Internet DRAFT - draft-bernardos-sfc-discovery
draft-bernardos-sfc-discovery
SFC WG CJ. Bernardos
Internet-Draft UC3M
Intended status: Experimental A. Mourad
Expires: April 24, 2022 InterDigital
October 21, 2021
Service Function discovery in fog environments
draft-bernardos-sfc-discovery-07
Abstract
Service function chaining (SFC) allows the instantiation of an
ordered set of service functions and subsequent "steering" of traffic
through them. Service functions provide an specific treatment of
received packets, therefore they need to be known so they can be used
in a given service composition via SFC. This document discusses the
need for service function discovery mechanisms and propose some
solutions for sfc-aware nodes to discover available service functions
in fog environments.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Problem statement . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Discovery of SF in a multi-provider fog/edge environment 4
4. Network-based SF discovery . . . . . . . . . . . . . . . . . 5
4.1. ICMPv6-based SF discovery . . . . . . . . . . . . . . . . 8
4.2. DHCPv6-based SF discovery . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
8. Informative References . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Virtualization of functions provides operators with tools to deploy
new services much faster, as compared to the traditional use of
monolithic and tightly integrated dedicated machinery. As a natural
next step, mobile network operators need to re-think how to evolve
their existing network infrastructures and how to deploy new ones to
address the challenges posed by the increasing customers' demands, as
well as by the huge competition among operators. All these changes
are triggering the need for a modification in the way operators and
infrastructure providers operate their networks, as they need to
significantly reduce the costs incurred in deploying a new service
and operating it. Some of the mechanisms that are being considered
and already adopted by operators include: sharing of network
infrastructure to reduce costs, virtualization of core servers
running in data centers as a way of supporting their load-aware
elastic dimensioning, and dynamic energy policies to reduce the
monthly electricity bill. However, this has proved to be tough to
put in practice, and not enough. Indeed, it is not easy to deploy
new mechanisms in a running operational network due to the high
dependency on proprietary (and sometime obscure) protocols and
interfaces, which are complex to manage and often require configuring
multiple devices in a decentralized way.
Service Functions are widely deployed and essential in many networks.
These Service Functions provide a range of features such as security,
WAN acceleration, and server load balancing. Service Functions may
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be instantiated at different points in the network infrastructure
such as data center, the WAN, the RAN, and even on mobile nodes.
Service functions (SFs), also referred to as VNFs, or just functions,
are hosted on compute, storage and networking resources. The hosting
environment of a function is called Service Function Provider or
NFVI-PoP (using ETSI NFV terminology).
With the arrival of virtualization, the deployment model for service
function is evolving to one where the traffic is steered through the
functions wherever they are deployed (functions do not need to be
deployed in the traffic path anymore). For a given service, the
abstracted view of the required service functions and the order in
which they are to be applied is called a Service Function Chain
(SFC). An SFC is instantiated through selection of specific service
function instances on specific network nodes to form a service graph:
this is called a Service Function Path (SFP). The service functions
may be applied at any layer within the network protocol stack
(network layer, transport layer, application layer, etc.).
A mobile terminal can benefit from using service function chaining at
the edge/fog to enhance existing applications or to enable new ones.
In order to do so, discovery of available service functions is
required. This document focuses on this aspect.
2. Terminology
The following terms used in this document are defined by the IETF in
[RFC7665] and [RFC9015]:
Service Function (SF): a function that is responsible for specific
treatment of received packets (e.g., firewall, load balancer).
Service Function Chain (SFC): for a given service, the abstracted
view of the required service functions and the order in which they
are to be applied. This is somehow equivalent to the Network
Function Forwarding Graph (NF-FG) at ETSI.
Service Function Forwarder (SFF): A service function forwarder is
responsible for forwarding traffic to one or more connected
service functions according to information carried in the SFC
encapsulation, as well as handling traffic coming back from the
SF.
SFI: SF instance.
