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Internet Engineering Task Force (IETF) A. Farrel, Ed.
Request for Comments: 9543 Old Dog Consulting
Category: Informational J. Drake, Ed.
ISSN: 2070-1721 Individual
R. Rokui
Ciena
S. Homma
NTT
K. Makhijani
Futurewei
L. Contreras
Telefonica
J. Tantsura
Nvidia
March 2024
A Framework for Network Slices in Networks Built from IETF Technologies
Abstract
This document describes network slicing in the context of networks
built from IETF technologies. It defines the term "IETF Network
Slice" to describe this type of network slice and establishes the
general principles of network slicing in the IETF context.
The document discusses the general framework for requesting and
operating IETF Network Slices, the characteristics of an IETF Network
Slice, the necessary system components and interfaces, and the
mapping of abstract requests to more specific technologies. The
document also discusses related considerations with monitoring and
security.
This document also provides definitions of related terms to enable
consistent usage in other IETF documents that describe or use aspects
of IETF Network Slices.
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/rfc9543.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Revised BSD License text as described in Section 4.e of the
Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.
Table of Contents
1. Introduction
2. Background
3. Terms and Abbreviations
3.1. Abbreviations
3.2. Core Terminology
4. IETF Network Slice
4.1. Definition and Scope of IETF Network Slice
4.2. IETF Network Slice Service
4.2.1. Connectivity Constructs
4.2.2. Mapping Traffic Flows to Network Realizations
4.2.3. Ancillary CEs
5. IETF Network Slice System Characteristics
5.1. Objectives for IETF Network Slices
5.1.1. Service Level Objectives
5.1.2. Service Level Expectations
5.2. IETF Network Slice Service Demarcation Points
5.3. IETF Network Slice Composition
6. Framework
6.1. IETF Network Slice Stakeholders
6.2. Expressing Connectivity Intents
6.3. IETF Network Slice Controller (NSC)
6.3.1. IETF Network Slice Controller Interfaces
6.3.2. Management Architecture
7. Realizing IETF Network Slices
7.1. An Architecture to Realize IETF Network Slices
7.2. Procedures to Realize IETF Network Slices
7.3. Applicability of ACTN to IETF Network Slices
7.4. Applicability of Enhanced VPNs to IETF Network Slices
7.5. Network Slicing and Aggregation in IP/MPLS Networks
7.6. Network Slicing and Service Function Chaining (SFC)
8. Isolation in IETF Network Slices
8.1. Isolation as a Service Requirement
8.2. Isolation in IETF Network Slice Realization
9. Management Considerations
10. Security Considerations
11. Privacy Considerations
12. IANA Considerations
13. Informative References
Appendix A. Examples
A.1. Multi-Point to Point Service
A.2. Service Function Chaining and Ancillary CEs
A.3. Hub and Spoke
A.4. Layer 3 VPN
A.5. Hierarchical Composition of Network Slices
A.6. Horizontal Composition of Network Slices
Acknowledgments
Contributors
Authors' Addresses
1. Introduction
A number of use cases would benefit from a network service that
supplements connectivity, such as that offered by a VPN service, with
an assurance of meeting a set of specific network performance
objectives. This connectivity and resource commitment is referred to
as a "network slice" and is expressed in terms of connectivity
constructs (see Section 4) and service objectives (see Section 5).
Since the term "network slice" is rather generic and has wider or
different interpretations within other standards bodies, the
qualifying term "IETF" is used in this document to limit the scope of
the network slices described to network technologies defined and
standardized by the IETF. This document defines the concept of "IETF
Network Slices" that provide connectivity coupled with a set of
specific commitments of network resources between a number of
endpoints (known as Service Demarcation Points (SDPs); see Sections
3.2 and 5.2) over a shared underlay network that utilizes IETF
technology. The term "IETF Network Slice Service" is also introduced
to describe the service requested by and provided to the service
provider's customer.
It is intended that the terms "IETF Network Slice" and "IETF Network
Slice Service" be used only in this document. Other documents that
need to indicate the type of network slice or network slice service
described in this document can use the terms "RFC 9543 Network Slice"
and "RFC 9543 Network Slice Service".
This document also provides a general framework for requesting and
operating IETF Network Slices. The framework is intended as a
structure for discussing interfaces and technologies.
Services that might benefit from IETF Network Slices include but are
not limited to:
* 5G services (e.g., enhanced Mobile Broadband (eMBB), Ultra-
Reliable and Low Latency Communications (URLLC), and massive
Machine Type Communications (mMTC) -- see [TS23.501])
* Network wholesale services
* Network infrastructure sharing among operators
* Network Function Virtualization (NFV) [NFVArch] connectivity and
Data Center Interconnect
Further analysis of the needs of IETF Network Slice Service customers
is provided in [USE-CASES].
IETF Network Slices are created and managed within the scope of one
or more network technologies (e.g., IP, MPLS, and optical) that use
an IETF-specified data plane and/or management/control plane. They
are intended to enable a diverse set of applications with different
requirements to coexist over a shared underlay network. A request
for an IETF Network Slice Service is agnostic to the technology in
the underlay network so as to allow customers to describe their
network connectivity objectives in a common format, independent of
the underlay technologies used.
Many preexisting approaches to service delivery and traffic
engineering already use mechanisms that can be considered as network
slicing. For example, Virtual Private Networks (VPNs) have served
the industry well as a means of providing different groups of users
with logically isolated access to a common network. The common or
base network that is used to support the VPNs is often referred to as
an "underlay network", and the VPN is often called an "overlay
network". An overlay network may, in turn, serve as an underlay
network to support another overlay network.
Note that it is conceivable that extensions to IETF technologies are
needed in order to fully support all the capabilities that can be
implemented with network slices. Evaluation of existing
technologies, proposed extensions to existing protocols and
interfaces, and creation of new protocols or interfaces are outside
the scope of this document.
2. Background
The concept of network slicing has gained traction, driven largely by
needs surfacing from 5G (see [NGMN-NS-Concept], [TS23.501], and
[TS28.530]). In [TS23.501], a Network Slice is defined as a "logical
network that provides specific network capabilities and network
characteristics", and a Network Slice Instance is defined as a "set
of Network Function instances and the required resources (e.g.
compute, storage and networking resources) which form a deployed
Network Slice". According to [TS28.530], an end-to-end (E2E) network
slice consists of three major types of network segments: Radio Access
Network (RAN), Transport Network (TN), and Core Network (CN). An
IETF Network Slice provides the required connectivity between
different entities in RAN and CN segments of an end-to-end network
slice, with a specific performance commitment (for example, serving
as a TN slice). For each end-to-end network slice, the topology and
performance requirement on a customer's use of an IETF Network Slice
can be very different, which requires the underlay network to have
the capability of supporting multiple different IETF Network Slices.
While network slices are commonly discussed in the context of 5G, it
is important to note that IETF Network Slices are a narrower concept
with a broader usage profile and focus primarily on particular
network connectivity aspects. Other systems, including 5G
deployments, may use IETF Network Slices as a component to create
entire systems and concatenated constructs that match their needs,
including end-to-end connectivity.
An IETF Network Slice could span multiple technologies and multiple
administrative domains. Depending on the IETF Network Slice Service
customer's requirements, an IETF Network Slice could be isolated from
other, often concurrent, IETF Network Slices in terms of data,
control, and management planes.
The customer expresses requirements for a particular IETF Network
Slice Service by specifying what is required rather than how the
requirement is to be fulfilled. That is, the IETF Network Slice
Service customer's view of an IETF Network Slice Service is an
abstract one.
Thus, there is a need to create logical network structures with
required characteristics. The customer of such a logical network can
require a level of isolation and performance that previously might
not have been satisfied by overlay VPNs. Additionally, the IETF
Network Slice Service customer might ask for some level of control
to, e.g., customize the service paths in a network slice.
This document specifies definitions and a framework for the provision
of an IETF Network Slice Service. Section 7 briefly indicates some
candidate technologies for realizing IETF Network Slices.
3. Terms and Abbreviations
3.1. Abbreviations
The following abbreviations are used in this document.
NSC: Network Slice Controller
SDP: Service Demarcation Point
SLA: Service Level Agreement
SLE: Service Level Expectation
SLI: Service Level Indicator
SLO: Service Level Objective
The meaning of these abbreviations is defined in greater detail in
the remainder of this document.
3.2. Core Terminology
The following terms are presented here to give context. Other
terminology is defined in the remainder of this document.
Customer: The requester of an IETF Network Slice Service. Customers
may request monitoring of SLOs. A customer may be an entity such
as an enterprise network or a network operator, an individual
working at such an entity, a private individual contracting for a
service, or an application or software component. A customer may
be an external party (classically, a paying customer) or a
division of a network operator that uses the service provided by
another division of the same operator. Other terms that have been
applied to the customer role are "client" and "consumer".
Provider: The organization that delivers an IETF Network Slice
Service. A provider is the network operator that controls the
network resources used to construct the network slice (that is,
the network that is sliced). The provider's network may be a
physical network or a virtual network created within the
operator's network or supplied by another service provider.
Customer Edge (CE): The customer device that provides connectivity
to a service provider. Examples include routers, Ethernet
switches, firewalls, 4G/5G RAN or Core nodes, application
accelerators, server load balancers, HTTP header enrichment
functions (such as proxy components adding the Forwarded HTTP
Extension Header [RFC7239]), and Performance Enhancing Proxies
(PEPs). In some circumstances, CEs are provided to the customer
and managed by the provider.
Provider Edge (PE): The device within the provider network to which
a CE is attached. A CE may be attached to multiple PEs, and
multiple CEs may be attached to a given PE.
Attachment Circuit (AC): A channel connecting a CE and a PE over
which packets that belong to an IETF Network Slice Service are
exchanged. An AC is, by definition, technology specific: that is,
the AC defines how customer traffic is presented to the provider
network. The customer and provider agree (for example, through
configuration) on which values in which combination of Layer 2
(L2) and Layer 3 (L3) header and payload fields within a packet
identify to which {IETF Network Slice Service, connectivity
construct, and SLOs/SLEs} that packet is assigned. The customer
and provider may agree to police or shape traffic, based on the
specific IETF Network Slice Service including connectivity
construct and SLOs/SLEs, on the AC in both the ingress (CE to PE)
direction and egress (PE to CE) direction. This ensures that the
traffic is within the capacity profile that is agreed upon in an
IETF Network Slice Service. Excess traffic is dropped by default,
unless specific out-of-profile policies are agreed upon between
the customer and the provider. As described in Section 5.2, the
AC may be part of the IETF Network Slice Service or may be
external to it. Because SLOs and SLEs characterize the
performance of the underlay network between a sending SDP and a
set of receiving SDPs, the traffic policers and traffic shapers
apply to a specific connectivity construct on an AC.
