The recording and playback of most media involves the recorder collecting packets from the network, and the player sending the packets back to the network. However, for media that use a reliable multicast mechanism this approach is not possible. It is necessary for the recorder and player to have an implementation of the reliable multicast code within themselves.
Consider the case where a recorder notices that some of the shared workspace data has not arrived. It is the recorder's responsibility to request that the lost data be retransmitted, but without full knowledge of the details of the retransmission scheme this cannot be done. Therefore, the data stays lost within the recording. At playback time, when then player sends out the recorded data this loss will be observed by the current receivers. They will send a retransmission request. However, a player without a retransmission scheme implementation will be in a poor situation. Firstly, it will not have the data to retransmit because the recorder never recorded it, and secondly it cannot reply to the requests because it does not have the relevant implementation.
This area of recording and playback is particularly tricky, and further work needs to be applied to this. It also requires the tool writers to have stand-alone implementations of their reliability and retransmission code, which can be slipped into servers as required.
Next: Address Allocation Up: Recording Previous: Command Propagation Jon CROWCROFT