VoIP Voice and Fax Signal Processing

11.9 SUMMARY ON VoIP BIT RATE

A summary on bit rates is given in Table 11.5 for G.711, G.729A, and G.723.1 for different packet sizes, over Ethernet, DSL, and cable interfaces. VoIP voice packets will demand less bit rate when compared with an available Ethernet interface bit rate of 10 to 100 Mbps. The bit rate from the cable modem closely matches with DSL at small packetization. On a DSL interface, the upstream rate is lower than the downstream rate. VoIP on a DSL interface is limited by the upstream bit rate of the DSL interface. The Internet service provider also limits the bit rate on a DSL interface. G.711 is supported in most VoIP deployments. Hence, the minimum bit rate available on DSL should support the requirements of the G.711 channel bit rate. Most deployments use 20 ms as default packetization. G.711-20 ms with PPPoE on a DSL interface consumes 106 kbps. In G.711, using higher packetization such as 20 ms (106 kbps), 30 ms (98.9 kbps), and 40 ms (95.4 kbps) gives a significant savings in bit rate compared with 5-ms (254 kbps) and 10-ms (170 kbps) packetization. G.711 with 5 ms is not popular because of higher bit rate requirements. In Asia and Europe, some deployments consider this as an advantage for lower end-to-end delay and improved voice quality. For G.711 with 5-ms packetization, a calculated bit rate value is listed in summary Table 11.5, and detailed break-up is not shown in the previous tables. In the case of G.729A on a DSL wide area network (WAN) interface, ...