Service Demarcation Point (SDP): The point at which an IETF Network
Slice Service is delivered by a service provider to a customer.
Depending on the service delivery model (see Section 5.2), this
may be a CE or a PE and could be a device, a software component,
or an abstract virtual function supported within the provider's
network. Each SDP must have a unique identifier (e.g., an IP
address or Media Access Control (MAC) address) within a given IETF
Network Slice Service and may use the same identifier in multiple
IETF Network Slice Services.
An SDP may be abstracted as a Service Attachment Point (SAP)
[RFC9408] for the purpose of generalizing the concept across
multiple service types and representing it in management and
configuration systems.
Connectivity Construct: A set of SDPs together with a communication
type that defines how traffic flows between the SDPs. An IETF
Network Slice Service is specified in terms of a set of SDPs, the
associated connectivity constructs, and the service objectives
that the customer wishes to see fulfilled. Connectivity
constructs may be grouped for administrative purposes.
4. IETF Network Slice
IETF Network Slices are created to meet specific requirements,
typically expressed as bandwidth, latency, latency variation, and
other desired or required characteristics. Creation of an IETF
Network Slice is initiated by a management system or other
application used to specify network-related conditions for particular
traffic flows in response to an actual or logical IETF Network Slice
Service request.
Once created, these slices can be monitored, modified, deleted, and
otherwise managed.
Applications and components will be able to use these IETF Network
Slices to move packets between the specified endpoints of the service
in accordance with specified characteristics.
A clear distinction should be made between the "IETF Network Slice
Service" and the IETF Network Slice:
IETF Network Slice Service: The function delivered to the customer
(see Section 4.2). It is agnostic to the technologies and
mechanisms used by the service provider.
IETF Network Slice: The realization of the service in the provider's
network achieved by partitioning network resources and by applying
certain tools and techniques within the network (see Sections 4.1
and 7).
4.1. Definition and Scope of IETF Network Slice
The term "Slice" refers to a set of characteristics and behaviors
that differentiate one type of user traffic from another within a
network. An IETF Network Slice is a logical partition of a network
that uses IETF technology. An IETF Network Slice assumes that an
underlay network is capable of changing the configurations of the
network devices on demand, through in-band signaling, or via
controllers.
An IETF Network Slice enables connectivity between a set of SDPs with
specific Service Level Objectives (SLOs) and Service Level
Expectations (SLEs) (see Section 5) over a common underlay network.
The SLOs and SLEs characterize the performance of the underlay
network between a sending SDP and a set of receiving SDPs. Thus, an
IETF Network Slice delivers a service to a customer by meeting
connectivity resource requirements and associated network
capabilities such as bandwidth, latency, jitter, and network
functions with other resource behaviors such as compute and storage
availability.
IETF Network Slices may be combined hierarchically so that a network
slice may itself be sliced. They may also be combined sequentially
so that various different networks can each be sliced and the network
slices placed into a sequence to provide an end-to-end service. This
form of sequential combination is utilized in some services such as
in 3GPP's 5G network [TS23.501].
It is intended that the term "IETF Network Slice" be used only in
this document. Other documents that need to indicate the type of
network slice described in this document can use the term "RFC 9543
Network Slice".
4.2. IETF Network Slice Service
A service provider delivers an IETF Network Slice Service for a
customer by realizing an IETF Network Slice in the underlay network.
The IETF Network Slice Service is agnostic to the technology of the
underlay network, and its realization may be selected based upon
multiple considerations, including its service requirements and the
capabilities of the underlay network. This allows an IETF Network
Slice Service customer to describe their network connectivity and
relevant objectives in a common format, independent of the underlay
technologies used.
The IETF Network Slice Service is specified in terms of a set of
SDPs, a set of one or more connectivity constructs between subsets of
these SDPs, and a set of SLOs and SLEs (see Section 5) for each SDP
sending to each connectivity construct. A communication type (Point-
to-Point (P2P), Point-to-Multipoint (P2MP), or Any-to-Any (A2A)) is
specified for each connectivity construct. That is, in a given IETF
Network Slice Service:
* There may be one or more connectivity constructs of the same or
different type.
* Each connectivity construct may be between a different subset of
SDPs.
* Each sending SDP has its own set of SLOs and SLEs for a given
connectivity construct, and the SLOs and SLEs in each set may be
different.
Note that different connectivity constructs can be specified in the
service request, but the service provider may decide how many
connectivity constructs per IETF Network Slice Service it wishes to
support such that an IETF Network Slice Service may be limited to one
connectivity construct or may support many.
An IETF Network Slice Service customer may provide IETF Network Slice
Services to other customers in a mode sometimes referred to as
"carrier's carrier" (see Section 9 of [RFC4364]). In this case, the
relationship between IETF Network Slice Service providers may be
internal to a commercial organization or may be external through
service provision contracts. As noted in Section 5.3, network slices
may be composed hierarchically or serially.
Section 5.2 provides a description of SDPs as endpoints in the
context of IETF network slicing. For a given IETF Network Slice
Service, the customer and provider agree, on a per-SDP basis, which
end of the attachment circuit provides the SDP (i.e., whether the
attachment circuit is inside or outside the IETF Network Slice
Service). This determines whether the attachment circuit is subject
to the set of SLOs and SLEs at the specific SDP.
It is intended that the term "IETF Network Slice Service" be used
only in this document. Other documents that need to indicate the
type of network slice service described in this document can use the
term "RFC 9543 Network Slice Service".
4.2.1. Connectivity Constructs
The approach of specifying a Network Slice Service as a set of SDPs
with connectivity constructs results in the following possible
connectivity constructs:
* For a P2P connectivity construct, there is one sending SDP and one
receiving SDP. This construct is like a private wire or a tunnel.
All traffic injected at the sending SDP is intended to be received
by the receiving SDP. The SLOs and SLEs apply at the sender (and
implicitly, at the receiver).
* For a P2MP connectivity construct, there is only one sending SDP
and more than one receiving SDP. This is like a P2MP tunnel or
multi-access VLAN segment. All traffic from the sending SDP is
intended to be received by all the receiving SDPs. There is one
set of SLOs and SLEs that applies at the sending SDP (and
implicitly, at all receiving SDPs).
* With an A2A connectivity construct, any sending SDP may send to
any one receiving SDP or any set of receiving SDPs in the
construct. There is an implicit level of routing in this
connectivity construct that is not present in the other
connectivity constructs because the provider's network must
determine to which receiving SDPs to deliver each packet. This
construct may be used to support P2P traffic between any pair of
SDPs or to support multicast or broadcast traffic from one SDP to
a set of other SDPs. In the latter case, whether the service is
delivered using multicast within the provider's network or using
"ingress replication" or some other means is out of scope of the
specification of the service. A service provider may choose to
support A2A constructs but to limit the traffic to unicast.
The SLOs/SLEs in an A2A connectivity construct apply to individual
sending SDPs regardless of the receiving SDPs, and there is no
linkage between sender and receiver in the specification of the
connectivity construct. A sending SDP may be "disappointed" if
the receiver is over-subscribed. If a customer wants to be more
specific about different behaviors from one SDP to another SDP,
they should use P2P connectivity constructs.
A given sending SDP may be part of multiple connectivity constructs
within a single IETF Network Slice Service, and the SDP may have
different SLOs and SLEs for each connectivity construct to which it
is sending. Note that a given sending SDP's SLOs and SLEs for a
given connectivity construct apply between it and each of the
receiving SDPs for that connectivity construct.
An IETF Network Slice Service provider may freely make a deployment
choice as to whether to offer a 1:1 relationship between an IETF
Network Slice Service and connectivity construct or to support
multiple connectivity constructs in a single IETF Network Slice
Service. In the former case, the provider might need to deliver
multiple IETF Network Slice Services to achieve the function of the
second case.
4.2.2. Mapping Traffic Flows to Network Realizations
A customer traffic flow may be unicast or multicast, and various
network realizations are possible:
* Unicast traffic may be mapped to a P2P connectivity construct for
direct delivery or to an A2A connectivity construct for the
service provider to perform routing to the destination SDP. It
would be unusual to use a P2MP connectivity construct to deliver
unicast traffic because all receiving SDPs would get a copy, but
this can still be done if the receivers are capable of dropping
the unwanted traffic.
* A bidirectional unicast service can be constructed by specifying
two P2P connectivity constructs. An additional SLE may specify
fate-sharing in this case.
* Multicast traffic may be mapped to a set of P2P connectivity
constructs, a single P2MP connectivity construct, or a mixture of
P2P and P2MP connectivity constructs. Multicast may also be
supported by an A2A connectivity construct. The choice clearly
influences how and where traffic is replicated in the network.
With a P2MP or A2A connectivity construct, it is the operator's
choice whether to realize the construct with ingress replication,
multicast in the core, P2MP tunnels, or hub-and-spoke. This
choice should not change how the customer perceives the service.
* The concept of a Multipoint-to-Point (MP2P) service can be
realized with multiple P2P connectivity constructs. Note that, in
this case, the egress may simultaneously receive traffic from all
ingresses. The SLOs at the sending SDPs must be set with this in
mind because the provider's network is not capable of coordinating
the policing of traffic across multiple distinct source SDPs. It
is assumed that the customer, requesting SLOs for the various P2P
connectivity constructs, is aware of the capabilities of the
receiving SDP. If the receiver receives more traffic than it can
handle, it may drop some and introduce queuing delays.
* The concept of a Multipoint-to-Multipoint (MP2MP) service can best
be realized using a set of P2MP connectivity constructs but could
be delivered over an A2A connectivity construct if each sender is
using multicast. As with MP2P, the customer is assumed to be
familiar with the capabilities of all receivers. A customer may
wish to achieve an MP2MP service using a hub-and-spoke
architecture where they control the hub; that is, the hub may be
an SDP or an ancillary CE (see Section 4.2.3), and the service may
be achieved by using a set of P2P connectivity constructs to the
hub and a single P2MP connectivity construct from the hub.
From the above, it can be seen that the SLOs of the senders define
the SLOs for the receivers on any connectivity construct. In
particular, the network may be expected to handle the traffic volume
from a sender to all destinations. This extends to all connectivity
constructs in an IETF Network Slice Service.
Note that the realization of an IETF Network Slice Service does not
need to map the connectivity constructs one-to-one onto underlying
network constructs (such as tunnels). The service provided to the
customer is distinct from how the provider decides to deliver that
service.
If a CE has multiple attachment circuits to PEs within a given IETF
Network Slice Service and they are operating in single-active mode,
then all traffic between the CE and its attached PEs transits a
single attachment circuit; if they are operating in all-active mode,
then traffic between the CE and its attached PEs is distributed
across all of the active attachment circuits.
