Internet DRAFT - draft-defoy-coms-subnet-interconnection
draft-defoy-coms-subnet-interconnection
none X. de Foy
Internet-Draft A. Rahman
Intended status: Informational InterDigital Inc.
Expires: September 9, 2020 A. Galis
University College London
K. Makhijani
L. Qiang
Huawei Technologies
S. Homma
NTT
P. Martinez-Julia
NICT
March 8, 2020
Interconnecting (or Stitching) Network Slice Subnets
draft-defoy-coms-subnet-interconnection-04
Abstract
This document defines the network slice (NS) subnet as a general
management plane concept that augments a baseline YANG network slice
model with management attributes and operations enabling
interconnections (or stitching) between network slices. The
description of NS subnet interconnections is technology agnostic, and
is not tied to a particular implementation of the interconnection in
data plane.
Status of This Memo
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This Internet-Draft will expire on September 9, 2020.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Motivation and Roles of NS Subnet . . . . . . . . . . . . 3
1.2. Usage of NS Subnets . . . . . . . . . . . . . . . . . . . 3
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. Information Model . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Base Information Model . . . . . . . . . . . . . . . . . 5
2.2. Interconnection Anchors . . . . . . . . . . . . . . . . . 6
2.3. Interconnection Instances . . . . . . . . . . . . . . . . 8
2.4. Stitching Operation . . . . . . . . . . . . . . . . . . . 9
2.4.1. Operation Overview . . . . . . . . . . . . . . . . . 9
2.4.2. Stitching Scenarios . . . . . . . . . . . . . . . . . 10
3. Security Considerations . . . . . . . . . . . . . . . . . . . 11
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
5. Informative References . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
Network Slicing enables deployment and management of services with
diverse requirements on end-to-end partitioned virtual networks over
the same infrastructure, including networking, compute and storage
resources. There were recent efforts in the IETF to define a
transport slice ([I-D.nsdt-teas-transport-slice-definition]) and to
define a north-bound interface for such a transport slice
([I-D.contreras-teas-slice-nbi]). The mapping of transport slices in
5G mobile systems is also studied in [I-D.clt-dmm-tn-aware-mobility]
and [I-D.geng-teas-network-slice-mapping].
Network slices may be managed through usage of YANG data models. For
example, [I-D.liu-teas-transport-network-slice-yang] describes how
existing YANG models can be augmented with network slice attributes.
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Nevertheless, defining and managing a network slice (NS) end-to-end
does not always have to be done directly. It may be convenient to
define and manage separately subsets of an end-to-end slice. The
concept of network slice subnet is defined originally in
[NGMN_Network_Slicing], though we only need to retain its definition
in the most universal form: network slice subnets are similar to
network slices in most ways but cannot be operated in isolation as a
complete network slice (e.g., a NS subnet can be seen as a network
slice with unconnected links). NS subnets are interconnected with
other NS subnets to form a complete, end-to-end network slice (i.e.
interconnection and/or stitching of NS subnets). In the present
draft, we describe a data model for describing interconnections
between NS subnets, that enables assembling them in a hierarchical
fashion.
1.1. Motivation and Roles of NS Subnet
NS subnet is a management plane concept that facilitates
interconnections (also known as stitching) of network slices. It
augments the base slice information model, that can be used to
represent an end-to-end network slice. The extensions described in
this document can be used to represent a slice subnet instead, and
can also be used to represent an interconnection inside an end-to-end
slice, i.e. they aim to represent interconnection points both
"before" and "after" the interconnection takes place. Operations
such as stitching subnets are also described.
The description of NS subnet interconnections is technology agnostic
following the approach of the slice information model. Some
interconnections may be implemented using the interplay between
management plane and gateways in the data plane.
[I-D.homma-rtgwg-slice-gateway] describes the requirements on such
data plane network elements, and will provide input for the
management plane mechanisms described in the present document.
