Network Working Group M. Day
Internet-Draft Cisco
Expires: September 2, 2001 B. Cain
Cereva
G. Tomlinson
CacheFlow
P. Rzewski
Inktomi
March 2, 2001
A Model for Content Internetworking
draft-day-cdnp-model-05.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
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This Internet-Draft will expire on September 2, 2001.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
There is wide interest in the technology for interconnecting Content
Networks, variously called "Content Peering" or "Content
Internetworking". A common vocabulary helps the process of
discussing such interconnection and interoperation. This document
introduces Content Networks and Content Internetworking, and
proposes elements for such a common vocabulary.
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Table of Contents
1. Introduction................................................ 3
2. Content Networks............................................ 3
2.1 Problem Description......................................... 4
2.2 Forward Proxy Caching....................................... 5
2.3 Server Farms................................................ 6
2.4 Content Distribution Networks............................... 7
2.4.1 Historic Evolution of CDNs.................................. 9
2.4.2 Describing CDN Value: Reach and Scale....................... 9
3. Content Network Model Terms.................................10
4. Content Network Examples and Commentary.....................12
4.1 Understanding CDNs..........................................12
4.2 Understanding content structure.............................12
5. Content Internetworking.....................................13
6. Content Internetworking Model Terms.........................13
7. Content Internetworking Examples and Commentary.............15
7.1 Understanding Content Internetworking.......................15
7.2 Content Signaling...........................................16
8. Operational Considerations..................................16
9. Security Considerations.....................................16
10. Acknowledgements............................................16
References..................................................16
Authors' Addresses..........................................17
Full Copyright Statement....................................18
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1. Introduction
Content Networks, such as CDNs, are of increasing importance to the
overall architecture of the Web. This document presents a
vocabulary for use in developing technology for interconnecting
Content Networks. By analogy with peering of IP networks, this
interconnection is sometimes called "content peering" or "content
internetworking".
Section 2 provides background on Content Networks. Section 3
introduces the terms used for elements of a Content Network and
explains how those terms are used. Section 5 deals with Content
Internetworking, introducing the terms and explaining how those
terms are used. The remainder of the document notes various
operational and security considerations that are relevant to Content
Internetworking.
The terminology in this document builds from the previous taxonomy
of web caching and replication [2]. In particular, we have attempted
to avoid the use of the common terms "proxies" or "caches" in favor
of the better-defined terms "caching proxy," "reverse caching
proxy," and "server accelerator."
The sections defining terms are organized alphabetically, which is
appropriate for reference but which makes them difficult to read the
first time. Rather than reading the document from beginning to end,
the authors recommend that the first-time reader skip past the
sections defining terms to the following sections with examples,
referring back to the definitions as necessary.
The interested reader is also referred to [3], which enumerates
scenarios for Content-Internetworking-related interactions; [4],
which describes requirements for accounting and associated issues;
[5], which gives an overall architecture of the elements for CDN
peering; and [6], which summarizes known mechanisms for request-
routing.
It should be noted that previous versions of this document and other
working drafts of CDI appear to be more specifically focused on
"Content Distribution Networks" (CDNs) and "CDN Peering". The use of
the more general terms "Content Networks" and "Content
Internetworking" are currently favored because they imply a wider
variety of real-life scenarios that may be encompassed in CDI's
work. Also, we are attempting to take the emphasis off use of the
word "peering" because the term is often taken to imply a
settlement-free arrangement (as is common with bandwidth peering).
2. Content Networks
The past several years have seen the evolution of technologies
centered around "content". Protocols, appliances, and entire markets
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have been created exclusively for the location, download, and usage-
tracking tracking of content. Some sample technologies in this area
have included web caching proxies, content management tools,
intelligent "web switches", and advanced log analysis tools.
When used together, these tools form new types of networks, dubbed
"Content Networks". Whereas network infrastructures previously have
traditionally occupied layers 1 through 3 of the OSI stack, Content
Networks include network infrastructure that exists in layers 4
through 7. Whereas lower-layer network infrastructures revolved
around the routing, forwarding, and switching of frames and packets,
Content Networks deal with the routing and forwarding of requests
and responses for content. The units of transported data in Content
Networks, such as web pages, movies, or songs, are often very large
and may span hundreds or thousands of packets.
