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Connection Establishment

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Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

A connection is a link between two or more computer systems that need to exchange messages and data. On a shared network and internetwork, connections are usually virtual, meaning that a connection state is set up in software that tracks the exchange of data across what appears to be a dedicated circuit to the application that is using it. These connections take place in the transport layer and are handled by TCP in the Internet protocol suite. This topic discusses TCP connections.

A connection is a requirement of a reliable data delivery service. It is set up before the actual data exchange takes place. The connection is used to acknowledge the receipt of packets and retransmit those that are lost. The opposite of this is a best-effort service. A file transfer is an example of a service that requires guaranteed delivery services. The delivered file must be an exact copy of the original. See "Reliable Data Delivery Services" and "Best-Effort Delivery."

To reliably exchange data, an application on one network system creates an end-to-end connection with an application on another network system. A single computer may establish and terminate multiple connections at any time. The packets from these connections are multiplexed over a single physical link. Thus, they are virtual connections. In addition, each connection is full duplex, allowing bidirectional packet exchange.

This topic continues in "The Encyclopedia of Networking and Telecommunications" with a discussion of the following:

  • Steps in establishing connections, including three-way handshakes
  • Use of ARP (Address Resolution Protocol) to find target MAC addresses
  • Use of NetBIOS, DNS and other methods for obtaining target addresses
  • TCP connection procedures including the use of the Sockets CONNECT procedure and a description of the SYN (synchronize) and ACK (acknowledgement) flags
  • How delay, including satellite delay, affects connection setup
  • How the connection sequence is prone to hacker attack

Refer to the following Internet RFCs for additional information:

  • RFC 793 (Transmission Control Protocol, September 1981)

  • RFC 1122 (Requirements for Internet Hosts-Communication Layers, October 1989) (see section 4.2)

  • RFC 1180 (A TCP/IP Tutorial, January 1991)

  • RFC 1379 (Extending TCP for Transactions, November 1992)

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