delay is to prioritize voice packets (vis à vis data). Objective <50 msec. Propagation delay. Variable. Major contributor to total delay. Geostationary satellite relay of circuits is a special problem. The trip to the satellite and back is budgeted at 250 msec. One way to speed things up is to increase the bit rate per voice data stream. To do this, the aggregate bit rate may have to be increased. Or the number of voice streams may be reduced on the aggregate bit rate SO that each stream can be transmitted at a faster rate. 15.4.4 Lost Packet Rate A second concern of the VoIP designer is lost packet rate. There are several ways a packet can be "lost." For example, Section 15.3.3 described a dejitterizing buffer. It has a finite size. Once the time is exceeded by a late packet, the packet in question is lost. In the case of G.711, this would be the time equivalent of 16 or 26 msec (duration of a packet including its header). Another reason for a packet to be lost may be excessive error rate on a packet whereby it is deleted. When the lost (discarded) packet rate begins to exceed 10%, quality of voice starts to deteriorate. If high-compression algorithms are employed such as G.723 or G.729, it is desirable to maintain the packet loss rate below 1%. Router buffer overflow is another source of packet loss. IP through TCP has excellent retransmission capabilities for errored frames or packets. However, they are not practical for voice-over IP because of the additional delay involved. When there is a packet or frame in error, the receive end of the link transmits a request (RQ) to the transmit end for a packet retransmission and its incumbent propagation delay. This must be added to the transmission delay (and some processing delay) to send the offending packet back to the receiver again. 15.4.4.1 Concealment of Lost Packets. A lost packet causes a gap in the reception stream. For a single packet we are looking at a 20- to 40-msec gap. The simplest measure to take for lost packets and the resulting gaps is to disregard