Final answer:
The total delay for transferring a large file using store-and-forward packet switching across N layer 3 devices is given by the formula Total Delay = N × [(S + h) / R] + N × P, combining both transmission and propagation delays.
Step-by-step explanation:
The total delay in transferring a large file F from host A to host B using store-and-forward packet switching can be understood by adding up the individual delays incurred at each hop along the path between the two hosts. In this context, the total delay consists of two main components: transmission delay and propagation delay.
The transmission delay (also known as serialization delay) is the time taken to put all the bits of a packet onto the link. This is calculated by dividing the total size of the packet (segment size plus headers, S + h) by the transmission rate R:
Transmission Delay = (S + h) / R
The propagation delay is the time it takes for a bit to travel from one end of the link to the other at the speed of light through the medium and is denoted by P.
For N Layer 3 devices, each of which introduces a transmission and a propagation delay, the total delay across all devices would be:
Total Delay = N × [(S + h) / R] + N × P
This assumes no processing delay at the devices and no queueing delay due to congestion, which have been neglected as per the instructions. The store-and-forward nature means that each device waits for the entire packet to be received before forwarding it, hence why transmission delay occurs at each hop.