Internet Engineering Task Force (IETF) K. Szarkowicz, Ed.
Request for Comments: 9889 HPE
Category: Informational R. Roberts, Ed.
ISSN: 2070-1721 Nokia
J. Lucek
Juniper Networks
HPE
M. Boucadair, Ed.
Orange
L.
LM. Contreras
Telefonica
October 2025
A Realization of Network Slices for 5G Networks Using Current IP/MPLS
Technologies
Abstract
Network 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 the service
objectives for 5G slicing connectivity. The realization model reuses
many building blocks commonly used in service provider networks at
the current time.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are candidates for any level of Internet
Standard; see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9889.
Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
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in the Revised BSD License.
Table of Contents
1. Introduction
2. Terminology
2.1. Definitions
2.2. Abbreviations
3. 5G Network Slicing Integration in Transport Networks
3.1. Scope of the Transport Network
3.2. 5G Network Slicing Versus Transport Network Slicing
3.3. Transport Network Reference Design
3.4. Orchestration Overview
3.5. Mapping 5G Network Slices to Transport Network Slices
3.6. First 5G Network Slice Versus Subsequent Slices
3.7. Overview of the Transport Network Realization Model
4. Handoff Between Domains
4.1. VLAN Handoff
4.2. IP Handoff
4.3. MPLS Label Handoff
5. QoS Mapping Realization Models
5.1. QoS Layers
5.2. QoS Realization Models
5.3. Transit Resource Control
6. PE Underlay Transport Mapping Models
6.1. 5QI-Unaware Model
6.2. 5QI-Aware Model
7. Capacity Planning/Management
7.1. Bandwidth Requirements
7.2. Bandwidth Models
8. Network Slicing OAM
9. Scalability Implications
10. IANA Considerations
11. Security Considerations
12. References
12.1. Normative References
12.2. Informative References
Appendix A. Example of Local IPv6 Addressing Plan for Network
Functions
Acknowledgments
Contributors
Authors' Addresses
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 (at the time of publication of this document) to
optimally control connectivity Service Level Agreements (SLAs)
offered for 5G Network 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).
The realization of an RFC 9543 Network Slice (i.e., connectivity with
performance commitments) involves the provider network and partially
the AC (the Provider Edge (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).
|------------------TN Slice------------------|
|------------Transport Network 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 and RFC 9543 Network Slice Scopes
This document focuses on RFC 9543 Network Slice deployments where the
Service Demarcation Points (SDPs) are located per Types 3 and 4 in
Figure 1 of [RFC9543].
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 RFC 9543 Network Slice Service (e.g.,
mapping of service parameters) are discussed in documents such as
[NS-APP].
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 Network Slices to the transport
domain by mapping to explicit data plane identifiers (e.g., Layer 2,
Layer 3, or Layer 4). Passing information between customer sites and
provider networks is referred to as the "handoff". Section 4 lists a
set of handoff methods for slice mapping purposes.
Unlike approaches that require new protocol extensions (e.g.,
[NS-IP-MPLS]), the realization model described in this document uses
a set of building blocks commonly used in service provider networks
(at the time of publication of this document). The model uses (1)
L2VPN [RFC4664] and/or L3VPN [RFC4364] service instances for logical
separation, (2) fine-grained resource control at the PEs, (3) coarse-
grained resource control within the provider network, and (4)
capacity planning and management. More details are provided in
Sections 3.7, 5, 6, and 7.
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 techniques that are readily available and widely
deployed. 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
[Book-5G].
2. Terminology
2.1. Definitions
The document uses the terms defined in [RFC9543]. Specifically, the
use of "Customer" is consistent with [RFC9543] but with the following
contextualization (see also Section 3.3):
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.
This document makes use of the following terms:
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. A provider is
responsible for interconnecting customer sites.
Examples of customer sites are a customer private locations (e.g.,
Point of Presence (PoP) and Data Center (DC)), a Virtual Private
Cloud (VPC), or servers hosted within the provider network or
colocation service.
Resource Control: In the context of this document, resource control
is used mainly to refer to buffer management and relevant Quality
of Service (QoS) functions.
"5G Network Slicing" and "5G Network Slice": Refer to "Network
Slicing" and "Network Slice" as defined in [TS-28.530].
2.2. Abbreviations
3GPP: 3rd Generation Partnership Project
5GC: 5G Core
5QI: 5G QoS Indicator
A2A: Any-to-Any
AC: Attachment Circuit
AMF: Access and Mobility Management Function
CE: Customer Edge
CIR: Committed Information Rate
CS: Customer Site
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 Service
DM: Data Model
DSCP: Differentiated Services Code Point
eCPRI: enhanced Common Public Radio Interface
FIB: Forwarding Information Base
GPRS: General Packet Radio Service
gNB: gNodeB
GTP: GPRS Tunneling Protocol
GTP-U: GPRS Tunneling Protocol User Plane
IGP: Interior Gateway Protocol
L2VPN: Layer 2 Virtual Private Network
L3VPN: Layer 3 Virtual Private Network
LSP: Label Switched Path
MACsec: Media Access Control Security
MIoT: Massive Internet of Things
MNO: Mobile Network Operator
MPLS: Multiprotocol Label Switching
NF: Network Function
NS: Network Slice
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
TN: Transport Network
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
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 in Section 1 of [TS-28.530]:
| part supporting connectivity within and between CN and RAN parts.
The 3GPP management system does not directly control the Transport
Network; it is considered a non-3GPP managed system. This is
discussed in Section 4.4.1 of [TS-28.530]:
| 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.
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.
+----------------------------------+
+----+ 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: 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
In [TS-28.530], the 3GPP defines 5G Network Slicing 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 CN domains together with
the underlying infrastructure.
Section 3.1 of [TS-28.530] defines a 5G Network Slice as:
| 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 "Transport Network Slice" refers to a slice in the Transport
Network domain of the 5G architecture. This section elaborates on
how Transport Network Slicing is defined in the context of this
document. It draws on the 3GPP definitions of "Transport Network"
and "Network Slicing" in [TS-28.530].
