Network Working Group M. Green
Internet-Draft CacheFlow
Expires: August 31, 2001 B. Cain
Cereva Networks
G. Tomlinson
CacheFlow
S. Thomas
TransNexus
P. Rzewski
Inktomi
March 2, 2001
Content Internetworking Architectural Overview
draft-green-cdnp-gen-arch-03.txt
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Copyright (C) The Internet Society (2001). All Rights Reserved.
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Abstract
There is wide interest in the technology for interconnecting Content
Networks, variously called "Content Peering" or "Content
Internetworking". We present the general architecture and core
building blocks used in the internetworking of Content Networks.
The scope of this work is limited to external interconnections with
Content Networks and does not address internal mechanisms used
within Content Networks, which for the purpose of the document are
considered to be black boxes. This work establishes an abstract
architectural framework to be used in the development of protocols,
interfaces, and system models for standardized Content
Internetworking.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 4
2. Content Internetworking System Architecture . . . . . . . 5
2.1 Conceptual View of Peered Content Networks . . . . . . . . 5
2.2 Content Internetworking Architectural Elements . . . . . . 7
3. Request-Routing Peering System . . . . . . . . . . . . . . 11
3.1 Request-Routing Overview . . . . . . . . . . . . . . . . . 11
3.2 Request Routing . . . . . . . . . . . . . . . . . . . . . 13
3.3 System Requirements . . . . . . . . . . . . . . . . . . . 13
3.4 Protocol Requirements . . . . . . . . . . . . . . . . . . 14
3.5 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.6 Request-Routing Problems to Solve . . . . . . . . . . . . 15
4. Distribution Peering System . . . . . . . . . . . . . . . 17
4.1 Distribution Overview . . . . . . . . . . . . . . . . . . 17
4.2 Distribution Models . . . . . . . . . . . . . . . . . . . 19
4.3 Distribution Components . . . . . . . . . . . . . . . . . 20
4.4 Distribution System Requirements . . . . . . . . . . . . . 20
4.4.1 Replication Requirements . . . . . . . . . . . . . . . . . 21
4.4.2 Signaling Requirements . . . . . . . . . . . . . . . . . . 21
4.4.3 Advertising Requirements . . . . . . . . . . . . . . . . . 21
4.5 Protocol Requirements . . . . . . . . . . . . . . . . . . 22
4.6 Distribution Problems to Solve . . . . . . . . . . . . . . 22
4.6.1 General Problems . . . . . . . . . . . . . . . . . . . . . 22
4.6.2 Replication Problems . . . . . . . . . . . . . . . . . . . 23
4.6.3 Signaling Problems . . . . . . . . . . . . . . . . . . . . 23
4.6.4 Advertising Problems . . . . . . . . . . . . . . . . . . . 23
5. Accounting Peering System . . . . . . . . . . . . . . . . 25
5.1 Accounting Overview . . . . . . . . . . . . . . . . . . . 25
5.2 Accounting System Requirements . . . . . . . . . . . . . . 27
5.3 Protocol Requirements . . . . . . . . . . . . . . . . . . 27
6. Security Considerations . . . . . . . . . . . . . . . . . 28
6.1 Threats to Content Internetworking . . . . . . . . . . . . 28
6.1.1 Threats to the CLIENT . . . . . . . . . . . . . . . . . . 28
6.1.1.1 Defeat of CLIENT's Security Settings . . . . . . . . . . . 28
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6.1.1.2 Delivery of Bad Accounting Information . . . . . . . . . . 28
6.1.1.3 Delivery of Bad CONTENT . . . . . . . . . . . . . . . . . 29
6.1.1.4 Denial of Service . . . . . . . . . . . . . . . . . . . . 29
6.1.1.5 Exposure of Private Information . . . . . . . . . . . . . 29
6.1.1.6 Substitution of Security Parameters . . . . . . . . . . . 29
6.1.1.7 Substitution of Security Policies . . . . . . . . . . . . 29
6.1.2 Threats to the PUBLISHER . . . . . . . . . . . . . . . . . 29
6.1.2.1 Delivery of Bad Accounting Information . . . . . . . . . . 29
6.1.2.2 Denial of Service . . . . . . . . . . . . . . . . . . . . 30
6.1.2.3 Substitution of Security Parameters . . . . . . . . . . . 30
6.1.2.4 Substitution of Security Policies . . . . . . . . . . . . 30
6.1.3 Threats to a CN . . . . . . . . . . . . . . . . . . . . . 30
6.1.3.1 Bad Accounting Information . . . . . . . . . . . . . . . . 30
6.1.3.2 Denial of Service . . . . . . . . . . . . . . . . . . . . 30
6.1.3.3 Transitive Threats . . . . . . . . . . . . . . . . . . . . 31
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 32
References . . . . . . . . . . . . . . . . . . . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 35
Full Copyright Statement . . . . . . . . . . . . . . . . . 36
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1. Introduction
Terms in ALL CAPS, except those qualified with explicit citations
are defined in [13].
This memo describes the overall architectural structure and the
fundamental building blocks used in the composition of Content
Internetworking. Consult [13] for the system model, and vocabulary
used in, this application domain. A key requirement of the
architecture itself is that it be able to address each of the
Content Internetworking scenarios enumerated in [14]. The scope of
this work is limited to external interconnections between Content
Networks (CN) (i.e. INTER-CN) and does not address internal
mechanisms used within Content Networks (i.e. INTRA-CN), which for
the purposes of the document are considered to be black boxes. This
work is intended to establish an abstract architectural framework to
be used in the development of protocols, interfaces and system
models for standardized, interoperable peering among Content
Networks.
We first present the architecture as an abstract system. Then we
develop a more concrete system architecture. For each core
architectural element, we first present the structure of the element
followed by system requirements. Protocol requirements for
individual core elements are presented in accompanying works
[17][18][15]. The assumptions and scenarios constraining the
architecture is explained in [14]. We intend that the architecture
should support a wide variety of business models.
