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draft-ietf-alto-cdni-request-routing-alto
Content Delivery Networks J. Seedorf
Interconnection NEC
Internet-Draft March 5, 2012
Intended status: Informational
Expires: September 6, 2012
CDNI Request Routing with ALTO
draft-seedorf-cdni-request-routing-alto-00
Abstract
Network Service Providers (NSPs) are currently considering to deploy
Content Delivery Networks (CDNs) within their networks. As a
consequence of this development, there is a need for interconnecting
these local CDNs. The necessary interfaces for inter-connecting CDNs
are currently being defined in the Content Delivery Networks
Interconnection (CDNI) WG. This document focusses on the Request
Routing Interface of CDNI, and more specifically on how the solutions
currently being defined in the Application Layer Traffic Optimization
(ALTO) WG can improve CDNI request routing. The overall intention
behind this document is to foster discussions (in the CDNI as well as
in the ALTO WG) regarding if, how, and under what conditions ALTO can
be useful to optimize CDNI request routing. As basis for this
discussion, this document provides concrete examples of how ALTO can
be integrated within CDNI request routing and in particular in the
process of selecting a downstream CDN. The examples in this document
are based on the use cases and examples currently being discussed in
the CDNI WG.
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
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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 September 6, 2012.
Copyright Notice
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Copyright (c) 2012 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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. ALTO within CDNI Request Routing . . . . . . . . . . . . . . . 4
3. Selection of a Downstream CDN with ALTO . . . . . . . . . . . 6
3.1. Footprint Advertisement with ALTO network map . . . . . . 6
3.2. Using ALTO cost maps for Downstream CDN Selection . . . . 6
3.3. Example of Selecting a Downstream CDN based on ALTO
Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.4. Advantages of using ALTO . . . . . . . . . . . . . . . . . 8
4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
5. Summary and Outlook . . . . . . . . . . . . . . . . . . . . . 10
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
7. Informative References . . . . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
Many Network Service Providers (NSPs) are currently considering or
have already started to deploy Content Delivery Networks (CDNs)
within their networks. As a consequence of this development, there
is a need for interconnecting these local CDNs. Content Delivery
Networks Interconnection (CDNI) has the goal of standardizing
protocols to enable such interconnection of CDNs
[refs.CDNIproblemstatement].
The CDNI problem statement envisions four interfaces to be
standardized within the IETF for CDN interconnection
[refs.CDNIproblemstatement]:
o CDNI Request Routing Interface
o CDNI Metadata Interface
o CDNI Logging Interface
o CDNI Control Interface
This document focusses solely on the CDNI Request Routing Interface.
In particular, this document shows concrete examples of how ALTO
[RFC5693] can be integrated in CDNI request routing. The goal of
this document is to show in what cases ALTO can benefit CDNI request
routing, giving concrete examples and explaining how ALTO improves
CDNI request routing in each of these examples. The examples used in
this document are based on the use cases and request routing
proposals currently being discussed in the CDNI WG
[refs.CDNIusecases] [refs.CDNIstrawman] and in the ALTO WG
[refs.altocdn]. The overall rationale of this document is to foster
discussions (in the CDNI as well as in the ALTO WG) regarding if,
how, and under what conditions ALTO can be useful to optimize CDNI
request routing. Most importantly, the document has the goal of
finding consensus regarding which part of the CDNI request routing
interface can use ALTO.
A previous version of this document [refs.altocdni] contained
detailed examples of actual request routing and surrogate selection
with ALTO. This version solely focuses on selection of a downstream
CDN and how ALTO can support such downstream CDN selection.
Throughout this document, we use the terminology for CDNI defined in
[refs.CDNIproblemstatement].
