The V.150.1 standard defines modem relay which allows VX users to interoperate with Type-1 encryption devices in a VoIP network, and between VoIP networks.

With V.150.1 support, VX can be positioned in network as an MoIP gateway, and also interoperate with V.150.1 compliant FNBDTs.

The diagram below shows typical user cases with VX as the modem relay gateway.

VX supports two modes: Modem Relay Mode (MRM) and Pass Through Mode (PTM).

In MRM, VX sites between DSN and IP network playing role of Universal Modem Relay (U-MR) gateway. The IP side protocols supported in this mode are BSP/VTP and SIP/RTP/SPRT. SPRT is Simple Packet Relay Transport protocol.

Note. DCEs used in this document only use procedures supported by V.150.1.

Following call paths are depicted in the diagram above.

DCE1  VX1(MRM)  <> VX2 (PTM)  <> VX3 (MRM) <> DCE2

DCE1 <>  VX1(MRM) <> VX2 (PTM) <> VX3 (MRM) <> V150IPE2

DCE1 <> VX1(MRM) <> VX2 (PTM) <> V150IPE1

V150IPE1 <> VX2(PTM) <> VX3 (PTM) <> V150IPE2

V150IPE1 <> VX2(PTM) <> V150IPE2

V150IPE2 <> VX3(MRM) <> DCE2

In PTM, VX sites in IP network playing proxy like role. The pass through applies between any combination BSP/VTP and SIP/RTP/SPRT. In this mode, VX can also, via SIP/RTP/SPRT, talk to V.150.1 compliance IP equipment (V150IPE) for example vIPer phone.