GATE CS 1998 Q1.16 — Concept of Layering: OSI and TCP/IP Protocol Stacks

In asynchronous serial communication, each character frame consists of the following bits:

• Start bit: $1$ bit (implicitly required to initiate transmission)
• Data bits: $8$ bits
• Parity bit: $1$ bit
• Stop bits: $2$ bits

Calculating the total number of bits per character:

To sustain a transfer rate of $300$ characters per second, the minimum required bit rate is:

Note: Even if we do not consider the start bit, the required rate would be $300 \times 11 = 3300\text{ bps}$.

Since serial communication channels operate at standard discrete baud rates (such as $1200$, $2400$, $4800$, $9600$, etc.), we must select the minimum standard baud rate that is greater than or equal to the required transmission rate of $3600\text{ bps}$ (assuming $1$ bit per baud):

• $2400\text{ baud} < 3600\text{ bps}$ (Insufficient)
• $4800\text{ baud} \ge 3600\text{ bps}$ (Sufficient and minimum)

Thus, the minimum baud rate required to sustain the transfer is $4800$ baud.