1.2. Usage of NS Subnets
Using NS subnets can help:
o Isolate management and maintenance of different portions of a
network slice, over multiple infrastructure domains, or even
within a single domain. For example, in Figure 1, NS orchestrator
(NSO) 2 manages subnet A, in isolation from subnets B and C
managed by NSO 3. NSO 1 can still manage the end-to-end slice as
a whole, but it does not need to deal in detail with each subnet.
o Isolate mapping towards different infrastructure technologies,
even within the same domain. This can simplify NS orchestrator
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implementation, since each NSO can specialize in managing a
smaller set of technologies.
o Enable advanced functions such as sharing a slice subnet between
several slices, or substituting one slice subnet for another, e.g.
for coping with load.
+-----------+
******| NS Orch. 1|********
* +-----------+ *
* *
* *
+-----------+ +-----------+
| NS Orch. 2| | NS Orch. 3|*****
+-----------+ +-----------+ *
* * *
* * *
* A-B Inter- * B-C Inter- *
* connection * connection *
+-----------------+ . +-----------------+ . +-----------------+
| +--+ | . | +--+ | . | +--+ |
| | +---------------------+ +--------------------+ | |
| ++-+ | . | ++-+ | . | ++-+ |
| | | . | | | . | | |
| +---+ | +---+ | . | +---+ | +---+ | . | +---+ | +---+ |
| | +-+--+ +-----------+ +-+--+ +----------+ +-+--+ | |
| +---+ +---+ | . | +---+ +---+ | . | +---+ +---+ |
+-----------------+ . +-----------------+ . +-----------------+
<.. NS subnet A ..> <.. NS subnet B ..> <.. NS subnet C ..>
<....................... end-to-end slice .........................>
Figure 1: Overview of Network Slice Subnets Interconnection
Figure 1 illustrates how an end-to-end network slice may be composed
of multiple slice subnets, each managed independently by a same or
different NSO. In multi-administrative domain scenarios, using NS
subnets can help limiting the information that needs to be shared
between domains. At the infrastructure layer (i.e. in the data
plane), the interconnection between NS subnets may involve:
o a gateway, that performs protocol and/or identifier/label
translation as needed,
o two gateways, especially in cases where interconnected NS subnets
are in different administrative domains,
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o nothing at all, in cases where the interconnection point can be
abstracted away, e.g. when the NS subnets share a common
infrastructure. In this case nodes from both NS subnets end up
being directly interconnected between each other.
More detailed usage scenarios are described in Section 2.4.2.
1.3. Terminology
Network slicing terminology, especially focusing on transport slices,
is defined in [I-D.nsdt-teas-transport-slice-definition].
Network Slice Subnet (NS subnet): a network slice designed to be
interconnected with other network slices.
NS Stitching: a management operation consisting in creating an end-
to-end NS or a larger NS subnet, by interconnecting a set of NS
subnets together.
Interconnection Anchor: a management plane entity, part of a NS
subnet model, representing an end point for use in future stitching
operation.
Interconnection Instance (or Interconnect): a management plane
entity, part of a NS subnet model, representing an interconnection
realized by a stitching operation. It is distinct from a (data
plane) gateway: an interconnect may be realized with or without using
a gateway in the data plane.
2. Information Model
2.1. Base Information Model
The information model we use as base for network slicing is the
network topology model ietf-network defined in [RFC8345], in which
networks are composed of nodes and links, and in which termination
points (TP), defined in nodes, are used to define source and
destination of links.
A network slice data model instance, i.e. a YANG data model augmented
using [I-D.liu-teas-transport-network-slice-yang]), represents a
network slice. When such a data model instance includes at least an
"interconnection anchor", as defined below, it represents a network
slice subnet instance.
At high level, the extensions defined in this document will augment
nodes and termination points:
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module: ietf-network
+--rw networks
+--rw network* [network-id]
+--rw network-id
+--rw network-types
+--rw supporting-network* [network-ref]
| +--rw network-ref
+--rw node* [node-id]
| +--... (augmented with attributes for
| | anchor/interconnection nodes)
| +--rw nt:termination-point* [tp-id]
| | ... (augmented with attributes for
| | anchor/interconnection TP)
2.2. Interconnection Anchors
To represent an anchor point for future interconnections (i.e. an
unconnected end of a link), a simple solution is to use an
"interconnection anchor" termination point (or anchor TP). Within
the data model describing a subnet, any link not entirely contained
within the NS subnet must be terminated with such an anchor TP as
source or destination. An anchor TP belongs to a "node" attribute,
which we refer to as interconnection anchor node (or anchor node).