Content Networks can be seen as a new virtual overlay to the OSI
stack: a "Content Layer", to enable richer services that rely on
underlying elements from all 7 layers of the stack. Whereas
traditional applications, such as file transfer (FTP), relied on
underlying protocols such as TCP/IP for transport, overlay services
in Content Networks rely on layer 7 protocols such as HTTP or RTSP
for transport.
The proliferation of Content Networks and Content Networking
capabilities gives rise to interest in interconnecting Content
Networks and finding ways for distinct Content Networks to cooperate
for better overall service.
2.1 Problem Description
Content Networks typically play some role in solving the "content
distribution problem". Abstractly, the goal in solving this problem
is to arrange a rendezvous between a content source at an origin
server and a content sink at a viewer's client. In the trivial case,
the rendezvous mechanism is that every client sends every request
directly to the origin server named in the host part of the URL
identifying the content.
As the audience for the content source grows, so do the demands on
the origin server. There are a variety of ways in which the trivial
system can be modified for better performance. The single logical
server may in fact be a large "farm" of server machines behind a
switch. Both caching proxies and reverse caching proxies can be
deployed between the client and server, so that requests can be
satisfied by some cache instead of by the server.
For the sake of background, several sample Content Networks are
described in the following sections that each attempt to address
this problem.
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2.2 Forward Proxy Caching
A type of Content Network that has been in use for several years is
a forward proxy cache deployment. Such a network might typically be
employed by an ISP for the benefit of end users accessing the
Internet, such as through dial or cable modem.
In the interest of improving performance and reducing bandwidth
utilization, caching proxies are deployed close to the end users.
These end users are encouraged to route their web requests through
the caches rather than directly to origin servers, such as by
configuring their browsers to do so. Note that when this is done,
the end user's entire browsing session goes through a specific proxy
cache. That proxy cache will therefore contain the "hot set" of all
Internet content being viewed by the totality of access users
utilizing that proxy cache.
When a request is being handled a caching proxy on behalf of a user,
other routing decisions may be made, such as:
o A provider that deploys access caches in many geographically
diverse locations may also deploy regional parent caches to
further aggregate user requests and responses. This may provide
additional performance improvement and bandwidth savings. When
parents are included, this is known as hierarchical caching.
o Using rich parenting protocols, redundant parents may be deployed
such that a failure in a primary parent is detected and a backup
is used instead.
o Using similar parenting protocols, requests may be partitioned
such that requests for certain content domains are sent to a
specific primary parent. This can help to maximize the efficient
use of caching proxy resources.
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The following diagram depicts a hierarchical cache deployment as
described above:
^ ^
| | requests to
| | origin servers
| |
-------- --------
|parent| |parent|
|cache | |cache |
|proxy | |proxy |
-------- --------
^ ^
requests for \ / requests for
foo.com \ / bar.com
content \ / content
\ /
------- ------- ------- -------
|edge | |edge | |edge | |edge |
|cache| |cache| |cache| |cache|
|proxy| |proxy| |proxy| |proxy|
------- ------- ------- -------
^
| all content
| requests
| for this
| client
|
--------
|client|
--------
2.3 Server Farms
Another type of Content Network that has been in widespread use for
several years is a server farm. A typical server farm makes use of
an intelligent switch that acts as a dispatcher for content
requests. The switch then routes requests among a (potentially
large) group of servers.
Some of the goals of a a server farm include:
o Creating the impression that the group of servers is actually a
single origin site.
o Load-balancing of requests across all servers in the group.
o Automatically routing of requests away from servers that fail.
o Routing all requests for a particular client's session to the
same server, in order to preserve session state.
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The following diagram depicts a simple server farm deployment:
--------- --------- --------- ---------
|content| |content| |content| |content|
|server | |server | |server | |server |
| | | | | | | |
--------- --------- --------- ---------
^ ^
request from \ / request from
client A \ / client B
\ /
-------------
|intelligent|
| switch |
-------------
^ ^
/ \
/ \
/ \
request from request from
client A client B
A similar type of Content Network may be constructed by replacing
the switch with a server accelerator [2].
