Data transmission method and apparatus

Abstract

The invention relates to a method and apparatus for transmitting and receiving video data arranged in data frames forming a data stream. Each frame has assigned a priority level. Once a data frame has been transmitted through an unreliable channel and has not been received at the receiver, the priority level of the missing data frame is compared with a priority threshold value, and is then retransmitted if its priority level is greater than the priority threshold value. The retransmission decision is performed either at the transmitting or at the receiving side. According to a preferred embodiment, the priority level of any data frame to be transmitted is compared with the threshold value. The priority decision may involve the calculation of the priority threshold value based on a measurement of the available channel bandwidths and eventually on the bit rate of previously sent frames. The retransmission decision further may include an estimation of the arrival time of the data frame to be retransmitted.

1 . Method for transmitting data from a server to a client, said data being arranged in data frames forming a data stream, each frame having assigned a priority level, the method comprising the steps of: 
 receiving at the server a client's retransmission request for a data frame;    comparing the priority level of the requested data frame with a priority threshold value; and    retransmitting the requested data frame if the priority level is greater than or equal to said priority threshold value, wherein the assignment of priority levels to frames is performed as P-frames are given different priority levels.    
   
   
       2 . Apparatus for transmitting data to a client, said data being arranged in data frames forming a data stream, each frame having assigned a priority level, the apparatus comprising: 
 receiver means for receiving a retransmission request from the client for a data frame;    a controller for comparing the priority level of the requested data frame with a priority threshold value; and    transmitter means for retransmitting the requested data frame if the priority level is greater than or equal to said priority threshold value,    wherein the assignment of priority levels to frames is performed as P-frames are given different priority levels.