Q4(b) · HTTP/2 multiplexing versus HTTP/1.1

Q4(b). RTT=4 time units; all four objects are requested at t=0 on an established connection. O1 has 10 frames, O2 has 1, O3 has 2, O4 has 1. One frame takes 1 time unit. HTTP/2 cycles O1,O2,O3,O4, skipping finished objects; HTTP/1.1 sends complete objects FCFS O1,O2,O3,O4. Find each completion time and average object download delay for both methods, including request and response propagation. [10 marks]

Answer

Given

RTT4; frame time1; O1/O2/O3/O4 have10/1/2/1 frames; established connection.

To find

Every object completion time and average delay.

Formula and why

LaTeX: T_j=RTT+\text{position of the last frame of object }j

Requests need2 units to reach the server and final frame bits need2 to return. Thus add4 to each last-frame transmission count; do not add a new RTT per frame.

Solution

Step 1. Write transmission orders and last-frame positions

Method	Frame order	O1 completion	O2 completion	O3 completion	O4 completion	Average
HTTP/2	O1, O2, O3, O4, O1, O3, O1, O1, O1, O1, O1, O1, O1, O1	18	6	10	8	10.5
HTTP/1.1	O1, O1, O1, O1, O1, O1, O1, O1, O1, O1, O2, O3, O3, O4	14	15	17	18	16.0

Step 2. Calculate averages explicitly

HTTP/2: (18+6+10+8)/4=42/4=10.5. HTTP/1.1: (14+15+17+18)/4=64/4=16. All objects finish by18 in both cases; multiplexing makes short objects finish earlier.