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Internet Engineering Task Force J. Arkko
Internet-Draft Ericsson
Intended status: Informational October 2017
Expires: April 4, 2018
Considerations on Network Virtualization and Slicing
draft-arkko-arch-virtualization
Abstract
Network virtualization is network management pertaining to treating
different traffic categories in separate virtual networks, with
independent resource, technology, and topology choices.
This document makes some observations on the effects virtualization
on Internet architecture. A further revision of this document will
also provide a summary of IETF technologies that relate to network
virtualization. An understanding of what current technologies there
exist and what they can or cannot do is the first step in developing
plans for possible extensions.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 4, 2018.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
Arkko Expires April 4, 2018 [Page 1]
Internet-Draft Network Virtualization October 2017
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. General Observations . . . . . . . . . . . . . . . . . . . . 3
4. Overview of IETF Virtualization Technologies . . . . . . . . 4
5. Architectural Observations . . . . . . . . . . . . . . . . . 4
6. Further Work . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
8. Informative References . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
Network virtualization is network management pertaining to treating
different traffic categories in separate virtual networks, with
independent resource, technology, and topology choices.
This document makes some observations on the effects virtualization
on Internet architecture.
A further revision of this document will also provide a summary of
IETF technologies that relate to network virtualization. An
understanding of what current technologies there exist and what they
can or cannot do is the first step in developing plans for possible
extensions.
In particular, whether one calls a particular piece of technology
"virtualization", "slicing", "separation", or "network selection"
does not matter at the level of a system. Any modern system will use
several underlying technology components that may use different terms
but provide some separation or management. So, for instance, in a
given system you may use VLAN tags in an ethernet segment, MPLS or
VPNs across the domain, NAIs to select the right AAA instance, and
run all this top of virtualized operating system and software-based
switches. As new needs are being recognised in the developing
virtualization technology, what should drive the work is the need for
specific capabilities rather than the need to distinghuish a
particular term from another term.
2. Definitions
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Internet-Draft Network Virtualization October 2017
Network function virtualization is defined in Wikipedia as follows:
"Network function virtualization or NFV is a network architecture
concept that uses the technologies of IT virtualization to
virtualize entire classes of network node functions into building
blocks that may connect, or chain together, to create
communication services.
NFV relies upon, but differs from, traditional server-
virtualization techniques, such as those used in enterprise IT. A
virtualized network function, or VNF, may consist of one or more
virtual machines running different software and processes, on top
of standard high-volume servers, switches and storage devices, or
even cloud computing infrastructure, instead of having custom
hardware appliances for each network function."
The related term slicing has been used to describe a virtualization
concept in planned 5G networks. The 3GPP architecture specification
[TS-3GPP.23.501] defines network slices as having potentially
different "supported features and network functions optimisations",
and spanning functions from core network to radio access networks.
[I-D.king-teas-applicability-actn-slicing] defined slicing as "an
approach to network operations that builds on the concept of network
abstraction to provide programmability, flexibility, and modularity.
It may use techniques such as Software Defined Networking (SDN) and
Network Function Virtualization (NFV) to create multiple logical
(virtual) networks, each tailored for a set of services that are
sharing the same set of requirements, on top of a common network.
3. General Observations
Software vs. Protocols
Many of the necessary tools for using virtualization are software,
e.g., tools that enable running processes or entire machines in a
virtual environment decoupled from physical machines and isolated
from each other, virtual switches that connect systems together,
management tools to set up virtual environments, and so on. From
a communications perspective these tools operate largely in the
same fashion as their real-world counterparts do, except that
there may not be wires or other physical communication channels,
and that connections can be made in the desired fashion.
In general, there is no reason for protocols to change just
because a function or a connection exists on a virtual platform.
However, sometimes there are useful underlying technologies that
facilitiate connection to virtualized systems, or optimised or
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Internet-Draft Network Virtualization October 2017
additional tools that are needed in the the virtualized
environment.
For instance, many underlying technologies enable virtualization
at hardware or physical networking level. For instance, Ethernet
networks have Virtual LAN (VLAN) tags and mobile networks have a
choice of Access Point Names (APNs). These techniques allow users
and traffic to be put on specific networks, which in turn may
comprise of virtual components.
Other examples of protocols providing helpful techniques include
virtual private networking mechanisms or management mechanisms and
data models that can assist in setting up and administering
virtualized systems.
4. Overview of IETF Virtualization Technologies
... general networking is largely agnostic to virtualization ...
Technologies for that assist separation and engineering of networks:
... at L2 ... VPNs ... MPLS ... segment routing ... traffic
engineering and TEAS ... data models ...
Management tools: ... data models ...