The objective of Transport Network Slicing is to isolate, guarantee,
or prioritize Transport Network resources for Slice Services.
Examples of such resources include 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 (Section 8 of [RFC9543]). 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 Transport Network Slices
based upon mechanisms such as Virtual Routing and Forwarding (VRF)
instances for logical separation, 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
modeling the Transport Network based on management perimeters
(customer vs. provider).
Customer Provider Customer
Orchestration Orchestration Orchestration
Domain Domain Domain
+----------------+ +---------------------+ +----------------+
| Customer | | Provider Network | | Customer |
| Site 1 | | | | Site 2 |
| +----+ | | +----+ +----+ | | +----+ |
| +--+ | | | AC | | | | | | AC | | | |
| |NF|....| CE +----------+ PE | | PE +-----------+ NF | |
| +--+ | | | | | | | | | | | | |
| +----+ | | +----+ +----+ | | +----+ |
| | | | | (CE) |
+----------------+ +---------------------+ +----------------+
<-----------------Transport Network--------------->
Figure 3: Reference Design with Customer Sites and Provider Network
The description of the main components shown in Figure 3 is provided
in the following subsections.
3.3.1. Customer Site (CS)
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 located
multiple IP hops from a CE.
In some contexts, the connectivity between NFs that belong to the
same site can be achieved via the provider network.
The orchestration of the TN within a customer site involves a set of
controllers for automation purposes (e.g., Network Function
Virtualization Infrastructure (NFVI), Container Network Interface
(CNI), Fabric Managers, or Public Cloud APIs). Documenting how these
controllers are implemented is out of scope for this document.
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
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 an L3VPN service based on a
distributed CE composed of a switch (SW) in Layer 2 and a router
(RTR) in Layer 3, as shown in 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
In most cases, CEs connect to PEs using IP (e.g., via Layer 3 VLAN
subinterfaces), but 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]. Thus, the CE has
awareness of provider service 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.
3.3.4. Provider Edge (PE)
A 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., the
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 that are
both managed by the provider (example (i) in Figure 5). The managed
CE can also be a Data Center Gateway as depicted in 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
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 the customer and provider orchestration domains,
respectively, while an AC interconnects these domains.
For consistency with the terminology used in AC data models (e.g.,
the data models defined in [RFC9834] and [RFC9835]), 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 VLAN ACs
configured on a physical interface (bearer) or Overlay VXLAN EVI ACs
configured on an IP underlay (bearer).
Deployment cases where the AC is also managed by the provider are not
discussed in this document because the setup of such an AC does not
require any coordination between the customer and provider
orchestration domains.
| Note: 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.
This framework is consistent with the management coordination example
shown in Figure 4.7.1 of [TS-28.530].
In 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 subdomains in conformance
with the reference design in Section 3.3:
Provider Network Orchestration Domain (simply referred to as
"Provider 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 allows for managing connectivity with SLOs.
Customer Site Orchestration Domain (simply referred to as
"Customer 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 Transport Network Slice relies upon resources that can involve both
the provider and customer TN domains. More details are provided in
Section 3.4.2.
A Transport Network Slice might be considered as a variant of
horizontal composition of network slices mentioned in Appendix A.6 of
[RFC9543].
.---------.
| 5G NSO |
'-+---+---'
| |
v |
.-------------. |
| 3GPP domains | |
.----------+ Orchestration +-)---------------------------.
| | (RAN and CN) | | |
| '-------------' | |
| v |
| .-----------------------------------------------. |
| | TN Transport Network 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-------------------|
|-------------Transport Network Slice-----------|
Figure 6: 5G End-to-End Slice Orchestration with TN
The various orchestrations depicted in Figure 6 encompass the 3GPP's
Network Slice Subnet Management Function (NSSMF) mentioned, for
instance, in Figure 5 of [NS-APP].
3.4.2. Transport Network Segments and Network Slice Instantiation
The concept of distributed PE (Section 3.3.4) assimilates the CE-
based SDPs defined in Section 5.2 of [RFC9543] (i.e., Types 1 and 2)
as SDP Types 3 or 4 in this document.
In the architecture depicted in Section 3.4.1, the connectivity
between NFs can be decomposed into three main segment types:
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., NF 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 Number (ASN),
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 an RFC 9543 Network Slice may rely on new or
existing ACs.
Figure 7 is a basic example of a Layer 3 CE-PE link realization
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) [NSSM] or Attachment
Circuits as a Service (ACaaS) [RFC9834].
.-------------. .----------------.
| | | RFC 9543 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 AC
Provisioning
3.5. Mapping 5G Network Slices to Transport Network Slices
There are multiple options for mapping 5G Network Slices to Transport
Network Slices:
1-to-N mapping: A single 5G Network Slice can be mapped to multiple
Transport Network Slices. For instance, consider the scenario
depicted in Figure 8, which illustrates the separation of the 5G
control plane and user plane in Transport Network 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 mapping: Multiple 5G Network Slices may rely upon the same
Transport Network 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 illustrated in Figure 9,
where a User Plane Function (UPF) UPF for the Ultra-Reliable Low-
Latency Low-Latency Communication
(URLLC) slice is instantiated at the edge cloud, close to the gNB
CU-UP, to improve latency and jitter control. The 5G control
plane and the UPF for the eMBB slice are instantiated in the
regional cloud.
M-to-N mapping: The mapping of 5G to Transport Network Slice
combines both approaches with a mix of shared and dedicated
associations.
In this scenario, a subset of the Transport Network Slices can be
intended for sharing by multiple 5G Network Slices (e.g., the
control plane Transport Network Slice is shared by multiple 5G
Network Slices).
In practice, for operational and scaling reasons, M-to-N mapping
would typically be used, with M much greater than N.
