1.3 Overview

Peer Content Caching and Retrieval: HTTP Extensions specify PeerDist Content Encoding used in HTTP/1.1, a client/server-based protocol. The purpose of PeerDist content encoding is to enable peer content caching and retrieval in HTTP/1.1, which allows an HTTP client to participate in the peer content caching and retrieval process.

Upon detecting PeerDist encoding support from a client, an HTTP/1.1 server that supports peer content caching can send a PeerDist-encoded response. The message body (that is, an encoded entity body) of such a response takes the form of the Content Information Data Structure as specified in [MS-PCCRC] section 2.3, constructed for the requested content using the algorithms described in [MS-PCCRC] sections 2.1 and 2.2. To receive a PeerDist-encoded response allows an HTTP/1.1 client to use the information present in the response to discover and download content from peers.

A typical PeerDist-encoded response is orders of magnitude smaller than a response that is not PeerDist encoded; the actual content transfer occurs between peers. Thus, PeerDist content encoding can reduce the burden of distributing the content from the HTTP/1.1 server.

A sequence diagram describing the communication between an HTTP/1.1 client and the HTTP/1.1 server is shown following.

Sequence diagram describing the communication between the HTTP/1.1 client and the HTTP/1.1 server

Figure 1: Sequence diagram describing the communication between the HTTP/1.1 client and the HTTP/1.1 server