er degrading the voice quality. jitter-free way. According to the ITU-T Recommendation G.114, Various AALs support various service classes Table 3.2-1 shows allowable delay limits for one-way capabilities. ATM switches have always been designed with effec- tive traffic management capabilities-for example, Table 3.2-1 Delay limits. call admission control, usage parameter control, traffic shaping, etc. Delay Acceptability It allows a single network for voice, data, and video. 0-150 ms Acceptable to most user applications Interworking with PSTN is relatively straightforward. 150-400ms Acceptable when the impact on user's Though ATM is equipped with transferring voice over the application is minimal network efficiently, ATM onto the desktop would not be More than 400 ms Unacceptable popular enough until the turn of the millennium. The Network infrastructure CHAPTER 3.2 transmission time for connections with adequate echo communication is a half-duplex, that is, one person is control. silent while the other speaks. One can take advantage of Delay occurs in ATM networks because of one or more these two characteristics to save bandwidth by halting of the following reasons: the transmission of cells during these silent periods. This a) Packetization delay (or cell construction delay) is known as silence suppression. This is the time taken to fill in a complete packet/ cell before it is transmitted. Normal PCM encoded Compression algorithms voice samples arrive at the rate of 64 Kbps, which ADPCM (Adaptive Differential Pulse Code Modulation) means it takes around 6 ms to fill the entire 48-byte and CELP (Code Excited Linear Prediction) are the two payload of the ATM cell. The problem can be major compression algorithms that are used. Now, LD- addressed either with partially filled cells or by CELP (Low Delay CELP), a derivative of CELP, is the mulitplexing several voice calls into a single ATM compression algorithm most commonly used on any VCC (Virtual Circuit Channel). voice signal. This has been standardized by ITU as 