Question

In a CDMA/CD CSMA/CD network with a data rate of 10Mbps, the minimum
frame size is found to be 512 bits for the correct operation of the collision detection
process. What Should be the minimum frame size if we increase the data rate to
a. 100 Mbps?
b. 1 Gbps?

Answer 1

Well, how long does it take for the other side to hear the transmission? See, in this type of communication the collision detection only occurs while transmitting.

Collision detected:

\(\begin{matrix}
A & ~ & ~ & ~ & ~ & B\\
A & \rightarrow & ~ & ~ & ~ & B\\
A & \rightarrow & \rightarrow & ~ & \leftarrow & B\\
A & \rightarrow & \rightarrow & \leftrightarrow & \leftarrow & B\\
A & \rightarrow & \leftrightarrow & \leftrightarrow & \leftrightarrow & B\\
\end{matrix}\)

The collision is discovered because both sides are transmitting and therefore looking for collisions. Contrast this to a late collision:

\(\begin{matrix}
A & ~ & ~ & ~ & ~ & B\\
A & \rightarrow & ~ & ~ & ~ & B\\
A & ~ & \rightarrow & ~ & \leftarrow & B\\
A & ~ & ~ & \leftrightarrow & \leftarrow & B\\
A & ~ & \leftarrow & \leftrightarrow & \rightarrow & B\\
\end{matrix}\)

There was a collision, but because transmission was stopped before the collision, it is not detected.

So what you are looking at his how long does it take to get from A to B and B to A compared with how fast do buts get put on the wire.