At the core of Content Internetworking are three principal
architectural elements that constitute the building blocks of the
Content Internetworking system. These elements are the
REQUEST-ROUTING PEERING SYSTEM, DISTRIBUTION PEERING SYSTEM, and
ACCOUNTING PEERING SYSTEM. Collectively, they control selection of
the delivery Content Network, content distribution between peering
Content Networks, and usage accounting, including billing settlement
among the peering Content Networks.
This work takes into consideration relevant IETF RFCs and IETF
works-in-progress. In particular, it is mindful of the end-to-end
nature [6][10] of the Internet, the current taxonomy of web
replication and caching [11], and the accounting, authorization and
authentication framework [12].
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2. Content Internetworking System Architecture
2.1 Conceptual View of Peered Content Networks
Before developing the system architecture, a conceptual view of
peered CNs is presented to frame the problem space. CNs are
comprised principally of four core system elements [13], the
REQUEST-ROUTING SYSTEM, the DISTRIBUTION SYSTEM, the ACCOUNTING
SYSTEM, and SURROGATES. In order for CNs to peer with one another,
it is necessary to interconnect several of the core system elements
of individual CNs. The interconnection of CN core system elements
occurs through network elements called Content Peering Gateways
(CPG). Namely, the CN core system elements that need to be
interconnected are the REQUEST-ROUTING SYSTEM, the DISTRIBUTION
SYSTEM, and the ACCOUNTING SYSTEM.
Figure 1 contains a conceptual peered Content Networks diagram.
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+---------------+ +---------------+
| CN A | | CN B |
|...............| +---------+ +---------+ |.......... ....+
|REQUEST-ROUTING|<=>| |<=>| |<=>|REQUEST-ROUTING|
|...............| | CONTENT | | CONTENT | |...............|
| DISTRIBUTION |<=>| PEERING |<=>| PEERING |<=>| DISTRIBUTION |
|...............| | GATEWAY | | GATEWAY | |...............|
| ACCOUNTING |<=>| |<=>| |<=>| ACCOUNTING |
|---------------| +---------+ +---------+ +---------------+
| ^ \^ \^ \^ ^/ ^/ ^/ | ^
v | \\ \\ \\ // // // v |
+---------------+ \\ \\ \\ // // // +---------------+
| SURROGATEs | \\ v\ v\ /v /v // | SURROGATEs |
+---------------+ \\+---------+// +---------------+
^ | v| |v ^ |
| | | CONTENT | | |
| | | PEERING | | |
| | | GATEWAY | | |
| | | | | |
| | +---------+ | |
| | ^| ^| ^| | |
| | || || || | |
| | |v |v |v | |
| | +------------- -+ | |
| | | CN C | | |
| | |...............| | |
| | |REQUEST-ROUTING| | |
| | |...............| | |
\ \ | DISTRIBUTION | / /
\ \ |...............| / /
\ \ | ACCOUNTING | / /
\ \ |---------------| / /
\ \ | ^ / /
\ \ v | / /
\ \ +---------------+ / /
\ \ | SURROGATEs | / /
\ \ +---------------+ / /
\ \ | ^ / /
\ \ | | / /
\ \ v | / /
\ \ +---------+ / /
\ \--->| CLIENTs |---/ /
\-----| |<---/
+---------+
Figure 1 Conceptual View of Peered Content Networks
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This conceptual view illustrates the peering of three Content
Networks; CN A, CN B, and CN C. The CNs are peered through
interconnection at Content Peering Gateways. The result is
presented as a virtual CN to CLIENTs for the DELIVERY of CONTENT by
the aggregated set of SURROGATES.
Note:
Not all Content Networks contain the complete set of core
elements. For these Content Networks, peering will be done with
only the core elements they do contain.
2.2 Content Internetworking Architectural Elements
The system architecture revolves around the general premise that
individual Content Networks are wholly contained within an
administrative domain [3] that is composed of either autonomous
systems [1] (physical networks) or overlay networks (virtual
networks). For the purpose of this memo, an overlay network is
defined as a set of connected CN network elements layered onto
existing underlying networks, and present the result as a virtual
application layer to both CLIENTs and ORIGINs. The system
architecture for CN peering accommodates this premise by assuring
that the information and controls are available for inter-CN-domain
administration . Content Internetworking involves the
interconnection of the individual CN administrative domains through
gateway protocols and mechanisms loosely modeled after BGP [5].
The system architecture depends on the following assumptions:
1. The URI [8] name space is the basis of PUBLISHER object
identifiers.
2. PUBLISHERs delegate authority of their object URI name space
being distributed by peering CNs to the REQUEST-ROUTING
PEERING SYSTEM.
3. Peering CNs use a common convention for encoding CN metadata
into the URI name space.
Figure 2 contains a system architecture diagram of the core elements
involved in Content Internetworking.
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+---------------+ 1
/-------------|REQUEST-ROUTING|<----\
/ 4 | PEERING | 7 |
/ /------------->| SYSTEM* |<-\ |
/ / +---------------+ | |
/ / ^ | |
/ / |3 | |
/ / | | |
/ / +--------------+ | |
5| | | DISTRIBUTION | 2| |
V | __| PEERING |<-\ |
+--------+ 6 +-----------+ 3 / | SYSTEM* | |\ | +---------+
| |<---| |<-/ +--------------+ | \ \_| |
| CLIENT | | SURROGATE | | \__| ORIGIN |
| |--->| |-\ +--------------+ | /-->| |
+--------+ +-----------+ \ 7 | ACCOUNTING |--// 7 +---------+
\->| PEERING |--/
| SYSTEM* |--\ +---------+
+--------------+ \ 7 | BILLING |
\-->| ORG. |
| |
+---------+
Note: * represents core elements of Content Internetworking
Figure 2 System Architecture Elements of a Content Internetworking
System
The System Architecture is comprised of 7 major elements, 3 of which
constitute the Content Internetworking system itself. The peering
elements are REQUEST-ROUTING PEERING SYSTEM, DISTRIBUTION PEERING
SYSTEM, and ACCOUNTING PEERING SYSTEM. Correspondingly, the system
architecture is a system of systems:
1. The ORIGIN delegates its URI name space for objects to be
distributed and delivered by the peering CNs to the
REQUEST-ROUTING PEERING SYSTEM.
