Abstract: A simple model of asynchronous distributed communication is presented in the paper.This model is used as an explanation of channel grammars,which specify the channel behavior.This model is called a PCAP model.Connected with channel grammars,the PCAP model is a common and convenient tool of communication.Using this tool,one could specify and compare different types of channels,as well as design channel implementations.Finally,the usefulness of this tool is demonstrated by presenting an implementation of hierarchical F channel.