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2. ALTO within CDNI Request Routing
The main purpose of the CDNI Request Routing Interface is described
in [refs.CDNIproblemstatement] as follows: "The CDNI Request Routing
interface enables a Request Routing function in an upstream CDN to
query a Request Routing function in a downstream CDN to determine if
the downstream CDN is able (and willing) to accept the delegated
content request and to allow the downstream CDN to control what the
upstream Request Routing function should return to the User Agent in
the redirection message". On a high level, the scope of the CDNI
Request Routing Interface therefore contains two main tasks:
o A) Determining if the downstream CDN is willing to accept a
delegated content request
o B) Redirecting the content request coming from an upstream CDN to
the proper entry point or entity in the downstream CDN
More precisely, in [refs.CDNIframework] the request routing interface
is broadly divided into two functionalities:
o 1) the asynchronous advertisement of footprint and capabilities by
a dCDN that allows a uCDN to decide whether to redirect particular
user requests to that dCDN;
o 2) the synchronous operation of actually redirecting a user
request.
Accorduing to consensus found at the last CDNI session at IETF-82, we
refer to 1) as "Request Routing Interface - Footprint and
Capabilities Advertisement" and 2) as "Request Routing Interface -
Redirection". A previous version of this document [refs.altocdni]
provided some concrete examples how ALTO could be used for the actual
"redirection" part of the request routing interface. Based on
feedback received at the IETF-82 meeting, this version solely focuses
on the "Footprint and Capabilities Advertisement" part of the request
routing interface. In particular, the scope of the current version
of this document is to show how ALTO [RFC5693] can be used for
selecting a downstream CDN. Thus, the scope of the current document
is to provide examples and discuss how a downstream CDN can advertise
its footprint and other information by means of ALTO.
Application Layer Traffic Optimization (ALTO) is an approach for
guiding the resource provider selection process in distributed
applications that can choose among several candidate resources
providers to retrieve a given resource. By conveying network layer
(topology) information, an ALTO server can provide important
information to "guide" the resource provider selection process in
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distributed applications. Usually, it is assumed that an ALTO server
conveys information these applications cannot measure themselves
[RFC5693].
Originally, ALTO was motivated by the huge amount of cross-ISP
traffic generated by P2P applications [RFC5693]. Recently, however,
ALTO is also being considered for improving the request routing in
CDNs [refs.altocdn]. In this context, it has also been proposed to
use ALTO for selecting an entry-point in a downstream NSP's network
(see section 3.4 "CDN delivering Over-The-Top of a NSP's network" in
[refs.altocdn]). Also, the CDNI problem statement explicitly
mentions ALTO as a candidate protocol for "algorithms for selection
of CDN or Surrogate by Request-Routing systems"
[refs.CDNIproblemstatement]. Yet, there have not been concrete
proposals so far on how to use ALTO in the context of CDN
interconnection. This document tries to close this gap by giving
some examples on how ALTO could be used within CDNI request routing.
As explicitly being out-of-scope for CDNI
[refs.CDNIproblemstatement], the examples used in this document
assume that ingestion of content or acquiring content across CDNs is
not part of request routing as considered within CDNI standardization
work. The focus of using ALTO (as considered in this document) is
hence on request routing only, assuming that the content (desired by
the end user) is available in the downstream CDN (or can be aquired
by the downstream CDN by some means).
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3. Selection of a Downstream CDN with ALTO
ALTO can help the upstream CDN provider to select a proper downstream
CDN provider for a given end user request as follows: Each downstream
CDN provider hosts an ALTO server which provides ALTO information
(i.e. ALTO network maps and ALTO cost maps [refs.altoprotocol]) to
an ALTO client at the upstream CDN provider. A network map provided
by each of several candidate downstream CDNs can provide information
to the upstream CDN provider regarding the geopgraphical coverage,
the location of "surrogates", or similar. In addition, an ALTO cost
map can provide an upstream CDN provider information about the
''cost'' of delivering certain content via the downstream CDN which
provided such a cost map. ''Cost'' in this context is a generic
term; many types of costs are possible and can be useful in the
context of CDNI request routing (see Section 3.2 for a detailed
discussion), e.g. average link load, expected delay, or monetary
costs.
