Media Resource Control Protocol

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MRCP is the Media Resource Control Protocol proposed to the IETF. It is a communication protocol which allows speech servers to provide various speech services (such as speech recognition and speech synthesis) to its clients. Typically, this means the server software will be running on one computer and clients can send MRCP messages to the server over a network, usually on top of another protocol, such as RTSP or TCP.

It is in the same style as HTTP and many other Internet protocols, where each message contains 3 sections: a first-line, a header and a body. The first line indicates the type of message as well as information such as response codes. The header contains a number of lines, each in the format <header>: <data>. The body, whose length is specified by the header, contains the details of the message.

Like HTTP, MRCP has requests (usually issued by the client) and responses, which may simply acknowledge receipt of the request or give other information regarding its processing. For example, an MRCP client may request to send some audio data for processing (say, for speech recognition), to which the server could respond with a suitable port to send the data (since MRCP does not have support for audio data specifically, this would have to be handled by some other protocol, such as RTP).

There are two versions of the MRCP protocol. Version 2 uses SIP as the control protocol, whereas version 1 uses RTSP.