12-02-2003 11:34 AM
I'm trying to connect two modems through voip over frame-relay network using the modem passthrough command but that is no working. The voice calls is operating very well but the modems no connect between them. I'm using G-729 codec with ip header compression and data fragment in 80 bytes.
12-02-2003 02:59 PM
what is the bandwith on your FR link? as far as i understand you have 64Kbit/s link. because your fragment size is 80 bytes and this is the recomended size for 64Kbit/sec. if so you cannot passthrough modem connection. for passing through modem connection you need "upspeed" your voip flow. routers must change codec to g711 for modem passthrough. as you know g711 requires the bandwith about 80Kbit/s.
12-04-2003 11:15 AM
The network bandwith is 128Kbps end the traffic is voice and data. The performance is good. As the network is real time working, I built a prototype at the laboratory and I have changed several parameters like bandwith to 256 Kbps,no fragment, direct codec G.711ulaw without passthrough command, and so forth. the results of that tests be no satisfactory. The IOS software version is c1700-sv3y-mz.121-2.T. What do I can to do?
12-05-2003 08:50 AM
There are some know issues with cisco dsps and V.90+ modems, but we have been able to get most modems to work correctly accross our network. If you are using g729 for all other voice calls you will want to use the modem passthrough command to have both gw's turn to modem passthrough. I typically set up each dial peer with the specific commands, since I have found the global commands are not consistently applied. Here is a sample dial peer config....
dial-peer voice 3 voip
description Default voip peer
preference 1
incoming called-number .T
destination-pattern .T
progress_ind setup enable 3
progress_ind connect enable 8
modem passthrough nse codec g711ulaw
voice-class codec 1
session protocol sipv2
session target sip-server
dtmf-relay rtp-nte
fax rate disable
fax protocol pass-through g711ulaw
ip qos dscp cs3 signaling
no vad
Some of these commands are specific to the isdn signaling set up we have at this site. Also, we are using sip hence the sip session target. But the modem and fax passthrough commands are pretty much universal.
Also, some of those commands are not supported until 12.2.13. You might want to think about an ios upgrade.
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