1 Introduction

The Peer Content Caching and Retrieval: Content Identification data structure specifies the Content Information (section 2.3) format used by the Peer Content Caching and Retrieval framework to uniquely identify content for discovery and retrieval purposes.

The Peer Content Caching and Retrieval framework is based on a peer (5)-to-peer (5) discovery and distribution model. It is designed to reduce bandwidth consumption on branch-office wide area network (WAN) links by having clients retrieve content from distributed caches when available instead of the servers, which are often located remotely from branch offices over the WAN links. The peers themselves act as caches from which they serve other requesting peers. The framework also supports using hosted caches in place of peer (5)-based caching. The main benefit is to reduce operation costs by reducing WAN link utilization, while providing faster downloads from the local area network (LAN) in the branch office.

Content Information contains all the necessary information to allow a peer to uniquely specify content for discovery, and for peer caches or hosted caches to determine whether they have the specific content requested by the querying peer. Additionally, the Content Information also ensures the confidentiality of content sent between peers, and allow peers to verify the integrity of downloaded content segments. To satisfy these requirements, Content Information utilizes cryptographic hashing and encryption algorithms to encrypt and generate hashes of the content units, and provides mechanisms to specify the starting point (offset) and length of the content range. Content Information is used in the discovery protocol specified in [MS-PCCRD] and the retrieval protocol described in [MS-PCCRR] to identify content for discovery, response, and retrieval requests.

Sections 1.7 and 2 of this specification are normative. All other sections and examples in this specification are informative.