The Ascend / Lucent APX8-SL-96DSP card
If you like to install a huge powerfull VOIP gateway system, you have better not to use a standard PC like an 3 Giga Hertz Intel or so, but to use a MAX TNT or APX 8000/8100 router with APX8-SL-96DSP boards.
This Ascend/Lucent board has 96 individual DSP CPUs for 96 ports to handle compression and decompression in real time.
Some experience in Germany with a Dual Pentium 2.8 and 2 gig RAM shows, that it cannot successfully handle 120 VOIP channels.
Even the 2 CPUs cannot handle line handling and compression for all channels in an acceptable timedelay.
There are 16 port DSP cards for the MAX 4000 and MAX 6000. We did never see a MAX4000 with VOIP working. So better goto a MAX 6000 to do this.
How many cards are needed ?
In the US, they have T1 or DS3 as the gateway hardware to the public voice switches. A T1 line can handle 26 ISDN channels with 56 Kilobit bandwidth. A DS3 line should handle 960 channels.
In Europe we have the E1 line (s2m) with 32 channels including 2 ISDN channels for handshake (signaling). So each E1 line has 30 data or voice channels and 4 boards with 8 x E1 ports each can handle a lot. But the throughput inside the MAX TNT is limited too. So dont expect too much.
so a full standard US configuration might be:
1TNT-SP-SC Controller
1TNT-SL-E100-V-C Ethernet w/dongle
1TNT-SL-CT3
10 APX8-SL-96DSP