2.4 Content Distribution Networks
Both hierarchical caching and server farms are useful techniques,
but have limits. Server farms and server accelerators can improve
the scalability of the origin server. However, since the multiple
servers and server accelerators are typically deployed near the
origin server, they do little to improve performance problems that
are due to network congestion. Caching proxies can improve
performance problems due to network congestion (since they are
situated near the clients) but they cache objects based on client
demand -- so they may not help the distribution load of a given
origin server.
Thus, a content provider with a popular content source can find that
it has to invest in large server farms, load balancing, and high-
bandwidth connections to keep up with demand. Even with those
investments, the user experience for viewers may still be relatively
poor due to congestion in the network as a whole.
To address these limitations. another type of Content Network that
has been deployed in increasing numbers in recent years is the
Content Distribution Network, or CDN. A CDN essentially combines the
cache-management approach of reverse caching proxies with the
network placement of (forward) caching proxies. A CDN has multiple
replicas of each content item being hosted. A request from a browser
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for a single content item is directed to a "good" replica, where
"good" usually means that the item is served to the client quickly
compared to the time it would take fetch it from the origin server,
with appropriate integrity and consistency. Static information about
geographic locations and network connectivity is usually not
sufficient to do a good job of choosing a replica. Instead, a CDN
typically incorporates dynamic information about network conditions
and load on the replicas, directing requests so as to balance the
load.
Compared to using servers and caches in a single data center, a CDN
is a relatively complex system encompassing multiple points of
presence, in locations that may be geographically far apart.
Operating a CDN is not easy for a content provider, since a content
provider wants to focus its resources on developing high-value
content, not on managing network infrastructure. Instead, a more
typical configuration is that a network service provider builds and
operates a CDN, offering a content distribution service to a number
of content providers.
A CDN enables a service provider to act on behalf of the content
provider to deliver copies of origin server content to clients from
multiple diverse locations. The increase in number and diversity of
location is intended to improve download times and thus improve the
user experience. A CDN has some combination of a request-routing
infrastructure, a content-delivery infrastructure, a distribution
infrastructure, and an accounting infrastructure. The content-
delivery infrastructure consists of a set of "surrogate" servers [2]
that deliver copies of content to sets of users. The request-routing
infrastructure consists of mechanisms that move a client toward a
rendezvous with a surrogate. The distribution infrastructure
consists of mechanisms that move content from the origin server to
the surrogates. Finally, the accounting infrastructure tracks and
collects data on request-routing, distribution, and delivery
functions within the CDN.
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The following diagram depicts a simple CDN as described above:
---------- ----------
|request-| |request-|
|routing | |routing |
| system | | system |
---------- ----------
^ |
(1) client's | | (2) response
content | | indicating
request | | location of -----------
| | content |surrogate|
| | -----------
----------- | |
|surrogate| | | -----------
----------- | | |surrogate|
| | -----------
| | ^
| v / (3) client opens
client--- connection to
retrieve content
Because CDNs are arguably the most complicated form of Content
Network currently deployed, they warrant further description.
2.4.1 Historic Evolution of CDNs
The first important use of CDNs was for the distribution of heavily-
requested graphic files (such as GIF files on the home pages of
popular servers). However, both in principle and increasingly in
practice, a CDN can support the delivery of any digital content --
including various forms of streaming media.
A number of CDN services have been built and offered commercially.
In addition, a number of hardware and software vendors have
developed products that enable the construction of a CDN with "off-
the-shelf" parts.
2.4.2 Describing CDN Value: Reach and Scale
There are two fundamental elements that give a CDN value:
outsourcing infrastructure and improved content delivery. A CDN
allows multiple surrogates to act on behalf of an orgin server,
therefore removing the delivery of content from a centralized site
to multiple and (usually) highly distributed sites. We refer to
increased aggregate infrastructure size as "scale." In addition, a
CDN can be constructed with copies of content near to end users,
overcoming issues of network size, network congestion, and network
failures. We refer to increased diversity of content locations as
"reach."
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In a typical (non-internetworked) CDN, a single service provider
operates the request-routers, the surrogates, and the content
distributors. In addition, that service provider establishes
(business) relationships with content publishers and acts on behalf
of their origin sites to provide a distributed delivery system. The
value of that CDN to a content provider is a combination of its
scale and its reach.
