Internet DRAFT - draft-homma-coms-slice-gateway
draft-homma-coms-slice-gateway
none S. Homma
Internet-Draft NTT
Intended status: Informational X. de Foy
Expires: September 6, 2018 InterDigital Inc.
A. Galis
University College London
March 5, 2018
Gateway Function for Network Slicing
draft-homma-coms-slice-gateway-01
Abstract
This document describes the roles and requirements for a slice
gateway that is a data plane function or function group for
connecting/disconnecting and compose/decompose network slice subnets
and providing network slices from end to end. The interworkings
between management and control elements at the management and control
planes with the gateway function for controlling and orchestrating
end-to-end network slices are also presented in this document.
Status of This Memo
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This Internet-Draft will expire on September 6, 2018.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 4
3. Motivations and Roles of SLG . . . . . . . . . . . . . . . . 5
4. Architecture Overview of NS Management . . . . . . . . . . . 8
5. Requirements for SLG . . . . . . . . . . . . . . . . . . . . 9
5.1. Management of NS as Infrastructure . . . . . . . . . . . 10
5.1.1. Data Plane Aspect . . . . . . . . . . . . . . . . . . 10
5.1.1.1. Identification/Classification . . . . . . . . . . 10
5.1.1.2. Transporting/Forwarding . . . . . . . . . . . . . 10
5.1.1.3. Isolation between NSs . . . . . . . . . . . . . . 12
5.1.1.4. Service Chaining as Infrastructural
Mechanism(*Optional) . . . . . . . . . . . . . . 12
5.1.2. Control/Management Planes Aspects . . . . . . . . . . 13
5.1.2.1. Interfaces to Controllers or Operation Systems . 13
5.1.2.2. Address Resolution/Routing . . . . . . . . . . . 13
5.1.2.3. Authentication Authorization Accounting (AAA) . . 13
5.1.2.4. Operation Administration and Maintenance(OAM) . . 13
5.2. Management of Services on NS (*Optional) . . . . . . . . 13
5.2.1. Data Plane Aspect . . . . . . . . . . . . . . . . . . 13
5.2.1.1. Identification/Classification . . . . . . . . . . 13
5.2.1.2. QoS Control . . . . . . . . . . . . . . . . . . . 14
5.2.1.3. Steering/Service Chaining(Cooperation with VNFs) 14
5.2.2. Control/Management Planes Aspects . . . . . . . . . . 14
5.2.2.1. Interfaces to Service Management Systems . . . . 14
5.2.2.2. Collection of Telemetry information . . . . . . . 14
6. Deployment of SLG . . . . . . . . . . . . . . . . . . . . . . 14
6.1. Examples of Components Required to Maintain SLG Functions 15
6.2. SLG Types Depending on Locations on NS . . . . . . . . . 15
6.2.1. Edge SLG(E-SLG) . . . . . . . . . . . . . . . . . . . 15
6.2.2. Inter-Subnet SLG(IS-SLG) . . . . . . . . . . . . . . 15
6.2.3. Inter-Domain SLG(ID-SLG) . . . . . . . . . . . . . . 15
6.3. Horizontal Connection . . . . . . . . . . . . . . . . . . 15
6.4. Vertical Connection . . . . . . . . . . . . . . . . . . . 18
6.5. Software vs. Hardware . . . . . . . . . . . . . . . . . . 19
7. Interconnection between NS subnets . . . . . . . . . . . . . 19
7.1. Pre-arrangement of transport protocols . . . . . . . . . 19
7.2. Quality Assurance between SLGs . . . . . . . . . . . . . 19
7.3. Secure Interconnection . . . . . . . . . . . . . . . . . 20
8. Security Considerations . . . . . . . . . . . . . . . . . . . 20
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
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10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 20
11. Informative References . . . . . . . . . . . . . . . . . . . 20
Appendix A. Position of SLG on ETSI NFV MANO . . . . . . . . . . 22
Appendix B. Requirements for each SLG Type . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction
Network slicing is an approach to create separate virtual networks in
support of service depending on several requirements on the same
physical resources, and it enables networks to adapt to requirements,
which is diverse more, inexpensively and flexibly. It's also
expected to enhance usability of infrastructural networks for tenants
and create new business opportunities. For example, by using network
slices lent from infrastructure operators, other industrial companies
can provide communication services including ensurance of network
transport without having physical infrastructure.
From a business point of view, a slice includes a combination of all
the relevant network resources, functions, and assets required to
fulfill a specific business case or service, including OSS, BSS and
DevOps processes.
From the network infrastructure point of view, network slice requires
the partitioning and assignment of a set of resources that can be
used in an isolated, disjunctive or non- disjunctive manner for that
slice.
