1.1 Glossary

This document uses the following terms:

block: A chunk of content that composes a segment. Each segment is divided into one or more blocks. Every block belongs to a specific segment, and within a segment, blocks are identified by their progressive index. (Block 0 is the first block in the segment, block 1 is the second, and so on.) See [MS-PCCRC] for more details.

block hash: A hash of a content block within a segment. Also known as a block ID.

block range: A set of consecutive blocks within a segment described by a pair of integers, the first being the index of the first blocks in the range, and the second the number of consecutive blocks in the range.

BranchCache: A Windows Content Caching and Retrieval feature that enables content from file and web servers on a wide area network (WAN) to be cached on computers at a local branch office. This feature is available in two modes: hosted cache and distributed cache.

client: For the Peer Content Caching and Retrieval Framework, a client is a client-role peer; that is, a peer that is searching for content, either from the server or from other peers or hosted cashes. In the context of the Retrieval Protocol, a client is a peer that requests a block-range from a server_role_peer. It acts as a Web Services Dynamic Discovery (WS-Discovery) [WS-Discovery] client.

client-role peer: A peer that is looking for content, either from the server or from other peers or hosted caches.

content: Cached data that is identified by segment and downloaded in blocks.

content block: A block of data in the content that can be retrieved from clients.

content server: The original source of the content that peers subsequently retrieve from each other.

decryption: In cryptography, the process of transforming encrypted information to its original clear text form.

discovery: The process used to discover other nodes in the mesh of interest.

distributed mode: A mode of operation for the client-role peer in the Peer Content Caching and Retrieval Framework, in which it discovers and obtains content blocks from other peers, and shares content blocks it has with other peers in the network.

encryption: In cryptography, the process of obscuring information to make it unreadable without special knowledge.

encryption key: One of the input parameters to an encryption algorithm. Generally speaking, an encryption algorithm takes as input a clear-text message and a key, and results in a cipher-text message. The corresponding decryption algorithm takes a cipher-text message, and the key, and results in the original clear-text message.

higher-layer application: An application that uses the Peer Content Caching and Retrieval: Retrieval Protocol, either by itself or as part of the Peer Content Caching and Retrieval Framework or other applications.

HoHoDk: A hash that represents the content-specific label or public identifier that is used to discover content from other peers or from the hosted cache. This identifier is disclosed freely in broadcast messages. Knowledge of this identifier does not prove authorization to access the actual content.

hosted cache: A centralized cache comprised of blocks added by peers.

hosted cache mode: A mode of operation for the client-role peer in the Peer Content Caching and Retrieval Framework, in which it obtains and shares content (only) with a single server whose location is preconfigured on the client-role peer.

Hypertext Transfer Protocol (HTTP): An application-level protocol for distributed, collaborative, hypermedia information systems (text, graphic images, sound, video, and other multimedia files) on the World Wide Web.

index: The block number within a segment.

initialization vector: A data block that some modes of the AES cipher block operation require as an additional initial data input. For more information, see [SP800-38A].

network byte order: The order in which the bytes of a multiple-byte number are transmitted on a network, most significant byte first (in big-endian storage). This may or may not match the order in which numbers are normally stored in memory for a particular processor.

peer: An instance of the Retrieval Protocol for the Peer Content Caching and Retrieval Framework running on a host. A peer can be both a client and a server in the Retrieval Protocol operations.

Peer Content Caching and Retrieval Framework (or Framework): The framework that creates Peer Content Caching and Retrieval Discovery Protocol instances to discover client-role peers and download the content blocks from either client-role peers (distributed mode) or hosted cache (hosted-cache mode).

Peer Content Caching and Retrieval: Retrieval Protocol (PCCRR): The Peer Content Caching and Retrieval: Retrieval Protocol [MS-PCCRR].

peer-to-peer: A server-less networking technology that allows several participating network devices to share resources and communicate directly with each other.

peer-to-peer (P2P): An Internet-based networking option in which two or more computers connect directly to each other in order to communicate.

segment: A subdivision of content. In version 1.0 Content Information, each segment has a size of 32 megabytes, except the last segment which can be smaller if the content size is not a multiple of the standard segment sizes. In version 2.0 Content Information, segments can vary in size.

segment ID (HoHoDk): A hash that represents the content-specific label or public identifier that is used to discover content from other peers or from the hosted cache. This identifier is disclosed freely in broadcast messages. Knowledge of this identifier does not prove authorization to access the actual content.

segment retrieval session: A session that defines a set of operations on a client-role peer that use the Discovery Protocol (in distributed mode) and the Retrieval Protocol to discover and retrieve ranges of blocks (partial or complete) of a segment.

server: For the Peer Content Caching and Retrieval Framework, a server is a server-role peer; that is, a peer that listens for incoming block-range requests from client-role peers and responds to the requests.

server-role peer: A peer that listens for incoming block-range requests from client-role peers and responds to the requests.

simple download: A GetBlocks request/response that is carried out without an associated GetBlockList request/response.

target segment: The segment for which the client-role peer is requesting a particular block range in a segment retrieval session, identified by the segment ID.

transport: routable transport that fits into the router architecture, for example, IPv4, IPv6, or IPX

Version 2.0: The protocol version that adds support for efficient discovery of multiple segments.

MAY, SHOULD, MUST, SHOULD NOT, MUST NOT: These terms (in all caps) are used as defined in [RFC2119]. All statements of optional behavior use either MAY, SHOULD, or SHOULD NOT.