5. Architectural Observations
Role of Software
...
Centralization of Functions
An interesting architectural trend is that virtualization and data
/software driven networking technologies are driving network
architectures where functionality moves towards central entities
such as various controllers, path computation servers, and
orchestration systems.
A natural consequence of this is the simplification (and perhaps
commoditization) of network elements, while the "intelligent" or
higher value functions migrate to the center.
The benefits are largely in the manageability, control, and speed
of change. There are, however, potential pitfalls to be aware of
as well. First off, networks need to continue to be operate even
under partial connectivity situations and breakage, and it is key
that designs can handle those situations as well.
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And it is important that network users and peers continue to be
able to operate and connect in the distributed, voluntary manner
that we have today. Today's virtualization technology is
primarily used to manage single administrative domains and to
offer specific service to others. One could imagine centralised
models being taken too far as well, limiting the ability of other
network owners to manage their own networks.
Tailored vs. general-purpose networking
The interest in building tailored solutions, tailored Quality-of-
Service offerings vs. building general-purpose "low touch"
networks seems to fluctuate over time.
It is important to find the right balance here. From an economics
perspective, it may not be feasible to provide specialised service
-- at least if it requires human effort -- for large fraction of
use cases. Even if those are very useful in critical
applications.
6. Further Work
There may be needs for further work in this area at the IETF. Before
discussing the specific needs, it may be useful to classify the types
of useful work that might come to question. And perhaps also outline
some types of work that is not appropriate for the IETF.
The IETF works primarily on protocols, but in many cases also with
data models that help manage systems, as well as operational guidance
documents. But the IETF does not work on software, such as
abstractions that only need to exist inside computers or ones that do
not have an effect on protocols either on real or simulated "wires".
The IETF also does not generally work on system-level design. IETF
is best at designing components, not putting those components
together to achieve a particular purpose or build a specific
application.
As a result, IETF's work on new systems employing virtualization
techniques (such as 5G slicing concept) is more at the component
improvement level than at the level of the concept. There needs to
be a mapping between a vision of a system and how it utilizes various
software, hardware, and protocol tools to achieve the particular
virtualization capabilities it needs to. Developing a new concept
does not necessarily mean that entirely new solutions are needed
throughtout the stack. Indeed, systems and concepts are usually
built on top of solid, well defined components such as the ones
produced by the IETF.
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That mapping work is necessarily something that those who want to
achieve some new functionality need to do; it is difficult for others
to take a position on what the new functionality is. But at the same
time, IETF working groups and participants typically have a
perspective on how their technology should develop and be extended.
Those two viewpoints must meet.
The kinds of potential new work in this space falls generally in the
following classes:
Virtualization selectors
Sometimes protocols need mechanisms that make it possible to use
them as multiple instances. E.g., VLAN tags were added to
Ethernet frames, NAIs were added to PPP and EAP, and so on. These
cases are rare today, because most protocols and mechanisms have
some kind of selector that can be used to run multiple instances
or connect to multiple different networks.
Traffic engineering
A big reason for building specific networks for specific purposes
is to provide an engineered service level on delay and other
factors to the given customer. There are a number of different
tools in the IETF to help manage and engineer networks, but it is
also an area that continues to develop and will likely see new
functionality.
Virtual service data models
Data models -- such as those described by L2SM or L3SM working
groups can represent a "service" offered by a network, a setup
built for a specific customer or purpose.
7. Acknowledgements
The author would like to thank Gonzalo Camarillo, Joel Halpern, Jeff
Tantsura, Gabriel Montenegro, Alex Galis, Adrian Farrell, Yi Zhao,
Hannu Flinck, and many others for interesting discussions in this
problem space.
8. Informative References
[CC2015] claffy, kc. and D. Clark, "Adding Enhanced Services to the
Internet: Lessons from History", September 2015 (https://
www.caida.org/publications/papers/2015/
adding_enhanced_services_internet/
adding_enhanced_services_internet.pdf).
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[I-D.king-teas-applicability-actn-slicing]
King, D. and Y. Lee, "Applicability of Abstraction and
Control of Traffic Engineered Networks (ACTN) to Network
Slicing", draft-king-teas-applicability-actn-slicing-01
(work in progress), July 2017.
[TS-3GPP.23.501]
3GPP, "3rd Generation Partnership Project; Technical
Specification Group Services and System Aspects; System
Architecture for the 5G System; Stage 2 (Release 15)",
3GPP Technical Specification 23.501, July 2017.
Author's Address
Jari Arkko
Ericsson
Kauniainen 02700
Finland
Email: [email protected]
Arkko Expires April 4, 2018 [Page 7]