Select the correct alternative from the given choices....

Select the correct alternative from the given choices. CSMA/CD LAN of 1 gbps is to be designed over $1 \mathrm{~km}$ cable without repeater. The minimum frame size that Data link layer should consider, if cable support signal speed of $20,000 \mathrm{~km} / \mathrm{sec}$ (A) $10 \mathrm{k}$ bits (B) $20 \mathrm{k}$ bits (C) $30 \mathrm{k}$ bits (D) $40 \mathrm{k}$ bits

Select the correct alternative from the given choices.
CSMA/CD LAN of 1 gbps is to be designed over $1 \mathrm{~km}$ cable without repeater. The minimum frame size that Data link layer should consider, if cable support signal speed of $20,000 \mathrm{~km} / \mathrm{sec}$
(A) $10 \mathrm{k}$ bits
(B) $20 \mathrm{k}$ bits
(C) $30 \mathrm{k}$ bits
(D) $40 \mathrm{k}$ bits

Key Concepts

Minimum Frame Size Requirement

The minimum frame size in a CSMA/CD network is determined by the need to allow sufficient time for a collision to be detected over the maximum network span. The frame must be long enough such that the transmission duration is at least equal to the round-trip propagation delay. If the frame is too short, a collision might occur but not be detected, leading to network inefficiencies. This concept is especially important in high-speed networks where the transmission times are very short compared to the propagation delays.

CSMA/CD Protocol

Carrier Sense Multiple Access with Collision Detection (CSMA/CD) is a network protocol used in Ethernet networks to control access to the shared communication medium. It works by having nodes listen to the network medium for existing traffic before transmitting, and by monitoring the transmission to detect collisions. If a collision is detected, the transmitting node stops and retries after a random time. This protocol is crucial in determining frame size requirements to ensure that collisions are detected reliably across the network.

Propagation Delay and Round-Trip Time

Propagation delay is the time it takes for a signal to travel from the sender to the receiver across a medium. In CSMA/CD networks, the round-trip time, which is twice the one-way propagation delay, is a critical parameter because the frame transmission must be long enough to allow a collision to propagate back to the sender before the transmission ends. This ensures that collisions can be detected by the transmitting node.

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