Future multimedia systems will rely on broadband networks and subnetworks which will be able to provide the required type of communication services and will meet the stringent quality of service (QOS) demands. However, it is likely that the introduction of multimedia communication will have to he based on networks providing simple services that are not directly meeting the multimedia requirements. This paper starts from this assumption and focuses on the end systems. Within the framework of the OS1 Reference Model, it examines the functionality and structuring of the higher protocol layers required to support multimedia communication. Furthermore, it discusses some important implementation and performance issues.