GATE CS - COMPUTER NETWORKS:Transport Layer

Transport Layer for GATE CS

GATE Transport questions favour TCP vs UDP properties, port roles, and sliding-window / stop-and-wait utilization numericals.

TCP vs UDP

UDP for DNS/video-style needs; TCP for byte-stream reliability.

Stop-and-Wait utilization

Frame size $L$ bits, bandwidth $B$ bps, propagation delay $T_p$.

Transmission time $T_t = L/B$.

Utilization ≈ $T_t / (T_t + 2T_p)$ when ACK is tiny and no errors (stop-and-wait).

Worked

$L = 3000$ bits, $B = 2000$ bps, $T_p = 100$ ms = 0.1 s.

$T_t = 3000/2000 = 1.5$ s.

$U = 1.5 / (1.5 + 0.2) = 1.5/1.7 ≈ 88.2\%$.

Sliding window of size $W$ multiplies throughput (idealized) by up to $W$ until the bandwidth-delay product saturates.

TCP mechanics (exam level)

Three-way handshake; sequence/ACK numbers; flow control (receiver window); congestion control phases named (slow start, congestion avoidance) when options list them. GATE rarely asks you to implement Reno — know the vocabulary and what grows cwnd.

Next: Data Link. Hub: GATE.