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`13C
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`Leighton
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`FefilpfurauEantEroffleTConsRAoffda~dANppropSriaaMonsAcltT200Ts(HA.R4Bl1~. L!A~p~p~lic~a~ti~o~n~N~u~m~b~e~r--l~(~ne~w~)~~~~~~~~~~~~--1
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`100
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`250
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`130
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`160
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`600
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`65
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`80
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`100
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`0
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`"Express Mail Post Office to Addressee" under 37 CFR § 1.10 on the date indicated above and are addressed to
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`Re:
`
`Content distribution system using an alternative domain name system (DNS) and
`content servers
`Inventors: F. Thomson Leighton and Daniel M. Lewin
`Docket: Akamai Technologies, Inc. 13C
`Assignee: Massachusetts Institute of Technology
`
`Dear Sir:
`
`A utility application is enclosed. Please direct all correspondence to the address associated with
`
`Customer Number 50086.
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`Respectfully submitted,
`
`By:
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`David H. Judson, Reg. No. 30,467
`
`· 15950 Dallas Parkway
`Suite 225
`Dallas, Texas 75248
`972-385-2018
`
`3
`
`

`
`13C
`
`1
`
`PATENT
`
`CONTENT DISTRIBUTION SYSTEM USING AN ALTERNATIVE
`DOMAIN NAME SYSTEM (DNS) AND CONTENT SERVERS
`
`CROSS-REFERENCE TO RELATED APPLICATIONS
`
`5
`
`This application is a continuation of prior application Serial No. 10/417,607,
`
`filed April 17, 2003, now U.S. Patent No. 7,103,645, which application was a
`
`continuation of prior application Serial No. 09/604,878, filed June 28, 2000, now U.S.
`
`Patent No. 6,553,413, which application was a continuation of prior application Serial
`
`No. 09/314,863, filed May 19, 1999, now U.S. Patent No. 6,108,703, which application
`
`10 was based on and claimed priority from Provisional Application 60/092,710, filed July
`
`14, 1998.
`
`Technical Field
`
`BACKGROUND OF THE INVENTION
`
`This invention relates generally to information retrieval in a computer network.
`
`15 More particularly, the invention relates to a novel method of hosting and distributing
`
`content on the Internet that addresses the problems of Internet Service Providers (ISPs) and
`
`Internet Content Providers.
`
`Description of the Related Art
`
`The World Wide Web is the Internet's multimedia information retrieval system. In
`
`20
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`the Web environment, client machines effect transactions to Web servers using the
`
`Hypertext Transfer Protocol (HTTP), which is a known application protocol providing
`
`users access to files (e.g., text, graphics, images, sound, video, etc.) using a standard page
`
`description language known as Hypertext Markup Language (HTML). HTML provides
`
`basic document formatting and allows the developer to specify "links" to other servers and
`
`2 5
`
`files. In the Internet paradigm, a network path to a server is identified by a so-called
`
`Uniform Resource Locator (URL) having a special syntax for defining a network
`
`connection. Use of an HTML-compatible browser (e.g., Netscape Navigator or Microsoft
`
`Internet Explorer) at a client machine involves specification of a link via the URL. In
`
`4
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`...
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`13C
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`PATENT
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`response, the client makes a request to the server identified in the link and, in return,
`
`receives a document or other object formatted according to HTML. A collection of
`
`documents supported on a Web server is sometimes referred to as a Web site.
`
`It is well known in the prior art for a Web site to mirror its content at another server.
`
`5
`
`Indeed, at present, the only method for a Content Provider to place its content closer to its
`
`readers is to build copies of its Web site on machines that are located at Web hosting farms
`
`in different locations domestically and internationally. These copies of Web sites are
`
`known as mirror sites. Unfortunately, mirror sites place unnecessary economic and
`
`operational burdens on Content Providers, and they do not offer economies of scale.