From the tenant point of view, network slice provides different
capabilities, specifically in terms of their management and control
capabilities, and how much of them the network service provider hands
over to the slice tenant. As such there are two kinds of slices: (A)
Inner slices, understood as the partitions used for internal services
of the provider, retaining full control and management of them. (B)
Outer slices, being those partitions hosting customer services,
appearing to the customer as dedicated networks.
Network slices are established with combination of various
technologies, such as software defined network (SDN), network
function virtualization (NFV), or traffic engineering, and managed/
operated with automation technologies such as orchestrator.
Assumed use cases of network slices include establishment of virtual
networks whose qualities are guaranteed from end to end under the
supervision of multi-domain orchstrators. In such cases, a network
slice subnet is created on each domain, such as access network and
core network, and such network slices are composed of connected
subnets.
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Network slice subnets are built based on specification of the
underlay network, and thus the used technologies might vary.
Therefore, a gateway function, which enables to connect subnets while
adapting the differentiations and forward data packets to/from the
appropriate next subnet, is required. Defining a new data plane
technology is not a goal of this draft. This draft aims to specify
management-related requirements for an SLG, which may be implemented
using existing data plane technologies.
In this document, the gateway function is called slice gateway or
SLG, and the role and requirements are described.
2. Definition of Terms
Network Slicing: Network slicing is a technology or an approach to
create separate virtual networks in support of services, depending
on several requirements, on the same physical resources. This is
possible by combinations of several network technologies.
Network Slice (NS): An NS is a virtual network established on
network infrastructure. Some include additional network functions
such as firewall or load-balancer in addition to basically
forwarding functions such as switches or routers. It has an
overlay architecture and is independent from the underlay
network's topology.
NS Subnet: An NS subnet is partially virtual network established
within a single domain.
End-to-End Network Slice (E2E-NS): An E2E-NS is a virtual network
connecting between end points. E2E slices are composed of a
single NS subnet or multiple NS subnets.
Network Slice as a Service (NSaaS): An NSaaS is a NS distribution
model in which a third-party provider hosts NSs and makes them
available to customers.
Network Slice Tenant (NS Tenant): An NS tenant is a person or group
that rents and occupies NSs from NS providers.
Domain: A domain is a group of a network and devices administrated
as a unit with common rules and procedures.
Administrative Domain: An administrative domain is a group of
networks and devices managed by an administrator.
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Resource: A resource is element used to create virtual networks.
There are several types of resources, i.e., connectivity,
computing and storage.
Network Function Virtualization (NFV): NFV is the concept or
technologies to provide dedicated network appliances as software.
Software Defined Network (SDN): SDN is the concept or technologies
to separate network control plane from data plane, and control
network devices dynamically and flexibly.
Virtual Network: A virtual network is a network running a number of
virtual network functions.
Virtual Network Function (VNF): A virtual network function (VNF) is
a network function whose functional software is decoupled from
hardware. One or more virtual machines running different software
and processes on top of industry-standard high-volume servers,
switches and storage, or cloud computing infrastructure, and
capable of implementing network functions traditionally
implemented via custom hardware appliances and middleboxes (e.g.,
router, NAT, firewall, load balancer, etc.)
Slice Gateway Function (SLG): An SLG is a function or a group of
functions to connect/disconnect NS subnets. The role is described
in the following sections.
Business Support System and Operation Support System (BSS/OSS): BSS/
OSS are systems to support service providing and operation of
network devices.
Orchestrator: Orchestrator is an entity to operate network
components automatically. There are several types of
orchestrators including NFV Orchestrator (NFVO) or service
orchestrator defined by ETSI NFV and Open Source MANO (OSM)
([NFV-Architectural-Framework] and [OSM-White-Paper]).
SLG Controller (SLG-Ctrl): An SLG-Ctrl is an entity that controls
SLGs. An SLG-Ctrl is controlled by upper-level operation systems
such as OSS/BSS or orchestrator.
3. Motivations and Roles of SLG
SLG main role is the enablement of interworkings between data plane
with management and control elements for controlling and
orchestrating end-to-end slices.
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Use cases of network slices are discussed in several Standard
Developing Organizations (SDOs). Some examples are described in use
cases document ([I-D.netslices-usecases]).
In some proposed use cases, an NS is structured across multiple
network domains. The capability of NS subnets might be different
because the components are domain-specific. In particular, the
differentiation in capability between different administrative
domains is large.
