I have a 2821 router with DSP and digital modem module installed. with vwic and e1 nm module. Every thing works ok when I have my E1 lines configured as Voice lines but I cant hear any modem answerback tone from the digital modems when the E1 line is configured for incoming modem. I have checked the E1 layer two and three status and every thing is ok. Connection is made only to be timed out after a whilesince there is no modem music. I thought there might be something wrong with the chasis so I tested the E1 line with a 2811 router, but the same thing happened.
The lines come in through fiber from the telco and there is a Huawei channelizer in between my router and the telco. there are other E1 lines from the channelizer that go to the local PBX system and they are working perfectly.