service (ACaaS)", Work in Progress,
Internet-Draft, draft-ietf-opsawg-teas-attachment-circuit-
15, 9 August 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-opsawg-teas-attachment-circuit-15>.
[I-D.ietf-teas-5g-network-slice-application]
Geng, X., Contreras, L. M., Rokui, R., Dong, J., and I.
Bykov, "IETF Network Slice Application in 3GPP 5G End-to-
End Network Slice", Work in Progress, Internet-Draft,
draft-ietf-teas-5g-network-slice-application-03, 10 June
2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
teas-5g-network-slice-application-03>.
[I-D.ietf-teas-ietf-network-slice-nbi-yang]
Wu, B., Dhody, D., Rokui, R., Saad, T., and J. Mullooly,
"A YANG Data Model for the RFC 9543 Network Slice
Service", Work in Progress, Internet-Draft, draft-ietf-
teas-ietf-network-slice-nbi-yang-16, 28 August 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-
ietf-network-slice-nbi-yang-16>.
[I-D.ietf-teas-ns-controller-models]
Contreras, L. M., Rokui, R., Tantsura, J., Wu, B., Liu,
X., Dhody, D., and S. Belotti, "IETF Network Slice
Controller and its associated data models", Work in
Progress, Internet-Draft, draft-ietf-teas-ns-controller-
models-02, 8 July 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-ns-
controller-models-02>.
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[IEEE802.1AE]
IEEE, "802.1AE: MAC Security (MACsec)", n.d.,
<https://1.ieee802.org/security/802-1ae/>.
[NG.113] GSMA, "NG.113: 5GS Roaming Guidelines Version 4.0", May
2021, <https://www.gsma.com/newsroom/wp-content/
uploads//NG.113-v4.0.pdf>.
[O-RAN.WG9.XPSAAS]
O-RAN Alliance, "O-RAN.WG9.XPSAAS: O-RAN WG9 Xhaul Packet
Switched Architectures and Solutions Version 04.00", March
2023, <https://www.o-ran.org/specifications>.
[RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities
Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,
<https://www.rfc-editor.org/rfc/rfc1997>.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/rfc/rfc2474>.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
<https://www.rfc-editor.org/rfc/rfc2475>.
[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/rfc/rfc2698>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/rfc/rfc3209>.
[RFC4026] Andersson, L. and T. Madsen, "Provider Provisioned Virtual
Private Network (VPN) Terminology", RFC 4026,
DOI 10.17487/RFC4026, March 2005,
<https://www.rfc-editor.org/rfc/rfc4026>.
[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/rfc/rfc4115>.
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[RFC4176] El Mghazli, Y., Ed., Nadeau, T., Boucadair, M., Chan, K.,
and A. Gonguet, "Framework for Layer 3 Virtual Private
Networks (L3VPN) Operations and Management", RFC 4176,
DOI 10.17487/RFC4176, October 2005,
<https://www.rfc-editor.org/rfc/rfc4176>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <https://www.rfc-editor.org/rfc/rfc4360>.
[RFC4365] Rosen, E., "Applicability Statement for BGP/MPLS IP
Virtual Private Networks (VPNs)", RFC 4365,
DOI 10.17487/RFC4365, February 2006,
<https://www.rfc-editor.org/rfc/rfc4365>.
[RFC4664] Andersson, L., Ed. and E. Rosen, Ed., "Framework for Layer
2 Virtual Private Networks (L2VPNs)", RFC 4664,
DOI 10.17487/RFC4664, September 2006,
<https://www.rfc-editor.org/rfc/rfc4664>.
[RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
IP Fast Reroute: Loop-Free Alternates", RFC 5286,
DOI 10.17487/RFC5286, September 2008,
<https://www.rfc-editor.org/rfc/rfc5286>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/rfc/rfc5440>.
[RFC5714] Shand, M. and S. Bryant, "IP Fast Reroute Framework",
RFC 5714, DOI 10.17487/RFC5714, January 2010,
<https://www.rfc-editor.org/rfc/rfc5714>.
[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation", RFC 5952,
DOI 10.17487/RFC5952, August 2010,
<https://www.rfc-editor.org/rfc/rfc5952>.
[RFC6136] Sajassi, A., Ed. and D. Mohan, Ed., "Layer 2 Virtual
Private Network (L2VPN) Operations, Administration, and
Maintenance (OAM) Requirements and Framework", RFC 6136,
DOI 10.17487/RFC6136, March 2011,
<https://www.rfc-editor.org/rfc/rfc6136>.
