A process on the local host, called a client, needs services from a process usually on the remote host, called a server. A transport layer protocol can either be connectionless or connection-oriented. In a connectionless service, the packets are sent from one party to another with no need for connection establishment or connection release. The packets are not numbered; they may be delayed or lost or may arrive out of sequence. In a connection-oriented service, a connection is first established between the sender and the receiver. Data are transferred. At the end, the connection is released.