In the context of communicating parallel process systems various paradigma for communication resp. synchronisation have been proposed. Two well-known theoretical models for communicating systems are CCS and TCSP. A variety of semantics has been proposed for these and similar languages which can be characterized by different criteria: true versus interleaving parallelism, linear versus branching time models, operational versus denotational approaches, choice of the mathematical discipline to handle recursion and domain equations. In recent years interest has shifted more and more towards semantics that model true parallelism. The most known are petri net semantics, event structure and pomset semantics. The present paper investigates the question whether the two closely related approaches of event structures and pomsets are equally suitable to provide semantics for language constructs as avaible in CCS or TCSP. Given the variety of approaches to semantic description comparative studies like the present one are importantas a guideline. They help us to decide which method suits which purpose. In addition, comparative studies enhance the better understanding of the language constructs, and finally comparative studies of semantics that yield consistency results strengthen our confidence in the correctness of each, of the semantics involved. The paper is divided into seven sections. Section 2 introdtices CCS and TCSP and discusses their communication mechanisms. Section3 introduces event structures. Section 4 defines pomset classes. Section 5 models the communication mechanisms of CCS and TCSP using event structures and section 6 discusses the problems that arise when pomset classes are used. Section 7 is the conclusion. The appendix contains some formal definitions
