1 Introduction

The Peer Content Caching and Retrieval: Retrieval Protocol is used by peers to query and retrieve content of interest on a Peer to Peer network. This protocol is used within the Peer Content Caching & Retrieval service framework. The Retrieval Protocol is an HTTP-based protocol used to retrieve content (specified using the Peer Content Caching & Retrieval Content: Identification data structure) from given peers.

The Retrieval Protocol defines four protocol message exchanges: to query the protocol version of the server, to query the server for the availability of certain content (two message exchanges), and to retrieve content from the server. The framework incorporates both the Retrieval Protocol (PCCRR) and the Discovery Protocol [MS-PCCRD] together to enable a client to discover and retrieve content from multiple peers that have the content instead of the original content server.

The Peer Content Caching and Retrieval Framework is based on a peer-to-peer discovery and distribution model, where the peers themselves act as caches from which they serve other requesting peers. The framework also supports the mode of using pre-provisioned hosted caches in place of peer-based caching. The framework is designed to reduce bandwidth consumption on branch-office wide-area-network (WAN) links by having clients retrieve content from distributed caches, when distributed caches are available, rather than from the content servers, which are often located remotely from branch offices over the WAN links. The main benefit of the framework is to reduce operation costs by reducing WAN link utilization, while providing faster downloads from the local area networks (LANs) in the branch offices.

Sections 1.5, 1.8, 1.9, 2, and 3 of this specification are normative. All other sections and examples in this specification are informative.