4.2.3. Ancillary CEs
It may be the case that the set of SDPs that delimits an IETF Network
Slice Service needs to be supplemented with additional senders or
receivers within the network that are not customer sites. An
additional sender could be, for example, an IPTV or DNS server either
within the provider's network or attached to it, while an extra
receiver could be, for example, a node reachable via the Internet.
This is modeled in the Network Slicing architecture as a set of
ancillary CEs that supplement the other SDPs in one or more
connectivity constructs or that are linked by their own connectivity
constructs. Note that an ancillary CE can either have a resolvable
address (e.g., an IP address or MAC address), or it may be a
placeholder (e.g., a named IPTV or DNS service or server) that is
resolved within the provider's network when the IETF Network Slice
Service is instantiated.
Thus, an ancillary CE may be a node within the provider network
(i.e., not a node at the edge of the customer's network). An example
is a node that provides a service function. Another example is a
node that acts as a hub. There will be times when the customer
wishes to explicitly select one of these. Alternatively, an
ancillary CE may be a service function at an unknown point in the
provider's network. In this case, the function may be a placeholder
that has its addresses resolved as part of the realization of the
slice service.
Appendices A.2 and A.3 give simple worked examples of the use of
ancillary CEs that may aid understanding the concept.
5. IETF Network Slice System Characteristics
The following subsections describe the characteristics of IETF
Network Slices in addition to the list of SDPs, the connectivity
constructs, and the technology of the ACs.
5.1. Objectives for IETF Network Slices
An IETF Network Slice Service is defined in terms of quantifiable
characteristics known as Service Level Objectives (SLOs) and
unquantifiable characteristics known as Service Level Expectations
(SLEs). SLOs are expressed in terms Service Level Indicators (SLIs)
and together with the SLEs form the contractual agreement between
service customer and service provider known as a Service Level
Agreement (SLA).
The terms are defined as follows:
Service Level Indicator (SLI): A quantifiable measure of an aspect
of the performance of a network. For example, it may be a measure
of throughput in bits per second, or it may be a measure of
latency in milliseconds.
Service Level Objective (SLO): A target value or range for the
measurements returned by observation of an SLI. For example, an
SLO may be expressed as "SLI <= target" or "lower bound <= SLI <=
upper bound". A customer can determine whether the provider is
meeting the SLOs by performing measurements on the traffic.
Service Level Expectation (SLE): An expression of an unmeasurable
service-related request that a customer of an IETF Network Slice
Service makes of the provider. An SLE is distinct from an SLO
because the customer may have little or no way of determining
whether the SLE is being met, but they still contract with the
provider for a service that meets the expectation.
Service Level Agreement (SLA): An explicit or implicit contract
between the customer of an IETF Network Slice Service and the
provider of the slice. The SLA is expressed in terms of a set of
SLOs and SLEs that are to be applied for a given connectivity
construct between a sending SDP and the set of receiving SDPs.
The SLA may describe the extent to which divergence from
individual SLOs and SLEs can be tolerated, and commercial terms as
well as any consequences for violating these SLOs and SLEs.
5.1.1. Service Level Objectives
SLOs define a set of measurable network attributes and
characteristics that describe an IETF Network Slice Service. SLOs do
not describe how an IETF Network Slice Service is implemented or
realized in the underlying network layers. Instead, they are defined
in terms of dimensions of operation (time, capacity, etc.),
availability, and other attributes.
An IETF Network Slice Service may include multiple connectivity
constructs that associate sets of endpoints (SDPs). SLOs apply to a
given connectivity construct and apply to a specific direction of
traffic flow. That is, they apply to a specific sending SDP and the
set of receiving SDPs.
5.1.1.1. Some Common SLOs
SLOs can be described as "Directly Measurable Objectives"; they are
always measurable. See Section 5.1.2 for the description of Service
Level Expectations, which are unmeasurable service-related requests
sometimes known as "Indirectly Measurable Objectives".
Objectives such as guaranteed minimum bandwidth, guaranteed maximum
latency, maximum permissible delay variation, maximum permissible
packet loss ratio, and availability are "Directly Measurable
Objectives". Future specifications (such as IETF Network Slice
Service YANG models) may precisely define these SLOs, and other SLOs
may be introduced as described in Section 5.1.1.2.
The definition of these objectives are as follows:
Guaranteed Minimum Bandwidth: Minimum guaranteed bandwidth between
two endpoints at any time. The bandwidth is measured in data rate
units of bits per second and is measured unidirectionally.
Guaranteed Maximum Latency: Upper bound of network latency when
transmitting between two endpoints. The latency is measured in
terms of network characteristics (excluding application-level
latency). [RFC7679] discusses one-way metrics.
Maximum Permissible Delay Variation: Packet Delay Variation (PDV) as
defined by [RFC3393] is the difference in the one-way delay
between sequential packets in a flow. This SLO sets a maximum
value PDV for packets between two endpoints.
Maximum Permissible Packet Loss Ratio: The ratio of packets dropped
to packets transmitted between two endpoints over a period of
time. See [RFC7680].
Availability: The ratio of uptime to the sum of uptime and downtime,
where uptime is the time the connectivity construct is available
in accordance with all of the SLOs associated with it.
Availability will often be expressed along with the time period
over which the availability is measured and the maximum allowed
single period of downtime.
5.1.1.2. Other Service Level Objectives
Additional SLOs may be defined to provide additional description of
the IETF Network Slice Service that a customer requests. These would
be specified in further documents.
If the IETF Network Slice Service is traffic-aware, other traffic-
specific characteristics may be valuable including MTU, traffic type
(e.g., IPv4, IPv6, Ethernet, or unstructured), or a higher-level
behavior to process traffic according to user application (which may
be realized using network functions).
5.1.2. Service Level Expectations
SLEs define a set of network attributes and characteristics that
describe an IETF Network Slice Service but are not directly
measurable by the customer (e.g., diversity, isolation, and
geographical restrictions). Even though the delivery of an SLE
cannot usually be determined by the customer, the SLEs form an
important part of the contract between customer and provider.
Quite often, an SLE will imply some details of how an IETF Network
Slice Service is realized by the provider, although most aspects of
the implementation in the underlying network layers remain a free
choice for the provider. For example, activating unicast or
multicast capabilities to deliver an IETF Network Slice Service could
be explicitly requested by a customer or could be left as an
engineering decision for the service provider based on capabilities
of the network and operational choices.
SLEs may be seen as aspirational on the part of the customer, and
they are expressed as behaviors that the provider is expected to
apply to the network resources used to deliver the IETF Network Slice
Service. Of course, over time, it is possible that mechanisms will
be developed that enable a customer to verify the provision of an
SLE, at which point it effectively becomes an SLO.
An IETF Network Slice Service may include multiple connectivity
constructs that associate sets of endpoints (SDPs). SLEs apply to a
given connectivity construct and apply to specific directions of
traffic flow. That is, they apply to a specific sending SDP and the
set of receiving SDPs. However, being more general in nature than
SLOs, SLEs may commonly be applied to all connectivity constructs in
an IETF Network Slice Service.
5.1.2.1. Some Common SLEs
SLEs can be described as "Indirectly Measurable Objectives"; they are
not generally directly measurable by the customer.
Security, geographic restrictions, maximum occupancy level, and
isolation are example SLEs as follows.
Security: A customer may request that the provider applies
encryption or other security techniques to traffic flowing between
SDPs of a connectivity construct within an IETF Network Slice
Service. For example, the customer could request that only
network links that have Media Access Control Security (MACsec)
[MACsec] enabled are used to realize the connectivity construct.
This SLE may include a request for encryption (e.g., [RFC4303])
between the two SDPs explicitly to meet the architectural
recommendations in [TS33.210] or for compliance with the HIPAA
Security Rule [HIPAA] or the PCI Data Security Standard [PCI].
Whether or not the provider has met this SLE is generally not
directly observable by the customer and cannot be measured as a
quantifiable metric.
Please see further discussion on security in Section 10.
Geographic Restrictions: A customer may request that certain
geographic limits are applied to how the provider routes traffic
for the IETF Network Slice Service. For example, the customer may
have a preference that its traffic does not pass through a
particular country for political or security reasons.
Whether or not the provider has met this SLE is generally not
directly observable by the customer and cannot be measured as a
quantifiable metric.
Maximal Occupancy Level: The maximal occupancy level specifies the
number of flows to be admitted and optionally a maximum number of
countable resource units (e.g., IP or MAC addresses) an IETF
Network Slice Service can consume. Because an IETF Network Slice
Service may include multiple connectivity constructs, this SLE
should state whether it applies to all connectivity constructs, a
specified subset of them, or an individual connectivity construct.
Again, a customer may not be able to fully determine whether this
SLE is being met by the provider.
Isolation: As described in Section 8, a customer may request that
its traffic within its IETF Network Slice Service is isolated from
the effects of other network services supported by the same
provider. That is, if another service exceeds capacity or has a
burst of traffic, the customer's IETF Network Slice Service should
remain unaffected, and there should be no noticeable change to the
quality of traffic delivered.
In general, a customer cannot tell whether a service provider is
meeting this SLE. They cannot tell whether the variation of an
SLI is because of changes in the underlay network or because of
interference from other services carried by the network. If the
service varies within the allowed bounds of the SLOs, there may be
no noticeable indication that this SLE has been violated.
Diversity: A customer may request that different connectivity
constructs use different underlay network resources. This might
be done to enhance the availability of the connectivity constructs
within an IETF Network Slice Service.
While availability is a measurable objective (see
Section 5.1.1.1), this SLE requests a finer grade of control and
is not directly measurable (although the customer might become
suspicious if two connectivity constructs fail at the same time).
5.2. IETF Network Slice Service Demarcation Points
As noted in Section 4.1, an IETF Network Slice provides connectivity
between sets of SDPs with specific SLOs and SLEs. Section 4.2 goes
on to describe how the IETF Network Slice Service is composed of a
set of one or more connectivity constructs that describe connectivity
between the Service Demarcation Points (SDPs) across the underlay
network.
The characteristics of IETF Network Slice SDPs are as follows.
* An SDP is the point of attachment to an IETF Network Slice
Service. As such, SDPs serve as the IETF Network Slice ingress/
egress points.
* An SDP is identified by a unique identifier in the context of an
IETF Network Slice Service customer.
* The provider associates each SDP with a set of provider-scope
identifiers such as IP addresses, encapsulation-specific
identifiers (e.g., VLAN tag and MPLS Label), interface/port
numbers, node ID, etc.
* SDPs are mapped to endpoints of services/tunnels/paths within the
IETF Network Slice during its initialization and realization.
- A combination of the SDP identifier and SDP provider-network-
scope identifiers define an SDP in the context of the Network
Slice Controller (NSC) (see Section 6.3).
- The NSC will use the SDP provider-network-scope identifiers as
part of the process of realizing the IETF Network Slice.
