Continuous transmission vs. stop-and-wait

Problem P28 (Kurose) · A and B 20,000 km apart, R = 2 Mbps, 800,000-bit file

Link A → B: two ways to send the same file

ready.

a) Continuous transmission, as a single message

message bits first bit last bit

link utilization

0 %

stopwatch0 s

b) Stop-and-wait, in N packets

data packet → B ACK ← A

link utilization

0 %

stopwatch0 s

–

t = 0 s

Space-time diagrams (same vertical scale)

Continuous transmission

Stop-and-wait

data ACK (dashed)

About this visualization

Compares two ways of sending the same file between A and B, following problem P28 from Kurose (20,000 km, 2 Mbps, 800,000 bits): as a single continuous message, and split into N packets with stop-and-wait, where each packet waits for its acknowledgement (ACK) before the next one is sent. It shows both scenarios animated, their space-time diagrams, link utilization and total time. The student changes file size, rate, distance and N, and can also try a window of several unacknowledged packets. The outcome shows that the RTT dominates the time and leaves the link mostly idle.

Concepts: stop-and-wait, continuous transmission, round-trip time (RTT), acknowledgement (ACK), link utilization, transmission delay, propagation delay, window.

Formulas:

d_trans = F / R
d_prop = distance / v_p
RTT = 2·d_prop
continuous time = F/R + d_prop
stop-and-wait time (window 1, negligible ACK) = N·(F/(N·R) + RTT)
utilization = total d_trans / total time

Network Architecture I, Lab 1.2, problem P28 · Enrique de la Hoz, University of Alcalá · License CC BY-SA 4.0 · Source and catalogue on GitHub · DOI 10.5281/zenodo.23285664