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A network socket is an endpoint of an inter-process communication across a computer network. Today, most communication between computers is based on the Internet Protocol; therefore most network sockets are Internet sockets. A socket API is an application programming interface (API), usually provided by the operating system, that allows application programs to control and use network sockets. Internet socket APIs are usually based on the Berkeley sockets standard. A socket address is the combination of an IP address and a port number, much like one end of a telephone connection is the combination of a phone number and a particular extension. Based on this address, internet sockets deliver incoming data packets to the appropriate application process or thread. ==Overview== An Internet socket is characterized by at least the following: * Local socket address: Local IP address and port number * Protocol: A transport protocol (e.g., TCP, UDP, raw IP). Thus, TCP port 53 and UDP port 53 are distinct sockets. A socket that has been connected to another socket, e.g. during the establishment of a TCP connection, also has a remote socket address. As discussed in the client-server section below, a TCP server may serve several clients concurrently. The server creates one socket for each client, and these sockets share the same local socket address from the point of view of the TCP server, and have a different remote address for each client. Within the operating system and the application that created a socket, a socket is referred to by a unique integer value called a ''socket descriptor''. The operating system forwards the payload of incoming IP packets to the corresponding application by extracting the socket address information from the IP and transport protocol headers and stripping the headers from the application data. In IETF Request for Comments, Internet Standards, in many textbooks, as well as in this article, the term ''socket'' refers to an entity that is uniquely identified by the socket number. In other textbooks,〔Cisco Networking Academy Program, CCNA 1 and 2 Companion Guide Revised Third Edition, P.480, ISBN 1-58713-150-1〕 the term ''socket'' refers to a local socket address, i.e. a "combination of an IP address and a port number". In the original definition of ''socket'' given in RFC 147, as it was related to the ARPA network in 1971, ''"the socket is specified as a 32 bit number with even sockets identifying receiving sockets and odd sockets identifying sending sockets."'' Today, however, socket communications are bidirectional. On Unix-like and Microsoft Windows-based operating systems, the netstat command line tool can be used to list all currently established sockets and related information. 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「network socket」の詳細全文を読む スポンサード リンク
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