Note that an ancillary CE (see Section 4.2.3) is the endpoint of a
connectivity construct and so is an SDP in this discussion.
For a given IETF Network Slice Service, the customer and provider
agree where the SDP is located. This determines what resources at
the edge of the network form part of the IETF Network Slice and are
subject to the set of SLOs and SLEs for a specific SDP.
Figure 1 shows different potential scopes of an IETF Network Slice
that are consistent with the different SDP locations. For the
purpose of this discussion and without loss of generality, the figure
shows Customer Edge (CE) and Provider Edge (PE) nodes connected by
Attachment Circuits (ACs). Notes after the figure give some
explanations.
|<---------------------- (1) ---------------------->|
| |
| |<-------------------- (2) -------------------->| |
| | | |
| | |<----------- (3) ----------->| | |
| | | | | |
| | | |<-------- (4) -------->| | | |
| | | | | | | |
V V AC V V V V AC V V
+-----+ | +-----+ +-----+ | +-----+
| |--------| | | |--------| |
| CE1 | | | PE1 |. . . . . . . . .| PE2 | | | CE2 |
| |--------| | | |--------| |
+-----+ | +-----+ +-----+ | +-----+
^ ^ ^ ^
| | | |
| | | |
Customer Provider Provider Customer
Edge 1 Edge 1 Edge 2 Edge 2
Figure 1: Positioning IETF Service Demarcation Points
Explanatory notes for Figure 1 are as follows:
1. If the CE is operated by the IETF Network Slice Service provider,
then the edge of the IETF Network Slice may be within the CE. In
this case, the IETF Network Slicing process may utilize resources
from within the CE such as buffers and queues on the outgoing
interfaces.
2. The IETF Network Slice may be extended as far as the CE to
include the AC but not to include any part of the CE. In this
case, the CE may be operated by the customer or the provider.
Slicing the resources on the AC may require the use of traffic
tagging (such as through Ethernet VLAN tags) or may require
traffic policing at the AC link ends.
3. The SDPs of the IETF Network Slice are the customer-facing ports
on the PEs. This case can be managed in a way that is similar to
a port-based VPN: each port (AC) or virtual port (e.g., VLAN tag)
identifies the IETF Network Slice and maps to an IETF Network
Slice SDP.
4. Finally, the SDP may be within the PE. In this mode, the PE
classifies the traffic coming from the AC according to
information (such as the source and destination IP addresses,
payload protocol and port numbers, etc.) in order to place it
onto an IETF Network Slice.
The choice of which of these options to apply is entirely up to the
network operator. It may limit or enable the provisioning of
particular managed services, and the operator will want to consider
how they want to manage CEs and what control they wish to offer the
customer over AC resources.
Note that Figure 1 shows a symmetrical positioning of SDPs, but this
decision can be taken on a per-SDP basis through agreement between
the customer and provider.
In practice, it may be necessary to map traffic not only onto an IETF
Network Slice but also onto a specific connectivity construct if the
IETF Network Slice supports more than one with a source at the
specific SDP. The mechanism used will be one of the mechanisms
described above, dependent on how the SDP is realized.
Finally, note (as described in Section 3.2) that an SDP is an
abstract endpoint of an IETF Network Slice Service and as such may be
a device, interface, or software component. An ancillary CE
(Section 4.2.3) should also be thought of as an SDP.
5.3. IETF Network Slice Composition
Operationally, an IETF Network Slice may be composed of two or more
IETF Network Slices as specified below. Decomposed network slices
are independently realized and managed.
Hierarchical (i.e., recursive) composition: An IETF Network Slice
can be further sliced into other network slices. Recursive
composition allows an IETF Network Slice at one layer to be used
by the other layers. This type of multi-layer vertical IETF
Network Slice associates resources at different layers.
Sequential composition: Different IETF Network Slices can be placed
into a sequence to provide an end-to-end service. In sequential
composition, each IETF Network Slice would potentially support
different data planes that need to be stitched together.
6. Framework
A number of IETF Network Slice Services will typically be provided
over a shared underlay network infrastructure. Each IETF Network
Slice consists of both the overlay connectivity and a specific set of
dedicated network resources and/or functions allocated in a shared
underlay network to satisfy the needs of the IETF Network Slice
Service customer. In at least some examples of underlay network
technologies, integration between the overlay and various underlay
resources is needed to ensure the guaranteed performance requested
for different IETF Network Slices.
This section sets out the principal stakeholders in an IETF Network
Slice and describes how the IETF Network Slice Service customer
requests connectivity. It then introduces the IETF Network Slice
Controller (the functional component responsible for receiving
requests from customers and converting them into network
configuration commands) and describes its interfaces.
6.1. IETF Network Slice Stakeholders
An IETF Network Slice and its realization involve the following
stakeholders.
Orchestrator: An orchestrator is an entity that composes different
services, resource, and network requirements. It interfaces with
the IETF NSC when composing a complex service such as an end-to-
end network slice.
IETF Network Slice Controller (NSC): The NSC realizes an IETF
Network Slice in the underlay network and maintains and monitors
the run-time state of resources and topologies associated with it.
A well-defined interface is needed to support interworking between
different NSC implementations and different orchestrator
implementations.
Network Controller: The Network Controller is a form of network
infrastructure controller that offers network resources to the NSC
to realize a particular network slice. This may be an existing
network controller associated with one or more specific
technologies that may be adapted to the function of realizing IETF
Network Slices in a network.
The IETF Network Slice Service customer and IETF Network Slice
Service provider (see Section 3.2) are also stakeholders. Clearly,
the service provider operates the network that is sliced to provide
the IETF Network Slice Service to the customer. The Network
Controller and NSC are management components used by the service
provider to operate their networks and deliver IETF Network Slice
Services. As indicated in Figures 2 and 3, the Orchestrator may be a
component in the customer environment that requests and coordinates
IETF Network Slice Services from one or more service providers. In
other circumstances, however, the Orchestrator may be a component
used by the service provider to request and administer IETF Network
Slices to deliver them to customers or to construct an infrastructure
to deliver other services to the customer.
6.2. Expressing Connectivity Intents
An IETF Network Slice Service customer communicates with the NSC
using the IETF Network Slice Service Interface.
An IETF Network Slice Service customer may be a network operator who,
in turn, uses the IETF Network Slice to provide a service for another
IETF Network Slice Service customer.
Using the IETF Network Slice Service Interface, a customer expresses
requirements for a particular slice by specifying what is required
rather than how that is to be achieved. That is, the customer's view
of a slice is an abstract one. Customers normally have limited (or
no) visibility into the provider network's actual topology and
resource availability information.
This should be true even if both the customer and provider are
associated with a single administrative domain, in order to reduce
the potential for adverse interactions between IETF Network Slice
Service customers and other users of the underlay network
infrastructure.
The benefits of this model can include the following.
Security: The underlay network components are less exposed to attack
because the underlay network (or network operator) does not need
to expose network details (topology, capacity, etc.) to the IETF
Network Slice Service customers.
Layered Implementation: The underlay network comprises network
elements that belong to a different layer network than customer
applications. Network information (advertisements, protocols,
etc.) that a customer cannot interpret or respond to is not
exposed to the customer. (Note that a customer should not rely on
network information not exposed directly to the customer by the
network operator, such as via the IETF Network Slice Service
Interface.)
Scalability: Customers do not need to know any information
concerning network topology, capabilities, or state beyond that
which is exposed via the IETF Network Slice Service Interface.
This protects the customer site from having to hold and process
extra information and from receiving frequent updates about the
status of the network.
The general issues of abstraction in a Traffic Engineered (TE)
network are described more fully in [RFC7926].
This framework document does not assume any particular technology
layer at which IETF Network Slices operate. A number of layers
(including virtual L2, Ethernet, or IP connectivity) could be
employed.
Data models and interfaces are needed to set up IETF Network Slices,
and specific interfaces may have capabilities that allow creation of
slices within specific technology layers.
Layered virtual connections are comprehensively discussed in other
IETF documents. For instance, GMPLS-based networks are discussed in
[RFC5212] and [RFC4397], and Abstraction and Control of TE Networks
(ACTN) is discussed in [RFC8453] and [RFC8454]. The principles and
mechanisms associated with layered networking are applicable to IETF
Network Slices.
There are several IETF-defined mechanisms for expressing the need for
a desired logical network. The IETF Network Slice Service Interface
carries data either in a protocol-defined format or in a formalism
associated with a modeling language.
For instance:
* The Path Computation Element (PCE) Communication Protocol (PCEP)
[RFC5440] and GMPLS User-Network Interface (UNI) using RSVP-TE
[RFC4208] use a TLV-based binary encoding to transmit data.
* The Network Configuration Protocol (NETCONF) [RFC6241] and
RESTCONF Protocol [RFC8040] use XML and JSON encoding.
* gRPC and gRPC Network Management Interface (gNMI) [GNMI] use a
binary encoded programmable interface. ProtoBufs can be used to
model gRPC and gNMI data.
* For data modeling, YANG [RFC6020] [RFC7950] may be used to model
configuration and other data for NETCONF, RESTCONF, and gNMI,
among others.
While several generic formats and data models for specific purposes
exist, it is expected that IETF Network Slice management may require
enhancement or augmentation of existing data models. Further, it is
possible that mechanisms will be needed to determine the feasibility
of service requests before they are actually made.
6.3. IETF Network Slice Controller (NSC)
An IETF NSC takes requests for IETF Network Slice Services and
implements them using a suitable underlay technology. An IETF NSC is
the key component for control and management of the IETF Network
Slice. It provides the creation/modification/deletion, monitoring,
and optimization of IETF Network Slices in a multi-domain, multi-
technology, and multi-vendor environment.
The main task of an IETF NSC is to map abstract IETF Network Slice
Service requirements to concrete technologies and establish required
connectivity, ensuring that resources are allocated to the IETF
Network Slice as necessary.
The IETF Network Slice Service Interface is used for communicating
details of an IETF Network Slice Service (configuration, selected
policies, operational state, etc.) as well as information about
status and performance of the IETF Network Slice. The details for
this IETF Network Slice Service Interface are not in scope for this
document, but further considerations of the requirements are
discussed in [USE-CASES].
The controller provides the following functions.
* Exposes an IETF Network Slice Service Interface for
creation/modification/deletion of the IETF Network Slices that are
agnostic to the technology of the underlay network. This API
communicates the Service Demarcation Points of the IETF Network
Slice, SLO parameters (and possibly monitoring thresholds),
applicable input selection (filtering), and various policies. If
SLEs have been agreed between the customer and the network
operator, and if they are supported for the IETF Network Slice
Service, the API will also allow SLEs to be selected for the IETF
Network Slice and will allow any associated parameters to be set.
The API also provides a way to monitor the slice.
