Internet DRAFT - draft-qiang-netslices-gap-analysis
draft-qiang-netslices-gap-analysis
none L. Qiang, Ed.
Internet-Draft Huawei
Intended status: Informational P. Martinez-Julia
Expires: January 4, 2018 NICT
L. Geng
China Mobile
J. Dong
K. Makhijani
Huawei
A. Galis
University College London
S. Hares
Hickory Hill Consulting
S. Kuklinski
Orange
July 3, 2017
Gap Analysis for Transport Network Slicing
draft-qiang-netslices-gap-analysis-01
Abstract
This document presents network slicing differentiation from the non-
partition network or from simply partition of connectivity resources.
It lists 7 standardization gaps related to 4 key requirements for
network slicing in transport network. It also presents an analysis
of existing related work and other potential solutions on network
slicing.
This gap analysis document aims to provide a basis for future works
in transport network slicing.
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This Internet-Draft will expire on January 4, 2018.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology and Abbreviation . . . . . . . . . . . . . . . . 4
3. Overall Requirements in Network Slicing . . . . . . . . . . . 4
4. Network Slicing Specification . . . . . . . . . . . . . . . . 7
4.1. Description . . . . . . . . . . . . . . . . . . . . . . . 7
4.2. Related Work in IETF . . . . . . . . . . . . . . . . . . 8
4.2.1. YANG Data Models . . . . . . . . . . . . . . . . . . 8
4.2.2. Building NSS from Protocol Independent Traffic
Engineering Models . . . . . . . . . . . . . . . . . 9
5. Network Slicing Cross-Domain Coordination . . . . . . . . . . 10
5.1. Description . . . . . . . . . . . . . . . . . . . . . . . 10
5.2. Related Work in IETF . . . . . . . . . . . . . . . . . . 11
5.2.1. Autonomic Networking Integrated Model and Approach
(ANIMA) . . . . . . . . . . . . . . . . . . . . . . . 11
5.2.2. Connectivity Provisioning Negotiation Protocol (CPNP) 12
5.2.3. Abstraction and Control of Traffic Engineered
Networks (ACTN) . . . . . . . . . . . . . . . . . . . 13
5.3. Other Potential Solutions . . . . . . . . . . . . . . . . 14
6. Network Slicing Performance Guarantee and Isolation . . . . . 14
6.1. Description . . . . . . . . . . . . . . . . . . . . . . . 14
6.2. Related Work in IETF . . . . . . . . . . . . . . . . . . 15
6.2.1. Virtual Private Networks . . . . . . . . . . . . . . 15
6.2.2. NVO3 . . . . . . . . . . . . . . . . . . . . . . . . 15
6.2.3. RSVP-TE . . . . . . . . . . . . . . . . . . . . . . . 15
6.2.4. Segment Routing . . . . . . . . . . . . . . . . . . . 16
6.2.5. Deterministic Networking . . . . . . . . . . . . . . 16
6.2.6. Flexible Ethernet . . . . . . . . . . . . . . . . . . 17
7. Network Slicing OAM with Customized Granularity . . . . . . . 17
7.1. Description . . . . . . . . . . . . . . . . . . . . . . . 17
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7.2. Related Work in IETF . . . . . . . . . . . . . . . . . . 18
7.2.1. Overview of OAM tools . . . . . . . . . . . . . . . . 18
7.2.2. Overlay OAM . . . . . . . . . . . . . . . . . . . . . 19
7.2.3. Service Function Chaining . . . . . . . . . . . . . . 19
7.2.4. Slice Identification . . . . . . . . . . . . . . . . 19
8. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
9. Security Considerations . . . . . . . . . . . . . . . . . . . 21
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
12.1. Normative References . . . . . . . . . . . . . . . . . . 22
12.2. Informative References . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26
1. Introduction
Network slicing is an approach to enable flexible isolation of
network resources and functions for dedicated services, providing a
certain level of customization and quality guarantee. It establishes
customized dedicated network upon a common infrastructure for
vertical industries with flexible design of functions, different
performance requirements, system isolation and OAM tools.
Several SDOs have investigated network slicing. To list a few: NGMN
initiated a study of network slicing in the context of 5G from the
mobile network point of view [NGMN-2016]. Around the same time ITU-T
IMT 2020 and ITU-T SG13 studied network softwarization that also
included network slicing concept. ITU-T has issued a number of
recommendations, such as: Gap Analysis [IMT2020-2015], Network
Softwarization [IMT2020-2016], Terms & Definitions [IMT2020-2016bis].
Open Network Foundation (ONF) has developed a recommendation on
applying SDN architecture to Network Slicing [ONF-2016]. Finally,
3GPP standards development for 5G includes network slicing in radio
access and core networks. 3GPP issued TS 23.501 [TS23-501] about the
system architecture for 5G in 2017. BBF started the project SD-406
focusing on the end-to-end architecture enhancement and requirements
gathering for transport networks. Although these SDOs have done a
lot of work, potential requirements especially in the transport
network and end-to-end enabling need to be investigated in order to
elicit and identify the technical gaps in IETF for transport network
slicing.
In order to establish a network slice that meets various customer's
demands, an infrastructure owner needs to understand how these
demands map with the available network resources and accessible
capabilities. This also requires end-to-end coverage and inter-
domain coordination. Meanwhile, the slice provider provides
customized OAM to the tenants under provisioning. Slicing OAM
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approach is a fundamental capability to guarantee stable, effective
and reliable services for the vertical industries. It is also
expected to be capable of operations with customized granularity
levels that provides robust management flexibilities.