2. The ORIGIN INJECTS CONTENT that is to be distributed and
delivered by the peering CNs into the DISTRIBUTION PEERING
SYSTEM.
Note:
CONTENT which is to be pre-populated (pushed) within the
peering CNs is pro-actively injected, while CONTENT which
is to be pulled on demand is injected at the time the
object is being requested for DELIVERY.
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3. The DISTRIBUTION PEERING SYSTEM moves content between CN
DISTRIBUTION SYSTEMs. Additionally this system interacts with
the REQUEST-ROUTING PEERING SYSTEM via feedback
ADVERTISEMENTs to assist in the peered CN selection process
for CLIENT requests.
4. The CLIENT requests CONTENT from what it perceives to be the
ORIGIN, however due to URI name space delegation, the request
is actually made to the REQUEST-ROUTING PEERING SYSTEM.
Note:
The request routing function may be implied by an in-path
network element such as caching proxy, which is typical
for a Access Content Network. In this case, request
routing is optimized to a null function, since the CLIENT
is a priori mapped to the SURROGATE.
5. The REQUEST-ROUTING PEERING SYSTEM routes the request to a
suitable SURROGATE in a peering CN. REQUEST-ROUTING PEERING
SYSTEMs interact with one another via feedback ADVERTISEMENTs
in order to keep request-routing tables current.
6. The selected SURROGATE delivers the requested content to the
CLIENT. Additionally, the SURROGATE sends accounting
information for delivered content to the ACCOUNTING PEERING
SYSTEM.
7. The ACCOUNTING PEERING SYSTEM aggregates and distills the
accounting information into statistics and content detail
records for use by the ORIGIN and BILLING ORGANIZATION.
Statistics are also used as feedback to the REQUEST-ROUTING
PEERING SYSTEM.
8. The BILLING ORGANIZATION uses the content detail records to
settle with each of the parties involved in the content
distribution and delivery process.
This process has been described in its simplest form in order to
present the Content Internetworking architecture in the most
abstract way possible. In practice, this process is more complex
when applied to policies, business models and service level
agreements that span multiple peering Content Networks. The
orthogonal core peering systems are discussed in greater depth in
Section 3, Section 4 and Section 5 respectively.
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Note:
Figure 2 simplifies the presentation of the core Content
Internetworking elements as single boxes, when in fact they
represent a collection of CPGs and interconnected individual CN
core system elements. This has been done to introduce the system
architecture at its meta level.
The system architecture does not impose any administrative domain
[3] restrictions on the core peering elements (REQUEST-ROUTING
PEERING SYSTEM, DISTRIBUTION PEERING SYSTEM and ACCOUNTING PEERING
SYSTEM). The only requirement is that they be authorized by the
principal parties (ORIGIN and peering CNs) to act in their behalf.
Thus, it is possible for each of the core elements to be provided by
a different organization.
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3. Request-Routing Peering System
The REQUEST-ROUTING PEERING SYSTEM represents the request-routing
function of the Content Internetworking system. It is responsible
for routing CLIENT requests to an appropriate peered CN for the
delivery of content.
Note:
When the DISTRIBUTION PEERING SYSTEM and/or the ACCOUNTING
PEERING SYSTEM is present, it is highly desirable to utilize
content location information within the peered CNs and/or system
load information in the selection of appropriate peered CNs in
the routing of requests.
3.1 Request-Routing Overview
REQUEST-ROUTING SYSTEMs route CLIENT requests to a suitable
SURROGATE, which is able to service a client request. Many
request-routing systems route users to the surrogate that is
"closest" to the requesting user, or to the "least loaded"
surrogate. However, the only requirement of the request-routing
system is that it route users to a surrogate that can serve the
requested content.
REQUEST-ROUTING PEERING is the 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.
In order for a PUBLISHER's CONTENT to be delivered by multiple
peering CNs, it is necessary to federate each Content Network
REQUEST-ROUTING SYSTEM under the URI name space of the PUBLISHER
object. This federation is accomplished by first delegating
authority of the PUBLISHER URI name space to an AUTHORITATIVE
REQUEST-ROUTING SYSTEM. The AUTHORITATIVE REQUEST-ROUTING SYSTEM
subsequently splices each peering Content Network REQUEST-ROUTING
SYSTEM into this URI name space and transitively delegates URI name
space authority to them for their participation in request-routing.
Figure 3 is a diagram of the entities involved in the
REQUEST-ROUTING PEERING SYSTEM.
Note:
For the null request routing case (in path caching proxy
present), the caching proxy acts as the SURROGATE. In this case,
the SURROGATE performs the request routing via its
pre-established proxy relationship with the CLIENT and is
implicitly the terminating level of request routing. In essence,
the SURROGATE is federated into the URI namespace without the
need to communicate with the AUTHORITATIVE REQUEST-ROUTING SYSTEM.
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+---------------+
| CLIENT |
+---------------+
|
(Request-Routing Tree Root) +---------------+
| AUTHORITATIVE |
|REQUEST-ROUTING|
| SYSTEM |
+---------------+
| | INTER-CN Request-Routing
/----------------/ \-----------------\
| |
(1st Level) +---------------+ +---------------+
.........|REQUEST-ROUTING|.......... .........|REQUEST-ROUTING|.........
. CN A | CPG | . . CN B | CPG | .
. +---------------+ . . +---------------+ .
. | . . | .
. +---------------+ . . +---------------+ .
. |REQUEST-ROUTING| . . |REQUEST-ROUTING| .
. | SYSTEM | . . | SYSTEM | .
. +---------------+ . . +---------------+ .
. | | . . | | .
. /---/ \-------\ . . /-----/ \----\ .
. | | . . | | .
. +---------------+ | . . | | .
. |REQUEST-ROUTING| +------------+ . . +-----------+ +------------+ .
..| CPG |.| SURROGATEs |.. ..| SURROGATE |....| SURROGATES |..
+---------------+ +------------+ +-----------+ +------------+
| INTER-CN Recursive Request-Routing
\------\
|
(2nd Level) +---------------+
.........|REQUEST-ROUTING|..........
. CN C | CPG | .
. +---------------+ .