3. Content Network Model Terms
This section consists of the definitions of a number of terms used
to refer to roles, participants, and objects involved in Content
Networks.
ACCOUNTING
Measurement and recording of DISTRIBUTION and DELIVERY
activities, especially when the information recorded is
ultimately used as a basis for the subsequent transfer of money,
goods, or obligations.
ACCOUNTING SYSTEM
A collection of NETWORK ELEMENTS that supports ACCOUNTING for a
single CONTENT NETWORK.
AUTHORITATIVE REQUEST-ROUTING SYSTEM
The REQUEST-ROUTING SYSTEM that is the correct/final authority
for a particular item of CONTENT.
CDN
Content Delivery Network or Content Distribution Network. A type
of CONTENT NETWORK in which the NETWORK ELEMENTS are arranged for
more effective delivery of CONTENT to CLIENTS. Typically a CDN
consists of a REQUEST-ROUTING SYSTEM, SURROGATES, a DISTRIBUTION
SYSTEM, and an ACCOUNTING SYSTEM.
CLIENT
The origin of a REQUEST and the destination of the corresponding
delivered CONTENT.
CONTENT
Digital data resources. [Editor note: discussion is currently
active about correct alignment between resource/entity/variant
model of HTTP and "content".] One important form of CONTENT with
additional constraints on DISTRIBUTION and DELIVERY is CONTINUOUS
MEDIA.
CONTENT NETWORK
A collection of NETWORK ELEMENTS that assist in the location,
download, and usage-tracking tracking of CONTENT.
CONTENT SIGNAL
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A message delivered through a DISTRIBUTION SYSTEM that specifies
information about an item of CONTENT. For example, a CONTENT
SIGNAL can indicate that the ORIGIN has a new version of some
piece of CONTENT.
CONTINUOUS MEDIA
CONTENT where there is a timing relationship between source and
sink; that is, the sink must reproduce the timing relationship
that existed at the source. The most common examples of
CONTINUOUS MEDIA are audio and motion video. CONTINUOUS MEDIA can
be real-time (interactive), where there is a "tight" timing
relationship between source and sink, or streaming (playback),
where the relationship is less strict.
DELIVERY
The activity of presenting a PUBLISHER's CONTENT for consumption
by a CLIENT. Contrast with DISTRIBUTION and REQUEST-ROUTING.
DISTRIBUTION
The activity of moving a PUBLISHER's CONTENT from its ORIGIN to
one or more SURROGATEs. DISTRIBUTION can happen either in
anticipation of a SURROGATE receiving a REQUEST (pre-positioning)
or in response to a SURROGATE receiving a REQUEST (fetching on
demand). Contrast with DELIVERY and REQUEST-ROUTING.
DISTRIBUTION SYSTEM
A collection of NETWORK ELEMENTS that support DISTRIBUTION for a
single CONTENT NETWORK. The DISTRIBUTION SYSTEM also propagates
CONTENT SIGNALs.
MAPPING
See REQUEST-ROUTING. Some earlier versions of this document and
others used the term MAPPING, but REQUEST-ROUTING is now
preferred.
NETWORK ELEMENT
A device or system that affects the processing of network
messages.
ORIGIN
The point at which CONTENT first enters a DISTRIBUTION SYSTEM.
The ORIGIN for any item of CONTENT is the server or set of
servers at the "core" of the distribution, holding the "master"
or "authoritative" copy of that CONTENT.
PUBLISHER
The party that ultimately controls the content and its
distribution.
REACHABLE SURROGATES
The collection of SURROGATES that can be contacted via a
particular DISTRIBUTION SYSTEM or REQUEST-ROUTING SYSTEM.
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REQUEST
A message identifying a particular item of CONTENT to be
delivered. [Editor Note: Brad Cain recommends distinguishing
REQUEST-ROUTING REQUEST from CONTENT REQUEST. Does this make the
model too closely tied to DNS-style request-routing? To be
discussed.]
REQUEST-ROUTING
The activity of steering or directing a REQUEST from a CLIENT to
a suitable SURROGATE.
REQUEST-ROUTING SYSTEM
A collection of NETWORK ELEMENTS that support REQUEST-ROUTING for
a single CONTENT NETWORK.
