Where does the time go?
Latency = propagation + transmission (+ queuing + processing). Which term is eating your delay?
Distance
1,000 km
1 km – 15,000 km. Signals travel at 2.4 × 10⁸ m/s in cable (Forouzan).
Bandwidth
1 Mbps
56 kbps – 10 Gbps (log scale).
Message size
1 MB
1 kB – 1 GB (log scale). 1 byte = 8 bits — the exam will check.
Same room, huge file
Satellite hop, one keystroke
Fibre to Singapore
The truck of hard drives
Propagation time
distance ÷ 2.4×10⁸ m/s
Transmission time
message size ÷ bandwidth
Total latency
t_prop + t_trans (queue ≈ 0 here)
Bits in flight
bandwidth × t_prop