Undetermined bit rate (UBR: unspecified? Bit? Rate): the transmission rate is not specified, but the reliability is very high, which is the so-called "Best transmission" (best? Try to do LAN simulation (LAN? Simulation).
Constant bit rate (CBR: constant? Bit? Rate): It has a fixed bandwidth (rate) requirement and is suitable for real-time voice and video signal transmission.
Available bit rate (ABR: available? Bit? Rate): You only need to specify the maximum and minimum cell rate, which is not widely used.
Variable bit rate (VBR: variable? Bit? Rate): Allow the bandwidth that can be changed at any time, but you must specify the peak bandwidth, maximum burst data length and minimum rate that must be maintained.