The Full Form of CONS is‍ Connection-Oriented Network Service.

A connection-oriented service is one that establishes a dedicated connection between the communicating entities before data communication commences. It is modeled after the telephone system. To use a connection-oriented service, the user first establishes a connection, uses it and then releases it. In connection-oriented services, the data streams/packets are delivered to the receiver in the same order in which they have been sent by the sender.

Connection-oriented services may be done in either of the following ways −

• Circuit-switched connection: In circuit switching, a dedicated physical path or a circuit is established between the communicating nodes and then data stream is transferred.
• Virtual circuit-switched connection: Here, the data stream is transferred over a packet switched network, in such a way that it seems to the user that there is a dedicated path from the sender to the receiver. A virtual path is established here. However, other connections may also be using this path.

Connection-oriented services may be of the following types −

• Reliable Message Stream: e.g. sequence of pages
• Reliable Byte Stream: e.g. song download
• Unreliable Connection: e.g. VoIP (Voice over Internet Protocol)