ibps-so 2016 · Question 28 of 394

A customer at a branch of Chandrabhaga Urban Bank in one district asks for a demand draft. The teller's workstation raises a request that must reach an application server standing in the data centre in another state. The request crosses the branch LAN, a leased line, four intermediate devices belonging to the bank's service provider and nally the data-centre LAN. At each of those intermediate devices the packet is examined, the destination address in its header is looked up in a table, and the packet is placed upon whichever outgoing interface the table names as the next step towards that destination. The hardware address of the frame changes at every hop, and the port numbers do not change at all. In the model of Figure 1, the layer that performs this routing function is:

1. AThe data link layer, layer 2, since it is the hardware address that is rewritten at every one of the intermediate devices
2. BThe transport layer, layer 4, since the delivery is end to end and the port numbers survive the whole journey unchanged
3. CThe session layer, layer 5, since a dialogue must be maintained between the teller's workstation and the application server
4. DThe network layer, layer 3, upon which alone rests the carriage of a packet from the host that raised it to the host for which it is meant, however many networks lie between the two, together with the path determination that such carriage requiresCorrect
5. EThe application layer, layer 7, since it is the application that names the server to which the request is to be delivered