Q. Is tcp Connection-oriented?

TCP is connection-oriented. This means a connection is established between source and destination machines before any data is sent it implies that a connection is established and maintained until such time as message or messages to be exchanged by application programs at each end have been exchanged. Connections provided by TCP are known as Virtual Connections. It means that there is not any physical direct connection between computers.

TCP is used along with Internet Protocol to send data in form of message units between computers over Internet. While IP takes care of handling actual delivery of the data, TCP takes care of keeping track of individual units of data (known as Packet) that a message is divided into for efficient routing through Internet. TCP provides for a reliable, connection-oriented data transmission channel between two programs. Reliable means that data sent is guaranteed to reach its destination in order sent or an error would be returned to sender.

For instance, when an HTML file is sent to someone from a Web server, Transmission Control Protocol (TCP) program layer in that server divides the file in one or more packets, numbers the packets after that forwards them individually. Though every packet has same destination IP address, it can get routed differently through network. At the other end (client program in our computer), TCP reassembles individual packets and waits till they have arrived to forward them as a single file.

TCP is responsible for making sure that a message is divided into the packets which IP manages and for reassembling packets back into complete message at the other end. In Open Systems Interconnection (OSI) communication model, TCP is in layer 4, Transport Layer.