elay. The process is called 'dejitterization'. The total delay gets worse at certain occasions: Connections over a long distance (especially when one or more satellite link(s) is used - a satellite hop adds a delay of about 240 ms). Voice is coded using advanced compression algorithms to save bandwidth (as in a GSM phone). See Chapter 5, Section 5.7.1 on coding delays. Connection is made over networks using different voice coding, requiring a translation in a gateway between the networks (for example PSTN-GSM or Internet-PSTN). The voice information is packet or cell switched and thus stored in buffers in the switches during the transport. Typically, a maximum total delay of 150 ms is acceptable in normal circumstances, and 400 ms in more exceptional cases. See Table 7.1. The corresponding figures for packet loss are typically 5 % and 10 % respectively. See also Chapter 5 on conversational class. For IP telephony the TCP protocol cannot be used, since TCP asks for retransmission in case of erroneous packets. This would cause a varying delay when retransmission occurs. Secondary Problems with Delay Echo and talker overlap are problems that arise from high end-to-end delays in a voice network. Echo is noticeable by the ear/brain at about 25 ms distance between talk and echo. Talker overlap is the problem of one caller stepping on the other talker's speech. Table 7.1 Acceptable delays One-way Description delay (ms) 0-150 Acceptable for most user applications 150-400 Acceptable provided that administrators are aware of the transmission time impact on the transmission quality of user applications Unacceptable for general network planning purposes, however, it is recognized that in some exceptional cases this limit will be exceeded Quality of Service Noise The signal-to-noise ratio should be as low as possible. The digitization of the trunk network, followed by the digital GSM and ISDN accesses, led to a significant improvement of the quality. One result was drastically reduced intelligible cross-talk. Comfort Noise In