ITU b) Buffering delay G.728. This provides a toll quality voice at 16 kbps with Sometimes, due to the delay in transit, some cells low encoding/decoding delay. Table 3.2-2 compares the might arrive late. If this happens, SAR (Segmenta- various compression techniques for their bandwidth tion and Reassembling) function provided by the usage, MIPS (millions of instructions per second), and Adaptation layer might have to under-run with no delay. voice data to process, which would result in gaps in the conversation. To prevent this the receiving SAR Signaling function would accumulate a buffer of information before starting the reconstruction. In order to This relates to the efficient utilization of resources and ensure no under-runs occur, the buffer size should the transfer of control and signaling information. There be kept in such a way it exceeds the maximum are two parts in a voice call-the actual voice samples and predicted delay. The size of the buffer translates the signaling information, such as dialed number, the on- into delay, as each cell must progress through the hook/off-hook status of the call, and other routing and buffer on arrival at the emulated circuit's line rate. control information. This signaling can be encoded and This implies that the Cell Delay Variation (CDV) may be sent as CCS, where signaling information from has to be controlled within the ATM network. different channels is aggregated into a single signaling channel, and CAS, where signaling information is em- c) Encoding delay bedded within each discrete voice channel. This is the processing time taken by the compres- sion algorithms to encode the analog signal to digital form. Synchronization The transport of voice demands that the data be syn- Silence suppression chronized between the speaker and the listener. There Voice is inherently variable. It is found that on an average, are two standard mechanisms that are used to achieve human voice has a speech activity factor of about synchronization between point-to-point applications. 4