A translator located in the transport layer is called a transport relay. The relay is located somewhere between the communicating nodes and enables IPv6-only hosts to exchange traffic (UDP or TCP) with IPv4-only hosts. If two nodes, for example a client and an application server, use different protocol stacks, they couldn’t communicate directly with each other, and traffic has to be passed over a relay. In case of TCP the relay terminates the IPv6 transport protocol session from the client, and thus acts as a transport destination endpoint to the client. At the same time it initializes a second IPv4 transport session with the server, and copies received data from each session to the other. In the case of UDP the datagram is just translated and forwarded to the target node.