, | .
. +---------------+ .
. |REQUEST-ROUTING| .
. | SYSTEM | .
. +---------------+ .
. | | .
. /----/ \-----\ .
. | | .
. +-----------+ +------------+ .
..| SURROGATE |....| SURROGATEs |...
+-----------+ +------------+
Figure 3 REQUEST-ROUTING PEERING SYSTEM Architecture
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The REQUEST-ROUTING PEERING SYSTEM is hierarchical in nature. There
exists exactly one request-routing tree for each PUBLISHER URI. The
AUTHORITATIVE REQUEST-ROUTING SYSTEM is the root of the
request-routing tree. There may be only one AUTHORITATIVE
REQUEST-ROUTING SYSTEM for a URI request-routing tree. Subordinate
to the AUTHORITATIVE REQUEST-ROUTING SYSTEM are the REQUEST-ROUTING
SYSTEMs of the first level peering CNs. There may exist recursive
subordinate REQUEST-ROUTING SYSTEMs of additional level peering CNs.
Note:
A PUBLISHER object may have more than one URI associated with it
and therefore be present in more than one request-routing tree.
3.2 Request Routing
The actual "routing" of a client request is through REQUEST-ROUTING
CPGs. The AUTHORITATIVE REQUEST-ROUTING CPG receives the CLIENT
request and forwards the REQUEST to an appropriate DISTRIBUTING CN.
This process of INTER-CN request-routing may occur multiple times in
a recursive manner between REQUEST-ROUTING CPGs until the
REQUEST-ROUTING SYSTEM arrives at an appropriate DISTRIBUTING CN to
deliver the content.
Note:
The Client request may be for resolution of a URI component and
not the content of the URI itself. This is the case when DNS is
being utilized in the request-routing process to resolve the URI
server component.
Request-Routing systems explicitly peer but do not have "interior"
knowledge of surrogates from other CNs. Each CN operates its
internal request-routing system. In this manner, request-routing
systems peer very much like IP network layer peering.
3.3 System Requirements
We assume that there is a peering relationship between
REQUEST-ROUTING CPGs. This peering relationship at a minimum must
exchange a set of CLIENT IP addresses that can be serviced, and a
set of information about the DISTRIBUTION SYSTEMs, for which they
are performing request-routing.
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Request-Routing Requirements
1. Use of a URI name space based request-routing mechanism. The
request-routing mechanism is allowed to use as much of the URI
name space as it needs to select the proper SURROGATE. For
example, DNS based mechanisms utilize only the host
subcomponent, while content aware mechanisms utilize use
multiple components.
2. Normalized canonical URI name space structure for peered CN
distribution of PUBLISHER objects. The default in the absence
of encoded meta data is the standard components as defined by
[8]. Encoded meta data must conform to the syntactical grammar
defined in [7].
3. Single AUTHORITATIVE REQUEST-ROUTING SYSTEM for PUBLISHER object
URI name space.
4. Assure that the request-routing tree remains a tree -- i.e., has
no cycles.
5. Assure that adjacent request-routing systems from different
administrative domains (different CNs) use a compatible
request-routing mechanism.
6. Assure that adjacent request-routing systems from different
administrative domains (different CNs) agree to forward requests
for the CONTENT in question.
7.
[Editor Note:
System requirements being generated in the request-routing
peering protocol design team have not yet been reconciled and
integrated into this document.]
3.4 Protocol Requirements
Consult [17] for request-routing peering protocol requirements.
3.5 Examples
Consult [16] for in-depth information on known request-routing
systems.
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3.6 Request-Routing Problems to Solve
[Editor Note:
This section is being preserved until it has been determined that
these issues have been addressed in the request-routing peering
protocol requirements draft.]
Specific problems in request-routing needing further investigation
include:
1. What is the aggregated granularity of CLIENT IP address being
serviced by a peering CN's DISTRIBUTION SYSTEM?
2. How do DNS request-routing systems forward a request? If a
given CN is peered with many other CNs, what are the criteria
that forwards a request to another CN?
3. How do content-aware request-routing systems forward a request?
If a given CN is peered with many other CNs, what are the
criteria that forwards a request to another CN?
4. What are the merits of designing a generalized content routing
protocol, rather than relying on request-routing mechanisms.
5. What is the normalized canonical URI name space for
request-routing? Because request-routing is federated across
multiple CNs, it is necessary to have agreed upon standards for
the encoding of meta data in URIs. There are many potential
elements, which may be encoded. Some of these elements are:
authoritative agent domain, publisher domain, content type,
content length, etc.
6. How are policies communicated between the REQUEST-ROUTING SYSTEM
and the DISTRIBUTION ADVERTISEMENT SYSTEM? A given CN may wish
to serve only a given content type or a particular set of users.
These types of policies must be communicated between CNs.
7. What are the request-routing protocols in DNS? When a request is
routed to a particular REQUEST-ROUTING CPG, a clear set of DNS
rules and policies must be followed in order to have a workable
and predictable system.
8. How do we protect the REQUEST-ROUTING SYSTEM against denial of
service attacks?
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9. How do we select the appropriate peering CN for DELIVERY?
The selection process must to consider the distribution
policies involved in Section 4. Investigation into other
policy "work in progress" within the IETF is needed to
understand the relationship of policies developed within
Content Internetworking.
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4. Distribution Peering System
The DISTRIBUTION PEERING SYSTEM represents the content distribution
function of the CN peering system. It is responsible for moving
content from one DISTRIBUTION CPG to another DISTRIBUTION CPG and
for supplying content location information to the REQUEST-ROUTING
PEERING SYSTEM.
4.1 Distribution Overview
One goal of the Content Internetworking system is to move content
closer to the CLIENT. Typically this is accomplished by copying
content from its ORIGIN to SURROGATEs. The SURROGATEs then have the
CONTENT available when it is requested by a CLIENT. Even with a
single PUBLISHER and single CN, the copying of CONTENT to a
SURROGATE may traverse a number of links, some in the PUBLISHER's
network, some in the CN's network, and some between those two
networks. For DISTRIBUTION PEERING, we consider only the
communication "between" two networks, and ignore the mechanisms for
copying CONTENT within a network.