SURROGATE
A delivery server, other than the ORIGIN. Receives a mapped
REQUEST and delivers the corresponding CONTENT. Note: This
definition has a narrower semantic context than the more
generally used term defined in [2].
4. Content Network Examples and Commentary
This section uses the terms of the previous to explain concepts of
CONTENT NETWORKs and CONTENT. Because CDNs contain all the major
components of Content Networking (i.e. REQUEST-ROUTING,
DISTRIBUTION, DELIVERY, ACCOUNTING), the example described is a CDN.
4.1 Understanding CDNs
With the elements defined so far, we can outline the operation of a
"typical" CDN at a high level. The CLIENT's REQUEST enters a
REQUEST-ROUTING SYSTEM, and the ORIGIN's CONTENT enters a
DISTRIBUTION SYSTEM. Note that the relative timing of these events
is unspecified. Both systems (REQUEST-ROUTING and DISTRIBUTION)
converge on SURROGATES, which are non-ORIGIN servers of CONTENT.
Effectively, the DISTRIBUTION SYSTEM is moving CONTENT out to
SURROGATES, and the REQUEST-ROUTING SYSTEM is then taking advantage
of that distribution of CONTENT.
[Editor Note: Could change this description to deal with REQUEST-
ROUTING REQUESTS and CONTENT REQUESTS.]
4.2 Understanding content structure
The model defines CONTENT as well as a subsidiary concept:
CONTINUOUS MEDIA.
Any identifiable resource of digital data is an item of CONTENT. So
CONTENT is the most generic description of what is transported and
served up by a CONTENT NETWORK.
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In many cases, an item of CONTENT can be delivered by a CONTENT
NETWORK without concern about maintaining timing relationships.
However, there are some forms of CONTENT where it is critical that
some timing relationships be met. The model refers to those forms of
CONTENT as CONTINUOUS MEDIA.
5. Content Internetworking
There are limits to how large any one network's scale and reach can
be. Increasing either scale or reach is ultimately limited by the
cost of equipment, the space available for deploying equipment,
and/or the demand for that scale/reach of infrastructure. Sometimes
a particular audience is tied to a single service provider or a
small set of providers by constraints of technology, economics, or
law. Other times, a network provider may be able to manage
surrogates and a distribution system, but may have no direct
relationship with content providers. Such a provider wants to have a
means of affiliating their delivery and distribution infrastructure
with other parties who have content to distribute.
Content Internetworking allows different Content Networks to share
resources so as to provide larger scale and/or reach to each
participant than they could otherwise achieve. By using commonly
defined protocols for Content Internetworking, each Content Network
can treat neighboring Content Networks as "black boxes", allowing
them to hide internal details from each other.
6. Content Internetworking Model Terms
This section consists of the definitions of a number of terms used
to refer to roles, participants, and objects involved in
internetworking Content Networks.
ACCOUNTING ADVERTISEMENT
ADVERTISEMENT from a CONTENT NETWORK's ACCOUNTING PEERING SYSTEM
about the collections of CONTENT for which that CONTENT NETWORK
requires ACCOUNTING information.
ACCOUNTING PEERING
Interconnection of two or more ACCOUNTING SYSTEMS so as to enable
the exchange of information between them. The form of ACCOUNTING
PEERING required may depend on the nature of the NEGOTIATED
RELATIONSHIP between the peering parties -- in particular, on the
value of the economic exchanges anticipated.
ACCOUNTING PEERING SYSTEM
See PEERING SYSTEM.
ADVERTISEMENT
Information about available resources, exchanged among PEERING
SYSTEMS. Types of ADVERTISEMENT include REQUEST-ROUTING
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ADVERTISEMENTS, DISTRIBUTION ADVERTISEMENTS and ACCOUNTING
ADVERTISEMENTS.
BILLING ORGANIZATION
An entity that operates an ACCOUNTING SYSTEM to support billing
within a NEGOTIATED RELATIONSHIP with a PUBLISHER.
CONTENT PEERING GATEWAY (CPG)
A point through which a CONTENT NETWORK can be peered with others
through one or more kinds of peering. A CPG may be the point of
contact for DISTRIBUTION PEERING, REQUEST-ROUTING PEERING, and/or
ACCOUNTING PEERING, and thus may incorporate some or all of the
corresponding PEERING SYSTEMs for the CONTENT NETWORK.