This document presents the identified key requirements and
investigates potential technical gaps accordingly. To assist
understanding of this document, Section 2 outlines the terminology.
Section 3 introduces overall requirements of network slicing.
Sections 4~7 illustrates resource specification, end-to-end
consideration, performance guarantee and OAM concerns respectively.
Section 8 summarizes the identified gaps.
2. Terminology and Abbreviation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.
All of the network slicing related words used in this document are to
interpreted as described in [NS-Framework]
3. Overall Requirements in Network Slicing
This section introduces 4 key requirements of network slicing derived
from [NS-UseCase] as shown in Table 1. These 4 requirements are
organized according to a general network slice working process as
shown in Figure 1:
1: describe network slicing resource/functions and capture
requirements (Req. 1)
2: network slicing cross-domain coordination (Req. 2)
3: construct a performance guaranteed and isolated end-to-end
network slice (Req. 3)
4: provide necessary Operation & Maintenance & Administration (OAM)
(Req. 4)
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+----------------------------------------------------------+
| network slice management and orchestration <-----+
+----------------------^-------^---------------------------+ |
| | resource/functions
| OAM | specification
| | |
+------------------------v-------+------------------------------+ |
| abstracted network slice instance 1 | |
+--------------------------------+------------------------------+ |
| |
+--------------------------------v------------------------------+ |
| abstracted network slice instance 2 | |
+---------------------------------------------------------------+ |
|
|
+---------+ +---------+ +---------+ |
|NS-Domain| cross-domain |NS-Domain| cross-domain |NS-Domain<-----+
| Manager <--------------> Manager <--------------> Manager |
+---------+ coordination +---------+ coordination +---------+
+---------+ +---------+ +---------+
| | | | | |
+-+---------+--------------+---------+--------------+---------+-+
| network slice instance 1 <---+
+-+---------+--------------+---------+--------------+---------+-+ |
| Domain 1| | Domain 2| | Domain 3| isolation
+-+---------+--------------+---------+--------------+---------+-+ |
| network slice instance 2 <---+
+-+---------+--------------+---------+--------------+---------+-+
| | | | | |
+---------+ +---------+ +---------+
Figure 1: Illustration of Key Requirements
Table 1: Requirement Association
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+-----------------------------------------+------------------------------+
| Requirements Illustrated in NS UseCase | Extracted KEY Requirements |
+-----------------------------------------+------------------------------+
|1) Resource Reservation | |
|2) Abstraction | Req 1. Network Slicing |
|3) Multi-Access Knowledge | |
|4) Multi-Dimensional Service Vertical | Specification |
|5) Agile Resource Adjustment | |
+-----------------------------------------+------------------------------+
|6) Multi-Domain Coordination | Req 2. Network Slicing |
| | Cross-Domain |
|7) Resource Assurance | Coordination |
+-----------------------------------------+------------------------------+
| | Req 3. Network Slicing |
|8) Performance/Operation Isolation | Performance Guarantee |
| | and Isolation |
+-----------------------------------------+------------------------------+
|9) Independent Slice Management Plane | Req 4. Network Slicing OAM |
| Reliability | |
+-----------------------------------------+------------------------------+
Table 1: Requirements Association
o Req 1. Network Slicing Specification (NSS) - The management
systems of both network slice providers and operators need to know
what and how much resources/network functions they have, so that
they can accurately and abstractedly describe the available
resources/network functions to tenants or peers. The objective of
NSS is to deliver the network slicing requests without incurring
any over-utilization of resources. In order to cooperate and
provide consistent network slicing service, the way that
resources/network functions are described should be homogeneous
and compatible among all of the involved technology-specific
domains, provides, and slicing platforms.
o Req 2. Network Slicing Cross-Domain Coordination (NS-CDC) - From
terminal to server (or other terminal), an end-to-end network
slice will involve different infrastructural domains (e.g., AN,
TN, CN, etc. ) that may be owned by different providers/operators.
Each infrastructural domain may be further divided into different
administrative domains. That is an end-to-end slice is a logical
entity composed by multiple separated components, and the cross-
domain coordination is a way to integrate these components
together.
o Req 3. Network Slicing Performance Guarantee and Isolation (NS-
PGI) - In order to enable the safe, secure, privacy-preservation
service for multi-tenancy on a common physical network, the
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isolation among network slices in each of the
Data/Control/Management/Service planes are needed. Furthermore,
network slices that provide differentiated services usually
require different resources. The resources allocated to a network
slice must be able to guarantee the service performance
requirement.
o Req 4. Network Slicing OAM (NS-OAM) - On one end of the spectrum
we have those operators that will require a finalized service that
they will simply commercialize. On the other end we have those
operators that may want to fine-tune all the low-level aspects of
the network resources that form their system or service.
Moreover, in the middle there is plenty of room for variations.
Therefore, the underlying network layers must offer different
levels of granularity for the management of their resources, that
the upper layer operators can choose according to their needs and
objectives.
