Protocols and Programming Languages
Protocols are to communications what algorithms or programming languages are to computations.
This analogy has important consequences for both the design and the development of protocols. One has to consider the fact that algorithms, programs and protocols are just different ways of describing expected behaviour of interacting objects. A familiar example of a protocolling language is the HTML language used to describe web pages which are the actual web protocols.
In programming languages the association of identifiers to a value is termed a definition. Program text is structured using block constructs and definitions can be local to a block. The localized association of an identifier to a value established by a definition is termed a binding and the region of program text in which a binding is effective is known as its scope. The computational state is kept using two components: the environment, used as a record of identifier bindings, and the store, which is used as a record of the effects of assignments.
In communications, message values are transferred using transmission media. By analogy, the equivalent of a store would be a collection of transmission media, instead of a collection of memory locations. A valid assignment in a protocol (as an analog of programming language) could be Ethernet:='message', meaning a message is to be broadcast on the local ethernet.
On a transmission medium there can be many receivers. For instance a mac-address identifies an ether network card on the transmission medium (the 'ether'). In our imaginary protocol, the assignment ethernet:=message value could therefore make sense.
By extending the assignment statement of an existing programming language with the semantics described, a protocolling language could easily be imagined.
Operating systems provide reliable communication and synchronization facilities for communicating objects confined to the same system by means of system libraries. A programmer using a general purpose programming language (like C or ADA) can use the routines in the libraries to implement a protocol, instead of using a dedicated protocolling language.
Read more about this topic: Communications Protocol
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