For connecting some different NS subnets and providing a NS that
guarantees the prescribed quality from end to end, SLGs are required
to connect such NS subnets. SLGs enable to provide E2E-NSs
independently of specifications of underlay networks by hiding the
differentiations and connecting between NS subnets. An overview of
this concept is shown in Figure 1. SLGs glue NS subnets established
on each domain and provide an E2E-NS.
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E2E-NS
________________________A_________________________
/ \
_____________ ____________ _________________
/ // / / /
end +---+ NS +---+ NS +---+ +---+ NS ,------.
host==>|SLG| Subnet |SLG| Subnet |SLG+-+SLG| Subnet( Server )
+---+ #1 +---+ #2 +---+ +---+ #3 `------'
/____________//___________/ /________________/
/____________//___________/ /________________/
: : :
: : :
.--. .--. .--.
( )-. ( )-. ( )-.
.' Access ' .' Core ' .' Data '
( Network ) ( Network ) ( Center )
( -' ( -' ( /Cloud -'
'-( ) '-( ) '-( )
'---' '---' '---'
\______ ______/ \_____ _____/ \________ ________/
V V V
Domain#1 Domain#2 Domain#3
\_____________ _____________/ \________ ________/
V V
Domain of Administrator#A Domain of Administrator#B
Figure 1: E2E-NS composed of multiple NS subnets
Moreover, identification of user service traffic and their
allocation/disallocation to the appropriate NS subnet are required at
the edges of E2E-NSs, as shown in Figure 2, and SLGs might take on
these roles.
+-----+ _______________
end | |-->/_______________
host ====>| SLG | NS Subnet#1
|@Edge| _______________
| |-->/______________
| | NS Subnet#2
| | : :
+-----+
Figure 2: NS subnet selection of SLG
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Note that, this model has the assumption that transitions of data
packets from one NS subnet to another are executed at only SLGs.
Also, an SLG is not necessarily implemented as a single device or
virtual machine (VM).
4. Architecture Overview of NS Management
The architecture overview of NS management system is shown in
Figure 3. Orchestrators manage whole resources including network
elements and server resources (i.e., routing, bandwidth, compute or
storage). In this figure, the resources including network elements
and server resources are managed by resource orchestrators installed
in each domain, and the E2E-orchestrator and network service
orchestrator handle resource orchestrators.
NSs are requested from NS tenants via the portal system and the order
of creations of an NS is given to the E2E orchestrator from the
portal system via BSS/OSS. When an NS across multiple administrative
domains are requested, the portal system that received the request
forwards the order to create NS subnets to the other infrastructure
providers' systems via Cross-Segment Slice Manager. The details of
COMS architecture are described in the architecture document ([I-
D.qiang-coms-architecture]).
SLGs are also controlled via orchestrators. An SLG basically belongs
to a network element, and it might also belong to server resource if
it runs as a VNF. (An example of position of SLG deployed as a VNF
is shown in Appendix A.)
SLGs are located at the edges of each NS subnet. They translate data
packets into the appropriate form and send them to the next NS
subnet. SLGs located at the end of E2E-NSs additionally provide
identification of data packets and select the assigned NS subnet
based on the identification result.
The information model used in this architecture is described in
information model document
([I-D.qiang-coms-netslicing-information-model]).
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NS Tenant
|
. .|. . . . . . . . . . . . . . . . . . . . .
. +-v---------+ .
. |Portal/GUI +--+ .
. +-+---------+ | . . . . . . . . . .
. | +-v-----------------------+ . . +------------+ .
. | |CSS-Mngr./TNS-Orch. |<------->|CSS-M/TNS-O | .
. | +-+-------+---------------+ . . +-+--------+-+ .
. | | | . . | | .
. +-v-----+ | | . . +-v-----+ | .
. |BSS/OSS|<-----+ | . . |BSS/OSS| | .
. +-+-----+ | . . +-+-----+ | .
. | | . . | | .
. +-v--------------------v-----------+ . . +-v--------v-+ .
. | E2E-Orch./Network Service-Orch. | . . |E2E-O/NS-O | .
. +-+--------------------+-----------+ . . +-+--------+-+ .
. | | . . | | .
. +-v----------------+ +-v----------------+ . . : .
. | Resource Orch.#1 | | Resource Orch.#2 |.. . . . . . . . . . .
. +-+---------+------+ +-+---------+------+ . Administrative
. | | | | . Domain#2
. +-v------++-v------+ +-v------++-v------+ .
. |Network ||NFV | |Network ||NFV | .
. |Ctrl. ||Ctrl. | |Ctrl. ||Ctrl. | .
. +-+------++-+------+ +-+------++-+------+ .
. | | | | .
. +-v------++-v------+ +-v------++-v------+ .