4. Network Slicing Specification
4.1. Description
Network Slicing Specification (NSS) is meant to describe the network
slicing resources and capture requirements from tenants or peer
networks to characterize the service expected to be delivered by a
network. These requirements include (non-exhaustive): reachability
scope (e.g., limited scope, Internet-wide), direction, bandwidth
requirements, performance metrics (e.g., one-way delay [RFC2679],
loss [RFC2680], or one-way delay variation [RFC3393]), protection and
high-availability guidelines (e.g., uRLLC service restoration in less
than 50 ms, 100 ms, or 1 second), traffic isolation constraints, and
flow identification. NSS is used by a network provider to decide
whether existing network slice instances can be reused or (some of
them) even combined, or if another network slice instance is needed
for a given service.
Technology-specific actions are then derived from the technology-
agnostic requirements depicted in an NSS. Such actions include
configuration tasks and operational procedures. A standard
definition of NSS is needed to facilitate the dynamic/ automated
negotiation procedure of NSS parameters, but also to homogenize the
processing of service requirements.
To explain by an example, a network slice may cross multiple domains:
o A cloud deployed, NFV enabled, chain of network functions in a
virtualized 5G core.
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o A segment routing [I-D.ietf-spring-segment-routing] based IGP
network transport/aggregation or slice-specific application
functions.
o A PCE [RFC4655] monitored TE-tunnel with ingress and egress
points.
o Optical, carrier Ethernet or cellular networks.
The network slice is a combination of the above technologies. It
creates a compelling need for a common resource specification
interface across these domains.
4.2. Related Work in IETF
4.2.1. YANG Data Models
As rightfully discussed in [I-D.wu-opsawg-service-model-explained],
the IETF has already published several YANG data models that are used
to model monolithic functions as well as very few services (e.g.,
L2SM, L3SM, EVPN). These models may be used in the context of
network slicing if corresponding technologies are required for a
given network slice, but none of them can be used to model an NSRD.
[RFC7297] describes the Connectivity Provisioning Profile (CPP) and
proposes a CPP template to capture connectivity requirements to be
met within a service delivery context. Such a generic CPP template
is meant to
o facilitate the automation of the service negotiation and
activation procedures, thus accelerating service provisioning;
o set (traffic) objectives of Traffic Engineering (TE) functions and
service management functions;
o improve service and network management systems with 'decision-
making' capabilities based upon negotiated/offered CPPs.
[RFC7297] may be considered as a candidate specification for NSRD.
Releasing a RFC7297-bis to take into account specific requirements
from network slicing is needed. Since [RFC7297] may not be
implemented by all providers, the [SLA-Exchange] may be adopted to
implement indirect SLA negotiation and SLA events report.
[SLA-Exchange] provides an in-band method to exchange the SLA
parameters, and then by the receiving devices to translate SLA in
technical specific provisioning languages. However, there still does
not exist any standard protocol to translate SLA agreements into
technical clauses and configurations.
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4.2.2. Building NSS from Protocol Independent Traffic Engineering
Models
The NSS requirement for reachability, direction, bandwidth
requirements, performance metrics, traffic isolation constraints, and
flow identification can be built utilizing protocol which can perform
operations (read, write, notification, actions (aka rpcs)) on a yang
service layer that supports these traffic engineer and resource
definition at the service layers. The network slicing service data
model can extend existing work in the TEAS and I2RS working group for
protocol-independent topology models. These models support
configuration or the dynamic datastores defined in [NMDA] which will
be abbreviated as NMDA in this section. This section provides the
detail on how the NSS can be built from these models and the RESTCONF
protocol.
4.2.2.1. Basic Topology Model
The basic topology model is defined in [I2RS-Yang] to include a
service layer. This topology model is protocol independent and can
be utilized as a configuration data model or a dynamic datastores
model. The configuration data model must abide by the configuration
persistence and referential requirements. The dynamic datastores do
not need to abide by the same requirements as the configuration
datastore. I2RS is defining a dynamic datastores reference model for
a data store which ephemeral. The network slices may want to use
configuration, ephemeral datastores, or define a third type of
dynamic datastores. The I2RS WG provides a place to collaborate this
work on the dynamic datastores.
4.2.2.2. TEAS Model Utilization of Basic Topology Model
The TEAS topology model [TE-Yang] provides a general description of a
Traffic engineering model that provides:
o abstract topologies with TE constraints (bandwidth, delay metrics,
links to lower layers, some traffic isolation constraints, and
some link identifiers);
o templates for links or resources;
o functionality to read, write, notification, and rpcs.
Options that need to be consider are:
Augmenting TEAS - The TEAS models provide substantial traffic
engineering. It was envisioned in the early topology model that a
service resource model would be part of the service layer. This
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work was delayed until the maturation of the service requirements
from L2VPN, L3VPN, and EVPN plus the maturation of resource
requirements from 5G. Network slicing provides a good application
use case for this work.
Why not Augment TEAS - The TEAS models are TE specific, lack of
the abstraction for Layer 3+ resources.
Dynamic models to combine TEAS models for network-slicing - The
network slicing controller operating across domains may wish to
create a multiple-domain data model based on the service layer
data models exposed by different providers. These service models
would not need to be configured, but only learned as providers
exchange data with one another. The rules for combining these
models could be defined as part of the dynamic datastore for
network-slicing.
Protocol within a domain - The RESTCONF and NETCONF protocol can
support read, write, notification and actions (rpcs) within a
domain.
Protocol across domains: The RESTCONF protocol currently supports
Configuration protocols and 90% of the dynamic datastores. The
RESTCONF protocol is being enhanced to support the push of
telemetry messages. The RESTCONF protocol could be used to
exchange a specific Yang network-slicing service-layer topology
(TE and Resources) and for the I2NSF security capabilities between
domains.
