T1 Frame Structure and Timing | Generated by AI

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Question: In the T1 carrier standard, what are the number of bits per frame and the time to transmit one frame?

Answer:

T1 Carrier Standard – Frame Structure Explained

Correct Answer: A — 193 bits, 125 μs

Key Concepts

1. T1 Carrier Overview

T1 is a North American digital transmission standard that multiplexes 24 voice channels using Time Division Multiplexing (TDM).

2. Frame Calculation

Parameter Value Explanation
Number of voice channels 24 T1 standard supports 24 DS0 channels
Bits per channel per frame 8 bits Each voice sample = 8-bit PCM encoding
Data bits total 24 × 8 = 192 bits All 24 channels combined
Framing/Sync bit +1 bit One synchronization bit added per frame
Total bits per frame 193 bits 192 + 1 = 193

Formula:
Total bits = (Number of channels × bits per sample) + 1 sync bit
= (24 × 8) + 1 = 193 bits

3. Frame Duration Calculation

The frame duration comes from voice sampling theory:

\[\text{Frame period} = \frac{1}{8000} = 0.000125 \text{ seconds} = \mathbf{125\ \mu s}\]

4. Why Option B is Wrong

Option Bits Time Status
A 193 bits 125 μs ✅ Correct
B 193 bits 250 μs ❌ Wrong – frame period should be 125 μs, not 250 μs
C 256 bits 125 μs ❌ Wrong – 256 bits is E1 standard, not T1
D 256 bits 250 μs ❌ Wrong – both values incorrect

250 μs would correspond to a sampling rate of only 4,000 Hz, which violates Nyquist sampling theorem for voice signals.

5. T1 vs E1 Comparison (Common Exam Trap)

Feature T1 (North America) E1 (Europe)
Channels 24 32 (30 voice + 2 control)
Bits per frame 193 256
Frame period 125 μs 125 μs
Total bit rate 1.544 Mbps 2.048 Mbps

⚠️ Exam tip: If you see 256 bits, that’s E1, not T1!

Summary

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