Like most software products, protocols are continuously enhanced and new protocols are developed. But especially new protocols of the transport layer can not be utilized widely easily. Even if the new protocols are made available, it is still necessary to adapt many applications or the protocols are not used by the majority of applications otherwise. The current situation is that only very limited enhancements of protocols are possible without changing applications. The proposed solution is to let applications use communications services only instead of protocols. A model for service-oriented communications systems that follows the concepts of service-oriented architectures is introduced. The model enables choosing and configuring protocols autonomously with regard to environmental and temporal conditions.