+---------------------------------------------------------------+
| 5G Network Slice eMBB |
| +------------------------------------+ |
| +-----+ N3 | +--------------------------------+ | N3 +-----+ |
| |CU-UP+------+ TN |CU-UP+------+Transport Network Slice UP_eMBB +-------+ UPF | |
| +-----+ | +--------------------------------+ | +-----+ |
| | | |
| +-----+ N2 | +--------------------------------+ | N2 +-----+ |
| |CU-CP+------+ TN Transport Network Slice CP +-------+ AMF | |
| +-----+ | +--------------------------------+ | +-----+ |
+------------|------------------------------------|-------------+
| |
| Transport Network |
+------------------------------------+
Figure 8: 1-to-N Mapping (Single 5G Network Slice to Multiple
Transport Network Slices)
+-------------+
| Edge Cloud |
| +---------+ |
| |UPF_URLLC| |
| +-----+---+ |
| | |
+-------|-----+
|
+---------------+ +-------|----------------------+
| | | | |
| Cell Site | | +-----+--------------------+ | +--------------+
| | | | | | | Regional |
| +-----------+ | | | | | | Cloud |
| |CU-UP_URLLC+-----+ Transport Network | | | +----------+ |
| +-----------+ | | | TN Slice ALL +-----+ 5GC CP | |
| | | | | | | +----------+ |
| +-----------+ | | | | | | |
| |CU-UP_eMBB +-----+ | | | +----------+ |
| +-----------+ | | | +-----+ UPF_eMBB | |
+---------------+ | | | | | +----------+ |
| +--------------------------+ | | |
| | +--------------+
| Transport Network |
+------------------------------+
Figure 9: M-to-1 Mapping (Multiple 5G Network Slices to Single
Transport Network Slice)
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 Network Slice identification
in the TN (e.g., the approach in Section 4.2) may simplify required
operations to map Transport Network Slices back to 5G Network Slices.
However, such considerations are not detailed in this document
because these are under the responsibility of the 3GPP orchestration.
3.6. First 5G Network Slice Versus Subsequent Slices
An operational 5G Network Slice incorporates both 5G control plane
and user plane capabilities. For instance, in some deployments, in
the case of a slice based on split CU in the RAN, both CU-UP and CU-
CP may 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 Network Slice relies on
the deployment of NF-CP and NF-UP functions together with two
Transport Network Slices for the control and user planes (TNS-CP and
TNS-UP1). Next, in many cases, the deployment of a second slice
relies solely on the instantiation of a UPF (NF-UP2) together with a
dedicated Transport Network Slice for the user plane (TNS-UP2). The
control plane of the first 5G Network Slice is also updated to
integrate the second slice; the Transport Network Slice (TNS-CP) and
Network Functions (NF-CP) are shared.
The model described here, in which the control plane is shared among
multiple slices, is likely to be common; it is not mandatory, though.
Deployment models with a separate control plane for each slice are
also possible.
Section 6.1.2 of [NG.113] specifies that the eMBB slice (SST-1 (SST=1 and no
Slice Differentiator (SD)) should be supported globally. This 5G
Network Slice would be the first slice in any 5G deployment.
(1) Deployment of first 5G slice Network Slice
+---------------------------------------------------------------+
| First 5G Network Slice |
| |
| +------------------------------+ |
| +-----+ | +--------------------------+ | +-----+ |
| |NF-CP+------+ CP TN Slice (TNS-CP) TNS-CP +------+NF-CP| |
| +-----+ | +--------------------------+ | +-----+ |
| | | |
| +-----+ | +--------------------------+ | +-----+ |
| |NF-UP+------+ UP TN Slice (TNS-UP1) TNS-UP1 +------+NF-UP| |
| +-----+ | +--------------------------+ | +-----+ |
+----------------|------------------------------|---------------+
| |
| Transport Network |
+------------------------------+
(2) Deployment of additional 5G slice Network Slice with shared control plane Control
Plane
+---------------------------------------------------------------+
| First 5G Network Slice |
| |
| +------------------------------+ |
| +-----+ | +--------------------------+ | +-----+ |
| |NF-CP+------+ CP TN Slice (TNS-CP) TNS-CP +------+NF-CP| |
| +-----+ | +--------------------------+ | +-----+ |
| SHARED | (SHARED) | SHARED |
| | | |
| +-----+ | +--------------------------+ | +-----+ |
| |NF-UP+------+ UP TN Slice (TNS-UP1) TNS-UP1 +------+NF-UP| |
| +-----+ | +--------------------------+ | +-----+ |
+----------------|------------------------------|---------------+
| |
| Transport Network |
| |
+----------------|------------------------------|---------------+
| | | |
| +------+ | +--------------------------+ | +------+ |
| |NF-UP2+-----+ UP TN Slice (TNS-UP2) TNS-UP2 +-----+NF-UP2| |
| +------+ | +--------------------------+ | +------+ |
| | | |
| +------------------------------+ |
| |
| Second 5G Network Slice |
+---------------------------------------------------------------+
Figure 10: First and Subsequent Slice Deployment
Transport Network Slice mapping policies can be enforced by an
operator (e.g., provided to a TN Orchestration or 5G NSO) to
determine whether existing Transport Network Slices can be reused for
handling a new Slice Service creation request. Providing such a
policy is meant to better automate the realization of 5G Network
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 Network 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.
Note that a variety of L2VPN mechanisms can be considered for
slice realization. A non-comprehensive list is provided below:
- Virtual Private LAN Service (VPLS) [RFC4761] [RFC4762]
- Virtual Private Wire Service (VPWS) (Section 3.1.1 of
[RFC4664])
- Various flavors of EVPNs:
o VPWS EVPN [RFC8214],
o Provider Backbone Bridging combined with EVPN (PBB-EVPN)
[RFC7623],
o EVPN over MPLS [RFC7432], and
o EVPN over Virtual Extensible LAN (VXLAN) [RFC8365].
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 part of the admission control is implemented on
the CE and the other part on the PE.
