Network Working Group M. Day Internet-Draft Cisco Expires: October 30, 2001 B. Cain Cereva G. Tomlinson CacheFlow P. Rzewski Inktomi May 2001 A Model for CDN Peering draft-day-cdnp-model-06.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on October 30, 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. Day, et. al. Expires October 30, 2001 [Page 1] Internet-Draft CDNPM May 2001 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Content Networks . . . . . . . . . . . . . . . . . . . . . . 4 2.1 Problem Description . . . . . . . . . . . . . . . . . . . . 4 2.2 Caching Proxies . . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . 11 4. Content Network Examples and Commentary . . . . . . . . . . 14 4.1 Understanding CDNs . . . . . . . . . . . . . . . . . . . . . 14 4.2 Understanding content structure . . . . . . . . . . . . . . 14 5. Content Internetworking . . . . . . . . . . . . . . . . . . 15 6. Content Internetworking Model Terms . . . . . . . . . . . . 16 7. Content Internetworking Examples and Commentary . . . . . . 19 7.1 Understanding Content Internetworking . . . . . . . . . . . 19 7.2 Content Signaling . . . . . . . . . . . . . . . . . . . . . 19 8. Operational Considerations . . . . . . . . . . . . . . . . . 20 9. Security Considerations . . . . . . . . . . . . . . . . . . 21 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22 References . . . . . . . . . . . . . . . . . . . . . . . . . 23 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 24 Full Copyright Statement . . . . . . . . . . . . . . . . . . 25 Day, et. al. Expires October 30, 2001 [Page 2] Internet-Draft CDNPM May 2001 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, or "content internetworking." For historical reasons, we sometimes abbreviate this term using the acronym CDI (from "content distribution internetworking"). By analogy with peering of IP networks, this interconnection has also sometimes been called "content peering," but we avoid that usage here. 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 6 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 [3] . 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 [4], which enumerates scenarios for Content-Internetworking-related interactions; [5], which describes requirements for accounting and associated issues; [6], which gives an overall architecture of the elements for CDI; and [7], 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. Day, et. al. Expires October 30, 2001 [Page 3] Internet-Draft CDNPM May 2001 2. Content Networks The past several years have seen the evolution of technologies centered around "content." Protocols, appliances, and entire markets have been created exclusively for the location, download, and usage 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 images, 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 user agent. In the trivial case, the rendezvous mechanism is that every user agent 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 Day, et. al. Expires October 30, 2001 [Page 4] Internet-Draft CDNPM May 2001 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. 2.2 Caching Proxies A type of content network that has been in use for several years is a caching proxy 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 caching proxy. That caching proxy will therefore contain the "hot set" of all Internet content being viewed by the totality of access users utilizing that caching proxy. 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. The following diagram depicts a hierarchical cache deployment as described above: Day, et. al. Expires October 30, 2001 [Page 5] Internet-Draft CDNPM May 2001 ^ ^ | | 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 user agent's session to the same server, in order to preserve session state. Day, et. al. Expires October 30, 2001 [Page 6] Internet-Draft CDNPM May 2001 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 [3] . 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 Day, et. al. Expires October 30, 2001 [Page 7] Internet-Draft CDNPM May 2001 replicas of each content item being hosted. A request from a browser 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 content-delivery infrastructure, a request-routing infrastructure, a distribution infrastructure, and an accounting infrastructure. The content- delivery infrastructure consists of a set of "surrogate" servers [3] 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. The following diagram depicts a simple CDN as described above: Day, et. al. Expires October 30, 2001 [Page 8] Internet-Draft CDNPM May 2001 ---------- ---------- |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." Day, et. al. Expires October 30, 2001 [Page 9] Internet-Draft CDNPM May 2001 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. Day, et. al. Expires October 30, 2001 [Page 10] Internet-Draft CDNPM May 2001 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. Although the following uses many terms that are based on those used in RFC 2616 [1] or RFC 3040 [3], there is no necessary connection to HTTP or web caching technology. Content internetworking and this vocabulary are applicable to other protocols and styles of content delivery. 