e the Table 3.3-1 Comparison of common speech coding standards. Internet, cannot give consistent sound quality because it cannot be optimized for VoIP. Factors of delay, jitter, and Standard Coding type bit rate (Kbps) packet loss are exacerbated over the public Internet, G.711 making the assurance of voice quality over the Internet especially problematic. G.729 CS-ACELP The bandwidth required for a given call varies with the voice codec used. Each codec converts the voice stream G.723.1 ACELP MP-MLQ into a digital representation using varying amounts of bits to represent a second of voice. In addition to the codec's VolP Technology CHAPTER 3.3 Table 3.3-2 Typical VolP packet. Table 3.3-3 Bandwidth consumption for voice payload only. Voice CODEC Sampling Voice payload Bandwidth per payload header header header header in bytes conversation X Bytes 12 Bytes 8 Bytes 20 Bytes X Bytes G.711 20 ms 80 kbps G.711 30 ms 53 kbps G.729A 20 ms 24 kbps bit rate, the IP packet framing adds overhead to the data stream. G.729A 30 ms 16 kbps Properly provisioning the network bandwidth is a major component of designing a successful network. You can calculate the required bandwidth adding the bandwidth requirements for each major application (for Table 3.3-4 shows the total bandwidth, including layer 2 headers for various transmission media example, voice, video, and data). This sum then repre- These numbers are for each direction in a conversa- sents the minimum bandwidth requirement for any given link. Many VoIP manufacturers recommend that mini- tion, SO a two-way conversation needs double this mum bandwidth should not exceed approximately 75 bandwidth across a given link. percent of the total available bandwidth for the link. This There are methods to lessen some of these bandwidth 75 percent rule assumes that some bandwidth is required needs. One is cRTP, which reduces the RTP header from for overhead traffic, such as routing and Layer 2 keep- 12 bytes per frame to 4. Another is to use silence sup- alives, as well as for addit