TCP (Transmission Control Protocol): The transport layer is responsible for error-free, end-to-end delivery of data from the source host to the destination host. It corresponds to the transport layer of the OSI model.The functions of the transport layer are:It facilitates the communicating hosts to carry on a conversation.It provides an interface for the users to the underlying network.It can provide for a reliable connection. It can also carry out error checking, flow control, and verification. Transmission Control Protocol (TCP):It is a reliable connection-oriented protocol that transmits data from the source to the destination machine without any error.A connection is established between the peer entities prior to transmission.At the sending host, TCP divides an incoming byte stream into segments and assigns a separate sequence number to each segment.At the receiving host, TCP reorders the segments and sends an acknowledgment to the sender for correct receipt of segments.TCP also manages flow control so that a fast sender does not overwhelm a slow receiver. User Datagram Protocol (UDP):It is a message-oriented protocol that provides a simple unreliable, connectionless, unacknowledged service.It is suitable for applications that do not require TCPs sequencing, error control or flow control.It is used for transmitting a small amount of data where the speed of delivery is more important than the accuracy of delivery. Stream Control Transmission Protocol (SCTP): It combines the features of both TCP and UDP. It is message oriented like the UDP, which providing the reliable, connection-oriented service like TCP. It is used for telephony over the Internet.UPD is used for real time multimedia, DNS and TCP is used for e-mail.