`
`1 O Economically, the overall cost to a Content Provider with one primary site and one mirror
`
`site is more than twice the cost of a single primary site. This additional cost is the result of
`
`two factors: (1) the Content Provider must contract with a separate hosting facility for each
`
`mirror site, and (2) the Content Provider must incur additional overhead expenses
`
`associated with keeping the mirror sites synchronized.
`
`15
`
`In an effort to address problems associated with mirroring, companies such as
`
`Cisco, Resonate, Bright Tiger, F5 Labs and Alteon, are developing software and hardware
`
`that will help keep mirror sites synchronized and load balanced. Although these
`
`mechanisms are helpful to the Content Provider, they fail to address the underlying problem
`
`of scalability. Even if a Content Provider is willing to incur the costs associated with
`
`2 0 mirroring, the technology itself will not scale beyond a few (i.e., less than 10) Web sites.
`
`In addition to these economic and scalability issues, mirroring also entails
`
`operational difficulties. A Content Provider that uses a mirror site must not only lease and
`
`manage physical space in distant locations, but it must also buy and maintain the software
`
`or hardware that synchronizes and load balances the sites. Current solutions require
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`2 5
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`Content Providers to supply personnel, technology and other items necessary to maintain
`
`multiple Web sites. In summary, mirroring requires Content Providers to waste economic
`
`and other resources on functions that are not relevant to their core business of creating
`
`content.
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`5
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`13C
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`3
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`PATENT
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`Moreover, Content Providers also desire to retain control of their content. ·Today,
`
`some ISPs are installing caching hardware that interrupts the link between the Content
`
`Provider and the end-user. The effect of such caching can produce devastating results to
`
`the Content Provider, including (1) preventing the Content Provider from obtaining
`
`5
`
`accurate hit counts on its Web pages (thereby decreasing revenue from advertisers), (2)
`
`preventing the Content Provider from tailoring content and advertising to specific audiences
`
`(which severely limits the effectiveness of the Content Provider's Web page), and (3)
`
`providing outdated information to its customers (which can lead to a frustrated and angry
`
`end user).
`
`10
`
`There remains a significant need in the art to provide a decentralized hosting
`
`solution that enables users to obtain Internet content on a more efficient basis (i.e., without
`
`burdening network resources unnecessarily) and that likewise enables the Content Provider
`
`to maintain control over its content.
`
`The present invention solves these and other problems associated with the prior art.
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`6
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`4
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`PATENT
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`BRIEF SUMMARY OF THE INVENTION
`
`It is a general object of the present invention to provide a computer network
`
`comprising a large number of widely deployed Internet servers that form an organic,
`
`massively fault-tolerant infrastructure designed to serve Web content efficiently,
`
`5
`
`effectively, and reliably to end users.
`
`Another more general object of the present invention is to provide a fundamentally
`
`new and better method to distribute Web-based content. The inventive architecture
`
`provides a method for intelligently routing and replicating content over a large network of
`
`distributed servers, preferably with no centralized control.
`
`10
`
`Another object of the present invention is to provide a network architecture that
`
`moves content close to the user. The inventive architecture al.lows Web sites to develop
`
`large audiences without worrying about building a massive infrastructure to handle the
`
`associated traffic.
`
`Still another object of the present invention is to provide a fault-tolerant network for
`
`15
`
`distributing Web content. The network architecture is used to speed-up the delivery of
`
`richer Web pages, and it allows Content Providers with large audiences to serve them
`
`reliably and economically, preferably from servers located close to end users.
`
`A further feature of the present invention is the ability to distribute and manage
`
`content over a large network without disrupting the Content Provider's direct relationship
`
`2 0 with the end user.
`
`Yet another feature of the present invention is to provide a distributed scalable
`
`infrastructure for the Internet that shifts the burden of Web content distribution from the
`
`Content Provider to a network of preferably hundreds of hosting servers deployed, for
`
`example, on a global basis.
`
`2 5
`
`In general, the present invention is a network architecture that supports hosting on a
`
`truly global scale. The inventive framework allows a Content Provider to replicate its most
`
`popular content at an unlimited number of points throughout the world. As an additional
`
`feature, the actual content that is replicated at any one geographic location is specifically
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`PATENT
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`tailored to viewers in that location. Moreover, content is automatically sent to the location
`
`where it is requested, without any effort or overhead on the part of a Content Provider.