. |Network ||Server | |Network ||Server | .
. |Elements||Resource| |Elements||Resource|.. .
. |in ||in | |in ||in | .
. |Domain#1||Domain#1| |Domain#2||Domain#2| .
. +--------++--------+ +--------++--------+ .
. . . . . . . . . . . . . . . . . . . . . . .
Administrative Domain#1
CSS-Mngr./CSS-M:Cross-Segment Slice Manager
TNS-Orch./TNS-O:Transport Network Slice Orchestrator
Figure 3: Overview of NS Management Architecture
5. Requirements for SLG
An SLG is basically a component in the data plane and has the roles
of data packet processing. Moreover, it is required to have
functions for control/management processes such as connecting to
underlay networks or managing NSs.
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Furthermore, an SLG might be required to support handling services
provided on NSs in addition to controlling of NS because an SLG is an
edge node on an E2E-NS.
In this section, we describe the requirements for an SLG in terms of
the following aspects and their interworkings.
1. Data plane for NSs as infrastructure
2. Control/management plane for NSs as infrastructure
3. Data plane for services on NSs
4. Control/management plane for services on NSs
5.1. Management of NS as Infrastructure
5.1.1. Data Plane Aspect
5.1.1.1. Identification/Classification
SLGs at the edge of E2E-NSs MUST have the capability to identify and
classify data packets, and assign them to the appropriate E2E-NS.
This requirement varies depending on the location.
Fixed Access: An SLG MUST identify and classify data packet with
access point, including CPE or WiFi-AP, or subscriber ID such as
VLAN-ID. Moreover, in some services, an SLG should identify and
classify data packets based on user device or application used in
the communication.
Mobile Access: An SLG MUST identify and classify data packet with
subscriber-ID such as IMSI, radio-wave bandwidth, or identifier of
tunnels. Moreover, in some services, an SLG should identify and
classify data packets based on application used in the
communication or location of the user equipment (UE).
Between NS subnets: An SLG MUST identify and classify data packet
based on the tunnel-ID or virtual routing and forwarding (VRF)
that received the packets. If specific slice identifier such as a
value mapped in the metadata field of the IP header is used; an
SLG should identify and classify data packets with the ID.
5.1.1.2. Transporting/Forwarding
SLGs MUST provide functions for transport data packets depending on
the specifications of the underlay networks.
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Encapsulation/Decapsulation/Tagging: In network slicing, duplication
of IP addresses of user packets between NSs MUST be accepted,
thus, using techniques that enable separation of a network
logically is preferred. In short, some tunnel protocols or
tagging approaches should be used as transport of NSs. For this
reason, SLG MUST support encapsulation or tagging of data packets
based on the specification of the underlay network. Also, SLG
MUST support the packets' decapsulation or untagging. Examples of
tunnel protocols and tags that can be used for creating NSs on L2/
L3 segments are described below.
L2 Segment: VLAN, MPLS, Segment Routing MPLS (SR-MPLS), PPPoE,
etc.
L3 Segment: GRE, L2TP, GTP-U, VxLAN, IPv6 Segment Routing (SRv6),
etc.
VxLAN, SR-MPLS, and SRv6 are described in their specification
documents ([RFC7348], [I-D.ietf-spring-segment-routing-mpls], and
[I-D.ietf-6man-segment-routing-header]).
Translation of Encapsulation/Tagging Form: SLG MUST support to
translate tunnel header or tag of received packets to the
appropriate tunnel header or tag when it forwards data packets to
the next NS subnet that has different transport capability.
Distribution of Traffic: Some NSs have multiple route between the
same end points within the same NS subnet because of traffic
engineering, switching to a redundant path, or other reasons, and
SLG MAY forward data packets with the appropriate route based on
some trigger information. An example of the overview of this
requirement is shown in Figure 4. In this figure, there are two
routes, main and sub, between SLGs, and an SLG switches forwarding
route depending on the network situation such as congestion
occurrence on the current route.
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____________________________
/ . . . . . /
+-----+ . . +-----+
| |. . . .| |
| SLG | | SLG |
| |* * * *| |
+-----+ * * +-----+
/ * * * * * /
/___________________________/
NS Subnet
*** : Main-route
... : Sub-route
Figure 4: An example of traffic distribution by SLG
5.1.1.3. Isolation between NSs
In NSaaS, isolation control is required for avoiding an NS being
affect by other NSs. Traffic engineering or QoS control is ones of
the most fundamental approaches to prevent disturbances between NSs.
Traffic Shaping/Policing: An SLG MUST execute traffic shaping and
policing at its egress and ingress ports to avoid an NS using
excessive traffic bandwidth.
