Content Distribution Networks State of the art Colophon Date : June 1, 2001 Version : 1.0 Change : - Project reference: CDN2 TI reference : TI/RS/2001xx Company reference : - URL : - Access permissions : Anyone Status : Final Editor : Bob Hulsebosch Company : Telematica Instituut Author(s) : Rogier Brussee, Henk Eertink, Wolf Huijsen, Bob Hulsebosch, Michiel Rougoor, Wouter Teeuw, Martin Wibbels, Hans Zandbelt. Synopsis: This document presents an overview of the current state-of-the-art of Content Distribution Networks. Copyright © 2001 Telematica Instituut Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from or via Telematica Instituut (http://www.telin.nl). Management Summary World-wide the Internet population is currently estimated at 170 million users. As Internet use continues to grow, greater access speeds create a need for more sophisticated bandwidth to support high-impact sites. E-businesses are experiencing increased pressure to provide fast, reliable content delivery to Web users as site performance can strongly impact a content provider's bottom line in that consumers are more likely to visit and/or purchase from sites that load quickly, reliably and consistently. Moreover, the increased use of rich-media content consisting of audio, video, and images puts a huge load on the storage and network infrastructure. Helping drive the use of such rich-media is a rapid adoption of broadband access technologies that enable applications such as movies-on- demand and videoconference calling. Content Delivery Networks (CDNs) optimise content delivery by putting the content closer to the consumer and shorting the delivery path via global networks of strategically placed servers. CDNs also manage and maintain the network elements that deliver Web content, such as text, images, and streaming audio and video, to the end user, streamlining the entire process. Moreover, a CDN offers unique possibility to provide for value added services like customisation and adaptation of content, virus scanning and ad insertion. This state of the art investigation presents a state-of-the-art survey of Content Distribution Networks. It gives insight in: ÷ The current content distribution landscape. It is concluded that there are many emerging competitors in the content-distribution space. To survive, CDN services must expand beyond cache-based delivery to offer application logic and point of interaction customisation. By delivering value-added applications at the edge of the network, content providers are able to develop a more profitable, personalised, and persistent relationship with end-user subscribers. ÷ The business models for content distribution networks. Based on the value chain of content delivery, we distinguish the following roles (business functions): ÷ Content provider (CP, originator, content creator, publisher) ÷ Syndicator (content assembler) ÷ Distributor (content distribution service provider, CDSP, content networker) ÷ Content consumer (consumer, customer, end-user) CDN peering allows multiple CDN resources to be combined so as to provide larger scale and / or reach to participants than any single CDN could achieve by itself. Future CDN service scenarios are virus scanning, insertion of ad banner, insertion of regional data, and adaptation of streaming media. ÷ CDN components, architectures and protocols. I.e., the components that constitute a CDN, the technicalities of finding the most appropriate surrogate server, replication techniques for content caching and distribution, proxy technologies and architectures for streaming and other media, and the protocols that are used within a CDN. ÷ Content negotiation in a CDN. Content negotiation provides a tool where the client can indicate his preferences and capabilities. It allows CDN providers to offer value- added services based on these negotiation elements. Several protocols for content negotiation are MIME-type based, HTTP, CC/PP, and SDP. The IETF ConNeg CONTENT DISTRIBUTION NETWORKS V working group has proposed and described a protocol-independent content negotiation framework. ÷ Content adaptation in a CDN. Besides delivering content, CDNs may also adapt content. For instance by transcoding multimedia streams or by translating from a particular language into another. There is currently new standardisation work being set-up that defines standard mechanism to extend HTTP-intermediates with application-specific value added services (such as virus checking or transcoding). The iCAP protocol for instance facilitates such content adaptation functionality. Middle boxes and media gateways are intermediary devices that may offer additional intelligence for content adaptation or transcoding. ÷ Authorisation, authentication and