`
`It is thus a more general object of this invention to provide a global hosting
`
`framework to enable Content Providers to retain control of their content.
`
`5
`
`The hosting framework of the present invention comprises a set of servers operating
`
`in a distributed manner. The actual content to be served is preferably supported on a set of
`
`hosting servers (sometimes referred to as ghost servers). This content comprises HTML
`
`page objects that, conventionally, are served from a Content Provider site. In accordance
`
`with the invention, however, a base HTML document portion of a Web page is served from
`
`l 0
`
`the Content Provider's site while one or more embedded objects for the page are served
`
`from the hosting servers, preferably, those hosting servers nearest the client machine. By
`
`serving the base HTML document from the Content Provider's site, the Content Provider
`
`maintains control over the content.
`
`The determination of which hosting server to use to serve a given embedded object
`
`15
`
`is effected by other resources in the hosting framework. In particular, the framework
`
`includes a second set of servers (or server resources) that are configured to provide top
`
`level Domain Name Service (DNS). In addition, the framework also includes a third set of
`
`servers (or server resources) that are configured to provide low level DNS functionality.
`
`When a client machine issues an HTTP request to the Web site for a given Web page, the
`
`2 0
`
`base HTML document is served from the Web site as previously noted. Embedded objects
`
`for the page preferably are served from particular hosting servers identified by the top- and
`
`low-level DNS servers. To locate the appropriate hosting servers to use, the top-level DNS
`
`server determines the user's location in the network to identify a given low-level DNS
`
`server to respond to the request for the embedded object. The top-level DNS server then
`
`2 5
`
`redirects the request to the identified low-level DNS server that, in tum, resolves the request
`
`into an IP address for the given hosting server that serves the object back to the client.
`
`More generally, it is possible (and, in some cases, desirable) to have a hierarchy of
`
`DNS servers that consisting of several levels. The lower one moves in the hierarchy, the
`
`closer one gets to the best region.
`
`8
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`

`
`13C
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`6
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`PATENT
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`A further aspect of the invention is a means by which content can be distributed and
`
`replicated through a collection of servers so that the use of memory is optimized subject to
`
`the constraints that there are a sufficient number of copies of any object to satisfy the
`
`demand, the copies of objects are spread so that no server becomes overloaded, copies tend
`
`5
`
`to be located on the same servers as time moves forward, and copies are located in regions
`
`close to the clients that are requesting them. Thus, servers operating within the framework
`
`do not keep copies of all of the content database. Rather, given servers keep copies of a
`
`minimal amount of data so that the entire system provides the required level of service.
`
`This aspect of the invention allows the hosting scheme to be far more efficient than
`
`10
`
`schemes that cache everything everywhere, or that cache objects only in pre-specified
`
`locations.
`
`The global hosting framework is fault tolerant at each level of operation. In
`
`particular, the top level DNS server returns a list of low-level DNS servers that may be used
`
`by the client to service the request for the embedded object. Likewise, each hosting server
`
`15
`
`preferably includes a buddy server that is used to assume the hosting responsibilities of its
`
`associated hosting server in the event of a failure condition.
`
`According to the present invention, load balancing across the set of hosting servers
`
`is achieved in part through a novel technique for distributing the embedded object requests.
`
`In particular, each embedded object URL is preferably modified by prepending a virtual
`
`2 0
`
`server hostname into the URL. More generally, the virtual server hostname is inserted into
`
`the URL. Preferably, the virtual server hostname includes a value (sometimes referred to as
`
`a serial number) generated by applying a given hash function to the URL or by encoding
`
`given information about the object into the value. This function serves to randomly
`
`distribute the embedded objects over a given set of virtual server hostnames. In addition, a
`
`2 5
`
`given fingerprint value for the embedded object is generated by applying a given hash
`
`function to the embedded object itself. This given value serves as a fingerprint that
`
`identifies whether the embedded object has been modified. Preferably, the functions used
`
`to generate the values (i.e., for the virtual server hostname and the fingerprint) are applied
`
`to a given Web page in an off-line process. Thus, when an HTTP request for the page is
`
`9
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`
`13C
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`7
`
`PATENT
`
`received, the base HTML document is served by the Web site and some portion of the
`
`. page's embedded objects are served from the hosting servers near (although not necessarily
`
`the closest) to the client machine that initiated the request.