* Determines an abstract topology connecting the SDPs of the IETF
Network Slice that meets criteria specified via the IETF Network
Slice Service Interface. The NSC also retains information about
the mapping of this abstract topology to underlay components of
the IETF Network Slice as necessary to monitor IETF Network Slice
status and performance.
* Supports "Mapping Functions" for the realization of IETF Network
Slices. In other words, it will use the mapping functions that:
- Map IETF Network Slice Service Interface requests that are
agnostic to the technology of the underlay network to
technology-specific network configuration interfaces.
- Map filtering/selection information to entities in the underlay
network so that those entities are able to identify which
traffic is associated with which connectivity construct and
IETF Network Slice.
- Depending on the realization solution, map to entities in the
underlay network according to how traffic should be treated to
meet the SLOs and SLEs of the connectivity construct.
* Collects telemetry data (e.g., Operations, Administration, and
Maintenance (OAM) results, statistics, states, etc.) via a network
configuration interface for all elements in the abstract topology
used to realize the IETF Network Slice.
* Evaluates the current performance against IETF Network Slice SLO
parameters using telemetry data from the underlying realization of
an IETF Network Slice (e.g., services, paths, and tunnels).
Exposes this performance to the IETF Network Slice Service
customer via the IETF Network Slice Service Interface. The IETF
Network Slice Service Interface may also include the capability to
provide notifications if the IETF Network Slice performance
reaches threshold values defined by the IETF Network Slice Service
customer.
6.3.1. IETF Network Slice Controller Interfaces
The interworking and interoperability among the different
stakeholders to provide common means of provisioning, operating, and
monitoring the IETF Network Slices is enabled by the following
communication interfaces (see Figure 2).
IETF Network Slice Service Interface: An interface between a
customer's higher-level operation system (e.g., a network slice
orchestrator or a customer network management system) and an NSC.
It is agnostic to the technology of the underlay network. The
customer can use this interface to communicate the requested
characteristics and other requirements for the IETF Network Slice
Service, and an NSC can use the interface to report the
operational state of an IETF Network Slice Service to the
customer. More discussion of the functionalities for the IETF
Network Slice Service Interface can be found in [USE-CASES].
Network Configuration Interface: An interface between an NSC and
network controllers. It is technology specific and may be built
around the many network models already defined within the IETF.
These interfaces can be considered in the context of the Service
Model and Network Service Model described in [RFC8309] and, together
with the Device Configuration Interface used by the Network
Controllers, provides a consistent view of service delivery and
realization.
+------------------------------------------+
| Customer higher-level operation system |
| (e.g., E2E network slice orchestrator, |
| customer network management system) |
+------------------------------------------+
A
| IETF Network Slice Service Interface
V
+------------------------------------------+
| IETF Network Slice Controller (NSC) |
+------------------------------------------+
A
| Network Configuration Interface
V
+------------------------------------------+
| Network Controllers |
+------------------------------------------+
Figure 2: Interfaces of the IETF Network Slice Controller
6.3.1.1. IETF Network Slice Service Interface
The IETF Network Slice Controller provides an IETF Network Slice
Service Interface that allows customers to manage IETF Network Slice
Services. Customers operate on abstract IETF Network Slice Services,
with details related to their realization hidden.
The IETF Network Slice Service Interface is also independent of the
type of network functions or services that need to be connected,
i.e., it is independent of any specific storage, software, protocol,
or platform used to realize physical or virtual network connectivity
or functions in support of IETF Network Slices.
The IETF Network Slice Service Interface uses protocol mechanisms and
information passed over those mechanisms to convey desired attributes
for IETF Network Slices and their status. The information is
expected to be represented as a well-defined data model and should
include at least SDP and connectivity information, SLO/SLE
specification, and status information.
6.3.2. Management Architecture
The management architecture described in Figure 2 may be further
decomposed as shown in Figure 3. This should also be seen in the
context of the component architecture shown in Figure 4 and
corresponds to the architecture in [RFC8309].
Note that the customer higher-level operation system of Figure 2 and
the Network Slice Orchestrator of Figure 3 may be considered
equivalent to the Service Management & Orchestration (SMO) of [ORAN].
--------------
| Network |
| Slice |
| Orchestrator |
--------------
| IETF Network Slice
| Service Request
| Customer view
....|................................
-v------------------- Operator view
|Controller |
| ------------ |
| | IETF | |
| | Network | |--> Virtual Network
| | Slice | |
| | Controller | |
| | (NSC) | |
| ------------ |
..| | Network |............
| | Configuration | Underlay Network
| v |
| ------------ |
| | Network | |
| | Controller | |
| | (NC) | |
| ------------ |
---------------------
| Device Configuration
v
Figure 3: Interface of IETF Network Slice Management Architecture
7. Realizing IETF Network Slices
Realization of IETF Network Slices is a mapping of the definition of
the IETF Network Slice to the underlying infrastructure and is
necessarily technology specific and achieved by an NSC over the
Network Configuration Interface. Details of how realizations may be
achieved is out of scope of this document; however, this section
provides an overview of the components and processes involved in
realizing an IETF Network Slice.
7.1. An Architecture to Realize IETF Network Slices
The architecture described in this section is deliberately at a high
level. It is not intended to be prescriptive: implementations and
technical solutions may vary freely. However, this approach provides
a common framework that other documents may reference in order to
facilitate a shared understanding of the work.
Figure 4 shows the architectural components of a network managed to
provide IETF Network Slices. The customer's view is of individual
IETF Network Slice Services with their SDPs and connectivity
constructs. Requests for IETF Network Slice Services are delivered
to an NSC.
Figure 4 shows, without loss of generality, the CEs, ACs, and PEs
that exist in the network. The SDPs are not shown and can be placed
in any of the ways described in Section 5.2.
-- -- --
|CE| |CE| |CE|
-- -- --
AC : AC : AC :
---------------------- -------
( |PE|....|PE|....|PE| ) ( IETF )
IETF Network ( --: -- :-- ) ( Network )
Slice Service ( :............: ) ( Slice )
Request ( IETF Network Slice ) ( ) Customer
v ---------------------- ------- View
v ............................\........./...............
v \ / Provider
v >>>>>>>>>>>>>>> Grouping/Mapping v v View
v ^ -----------------------------------------
v ^ ( |PE|.......|PE|........|PE|.......|PE| )
--------- ( --: -- :-- -- )
| | ( :...................: )
| NSC | ( Network Resource Partition )
| | -----------------------------------------
| | ^
| |>>>>> Resource Partitioning |
--------- of Filtered Topology |
v v |
v v ----------------------------- --------
v v (|PE|..-..|PE|... ..|PE|..|PE|) ( )
v v ( :-- |P| -- :-: -- :-- ) ( Filter )
v v ( :.- -:.......|P| :- ) ( Topology )
v v ( |P|...........:-:.......|P| ) ( )
v v ( - Filtered Topology ) --------
v v ----------------------------- ^
v >>>>>>>>>>>> Topology Filter ^ /
v ...........................\............../...........
v \ / Underlay
---------- \ / (Physical)
| | \ / Network
| Network | ----------------------------------------------
|Controller| ( |PE|.....-.....|PE|...... |PE|.......|PE| )
| | ( -- |P| -- :-...:-- -..:-- )
---------- ( : -:.............|P|.........|P| )
v ( -......................:-:..- - )
>>>>>>> ( |P|.........................|P|......: )
Program the ( - - )
Network ----------------------------------------------
Figure 4: Architecture of an IETF Network Slice
The network itself (at the bottom of Figure 4) comprises an underlay
network. This could be a physical network but may be a virtual
network. The underlay network is provisioned through network
controllers [RFC8309] that may, themselves, utilize device
controllers.
The underlay network may optionally be filtered or customized by the
network operator to produce a number of network topologies that we
call "Filtered Topologies". Customization is just a way of selecting
specific resources (e.g., nodes and links) from the underlay network
according to their capabilities and connectivity in the underlay
network. Filtering and customization are configuration options or
operator policies that preselect links and nodes with certain
performance characteristics to enable easier construction of Network
Resource Partitions (NRPs; see below) that can reliably support
specific IETF Network Slice SLAs, for example, preselection of links
with certain security characteristics, preselection of links with
specific geographic properties, or mapping to colored topologies.
The resulting topologies can be used as candidates to host IETF
Network Slices and provide a useful way for the network operator to
know in advance that all of the resources they are using to plan an
IETF Network Slice would be able to meet specific SLOs and SLEs. The
creation of a Filtered Topology could be an offline planning activity
or could be performed dynamically as new demands arise. The use of
Filtered Topologies is entirely optional in the architecture, and
IETF Network Slices could be hosted directly on the underlay network.
Recall that an IETF Network Slice is a service requested by and/or
provided for the customer. The IETF Network Slice Service is
expressed in terms of one or more connectivity constructs. An
implementation or operator is free to limit the number of
connectivity constructs in an IETF Network Slice to exactly one.
Each connectivity construct is associated within the IETF Network
Slice Service request with a set of SLOs and SLEs. The set of SLOs
and SLEs does not need to be the same for every connectivity
construct in the IETF Network Slice, but an implementation or
operator is free to require that all connectivity constructs in an
IETF Network Slice have the same set of SLOs and SLEs.
An NRP is a subset of the buffer/queuing/scheduling resources and
associated policies on each of a connected set of links in the
underlay network (for example, as achieved in
[RESOURCE-AWARE-SEGMENTS]). The connected set of links could be the
entire set of links with all of their buffer/queuing/scheduling
resources and behaviors in the underlay network, and in this case,
there would be just one NRP supported in the underlay network. The
amount and granularity of resources allocated in an NRP is flexible
and depends on the operator's policy. Some NRP realizations may
build NRPs with dedicated topologies, while other realizations may
use a shared topology for multiple NRPs. Realizations of an NRP may
be built on a range of existing or new technologies, and this
document does not constrain solution technologies.
One or more connectivity constructs from one or more IETF Network
Slices are mapped to an NRP. A single connectivity construct is
mapped to only one NRP (that is, the relationship is many to one).
Thus, all traffic flows in a connectivity construct assigned to an
NRP are assigned to that NRP. Further, all PEs connected by a
connectivity construct must be present in the NRP to which that
connectivity construct is assigned.
An NRP may be chosen to support a specific connectivity construct
because of its ability to support a specific set of SLOs and SLEs,
its ability to support particular connectivity constructs, or any
administrative or operational reason. An implementation or operator
is free to map each connectivity construct to a separate NRP,
although there may be scaling implications depending on the solution
implemented. Thus, the connectivity constructs from one slice may be
mapped to one or more NRPs. By implication from the above, an
implementation or operator is free to map all the connectivity
constructs in a slice to a single NRP and to not share that NRP with
connectivity constructs from another slice.