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Service Function Path (SFP): the selection of specific service
function instances on specific network nodes to form a service
graph through which an SFC is instantiated.
A Service Function Type (SFT) that is the category of Service
Function that is provided (such as "firewall").
3. Problem statement
[RFC7665] describes an architecture for the specification, creation,
and ongoing maintenance of Service Function Chains (SFCs) in a
network. It includes architectural concepts, principles, and
components used in the construction of composite services through
deployment of SFCs. In this architecture, a key element is the
service function (SF), which is a function that is responsible for
specific treatment of received packets (e.g., a firewall).
So far, how the SFs are discovered and composed has been out of the
scope of discussions in IETF. There is however a need to define
mechanisms that allow SF discovery in fog environments
[I-D.bernardos-sfc-fog-ran]. Note that the mechanisms described in
this document address fog environments. There are other mechanisms
described, like [RFC9015], that cover generic SF discovery in more
traditional environments. Some of the solutions described in the
present document might be of applicable to other scenarios as well.
3.1. Discovery of SF in a multi-provider fog/edge environment
The need to provide networking, computing, and storage capabilities
closer to the users has recently emerged, due to the demands from 5G
applications of very low latency, leading to what is known today as
the concept of intelligent edge. ETSI has been the first to address
this need recently by developing the framework of mobile edge
computing (MEC). Such an intelligent edge could not be envisaged
without virtualization. Beyond applications, it raises a clear
opportunity for networking functions to execute at the edge
benefiting from inherent low latencies. Being in close proximity to
the access, the edge becomes an attractive place for hosting
different functions, saving bandwidth in their respective domains and
offering local breakout options where required. Whilst it is
appreciated the particular challenge for the intelligent edge concept
in dealing with mobile users, the edge virtualization substrate has
been largely assumed to be fixed or stationary. Although little
developed, the intelligent edge concept is being extended further to
scenarios where for example the edge computing substrate is on the
move, e.g., on-board a car or a train, or that it is distributed
further down the edge, even integrating resources from different
stakeholders, into what is known as the fog.
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Service composition is a powerful tool which can provide significant
benefits when applied in a softwarized network environment. While it
is being explored in the core part of networks to compose services
using DPIs (Deep Packet Inspections), firewalls, parental control,
video accelerators, etc., its applicability to the RAN (Radio Access
Network), and in particular to the edge and the fog, has not been
explored yet.
Running functions (standalone functions or service function chains)
at the edge of the network has clear advantages. For example, it
enables offloading functions from the end-user terminal so that it
can become more efficient in terms of cost and energy consumption.
A mobile terminal can benefit from using service function chaining at
the edge/fog to enhance existing applications or to enable new ones.
Some examples of such applications are: privacy enhancement by local
anchoring, opportunistic local breakout, assisted encryption, video
transcoding, personal firewalling, etc. The mobile terminal might
look for function hosting opportunities at the edge for various
reasons such as:
o to increase battery life in critical situations by offloading
energy demanding operations (e.g., video transcoding, augmented
reality) to the edge/cloud;
o to reduce communications latency (e.g., by using local breakout at
the edge for selected applications demanding low latency);
o to enable new functions (e.g., privacy improvements, personal
firewalling) which demand additional intelligence/resources at the
network;
o to benefit from context information available at the edge (e.g.,
enrich networking decisions by executing functions at the edge
using RAN information);
Several key challenges need to be addressed to enable controlled
service function chaining for a mobile terminal, and one of them is
the discovery of the functions available for use at the Fog/Edge/
Cloud.
4. Network-based SF discovery
In this section we describe several mechanisms for a mobile SFC-aware
node to discover what SFs are available in the network. Different
alternatives (protocol containers) are considered to enable the
mobile node to obtain the following information per SF available:
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o Service Function Type, identifying the category of SF provided.
o SFC-aware: Yes/No. Indicates if the SF is SFC-aware.
o Route Distinguisher (RD): IP address indicating the location of
the SF(I).
o Pricing/costs details.
o Migration capabilities of the SF: whether a given function can be
moved to another provider (potentially including information about
compatible providers topologically close).
o Mobility of the device hosting the SF, with e.g. the following
sub-options:
Level: no, low, high; or a corresponding scale (e.g., 1 to 10).