DISTRIBUTING CONTENT NETWORK
A CONTENT NETWORK that does not have a NEGOTIATED RELATIONSHIP
with the PUBLISHER for the CONTENT being delivered.
DISTRIBUTION ADVERTISEMENT
An ADVERTISEMENT from a CONTENT NETWORK's DISTRIBUTION PEERING
SYSTEM describing the availability of collections of CONTENT via
the CONTENT NETWORK's DISTRIBUTION SYSTEM.
DISTRIBUTION PEERING
Interconnection of two or more DISTRIBUTION SYSTEMS so as to
propagate CONTENT SIGNALS and copies of CONTENT to groups of
SURROGATES.
DISTRIBUTION PEERING SYSTEM
See PEERING SYSTEM.
INJECTION
A "send-only" form of DISTRIBUTION PEERING that takes place from
an ORIGIN to a peer CONTENT NETWORK.
INTER-
Describes activity that involves more than one CONTENT NETWORK
(e.g. INTER-CDN). Contrast with INTRA-.
INTRA-
Describes activity within a single CONTENT NETWORK (e.g. INTRA-
CDN). Contrast with INTER-.
NEGOTIATED RELATIONSHIP
A relationship whose terms and conditions are partially or
completely established outside the context of CONTENT NETWORK
peering protocols.
PEERING SYSTEM
A collection of NETWORK ELEMENTS supporting some form of
interconnected operation among two or more CDNs. Examples (not
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separately defined): ACCOUNTING PEERING SYSTEM, DISTRIBUTION
PEERING SYSTEM, REQUEST-ROUTING PEERING SYSTEM.
REMOTE CONTENT NETWORK
A CONTENT NETWORK able to deliver CONTENT for a particular
REQUEST that is not the AUTHORITATIVE REQUEST-ROUTING SYSTEM for
that REQUEST.
REQUEST-ROUTING ADVERTISEMENT
An ADVERTISEMENT from a CONTENT NETWORK's REQUEST-ROUTING PEERING
SYSTEM describing the availability of collections of CONTENT via
that CONTENT NETWORK's REQUEST-ROUTING SYSTEM.
REQUEST-ROUTING PEERING
Interconnection of two or more REQUEST-ROUTING SYSTEMS so as to
increase the number of REACHABLE SURROGATES for at least one of
the interconnected systems.
REQUEST-ROUTING PEERING SYSTEM
See PEERING SYSTEM.
7. Content Internetworking Examples and Commentary
This section uses the terms of the previous to explain concepts of
CONTENT NETWORK peering. Because CDNs contain all the major
components of Content Networking (i.e. REQUEST-ROUTING,
DISTRIBUTION, DELIVERY, ACCOUNTING), the example describes
internetworking among CDNs.
7.1 Understanding Content Internetworking
The model offers a number of ways in which different CDNs can be
interconnected. An arrangement of interconnected REQUEST-ROUTING
SYSTEMS is called REQUEST-ROUTING PEERING. Analogously,
interconnected DISTRIBUTION SYSTEMS give rise to DISTRIBUTION
PEERING, and interconnected ACCOUNTING SYSTEMS give rise to
ACCOUNTING PEERING. The communicating elements on each side are
referred to as PEERING SYSTEMS. So when two or more DISTRIBUTION
SYSTEMS may be interconnected by PEERING, it is actually the
DISTRIBUTION PEERING SYSTEMS that are communicating with each other
to accomplish the exchange of information required. A CONTENT
PEERING GATEWAY (CPG) is a generic term used in the model for one or
more PEERING SYSTEMS when it is not important to distinguish the
PEERING SYSTEM or form of PEERING involved.
CPGs exchange ADVERTISEMENTS. There are three main kinds of
ADVERTISEMENT: ACCOUNTING ADVERTISEMENTS, REQUEST-ROUTING
ADVERTISEMENTS, and DISTRIBUTION ADVERTISEMENTS. An ACCOUNTING
ADVERTISEMENT describes a collection of URLs for which a given
ACCOUNTING SYSTEM wants to receive accounting information when the
content is delivered. [Editor note: is accounting information
potentially collected for REQUEST-ROUTING or DISTRIBUTION (for
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purposes other than tracking operational health) as well?] A
REQUEST-ROUTING ADVERTISEMENT describes a collection of URLs whose
content can be delivered by REQUEST-ROUTING through the
corresponding CDN. A DISTRIBUTION ADVERTISEMENT describes the
service level(s) available from a CDN's SURROGATES (as a whole) to
some collection of CLIENT addresses.