* Coarse-grained resource control at the transit links (non-
attachment circuits) 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 transit links in the provider network.
* Capacity planning/management for efficient usage of provider
network resources:
The role of capacity planning/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 that
ensures a more or less equal traffic distribution (i.e., equal-
cost load balancing) to advanced TE techniques, with or without
bandwidth reservations, that 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
The P nodes shown in Figure 11 are routers that do not 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. Handoff 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 Network 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. The following subsections list a
few handoff 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 [NS-APP].
4.1. VLAN Handoff
In this option, the RFC 9543 Network Slice, fulfilling connectivity
requirements between NFs that belong to a 5G Network 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
| +-------------------+ | |
| | | | |
+------+ | +-+----+ Provider +---+--+ | +-----+ | +------+
| | v | | | | v | | v | |
| x------x * | | * x------x x.......x |
| NF x------x * PE | | PE * x------xL2/L3x.......x NF |
| x------x * | | * x------x x.......x |
| | | | | | | | | |
+------+ AC +--+---+ Network +---+--+ AC +-----+ +------+
| |
+------------------+
x Logical interface represented by a VLAN on a physical interface
* SDP
Figure 12: Example of 5G Network Slice with VLAN Handoff
Providing End-to-End Connectivity
Each VLAN represents a distinct logical interface on the ACs and
hence 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 the 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 the same slice at different locations may use
different VLAN values. Therefore, a table mapping VLANs to RFC 9543
Network Slices is maintained for each AC, and the VLAN allocation is
coordinated between customer orchestration and provider
orchestration.
While VLAN handoff 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 Handoff
In this option, an explicit mapping between source/destination IP
addresses and a slice's specific S-NSSAI is used. The mapping can
have either local (e.g., pertaining to a 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
* S-NSSAI to SRv6 Locators or Segment Identifiers (SIDs) [RFC8986]
* Use of a deterministic algorithm to map S-NSSAI 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 enforcement in the Transport Network (e.g.,
differentiated services, traffic steering, bandwidth allocation,
security policies, and monitoring).
One example of the IP handoff realization is the arrangement in which
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 Network Slice might be
constructed with multiple such tunnels, since a typical 5G Network
Slice contains many NFs, especially DUs and CUs. If a shared NF
(i.e., an NF that serves multiple slices, such as a shared DU) is
deployed, multiple tunnels from the 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, etc.) termination point
* SDP
Figure 13: Example of 5G Network Slice with IP Handoff Providing
End-to-End Connectivity
As opposed to the VLAN handoff 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
handoffs 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 handoff 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 field, while
the S-NSSAI is a 32-bit field: The Slice/Service Type (SST) is 8
bits, and the Slice Differentiator (SD) is 24 bits. Out of the 128
bits of the IPv6 address, 32 bits 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].
Intermediary TN nodes are not required to associate any additional
semantic with the IPv6 address.
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.
An example of a local IPv6 addressing plan for NFs is provided in
Appendix A.
4.3. MPLS Label Handoff
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.
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 14 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 14: Example of MPLS-Based Attachment Circuit
4.3.1. Option A
This option is based on the VLAN handoff, described in Section 4.1;
it is not based on the MPLS label handoff.
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 15, 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 15, 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.
<------ <------ <------
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 15: Example of MPLS Handoff 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 (nhs), and a new label is dynamically allocated, as shown in
Figure 15 (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 15, 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 a 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 15.
In that case, the route target extended community (Section 4 of
[RFC4360]) might be used as a 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 also be 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
programming 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 16. As a result,
a node in a customer site performs hierarchical next-hop resolution.
<----------------------------------------
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 a physical interface
# Service instances (with unique MPLS label)
* SDP
Figure 16: Example of MPLS Handoff 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 and provider network) boundaries,
the NEXT_HOP attribute for IPv4/IPv6 labeled unicast needs to be
modified to next-hop self (nhs), which results in a new IPv4/IPv6
labeled unicast label allocation. Appropriate forwarding entries for
label swaps for IPv4/IPv6 labeled unicast labels are programmed in
the data plane. There is no additional "labeled transport" protocol
on the AC (e.g., no LDP, RSVP, or SR).
Packets are transmitted over the AC with the IPv4/IPv6 labeled
unicast as the top label, with the 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
labeled unicast host routes, which are used as NEXT_HOP for service
prefixes. Also, since one IPv4/IPv6 labeled unicast host route
represents 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 detail in Section 3.7, the PE needs 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 using those ranges for slice identification
purposes on the 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 a packet switched provider network use two layers of
QoS, which are discussed in the following subsections.
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]. The 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, 5G network functions might set DSCP with a
value representing 5QI so that differentiated treatment can be
implemented in the provider network as well. Based on these DSCP
values, very granular QoS enforcement might be implemented at the SDP
of each provider network segment used to construct transport for
given 5G Network Slice.
The exact mapping between 5QI and DSCP is out of scope for this
document. Mapping recommendations are documented, e.g., in
[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".
5.1.2. Transport Network (TN) QoS Layer
Control of the TN resources and traffic scheduling/prioritization on
provider network transit links are 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, this document
assumes support for 8 traffic queues per port 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 a DSCP or MPLS Traffic Class (TC). This layer of QoS is
referred to as "TN QoS Class" ("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 a 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
(see 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 Network 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.
5.2.1. 5QI-Unaware Model
In the 5QI-unaware model, 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 low
number of deployed 5G Network Slices (for example, only two 5G
Network 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 Network Slices (and thus the 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 17.
+----------------------------------------------------------------+
+-------------------. 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 17: Mapping of Slice to TN QoS (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.