Several anchor TPs can be grouped together in an anchor node, and
such grouping may be used as a hint during a stitching operation
(e.g. to place all interconnection points at a same location).
Figure 2 represents 2 interconnected network slice subnets.
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Slice Provider
|
+---------------------------------v---------------------------------+
| Network Slice Orchestrator |
| |
| +---------------------------------------------------------------+ |
| | Data model: network slice composed of NS subnet 1 and 2 | |
| | | |
| | Network Slice Subnet 1 Network Slice Subnet 2 | |
| | +---------------------------+ +----------------------------+ | |
| | | cross-subnet link | | cross-subnet | | |
| | | +----------------+ | | link +------+ | | |
| | | | | | | +--------o node | | | |
| | | | |Interconnection| +---o--+ | | |
| | |+---o--+ +-------|-----+--+------|------+ | | | |
| | || node | | | | | | | | | | |
| | |+---o--+ | +-----|---+ | | +----|----+ | | | | |
| | | | | | | | | | | | | | | | | |
| | | | | | O - - - - - - - O | | | | | |
| | | | | | | | | | | | | | | |
| | | | | | anchor | | | | anchor | | | | | |
| | | | | | node | | | | node | | | | | |
| | | | | | | | | | | | +---+ | | |
| | | | | | O - - - - - - - O | | | | | |
| | | | | | | | | | | | | | | | | |
| | | | | +-----|---+ | | +----|----+ | +---o--+ | | |
| | | | | | | | | | | node | | | |
| | | | +-------|-----+--+------|------+ +---o--+ | | |
| | | | +------+ | | | | | | | |
| | | +-o node o-------+ | | +----------------+ | | |
| | | +------+ cross-subnet| | cross-subnet | | |
| | | link | | link | | |
| | +---------------------------+ +----------------------------+ | |
| +---------------------------------------------------------------+ |
+--------------------------------+----------------------------------+
|
v
Network Infrastructure
Legend: o = termination point, O = anchor termination point
Figure 2: Network Slice Subnets Interconnection
Attributes of interconnection anchor nodes and termination points
include:
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o Information enabling NS orchestrators to match anchor nodes and
TPs from both NS during a stitching operation. A label may be a
simple way to enable this.
o Information to help locate the interconnection. For example, it
could be a (sub-)domain name or geo-location information, that
indicates where the interconnection point should be located. This
can help for example in cases where the subnet is instantiated
before stitching.
o Information to help select the type of interconnection
establishment: for example, this can indicate a preference for
using interconnection over a gateway, or for abstracting away the
interconnection point in the infrastructure plane.
+--rw node* [node-id]
+-- (...)
+-- anchor_node_config
| +-- label (and/or other auto stitching help)
| +-- hint for location (domain, geolocation, etc.)
| +-- hint for type (1 gateway, 2 gateways, ...)
+--rw nt:termination-point* [tp-id]
+-- (...)
+-- anchor_tp_config
+-- label (and/or other auto stitching help)
+-- location (domain, geolocation, etc.)
+-- type (1 gateway, 2 gateways, ...)
2.3. Interconnection Instances
There are two options for representing post-stitching network slices
(or subnets). They are not mutually exclusive:
o Option 1: subnet data models are updated with information
describing the interconnection (e.g. anchor TPs and nodes are
updated with new attributes representing the existing connection,
if necessary).
o Option 2: a new data model is generated to represent the resulting
network slice (or subnet). In this composite data model, the
interconnection may or may not be represented, this can be a
choice made by the operator.
Option 1 and 2 can be used concurrently in a network. For example, a
parent NS orchestrator may manage stitched NS subnets through
underlying NS orchestrators, and at the same time expose to the NS
operator a composite data model representing the resulting end-to-end
slice.
