This feature supports carrying 64 kbit/s channel data transparently in RTP packets, using Clearmode. Clearmode is a basic feature of VOIP media gateways. This mode is often referred to as "clear-channel data" or "64 kbits/s unrestricted".
No encoder/decoder is needed in that case, but a unique RTP payload type is necessary. It just provides packetization.
Besides packetization or depacketization, a VOIP Media Gateway also does some other processing on the data it converts, which includes echo cancellation, dual tone multifrequency detection, coding/decoding. But there is a certain class of data streams that do not allow any processing other than packetization or depacketization within the VOIP Media Gateway.
ISDN Data terminals produce data streams that are not compatible with a non-linear encoding as used for voice.
Such applications require a transparent relay of 64kbit/s data streams in real-time transport protocol (RTP) packets using "Clearmode".
This guide provides a quick start for setting up VX to support RFC 4040.