The original IP header retains the DSCP marking (which is ignored in
the 5QI-unaware model), while the new header (MPLS or IPv6) carries
the QoS marking (MPLS Traffic Class bits for MPLS encapsulation or
DSCP for SRv6/IPv6 encapsulation) related to the TN Class of Service
(CoS). Based on the 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 18 for MPLS encapsulation and in Figure 19 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 18: QoS with MPLS Encapsulation
+--------------+
| IPv6 Header |
| +-------+
| |TN DSCP|
+------+-------+
: Optional :
: IPv6 :
: Headers :
+--------------+ - - - - - - - - +-----+-----+--+
| IP Header | |\ | IP Header |
| +-------+ | \ | +-------+
| |5G DSCP|---------+ \ | |5G DSCP|
+------+-------+ \ +------+-------+
| | \ | |
| | \ | |
| | | |
| Payload | / | Payload |
|(GTP-U/IPsec) | / |(GTP-U/IPsec) |
| | / | |
| |---------+ / | |
| | | / | |
| | |/ | |
+--------------+ - - - - - - - - +--------------+
Figure 19: QoS with SRv6 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
and out-of-profile traffic, as discussed in Section 5.2.1.1.
Provider network edge resources are controlled in a fine-grained
manner, with dedicated resource allocation for each RFC 9543 Network
Slice. Resource control and 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
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 the following parameters
[NSSM]:
* 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 the 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].
[RFC2475] (though not termed “1r2c” in that document). At the
SDP, it meters a traffic stream of a given slice and marks its
packets as in-profile (below CIR being enforced) or out-of-profile
(above CIR being enforced). In-
profile In-profile packets are accepted and
forwarded. Out-of-profile packets are either dropped right at the
SDP (hard rate limiting) or re-marked (with different MPLS TC or
DSCP TN markings) to signify "this packet should be dropped in the
first place, if there is congestion" (soft rate limiting),
depending on the business policy of the provider network. In the
latter 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 an improved version
is defined 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 CE devices. In
general, 2r3c meters give greater flexibility for provider network
edge enforcement regarding accepting the traffic (green),
deprioritizing and potentially dropping the traffic on transit
during congestion (yellow), or hard-dropping the traffic (red).
Inbound provider network edge enforcement for the 5QI-unaware model,
where all packets belonging to the slice are treated the same way in
the provider network (no 5G QoS Class differentiation in the
provider), is outlined in Figure 20.
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 20: Ingress Slice Admission Control (5QI-Unaware Model)
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 fulfill the aggregate of slice
CIRs. If, at any given time, some slices send the traffic above
CIR, congestion in the 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 the 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 the 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 21 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.
+---------+ 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 21: Ingress Slice Admission Control (5QI-Unaware Model) -
Output
5.2.2. 5QI-Aware Model
In the 5QI-aware model, a potentially large number of 5G QoS Classes,
represented via the DSCP set by NFs (the architecture scales to
thousands of 5G Network Slices), is mapped (multiplexed) to up to 8
TN QoS Classes used in a provider network transit equipment, as
outlined in Figure 22.
+---------------------------------------------------------------+
+-------------------+ 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 22: Mapping of Slice 5G QoS to TN QoS (5QI-Aware Model)
Given that in deployments with a large number of 5G Network 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 the 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 approach is outlined in Figure 23. A provider may
decide to implement Diffserv-Intercon PHBs at the boundaries of its
network domain [RFC8100].
| Note: The numbers indicated in Figure 23 (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 23: Example of 3GPP QoS Mapped to TN QoS
In current SDO progress of 3GPP (Release 17) 19) 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
DSCP marking corresponding to 5QI (5G QoS Class), while the new
header (MPLS or IPv6) carries the QoS marking related to TN QoS
Class. Based on the 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 inbound/
outbound enforcement per slice and per 5G QoS Class on the AC.
In the 5QI-aware model, compared to the 5QI-unaware model, provider
network edge resources are controlled in an even more fine-grained
manner, with dedicated resource allocation for each RFC 9543 Network
Slice and for a number of traffic classes (most commonly, up to 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-unaware model, admission control (traffic
conditioning) in the 5QI-aware model is more granular, as it not only
enforces per-slice capacity constraints, but may also enforce the
constraints per 5G QoS Class within each slice.
A 5G Network 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). A 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 24. In this model,
if a premium class doesn't consume all available class capacity, it
cannot be reused by a non-premium class (i.e., best effort) class. best-effort).
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 24: Ingress Slice Admission Control (5QI-Aware Model)
The second option combines the advantages of the 5QI-unaware model
(per-slice admission control) with per-traffic-class admission
control, as outlined in Figure 24. Ingress admission control is at
class granularity for premium classes (CIR only). A non-premium
class (i.e., best-effort class) 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 25.
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 25: Ingress Slice Admission Control (5QI-Aware Model) -
Hierarchical
5.2.2.2. Outbound Edge Resource Control
Figure 26 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 5G QoS
queue CIRs within the slice, should not exceed the CIR of the slice
itself. And, similar to the 5QI-aware model, the sum of slice CIRs
should not exceed the physical capacity of the AC.
+---------+ 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 | ... | weight-Slice-3-CIR
| | c | | shaping-Slice-3-PIR
| | e .-----------------------------. |
| | | | |
| | 3 '-----------------------------' /|\
| +---|---+ - - - - - - - - - - - - - - - - - - - - - - - - -
+---------+
Figure 26: Egress Slice Admission Control (5QI-Aware Model)
5.3. Transit Resource Control
Transit resource control is much simpler than edge resource control
in the provider network. As outlined in Figure 22, at the provider
network edge, 5G 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 an outer header (MPLS or IPv6), the TN
QoS Class marking (MPLS TC or IPv6 DSCP in outer header, as depicted
in Figures 18 and 19) 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 uses an outbound interface policy, which is
based on the priority queue combined with a 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, events caused by network failures or temporary
rerouting), premium classes are prioritized, and any drops only occur
in traffic that was deprioritized by ingress admission control (see
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. For example, the
TN domain can be operated with 8 TN QoS Classes (representing 8
hardware queues in the routers) and two underlay transports (e.g., a
latency-optimized underlay transport using link-latency metrics for
path calculation and an underlay transport following IGP metrics).
The 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 the provider network based
on the operator's requirements. This path can be optimized or
constrained.
