7. The Presentation LayerApplicatio

7. The Presentation LayerApplications use a variety of forms of data, ranging in complexity from very simple(e.g., textual) to elaborate and complex (e.g., nested data structures).Communication between applications involves the exchange of such data. However,all forms of data have inherent programming language and machine dependencies,which means that unless application data is accurately converted to a formatacceptable by the peer application, the meaning of the data will be lost duringtransmission.The role of the presentation layer is to facilitate semantic-preserving dataexchange between two peer applications. The presentation layer achieves this in twostages: (i) by having the two peer applications adopt a common high-level syntax fordata definition, and (ii) by negotiating a transfer syntax for the sole purpose oftransmission, which both applications can convert to and from.We will first look at the notion of abstract data syntax, and then describepresentation service primitives and functional units. ASN.1 will be presented as astandard abstract syntax definition notation for the use of applications, together withBER for defining data at the binary level. Use of ASN.1 and BER will be illustratedusing some simple examples. Next, we will discuss the presentation protocol, andconclude by listing a number of presentation standards.