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[RFC6291] Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
D., and S. Mansfield, "Guidelines for the Use of the "OAM"
Acronym in the IETF", BCP 161, RFC 6291,
DOI 10.17487/RFC6291, June 2011,
<https://www.rfc-editor.org/rfc/rfc6291>.
[RFC6624] Kompella, K., Kothari, B., and R. Cherukuri, "Layer 2
Virtual Private Networks Using BGP for Auto-Discovery and
Signaling", RFC 6624, DOI 10.17487/RFC6624, May 2012,
<https://www.rfc-editor.org/rfc/rfc6624>.
[RFC7276] Mizrahi, T., Sprecher, N., Bellagamba, E., and Y.
Weingarten, "An Overview of Operations, Administration,
and Maintenance (OAM) Tools", RFC 7276,
DOI 10.17487/RFC7276, June 2014,
<https://www.rfc-editor.org/rfc/rfc7276>.
[RFC7422] Donley, C., Grundemann, C., Sarawat, V., Sundaresan, K.,
and O. Vautrin, "Deterministic Address Mapping to Reduce
Logging in Carrier-Grade NAT Deployments", RFC 7422,
DOI 10.17487/RFC7422, December 2014,
<https://www.rfc-editor.org/rfc/rfc7422>.
[RFC7510] Xu, X., Sheth, N., Yong, L., Callon, R., and D. Black,
"Encapsulating MPLS in UDP", RFC 7510,
DOI 10.17487/RFC7510, April 2015,
<https://www.rfc-editor.org/rfc/rfc7510>.
[RFC7799] Morton, A., "Active and Passive Metrics and Methods (with
Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
May 2016, <https://www.rfc-editor.org/rfc/rfc7799>.
[RFC7806] Baker, F. and R. Pan, "On Queuing, Marking, and Dropping",
RFC 7806, DOI 10.17487/RFC7806, April 2016,
<https://www.rfc-editor.org/rfc/rfc7806>.
[RFC8100] Geib, R., Ed. and D. Black, "Diffserv-Interconnection
Classes and Practice", RFC 8100, DOI 10.17487/RFC8100,
March 2017, <https://www.rfc-editor.org/rfc/rfc8100>.
[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/rfc/rfc8299>.
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[RFC8355] Filsfils, C., Ed., Previdi, S., Ed., Decraene, B., and R.
Shakir, "Resiliency Use Cases in Source Packet Routing in
Networking (SPRING) Networks", RFC 8355,
DOI 10.17487/RFC8355, March 2018,
<https://www.rfc-editor.org/rfc/rfc8355>.
[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/rfc/rfc8466>.
[RFC8641] Clemm, A. and E. Voit, "Subscription to YANG Notifications
for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641,
September 2019, <https://www.rfc-editor.org/rfc/rfc8641>.
[RFC8969] Wu, Q., Ed., Boucadair, M., Ed., Lopez, D., Xie, C., and
L. Geng, "A Framework for Automating Service and Network
Management with YANG", RFC 8969, DOI 10.17487/RFC8969,
January 2021, <https://www.rfc-editor.org/rfc/rfc8969>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/rfc/rfc8986>.
[RFC9099] Vyncke, É., Chittimaneni, K., Kaeo, M., and E. Rey,
"Operational Security Considerations for IPv6 Networks",
RFC 9099, DOI 10.17487/RFC9099, August 2021,
<https://www.rfc-editor.org/rfc/rfc9099>.
[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/rfc/rfc9182>.
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/rfc/rfc9256>.
[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/rfc/rfc9291>.
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[RFC9330] Briscoe, B., Ed., De Schepper, K., Bagnulo, M., and G.
White, "Low Latency, Low Loss, and Scalable Throughput
(L4S) Internet Service: Architecture", RFC 9330,
DOI 10.17487/RFC9330, January 2023,
<https://www.rfc-editor.org/rfc/rfc9330>.
[RFC9350] Psenak, P., Ed., Hegde, S., Filsfils, C., Talaulikar, K.,
and A. Gulko, "IGP Flexible Algorithm", RFC 9350,
DOI 10.17487/RFC9350, February 2023,
<https://www.rfc-editor.org/rfc/rfc9350>.
[RFC9375] Wu, B., Ed., Wu, Q., Ed., Boucadair, M., Ed., Gonzalez de
Dios, O., and B. Wen, "A YANG Data Model for Network and
VPN Service Performance Monitoring", RFC 9375,
DOI 10.17487/RFC9375, April 2023,
<https://www.rfc-editor.org/rfc/rfc9375>.
[RFC9408] Boucadair, M., Ed., Gonzalez de Dios, O., Barguil, S., Wu,
Q., and V. Lopez, "A YANG Network Data Model for Service
Attachment Points (SAPs)", RFC 9408, DOI 10.17487/RFC9408,
June 2023, <https://www.rfc-editor.org/rfc/rfc9408>.
