A transmission system for sub-networks having different transmission protocols. Control codes which are assigned to a message in a source sub-network are converted at the transition with a first intermediate sub-network, into reference codes which are compatible with a reference protocol...http://www.google.com/patents/US5740374?utm_source=gb-gplus-sharePatent US5740374 - System for transferring messages via different sub-networks by converting control codes into reference code compatible with a reference protocol and encapsulating the code with the message 