An NRP may use work-conserving schedulers, non-work-conserving
schedulers, or both (see Section 2 of [RFC3290]) according to the
function that it needs to deliver. The choice of how network
resources are allocated and managed for an NRP, and whether a work-
conserving scheduling approach or a non-work-conserving scheduling
approach is adopted, is technology specific: an implementation or
operator is free to choose the set of techniques for NRP realization.
The process of determining the NRP may be made easier if the underlay
network topology is first filtered into a Filtered Topology in order
to be aware of the subset of network resources that are suitable for
specific NRPs. In this case, each Filtered Topology is treated as an
underlay network on which NRPs can be constructed. The stage of
generating Filtered Topologies is optional within this framework.
The steps described here can be applied in a variety of orders
according to implementation and deployment preferences. Furthermore,
the steps may be iterative so that the components are continually
refined and modified as network conditions change and as service
requests are received or relinquished, and even the underlay network
could be extended if necessary to meet the customers' demands.
7.2. Procedures to Realize IETF Network Slices
There are a number of different technologies that can be used in the
underlay, including physical connections, MPLS, Time-Sensitive
Networking (TSN), Flex-E, etc.
An IETF Network Slice can be realized in a network, using specific
underlay technology or technologies. The creation of a new IETF
Network Slice will be realized with the following steps:
1. An NSC exposes the network slicing capabilities that it offers
for the network it manages so that the customer can determine
whether to request services and what features are in scope.
2. The customer may issue a request to determine whether a specific
IETF Network Slice Service could be supported by the network. An
NSC may respond indicating a simple yes or no and may supplement
a negative response with information about what it could support
were the customer to change some requirements.
3. The customer requests an IETF Network Slice Service. An NSC may
respond that the slice has or has not been created and may
supplement a negative response with information about what it
could support were the customer to change some requirements.
4. When processing a customer request for an IETF Network Slice
Service, an NSC maps the request to the network capabilities and
applies provider policies before creating or supplementing the
NRP.
Regardless of how an IETF Network Slice is realized in the network
(e.g., using tunnels of different types), the definition of the IETF
Network Slice Service does not change at all. The only difference is
how the slice is realized. The following sections briefly introduce
how some existing architectural approaches can be applied to realize
IETF Network Slices.
7.3. Applicability of ACTN to IETF Network Slices
Abstraction and Control of TE Networks (ACTN) [RFC8453] is a
management architecture and toolkit used to create virtual networks
(VNs) on top of a TE underlay network. The VNs can be presented to
customers for them to operate as private networks.
In many ways, the function of ACTN is similar to IETF network
slicing. Customer requests for connectivity-based overlay services
are mapped to dedicated or shared resources in the underlay network
in a way that meets customer guarantees for SLOs and for separation
from other customers' traffic. [RFC8453] describes the function of
ACTN as collecting resources to establish a logically dedicated
virtual network over one or more TE networks. Thus, in the case of a
TE-enabled underlay network, the ACTN VN can be used as a basis to
realize IETF network slicing.
While the ACTN framework is a generic VN framework that can be used
for VN services beyond the IETF Network Slice, it is also a suitable
basis for delivering and realizing IETF Network Slices.
Further discussion of the applicability of ACTN to IETF Network
Slices, including a discussion of the relevant YANG models, can be
found in [ACTN-NS].
7.4. Applicability of Enhanced VPNs to IETF Network Slices
An enhanced VPN is designed to support the needs of new applications,
particularly applications that are associated with 5G services. The
approach is based on existing VPN and TE technologies but adds
characteristics that specific services require over and above those
previously associated with VPN services.
An enhanced VPN can be used to provide enhanced connectivity services
between customer sites and can be used to create the infrastructure
to underpin an IETF Network Slice Service.
It is envisaged that enhanced VPNs will be delivered using a
combination of existing, modified, and new networking technologies.
[ENHANCED-VPN] describes the framework for enhanced VPN services.
7.5. Network Slicing and Aggregation in IP/MPLS Networks
Network slicing provides the ability to partition a physical network
into multiple logical networks of varying sizes, structures, and
functions so that each slice can be dedicated to specific services or
customers. The support of resource preemption between IETF Network
Slices is deployment specific.
Many approaches are currently being worked on to support IETF Network
Slices in IP and MPLS networks with or without the use of Segment
Routing. Most of these approaches utilize a way of marking packets
so that network nodes can apply specific routing and forwarding
behaviors to packets that belong to different IETF Network Slices.
Different mechanisms for marking packets have been proposed
(including using MPLS labels and Segment Routing segment IDs), and
those mechanisms are agnostic to the path control technology used
within the underlay network.
These approaches are also sensitive to the scaling concerns of
supporting a large number of IETF Network Slices within a single IP
or MPLS network and so offer ways to aggregate the connectivity
constructs of slices (or whole slices) so that the packet markings
indicate an aggregate or grouping where all of the packets are
subject to the same routing and forwarding behavior.
At this stage, it is inappropriate to cite any of these proposed
solutions that are currently work in progress and not yet adopted as
IETF work.
7.6. Network Slicing and Service Function Chaining (SFC)
A customer may request an IETF Network Slice Service that involves a
set of service functions (SFs) together with the order in which these
SFs are invoked. Also, the customer can specify the service
objectives to be met by the underlay network (e.g., one-way delay to
cross a service function path, one-way delay to reach a specific SF).
These SFs are considered as ancillary CEs and are possibly
placeholders (i.e., the SFs are identified, but not their locators).
Service Function Chaining (SFC) [RFC7665] techniques can be used by a
provider to instantiate such an IETF Network Slice Service. An NSC
may proceed as follows.
* Expose a set of ancillary CEs that are hosted in the underlay
network.
* Capture the SFC requirements (including traffic performance
metrics) from the customer. One or more service chains may be
associated with the same IETF Network Slice Service as
connectivity constructs.
* Execute an SF placement algorithm to decide where to locate the
ancillary CEs in order to fulfill the service objectives.
* Generate SFC classification rules to identify part of the slice
traffic that will be bound to an SFC. These classification rules
may be the same as or distinct from the identification rules used
to bind incoming traffic to the associated IETF Network Slice.
An NSC also generates a set of SFC forwarding policies that govern
how the traffic will be forwarded along a Service Function Path
(SFP).
* Identify the appropriate Classifiers in the underlay network and
provision them with the classification rules. Likewise, an NSC
communicates the SFC forwarding policies to the appropriate
Service Function Forwarders (SFFs).
The provider can enable an SFC data plane mechanism, such as those
described in [RFC8300], [RFC8596], or [RFC9491].
8. Isolation in IETF Network Slices
8.1. Isolation as a Service Requirement
An IETF Network Slice Service customer may request that the IETF
Network Slice delivered to them is such that changes to other IETF
Network Slices or to other services do not have any negative impact
on the delivery of the IETF Network Slice. The IETF Network Slice
Service customer may specify the extent to which their IETF Network
Slice Service is unaffected by changes in the provider network or by
the behavior of other IETF Network Slice Service customers. The
customer may express this via an SLE it agrees with the provider.
This concept is termed "isolation".
In general, a customer cannot tell whether a service provider is
meeting an isolation SLE. If the service varies such that an SLO is
breached, then the customer will become aware of the problem, and if
the service varies within the allowed bounds of the SLOs, there may
be no noticeable indication that this SLE has been violated.
8.2. Isolation in IETF Network Slice Realization
Isolation may be achieved in the underlay network by various forms of
resource partitioning, ranging from dedicated allocation of resources
for a specific IETF Network Slice to sharing of resources with
safeguards. For example, traffic separation between different IETF
Network Slices may be achieved using VPN technologies, such as L3VPN,
L2VPN, EVPN, etc. Interference avoidance may be achieved by network
capacity planning, allocating dedicated network resources, traffic
policing or shaping, prioritizing in using shared network resources,
etc. Finally, service continuity may be ensured by reserving backup
paths for critical traffic and dedicating specific network resources
for a selected number of IETF Network Slices.
9. Management Considerations
IETF Network Slice realization needs to be instrumented in order to
track how it is working, and it might be necessary to modify the IETF
Network Slice as requirements change. Dynamic reconfiguration might
be needed.
The various management interfaces and components are discussed in
Section 6.
10. Security Considerations
This document specifies terminology and has no direct effect on the
security of implementations or deployments. In this section, a few
of the security aspects are identified.
Conformance to security constraints: Specific security requests from
customer-defined IETF Network Slice Services will be mapped to
their realization in the underlay networks. Underlay networks
will require capabilities to conform to customer's requests as
some aspects of security may be expressed in SLEs.
IETF NSC authentication: Underlay networks need to be protected
against attacks from an adversary NSC as this could destabilize
overall network operations. An IETF Network Slice may span
different networks; therefore, an NSC should have strong
authentication with each of these networks. Furthermore, both the
IETF Network Slice Service Interface and the Network Configuration
Interface need to be secured with a robust authentication and
authorization mechanism and associated auditing mechanism.
Specific isolation criteria: The nature of conformance to isolation
requests means that it should not be possible to attack an IETF
Network Slice Service by varying the traffic on other services or
slices carried by the same underlay network. In general,
isolation is expected to strengthen the IETF Network Slice
security.
Data confidentiality and integrity of an IETF Network Slice: An IETF
Network Slice might include encryption and other security features
as part of the service (for example, as SLEs). However, a
customer wanting to guarantee that their data is secure from
inspection or modification as it passes through the network of the
operator that provides the IETF Network Slice Service will need to
provision their own security solutions (e.g., with IPsec) or send
only already otherwise-encrypted traffic through the slice.
See [NGMN-SEC] on 5G network slice security for discussion relevant
to this section.
IETF Network Slices might use underlying virtualized networking. All
types of virtual networking require special consideration to be given
to the separation of traffic between distinct virtual networks, as
well as some amount of protection from effects of traffic use of
underlay network (and other) resources from other virtual networks
sharing those resources.
For example, if a service requires a specific upper bound on latency,
then that service could be degraded with added delay caused by the
processing of packets from another service or application that shares
the same network resources. Thus, without careful planning or
traffic policing, it may be possible to attack an IETF Network Slice
Service simply by increasing the traffic on another service in the
network.
Similarly, in a network with virtual functions, noticeably impeding
access to a function used by another IETF Network Slice (for
instance, compute resources) can be just as service-degrading as
delaying physical transmission of associated packet in the network.
Again, careful planning and policing of service demands may mitigate
such attacks.
Both of these forms of attack may also be mitigated by reducing the
access to information about how IETF Network Slice Services are
supported in a network.
11. Privacy Considerations
Privacy of IETF Network Slice Service customers must be preserved.
It should not be possible for one IETF Network Slice Service customer
to discover the presence of other customers, nor should sites that
are members of one IETF Network Slice be visible outside the context
of that IETF Network Slice.