[RFC9522] Farrel, A., Ed., "Overview and Principles of Internet
Traffic Engineering", RFC 9522, DOI 10.17487/RFC9522,
January 2024, <https://www.rfc-editor.org/rfc/rfc9522>.
[TR-GSTR-TN5G]
ITU-T, "Technical Report GSTR-TN5G", 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)", 2023,
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId-3273>.
[_5G-Book] Peterson, L., Sunay, O., and B. Davie, "5G Mobile
Networks: A Systems Approach", 2022,
<https://5g.systemsapproach.org/>.
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Appendix A. Acronyms and Abbreviations
3GPP: 3rd Generation Partnership Project
5GC: 5G Core
5QI: 5G QoS Indicator
A2A: Any-to-Any
AC: Attachment Circuit
CE: Customer Edge
CIR: Committed Information Rate
CN: Core Network
CoS: Class of Service
CP: Control Plane
CU: Centralized Unit
CU-CP: Centralized Unit Control Plane
CU-UP: Centralized Unit User Plane
DC: Data Center
DDoS: Distributed Denial of Services
DSCP: Differentiated Services Code Point
eCPRI: enhanced Common Public Radio Interface
FIB: Forwarding Information Base
GPRS: Generic Packet Radio Service
gNB: gNodeB
GTP: GPRS Tunneling Protocol
GTP-U: GPRS Tunneling Protocol User plane
IGP: Interior Gateway Protocol
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L2VPN: Layer 2 Virtual Private Network
L3VPN: Layer 3 Virtual Private Network
LSP: Label Switched Path
MIoT: Massive Internet of Things
MPLS: Multiprotocol Label Switching
NF: Network Function
NRP: Network Resource Partition
NSC: Network Slice Controller
PE: Provider Edge
PIR: Peak Information Rate
QoS: Quality of Service
RAN: Radio Access Network
RIB: Routing Information Base
RSVP: Resource Reservation Protocol
SD: Slice Differentiator
SDP: Service Demarcation Point
SLA: Service Level Agreement
SLO: Service Level Objective
S-NSSAI: Single Network Slice Selection Assistance Information
SST: Slice/Service Type
SR: Segment Routing
SRv6: Segment Routing version 6
TC: Traffic Class
TE: Traffic Engineering
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TN: Transport Network
UE: User Equipment
UP: User Plane
UPF: User Plane Function
URLLC: Ultra Reliable Low Latency Communication
VLAN: Virtual Local Area Network
VPN: Virtual Private Network
VRF: Virtual Routing and Forwarding
VXLAN: Virtual Extensible Local Area Network
Acknowledgments
The authors would like to thank Adrian Farrel, Joel Halpern, Tarek
Saad, Greg Mirsky, Rüdiger Geib, Nicklous D. Morris, Daniele
Ceccarelli, Bo Wu, Xuesong Geng, and Deborah Brungard for their
review of this document and for providing valuable comments.
Special thanks to Jie Dong and Adrian Farrel for the detailed and
careful reviews.
Thanks to Alvaro Retana for the rtg-dir review, Yoshifumi Nishida for
the tsv-art review, and Timothy Winters for the int-dir review.
Contributors
John Drake
Sunnyvale,
United States of America
Email: je_drake@yahoo.com
Ivan Bykov
Ribbon Communications
Tel Aviv
Israel
Email: ivan.bykov@rbbn.com
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Reza Rokui
Ciena
Ottawa
Canada
Email: rrokui@ciena.com
Luay Jalil
Verizon
Dallas, TX,
United States of America
Email: luay.jalil@verizon.com
Beny Dwi Setyawan
XL Axiata
Jakarta
Indonesia
Email: benyds@xl.co.id
Amit Dhamija
Rakuten
Bangalore
India
Email: amitd@arrcus.com
Mojdeh Amani
British Telecom
London
United Kingdom
Email: mojdeh.amani@bt.com
Authors' Addresses
Krzysztof G. Szarkowicz (editor)
Juniper Networks
Wien
Austria
Email: kszarkowicz@juniper.net
Richard Roberts (editor)
Juniper Networks
Rennes
France
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Email: rroberts@juniper.net
Julian Lucek
Juniper Networks
London
United Kingdom
Email: jlucek@juniper.net
Mohamed Boucadair (editor)
Orange
France
Email: mohamed.boucadair@orange.com
Luis M. Contreras
Telefonica
Ronda de la Comunicacion, s/n
Madrid
Spain
Email: luismiguel.contrerasmurillo@telefonica.com
URI: http://lmcontreras.com/
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