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Q1(c) · HTTP/1.1 delay

2024-02-06 · AI-only Sem V variant

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

Q1(c). 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. The base HTML references one JPEG on gaia.cs.umass.edu; download both sequentially on the same persistent HTTP/1.1 connection. Find total RTTs. [5 marks]

Answer

Given

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

To find

Time to obtain both the base HTML and its referenced JPEG.

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.