Hi,

A codec is basically the "format" of the audio sent from point to point.

When you choose a codec, you make a trade off between bandwidth used and the quality of the audio.

For example:
G.711, a higher quality audio which takes up 64 Kbps.
G.729, a low quality audio which takes up 8 Kbps.

The commonest problem with sending a FAX over VoIP networks is the easiest to deal with. A low bit rate voice codec is unable to carry a fast modem signal without severe distortion. Would you really expect an 8kbps G.729 codec to convey a 9.6kbps FAX modem signal correctly?

At the end of the day, faxing over GSM codecs will always be unreliable - and i highly suspect BT uses one of these codecs.

There is now a protocol/codec standard designed for faxing. T.38 is an ITU standard for sending FAX across IP networks in a real-time mode. Drop a message over to BT asking if a) their netowork offers T.38, and b)if the hardware supplied will support it.

Hope this will help.

Matt

__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.