If a multicast of telemetry data is required between domains, then
the push model for telemetry information or the IPFIX protocol may
be utilized.
5. Network Slicing Cross-Domain Coordination
5.1. Description
The network slicing cross-domain coordination (NS-CDC) requirement
includes the following aspects:
o Network slice resource/functions coordination: for example, a
tenant requests for a network slice with at most 10 ms latency
from terminal to server. Different infrastructure/administrative
domains should coordinate and negotiate to reach an agreement such
as RAN provides at most 2 ms service, TN domain I provides at most
4ms service, TN domain II provides at most 2 ms service and CN
provides at most 2 ms service;
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o Configuration information coordination: for example, for a given
TN domain, the configuration information such as VLAN ID, remote
IP address, physical port ID, etc. need to be coordinated with
other TN domains;
o Other coordination: for example, RAN (or other access network)
needs to notify TN about the information of new attachment point
when user moves.
From terminal to server, an end-to-end network slice will involve
different infrastructure domains (e.g., RAN, TN and CN). An
infrastructure domain may be further divided into multiple domains
due to geographic isolation, administrative isolation and other
reasons. There are two ways to enable an end-to-end network slice:
based on a common platform or based on cross-domain coordination.
If all of the involved domains belong to the same operator or the
same operator union, the common platform solution may be work. In
this case, all of the domain controllers only need to communicate
with the common platform, and follow the coordination management of
this common platform. Whilst the most common case is that the
domains belong to different owners/operators/administrators, making
it difficult to realize such a common platform. Consequently, the
cross-domain coordination will be essential throughout the whole
lifecycle of an end-to-end network slice.
5.2. Related Work in IETF
There are some related works studies the inter-operation/coordination
between different entities. Coordination of different components of
a slice requires automation. It can be achieved either by
1. Coordination protocols such as ANIMA, CPNP
2. Or through abstraction and corresponding interfaces as in ACTN.
This subsection will briefly review these related work to provide a
basis for the gap analysis.
5.2.1. Autonomic Networking Integrated Model and Approach (ANIMA)
Autonomic Networking Integrated Model and Approach (ANIMA) WG
provides a series of tools for distributed and automatic management,
which includes: Generic Autonomic Signaling Protocol (GRASP),
Autonomic Networking Infrastructure (ANI), etc.
GRASP [ANIMA-GRASP] is a protocol for the negotiation between ASAs
(Autonomic Service Agent). In GRASP, ASAs could be considered as
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"APPs" installed on a device. Different ASAs fulfill different
management tasks such as parameter configuration, service delivery,
etc. Based on GRASP, the same purpose ASAs that installed on
different devices are able to inter-operate and negotiate with each
other. Network slicing could make use of GRASP for the coordination
among devices in the underlying infrastructure layer, as well as the
negotiation among different domain managers. However, the security
issue incurred by cross-domain usage should be fixed in GRASP.
ANI [ANI] is a technical packet consisting of BootStrap (for
authentication, domain certification distribution, etc.), ACP (a
separate control plane), and GRASP (for control message
coordination). ANI could be used to construct the management tunnel
among devices in underlying infrastructure layer within a single
domain. While the network slicing and cross-domain oriented
extensions are necessary.
5.2.2. Connectivity Provisioning Negotiation Protocol (CPNP)
[I-D.boucadair-connectivity-provisioning-protocol] defines the
Connectivity Provisioning Negotiation Protocol (CPNP) that is meant
to dynamically exchange and negotiate connectivity provisioning
parameters, and other service-specific parameters, between a Customer
and a Provider. CPNP is a tool that introduces automation in service
negotiation and activation procedures, thus fostering the overall
service provisioning process.
CPNP runs between a Customer and a Provider carrying service orders
from the Customer and respective responses from the Provider to the
end of reaching a connectivity service provisioning agreement. As
the services offered by the Provider are well-described, by means of
the CPP template, the negotiation process is essentially a value-
settlement process, where an agreement is pursued on the values of
the commonly understood information items (service parameters)
included in the service description template.
The protocol is transparent to the content that it carries and to the
negotiation logic, at Customer and Provider sides, that manipulates
the content.
The protocol aims at facilitating the execution of the negotiation
logic by providing the required generic communication primitives.
CPNP can be used in the context of network slicing to request for
network resources together with a set of requirements that need to be
satisfied by the Provider. Such requirements are not restricted to
basic IP forwarding capabilities, but may also include a
characterization of a set of service functions that may be invoked.
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5.2.3. Abstraction and Control of Traffic Engineered Networks (ACTN)
ACTN [TEAS-ACTN] is an information model proposed by TEAS WG, which
enables the multi-domain coordination in Traffic Engineering (TE)
network. In order to enable network slicing in transport networks,
portion of transport domain will need to be engineered. In
particular, building a TE entity and stitching service for this
entity is within the scope of ACTN. As an end-to-end network slicing
solution, ACTN is able to provide cross-domain coordination. In
ACTN, each physical transport network domain is under the control of
a Physical Network Controller (PNC) as shown in Figure 2. A Multi-
Domain Service Coordinator (MDSC) controls multiple PNCs. Although
the MDSCs may form a hierarchical structure, a hierarchical MDSC can
still be regarded as a logical common platform. As Section 5.1
discussed, such a common platform solution has a strict presumption
that all domains are assumed to follow a common coordination
management.
