A second issue is whether the current source protocols and coding schemes are optimal for multicast multimedia to mobile users. After each call handoff the new wireless cell may not support the same QoS as the previous cell. If a user, with an active connection, moves to a cell where all of the cellular channels are in use then that user's call is terminated. An alternative to forced call termination is to dynamically adjust the user's QoS. Hierarchical coding is one technique that permits this, although there are issues of simplicity versus cost. Multicast complicates this further.
Proactive schemes attempt to predict the user's movement.
QoS parameters are then pre-allocated in neighboring cells. However, mobile, multimedia users may require some form of proactive resource management. Researchers have studied some of these traffic engineering issues already. However, further research is needed. Current routing protocols are optimized for fixed endsystems and fixed routing elements.