In the above example the last server on the content provider's
network in the path, and the first server on the CN's network in the
path, must contain DISTRIBUTION CPGs which communicate directly with
each other. The DISTRIBUTION CPGs could be located in the ORIGIN
server and the SURROGATE server. Thus in the simplest form the
ORIGIN server is in direct contact with the SURROGATE. However the
DISTRIBUTION CPG in the content provider's network could aggregate
content from multiple ORIGIN servers and the DISTRIBUTION CPG in the
CN's network could represent multiple SURROGATEs. These DISTRIBUTION
CPGs could then be co-located in an exchange facility. In fact,
given the common practice of independently managed IP peering
co-location exchange facilities for layer 3, there exists the
distinct opportunity to create similar exchanges for CPGs.
Figure 4 is a diagram of the entities involved in the DISTRIBUTION
PEERING SYSTEM.
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+--------+
| ORIGIN |
+--------+
| | INJECTION
/------------------/ \----------------\
| |
+--------------+ +--------------+
.........| DISTRIBUTION |........... ...........| DISTRIBUTION |........
. CN A | CPG | . . CN B | CPG | .
. +--------------+ . . +--------------+ .
. | . . | .
. +--------------+ . . +--------------+ .
. | DISTRIBUTION | . . | DISTRIBUTION | .
. | SYSTEM | . . | SYSTEM | .
. +--------------+ . . +--------------+ .
. | | . . | | .
. /-----/ \-------\ . . /-----/ \----\ .
. | | . . | | .
. | +--------------+ . . +--------------+ | .
. +------------+ | DISTRIBUTION | . . | DISTRIBUTION | +------------+ .
..| SURROGATEs |.| CPG |... ..| CPG |.| SURROGATEs |..
+------------+ +--------------+ +--------------+ +------------+
| | | |
| \-----------------/ |
\----------\ /-----------/
| | INTER-CN DISTRIBUTION PEERING
| |
+--------------+
.........| DISTRIBUTION |...........
. CN C | CPG | .
. +--------------+ .
. | .
. +--------------+ .
. | DISTRIBUTION | .
. | SYSTEM | .
. +--------------+ .
. | | .
. /-----/ \-------\ .
. | | .
. | | .
. +-----------+ +------------+ .
..| SURROGATE |.....| SURROGATEs |..
+-----------+ +------------+
Figure 4 DISTRIBUTION PEERING SYSTEM Architecture
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While Content Internetworking in general relates to interfacing with
CNs, there are two CN distribution peering relationships we expect
to be common; INTER-CN distribution peering and INJECTION peering.
INTER-CN distribution peering involves distributing CONTENT between
individual CNs in a inter-network of peered CNs. INJECTION peering
involves the publishing of CONTENT directly into CNs by ORIGINs.
4.2 Distribution Models
Replication ADVERTISEMENTs may take place in a model similar to the
way IP routing table updates are done between BGP routers.
DISTRIBUTION CPGs could take care of exterior content replication
between content providers and CNs, while at the same time performing
content replication interior to their networks in an independent
manner. If this model is used then the internal structure of the
networks is hidden and the only knowledge of other networks is the
locations of DISTRIBUTION CPGs.
Replication of content may take place using a push model, or a pull
model, or a combination of both. Use initiated replication, where
SURROGATEs, upon getting a cache miss, retrieve CONTENT from the
DISTRIBUTION SYSTEM, represents the pull model. ORIGIN initiated
replication of CONTENT to SURROGATEs represents the push model.
DISTRIBUTION CPGs may be located at various points in these models
depending on the topologies of the networks involved.
With Content Internetworking it may be desirable to replicate
content through a network, which has no internal SURROGATEs. For
example add a exchange network between the content provider network
and the CN network to the example above. The exchange network could
have a DISTRIBUTION CPG co-located with the content provider's
DISTRIBUTION CPG, which acts as a proxy for the CN. The exchange
network could also have a DISTRIBUTION CPG co-located with the CN's
DISTRIBUTION CPG, which acts as a proxy for the content provider. In
a consolidated example, the exchange network could have a single
DISTRIBUTION CPG that acts as a proxy for both the content provider
and the CN.
Replication of CONTINUOUS MEDIA that is not to be cached on
SURROGATEs, such as live streaming broadcasts, takes place in a
different model from content that is to be persistently stored.
Replication in this case, typically takes the form of splitting the
live streaming data at various points in the network. In Content
Internetworking, DISTRIBUTION CPGs may support CONTINUOUS MEDIA
splitting replication, as they likely provide ideal network
topologic points for application layer multicasting.
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4.3 Distribution Components
The three main components of DISTRIBUTION PEERING are replication,
signaling and advertising.
The first component of content distribution is replication.
Replication involves moving the content from an ORIGIN server to
SURROGATE servers. The immediate goal in CN peering is moving the
content between DISTRIBUTION CPGs.
The second component of content distribution is content signaling.
Content signaling is the propagation of content meta-data. This
meta-data may include such information such as the immediate
expiration of content or a change in the expiration time of CONTENT.
The immediate goal in signaling is exchanging signals between
DISTRIBUTION CPGs.
The third component of content distribution is content advertising.
Content providers must be able to advertise content that can be
distributed by CNs and its associated terms. It is important that
the advertising of content must be able to aggregate content
information. The immediate goal in advertising is exchanging
advertisements between DISTRIBUTION CPGs.
4.4 Distribution System Requirements
Replication systems must have a peering relationship. This peering
relationship must exchange sets of aggregated content and its
meta-data. Meta-data may change over time independently of the
content data and must be exchanged independently as well.
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4.4.1 Replication Requirements
The specific requirements in content replication are:
1. A common protocol for the replication of content.
2. A common format for the actual content data in the protocol.
3. A common format for the content meta-data in the protocol.
4. Security mechanisms (see Section 6).
5. Scalable distribution of the content.
4.4.2 Signaling Requirements
The specific requirements in content signaling are:
1. Signals for (at least) "flush" and "expiration time update".
2. Security mechanisms (see Section 6).
3. Scalable distribution of the signals on a large scale.
Editor Note:
We have to start being quantitative about what we mean by
"large scale". Are we thinking in terms of the number of
content items, the number of networks, or the number of
signals? For each of those, how big is "large scale"?
