The TCPMUX (TCP port service multiplexer) is an obsolete Internet Protocol defined in Request for Comments 1078. Its purpose is to multiplexing more than one service through a single Transmission Control Protocol port.

A host may connect to a server that supports the TCPMUX protocol, on Transmission Control Protocol port 1. The host then sends a name of the service required, followed by carriage return and line feed characters (CRLF). The server replies with a + , an optional message and CRLF, or with a - . In case of a positive reply ( + ) the protocol or service requested is started, otherwise the connection is closed.

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