7.2 Content Signaling
CDNs operate on behalf of PUBLISHERs and ORIGINs and therefore must
provide accurate, up-to-date copies of CONTENT. A CDN DISTRIBUTION
SYSTEM may deliver CONTENT SIGNALS to relevant SURROGATES when
appropriate. In the presence of peered distribution where the peered
systems support such signals, CONTENT SIGNALS must be propagated to
each SURROGATE with a copy of the relevant CONTENT.
8. Operational Considerations
[Editor's Note: Consider problem of incorrect advertisements of
content or service levels. Need to ensure that there are means
within the protocol or recommended practices so that CDNs aren't
encouraged to pull traffic they can't really handle.]
9. Security Considerations
Content Internetworking raises some security-related issues, and a
detailed discussion of those issues appears in [5].
10. Acknowledgements
The definition of CONTINUOUS MEDIA is adapted from RFC 2326. The
authors acknowledge the contributions and comments of Fred Douglis
(AT&T), Don Gilletti (CacheFlow), Markus Hoffmann (Lucent), Barron
Housel (Cisco), Barbara Liskov (Cisco), John Martin (Network
Appliance), Raj Nair (Cisco), Hilarie Orman (Novell), Doug Potter
(Cisco), Oliver Spatscheck (AT&T), and Nalin Mistry (Nortel).
References
[1] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999,
<URL:http://www.rfc-editor.org/rfc/rfc2616.txt>.
[2] Cooper, I., Melve, I. and G. Tomlinson, "Internet Web
Replication and Caching Taxonomy", RFC3040, January 2001,
<URL:http://www.ietf.org/rfc/rfc3040.txt>.
[3] Day, M., Gilletti, D., and P. Rzewski, "Content Internetworking
Scenarios", draft-day-cdnp-scenarios-03.txt (work in progress),
March 2001,
Day, et. al. Expires September 2, 2001 [Page 16]
Internet-Draft CDI Model March 2001
<URL:http://www.ietf.org/internet-drafts/draft-day-cdnp-
scenarios-03.txt>.
[4] Gilletti, D., Nair, R., Scharber, J., and J. Guha, "CDN-I
Internetworking Authentication, Authorization, and Accounting
Requirements", draft-gilletti-cdnp-aaa-reqs-01.txt (work in
progress), March 2001,
<URL:http://www.ietf.org/internet-drafts/draft-gilletti-cdnp-
aaa-reqs-01.txt>.
[5] Green, M., Cain, B., Tomlinson, G., Thomas, S., and P. Rzewski,
"Content Internetworking Architectural Overview", draft-green-
cdnp-gen-arch-03.txt (work in progress), March 2001,
<URL:http://www.ietf.org/internet-drafts/draft-green-cdnp-gen-
arch-03.txt>.
[6] Barbir, A., Cain, B., Douglis, F., Green, M., Hoffmann, M.,
Nair, R., Potter, D. and O. Spatscheck, "Known CDN Request-
Routing Mechanisms", draft-cain-cdnp-known-request-routing-
01.txt (work in progress), February 2001,
<URL:http://www.ietf.org/internet-drafts/draft-cain-cdnp-known-
request-routing-01.txt>.
Authors' Addresses
Mark S. Day
Cisco Systems
135 Beaver Street
Waltham, MA 02452
US
Phone: +1 781 663 8310
EMail: markday@cisco.com
Brad Cain
Cereva Networks
Email: bcain@cereva.com
Gary Tomlinson
CacheFlow Inc.
12034 134th Ct. NE Suite 201
Redmond, WA 98052
US
Phone: +1 425 820 3009
EMail: garyt@cacheflow.com
Phil Rzewski
Day, et. al. Expires September 2, 2001 [Page 17]
Internet-Draft CDI Model March 2001
Inktomi
4100 East Third Avenue
MS FC1-4
Foster City, CA 94404
US
Phone +1 650 653 2487
Email: philr@inktomi.com
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