4. Content location and serviced CLIENT IP aggregate address
exchanges with REQUEST-ROUTING CPGs.
4.4.3 Advertising Requirements
The specific requirements in CONTENT ADVERTISEMENT are:
1. A common protocol for the ADVERTISEMENT of CONTENT.
2. A common format for the actual ADVERTISEMENTs in the protocol.
Editor Note:
The following requirements need further discussion. As it
stands now, there isn't sufficient information to
substantiate them.
3. A well-known state machine.
4. Use of TCP or SCTP (because soft-state protocols will not scale).
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5. Well-known error codes to diagnose protocols between different
networks.
6. Capability negotiation.
7. Ability to represent policy.
[Editor Note:
System requirements being generated in the distribution peering
protocol design team have not yet been reconciled and integrated
into this document.]
4.5 Protocol Requirements
Consult [18] for distribution peering protocol requirements.
4.6 Distribution Problems to Solve
[Editor Note:
This section is being preserved until it has been determined that
these issues have been addressed in the distribution peering
protocol requirements draft.]
Some of the problems in distribution revolve around supporting both
a push model and a pull model for replication of content in that
they are not symmetric. The push model is used for pre-loading of
content and the pull model is used for on-demand fetching and
pre-fetching of content. These models are not symmetric in that the
amount of available resources in which to place the content on the
target server must be known. In the fetching cases the server that
pulls the content knows the available resources on the target
server, itself. In the pre-loading case the server that pushes the
content must find out the available resources from the target server
before pushing the data.
4.6.1 General Problems
General problems in distribution peering needing further
investigation include:
1. How would a single distribution peering protocol adequately
support replication, signaling and advertising?
2. Should a single distribution peering protocol be considered,
rather than separate protocols for each component?
3. How do we prevent looping of distribution updates? That is to
say, detect and stop propagating replication, signaling and
advertisement of events a DISTRIBUTION CPG has already issued.
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Looping here has the possibility of becoming infinite, if not
bounded by the protocol(s). IP route updating and forwarding
has faced similar issues and has solved them.
4.6.2 Replication Problems
Specific problems in replication needing further investigation
include:
1. How do replication systems forward a request?
2. How do we keep pull based replication serviced within the
DISTRIBUTION CPGs in order to prevent it from inadvertently
bleeding out into REQUEST-ROUTING SYSTEM and potentially getting
into a recursive loop?
3. How are policies communicated between the replication systems?
4. What are the replication protocols?
5. Does replication only take place between CPGs?
4.6.3 Signaling Problems
Specific problems in content signaling needing further investigation
include:
1. How do we represent a content signal?
2. What content meta-data needs to be signaled?
3. How do we represent aggregates of meta-data in a concise and
compressed manner?
4. What protocol(s) should be used for content signals?
5. What is a scalable architecture for delivering content signals?
6. Do content signals need a virtual distribution system of their
own?
4.6.4 Advertising Problems
Specific problems in CONTENT ADVERTISEMENT needing further
investigation include:
1. How do we represent aggregates of content to be distributed in a
concise and compressed manner?
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2. What protocol(s) should be used for the aggregation of this data?
3. What are the issues involved in the creation of CPG exchanges?
This is actually a broader question than just for distribution,
but needs to be considered for all forms of CPGs
{REQUEST-ROUTING, DISTRIBUTION, ACCOUNTING}.
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5. Accounting Peering System
The ACCOUNTING PEERING SYSTEM represents the accounting data
collection function of the Content Internetworking system. It is
responsible for moving accounting data from one ACCOUNTING CPG to
another ACCOUNTING CPG.
5.1 Accounting Overview
Content Internetworking must provide the ability for the content
provider to collect data regarding the delivery of their CONTENT by
the peered CNs. ACCOUNTING CPGs exchange the data collected by the
interior ACCOUNTING SYSTEMS. This interior data may be collected
from the SURROGATEs by ACCOUNTING CPGs using SNMP or FTP, for
example. ACCOUNTING CPGs may transfer the data to exterior
neighboring ACCOUNTING CPGs on request (push), in an asynchronous
manner (push), or a combination of both. Accounting data may also be
aggregated before it is transferred.
Figure 5 is a diagram of the entities involved in the ACCOUNTING
PEERING SYSTEM.
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+---------+
| BILLING | +--------+
| ORG. | | ORIGIN |
+---------+ +--------+
BILLING | | ACCOUNTING PEERING | | ORIGIN ACCOUNTING PEERING
/-----/ \-----------------------|-|----\
| /-----------------------------/ \----|-\
| | | |
+--------------+ +--------------+
.........| ACCOUNTING |........... ...........| ACCOUNTING |........
. CN A | CPG | . . CN B | CPG | .
. +--------------+ . . +--------------+ .
. | . . | .
. +--------------+ . . +--------------+ .
. | ACCOUNTING | . . | ACCOUNTING | .
. | SYSTEM | . . | SYSTEM | .
. +--------------+ . . +--------------+ .
. | | . . | | .
. /-----/ \-------\ . . /-----/ \----\ .
. | | . . | | .
. | +--------------+ . . +--------------+ | .
. +------------+ | ACCOUNTING | . . | ACCOUNTING | +------------+ .
..| SURROGATEs |.| CPG |... ..| CPG |.| SURROGATEs |..
+------------+ +--------------+ +--------------+ +------------+
| | | |
| \-----------------/ |
\----------\ /-----------/
| | INTER-CN ACCOUNTING PEERING
| |
+--------------+
.........| ACCOUNTING |...........
. CN C | CPG | .
. +--------------+ .
. | .
. +--------------+ .
. | ACCOUNTING | .
. | SYSTEM | .
. +--------------+ .
. | | .
. /-----/ \-------\ .
. | | .
. | | .
. +-----------+ +------------+ .
..| SURROGATE |.....| SURROGATEs |..