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 CONTENT 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 CONTENT 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 A program that sends REQUESTs and receives corresponding RESPONSEs. [Note: this is similar to the definition in RFC 2616 [1] but we do not require establishment of a connection.] CONTENT Any form of digital data, CONTENT approximately corresponds to what is referred to as an "entity" in RFC 2616. [1] One important form of CONTENT with additional constraints on DISTRIBUTION and DELIVERY is CONTINUOUS MEDIA. CONTENT NETWORK An arrangement of CONTENT NETWORK ELEMENTS, controlled by a common management in some fashion. CONTENT NETWORK ELEMENT A network device that performs at least some of its processing by examining CONTENT-related parts of network messages. In IP-based Day, et. al. Expires October 30, 2001 [Page 11] Internet-Draft CDNPM May 2001 networks, a CONTENT NETWORK ELEMENT is a device whose processing depends on examining some or all of an IP packet's body; network elements (as defined in RFC 3040) examine only the header of an IP packet. CONTENT SIGNAL 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. [Note: This definition is essentially identical to the definition of continuous media in [2]] 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 CONTENT NETWORK ELEMENTS that support DISTRIBUTION for a single CONTENT NETWORK. The DISTRIBUTION SYSTEM also propagates CONTENT SIGNALs. 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. [Note: We believe this defnition is compatible with that for "origin server" in RFC 2616 [1] but includes additional constraints useful for CDI.] PUBLISHER The party that ultimately controls the CONTENT and its distribution. Day, et. al. Expires October 30, 2001 [Page 12] Internet-Draft CDNPM May 2001 REACHABLE SURROGATES The collection of SURROGATES that can be contacted via a particular DISTRIBUTION SYSTEM or REQUEST-ROUTING SYSTEM. CONTENT REQUEST [Update based on request-routing requirements: initial request, final request, etc.] A message identifying a particular item of CONTENT to be delivered. REQUEST-ROUTING The activity of steering or directing a CONTENT REQUEST from a USER AGENT to a suitable SURROGATE. REQUEST-ROUTING SYSTEM A collection of CONTENT NETWORK ELEMENTS that support REQUEST-ROUTING for a single CONTENT NETWORK. CONTENT RESPONSE A message containing a particular item of CONTENT, identified in a previous CONTENT REQUEST. SERVER A program that accepts REQUESTS and services them by sending back RESPONSES. Any given program may be capable of being both a client and a server; our use of these terms refers only to the role being performed by the program. [Note: this is adapted from a similar definition in RFC 2616 [1].] SURROGATE A delivery server, other than the ORIGIN. Receives a CONTENT REQUEST and delivers the corresponding CONTENT RESPONSE. [Note: this is a different definition from that in RFC 3040 [3], which appears overly elaborate for our purposes.] USER AGENT The CLIENT which initiates a REQUEST. These are often browsers, editors, spiders (web-traversing robots), or other end user tools. [Note: this definition is identical to the one in RFC 2616 [1].] Day, et. al. Expires October 30, 2001 [Page 13] Internet-Draft CDNPM May 2001 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. 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. Day, et. al. Expires October 30, 2001 [Page 14] Internet-Draft CDNPM May 2001 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. Day, et. al. Expires October 30, 2001 [Page 15] Internet-Draft CDNPM May 2001 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. AREA ADVERTISEMENT ADVERTISEMENT from a CONTENT NETWORK's REQUEST-ROUTING SYSTEM about aspects of topology, geography and performance of a CONTENT NETWORK. Contrast with CONTENT ADVERTISEMENT, DISTRIBUTION ADVERTISEMENT. ACCOUNTING INTERNETWORKING Interconnection of two or more ACCOUNTING SYSTEMS so as to enable the exchange of information between them. The form of ACCOUNTING INTERNETWORKING required may depend on the nature of the NEGOTIATED RELATIONSHIP between the peering parties -- in particular, on the value of the economic exchanges anticipated. ADVERTISEMENT Information about resources available to other CONTENT NETWORKS, exchanged via CONTENT INTERNETWORKING GATEWAYS. Types of ADVERTISEMENT include AREA ADVERTISEMENTS, CONTENT ADVERTISEMENTS, and DISTRIBUTION ADVERTISEMENTS. BILLING ORGANIZATION An entity that operates an ACCOUNTING SYSTEM to support billing within a NEGOTIATED RELATIONSHIP with a PUBLISHER. CONTENT ADVERTISEMENT ADVERTISEMENT from a CONTENT NETWORK's REQUEST-ROUTING SYSTEM about the availability of one or more collections of CONTENT on a CONTENT NETWORK. Contrast with AREA ADVERTISEMENT, DISTRIBUTION ADVERTISEMENT CONTENT DESTINATION A CONTENT NETWORK or DISTRIBUTION SYSTEM that is accepting CONTENT from another such