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To represent an existing interconnection in option 1, a simple
solution is to add attributes to existing anchor nodes and anchor
TPs. Those attributes will be described below. They aim to describe
state and configuration associated with an active interconnection.
To represent an existing interconnection in option 2, a simple
solution is to create new interconnection instance nodes and
termination point. The same attributes as in option 1 may be
associated with these nodes and TPs.
Attributes of interconnection instance nodes and termination points
include:
o State information (interconnection type, status, location...).
o Service assurance related information: besides measurements (on
throughput, loss rate, etc.), triggers depending on throughput,
latency, etc. can be linked with a management action or event. A
NS operator can use such events to take the decision to disable a
NS subnet, replace a NS subnet with another, etc. to maintain
overall service performance.
+--rw node* [node-id]
+-- (...)
+-- interconnection_instance_node_state
| +-- status
| +-- location (domain, geolocation, etc.)
| +-- type (1 gateway, 2 gateways, ...)
+-- interconnection_instance_node_service_assurance
| +-- events (including triggers and event IDs)
| +-- measurements
+--rw nt:termination-point* [tp-id]
+-- (...)
+-- interconnection_instance_tp_state
| +-- status
| +-- location (domain, geolocation, etc.)
| +-- type (1 gateway, 2 gateways, ...)
+-- interconnection_instance_node_service_assurance
+-- events (including triggers and event IDs)
+-- measurements
2.4. Stitching Operation
2.4.1. Operation Overview
Stitching is an operation that takes two or more NS subnets as input,
and produces a single composite NS subnet or end-to-end slice. It
may occur when the slice subnets are being instantiated, or later.
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The first step in this operation is to identify the anchors that will
be used in the interconnection. This may be done by an automated
algorithm that matches the possible interconnection points and
decides which one will be used, according to the policies established
by the NS operator. The operation in this case will require the
presence of semantically-rich attributes in the candidate anchors to
enable automatic matching without human intervention.
Other attributes of slices and anchors will also influence the
operation and the resulting stitched (composite) object. For
instance, network links that are interconnected must have compatible
QoS attributes. Moreover, available networking protocols must also
match among the underlying network elements that are being stitched.
Otherwise, the operation will fail unless the NS operator (based on
policy and/or NS subnet attributes) enables it to search for, and
use, some "bridge" element in the underlying infrastructure.
2.4.2. Stitching Scenarios
This section briefly describes examples of usage for subnet
stitching.
Traversal through a transport network.
Let's consider a network slice composed of (NS) subnet-A, and
subnet-C (Figure 3). Subnet-A and subnet-C are deployed in
independent domains and are mapped into a slice information model;
in order to stitch these two together a transport segment is
needed. N1 and N2 are anchor nodes within NS subnets A and C.
Segment-B could be a simple link between the two NS subnets but it
may also be a TE-link made available by a transport network
provider. Segment-B may be involved in the stitching operation in
one of several ways:
Segment-B may be set up as part of the stitching operation
between NS subnets A and C, as a form of "bridge" mentioned in
Section 2.4. Segment-B will need to comply with service
specific traffic constraints that are determined during the
stitching operation, possibly using attributes from NS subnets
A and C. In this case, the data plane implementation of N1 and
N2 in the composite slice may be, for example, 2 distinct
gateway functions terminating segment-B.
Segment-B may alternatively be represented as a distinct NS
subnet, e.g. in cases where segment-B is complex and/or
involves multiple network functions. In this case, the
stitching operation may therefore involve 3 NS subnets A-B-C.
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+-----------+ +----------+
| +--+ | ______ | +--+ |
| |N1+==========(______)============|N2| |
| +--+ | --transport-- | +--+ |
+-----------+ +----------+
--subnet-A--- --segment-B------ --subnet-C--
<---------------end to end slice ------------>
Figure 3: Example of NS subnets interconnection through transport
network
Subnets in a single domain.