3.1. Footprint Advertisement with ALTO network map
An ALTO network map contains a "set of Network Location groupings"
[refs.altoprotocol]. The groupings are defined in the form of so-
called "PIDs". A PID is an identifier to group network location
endpoints, e.g. IP-addresses in the form of prefixes (see section 4
in [refs.altoprotocol] for details).
The concept of an ALTO network map (and the PIDs contained therein)
is a natural and straightforward candidate for CDNI fooprint
advertisement: The downstream CDN provider groups the IP-addresses in
its footprint into PIDs and makes these grouping available to an
upstream CDN via an ALTO network map. With such a network map, the
upstream CDN provider can easily match an end user request with the
footprint of the downstream CDN provider to see if a given downstream
CDN can provide "coverage" for the IP-address of the end user.
Whenever the footprint changes, the downstream CDN creates an updated
network map and makes it available via its ALTO server.
3.2. Using ALTO cost maps for Downstream CDN Selection
An ALTO cost map contains costs between defined groupings of a
corresponding network map (i.e. costs between PIDs): "An ALTO Cost
Map defines Path Costs pairwise amongst sets of source and
destination Network Locations" [refs.altoprotocol]. This concept
enables the provider of a cost map to express (and quantify)
preferences of a destination network location with respect to a given
source network location.
In the context of CDNI, the ALTO cost map concept is an extensive
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tool to facilitate selection of the "best" downstream CDN because it
enables the upstream CDN provider to assess a candidate downstream
CDN based on other factors besides simply network coverage
(footprint). Most importantly, the cost map concept provides a means
for a downstream CDN provider to convey a multitude of dynamically
changing information which the upstream CDN provider cannot measure
itself (or only roughly estimate) otherwise.
For instance, the following types of ''delivery cost'' can be
conveyed by a downstream CDN provider via ALTO for each combination
of source PID and destination PID:
o Latency: the expected/average RTT
o Bandwidth: the maximum bandwidth (e.g. due too bottlenecks)
o Monetary Costs: The amount of actual monetary costs the downstream
CDN provider would charge for the delivery of content to a given
destination (see also [refs.CDNIcostperspective])
3.3. Example of Selecting a Downstream CDN based on ALTO Maps
Consider the following example. An upstream CDN (uCDN) receives a
request from an end user. Based on the IP-address of the end user,
uCDN determines that it is possible to deliver the content from one
of several candidate downstream CDNs (dCDN-a, dCDN-b, and dCDN-c).
Each of these downstream CDNs runs an ALTO server to provide
information about what locations it can deliver content to
(footprint) and at which ''cost'' (additional information). uCDN
downloads from each candidate downstream CDN an ALTO network map and
one or more ALTO cost maps (e.g. by using the "Filtered Cost Map"
option and different "cost-types" as specified in 7.7.3.2. of
[refs.altoprotocol]). The ALTO network map provides ''coverage''
(footprint) for each downstream CDN as aggregated network locations
in the form of ALTO PIDs. The cost maps provide the upstream CDN
information regarding the ''costs'' the selection of each individual
donwstraem CDN would imply.
Assume that only the ALTO network maps provided by dCDN-a and dCDN-c
indicate that these downstream CDNs can deliver content for the
location of the end user requesting content. In this case, the ALTO
costs maps provide useful information to the upstream CDN, uCDN, in
order to make a selection decision regarding either dCDN-a or dCDN-c.
For instance, if both downstream CDNs have provided two ALTO cost
maps - one regarding monetary delivery cost and one regarding
expected latency for delivery - uCDN can make a downstream CDN
selection based on its preferences: If one downstream CDN can deliver
cheaper, but the other faster, ALTO cost maps provide such
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information in detail to the upstream CDN. This enables the upstream
CDN to make a well-considered downstream CDN selection which may take
into account different factors (which can for instance be weighted by
the upstream CDN to make a decision).