Current geographical area (e.g., GPS coordinates, post code).
Target moving area (e.g., GPS coordinates, post code).
o Power source of the device hosting the SF, with e.g. the following
sub-options:
Battery: Yes/No. If Yes, the following sub-options could be
defined:
Capacity of the battery (e.g., mmWh).
Charge status (e.g., %).
Lifetime (e.g., minutes).
Figure 1 shows the generic mechanism for SF discovery, with network
support. In this scenario, SFs (which might belong to different
administrative domains) are previously registered at the network,
which can then reply to requests sent from mobile nodes that have
just attached to the network. A request might optionally include the
SFs of interest for the terminal, instead of a request for all known
SFs.
The network might also send periodic advertisements in addition to
responses to solicited requests. These responses/advertisements
include the information about known SFs (or only about the ones
queried by the terminal), which can then be used by the terminal to
decide whether to use (some of) them in a certain SFC. How the
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mobile terminal then configures this SFC is not covered in this
document.
___________
_( )_
_( SF1 SF2 )_
------------ ----------- _( SF3 )_
| terminal | | network |-(_ SF4 SF5 _)
------------ ----------- (_ SF6 SF7 _)
| | (_ SF8 _)
XXX (1. attachment) | (___________)
| |
+---2. Request (optional)------>|
| |
|<--------3. Response/Advert.---|
| (SF1,SF2...,SF8) |
| |
Figure 1: SF (network) discovery
In addition to the discovery of SFs at the infrastructure, mobile
terminals can also host SF(I)s, and therefore they also need to be
discovered. A similar approach can be followed, as showin in
Figure 2.
------------
| SF3 |
------------ | terminal | ------------
| SF1 SF2 | ------------ | SF4 SF5 |
| terminal | | | terminal |
------------ | ------------
| | |
+--1. Request->+-------------->|
| (SF1,SF2) | |
|<----------------2. Response--+
| (SF4,SF5) |
|<-2. Response-+ |
| (SF3) | |
| | |
Figure 2: SF (mobiles) discovery
SFs might belong to different administrative domains. This might
require the use of additional security and authentication mechanisms.
Policies can be used (both in single and multi-domain scenarios) to
adapt/limit the type and number of SFs that are advertised, depending
on the relationship of the requester and the advertiser.
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Next sections describe different protocol alternatives for this SF
discovery in fog environments.
4.1. ICMPv6-based SF discovery
TBD.
4.2. DHCPv6-based SF discovery
TBD.
5. IANA Considerations
N/A.
6. Security Considerations
TBD.
7. Acknowledgments
The work in this draft has been explored under the framework of the
H2020 5G-DIVE project (Grant 859881).
8. Informative References
[I-D.bernardos-sfc-fog-ran]
Bernardos, C. J., Rahman, A., and A. Mourad, "Service
Function Chaining Use Cases in Fog RAN", draft-bernardos-
sfc-fog-ran-09 (work in progress), March 2021.
[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>.
[RFC9015] Farrel, A., Drake, J., Rosen, E., Uttaro, J., and L.
Jalil, "BGP Control Plane for the Network Service Header
in Service Function Chaining", RFC 9015,
DOI 10.17487/RFC9015, June 2021,
<https://www.rfc-editor.org/info/rfc9015>.
Authors' Addresses
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Carlos J. Bernardos
Universidad Carlos III de Madrid
Av. Universidad, 30
Leganes, Madrid 28911
Spain
Phone: +34 91624 6236
Email: cjbc@it.uc3m.es
URI: http://www.it.uc3m.es/cjbc/
Alain Mourad
InterDigital Europe
Email: Alain.Mourad@InterDigital.com
URI: http://www.InterDigital.com/
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