Connection-Oriented Networking

Connection-Oriented Networking

ATM differs from the packet-switching networks described earlier because it offers connection-oriented service. Before a computer connected to an ATM switch can send cells, a connection must be established manually or the host must first interact with the switch to specify a destination. The interaction is analogous to placing a telephone call.

The requesting computer specifies the remote computer's address, and waits for the ATM switch to find a path through the network and establish a connection. If the remote computer rejects the request, does not respond, or the ATM switches between the sender and receiver cannot currently establish a path, the request to establish communication fails.

Once a connection succeeds, the local ATM switch chooses an identifier for the connection, and passes the connection identifier to the computer along with a message that informs the computer of success. The computer uses the connection identifier when sending or receiving cells.

When it finishes using a connection, the computer again communicates with the ATM switch to request that the connection be broken. The switch then disconnects the two computers. Disconnection is equivalent to hanging up a telephone at the end of a telephone call; after a disconnection, the computers cannot communicate until they establish a new connection. Furthermore, identifiers used for a connection can be recycled; once a disconnection occurs, the switch can reuse the connection identifier for a new connection.