Quality of service (QoS) Control: If there is an order of priority
between NSs on the same underlay infrastructure, an SLG should
remark the appropriate QoS parameter of the outer-most header of
each packet following the preconfigured setting and provide packet
scheduling based on the QoS parameter for providing priority
control. The field that SLG refers may vary depending on the
specification of the underlay network. For example, COS value is
remarked in L2 segments; on the other hand, DSCP value is remarked
in L3 segments.
5.1.1.4. Service Chaining as Infrastructural Mechanism(*Optional)
If an SLG is composed of a combination of several components, a
service chaining mechanism is required to make them work together and
achieve SLG functionality.
Moreover, some NSs may traverse NFVs such as firewalls or cache
servers for providing value-added services to their users. In such
cases, SLG might be required to support service chaining mechanisms,
such as handling of network service header (NSH) defined in
[RFC8300]. If an NS includes the service chaining architecture
defined in [RFC7665], some SLG would be required to support following
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functions; classifier(CF), service function forwarder (SFF), and
inter boundary node(IBN). (Details of CF, SFF and IBN are described
in SFC documents; [RFC7665], [I-D.ietf-sfc-hierarchical].)
5.1.2. Control/Management Planes Aspects
5.1.2.1. Interfaces to Controllers or Operation Systems
SLG MUST have interface to its controller or operation systems for
set parameters related to the data plane functions described in
Section 5.1.1. In addition, an SLG at the edges of E2E-NSs MUST have
interfaces to authentication servers.
5.1.2.2. Address Resolution/Routing
An SLG MUST support address resolution or routing mechanisms to
connect to underlay network elements including routers or L2
switches.
5.1.2.3. Authentication Authorization Accounting (AAA)
For preventing entry of irregular traffic to NSs, an SLG at the edge
of E2E-NS MUST support AAA mechanism for incoming traffic. Also,
when an SLG connects to another SLG in other administrative domain,
SLGs should have a mechanism to confirm that the connection is
established with the regular processes. For example, an SLG is
required to support authentication of the opponent SLG with key
information indicated from higher-level operation systems.
5.1.2.4. Operation Administration and Maintenance(OAM)
In management of NSs, OAM or monitoring mechanisms for both underlay
and overlay networks is required for SLGs. For an underlay network,
an SLG MUST have OAM functions to confirm connectivity to
interconnect equipment. For an overlay network, an SLG MUST have OAM
functions to confirm connectivity to the some node on the same NS,
and measure the traffic amount of flowing packets on each NS.
5.2. Management of Services on NS (*Optional)
5.2.1. Data Plane Aspect
5.2.1.1. Identification/Classification
In NSaaS, some NS tenants may need delivery of an individual service
to each user, device, or application on the same NS. For such
service deliveries, an SLG might be required to identify and classify
user traffic based on some information such as subscriber ID or
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payload of data packets. Also, an SLG should be controllable from
the NS tenant.
5.2.1.2. QoS Control
An NS accommodates several communication devices and SLGs might be
required to have fair queueing mechanisms for maintaining service
quality of each user. Also, different types of service traffic that
have different priorities might coexist on an NS. For example, some
NS providers might provide telephone and internet access services to
their users with an NS. In such cases, SLG might be required to
provide QoS control mechanisms for enforcing priority control based
on service priorities.
These QoS controls are executed depending on the information of inner
packets and are independent of isolation mechanisms as
infrastructure. An SLG might be required to have a hierarchical QoS
control mechanism in case that both QoS controls for services over
NSs and isolation between NSs are required.
5.2.1.3. Steering/Service Chaining(Cooperation with VNFs)
SLG might be required to support steering or service chaining
function for conveying data packets to the appropriate network
functions deployed on an NS based on the classification result and
user's contract information.
5.2.2. Control/Management Planes Aspects
5.2.2.1. Interfaces to Service Management Systems
An SLG might have interfaces to controllers for managing user
policies on each NS. Some controllers might be deployed on the same
NS. If some controllers are located at external networks, they might
require SLGs to have APIs.
5.2.2.2. Collection of Telemetry information
In an NSaaS, collection of telemetry information of each NS might be
required for understanding traffic usage. Thus, an SLG might be
required to support to collect and report telemetry information of
connected NSs.
6. Deployment of SLG
This section describes considerations related with deployment of
SLGs.
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6.1. Examples of Components Required to Maintain SLG Functions
For providing E2E-NSs on existing network infrastructures, some
components located at boundaries of domains are required to have the
same set of functionality as an SLG. Examples of such components in
each domain type are described below.
Fixed Network: CPE/HGW, Service Edge, Gateway Router, etc.
