MGCP problems with CCM 4.1(2) & C2801

[kdotzoltan_2004]

Hi!

I have a CallManager 4.1(2) witha Cisco 2801 acting as a IOS MGCP voice gateway.

The latter has two E1 interfaces, for two different TSPs, four FXO ports, but only 56 voice resources. Thus above the four FXO lines I have 28 channels for S0/SU3/DS1-0 (E1/0 for short) and 25 channels for S0/SU3/DS1-0 (E1/1 for short).

Until yesterday, everything worked fine, just as expected, but since yesterday I've got complaints, that about half of the calls from the outside to numbers assigned on E1/0 respond with a busy tone to the caller, ring once inside on the called number, but disconnect immediately afetrwards. There is no problem calling out on E1/0, and calls still work both ways on E1/1.

By looking at the traces, I've found a large number of MGCP errors related to E1/0:

CRCX, return_code: 400

this is a generic, "transient" create connection error.

Then I looked to the router, and #show mgcp statistics (with system resource check enabled) told me, that indeed there are a number of CreateConn rx failures, but also, that none were rejected by SRC. Thus it can't be a resource problem (there aren't really that many active calls at once, to cover all 28 channels)

I also tried modifying channel order in CallManager from top down to bottom up and vice versa, but no luck.

Any help or ideas would be appreciated.

Thanks,

Zoltan

[lpezj]

Zoltan,

I am quite sure, but I think that 2801 only supports one E1, i.e., only supports 30 digital voice calls. You would need a 2811 at least.

Hope this helps,

Juan Luis

[kdotzoltan_2004]

Hi,

sorry, if I might not have been explicit enough. The module is a VWIC-2MFT-E1, a two-port E1 module. The 2801 supports it, allocates the appropriate resources (I have a 48, and an 8 channel PVDM, offering 56 voice channels on g711 as mentioned above) and most importantly, it was working fine a few days ago, has currently 2 weeks uptime, but the configuration is working for at least a month now.

Also, CCM is 4.1(2)sr1, as that is needed for 2801 MGCP support in CCM.

thanks,

Zoltan

[marinaibm · Accepted solution]

Hi,

Do you have "pri-group timeslots 1-30 service mgcp" configured for both controllers?

I had a similar problem when i configured only 25 channels to save DSP resources and Telco instead of sending the calls in the top down order a couple of weeks after the installation decided to choose a random channel instead and i had lots of calls failing on the last 5 channels.

You can do debug isdn q931 and see if your calls are failing on specific channels.

[kdotzoltan_2004]

This is just what we suspected all along, however I tried both top-down and bottom up ordering, and that din't help. Thus I dissmissed the idea.

I only had 28 channels available for that TSP indded, and I couldn't change that in the daytime, as you know, modifying pri channels is a pain in the .. anyway, it would have taken too much time, with both telco lines down (as I had to take away some channels from the other one, to compensate. See my case in the first post)

Now I fixed it this way, as the other telco seems to behave "the right way", and that line isn't quite as used anyway. I just hope, tomorrow morning everything will work out fine :) (as I had to make the changes remotely)