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New Member

VG200 Transcoding

We have two E1 ISDN gateways using VG200s, and recently added a 1760-V on a third ISDN.

We've previously used G711 throught the company as the system has been pretty much sat on three sites with fast links.

However, we now need to thin down our bandwidth usage for lots of good reasons. Problem is, our VG200s drop calls made through them using G.729.

Calls using G711 are fine, any other codec drops the call as soon as the outside leg of the call starts ringing.

The 1760V accepts these calls and makes them fine every time.

Anyone know if this is a problem with our IOS version or just the hardware doesn't support it? Or any ideas how to troubleshoot this?

Thanks

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Re: VG200 Transcoding

ip routing is used to send calls to and from the codecs. Even though the same codec may be used on the PSTN side vs the voip side, the call is still terminated on the codecs so routing must be enabled.

Calls dropped as soon as audio cut-through is effected is a common symptom of codec mis-match. What are the endpoints? Cisco IP phones support either, so shouldn't be a problem. It sounds like you are trying to go to an endpoint that doesn't support G.729. Are these calls terminated in the IP-AA or other CRS application? I don't know why the 1760 works vs the VG200. Some more detail will be helpful - what are the endpoints, are both gateways mgcp controlled, etc. To avoid these problems I always use a codec-class on H.323 dial-peers -

voice class codec 1

codec preference 1 g711ulaw

codec preference 2 g729r8

Of course this has the ability to mask your problem. There is a codec mis-match, or other problem, going on...

6 REPLIES
Cisco Employee

Re: VG200 Transcoding

This is probably a config issue where g729 is not enabled somewhere.

If these are H323 gateways, do a 'debug h225 asn1' and 'debug h245 asn1' and look at the capabilities exchange. (do this at a time of low call volume since the debugs are verbose). Make sure that you have both codecs enabled on the dial-peers.

New Member

Re: VG200 Transcoding

Make sure your VG200 has IP routing enabled. Sounds wierd but it is required for it to work properly. just do 'ip routing' from config mode...

-Jaret

New Member

Re: VG200 Transcoding

If IP routing weren't enabled I suspect the G711 calls wouldn't work either.

New Member

Re: VG200 Transcoding

If the call is g711 to g711 then no transcoding would be neccessary. Only when there are two diferent codecs being used would the transcoder be utilized. example: a g729 call through the WAN to Cisco CRA (IP IVR).

Unless i am mis-understanding the question. I believe what the author is saying is that they are using the vg200 as a transcoder, not a gateway.

-Jaret

Cisco Employee

Re: VG200 Transcoding

ip routing is used to send calls to and from the codecs. Even though the same codec may be used on the PSTN side vs the voip side, the call is still terminated on the codecs so routing must be enabled.

Calls dropped as soon as audio cut-through is effected is a common symptom of codec mis-match. What are the endpoints? Cisco IP phones support either, so shouldn't be a problem. It sounds like you are trying to go to an endpoint that doesn't support G.729. Are these calls terminated in the IP-AA or other CRS application? I don't know why the 1760 works vs the VG200. Some more detail will be helpful - what are the endpoints, are both gateways mgcp controlled, etc. To avoid these problems I always use a codec-class on H.323 dial-peers -

voice class codec 1

codec preference 1 g711ulaw

codec preference 2 g729r8

Of course this has the ability to mask your problem. There is a codec mis-match, or other problem, going on...

New Member

Re: VG200 Transcoding

Ok, to clarify... endpoints are a mixture of Cisco IP Phones, the one I have been and will be testing with is a 7960G. These should support the two worthwhile codecs (711 and 729).

The VG200 is acting as an E1 gateway, but calls using 729 are dropped; calls using 711 progress without problems.

If I route my calls through our 1760V on another site I can make 729 and 711 calls without any problem.

In general use, we will have some phones making G711 calls (from the same subnet) and others (other sites) using G729 - I'd like the VG200 to pass both without fuss in the same way as the 1760V does.

The VG200 is running h323, I'll try your suggestions later on tonight when it's quiet, but keep them coming in the meantime.

Thanks everyone.

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