While ACTN does carry out network slicing-related work, some proposed
concepts are similar the concepts of today's network slicing: in
particular, the virtual network (VN) is similar to a slice instance.
ACTN enables VN based on LSP technique, different LSP tunnels
correspond to different VNs. However, ACTN focuses on resource
abstraction and management on Layer 2 and Layer 1. For transport
network slicing, resources abstraction and management on Layer 3+
(e.g., IP routing table, etc.) may also be necessary but have not
been addressed by ACTN.
+-------+ +-------+ +-------+
| CNC-A | | CNC-B | | CNC-C |
+---+---+ +---+---+ +---+---+
| | |
+-------\ |CMI /------+
\ | /
+---------+----------+
| (Hierarchical)MDSC |
+---------+----------+
/ | \
+-------+ |MPI +---------+
| | |
+---+---+ +-------+ +----+--+
| PNC | | PNC | | PNC |
+-------+ +-------+ +-------+
Figure 2: A Three-tier ACTN Control Hierarchy
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5.3. Other Potential Solutions
5G Exchange (5GEx) [FGEx] is a 5G-PPP project which aims to enable
cross-domain orchestration of services over multiple administrations
or over multi-domain single administration networks. The main
infrastructure considered in 5GEx is the NFV/SDN compatible software
defined infrastructure, which limits the scope of network slicing to
SDN based architecture.
6. Network Slicing Performance Guarantee and Isolation
6.1. Description
Network slicing is expected to enable the deployment of various
services with diverse requirements, independently on a common
physical network. Each network slice is characterized by particular
service requirements, which usually are expressed using in the form
of several key performance indicators (KPIs) such as bandwidth,
latency, jitter, packet loss, etc., and different degrees of
isolation. Isolation requirements include performance isolation,
which means performance guarantee are maintained regardless of
activity in other slices, as well as secure isolation (e.g.,
including privacy), and management (or OAM) isolation. Additionally,
performance isolation in network slicing has to maintain while
scaling up or down computing capabilities of a slice (i.e., for
elastic scaling). Moreover, since IoT is also a use case for NS, and
since some IoT applications are sensitive to data plane or bits on
wire overheads, data path encapsulation in the form of labels, VLANs,
VxLANs should be optional, or minimized for those cases.
As we will discuss in the detailed sections below, each of these
technologies can address some but not all performance and isolation
requirements:
o RSVP-TE, Segment Routing (SR), DETNET, FlexE are mostly related to
performance guarantee and performance isolation requirements
o Virtual Private Networks (VPN), NVO3 are mostly related to
security and management isolation requirements
A Network Slicing solution, to support performance guarantee and
isolation requirements, will therefore need to merge in some way
characteristics from these two families of technologies, through the
combination of (possibly enhanced) existing technologies and/or
specifically developed ones. We can also consider the possibility
that multiple such technology stacks may be deployed in different
domains, and rely on cross-domain coordination, as described
inSection 5, to form a single abstracted network slice.
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6.2. Related Work in IETF
6.2.1. Virtual Private Networks
VPN technologies such as L3VPN [RFC4364], L2VPN [RFC4664], EVPN
[RFC7432], etc. have been widely deployed to provide different
virtual networks on common service provider networks. Although VPNs
can provide logically separated routing/bridging domains between
different VPN customers, essentially it is an overlay network
technology with little control of the network resources, so it is
challenging for VPN to meet the performance and isolation requirement
of some emerging application scenarios such as industrial verticals.
VPNs essentially are private networks of enterprises by connecting
remote sites. The following two issues illustrate limitations of
VPNs for network slicing:
o An end-to-end VPN tunnel competes with other traffic in the
network and end-to-end network resource policies cannot be
guaranteed.
o The reachability and resource reservation protocols are not
tightly integrated and often solutions require centralized PCE-P
like methods.
6.2.2. NVO3
[NVO3-WG] defines several network encapsulations which support the
network virtualization and multi-tenancy in the data center networks.
Similar to the VPN technologies of service provider networks, NVO3 is
also an overlay network technology, which relies on the performance
characteristics provided by the IP-based underlay networks. Thus
NVO3 may not meet by itself the performance and isolation
requirements of network slicing.
6.2.3. RSVP-TE
RSVP-TE [RFC3209] is the signaling protocol to establish end-to-end
traffic-engineered Label Switched Paths (LSPs). It can reserve the
required link bandwidth along an end-to-end path for specific network
flows, which is suitable for services with particular requirement on
traffic bandwidth. RSVP-TE LSPs can be used as the underlay tunnels
of the VPN service connections. However, the requirement of some
emerging services is not only about traffic bandwidth, but also has
quite strict requirement on latency, jitter, etc. Such requirements
can hardly be met with existing RSVP-TE.
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6.2.4. Segment Routing
[I-D.ietf-spring-segment-routing] provides the ability to specify a
traffic-engineered path by the source node of data packets. It can
provide traffic-engineering features comparable to RSVP-TE with
better scalability, by eliminating the per-path state in the transit
network nodes. It is therefore a candidate method of creating an
NSI, mapping a packet into an NSI and specifying the passage of the
packet through the resources dedicated to the NSI. Further study
will be required to determine if/how SR as designed today can be used
as a core technology for building an NSI. With respect to
performance guarantee and isolation, some further investigation may
be needed to understand whether SR can provide the same or better
performance characteristics as RSVP-TE. In addition, it is not clear
whether SR-based LSPs can provide the guaranteed latency and jitter
performance required by network slicing.
