Could any one tell me why cisco use T38FaxMaxDatagram: 72 in sip's sdp? Why 72?
I've an issue with t38 cisco+asterisk, 72 is too small for asterisk! 72 is too small at all.
Send: The T38FaxMaxDatagram attribute MUST be included. The value indicated MUST be
sufficient to accommodate the T.38 Internet Fax Packet (IFP) at the allowed maximum data
rate and packetization time, the RFC 2198 redundancy header, and the redundant IFP
packets. For T.38 carried over RTP, the T38FaxMaxDatagram value is defined as the RTP
payload. To allow a remote T.38 device to transmit using a 40ms packetization period, the
value SHOULD be 173 bytes for a 14.4 kb/s Group 3 transmission or 367 bytes for a 33.6
kb/s Super Group 3 transmission using a redundancy level of 1. If redundancy level of 2 is
applied, the value SHOULD be 255 bytes for a 14.4 kb/s Group 3 transmission or 546 bytes
for a 33.6 kb/s Super Group 3 transmission.