accounting. The AAA requirements for a CDN service environment are driven by the need to ensure authorisation of the client, publishing server or administrative server attempting to inject proxylet functionality, to authenticate injected proxylets, and to perform accounting on proxylet functions so the client or publishing server can be billed for the services. In addition, AAA is also required for a host willing to act as a remote callout server. Digital Rights Management (DRM), i.e. the process of protecting and managing the rights of all participants engaged in the electronic commerce and digital distribution of content, will become an important issue in a CDN since original content will be adapted and distributed over the network. ÷ Related platforms and architectures. In a way, CDN providers offer a (middleware) platform for a wide range of interactive functions, from searching to user profiling to order processing. The Globe middleware platform helps design wide area distributed applications and is in many aspects similar to a CDN platform. Globus, a Grid middleware layer is another example. The areas of distributed operating systems and parallel computing on the one hand (from which Grid comes) and middleware platforms on the other hand (from which CDN comes) seem come closer and might even benefit from each other. Parlay, OSA, and JAIN define standard application programming interfaces that may facilitate rapid deployment of new CDN services. Based on an analysis of the strengths, weaknesses, opportunities and future threats for a CDN we have observed the following research opportunities: ÷ ASP and CDN synergy, ÷ Grid and CDN synergy, ÷ Broadcasting of streaming media in a CDN, ÷ Personalisation and localisation (mobility), ÷ Globalisation. TELEMATICA INSTITUUT VI Table of Contents 1 Introduction 1 1.1 How do CDNs work? 1 1.2 Reading guide 2 2 Current content delivery landscape 4 2.1 CDN service providers 4 2.2 CDN market forecasts 6 2.3 Standardisation activities 7 2.3.1 Within the IETF 7 2.3.2 Outside the IETF 7 2.4 Streaming content delivery 8 2.5 Telematica Instituut point of view 9 2.5.1 Bridging distance 10 2.5.2 Bridging time 10 2.5.3 Bridging heterogeneity 10 3 Content distribution services: business models 12 3.1 Internet developments 12 3.1.1 Internet trends 12 3.1.2 Internet business models 13 3.1.3 Content Distribution Networks 14 3.1.3.1 Functionality 14 3.1.3.2 CDN Business models 14 3.2 Business roles 15 3.2.1 Content provider 16 3.2.2 Syndicator 16 3.2.3 Content distribution service provider 16 3.2.4 Content consumer 17 3.2.5 ISP or local access provider 18 3.2.6 Server capacity provider 18 3.2.7 CDN product manufacturers 18 3.3 Peering CDNs 19 3.4 Future scenarios 21 3.4.1 Virus scanning 21 3.4.2 Insertion of ad banners 21 3.4.3 Insertion of regional data 21 3.4.4 Content adaptation for alternate Web access devices 21 3.4.5 Adaptation of streaming media 22 3.5 Mapping value-added services on business roles 22 4 CDN components, architectures and protocols 23 4.1 Introduction 23 4.2 Replication 23 4.2.1 Client-Replica protocols 23 4.2.2 Inter-Replica protocols 23 4.3 Caching 24 4.3.1 Proxies 24 4.3.1.1 Filtering Requests 24 4.3.1.2 Sharing Connections 24 4.3.1.3 Improving Performance 25 4.3.2 Caching proxies 25 4.3.3 Web Cache Architectures 26 CONTENT DISTRIBUTION NETWORKS VII 4.3.4 Caching Protocols 27 4.3.4.1 ICP 27 4.3.4.2 Cache Digests 27 4.3.4.3 HTCP 29 4.3.4.4 CARP 29 4.4 OPES 30 4.5 Streaming Proxies 31 4.5.1 Cached Delivery 32 4.5.2 Replication 32 4.5.3 Unicast Split 33 4.5.4 Multicast Split 33 4.5.5 Pass-Through Delivery 33 4.6 Products 34 5 Content negotiation 35 5.1 MIME-type based content negotiation 35 5.2 Content negotiation in HTTP 35 5.3 IETF Content Negotiation working group 38 5.4 Transparent Content Negotiation 39 5.5 User (agent) profiles 39 5.5.1 W3C CC/PP (Composite Capability / Preference Profiles) 40 5.6 SDP version 2 41 6 Content adaptation 43 6.1 ICAP – Internet Content Adaptation Protocol. 45 6.1.1 Benefits of iCAP 45 6.1.2 ICAP architecture 45 6.1.3 Trends and iCAP opportunities 48 6.1.4 ICAP limitations 49 6.2 Middle boxes 49 6.3 Transcoding and media gateways 49 6.4 Transcoding and XML/HTML 50 7 Authorisation, authentication, and accounting51 7.1 What is AAA? 51 7.2 AAA definitions 51 7.3 AAA standardisation 52 7.4 AAA in a CDN 53 7.4.1 AAA in the existing Web system model 54 7.4.2 AAA in the service environment caching proxy model 55 7.4.3 AAA in the Remote Callout Server model 55 7.4.4 AAA in the Administrative Server model 57 7.5 Accounting in peered CDNs 57 7.6 DRM 58 7.7 Lack of AAA in current CDNs 61 7.8 Accounting revenue sources 62 8 Other platforms and system architectures 63 8.1 The Globe middleware, GlobeDoc and the GDN.