There are a setting: FAX T38 Redundancy in spa2102 in LINE tab. How it works?
Some time SPA2102 do not detect that is a fax, and do not do a ReInvite with T38. How can I better set up SPA2102 to detect fax ?
Great question. This feature is not documented. I had to request this information from Engineering. I will let the docs group know to update next time they revise the ATA admin guide.
Voice tab > Line N tab > Audio Configuration > FAX T38 Redundancy:
The number corresponds to how many previous packet payloads are repeated with each packet. Zero means no payload redundancy. Default is 1 (which matches previous behavior, that is we have been using redundancy = 1 all along). The higher the number, the larger the packet size and hence the larger the bandwidth consumed. This is independent of packet rate.
The Admin Guide describes configuring T.38 faxing in detail on page 55 in the Using a Fax Machine section.
Available from: https://www.myciscocommunity.com/docs/DOC-2149