+-----------+ +------------+
Figure 5 ACCOUNTING Peering system Architecture
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There are three CN accounting peering relationships we expect to be
common; INTER-CN accounting peering, BILLING ORGANIZATION accounting
peering and ORIGIN accounting peering. INTER-CN accounting peering
involves exchanging accounting information between individual CNs in
a inter-network of peered CNs. BILLING ORGANIZATION peering involves
exchanging to accounting information between CNs and a billing
organization. ORIGIN accounting peering involves the exchanging of
accounting information between CNs and ORIGINs.
Note:
It is not necessary for an ORIGIN to peer directly with multiple
CNs in order to participate in Content Internetworking. ORIGINs
participating in a single home CN will be indirectly peered by
their home CN with the inter-network of CNs the home CN is a
member of. Nor is it necessary to have a BILLING ORGANIZATION
peer, since this function may also be provided by the home CN.
However, ORIGINs that directly peer for ACCOUNTING may have
access to greater accounting detail. Also, through the use of
ACCOUNTING peering, 3rd party billing can be provided.
5.2 Accounting System Requirements
[Editor Note:
System requirements being generated in the accounting peering
protocol design team have not yet been reconciled and integrated
into this document.]
5.3 Protocol Requirements
Consult [15] for accounting peering protocol requirements.
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6. Security Considerations
Security concerns with respect to Content Internetworking can be
generally categorized into trust within the system and protection of
the system from threats. The trust model utilized with Content
Internetworking is predicated largely on transitive trust between
the ORIGIN, REQUEST-ROUTING PEERING SYSTEM, DISTRIBUTION PEERING
SYSTEM, ACCOUNTING PEERING SYSTEM and SURROGATES. Network elements
within the Content Internetworking system are considered to be
"insiders" and therefore trusted.
6.1 Threats to Content Internetworking
The following sections document key threats to CLIENTs, PUBLISHERs,
and CNs. The threats are classified according to the party that they
most directly harm, but, of course, a threat to any party is
ultimately a threat to all. (For example, having a credit card
number stolen may most directly affect a CLIENT; however, the
resulting dissatisfaction and publicity will almost certainly cause
some harm to the PUBLISHER and CN, even if the harm is only to those
organizations' reputations.)
6.1.1 Threats to the CLIENT
6.1.1.1 Defeat of CLIENT's Security Settings
Because the SURROGATE's location may differ from that of the ORIGIN,
the use of a SURROGATE may inadvertently or maliciously defeat any
location-based security settings employed by the CLIENT. And since
the SURROGATE's location is generally transparent to the CLIENT, the
CLIENT may be unaware that its protections are no longer in force.
For example, a CN may relocate CONTENT from a Internet Explorer
user's "Internet Web Content Zone" to that user's "Local Intranet
Web Content Zone." If the relocation is visible to the Internet
Explorer browser but otherwise invisible to the user, the browser
may be employing less stringent security protections than the user
is expecting for that CONTENT. (Note that this threat differs, at
least in degree, from the substitution of security parameters threat
below, as Web Content Zones can control whether or not, for example,
the browser executes unsigned active content.)
6.1.1.2 Delivery of Bad Accounting Information
In the case of CONTENT with value, CLIENTs may be inappropriately
charged for viewing content that they did not successfully access.
Conversely, some PUBLISHERs may reward CLIENTs for viewing certain
CONTENT (e.g. programs that "pay" users to surf the Web). Should a
CN fail to deliver appropriate accounting information, the CLIENT
may not receive appropriate credit for viewing the required CONTENT.
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6.1.1.3 Delivery of Bad CONTENT
A CN that does not deliver the appropriate CONTENT may provide the
user misleading information (either maliciously or inadvertently).
This threat can be manifested as a failure of either the
DISTRIBUTION SYSTEM (inappropriate content delivered to appropriate
SURROGATEs) or REQUEST-ROUTING SYSTEM (request routing to
inappropriate SURROGATEs, even though they may have appropriate
CONTENT), or both. A REQUEST-ROUTING SYSTEM may also fail by
forwarding the CLIENT request when no forwarding is appropriate, or
by failing to forward the CLIENT request when forwarding is
appropriate.
6.1.1.4 Denial of Service
A CN that does not forward the CLIENT appropriately may deny the
CLIENT access to CONTENT.
6.1.1.5 Exposure of Private Information
CNs may inadvertently or maliciously expose private information
(passwords, buying patterns, page views, credit card numbers) as it
transits from SURROGATEs to ORIGINs and/or PUBLISHERs.
6.1.1.6 Substitution of Security Parameters
If a SURROGATE does not duplicate completely the security facilities
of the ORIGIN (e.g. encryption algorithms, key lengths, certificate
authorities) CONTENT delivered through the SURROGATE may be less
secure than the CLIENT expects.
6.1.1.7 Substitution of Security Policies
If a SURROGATE does not employ the same security policies and
procedures as the ORIGIN, the CLIENT's private information may be
treated with less care than the CLIENT expects. For example, the
operator of a SURROGATE may not have as rigorous protection for the
CLIENT's password as does the operator of the ORIGIN server. This
threat may also manifest itself if the legal jurisdiction of the
SURROGATE differs from that of the ORIGIN, should, for example,
legal differences between the jurisdictions require or permit
different treatment of the CLIENT's private information.
6.1.2 Threats to the PUBLISHER
6.1.2.1 Delivery of Bad Accounting Information
If a CN does not deliver accurate accounting information, the
PUBLISHER may be unable to charge CLIENTs for accessing CONTENT or
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it may reward CLIENTs inappropriately. Inaccurate accounting
information may also cause a PUBLISHER to pay for services (e.g.
content distribution) that were not actually rendered.) Invalid
accounting information may also effect PUBLISHERs indirectly by, for
example, undercounting the number of site visitors (and, thus,
reducing the PUBLISHER's advertising revenue).
6.1.2.2 Denial of Service
A CN that does not distribute CONTENT appropriately may deny CLIENTs
access to CONTENT.
6.1.2.3 Substitution of Security Parameters
If a SURROGATE does not duplicate completely the security services
of the ORIGIN (e.g. encryption algorithms, key lengths, certificate
authorities, client authentication) CONTENT stored on the SURROGATE
may be less secure than the PUBLISHER prefers.
