Serial Asynchronous vs Synchronous Transmission Transfer Rates at 1200 bps | AI Research

Serial (Asynchronous vs Synchronous) Transmission Transfer Rates at 1200 bps

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Nov 4, 2026

To compare transmission speeds, we treat both systems as using the same physical bit rate $R_b = 1200$ bits/second, and compute how many useful information characters arrive per second based on the number of transmitted bits per character/frame.

Key ideas:

bit rate: given as $1200$ bps in both cases.
frame: determines overhead.
sync character.
information character.

For T1 (serial/async), each character has overhead: start + stop + parity. For T2 (synchronous), each block begins with a sync sequence (3 bytes), followed by data (30 bytes), forming a larger repeating frame.

Mermaid overview of bit accounting:

Asynchronous vs Synchronous Serial Communication (Frame/Overhead Intuition)

Given

Bit rate (both): $R_b = 1200$ bits/s.

T1 (serial transmission)

Each character consists of:

8 information bits
1 parity bit
2 start bits
1 stop bit

Total bits per character:

N_{T1} = 8 + 1 + 2 + 1 = 12 \text{ bits/character}

T2 (synchronous transmission)

Each block/frame contains:

3 sync characters (each is 8 bits) $\Rightarrow 3\times 8$ bits
30 information characters (each is 8 bits) $\Rightarrow 30\times 8$ bits

Total bits per block:

N_{T2} = (3+30)\times 8 = 33\times 8 = 264 \text{ bits/block}

Useful information in T2 per block:

30 information characters per block

Compute transfer rate in characters/s for T1 and T2

1
Step 1
For any scheme, frames/s $= \frac{R_b}{\text{bits per frame}}$ .
2
Step 2
Bits per character $N_{T1}=12$ , so $\text{characters/s} = \frac{1200}{12}=100$ .
3
Step 3
Bits per block $N_{T2}=264$ , so $\text{blocks/s} = \frac{1200}{264} = \frac{100}{22}=\frac{50}{11}$ .
4
Step 4
Each block carries 30 information characters, so $\text{characters/s}=30\cdot\frac{50}{11}=\frac{1500}{11}\approx 136.36$ .
5
Step 5
Report T1 = 100 characters/s and T2 ≈ 136.36 information characters/s.

Final Answers (Transfer Rates)

T1 transfer rate

R_{T1} = \frac{1200\ \text{bits/s}}{12\ \text{bits/character}} = 100\ \text{information characters/s}

T2 transfer rate

R_{T2} = 30 \cdot \frac{1200\ \text{bits/s}}{264\ \text{bits/block}} = 30 \cdot \frac{1200}{264} = 30 \cdot \\frac{50}{11} = \\frac{1500}{11} \\approx 136.36\ \text{information characters/s}

Answer:

T1: $100$ information characters/second
T2: $\approx 136.36$ information characters/second

Character Transfer Rate Comparison (Information Characters/s)

Computed from the same 1200 bps bit rate using different framing overhead.

How to avoid common mistakes

Always convert bit rate to character/block rate using the total transmitted bits per unit. For T2, remember only the 30 data bytes count as “information characters,” not the 3 sync bytes.

Frame definition matters

In T1, the overhead is per character. In T2, the overhead (3 sync bytes) is per block of 33 bytes total. Mixing these (e.g., treating T2 sync bytes as per character) gives the wrong result.

Quick Checks

Knowledge Check

Question 1 of 4

Q1Single choice

For T1, the number of transmitted bits per character is:

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