In this sense, it is of paramount importance that the system uses the
privacy protection mechanism defined for the specific underlay
technologies that support the slice, including in particular those
mechanisms designed to preclude acquiring identifying information
associated with any IETF Network Slice Service customer.
12. IANA Considerations
This document has no IANA actions.
13. Informative References
[ACTN-NS] King, D., Drake, J., Zheng, H., and A. Farrel,
"Applicability of Abstraction and Control of Traffic
Engineered Networks (ACTN) to Network Slicing", Work in
Progress, Internet-Draft, draft-ietf-teas-applicability-
actn-slicing-05, 11 February 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-
applicability-actn-slicing-05>.
[ENHANCED-VPN]
Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
Framework for NRP-based Enhanced Virtual Private Network",
Work in Progress, Internet-Draft, draft-ietf-teas-
enhanced-vpn-17, 25 December 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-
enhanced-vpn-17>.
[GNMI] Shakir, R., Shaikh, A., Borman, P., Hines, M., Lebsack,
C., and C. Morrow, "gRPC Network Management Interface
(gNMI)", Work in Progress, Internet-Draft, draft-
openconfig-rtgwg-gnmi-spec-01, 5 March 2018,
<https://datatracker.ietf.org/doc/html/draft-openconfig-
rtgwg-gnmi-spec-01>.
[HIPAA] HHS, "The Security Rule", <https://www.hhs.gov/hipaa/for-
professionals/security/index.html>.
[MACsec] IEEE, "IEEE Standard for Local and metropolitan area
networks - Media Access Control (MAC) Security", IEEE Std
802.1AE-2018, DOI 10.1109/IEEESTD.2018.8585421, December
2018, <https://ieeexplore.ieee.org/document/8585421>.
[NFVArch] ETSI, "Network Functions Virtualisation (NFV);
Architectural Framework", V1.1.1, ETSI GS NFV 002, October
2013, <http://www.etsi.org/deliver/etsi_gs/
nfv/001_099/002/01.01.01_60/gs_nfv002v010101p.pdf>.
[NGMN-NS-Concept]
NGMN Alliance, "Description of Network Slicing Concept",
January 2016, <https://ngmn.org/wp-content/
uploads/160113_NGMN_Network_Slicing_v1_0.pdf>.
[NGMN-SEC] NGMN, "5G security recommendations Package #2 - Network
Slicing", April 2016, <https://www.ngmn.org/wp-
content/uploads/Publications/2016/160429_NGMN_5G_Security_
Network_Slicing_v1_0.pdf>.
[ORAN] O-RAN, "O-RAN Working Group 1 Slicing Architecture",
O-RAN.WG1 v06.00, 2022,
<https://orandownloadsweb.azurewebsites.net/
specifications>.
[PCI] PCI Security Standards Council, "PCI DSS", March 2022,
<https://www.pcisecuritystandards.org/document_library>.
[RESOURCE-AWARE-SEGMENTS]
Dong, J., Miyasaka, T., Zhu, Y., Qin, F., and Z. Li,
"Introducing Resource Awareness to SR Segments", Work in
Progress, Internet-Draft, draft-ietf-spring-resource-
aware-segments-08, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
resource-aware-segments-08>.
[RFC3290] Bernet, Y., Blake, S., Grossman, D., and A. Smith, "An
Informal Management Model for Diffserv Routers", RFC 3290,
DOI 10.17487/RFC3290, May 2002,
<https://www.rfc-editor.org/info/rfc3290>.
[RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation
Metric for IP Performance Metrics (IPPM)", RFC 3393,
DOI 10.17487/RFC3393, November 2002,
<https://www.rfc-editor.org/info/rfc3393>.
[RFC4208] Swallow, G., Drake, J., Ishimatsu, H., and Y. Rekhter,
"Generalized Multiprotocol Label Switching (GMPLS) User-
Network Interface (UNI): Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Support for the Overlay
Model", RFC 4208, DOI 10.17487/RFC4208, October 2005,
<https://www.rfc-editor.org/info/rfc4208>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.
[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>.
[RFC4397] Bryskin, I. and A. Farrel, "A Lexicography for the
Interpretation of Generalized Multiprotocol Label
Switching (GMPLS) Terminology within the Context of the
ITU-T's Automatically Switched Optical Network (ASON)
Architecture", RFC 4397, DOI 10.17487/RFC4397, February
2006, <https://www.rfc-editor.org/info/rfc4397>.
[RFC5212] Shiomoto, K., Papadimitriou, D., Le Roux, JL., Vigoureux,
M., and D. Brungard, "Requirements for GMPLS-Based Multi-
Region and Multi-Layer Networks (MRN/MLN)", RFC 5212,
DOI 10.17487/RFC5212, July 2008,
<https://www.rfc-editor.org/info/rfc5212>.
[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>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<https://www.rfc-editor.org/info/rfc6020>.
[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>.
[RFC7239] Petersson, A. and M. Nilsson, "Forwarded HTTP Extension",
RFC 7239, DOI 10.17487/RFC7239, June 2014,
<https://www.rfc-editor.org/info/rfc7239>.
[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665,
DOI 10.17487/RFC7665, October 2015,
<https://www.rfc-editor.org/info/rfc7665>.
[RFC7679] Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
Ed., "A One-Way Delay Metric for IP Performance Metrics
(IPPM)", STD 81, RFC 7679, DOI 10.17487/RFC7679, January
2016, <https://www.rfc-editor.org/info/rfc7679>.
[RFC7680] Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
Ed., "A One-Way Loss Metric for IP Performance Metrics
(IPPM)", STD 82, RFC 7680, DOI 10.17487/RFC7680, January
2016, <https://www.rfc-editor.org/info/rfc7680>.
[RFC7926] Farrel, A., Ed., Drake, J., Bitar, N., Swallow, G.,
Ceccarelli, D., and X. Zhang, "Problem Statement and
Architecture for Information Exchange between
Interconnected Traffic-Engineered Networks", BCP 206,
RFC 7926, DOI 10.17487/RFC7926, July 2016,
<https://www.rfc-editor.org/info/rfc7926>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[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>.
[RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
"Network Service Header (NSH)", RFC 8300,
DOI 10.17487/RFC8300, January 2018,
<https://www.rfc-editor.org/info/rfc8300>.
[RFC8309] Wu, Q., Liu, W., and A. Farrel, "Service Models
Explained", RFC 8309, DOI 10.17487/RFC8309, January 2018,
<https://www.rfc-editor.org/info/rfc8309>.
[RFC8453] Ceccarelli, D., Ed. and Y. Lee, Ed., "Framework for
Abstraction and Control of TE Networks (ACTN)", RFC 8453,
DOI 10.17487/RFC8453, August 2018,
<https://www.rfc-editor.org/info/rfc8453>.
[RFC8454] Lee, Y., Belotti, S., Dhody, D., Ceccarelli, D., and B.
Yoon, "Information Model for Abstraction and Control of TE
Networks (ACTN)", RFC 8454, DOI 10.17487/RFC8454,
September 2018, <https://www.rfc-editor.org/info/rfc8454>.
[RFC8596] Malis, A., Bryant, S., Halpern, J., and W. Henderickx,
"MPLS Transport Encapsulation for the Service Function
Chaining (SFC) Network Service Header (NSH)", RFC 8596,
DOI 10.17487/RFC8596, June 2019,
<https://www.rfc-editor.org/info/rfc8596>.
[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>.
[RFC9491] Guichard, J., Ed. and J. Tantsura, Ed., "Integration of
the Network Service Header (NSH) and Segment Routing for
Service Function Chaining (SFC)", RFC 9491,
DOI 10.17487/RFC9491, November 2023,
<https://www.rfc-editor.org/info/rfc9491>.
[TS23.501] 3GPP, "System architecture for the 5G System (5GS)", 3GPP
TS 23.501, 2019.
[TS28.530] 3GPP, "Management and orchestration; Concepts, use cases
and requirements", 3GPP TS 28.530, 2019.
[TS33.210] 3GPP, "Network Domain Security (NDS); IP network layer
security", Release 14, December 2016,
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=2279>.
[USE-CASES]
Contreras, L. M., Homma, S., Ordonez-Lucena, J. A.,
Tantsura, J., and H. Nishihara, "IETF Network Slice Use
Cases and Attributes for the Slice Service Interface of
IETF Network Slice Controllers", Work in Progress,
Internet-Draft, draft-ietf-teas-ietf-network-slice-use-
cases-01, 24 October 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-
ietf-network-slice-use-cases-01>.
Appendix A. Examples
This appendix contains realization examples. This is not intended to
be a complete set of possible deployments, nor does it provide
definitive ways to realize these deployments.
The examples shown here must not be considered to be normative. The
descriptions of terms and concepts in the body of the document take
precedence.
A.1. Multi-Point to Point Service
As described in Section 4.2, an MP2P service can be realized with
multiple P2P connectivity constructs. Figure 5 shows a simple MP2P
service where traffic is sent from any of CE1, CE2, and CE3 to the
receiver, which is CE4. The service comprises three P2P connectivity
constructs: CE1-CE4, CE2-CE4, and CE3-CE4.
CE1
___|________
/ \ \
( \______ )
( \)
CE2---(--------------)---CE4
( _______/)
( / )
\___|________/
|
CE3
Figure 5: Example MP2P Service with P2P Connections
A.2. Service Function Chaining and Ancillary CEs
Section 4.2.3 introduces the concept of ancillary CEs. Figure 6
shows a simple example of IETF Network Slices with connectivity
constructs that are used to deliver traffic from CE1 to CE3, taking
in a service function along the path.
CE1 CE2 CE3
xo* * * *ox
____xo*_________*_*_________*ox____
_/ xo* * * *ox \_
/ xo*********** ***********ox \
( xo ox )
( xooooooooo(ACE1)oooooooooox )
( x x )
( x ------------------ x )
( x | Service Function | x )
( x | ....(ACE2).... | x )
( x | : : | x )
( xxxx.:....(ACE3)....:.xxxxx )
( | : : | )
( | ....(ACE4).... | )
( | | )
( ------------------ )
( )
\_ Operator Network _/
\___________________________________/
Figure 6: Example with Ancillary CEs
A customer may want to utilize a service where traffic is delivered
from CE1 to CE3, including a service function sited within the
customer's network at CE2. To achieve this, the customer may request
an IETF Network Slice Service comprising two P2P connectivity
constructs: CE1-CE2 and CE2-CE3 (represented with "*" in Figure 6).
Alternatively, the service function for the same CE1 to CE3 flow may
be hosted at a node within the network operator's infrastructure.
This is an ancillary CE in the IETF Network Slice Service that the
customer requests. This service contains two P2P connectivity
constructs: CE1-ACE1 and ACE1-CE3 (represented with "o" in Figure 6).
How the customer knows of the existence of the ancillary CE and the
service functions it offers is a matter for agreement between the
customer and the network operator.