6.2.5. Deterministic Networking
[DETNET-WG] is working on the deterministic data paths over layer 2
and layer 3 network segments. Such deterministic paths can provide
identified flows with extremely low packet loss rates, low packet
delay variation (jitter) and assured maximum end-to-end delivery
latency. This is accomplished by dedicating network resources such
as link bandwidth and buffer space to DetNet flows and/or classes of
DetNet flows. DetNet also aims to provide high reliability by
replicating packets along multiple paths. It is a characteristic of
DetNet that it is concerned solely with worst-case values for the
end-to-end latency.
The primary target of DetNet is real-time systems and as such
average, mean, or typical latency values are not protected, because
they do not affect the ability of a real-time system to perform their
tasks. This contrasts with a normal priority-based queuing scheme
which will give better average latency to a data flow than DetNet,
but, on the other side, the worst-case latency can be essentially
unbounded. As such DetNet seems to be a useful technique that may be
applied to either a complete NSI, or to part of the traffic within an
NSI to address the emerging low latency requirement for real time
application.
DetNet can therefore address some of the requirements of NS. It was
however not designed with network slicing in mind, which means a
mapping between an NSI and a DetNet service may need to be defined.
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6.2.6. Flexible Ethernet
[FLEXE-1.0] was initially defined by Optical Internetworking Forum
(OIF) as an interface technology which allows the complete decoupling
of the Media Access Control layer (MAC) data rates and the standard-
based Ethernet Physical layer (PHY) rates. The channelization
capability of FlexE can be used to partition a FlexE interface into
several independent sub-interfaces, which can be considered as a
useful component for the slicing of network interfaces. Currently
there is ongoing work in IETF to define the control plane framework
for FlexE [FlexE-FWK], which aims to identify the routing and
signaling extensions needed for establishing FlexE-based end-to-end
LSPs in IP/MPLS networks.
7. Network Slicing OAM with Customized Granularity
7.1. Description
In accordance with [RFC6291], OAM is used to denote the following:
o Operations: refer to activities that are undertaken to keep the
network and the services it deliver up and running. It includes
monitoring the underlying resources and identifying problems.
o Administration: refer to activities to keep track of resources
within the network and how they are used.
o Maintenance: refer to activities to facilitate repairs and
upgrades. Maintenance also involves corrective and preventive
measures to make the managed network run more effectively, e.g.,
adjusting configuration and parameters.
As per [RFC6291], network slicing provisioning operations are not
considered as part of OAM. Provisioning operations are discussed in
other sections.
Maintaining automatically-provisioned slices within a network raises
the following requirements:
o Ability to run OAM activities on a provider's customized
granularity level. In other words, ability to run OAM activities
at any level of granularity that a service provider see fit. In
particular:
* Per slice OAM: An operator must be able to execute OAM tasks on
a per slice basis.
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* Per domain OAM: These tasks can cover the "whole" slice within
a domain or a portion of that slice (for troubleshooting
purposes, for example).
* Per service OAM: When a given slice is shared among multiple
services/customers, an operator must be able to execute (per-
slice) OAM tasks for a particular service or customer.
* For example, OAM tasks can consist in tracing resources that
are bound to a given slice, tracing resources that are invoked
when forwarding a given flow bound to a given network slice,
assessing whether flow isolation characteristics are in
conformance with the NS Resource Specification, or assessing
the compliance of the allocated slice resource against flow/
customer requirements.
* An operator must be able to enable differentiated failure
detect and repair features for a specific/subset of network
slices. For example, a given slice may require fast detect and
repair mechanisms (e.g., as a function of the nature of the
traffic (pattern) forwarded through the NS), while others may
not be engineered with such means.
o Ability to automatically discover the underlying service functions
and the slices they are involved in or they belong to.
o Ability to dynamically discover the set of network slicing that
are enabled within a network. Such dynamic discovery capability
facilitates the detection of any mismatch between the view
maintained by the control plane and the actual network
configuration. When mismatches are detected, corrective actions
must be undertaken accordingly.
o Ability to efficiently OAM on shared resources. If multiple
network slices share some resources, the same kind of OAM
operations from different network slices should be performed only
once for efficiency. For example, several network slices share a
link. We only need to execute once status query, and directly
return the queried result to other status query requests.
7.2. Related Work in IETF
7.2.1. Overview of OAM tools
The reader may refer to [RFC7276] for an overview about available OAM
tools. These technology-specific tools can be reused in the context
of network slicing. Providers that deploy network slicing
capabilities should be able to select whatever OAM technology-
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specific feature that would be address their needs. No gap that
would legitimate specific requirements has been identified so far.
7.2.2. Overlay OAM
[I-D.ooamdt-rtgwg-ooam-header] specifies a generic OAM header that
can be used if overlay technologies are enabled. Obviously, this
effort can be reused in the context of network slicing when overlay
techniques are in use. Nevertheless, For slice designs that do not
assume an overlay technology, OAM packets must be able to fly over
the appropriate slice and for a given service/customer. This is
possible by reusing some existing tools if and only if no specific
fields are required (e.g., carry a slice identifier as Req. 5
stated).