network or system. Contrast with CONTENT SOURCE. CONTENT INTERNETWORKING GATEWAY (CIG) An identifiable element or system through which a CONTENT NETWORK can be interconnected with others. through one or more kinds of peering. A CIG may be the point of contact for DISTRIBUTION INTERNETWORKING, REQUEST-ROUTING INTERNETWORKING, and/or ACCOUNTING INTERNETWORKING, and thus may incorporate some or all of the corresponding systems for the CONTENT NETWORK. CONTENT REPLICATION Day, et. al. Expires October 30, 2001 [Page 16] Internet-Draft CDNPM May 2001 The movement of CONTENT from a CONTENT SOURCE to a CONTENT DESTINATION. Note that this is specifically the movement of CONTENT from one system or network to another. There may be similar or different mechanisms that move CONTENT around within a single network's DISTRIBUTION SYSTEM. CONTENT SOURCE A CONTENT NETWORK or DISTRIBUTION SYSTEM that is distributing CONTENT to another such network or system. Contrast with CONTENT DESTINATION. DISTRIBUTION ADVERTISEMENT An ADVERTISEMENT from a CONTENT NETWORK's DISTRIBUTION SYSTEM to potential CONTENT SOURCES, describing the capabilities of one or more CONTENT DESTINATIONS. Contrast with AREA ADVERTISEMENT, CONTENT ADVERTISEMENT. DISTRIBUTION INTERNETWORKING Interconnection of two or more DISTRIBUTION SYSTEMS so as to propagate CONTENT SIGNALS and copies of CONTENT to groups of SURROGATES. INJECTION A "send-only" form of DISTRIBUTION INTERNETWORKING that takes place from an ORIGIN to a CONTENT DESTINATION. 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 internetworking protocols. 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. Day, et. al. Expires October 30, 2001 [Page 17] Internet-Draft CDNPM May 2001 REQUEST-ROUTING INTERNETWORKING 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. Day, et. al. Expires October 30, 2001 [Page 18] Internet-Draft CDNPM May 2001 7. Content Internetworking Examples and Commentary This section uses the terms of the previous to explain concepts of interconnecting CONTENT NETWORKs. 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 INTERNETWORKING. Analogously, interconnected DISTRIBUTION SYSTEMS give rise to DISTRIBUTION INTERNETWORKING, and interconnected ACCOUNTING SYSTEMS give rise to ACCOUNTING INTERNETWORKING. A CONTENT INTERNETWORKING GATEWAY (CIG) is a generic term used in the model for the means of interconnection between the various kinds of systems. CIGs exchange ADVERTISEMENTS. There are three main kinds of ADVERTISEMENT: AREA ADVERTISEMENTS, CONTENT ADVERTISEMENTS, and DISTRIBUTION ADVERTISEMENTS. An AREA ADVERTISEMENT [...need to finish this section]. 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 internetworked distribution where the connected systems support such signals, CONTENT SIGNALS must be propagated to each SURROGATE with a copy of the relevant CONTENT. Day, et. al. Expires October 30, 2001 [Page 19] Internet-Draft CDNPM May 2001 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.] Day, et. al. Expires October 30, 2001 [Page 20] Internet-Draft CDNPM May 2001 9. Security Considerations Content Internetworking raises some security-related issues, and a detailed discussion of those issues appears in [6]. Day, et. al. Expires October 30, 2001 [Page 21] Internet-Draft CDNPM May 2001 10. Acknowledgements 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). Day, et. al. Expires October 30, 2001 [Page 22] Internet-Draft CDNPM May 2001 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, . [2] Schulzrinne, H., Rao, A. and R. Lanphier, "Real Time Streaming Protocol", RFC 2326, April 1998, . [3] Cooper, I., Melve, I. and G. Tomlinson, "Internet Web Replication and Caching Taxonomy", RFC 3040, June 2000, . [4] Day, M. and D. Gilletti, "CDN Peering Scenarios", draft-day-cdnp-scenarios-02.txt (work in progress), Novmber 2000, . [5] Gilletti, D., Nair, R. and J. Scharber, "CDN Peering Authentication, Authorization, and Accounting Requirements", draft-gilletti-cdnp-aaa-reqs-00.txt (work in progress), November 2000, . [6] Green, M., Cain, B., Tomlinson, G. and S. Thomas, "CDN Peering Architectural Overview", draft-green-cdnp-gen-arch-02.txt (work in progress), November 2000, . [7] Cain, B., Douglis, F., Green, M., Hoffmann, M., Nair, R., Potter, D. and O. Spatscheck, "Known CDN Request-Routing Mechanisms", draft-green-cdnp-gen-arch-02.txt (work in progress), November 2000, . Day, et. al. Expires October 30, 2001 [Page 23] Internet-Draft CDNPM May 2001 Authors' Addresses Mark Stuart Day Cisco Systems 135 Beaver Street Waltham, MA 02452 US Phone: +1 781 663 8310 EMail: markday@cisco.com Brad Cain Cereva Networks 3 Network Drive Marlborough, MA 01752 US Phone: +1 508-787-5000 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 Inktomi 4100 East Third Avenue, MS FC1-4 Foster City, CA 94404 US Phone: +1 650 653 2487 EMail: philr@inktomi.com Day, et. al. Expires October 30, 2001 [Page 24] Internet-Draft CDNPM May 2001 Full Copyright Statement Copyright (C) The Internet Society (2001). All Rights Reserved. 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