3.4. Advantages of using ALTO
The following reasons make ALTO a suitable candidate protocol for
downstream CDN selection as part of CDNI request routing:
o The semantics of an ALTO network are an exact match for the needed
information to convey a footprint by a downstream CDN
o ALTO cost maps can express delivery ''cost'' and thus convey
relevant network topology information other than simply routing
hops or a footprint. This facilitiates advanced and more
sophiosticated selection of a downstream CDN based on various
metrics by the upstream CDN
o ALTO maps can be signed and hence provide inherent integrity
protection (see Section 4)
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4. Security Considerations
One important security consideration is the proper authentication of
advertisement information provided by a downstream CDN. The ALTO
protocol provides a specification for a signature of ALTO maps (see
8.2.2. of [refs.altoprotocol]. ALTO thus provides a proper means for
protecting the integrity of footprint advertisment information.
More Security Considerations will be discussed in a future version of
this document.
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5. Summary and Outlook
This document presented conrete examples of how ALTO can be used
within the downstream CDN selection of CDNI Request Routing.
Further, the document provides arguments why ALTO is a meaningful
protocol in this context. Most importantly, the concept of the ALTO
cost map is a means to provide detailed and various types of
information to an upstream CDN to facilitate well-considered
downstream CDN selection.
The intention of this document is to find consensus in the CDNI WG
that ALTO is a useful protocol for CDNI request routing and in
particular has many benefits for proper selection of a downstream
CDN. The overall objective is to form agreement on how ALTO should
be used within the CDNI request routing protocol. It is the
intention to capture the outcome of such continuing discussions in
future versions of this document.
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6. Acknowledgements
Jan Seedorf is partially supported by the COAST project (COntent
Aware Searching, retrieval and sTreaming, http://www.coast-fp7.eu), a
research project supported by the European Commission under its 7th
Framework Program (contract no. 248036). The views and conclusions
contained herein are those of the authors and should not be
interpreted as necessarily representing the official policies or
endorsements, either expressed or implied, of the COAST project or
the European Commission.
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7. Informative References
[refs.CDNIusecases]
Bertrand, G., Stephan, E., Watson, G., Burbridge, T., and
P. Eardley, "Use Cases for Content Delivery Network
Interconnection", draft-ietf-CDNI-use-cases-00 (work in
progress), September 2011.
[refs.CDNIproblemstatement]
Niven-Jenkins, B., Le Faucheur, F., and N. Bitar, "Content
Distribution Network Interconnection (CDNI) Problem
Statement", draft-ietf-CDNI-problem-statement-00 (work in
progress), September 2011.
[refs.altocdn]
Niven-Jenkins, B., Watson, G., Bitar, N., Medved, J., and
S. Previdi, "Use Cases for ALTO within CDNs",
draft-jenkins-alto-cdn-use-cases-01 (work in progress),
June 2011.
[refs.altocdni]
Seedorf, J., "ALTO for CDNi Request Routing",
draft-seedorf-alto-for-cdni-00 (work in progress),
October 2011.
[RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic
Optimization (ALTO) Problem Statement", RFC 5693,
October 2009.
[refs.CDNIstrawman]
Peterson, L. and J. Hartman, "Content Distribution Network
Interconnection (CDNI) Problem Statement",
draft-peterson-CDNI-strawman-01 (work in progress),
May 2011.
[refs.CDNIcostperspective]
Liu, H., "A Cost Perspective on Using Multiple CDNs",
draft-liu-cdni-cost-00 (work in progress), Oct 2011.
[refs.CDNIframework]
Davie, B. and L. Peterson, "Framework for CDN
Interconnection", draft-davie-CDNI-framework-00 (work in
progress), July 2011.
[refs.altoprotocol]
Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol",
draft-ietf-alto-protocol-09 (work in progress), June 2011.
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Author's Address
Jan Seedorf
NEC Laboratories Europe, NEC Europe Ltd.
Kurfuersten-Anlage 36
Heidelberg 69115
Germany
Phone: +49 (0) 6221 4342 221
Email: jan.seedorf@neclab.eu
URI: http://www.neclab.eu
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