Finally, it may be that the customer knows that the network operator
is able to provide the service function but does not know the
location of the ancillary CE at which the service function is hosted.
Indeed, it may be that the service function is hosted at a number of
ancillary CEs (ACE2, ACE3, and ACE4 in Figure 6); the customer may
know the identities of the ancillary CEs but be unwilling or unable
to choose one, or the customer may not know about the ancillary CEs.
In this case, the IETF Network Slice Service request contains two P2P
connectivity constructs: CE1-ServiceFunction and ServiceFunction-CE3
(represented with "x" in Figure 6). It is left as a choice for the
network operator as to which ancillary CE to use and how to realize
the connectivity constructs.
A.3. Hub and Spoke
Hub and spoke is a popular way to realize A2A connectivity in support
of multiple P2P traffic flows (where the hub performs routing) or
P2MP flows (where the hub is responsible for replication). In many
cases, it is the network operator's choice whether to use hub and
spoke to realize a mesh of P2P connectivity constructs or P2MP
connectivity constructs; this is entirely their business as the
customer is not aware of how the connectivity constructs are
supported within the network.
However, it may be the case that the customer wants to control the
behavior and location of the hub. In this case, the hub appears as
an ancillary CE as shown in Figure 7.
For the P2P mesh case, the customer does not specify a mesh of P2P
connectivity constructs (such as CE1-CE2, CE1-CE3, CE2-CE3, and the
equivalent reverse direction connectivity) but connects each CE to
the hub with P2P connectivity constructs (as CE1-Hub, CE2-Hub,
CE3-Hub, and the equivalent reverse direction connectivity). This
scales better in terms of provisioning compared to a full mesh but
requires that the hub is capable of routing traffic between
connectivity constructs.
For the P2MP case, the customer does not specify a single P2MP
connectivity construct (in this case, CE3-{CE1+CE2}) but requests
three P2P connectivity constructs (as CE3-Hub, Hub-CE1, and Hub-CE2).
It is the hub's responsibility to replicate the traffic from CE3 and
send it to both CE1 and CE2.
------------
CE1 | Hub | CE2
|| ------------ ||
___||_____||__||__||_____||___
/ || || || || || \
( ====== || ====== )
( || )
( || )
\______________||______________/
||
CE3
Figure 7: Example Hub and Spoke under Customer Control
A.4. Layer 3 VPN
Layer 3 VPNs are a common service offered by network operators to
their customers. They may be modeled as an A2A service but are often
realized as a mesh of P2P connections, or if multicast is supported,
they may be realized as a mesh of P2MP connections.
Figure 8 shows an IETF Network Slice Service with a single A2A
connectivity construct between the SDPs CE1, CE2, CE3, and CE4. It
is a free choice how the network operator realizes this service.
They may use a full mesh of P2P connections, a hub-and-spoke
configuration, or some combination of these approaches.
CE1 CE2
____|_______________|____
/ :...............: \
( :. . : )
( : ...... . : )
( : ..... : )
( : .... . : )
( : . .... : )
( : . . : )
( :...............: )
\____:_______________:____/
| |
CE3 CE4
Figure 8: Example L3VPN Service
A.5. Hierarchical Composition of Network Slices
As mentioned in Section 5.3, IETF Network Slices may be arranged
hierarchically. There is nothing special or novel about such an
arrangement, and it models the hierarchical arrangement of services
of virtual networks in many other environments.
As shown in Figure 9, an Operator's Controller (NSC) that is
requested to provide an IETF Network Slice Service for a customer
may, in turn, request an IETF Network Slice Service from another
carrier. The Operator's NSC may manage and control the underlay IETF
Network Slice by modifying the requested connectivity constructs and
changing the SLAs. The customer is entirely unaware of the hierarchy
of slices, and the underlay carrier is entirely unaware of how its
slice is being used.
This stacking of IETF Network Slice constructs is not different to
the way virtual networks may be arranged.
--------------
| Network |
| Slice |
| Orchestrator |
--------------
| IETF Network Slice
| Service Request
| Customer view
....|................................
-v---------------- Operator view
|Controller |
| ------------ |
| | IETF | |
| | Network |---|---
| | Slice | | |
| | Controller | | |
| | (NSC) | | |
| ------------ | |
------------------ |
| IETF Network Slice
| Service Request
|
.........................|.....................
----------v------- Carrier view
|Controller |
| ------------ |
| | IETF | |
| | Network | |
| | Slice | |
| | Controller | |
| | (NSC) | |
| ------------ |
....| | Network |............
| | Configuration | Underlay Network
| v |
| ------------ |
| | Network | |
| | Controller | |
| | (NC) | |
| ------------ |
------------------
| Device Configuration
v
Figure 9: Example Hierarchical Arrangement of IETF Network Slices
In this case, the network hierarchy may also be used to provide
connectivity between points in the higher-layer network, as shown in
Figure 10. Here, an IETF Network Slice may be requested of the
lower-layer network to provide the desired connectivity constructs to
supplement the connectivity in the higher-layer network where this
connectivity might be presented as a virtual link.
CE1 CE2
| |
| |
_|_________________________________________|_
( : : )
( :.............. ..............: )
(_______________:_____________:_______________)
__|_____________|__
( : : )
( :.............: )
(___________________)
Figure 10: Example Hierarchical Arrangement of IETF Network
Slices to Bridge Connectivity
A.6. Horizontal Composition of Network Slices
It may be that end-to-end connectivity is achieved using a set of
cooperating networks as described in Section 5.3. For example, there
may be multiple interconnected networks that provide the required
connectivity as shown in Figure 11. The networks may utilize
different technologies and may be under separate administrative
control.
CE1 CE2
| |
SDP1 SDP2
| |
_|____ ______ ______ ____|_
( ) ( ) ( ) ( )
( )---( )---( )---( )
(______) (______) (______) (______)
Figure 11: Example Customer View of Interconnected Networks
Providing End-to-End Connectivity
In this scenario, the customer (represented by CE1 and CE2) may
request an IETF Network Slice Service connecting the CEs. The
customer considers the SDPs at the edge (shown as SDP1 and SDP2 in
Figure 11) and might not be aware of how the end-to-end connectivity
is composed.
However, because the various networks may be of different
technologies and under separate administrative control, the networks
are sliced individually, and coordination is necessary to deliver the
desired connectivity. The Network-to-Network Interfaces (NNIs) are
present as SDPs for the IETF Network Slices in each network, so that
each network is individually sliced. In the example in Figure 12,
this is illustrated as network 1 (N/w1) being sliced between SDP1 and
SDPX, N/w2 being sliced between SDPY and SDPU, etc. The coordination
activity involves binding the SDPs, and hence the connectivity
constructs, to achieve end-to-end connectivity with the required SLOs
and SLEs. In this way, simple and complex end-to-end connectivity
can be achieved with a variety of connectivity constructs in the IETF
Network Slices of different networks "stitched" together.
CE1 CE2
| |
SDP1 SDP2
| |
_|____ ______ ______ ____|_
( ) SDPX ( ) SDPU ( ) SDPS ( )
( N/w1 )------( N/w2 )------( N/w3 )------( N/w4 )
(______) SDPY (______) SDPV (______) SDPT (______)
Figure 12: Example Delivery of an End-to-End IETF Network Slice with
Interconnected Networks
The controller/coordinator relationship is shown in Figure 13.
--------------
| Network |
| Slice |
| Orchestrator |
--------------
| IETF Network Slice
| Service Request
| Customer view
....|................................
-v---------------- Coordinator view
|Coordinator |
| |
------------------
| |_________________
| |
| |
....|....................... ....|.....................
-v-------------- -v--------------
|Controller1 | Operator1 |Controller2 | Operator2
| ------------ | | ------------ |
| | IETF | | | | IETF | |
| | Network | | | | Network | |
| | Slice | | | | Slice | |
| | Controller | | | | Controller | |
| | (NSC) | | | | (NSC) | |
| ------------ | | ------------ |
....| | Network |............ | | Network |............
| | Config | Underlay1 | | Config | Underlay2
| v | | v |
| ------------ | | ------------ |
| | Network | | | | Network | |
| | Controller | | | | Controller | |
| | (NC) | | | | (NC) | |
| ------------ | | ------------ |
---------------- ----------------
| Device Configuration
v
Figure 13: Example Relationship of IETF Network Slice Coordination
Acknowledgments
The entire TEAS Network Slicing design team and everyone
participating in related discussions has contributed to this
document. Some text fragments in the document have been copied from
the [ENHANCED-VPN], for which we are grateful.
Significant contributions to this document were gratefully received
from the contributing authors listed in the "Contributors" section.
In addition, we would like to also thank those others who have
attended one or more of the design team meetings, including the
following people not listed elsewhere:
* Aihua Guo
* Bo Wu
* Greg Mirsky
* Lou Berger
* Rakesh Gandhi
* Ran Chen
* Sergio Belotti
* Stewart Bryant
* Tomonobu Niwa
* Xuesong Geng
Further useful comments were received from Daniele Ceccarelli, Uma
Chunduri, Pavan Beeram, Tarek Saad, Kenichi Ogaki, Oscar Gonzalez de
Dios, Xiaobing Niu, Dan Voyer, Igor Bryskin, Luay Jalil, Joel
Halpern, John Scudder, John Mullooly, Krzysztof Szarkowicz, Jingrong
Xie, Jia He, Reese Enghardt, Dirk Von Hugo, Erik Kline, and Éric
Vyncke.
This work is partially supported by the European Commission under
Horizon 2020 grant agreement number 101015857 Secured autonomic
traffic management for a Tera of SDN flows (Teraflow).
Contributors
The following people contributed substantially to the content of this
document and should be considered coauthors. Eric Gray was the
original editor of the foundation documents.
Eric Gray
Retired
Jari Arkko
Ericsson
Email: jari.arkko@piuha.net
Mohamed Boucadair
Orange
Email: mohamed.boucadair@orange.com
Dhruv Dhody
Huawei
India
Email: dhruv.ietf@gmail.com
Jie Dong
Huawei
Email: jie.dong@huawei.com
Xufeng Liu
Volta Networks
Email: xufeng.liu.ietf@gmail.com
Authors' Addresses
Adrian Farrel (editor)
Old Dog Consulting
United Kingdom
Email: adrian@olddog.co.uk
John Drake (editor)
Individual
United States of America
Email: je_drake@yahoo.com
Reza Rokui
Ciena
Email: rrokui@ciena.com
Shunsuke Homma
NTT
Japan
Email: shunsuke.homma.ietf@gmail.com
Kiran Makhijani
Futurewei
United States of America
Email: kiran.ietf@gmail.com
Luis M. Contreras
Telefonica
Spain
Email: luismiguel.contrerasmurillo@telefonica.com
Jeff Tantsura
Nvidia
Email: jefftant.ietf@gmail.com