Implementation of connection-oriented services

We need a virtual-circuit subnet for connection-oriented service. Virtual circuits were designed to avoid having to choose a new route for every packet sent, providing a more efficient and predictable communication path.

Instead, a route from the source machine to the destination machine is chosen as part of the connection setup and stored in tables inside the routers when a connection is established. That route is utilized for all traffic flowing over the connection, exactly the same manner as telephone networks operate.

The virtual circuit is terminated when the connection is released. In connection-oriented service, every packet carries an identifier that tells which virtual circuit it belongs to, enabling proper routing and delivery.

How Virtual Circuit Setup Works

Step 1 ? Host H1 establishes connection 1 with host H2. This connection is remembered as the first entry in every router's routing table along the path.

Step 2 ? Router A's table shows that packets with connection identifier 1 coming from H1 should be sent to router W with the same connection identifier 1.

Step 3 ? Similarly, router W routes packets with connection identifier 1 to router Y, maintaining the same identifier.

Step 4 ? When H3 wants to establish a connection to H2, it also chooses connection identifier 1. This creates a second entry in the routing tables.

Step 5 ? A conflict arises because router W cannot distinguish between connection 1 packets from H1 and connection 1 packets from H3, since both arrive with the same identifier.

Step 6 ? To resolve this conflict, routers assign different connection identifiers to outgoing traffic. This process is called label switching, where routers replace connection identifiers in packets to avoid conflicts while maintaining proper routing.

Key Features

• Route establishment ? A fixed path is determined during connection setup and used for all packets in that session.

• Connection identifiers ? Each packet carries a label that identifies which virtual circuit it belongs to.

• Label switching ? Routers can modify connection identifiers to resolve conflicts and ensure proper routing.

• State maintenance ? Routers maintain connection state information in their routing tables.

Conclusion

Connection-oriented services use virtual circuits with pre-established routes and connection identifiers. Routers employ label switching to resolve identifier conflicts, ensuring reliable packet delivery through a fixed path for the entire communication session.