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., a Media Access Control Security (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 at the time of writing this document.
Similar to the QoS mapping models discussed in Section 5, for mapping
to underlay transports at the ingress PE, both the 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 27 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 per-path
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.
+---------------+ +------+
| Ingress PE | +------------------------------->| PE-A |
| | | +-------------------------->>| |
| | | | +------+
| +----------+ | | +---------------------+
| | | | | |
| | x------+ +---------------------+
| |Underlay x----------|-------------+ +------+
| |Transport x----------)--+ +------------->| PE-B |
| | A x-------+ | | +---+ +------>>| |
| +----------+ | | | | | | | +------+
| | | | | | +---------+
| +----------+ | | | | |
| | | | | | | | +------+
| | o-------)--+ +--)--------------------->| PE-C |
| |Underlay o-------|--------+ +---->>| |
| |Transport o-------|-----------------+ | +------+
| | B o-----+ +---------------+ | |
| | | | | | | |
| +----------+ | | +---+ +---+ | +------+ +------+
| | | | | | | +-------------->| PE-D |
+---------------+ +---+ +---+ +--------------->>| |
+------+
Figure 27: Example of Underlay Transport Relying on TE Tunnels
For illustration purposes, Figure 27 shows only single tunnels per
underlay transport for an (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-unaware model, the provider
network doesn't take into account 5G QoS during execution of per-hop
behavior. The entire slice is mapped to a single TN QoS Class;
therefore, the entire slice is subject to the same per-hop behavior.
Similarly, in the 5QI-unaware PE underlay transport mapping model,
the entire slice is mapped to a single underlay transport, as
depicted in Figure 28.
+-------------------------------------------+
|.. .. .. .. .. .. . |
: AC : PE |
: .--------------. : |
: | SDP | : |
: | +----------+ | : |
: | | NS 1 +-----------+ |
: | +----------+ | : | |
: '--------------' : | |
: .--------------. : | +---------+ |
: | SDP | : | | | |
: | +----------+ | : | |Underlay | |
: | | NS 2 +-------+ +--->Transport| |
: | +----------+ | : | | | A | |
: '--------------' : | | | | |
: .--------------. : | | +---------+ |
: | SDP | : | | |
: | +----------+ | : | | |
: | | NS 3 +-------+ | |
: | +----------+ | : | | +---------+ |
: '--------------' : | | | | |
: .--------------. : | | |Underlay | |
: | SDP | : +---)--->Transport| |
: | +----------+ | : | | | B | |
: | | NS 4 +-------+ | | | |
: | +----------+ | : | +---------+ |
: '--------------' : | |
: .--------------. : | |
: | SDP | : | |
: | +----------+ | : | |
: | | NS 5 +-----------+ |
: | +----------+ | : |
: '--------------' : |
'.. .. .. .. .. .. .' |
+-------------------------------------------+
Figure 28: Mapping of Network Slice to Underlay Transport (5QI-
Unaware Model)
6.2. 5QI-Aware Model
In the 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 29.
+---------------------------------------------+
|.. .. .. .. .. .. . |
: 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 29: Mapping of Network Slice to Underlay Transport (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.
Figure 30 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. In
addition, 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 it 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 Network
Slices)
Figure 30: Example of Multi-DC Architecture
Let us consider 5G Network 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
Network Slice "X", rather than other DCs. For its decision-making,
the 5G NSO needs 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 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 Network 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 "DC 1"
might be sending traffic to multiple NFs in "DC 2", but this is
expressed as one value in the traffic matrix: the total bandwidth
required for 5G Network Slice "X" from "DC 1" to "DC 2" (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 "DC 1" 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)
The YANG data model defined in [NSSM] 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
PE1B that face DC 1, as this is the total bandwidth that DC 1 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 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. On the other hand, if the DC-to-DC
demand information is not used by the NSC, the IETF YANG data models
for L3VPN service delivery [RFC8299] or L2VPN service delivery
[RFC8466] could be used instead of the YANG data model defined in
[NSSM], 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 from 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 the YANG data model defined in [NSSM] to request low-
latency transport for a given slice if required. However, the YANG
data models in [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.
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 [RFC9256] paths 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
current SR-TE technology at the time of writing this document) 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.
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 "DC 1" to
"DC 2" 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 30, suppose a new slice is
instantiated that needs 0.8 Gbps from "DC 1" to "DC 2". The
transport controller would increase its notion of the bandwidth
requirement from "DC 1" to "DC 2" 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 "DC 1" to "DC
2" bandwidth requirement to bandwidth reservations of TE LSPs from
"DC 1" to "DC 2". For example, if the routing configuration is
arranged such that in the absence of any network failure, traffic
from "DC 1" to "DC 2" always enters "PE1A" and goes to "PE2A", the
controller reserves 12.8 Gbps of bandwidth on the path from "PE1A" to
"PE2A". On the other hand, if the routing configuration is arranged
such that in the absence of any network failure, traffic from "DC 1"
to "DC 2" 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 "DC 1" that causes traffic from "DC 1" 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" and "PE2B".
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 a given
link exceeds a threshold, the controller, knowing how much actual
data plane traffic is currently traveling along each RSVP or SR-TE
path, can tune 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, for example:
* 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,
- 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 and 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 detection and
repair features for a subset of network slices. For example, a
given network slice may require fast detection and repair
mechanisms, while others may not be engineered with such means.
The provider can use techniques such as those described in
[RFC5286], [RFC5714], and [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 L2VPN/L3VPNs that are used to deliver
Network Slice Services. The correlation between an L2VPN/L3VPN
instance and a Network Slice Service is maintained using the
"parent-service-id" attribute (Section 7.3 of [RFC9182]).
* Providers should provide the 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 detection purposes. For example, the YANG data
model in [RFC9375] can be used to report the one-way delay and
one-way delay variation of links. Both conventional active/
passive measurement methods [RFC7799] and more recent telemetry
methods (e.g., YANG Push [RFC8641]) can be used.
