Network systems: Definition and types 17 body of networking and communications literature is dedicated to the study of pro- tocol mechanisms in various protocols and environments in order to identify the appropriate methods and the specification of their parameters, for example, flow control window size, rate or credit-based flow control, and CRC polynomials for error checking [35, 154]. Protocol syntax specifies the structure of packets (data units), enabling the correct interpretation of each transmitted information bit. In a packet protocol, for example, the syntax specifies the use of headers or trailers, the fields in a header or trailer, the packet size, and so on. System design and implementation refer to the structure of the system that executes the protocol itself and implements communication as defined by the protocols of the protocol stack it implements. Standards typically define the first two protocol elements, that is, the mechan- isms and the syntax of protocols. Standards do not specify the structure of the sys- tems that implement protocols. Thus, a network system developer is able to develop any architecture and implementation one considers appropriate and will be standards-compliant as long as it implements the mechanisms defined for the protocol and follows the syntax. This is a very important observation because it enables a developer to implement any necessary function by any appropriate means