 to buffer all other data that has arrived as the delayed packets are anticipated. This has implications for the hardware required, interactivity requirements, and audio- video lip synchronization. When the maximum acceptable delay has been exceeded, all late packets are then regarded as lost. Packets damaged during transit will be discarded by a node if they do not pass parity checks. Hence, packets received will either be correct, errone- ous but having passed parity checks, or simply absent. Internet-type networks are very prone to packet loss and more particularly burst loss. Under the current version of IPv4, no facility exists for prioritization, and all packets at a router are queued and treated equiprobably. Under the UDP protocol: 1. Most packet losses are isolated. 2. Packet loss periods are generally short in duration, assuming the network has not failed. 3. The probability of a loss period duration N decreases geometrically with N. 4. Packet arrival and delays follow a Poisson process. 5. Out-of-order delivery is common, although MBONE routers are more consistent. 6. Geographic location is very important. The quality of the media delivered to the destination relies essentially on the number of lost packets and the delay variation (i.e., jitter between successive packets). From experi- ment, packet loss and delay characteristics vary with the time of day and geographical location of the site. Many different measures can be used to characterize the loss process; the most obvious measure is mean packet loss. Experimental results show mean packet loss rates are typically between 1 and 30 percent for the majority of locations. An alternative way to categorize loss is the amount of burstiness-in other words, the number of consecutively lost packets. Figure 3.21 shows a histogram for consecutively lost packets. Most loss periods are less than two packets in duration. This suggests that such loss might be accommodated using Forward Error Correction (FEC) techniques; however, FEC requires the use of overhead i