* Providers should have the means to report and expose observed
performance metrics and other OAM state to customer. For example,
the YANG data model defined in [NSSM] exposes a set of statistics
per SDP, connectivity construct, and connection group.
9. Scalability Implications
The mapping of 5G Network Slices to Transport Network 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 an M-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 the mapping of Slice Services to network
slices) would ease slice migration operations.
The realization model described in this 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 has no IANA actions.
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 (Section 6) that avoids that region.
NSC authentication:
Per [RFC9543], underlay networks need to be protected against
attacks from an adversary NSC as this could destabilize overall
network operations. The interaction between an NSC and the
underlay network is used to pass service provisioning requests
following a set of YANG modules that are designed to be accessed
via YANG-based management protocols, such as NETCONF [RFC6241] and
RESTCONF [RFC8040]. These YANG-based management protocols have to
use (1) a secure transport layer (e.g., SSH [RFC4252], TLS
[RFC8446], and QUIC [RFC9000]) and (2) mutual authentication.
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.
Readers may refer to documents that describe NSC realization, such
as [NSC-MODEL].
Specific isolation criteria:
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 RFC 9543 Network Slice:
As described in Section 5.1.2.1 of [RFC9543], the customer might
request a Service Level Expectation (SLE) that mandates
encryption.
This can be achieved, e.g., by mapping the traffic to an underlay
transport (Section 6) that uses only MACsec-encrypted links.
In order to avoid the need for a mapping table to associate source/
destination IP addresses and the specific S-NSSAIs of slices,
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 a packet belongs. It may
also alter these bits, which may lead to steering the packet via a
distinct network slice and thus to service disruption. Note that
such an attacker from within the Transport Network may inflict 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. In particular, readers should
refer to the "Security Framework for Provider-Provisioned Virtual
Private Networks (PPVPNs)" [RFC4111], the "Applicability Statement
for BGP/MPLS IP Virtual Private Networks (VPNs)" (Section 6 of
[RFC4365]), and the "Analysis of the Security of BGP/MPLS IP Virtual
Private Networks (VPNs)" [RFC4381] for a comprehensive discussion
about security considerations related to VPN technologies (including
authentication and encryption between PEs, use of IPsec tunnels that
terminate within the customer sites to protect user data, prevention
of illegitimate traffic from entering a VPN instance, etc.). Also,
readers may refer to Section 9 of [RFC9522] for a discussion about
security considerations related to TE mechanisms.
12. References
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/info/rfc4364>.
[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/info/rfc7608>.
[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/info/rfc8341>.
[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/info/rfc9543>.
12.2. Informative References
[Book-5G] Peterson, L., Sunay, O., and B. Davie, "Private 5G: A
Systems Approach", 2023,
<https://5g.systemsapproach.org/>.
[ECPRI] Common Public Radio Interface, "Common Public Radio
Interface: eCPRI Interface Specification",
<https://www.cpri.info/downloads/
eCPRI_v_2.0_2019_05_10c.pdf>.
[IEEE802.1AE]
IEEE, "802.1AE: MAC Security (MACsec)",
<https://1.ieee802.org/security/802-1ae/>.
[MAPPING] Contreras, L. M., Ed., Bykov, I., Ed., and K. G.
Szarkowicz, Ed., "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-04, 5 July 2025,
<https://datatracker.ietf.org/doc/html/draft-cbs-teas-5qi-
to-dscp-mapping-04>.
[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>.
[NS-APP] Geng, X., Contreras, L. M., Ed., 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-05, 7 July
2025, <https://datatracker.ietf.org/doc/html/draft-ietf-
teas-5g-network-slice-application-05>.
[NS-IP-MPLS]
Saad, T., Beeram, V., Dong, J., Halpern, J., and S. Peng,
"Realizing Network Slices in IP/MPLS Networks", Work in
Progress, Internet-Draft, draft-ietf-teas-ns-ip-mpls-05, 2
March 2025, <https://datatracker.ietf.org/doc/html/draft-
ietf-teas-ns-ip-mpls-05>.
[NSC-MODEL]
Contreras, L. M., Rokui, R., Tantsura, J., Wu, B., and X.
Liu, "IETF Network Slice Controller and its Associated
Data Models", Work in Progress, Internet-Draft, draft-
ietf-teas-ns-controller-models-06, 20 October 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-ns-
controller-models-06>.
[NSSM] 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-25, 9 May 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-
ietf-network-slice-nbi-yang-25>.
[O-RAN.WG9.XPSAAS]
O-RAN Alliance, "Xhaul Packet Switched Architectures and
Solutions", O-RAN.WG9.XPSAAS, Version 09.00, October 2025,
<https://specifications.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/info/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/info/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/info/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/info/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/info/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/info/rfc4026>.
[RFC4111] Fang, L., Ed., "Security Framework for Provider-
Provisioned Virtual Private Networks (PPVPNs)", RFC 4111,
DOI 10.17487/RFC4111, July 2005,
<https://www.rfc-editor.org/info/rfc4111>.
[RFC4115] Aboul-Magd, O. and S. Rabie, "A Differentiated Service
Two-Rate, Three-Color Marker with Efficient Handling of
in-Profile Traffic", RFC 4115, DOI 10.17487/RFC4115, July
2005, <https://www.rfc-editor.org/info/rfc4115>.
[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/info/rfc4176>.
[RFC4252] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,
January 2006, <https://www.rfc-editor.org/info/rfc4252>.
[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/info/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/info/rfc4365>.
[RFC4381] Behringer, M., "Analysis of the Security of BGP/MPLS IP
Virtual Private Networks (VPNs)", RFC 4381,
DOI 10.17487/RFC4381, February 2006,
<https://www.rfc-editor.org/info/rfc4381>.
[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/info/rfc4664>.
