Delivery refers to the way a packet is handled by the underlying network under the control of the network layer. Various delivery concepts are explained below.
Delivery of a packet in the network layer is accomplished by either a connection oriented service or a connection-less service.
Connection Oriented Service:
- At first a connection gets establishment between the source and the destination’s network layer protocol.
- Then the packets of the message to be delivered travel through the established path in a sequential order like, 1st packet -> 2nd packet -> 3rd packet ->…. Or 3rd packet -> 2nd packet -> 1st packet.
- They will reach the destination’s network layer in the same path and order and will combine to make the whole message.
- After the transfer has been done the connection will be terminated.
- Here each packet is individual.
- Each router will determine the path for a packet.
- The paths for the packets may or may not be the same.
- Packets can reach the destination with a random order and they will be sorted at the destination’s network layer to become the whole message.
The delivery of a packet to its final destination is accomplished by using two different methods, Direct and Indirect methods.
Direct delivery is done while the source and destination relies in the same network. The sender can easily determine if the delivery is direct or not by extracting the network address of the destination and comparing this address with the addresses of the network with which it is connected.
Here, the sender uses the destination IP address to find the destination physical address. The IP software then gives the destination IP address with the destination physical address to the data link layer for actual delivery.
While the source and the destination are on different networks the delivery will be an indirect delivery. Here, the packet goes from router to router until it finds the one connected to same physical network as its final destination.
In an indirect delivery the sender uses the destination IP address and a routing table to find out the IP address of the next router to which the packet should be delivered and this process goes on.