Suppose there is exactly one packet switch between a sending host and a receiving host. the transmission rates between the sending host and the switch and between the switch and the receiving host are r1 and r2, respectively. assuming that the switch uses store-and-forward packet switching, what is the total end-to-end delay to send a packet of length l? (ignore queuing, propagation delay, and processing delay.)

T = L/R1 + L/R2

Explanation:

The transmission rate is the amount of information for unit time, therefore, the length of the paket 'L' divided by the transmission rate 'R' gives you the speed of the chanel, please notice that the units of 'R' and 'L' must agree so if for example 'R' is given in bits per second 'L' must be given in bits. Because we don't consider propagation or processing delay the total delay 'T' is the delay form the sender to the switch plus the delay from the switch to the receiver.

T = L/R1 + L/R2