`
`The foregoing has outlined some of the more pertinent objects and features of the
`
`5
`
`present invention. These objects should be construed to be merely illustrative of some of
`
`the more prominent features and applications of the invention. Many other beneficial
`
`results can be attained by applying the disclosed invention in a different manner or
`
`modifying the invention as will be described. Accordingly, other objects and a fuller
`
`understanding of the invention may be had by referring to the following Detailed
`
`10 Description of the Preferred Embodiment.
`
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`For a more complete understanding of the present invention and the advantages
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`thereof, reference should be made to the following Detailed Description taken in connection
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`with the accompanying drawings in which:
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`Figure 1 is a representative system in which the present invention is implemented;
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`Figure 2 is a simplified representation of a markup language document illustrating
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`the base document and a set of embedded objects;
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`Figure 3 is a high level diagram of a global hosting system according to the present
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`invention;
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`Figure 4 is a simplified flowchart illustrating a method of processing a Web page to
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`modified embedded object URLs that is used in the present invention;
`Figure 5 is a simplified state diagram illustrating how the present invention
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`responds to a HTTP request for a Web page.
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`DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
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`A known Internet client-server system is implemented as illustrated in Figure 1. A
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`client machine 10 is connected to a Web server 12 via a network 14. For illustrative
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`purposes, network 14 is the Internet, an intranet, an extranet or any other knoWn network.
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`5 Web server 12 is one of a plurality of servers which are accessible by clients, one of which
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`is illustrated by machine 10. A representative client machine includes a browser 16, which
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`is a known software tool used to access the servers of the network. The Web server
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`supports files (collectively referred to as a "Web" site) in the form of hypertext documents
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`and objects. In the Internet paradigm, a network path to a server is identified by a so-called
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`10 Uniform Resource Locator (URL).
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`A representative Web server 12 is a computer comprising a processor 18, an
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`operating system 20, and a Web server program 22, such as Netscape Enterprise Server.
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`The server 12 also includes a display supporting a graphical user interface (GUI) for
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`management and administration, and an Application Programming Interface (API) 26
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`that provides extensions to enable application developers to extend and/or customize the
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`core functionality thereof through software programs including Common Gateway
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`Interface (CGI) programs, plug-ins, servlets, active server pages, server side include
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`(SSI) functions or the like.
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`A representative Web client is a personal computer that is x86-, PowerPC®- or
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`RISC-based, that includes an operating system such as IBM® OS/2® or Microsoft
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`Windows '95, and that includes a Web browser, such as Netscape Navigator 4.0 (or higher),
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`having a Java Virtual Machine (JVM) and support for application plug-ins or helper
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`applications. A client may also be a notebook computer, a handheld computing device
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`(e.g., a PDA), an Internet appliance, or any other such device connectable to the computer
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`network.
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`As seen in Figure 2, a typical Web page comprises a markup language (e.g. HTML)
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`master or base document 28, and many embedded objects (e.g., images, audio, video, or the
`like) 30. Thus, in a typical page, twenty or more embedded images or objects are quite
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`common. Each of these images is an independent object in the Web, retrieved (or validated
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`for change) separately. The common behavior of a Web client, therefore, is to fetch the
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`base HTML document, and then immediately fetch the embedded objects, which are
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`typically (but not always) located on the same server. According to the present invention,
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`preferably the markup language base document 28 is served from the Web server (i.e., the
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`Content Provider site) whereas a given number (or perhaps all) of the embedded objects are
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`served from other servers. As will be seen, preferably a given embedded object is served
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`from a server (other than the Web server itself) that is close to the client machine, that is not
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`overloaded, and that is most likely to already have a current version of the required file.
