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Transfer Rates for Serial Transmissions (T1 vs T2)

Transfer Rates for Serial Transmissions (T1 vs T2)

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Nov 4, 2026

We are given a shared physical-layer bit rate of 1200 bits/s1200\ \text{bits/s} for both cases. The transfer rate (in this context) refers to how many characters (characters/frame payload units) are carried per second over the line, i.e.,

  • transfer rate=bit ratenumber of line bits per character/frame \text{transfer rate} = \dfrac{\text{bit rate}}{\text{number of line bits per character/frame}}

Key terms:

  • character frame
  • asynchronous serial
  • synchronous serial

We compute the number of transmitted line bits per unit for each transmission.

Compute T1 (Asynchronous) transfer rate

  1. 1
    Step 1

    T1 uses 8 information bits + 2 start bits + 1 parity bit + 1 stop bit, so total bits per character is 8+2+1+1=128+2+1+1=12 bits.

  2. 2
    Step 2

    Given bit rate 1200 bits/s1200\ \text{bits/s}, transfer rate (characters/s) is 120012=100 characters/s\dfrac{1200}{12}=100\ \text{characters/s}.

  3. 3
    Step 3

    Therefore, T1 transfer rate is 100 characters/s100\ \text{characters/s} (equivalently 100\ \text{frames/s}$, one frame per character in T1).

Compute T2 (Synchronous) transfer rate

  1. 1
    Step 1

    T2 sends 3 sync characters (each is 8 bits) followed by 30 eight-bit information characters. Total bits per block is (3×8)+(30×8)=33×8=264(3\times 8)+(30\times 8)=33\times 8=264 bits.

  2. 2
    Step 2

    Bit rate is 1200 bits/s1200\ \text{bits/s}, so blocks/s is 1200264=10022=5011≈4.545 blocks/s\dfrac{1200}{264}=\dfrac{100}{22}=\dfrac{50}{11}\approx 4.545\ \text{blocks/s}.

  3. 3
    Step 3

    Each block carries 30 information characters, so information character transfer rate is 30×5011=150011≈136.36 characters/s30\times \dfrac{50}{11}=\dfrac{1500}{11}\approx 136.36\ \text{characters/s}.

  4. 4
    Step 4

    Therefore, T2 information transfer rate is approximately 136.36 characters/s136.36\ \text{characters/s}.

Summary

TransmissionLine bits per unitUnits per secondTransfer rate result
T1 (asynchronous)1212 bits/character1200/121200/12100 characters/s100\ \text{characters/s}
T2 (synchronous)264264 bits/block, 3030 chars/block1200/2641200/264 blocks/s≈136.36 characters/s\approx 136.36\ \text{characters/s} (information chars)

Transfer rates at 1200 bits/s

Comparing T1 character transfer rate vs T2 information character transfer rate

Pro Tip: What exactly is 'transfer rate'?

For asynchronous T1, a natural unit is the character frame. For synchronous T2, a natural unit is the sync+data block; the question typically asks for the rate of information characters, so multiply blocks/s by 30.

Avoid mixing units (block vs character)

Do not report only the block rate for T2 unless explicitly asked. If you divide by total bits per block, you get blocks/s, not characters/s.

Quick reference: formulas used

Framing view of the two transmissions

Per-character framing

T1

Start(2 bits) → Info(8 bits) → Parity(1) → Stop(1)"

Block framing

T2

Sync(3×8 bits) → Info(30×8 bits)"

Knowledge Check

Question 1 of 4
Q1Single choice

In T1, the total number of line bits per character is:

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