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Q2(a) · Persistent HTTP delay

2023-01-27 · AI-only Sem V

Exact historical variant. Current-syllabus questions solved; excluded topics and source limitations stated.

Q2(a). An HTTP client knows the server IP, but has no recent TCP connection. GET transmission time is zero; each object takes 1/2 RTT to transmit. Include connection setup, request/response propagation and object transmission. (1) Find the delay for the base object alone. (2) The base object references one JPEG downloaded afterwards on the same persistent HTTP/1.1 connection. Find the total delay for both objects. [10 marks]

Answer

Given

Known IP; new initial TCP connection; zero GET transmission; each object transmission=0.5 RTT.

To find

Time to obtain the base object and then the pair of objects.

Formula and why

T_{object}=T_{setup}+RTT+T_{transmission}LaTeX: T_{object}=T_{setup}+RTT+T_{transmission}

A referenced object cannot be requested until the HTML reveals it. HTTP/1.0 here uses a fresh connection per object; persistent HTTP/1.1 reuses one.

Solution

Step 1. Download base HTML

1 RTT for TCP setup + 1 RTT for GET/first response bit + 0.5 RTT to transmit = 2.5 RTT.

Step 2. Download referenced JPEG

Existing TCP connection: 0 setup + 1 RTT for GET/response + 0.5 RTT transmission = 1.5 RTT.

Step 3. Add sequential delays

Total = 2.5+1.5=4 RTT. DNS adds zero here because the IP address is already known.