Mobile Network: User Equipment, Radio-AP, eNodeB, S/P-GW
([LTE-Specs]), etc.
Data Center: Gateway Router, L2 switch, ToR switch, Server, etc.
6.2. SLG Types Depending on Locations on NS
There are mainly three types of SLG for creating E2E-NS across
multiple administrative domains. The requirements of each SLG type
are listed in Appendix B.
6.2.1. Edge SLG(E-SLG)
This is located at an edge of an E2E-NS, and supports identification,
classification and authentication of user traffic in addition to
fundamental SLG functions, such as transport and isolation. Also, it
might be required to have capabilities for services delivered on an
NS.
6.2.2. Inter-Subnet SLG(IS-SLG)
This is located between NS subnets within a single administrative
domain and has only fundamental functions. It is not necessarily
required if a common transport mechanism in all domains is used.
6.2.3. Inter-Domain SLG(ID-SLG)
This is located between NS subnets established on different domains.
It supports authentication for connecting to the opponent SLG in
addition to fundamental functions.
6.3. Horizontal Connection
The connection form of an SLG varies depending on which type it is.
Examples of horizontal connection forms of each SLG type are
described below.
E-SLG: An E-SLG accommodates several hosts and NS subnets. This has
a forwarding table of end hosts and insert their packets to the
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appropriate NS subnet. An overview of this connection is shown in
Figure 5.
*Virtual Layer*
+-----+
host#1 ====>| | _______________
| |-->/_______________
host#2 ====>|E-SLG| NS Subnet#1
| | _______________
host#3 ====>| |-->/_______________
| | NS Subnet#2
: : | | : :
+-----+
////////////////////////////////////////
*Physical Layer*
,--------------------
[UE#1] -----\ /
[UE#2] -----[Edge] Domain#1
[UE#3] -----/ \
: : `-------------------
Edge: Edge Node
Figure 5: Overview of horizontal connection of E-SLG
IS-SLG: An IS-SLG has the role of mediator between NS subnets and
passes packets received from an NS subnet to the next one. If
transport methods used in each domain are different, the IS-SLG
translate packet form to the appropriate one. An overview of this
connection is shown in Figure 6.
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*Virtual Layer*
+------+
_________ | | ___________
_________/-->|IS-SLG|--> /__________
NS Subnet#1 | | NS Subnet#2
+------+
///////////////////////////////////////
*Physical Layer*
--------------. ,--------------
\ /
Domain#1 [ GW ] Domain#2
/ \
--------------' `--------------
GW: Gateway Node
Figure 6: Overview of horizontal connection of IS-SLG
ID-SLG: An ID-SLG passes data packets to another ID-SLG located on a
different administrative domain. Some tunnel established between
them in advance may be used for the passing of packets. An
overview of this connection is shown in Figure 7.
*Virtual Layer*
+------+ +------+
_________ | | ______ | | ___________
_________/-->|ID-SLG|O______)|ID-SLG|-->/__________
NS Subnet#1 | | Tunnel | | NS Subnet#2
+------+ +------+
///////////////////////////////////////////////////////
*Physical Layer*
--------------------. ,-------------------
Administrative \ / Administrative
Domain#1 [ GW ]---[ GW ] Domain#2
/ \
--------------------' `-------------------
GW: Gateway Node
Figure 7: Overview of horizontal connection of ID-SLG
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6.4. Vertical Connection
There are two patterns of vertical connection of SLGs in the middle
of E2E-NSs. The first pattern is that the SLGs accommodate only a
set of NS subnets, which are composition of the same E2E-NS. In this
pattern, such SLGs are not required to support NS subnet selection,
however, establishment of a new SLG is required when a new E2E-NS is
created. This might causes extra overheads because of deploying many
SLGs.
The other pattern is that such SLGs are acceptable to accommodate
multiple NS subnets from each domain. In this pattern, SLGs are
support NS subnet selection. On the other hand, this pattern can
restrain the number of SLGs. Also, it is easy to provide transit of
data packets from an NS subnet to other subnet on the same domain.
The overviews of these patterns are shown in Figure 8 and Figure 9.