7.2.3. Service Function Chaining
SFC WG [SFCWG] is chartered to describe data plane service
encapsulation, control and manageability aspects of service
functions. Extensions that will be specified by the SFC WG will be
reused in the context of network slicing. Nevertheless, The current
charter of the WG does not imply work on the automated discovery of
SF instances and their capabilities, nor the automatic discovery of
control elements. An additional specification effort is therefore
required in this area.
7.2.4. Slice Identification
A network slice data plane, may or may not follow traditional data
plane tagging/labeling. However, each network element (router/
switch) still has to classify an incoming packet and associated with
the slice instance for proper treatment. Network slice instance
identification is essential for network element to make local
decisions on forwarding policies, QoS mechanism and etc. The
performance requirements of a network slice instance can therefore
been met by making the correct decision. Meanwhile, it is also
important for OAM so that configuration and provisioning can be
delicately performed to particular network slice instances by their
identifications.
For flow identification, many existing technologies provide mature
solutions. These approaches might be able to be re-used in network
slicing by adding an additional layer of mapping to a network slice
instance ID. The network slice instance ID further maps to a group
of performance requirements and OAM profiles, based on which the
network elements within the slice can make local decisions. However,
per flow level identification could have adverse impact on the scale
of the forwarding entries in the routers.
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With traditional IP/MPLS VPNs, the set of Route Targets configured
for the VPN can be used as some sort of identifier of the VPN in the
control plane, and in the data plane, the VPN service labels can be
used to identify the data packets belonging to a particular VPN.
NVO3 uses the Virtual Network Identifiers (VNIs) in the header of
data packets to identify different overlay network tenants. However,
It is not clear if the existing identifiers can meet the requirements
of network slicing in terms of making local decisions on forwarding
policy, QoS and OAM mechanisms, etc.
8. Summary
The following table is a summary of the identified gaps based on
previous analysis in this document.
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+--------------------------------+---------------------------------------+
| Requirements | Gaps |
+--------------------------------+---------------------------------------+
| | |
|Req 1. Network Slicing | 1) A detailed specification of NSS |
| Specification | |
| (NSS) | 2) A companion YANG data model for |
| | NSS |
+--------------------------------+---------------------------------------+
| | |
|Req 2. Network Slicing Cross- | |
| Domain Coordination | 3) A companion data model for |
| (NS-CDC) | NS-CDC |
| | |
+--------------------------------+---------------------------------------+
| | |
|Req 3. Network Slicing | 4) Slicing specific extension on |
| Performance Guarantee and| existing technologies |
| Isolation (NS-PGI) | |
| | |
+--------------------------------+---------------------------------------+
| | |
| | 5) Mechanisms for dynamic discovery |
| | of service function instances and |
| | their capabilities. Mechanisms for|
|Req 4. Network Slicing OAM | dynamic discovery of instantiated |
| (NS-OAM) | network slices |
| | |
| | 6) non-overlay OAM solution |
| | |
| | 7) Mechanisms for customized |
| | granularity OAM |
| | |
+--------------------------------+---------------------------------------+
Table 2: Summary of Gaps
9. Security Considerations
This document analyzes the standardization work on network slicing in
different WGs. As no solution proposed in this document, no security
concern raised.
10. IANA Considerations
There is no IANA action required by this document.
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11. Acknowledgements
The authors wish to thank Hannu Flinck, Akbar Rahman, Ravi Ravindran,
Xavier de Foy, Young Lee and Igor Bryskin for their detailed and
constructive reviews. Many thanks to Mohamed Boucadair, Christian
Jacquenet and Stewart Bryant for their valuable contributions and
comments.
12. References
12.1. Normative References
[NS-Framework]
"NS Framework", <https://datatracker.ietf.org/doc/draft-
geng-netslices-architecture/>.
[NS-UseCase]
"NS Use Case", <https://datatracker.ietf.org/doc/draft-
netslices-usecases/>.
12.2. Informative References
[ANI] "A Reference Model for Autonomic Networking",
<https://datatracker.ietf.org/doc/draft-ietf-anima-
reference-model/?include_text=1>.
[ANIMA-GRASP]
"A Generic Autonomic Signaling Protocol (GRASP)",
<https://datatracker.ietf.org/doc/draft-ietf-anima-
grasp/>.
[DETNET-WG]
"Deterministic Networking",
<https://datatracker.ietf.org/wg/detnet/about/ >.
[FGEx] "5G Exchange (5GEx) - Multi-domain Orchestration for
Software Defined Infrastructures",
<https://www.researchgate.net/
publication/296486303_5G_Exchange_5GEx_-_Multi-domain_Orch
estration_for_Software_Defined_Infrastructures>.
[FLEXE-1.0]
"Flexible Ethernet 1.0", <http://www.oiforum.com/wp-
content/uploads/OIF-FLEXE-01.0.pdf>.
[FlexE-FWK]
"FlexE-FWK", <https://datatracker.ietf.org/doc/draft-izh-
ccamp-flexe-fwk/>.
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[I-D.boucadair-connectivity-provisioning-protocol]
Boucadair, M., Jacquenet, C., Zhang, D., and P.
Georgatsos, "Connectivity Provisioning Negotiation
Protocol (CPNP)", draft-boucadair-connectivity-
provisioning-protocol-14 (work in progress), May 2017.
[I-D.ietf-spring-segment-routing]
Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
and R. Shakir, "Segment Routing Architecture", draft-ietf-
spring-segment-routing-12 (work in progress), June 2017.
