VoIP Voice and Fax Signal Processing

16.10 T.38 BIT RATE RECOMMENDATIONS

Most available fax machines support up to 14,400 bps. For bit rates up to 14,400 bps, T.38 takes less bit rate compared with G.711. In Europe, 33,600 supported fax machines are also coming to the market. At the 33,600 V.34 rate, T.38 can be sent at 3-times more redundancy compared with G.711 pass-through mode in the same bit rate. This process can be observed from Table 16.8 and 16.1 for a network bit rate of 169.6 kbps. In some countries like Japan and Korea, many users receive a 50- to 100-Mbps Internet bandwidth/bit rate (bandwidth is more commonly used, even though the bit rate coveys more correct meaning). It is expected that more users will receive higher bandwidth in the future. The G.711 pass-through requirements even with redundancies are negligible compared with the available bandwidth. In this situation, G.711 pass-through should take care of VoIP fax requirements. In general, when end-to-end packet delivery is perfect and network bit rate is unlimited compared with fax pass-through requirements, G.711 should be sufficient for VoIP fax transmission. T.38 and T.37 provide bandwidth advantage, and T.37 provides the benefit of fax pages that can be retrieved off-line.

VoIP Voice and Fax Signal Processing, by Sivannarayana NagireddiCopyright © 2008 by John Wiley & Sons, Inc.