NETWORK SOFTWARE, CONNECTION ORIENTED SERVICES AND CONNECTION LESS SERVICES WITH EXAMPLE

Network Software:

The first computer networks were designed with the hardware as the main concern and the software as anafterthought. This strategy no longer works. Network software is now highly structured. In the following sectionswe examine the software structuring technique in some detail. The method described here forms the keystone of the entire book and will occur repeatedly later on.

Connection-Oriented Services:

Connection-oriented service is modeled after the telephone system. To talk to someone, you pick up the phone,dial the number, talk, and then hang up. Similarly, to use a connection-oriented network service, the service user first establishes a connection, uses the connection, and then releases the connection.

* E.g., for file transfer, we want that all bits arrive correctly and in the order they were sent

TCP is a connection-oriented protocol. That means that the sender is aware if packets get lost in transit. It does that by

means of acknowledgements from the receiver and serial numbers of packets. So if the receiver receives a packet it will send

an acknowledgement about that packet to the sender. If the sender doesn't receive an acknowledgement for a packet it sent,

then it'll send it again. This ensures that connections are "complete".

Connectionless Services:

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, lost, or arrive out of sequence.

connectionless service is modeled after the postal system. Each message (letter) carries the fulldestination address, and each one is routed through the system independent of all the others. Normally, whentwo messages are sent to the same destination, the first one sent will be the first one to arrive. However, it ispossible that the first one sent can be delayed so that the second one arrives first.

*E.G. UDP on the other hand is connectionless. This means that the sender just sends packets towards the receiver without caring if the receiver actually received them.