[I-D.ooamdt-rtgwg-ooam-header]
Mirsky, G., Kumar, N., Kumar, D., Chen, M., Yizhou, L.,
and D. Dolson, "OAM Header for use in Overlay Networks",
draft-ooamdt-rtgwg-ooam-header-03 (work in progress),
March 2017.
[I-D.wu-opsawg-service-model-explained]
Wu, Q., LIU, W., and A. Farrel, "Service Models
Explained", draft-wu-opsawg-service-model-explained-06
(work in progress), May 2017.
[I2RS-Yang]
"A Data Model for Network Topologies",
<https://datatracker.ietf.org/doc/draft-ietf-i2rs-yang-
network-topo/ >.
[IMT2020-2015]
"Report on Gap Analysis", <http://www.itu.int/en/ITU-
T/focusgroups/imt-2020/Pages/default.aspx >.
[IMT2020-2016]
"Draft Technical Report Application of network
softwarization to IMT-2020 (O-041)",
<http://www.itu.int/en/ITU-T/focusgroups/imt-2020/Pages/
default.aspx >.
[IMT2020-2016bis]
"Draft Terms and definitions for IMT-2020 in ITU-T
(O-040)", <http://www.itu.int/en/ITU-T/focusgroups/imt-
2020/Pages/default.aspx >.
[NGMN-2016]
"Description of Network Slicing Concept",
<https://www.ngmn.org/uploads/
media/160113_Network_Slicing_v1_0.pdf>.
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[NMDA] "Network Management Datastore Architecture",
<https://datatracker.ietf.org/doc/draft-ietf-netmod-
revised-datastores/>.
[NVO3-WG] "Network Virtualization Overlays".
[ONF-2016]
TS, "Applying SDN Architecture to 5G Slicing",
<https://www.opennetworking.org/images/stories/downloads/
sdn-resources/technical-reports/
Applying_SDN_Architecture_to_5G_Slicing_TR-526.pdf >.
[RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Delay Metric for IPPM", RFC 2679, DOI 10.17487/RFC2679,
September 1999, <http://www.rfc-editor.org/info/rfc2679>.
[RFC2680] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Packet Loss Metric for IPPM", RFC 2680,
DOI 10.17487/RFC2680, September 1999,
<http://www.rfc-editor.org/info/rfc2680>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<http://www.rfc-editor.org/info/rfc3209>.
[RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation
Metric for IP Performance Metrics (IPPM)", RFC 3393,
DOI 10.17487/RFC3393, November 2002,
<http://www.rfc-editor.org/info/rfc3393>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <http://www.rfc-editor.org/info/rfc4364>.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<http://www.rfc-editor.org/info/rfc4655>.
[RFC4664] Andersson, L., Ed. and E. Rosen, Ed., "Framework for Layer
2 Virtual Private Networks (L2VPNs)", RFC 4664,
DOI 10.17487/RFC4664, September 2006,
<http://www.rfc-editor.org/info/rfc4664>.
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[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<http://www.rfc-editor.org/info/rfc5440>.
[RFC6291] Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
D., and S. Mansfield, "Guidelines for the Use of the "OAM"
Acronym in the IETF", BCP 161, RFC 6291,
DOI 10.17487/RFC6291, June 2011,
<http://www.rfc-editor.org/info/rfc6291>.
[RFC7276] Mizrahi, T., Sprecher, N., Bellagamba, E., and Y.
Weingarten, "An Overview of Operations, Administration,
and Maintenance (OAM) Tools", RFC 7276,
DOI 10.17487/RFC7276, June 2014,
<http://www.rfc-editor.org/info/rfc7276>.
[RFC7297] Boucadair, M., Jacquenet, C., and N. Wang, "IP
Connectivity Provisioning Profile (CPP)", RFC 7297,
DOI 10.17487/RFC7297, July 2014,
<http://www.rfc-editor.org/info/rfc7297>.
[RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
2015, <http://www.rfc-editor.org/info/rfc7432>.
[SFCWG] "\Service Function Chaining (sfc)",
<https://datatracker.ietf.org/wg/sfc/about/>.
[SLA-Exchange]
"Inter-domain SLA Exchange Attribute",
<https://datatracker.ietf.org/doc/draft-ietf-idr-sla-
exchange/>.
[TE-Yang] "YANG Data Model for TE Topologies",
<https://datatracker.ietf.org/doc/draft-ietf-teas-yang-te-
topo/>.
[TEAS-ACTN]
"Information Model for Abstraction and Control of TE
Networks (ACTN)", <https://datatracker.ietf.org/doc/html/
draft-ietf-teas-actn-info-model>.
[TS23-501]
"System Architecture for the 5G System",
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3144>.
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Authors' Addresses
Li Qiang (editor)
Huawei
Email: qiangli3@huawei.com
Pedro Martinez-Julia
NICT
Email: pedro@nict.go.jp
Liang Geng
China Mobile
Email: gengliang@chinamobile.com
Jie Dong
Huawei
Email: jie.dong@huawei.com
Kiran Makhijani
Huawei
Email: Kiran.Makhijani@huawei.com
Alex Galis
University College London
Email: a.galis@ucl.ac.uk
Susan Hares
Hickory Hill Consulting
Email: shares@ndzh.com
Slawomir
Orange
Email: slawomir.kuklinski@orange.com
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