VoIP Voice and Fax Signal Processing

16.8 T.38 UDPTL-BASED BIT RATE CALCULATION WITH REDUNDANCY

UDP primary and secondary payload for redundancies from R = 1, 2, and 3 are given in Fig. 16.3(c). In Table 16.6, UDP payload for primary packet and redundancies up to R = 3 (i.e., first, second, and third secondary packets) are given. In general, this payload can be extended to higher redundancies. For data packets, redundancies of one to three are commonly used in the deployments. The bit rate calculations for UDPTL are given with a single data field item of T.4/T.6 non-ecm data. Summary points are given here.

• For R = 0, UDP payload = UDPTL header + primary IFP + 2-byte error recovery and secondary bytes = 10 bytes + raw fax bytes payload.
• For R = 1, UDP payload = UDPTL header + primary IFP + 2-byte error recovery and secondary bytes + first secondary IFP = 10 bytes + primary raw payload + 6 byte + secondary raw payload.
• For R = 2, UDP payload = UDPTL header + primary IFP + 2-byte error recovery and secondary bytes + first secondary IFP + second secondary IFP.
• For R = 3, UDP payload = UDPTL header + primary IFP + 2-byte error recovery and secondary bytes + first secondary IFP + second secondary IFP + third secondary IFP.

Table 16.6. UDP Payload Bytes for Multiple Fax Rates with Redundancies One to Three

Table 16.6 summarizes the actual data and header combination as UDP payload for various fax modules and redundancy ...