ns across systems are known as well-known ports. For example data is routed through well-known TCP port 80 while using the Internet. While an IP address can be used to route data to a specific network element and the port number to direct data to a specific application, both of these tasks can be jointly done by an identifier called the socket. A socket is an identifier that binds a specific port to an IP address. Transport layer supports both connection-oriented protocol and connection- less protocol. Connection-oriented protocol is the more common for reliable data Seven-Layer Communication Model communication as a connection needs to be established before data transfer. It allows for error checking functionality and stability. Connectionless protocol does not require a reliable connection established between the application during the entire duration of data transfer and it lacks extensive error checking. Connectionless protocol is considered to be much faster than connection-oriented protocol and is mainly used in intermittent communication. The functions of the transport layer are: Connection management: In case of a connection-oriented protocol the transport layer ensures establishing the connection, maintaining the connec- tion during data transfer and termination of connection after the transfer is complete. Congestion avoidance and flow control: There can be a scenario when the sender transmits data at a rate higher than the value that the receiver can 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