Variable Bit Rate Applications
LAN TV, modern video codecs (i.e. using MPEG2) produce a variable bit rate traffic in networks.
The stream is bursty. Sometimes the bandwidth required is low and sometimes it is high.
When the VBR traffic is below the peak rate, the extra bandwidth is not used.
Packet/cell switched networks are designed to provide the average bandwidth, while peaks are handled by statistical sharing of extra bandwidth.