Remove Voice Protocol (RVP or RVP/IP) is a proprietary specification developed by MCK Communications for transporting digital telephony sessions over packet- or circuit-based data networks. The protocol is used primarily in MCK’s Extender product family, which extends PBX services over Wide Area Networks (WANs).

How it Works

RVP provides facilities for connection establishment and configuration between a client (or remote station set) device and a server (or phone switch) device. When a remote caller attempts to make a connection with the PBX, the MCK Extender initiates a TCP session to the Extender PBXgateway. The initiation occurs from a high TCP to TCP 2698.

RVP/IP uses Transmission Control Protocol (TCP) to transport signaling and control data, and User Datagram Protocol (UDP) to transport voice data. Both TCP and UDP work in conjunction with IP to ensure that packets reach their intended destinations. The signaling occurs through the TCP session and the voice is transferred via the UDP session. RVP over IP depends on the network configuration and the level of Quality-of-Service (QoS).

The devices communicate as client and server with the MCK Extender products functioning as clients. A client initiates the RVP over IP session opens the first TCP port to begin with 1024 or higher. The client then sends a request to TCP 2698. Voice and network parameters make up the data packets. The voice parameter consists of a voice path, voice compression algorithm, DTMF encoding, comfort noise generator, echo cancellation, silence detection. The network parameters comprise packet size and jitter buffer.

The remote MCK extender starts the UDP stream upon the successful establishment of the TCP session. The UDP stream starts from port 12288 (0×3000) up to 12544 (0×30FF). The UDP listening port is 2698. RVP over IP reduces network traffic congestion and packet loss by employing a “packetizer” that uses a data packet for holding several voice samples. The CODEC and packet size determine the interval at which voice is transmitted.

Basic Usage

RVP Control Protocol was originally developed for point-to-point applications, so most of its functionality is unnecessary when using TCP/IP. During the RVP/IP session, one class of RVP/IP control message is exchanged. RVPCP ADD VOICE (operation code 12) packet takes a single parameter of type and the server responds with a single packet containing the code RVPCP ADD VOICE ACK (operation code 13). If RVP/IP is operating in “dynamic voice” mode, this exchange must be repeated whenever the voice channel needs to be reestablished, i.e., whenever the connection is broken.

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