+-----+
_________ | | ___________
_________/-->|SLG#1|-->/__________
NS Subnet#1 | | NS Subnet#2
+-----+
+-----+
_________ | | ___________
_________/-->|SLG#2|-->/__________
NS Subnet#3 | | NS Subnet#4
+-----+
: : :
Figure 8: Overview of vertical connection of SLG: Separated Pattern
+-----+
_________ | | ___________
_________/-->| |-->/__________
NS Subnet#1 |SLG#1| NS Subnet#2
_________ | | ___________
_________/-->| |-->/__________
NS Subnet#3 | | NS Subnet#4
| |
: | | :
+-----+
Figure 9: Overview of vertical connection of SLG: Shared Pattern
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6.5. Software vs. Hardware
An SLG can be created as either a software or hardware function. NSs
are virtual networks created depending on requests from external NS
tenants, and thus software would be more compatible with usage for
NSs in terms of flexibility or manageability. Moreover, it enables
to increase or decrease for each function if SLG is composed of
combination of several components. However, it is difficult to
provide high performance or sufficient throughput for carrier-grade
networks with software function. In addition, it would be difficult
to implement sufficient QoS control mechanisms with general servers,
because they requires special hardware structures.
On the other hand, hardware appliances are able to provide high
throughput compared with software. However, they are inflexible in
terms of provisioning.
From the above considerations, operators should prepare SLG in
appropriate ways depending on their usages or locations.
7. Interconnection between NS subnets
SLG provides interconnectivity between NS subnets. The concept and
fundamental framework including the related NS information model are
described in subnets interconnection document
([I-D.defoy-coms-subnet-interconnection]).
This section is focused on interconnection between NS subnets
established on different administrative domains, and describes
considerations related to this condition.
7.1. Pre-arrangement of transport protocols
For interconnection between different administrative NS subnets, pre-
arrangement of the transport protocol, which is used to connect
between SLGs is required. Orchestration systems indicate the
protocol and configuration to each SLG.
7.2. Quality Assurance between SLGs
In addition to establishing connection, quality control of
communication is important. SLGs of egress side should execute
traffic shaping to prevent some NSs from excessively occupying the
link between SLGs. Moreover, some SLGs are connected to several
other SLGs that are deployed on the different locations. Therefore
SLGs of the ingress side should execute traffic policing to avoid
excessive inflow of traffic into some NSs. The parameters for these
controls are pre-configured by orchestration systems.
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The above approaches are ones of the simplest ways to provide quality
assurance of inter-administrative subnets. If there is stricter
isolation request, more considerations would be required.
7.3. Secure Interconnection
For connecting networks of different administrators, secure
interconnection schemes are required. Especially, in an NSaaS,
networks might be connected to several networks, and schemes for
ensuring secure connectivity would be more important.
SLGs confirm whether the opponent SLG is regular when it requests to
connect, and reject the request if the SLG is not regular. In some
cases, SLGs might be confirm whether the inner packets received from
the other SLGs are sent from regular users.
8. Security Considerations
Requirements and considerations for SLG related to security are
described in Section 5 and Section 7.
9. IANA Considerations
This memo includes no request to IANA.
10. Acknowledgement
The authors would like to thank Li Qiang for her kind review and
valuable feedback.
11. Informative References
[I-D.defoy-coms-subnet-interconnection]
Foy, X., Rahman, A., Galis, A.,
kiran.makhijani@huawei.com, k., and L. Qiang,
"Interconnecting (or Stitching) Network Slice Subnets",
draft-defoy-coms-subnet-interconnection-01 (work in
progress), October 2017.
[I-D.ietf-6man-segment-routing-header]
Previdi, S., Filsfils, C., Raza, K., Dukes, D., Leddy, J.,
Field, B., daniel.voyer@bell.ca, d.,
daniel.bernier@bell.ca, d., Matsushima, S., Leung, I.,
Linkova, J., Aries, E., Kosugi, T., Vyncke, E., Lebrun,
D., Steinberg, D., and R. Raszuk, "IPv6 Segment Routing
Header (SRH)", draft-ietf-6man-segment-routing-header-08
(work in progress), January 2018.
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[I-D.ietf-sfc-hierarchical]
Dolson, D., Homma, S., Lopez, D., and M. Boucadair,
"Hierarchical Service Function Chaining (hSFC)", draft-
ietf-sfc-hierarchical-05 (work in progress), November
2017.
[I-D.ietf-spring-segment-routing-mpls]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing with MPLS
data plane", draft-ietf-spring-segment-routing-mpls-11
(work in progress), October 2017.
[I-D.netslices-usecases]
kiran.makhijani@huawei.com, k., Qin, J., Ravindran, R.,
67, 4., Qiang, L., Peng, S., Foy, X., Rahman, A., Galis,
A., and G. Fioccola, "Network Slicing Use Cases: Network
Customization and Differentiated Services", draft-
netslices-usecases-02 (work in progress), October 2017.
[I-D.qiang-coms-netslicing-information-model]
Qiang, L., Galis, A., 67, 4., kiran.makhijani@huawei.com,
k., Martinez-Julia, P., Flinck, H., and X. Foy,
"Technology Independent Information Model for Network
Slicing", draft-qiang-coms-netslicing-information-model-01
(work in progress), October 2017.
