rmed in the presentation layer, but to improve the throughput of data, compression and decompression can be performed in this layer. Some functions, like com- pression to increase throughput and encryption to increase security, can be performed in almost any layer of the OSI model. Encryption of data: Implementing security for the data that travels down the protocol stack is a key functionality of the presentation layer. Encryption is performed on the data at the presentation layer and it can also be performed at the layers below the presentation layer. One of the most popular encryp- tion schema associated with the presentation layer is the secure sockets layer (SSL) protocol. The presentation layer is not always used in network communication. This is because most of its functionalities are optional. The encryption and compression can be formed at other layers in the OSI model. For data translation to come up with a common format is only required when handling heterogeneous systems. The remaining functions of the presentation layer can be performed by the application layer. Most of the protocol stack implementations may not have a presentation layer. Fundamentals of EMS, NMS and OSS/BSS There are three syntactic versions that are important when two applications interact: Syntax of the application entity that requested the connection. Syntax of the application entity that receives the connection. Syntax used by the presentation entities in giving a common format. The syntax of the application entity at the transmitting or requesting end is con- verted to syntax used by the presentation entity at the presentation layer of a request- ing system. In the same way, the syntax used by the presentation entity is converted to the syntax used by an application entity at the receiving end at the presentation layer of the receiving system. Another example of a presentation layer protocol is XDR (external data rep- resentation). XDR is used as the common data format mostly when interaction is involved with a system running U