Specific transport protocols are derived from these MTL classes. In general, the units of information exchange in a protocol are called packets, and the state structures are called protocol control blocks or contexts. The mechanisms that parse the incoming packets and service requests and, in doing so, provide the service char acteristics of the protocol are called the protocol procedures. There are two central data structures, the packet and the context. The protocol procedures operate on these structures.
Packets require construction, data insertion, transmission, reception, and data retrieval.
The endpoint state structure is changed according to the parsing of packets and the servicing of user requests. In both cases there is a central repository of data and actors, or methods, on the reposed data. This profile matches the definition of an object. The object-oriented programming paradigm forces ownership of functionality. An instance of this can be seen with packets.