Modem Pass Through on 3660 and 6624 FXS module

[vcornett]

We are using a 3660 with a PRI (NM-HDV-1T1E) as the PSTN Gateway (IOS 12.1(3a)XI5). We also have a 6509 with a 6624 FXS module providing analog ports to a modem pool. Sys admins dial into these modems for access to their systems but are unable to maintain a modem connection. If they do connect, it is at very low speeds (9.6kbps), and usually drops after 20 or 30 seconds. I am running Call Manager ver 3.0(10).

QOS etc. is set up end to end and we are running the G711ulaw codec. Any help on getting this resolved is appreciated.

Thanks,

Vince

[sdrennan]

I too have experienced problems in NON Avvid enviroments. Cisco Docs state Modem support is only available on the 5300 Access server. This supports Modems as it disables VAD and fixes the Jitter Buffer at a set value when a modem call is detected

[vcornett]

We are running an AVVID environment. The 6624 FXS module documents state that it does support modem pass through. I have not found any documentation that states the 3660 supports modem pass through but I was hoping that an IOS upgrade would fix this. From what I have read in other forums the 3660 is the gateway of choice for most VoIP implementations and no modem support is hurting alot of customers.

[paul.stephens]

I had exactly the same problem with a 3640 router. In the end we got it to work but had to add various lines to the config here are some extracts;

interface FastEthernet0/0

ip address 10.1.1.254 255.255.255.0

no ip route-cache

no ip mroute-cache

speed 100

full-duplex

h323-gateway voip bind srcaddr 10.1.1.254

The h323-gateway voip bind srcaddr 10.1.1.254 command was the one that got it to work, I don't know why nor did tac.

dial-peer voice 1 voip

destination-pattern 8...

session target ipv4:10.1.1.1

codec g711ulaw

fax rate disable

no vad

I have noticed that modems only connect at low rates but I did read in the release notes for 3.1 that a new image load for the 6624 and 6608 cards allows faster connection rates

Hope this helps

[sdrennan]

The URL below details the support for Modems. It does not mention however what rate the modems will connect at in the platforms they currently support

http://www.cisco.com/univercd/cc/td/doc/product/voice/ip_tele/solution/4_design.htm#xtocid503053