In this scenario multiple network slice subnets are defined as
basic building blocks with specific service functions (or chains),
topologies and traffic handling characteristics. These building
blocks can be assembled through stitching to build end-to-end
customized slices, but also to dynamically extend slices to adapt
to traffic load. Additionally, stitching can also be used to
share building blocks between multiple slices, e.g. to
interconnect multiple slices with a shared function. In all these
cases, interconnection instances may be entirely abstracted away,
although they may also be implemented through one or multiple
gateways, e.g. when stitched subnets belong to different sub-
domains.
3. Security Considerations
Security aspects relative to network slices (e.g., for transport
slices, in [I-D.liu-teas-transport-network-slice-yang]) are
applicable to slice subnets, including transport security aspects,
access control and protection of write operation on newly introduced
nodes (e.g., termination-point).
4. IANA Considerations
This document has no actions for IANA.
5. Informative References
[I-D.clt-dmm-tn-aware-mobility]
Chunduri, U., Li, R., Bhaskaran, S., Kaippallimalil, J.,
Tantsura, J., Contreras, L., and P. Muley, "Transport
Network aware Mobility for 5G", draft-clt-dmm-tn-aware-
mobility-05 (work in progress), November 2019.
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[I-D.contreras-teas-slice-nbi]
Contreras, L., Homma, S., and J. Ordonez-Lucena,
"Considerations for defining a Transport Slice NBI",
draft-contreras-teas-slice-nbi-00 (work in progress),
November 2019.
[I-D.geng-teas-network-slice-mapping]
Geng, X., Dong, J., Niwa, T., and J. Jin, "5G End-to-end
Network Slice Mapping from the view of Transport Network",
draft-geng-teas-network-slice-mapping-00 (work in
progress), February 2020.
[I-D.homma-rtgwg-slice-gateway]
Homma, S., Foy, X., Galis, A., and L. Contreras, "Gateway
Function for Network Slicing", draft-homma-rtgwg-slice-
gateway-01 (work in progress), November 2019.
[I-D.liu-teas-transport-network-slice-yang]
Liu, X., Tantsura, J., Bryskin, I., Contreras, L., and Q.
WU, "Transport Network Slice YANG Data Model", draft-liu-
teas-transport-network-slice-yang-00 (work in progress),
November 2019.
[I-D.nsdt-teas-transport-slice-definition]
Rokui, R., Homma, S., and K. Makhijani, "IETF Definition
of Transport Slice", draft-nsdt-teas-transport-slice-
definition-00 (work in progress), November 2019.
[NGMN_Network_Slicing]
NGMN, "Description of Network Slicing Concept", 10 2016,
<https://www.ngmn.org/uploads/
media/161010_NGMN_Network_Slicing_framework_v1.0.8.pdf>.
[RFC8345] Clemm, A., Medved, J., Varga, R., Bahadur, N.,
Ananthakrishnan, H., and X. Liu, "A YANG Data Model for
Network Topologies", RFC 8345, DOI 10.17487/RFC8345, March
2018, <https://www.rfc-editor.org/info/rfc8345>.
Authors' Addresses
Xavier de Foy
InterDigital Inc.
1000 Sherbrooke West
Montreal
Canada
Email: Xavier.Defoy@InterDigital.com
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Akbar Rahman
InterDigital Inc.
1000 Sherbrooke West
Montreal
Canada
Email: Akbar.Rahman@InterDigital.com
Alex Galis
University College London
Torrington Place
London WC1E 7JE
United Kingdom
Email: a.galis@ucl.ac.uk
Kiran Makhijani
Huawei Technologies
2890 Central Expressway
Santa Clara CA 95050
USA
Email: kiran.makhijani@huawei.com
Li Qiang
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: qiangli3@huawei.com
Shunsuke Homma
NTT, Corp.
3-9-11, Midori-cho
Musashino-shi, Tokyo 180-8585
Japan
Email: homma.shunsuke@lab.ntt.co.jp
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Pedro Martinez-Julia
National Institute of Information and Communications Technology
Japan
Email: pedro@nict.go.jp
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