GATE CS 2005 Q74 — Data Link Layer: Framing, Error Detection, MAC, Ethernet Bridging

To ensure reliable collision detection in a CSMA/CD network (like Ethernet), a transmitting station must continue transmitting long enough for the collision signal to travel back to it, even in the worst-case scenario. This requires the frame transmission time ($T_x$) to be at least the round-trip propagation delay ($RTT$) plus the time required to transmit the jamming signal ($T_{jam}$):

We are given:

• Bandwidth ($B$) = $10\text{ Mbps} = 10 \times 10^6\text{ bits/sec}$
• Round-trip propagation delay ($RTT$) = $46.4\ \mu\text{s} = 46.4 \times 10^{-6}\text{ s}$
• Jamming signal size = $48\text{ bits}$

The minimum frame size (in bits) can be calculated as:

Thus, the minimum frame size is 512 bits.