. At the end of this chapter the reader will have an understanding of the seven layers and the tasks and protocols associated with each layer. 10.1 Introduction OSI (open system interconnect) seven layer communication model was developed by ISO as a framework for interoperability and the Internet working between devices or elements in the network (see Figure 10.1). The different functions involved in the communication between two elements are split as a set of tasks to be performed by each of the seven layers. Each layer is self-contained making the tasks specific to each layer easy to implement. The layers start with the physical layer at the bottom, followed by data link layer, network layer, transport layer, session layer, presentation layer, and application layer. The lowest layer is referred to a layer 1 (L1) and moving up, the top most layer is layer 7 (L7). The physical layer is closest to the physical media for connecting two devices and hence is responsible for placing data in the physical medium. In most scenarios the physical layer is rarely a pure software component and is usually imple- mented as a combination of software and hardware. The application layer is closest Fundamentals of EMS, NMS and OSS/BSS Application layer Application layer Presentation layer Presentation layer Session layer Session layer Transport layer Transport layer Network layer Network layer Data link layer Data link layer Physical layer Physical layer Device A Device B Figure 10.1 OSI communication model. to the end user and is mostly implemented as software. Communication involves transfer of data between devices. There are two key areas of focus here: the data and the device. Layers 7-4 deal with end to end communications between the "data" source and destinations. Layers 3-1 deal with communications between network "devices." This chapter handles each of the layers in detail along with the proto- cols used to implement a specific layer. Network management protocols are usually application layer protocols but a basic understa