an handle. This scenario of flooding the receiver is called congestion. Regulating the flow of data or flow control can avoid congestion. Transport layer can implement flow control. Reliable data transfer: Acknowledgments can be used by the receiver to inform the sender about safe delivery or loss of data. Retransmission of lost data can also be implemented in the transport layer. Process level communication using ports and sockets. Data processing: Data segments from different processes can be combined to a single stream at the sender and again fragmented at the receiver. Also a large bulk of data can be split into segments at the sender and then combined again at the receiver. The TCP (transport control protocol) and UDP (user datagram protocol) are the most popular transport layer protocols. TCP sends data as packets while UDP sends data as datagrams. TCP is connection oriented and UDP is connectionless. Connection-oriented services can be handled at the network layer itself, though it is commonly implemented at the transport layer. 10.6 Session Layer This is the fifth lowest layer (L5) in the ISO/OSI model. All the functionality of identifying the destination and application to communicate is done in the layers lower to the session layer. So addressing and data processing is not done in the ses- sion layer. As the name suggests, session layer is mainly intended for session manage- ment, which includes establishing, maintaining, and terminating a session. Session is a logical linking of software application processes, to allow them to exchange data. A session is usually established between applications to transfer a file, send log-on information and for any type of data transfer. Fundamentals of EMS, NMS and OSS/BSS Session can be of two types: Half duplex: In half duplex only one way communication is permitted at any point of time. So when a session is established between two network elements, each element has to communicate in turn as only one element is permitted to send data in half duplex mode. Full duple