VoIP Voice and Fax Signal Processing

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VoIP VOICE—NETWORK BIT RATE CALCULATIONS

In VoIP deployment, the VoIP network bit rate, which is also referred as to the bandwidth requirement, is higher than the actual compression rate of the codec. It is important to know the actual network bit rate to cater to end-to-end planning and to arrive at recommendations for the right Internet service. This chapter describes the bit rate requirements for VoIP voice services with G.711, G.729A, and G.723.1 compression codecs [ITU-T-G.711 (1988), ITU-T-G.729A (1996), ITU-T-G.723.1 (2006), Kondoz (1999), Goldberg and Riek (2000), Hersent et al. (2005)] on Ethernet, digital subscriber line (DSL), and cable-based Internet services. In addition to bit rate requirements, service providers will consider several quality and interoperation aspects to take care of wider end-to-end deployment requirements.

VoIP is considered a network-bit-rate-saving voice communication compared with the public switched telephone network's (PSTN's) 64-kilobits per second (kbps) rate, which is not always true. The most popular G.729A compresses voice to 8 kbps, but it takes 70.4 kbps on the Ethernet and 84.8 kbps on the DSL interface with 10-ms frames, which is more than PSTN's 64 kbps. Internet Protocol (IP) packet headers and extra bytes from IP network interfaces are causing the 8-kbps G.729A to increase to a much higher rate of 84.8 kbps. In this chapter, bit rate calculations with interpretation of headers, examples with codec payloads, calculations, and ...