3Com 3C63311 Reference Guide - Page 253

Voice Compression Module 241 Voice Compression Module To set up multi-point video conferencing, you build virtual circuits (defined by transmit and receive vpi/vci combinations) between the remote units and between the remote units and the central unit. The remote units can use the same vpi/vci to communicate with the central unit (one at a time), or you can allocate different channels and set up separate virtual connections to each remote unit. Table 36,Table 37, Table 38, and Table 39 list possible routing tables when the remote units have been allocated different channels on the central unit's T1 line. Table 36 Multi-point Video Conferencing Routing Table (Remote Unit #1111) Destination # 2222 3333 4444 Tx vpi/vci 0/1 0/1 0/1 Rx vpi/vci 0/2 0/3 0/2 Speed 384k 384k 384k Status idle idle active Table 37 Multi-point Video Conferencing Routing Table (Remote Unit #2222) Destination # 1111 3333 4444 Tx vpi/vci 0/2 0/2 0/6 Rx vpi/vci 0/1 0/3 0/7 Speed 384k 384k 384k Status idle idle active Table 38 Multi-point Video Conferencing Routing Table (Remote Unit #3333) Destination # 1111 2222 4444 Tx vpi/vci 0/3 0/3 0/12 Rx vpi/vci 0/1 0/2 0/13 Speed 384k 384k 384k Status idle idle active Table 39 Multi-point Video Conferencing Routing Table (Central Unit #4444) Source 1111 2222 3333 Tx vpi/vci 0/2 0/7 0/13 Rx vpi/vci 0/1 0/6 0/12 DSOs channels 0-5 channels 6-11 channels 12-17 The optional Voice Compression module (VCM) provides one T1 or E1 port. It is similar in function to the CBR module, but it employs compression algorithms that allow more voice calls to be placed through the same bandwidth. The incoming voice signal is carried on one or more of the T1/E1 port's 24/31 DS0 channels. The voice data in each DS0 channel is in PCM format. This data is compressed by the DSP, and the output from the DSP is encapsulated into FRF.11 packets by the host CPU on the VCM daughtercard. The packets are then passed to the mother board through the PCI interface, handed over to the AAL5 SAR, and transmitted to the ATM interface. In the reverse direction, compressed voice packets are received by the SAR on the ATM interface in FRF.11 format. The packets are then passed to the VCM daughtercard via the PCI interface. The packets are unpacked by the daughtercard CPU before they are handed to the DSP, which decompressed the voice data and plays out the voice onto the T1/E1 PCM interface.