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`Referring now to Figure 3, this operation is achieved by the hosting system of the
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`present invention. As will be seen, the hosting system 35 comprises a set of widely- ·
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`deployed servers (or server resources) that form a large, fault-tolerant infrastructure
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`designed to serve Web content efficiently, effectively, and reliably to end users. The servers
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`may be deployed globally, or across any desired geographic regions. As will be seen, the
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`hosting system provides a distributed architecture for intelligently routing and replicating
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`such content.· To this end, the global hosting system 35 comprises three (3) basic types of
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`servers (or server resources): hosting servers (sometimes called ghosts) 36, top-level DNS
`servers 38, and low-level DNS servers 40. Although not illustrated, there may be additional
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`levels in the DNS hierarchy. Alternatively, there may be a single DNS level that combines
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`the functionality of the top level and low-level servers. In this illustrative embodiment, the·
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`inventive framework 35 is deployed by an Internet Service Provider (ISP), although this is
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`not a limitation of the present invention. The ISP or ISPs that deploy the inventive global
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`hosting framework 35 preferably have a large number of machines that run both the ghost
`server component 36 and the low-level DNS component 40 on their networks. These
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`machines are distributed throughout the network; preferably, they are concentrated around
`network exchange points 42 and network access points 44, although this is not a
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`requirement. In addition, the ISP preferably has a small number of machines running the
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`top-level DNS 38 that may also be distributed throughout the network.
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`Although not meant to be limiting, preferably a given server used in the framework
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`35 includes a processor, an operating system (e.g., Linux, UNIX, Windows NT, or the like),
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`a Web server application, and a set of application routines used by the invention. These
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`routines are conveniently implemented in software as a set of instructions executed by the
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`processor to perform various process or method steps as will be described in more detail
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`below. The servers are preferably located at the edges of the network (e.g., in points of
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`presence, or POPs).
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`Several factors may determine where the hosting servers are placed in the network.
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`Thus, for example, the server locations are preferably determined by a demand driven
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`network map that allows the provider (e.g., the ISP) to monitor traffic requests. By
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`studying traffic patterns, the ISP may optimize the server locations for the given traffic
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`profiles.
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`According to the present invention, a given Web page (comprising a base HTML
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`document and a set of embedded objects) is served in a distributed manner. Thus,
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`preferably, the base HTML document is served from the Content Provider Site 45 that
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`normally hosts the page. The embedded objects, or some subset thereof, are preferentially
`served from the hosting servers 36 and, specifically, given hosting servers 36 that are near
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`the client machine that in the first instance initiated the request for the Web page. In
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`addition, preferably loads across the hosting servers are balanced to ensure that a given
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`embedded object may be efficiently served from a given hosting server near the client when
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`such client requires that object to complete the page.
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`To serve the page contents in this manner, the URL associated with an embedded
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`object is modified. As is well-known, each embedded object that may be served in a page
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`has its own URL. Typically, the URL has a hostname identifying the Content Provider's
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`site from where the object is conventionally served, i.e., without reference to the present
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`invention. According to the invention, the embedded object URL is first modified,
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`preferably in an off-line process, to condition the URL to be served by the global hosting
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`servers. A flowchart illustrating the preferred method for modifying the object URL is
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`illustrated in Figure 4.
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`The routine begins at step 50 by determining whether all of the embedded objects in
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`a given page have been processed. If so, the routine ends. If not, however, the routine gets
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`the next embedded object at step 52. At step 54, a virtual server hostname is prepended
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`into the URL for the given embedded object. The virtual server hostname includes a value
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`(e.g., a number) that is generated, for example, by applying a given hash function to the
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`URL. As is well-known, a hash function takes arbitrary length bit strings as inputs and
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`produces fixed length bit strings (hash values) as outputs. Such functions satisfy two
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`conditions: (I) it is infeasible to find two different inputs that produce the same hash value,
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`and (2) given an input and its hash value, it is infeasible to find a different input with