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problem with T38 fax transmition

Hi!

I have problems with fax transmition to one of my destinations (only this one). Approximately 80% faxes fail in 41st or 43rd second. Those which succeed, have rate of 4800 (even that would be acceptable, if all of them worked).

Here is dial-peer configuration:

dial-peer voice 2042 voip

description Problematic fax

destination-pattern 505111222

session target ipv4:A.B.C:.D

dtmf-relay h245-alphanumeric

fax protocol t38 ls-redundancy 5 hs-redundancy 0 fallback none

ip qos dscp cs5 media

no vad

On the far side, conf is similar. Sometimes there is slight packet loss (around 3-5%), but not always.

Has anyone encountered this before? If you did, please advise!

Thanks,

Nikola

1 REPLY
New Member

Re: problem with T38 fax transmition

Hi Nikola,

we had a related problem when including T.38 fax transmissions. I can see that you're using H.245 - I'm wondering what version of H.245 you are using at both ends.

We found that we were getting failed call setups to NetMeeting because the H.245 version on NM was 3, whereas in our gateway it was ver.7. Ver.3 of H.245 does not support T.38 fax at all.

This probably isn't the problem though, so I noted that you didn't use 'fax rate' command, in which case the default is the highest transmission speed allowed by the voice rate. This may conflict with other configuration:

ip qos dscp cs5 media - the interface that this is applied to may have a particular transmission speed.

Probably the best thing is to decode the H.225.0 and H.245 call setup messages, and from there determine what the bandwidth, if any, is required.

Apologies if you have alreayd looked at this.

HTHs,

Matthew.

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