6.1.2.4 Substitution of Security Policies
If a SURROGATE does not employ the same security policies and
procedures as the ORIGIN, the CONTENT may be treated with less care
than the PUBLISHER expects. This threat may also manifest itself if
the legal jurisdiction of the SURROGATE differs from that of the
ORIGIN, should, for example, legal differences between the
jurisdictions require or permit different treatment of the CONTENT.
6.1.3 Threats to a CN
6.1.3.1 Bad Accounting Information
If a CN is unable to collect or receive accurate accounting
information, it may be unable to collect compensation for its
services from PUBLISHERs.
6.1.3.2 Denial of Service
Misuse of a CN may make that CN's facilities unavailable, or
available only at reduced functionality, to legitimate customers or
the CN provider itself. Denial of service attacks can be targeted at
a CN's ACCOUNTING SYSTEM, DISTRIBUTION SYSTEM, or REQUEST-ROUTING
SYSTEM.
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6.1.3.3 Transitive Threats
To the extent that a CN acts as either a CLIENT or a PUBLISHER (such
as, for example, in transitive implementations) such a CN may be
exposed to any or all of the threats described above for both roles.
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7. Acknowledgements
The authors would like to acknowledge the contributions and comments
of Mark Day (Cisco), Fred Douglis (AT&T), Patrik Falstrom (Cisco),
Don Gilletti (CacheFlow), Barron Housel (Cisco) John Martin (Network
Appliance), Raj Nair (Cisco), Hilarie Orman (Novell), Doug Potter
(Cisco), John Scharber (CacheFlow), and Oliver Spatscheck (AT&T).
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References
[1] Hawkinson, J. and T. Bates, "Guidelines for creation,
selection, and registration of an Autonomous System (AS)", BCP
6, March 1996,
<URL:http://www.rfc-editor.org/rfc/bcp/bcp6.txt>.
[2] Postel, J., "Internet Protocol, DARPA Internet Program
Protocol Specification", RFC 791, September 1981,
<URL:http://www.rfc-editor.org/rfc/rfc791.txt>.
[3] Hares, S. and D. Katz, "Administrative Domains and Routing
Domains A Model for Routing in the Internet", RFC 1136,
December 1989,
<URL:http://www.rfc-editor.org/rfc/rfc1136.txt>.
[4] Postel, J., "Domain Name Structure and Delegation", RFC 1591,
March 1994,
<URL:http://www.rfc-editor.org/rfc/rfc1591.txt>.
[5] Rekhter, Y. and T. Li, "A Border Gateway Protocol 4 (BGP-4)",
RFC 1771, March 1995,
<URL:http://www.rfc-editor.org/rfc/rfc1771.txt>.
[6] Carpenter, B., "Architecture Principles of the Internet", RFC
1958, June 1996,
<URL:http://www.rfc-editor.org/rfc/rfc1958.txt>.
[7] Schulzrinne, H., Rao, A. and R. Lanphier, "Real Time Streaming
Protocol", RFC 2326, April 1998,
<URL:http://www.rfc-editor.org/rfc/rfc2326.txt>.
[8] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, August
1998,
<URL:http://www.rfc-editor.org/rfc/rfc2396.txt>.
[9] 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>.
[10] Carpenter, B., "Internet Transparency", RFC 2775, February
2000,
<URL:http://www.rfc-editor.org/rfc/rfc2775.txt>.
[11] Cooper, I., Melve, I. and G. Tomlinson, "Internet Web
Replication and Caching Taxonomy", RFC 3040, January 2001,
<URL:http://www.ietf.org/rfc/rfc3040.txt>.
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[12] Volbrecht, J., Calhoun, P., Farrell, S., Gommans, L., Gross,
G., de Bruijn, B., de Laat, C., Holdrege, M. and D. Spence,
"AAA Authorization Framework",
draft-ietf-aaa-authz-arch-00.txt (work in progress), October
1999,
<URL:http://www.ietf.org/internet-drafts/draft-ietf-aaa-authz-a
rch-00.txt>.
[13] Day, M., Cain, B., Tomlinson, G. and P. Rzewski, "A Model for
Content Internetworking", draft-day-cdnp-model-05.txt (work in
progress), March 2001,
<URL:http://www.ietf.org/internet-drafts/draft-day-cdnp-model-0
5.txt>.
[14] Day, M., Gilletti, D. and P. Rzewski, "Content Internetworking
Scenarios", draft-day-cdnp-scenarios-03.txt (work in
progress), March 2001,
<URL:http://www.ietf.org/internet-drafts/draft-day-cdnp-scenari
os-03.txt>.
[15] Gilletti, D., Nair, R., Scharber, J. and J. Guha, "Content
Internetworking Authentication, Authorization, and Accounting
Requirements", draft-gilletti-cdnp-aaa-reqs-01.txt (work in
progress), January 2001,
<URL:http://www.ietf.org/internet-drafts/draft-gilletti-cdnp-aa
a-reqs-01.txt>.
[16] Barbir, A., Cain, B., Douglis, F., Green, M., Hofmann, 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.
[17] Cain, B., Spatscheck, O., May, M. and A. Barbir,
"Request-Routing Requirements for Content Internetworking",
draft-ietf-cain-request-routing-req-01.txt (work in progress),
March 2001.
[18] Amini, L., Thomas, S. and O. Spatscheck, "Distribution Peering
Requirements for Content Distribution Internetworking",
draft-amini-cdi-distribution-reqs-00.txt (work in progress),
February 2001.
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Authors' Addresses
Mark Green
CacheFlow Inc.
650 Almanor Avenue
Sunnyvale, CA 94086
US
Phone: +1 408 543 0470
EMail: markg@cacheflow.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
Stephen Thomas
TransNexus, Inc.
430 Tenth Street NW
Suite N204
Atlanta, GA 30318
US
Phone: +1 404 872 4887
EMail: stephen.thomas@transnexus.com
Phil Rzewski
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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Acknowledgement
Funding for the RFC editor function is currently provided by the
Internet Society.
Green, et. al. Expires August 31, 2001 [Page 36]