As a novel optical switching technology proposed in recent years

Optical Burst Switching（OBS） combines the advantages of Optical Circuit Switching（OCS） and Optical Packet Switching（OPS）

but it is more flexible than OCS and provides more easily realizable statistical multiplexing capabilities at the optical layer than OPS.In addition

OBS provides high throughput

high-bandwidth availability and low transfer delay

making it a forceful competitor for the next-generation MAN.Using the M/G/1 queuing model

we develop an analytical approximation for the transfer delays of different priority burst packages under a constrained condition and derivate the transfer delays of the burst packages in OBS ring networks.