[LTE-Specs]
3rd Generation Partnership Project (3GPP), "3GPP TS
36.300", December 2007,
<http://www.qtc.jp/3GPP/Specs/36300-830.pdf>.
[NFV-Architectural-Framework]
Network Functions Virtualisation (NFV) ETSI Industry
Specification Group (ISG), "Network Functions
Virtualisation (NFV); Architectural Framework", December
2014, <http://www.etsi.org/deliver/etsi_gs/
NFV/001_099/002/01.02.01_60/gs_NFV002v010201p.pdf>.
[OSM-White-Paper]
ETSI, "OSM White Paper", October 2016,
<https://osm.etsi.org/images/
OSM-Whitepaper-TechContent-ReleaseONE-FINAL.pdf>.
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[RFC7348] Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
eXtensible Local Area Network (VXLAN): A Framework for
Overlaying Virtualized Layer 2 Networks over Layer 3
Networks", RFC 7348, DOI 10.17487/RFC7348, August 2014,
<https://www.rfc-editor.org/info/rfc7348>.
[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>.
[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>.
Appendix A. Position of SLG on ETSI NFV MANO
The mapping of SLG as a VM into ETSI NFV MANO architecture is
described in Figure 10.
+---------------------------+
| BSS/OSS, Orchestrator |
+-+---------------+---------+
| |
+-v------+ +-v---------+
|SLG-Ctrl| | NFV Orch. |
+-+------+ +-+---------+
| |
,-v------. |
| SLG | |
:========: +-v---------+
| VM |<-----+ VNF Mngr. |
`--------' +-+---------+
+--------+ |
|HostOS/ | +-v---------+
|Server |<-----| VIM |
+--------+ +-----------+
Figure 10: Position of SLG as a VM on ETSI NFV MANO
Appendix B. Requirements for each SLG Type
The requirements for each SLG type are listed in Figure 11.
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+---------------++-------+-------+-------+----------------+
| || E-SLG |IS-SLG |ID-SLG | Reference |
+=========================================================+
|*Data-Plane of NS as Infrastructure |
+=========================================================+
|Identification/|| M | O | O |Section 5.1.1.1.|
|Classification || | | | |
+---------------++-------+-------+-------+----------------+
|Transport/ || M | O | M |Section 5.1.1.2.|
|Forwarding || | | | |
+---------------++-------+-------+-------+----------------+
|Isolation || M | M | M |Section 5.1.1.3.|
+---------------++-------+-------+-------+----------------+
|Service Chain || O | O | O |Section 5.1.1.4.|
+=========================================================+
|*Control/Management-Plane of NS as Infrastructure |
+=========================================================+
|IF to Ctrl/OpS || M | M | M |Section 5.1.2.1.|
+---------------++-------+-------+-------+----------------+
|Addr Resolution|| M | M | M |Section 5.1.2.2.|
|/Routing || | | | |
+---------------++-------+-------+-------+----------------+
|AAA || M | - | M |Section 5.1.2.3.|
+---------------++-------+-------+-------+----------------+
|OAM || M | M | M |Section 5.1.2.4.|
+=========================================================+
|*Data-Plane for Service on NS |
+=========================================================+
|Identification/|| O | - | O |Section 5.2.1.1.|
|Classification || | | | |
+---------------++-------+-------+-------+----------------+
|QoS Control || O | O | O |Section 5.2.1.2.|
+---------------++-------+-------+-------+----------------+
|Steering/ || O | - | O |Section 5.2.1.3.|
|Service Chain || | | | |
+=========================================================+
|*Control/Management-Plane for Service on NS |
+=========================================================+
|IF to Service || O | O | O |Section 5.2.2.1.|
|Manager || | | | |
+---------------++-------+-------+-------+----------------+
|Telemetory || O | O | O |Section 5.2.2.2.|
+---------------++-------+-------+-------+----------------+
M: Mandatry, O: Optional, - : Not Required
Figure 11: List of Requirements for each SLG
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Authors' Addresses
Shunsuke Homma
NTT, Corp.
3-9-11, Midori-cho
Musashino-shi, Tokyo 180-8585
Japan
Email: homma.shunsuke@lab.ntt.co.jp
Xavier de Foy
InterDigital Inc.
1000 Sherbrooke West
Montreal
Canada
Email: Xavier.Defoy@InterDigital.com
Alex Galis
University College London
Torrington Place
London WC1E 7JE
United Kingdom
Email: a.galis@ucl.ac.uk
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