[RFC4761] Kompella, K., Ed. and Y. Rekhter, Ed., "Virtual Private
LAN Service (VPLS) Using BGP for Auto-Discovery and
Signaling", RFC 4761, DOI 10.17487/RFC4761, January 2007,
<https://www.rfc-editor.org/info/rfc4761>.
[RFC4762] Lasserre, M., Ed. and V. Kompella, Ed., "Virtual Private
LAN Service (VPLS) Using Label Distribution Protocol (LDP)
Signaling", RFC 4762, DOI 10.17487/RFC4762, January 2007,
<https://www.rfc-editor.org/info/rfc4762>.
[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/info/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/info/rfc5440>.
[RFC5714] Shand, M. and S. Bryant, "IP Fast Reroute Framework",
RFC 5714, DOI 10.17487/RFC5714, January 2010,
<https://www.rfc-editor.org/info/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/info/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/info/rfc6136>.
[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/info/rfc6241>.
[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/info/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/info/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/info/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/info/rfc7422>.
[RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
2015, <https://www.rfc-editor.org/info/rfc7432>.
[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/info/rfc7510>.
[RFC7623] Sajassi, A., Ed., Salam, S., Bitar, N., Isaac, A., and W.
Henderickx, "Provider Backbone Bridging Combined with
Ethernet VPN (PBB-EVPN)", RFC 7623, DOI 10.17487/RFC7623,
September 2015, <https://www.rfc-editor.org/info/rfc7623>.
[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/info/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/info/rfc7806>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.
[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/info/rfc8100>.
[RFC8214] Boutros, S., Sajassi, A., Salam, S., Drake, J., and J.
Rabadan, "Virtual Private Wire Service Support in Ethernet
VPN", RFC 8214, DOI 10.17487/RFC8214, August 2017,
<https://www.rfc-editor.org/info/rfc8214>.
[RFC8299] Wu, Q., Ed., Litkowski, S., Tomotaki, L., and K. Ogaki,
"YANG Data Model for L3VPN Service Delivery", RFC 8299,
DOI 10.17487/RFC8299, January 2018,
<https://www.rfc-editor.org/info/rfc8299>.
[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/info/rfc8355>.
[RFC8365] Sajassi, A., Ed., Drake, J., Ed., Bitar, N., Shekhar, R.,
Uttaro, J., and W. Henderickx, "A Network Virtualization
Overlay Solution Using Ethernet VPN (EVPN)", RFC 8365,
DOI 10.17487/RFC8365, March 2018,
<https://www.rfc-editor.org/info/rfc8365>.
[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/info/rfc8446>.
[RFC8466] Wen, B., Fioccola, G., Ed., Xie, C., and L. Jalil, "A YANG
Data Model for Layer 2 Virtual Private Network (L2VPN)
Service Delivery", RFC 8466, DOI 10.17487/RFC8466, October
2018, <https://www.rfc-editor.org/info/rfc8466>.
[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/info/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/info/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/info/rfc8986>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
[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/info/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/info/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/info/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/info/rfc9291>.
[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/info/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/info/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/info/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/info/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/info/rfc9522>.
[RFC9834] Boucadair, M., Ed., Roberts, R., Ed., Gonzalez de Dios,
O., Barguil, S., and B. Wu, "YANG Data Models for Bearers
and Attachment Circuits as a Service (ACaaS)", RFC 9834,
DOI 10.17487/RFC9834, September 2025,
<https://www.rfc-editor.org/info/rfc9834>.
[RFC9835] Boucadair, M., Ed., Roberts, R., Gonzalez de Dios, O.,
Barguil, S., and B. Wu, "A Network YANG Data Model for
Attachment Circuits", RFC 9835, DOI 10.17487/RFC9835,
September 2025, <https://www.rfc-editor.org/info/rfc9835>.
[TS-23.501]
3GPP, "System architecture for the 5G System (5GS)",
Version 19.5.0, Release 19, 3GPP TS 23.501, September
2025, <https://www.3gpp.org/ftp/Specs/
archive/23_series/23.501/23501-j50.zip>.
[TS-28.530]
3GPP, "Management and orchestration; Concepts, use cases
and requirements", Version 19.0.0, Release 19, 3GPP
TS 28.530, March 2025, <https://www.3gpp.org/ftp/Specs/
archive/28_series/28.530/28530-j00.zip>.
Appendix A. Example of Local IPv6 Addressing Plan for Network Functions
Different IPv6 address allocation schemes following the approach in
Section 4.2 may be used, with one example allocation shown in
Figure 31.
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 31: Example of S-NSSAI Embedded into an IPv6 Address
In reference to Figure 31, 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.
Figure 32 uses the example from Figure 31 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::/96, while "NF-B" uses a set of tunnel termination points
with per-slice IP addresses allocated from 2001:db8:b::/96. This
example shows two slices: "customer A eMBB" (SST=1, SD-00001) SD=00001) and
"customer B MIoT" (SST=3, SD-00003). 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) 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 32: Deployment Example with S-NSSAI Embedded into IPv6
Addresses
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 and Mike McBride for the rtg-dir reviews,
Yoshifumi Nishida for the tsv-art review, Timothy Winters for the
int-dir review, Lars Eggert for the genart review, Joseph Salowey for
the secdir review, and Tim Wicinski for the opsdir review.
Thanks to Jim Guichard for the AD review.
Thanks to Erik Kline, Ketan Talaulikar, and Deb Cooley for the IESG
review.
Contributors
John Drake
Sunnyvale, CA
United States of America
Email: je_drake@yahoo.com
Ivan Bykov
Ribbon Communications
Tel Aviv
Israel
Email: ivan.bykov@rbbn.com
Reza Rokui
Ciena
Ottawa
Canada
Email: rrokui@ciena.com
Luay Jalil
Verizon
Dallas, TX
United States of America
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)
HPE
Wien
Austria
Email: kszarkowicz@juniper.net
Richard Roberts (editor)
Nokia
Rennes
France
Email: richard.roberts@nokia.com
Julian Lucek
Juniper Networks
HPE
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: https://lmcontreras.com/