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In computer networking, peering is a voluntary interconnection of administratively separate Internet networks for the purpose of exchanging traffic between the users of each network. The pure definition of peering is settlement-free, "bill-and-keep," or "sender keeps all," meaning that neither party pays the other in association with the exchange of traffic; instead, each derives and retains revenue from its own customers. An agreement by two or more networks to peer is instantiated by a physical interconnection of the networks, an exchange of routing information through the Border Gateway Protocol (BGP) routing protocol and, in one case out of every two hundred agreements, a formalized contractual document. Occasionally the word "peering" is used to describe situations where there is some settlement involved. In the face of such ambiguity, the phrase "settlement-free peering" is sometimes used to explicitly denote pure cost-free peering. ==How peering works== The Internet is a collection of separate and distinct networks referred to as autonomous systems, each one operating under a common framework of globally unique IP addressing and global BGP routing. The relationships between these networks are generally described by one of the following three categories: * Transit (or ''pay'') – The network operator pays money (or ''settlement'') to another network for Internet access (or ''transit''). * Peer (or ''swap'') – Two networks exchange traffic between their users freely, and for mutual benefit. * Customer (or ''sell'') – A network pays another network money to be provided with Internet access. Furthermore, in order for a network to reach any specific other network on the Internet, it must either: * Sell ''transit'' (or Internet access) service to that network (making them a 'customer'), * Peer directly with that network, or with a network which sells transit service to that network, or * Pay another network for transit service, where that other network must in turn also sell, peer, or pay for access. The Internet is based on the principle of ''global reachability'' (sometimes called ''end-to-end reachability''), which means that any Internet user can reach any other Internet user as though they were on the same network. Therefore, any Internet connected network must by definition either pay another network for transit, or peer with every other network which also does not purchase transit. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「peering」の詳細全文を読む スポンサード リンク
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