V.150.1 Gateway

Vocal’s V.150.1 Gateway is a standards based implementation that incorporates reliable and efficient transport of any type of modem signal across IP network by using Simple Packet Relay Protocol (SPRT). This solution supports modem over IP (MoIP) operation in Voice Band Data (VBD) and the Modem Relay (MR) modes.

SSE – Signaling State Events are Supported.
SPRT – Simple Packet Relay Transport for modem relay is supported.
SDP – Different variations of the Session description based on the requirement available.
Scalability – A large number of channels on a single gateway can be supported, starting from 10s to 100s based on the gateway and modem rates.
Flexibility – Vocal’s V.150.1 Gateway runs in the form of hardware independent library for a number of the target environment platform (any standard Linux or Windows distribution).


  • Digital control messages replacing analog tone events, for passing the protocol over hops.
  • Supported data modulations include V.34, V.32, V.32bis, V.22bis, V.22, V.21, V.23, V.90, V.91 and V.92 modem standards as well as standard fax modulations.

ITU V.150.1 identifies different modes for transmitting modem over IP networks.

Modem Relay – the audio signal from the local modem is demodulated at the on-ramp gateway and transmitted over the network and re-modulated at the off-ramp gateway for transmission to the local modem. The gateways maintain state for the call session. Modem relay mode may be used for more reliable communications over networks where transmission delays and packet loss may degrade modem communications.

Voiceband (VBD) – audio is encoded by a speech codec such as G.711 and transmitted as data packets over the network. VBD mode may be used over reliable networks with predictable throughput and negligible packet loss.

Vocal’s V.150.1 endpoint /terminal is MoIP termination solution that runs VOCAL SIP Analog Modem Server (SAMS) along with the V.150.1 gateway. It is compliant with ITU-T V.150.1 recommendations. So, the virtual modem servers can get to the IP network through the V.150.1 gateways and talk to any physical modem behind a PSTN connection on the other side. It will have all the features similar to the SAMS. Our implementation also provides a methodology for internetworking between newer IP based instruments and legacy devices.

Flexible Implementation:

  • Based on decades of experience engineering modems and VoIP telecommunication systems, VOCAL is uniquely capable of creating modem systems that run purely in software, or on your custom hardware system, and interfacing with your customized interfaces and specialized applications. Whether your modems are on one or both ends of the network, VOCAL has a safe and reliable solution.
  • VOCAL’s systems are standards based and fully compatible, so replacing an existing v.150.1 gateway will happen seamlessly. Variations include communications with gateways or standalone endpoints that send v.150.1 messages directly on the IP link.
  • Vocal’s v.150.1 implementation adheres to the Secure Communication Interoperability Protocol (SCIP-216 Rev 2.2). Our v.150.1 End-Terminal software uses V.150.1 directly, to communicates with a modem located on the PSTN via a v.150.1 gateway.