Your organization subscribes to a T1 line that connects to the Central Office (CO) as the Private Branch Exchange (PBX) trunk for voice communication. Which one of the following mechanisms best describes how the T1 line works? (Wentz QOTD)
A. Simplex
B. Half-duplex (HDX)
C. Full-duplex (FDX)
D. Multiplex
Kindly be reminded that the suggested answer is for your reference only. It doesn’t matter whether you have the right or wrong answer. What really matters is your reasoning process and justifications.
My suggested answer is D. Multiplex.
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Communication between two parties can be simplex (unidirectional) or duplex (bidirectional). However, signals from multiple parties can be concentrated into and carried by a single transmission media.
T1 Line
A T1 line is a specific type of copper cable that carries 24 channels of Digital Signal 0 (DS0) per the T1-carrier system using time-division multiplexing (TDM) so that signals from 24 parties can be combined into and transmitted over the media.
Multiplexing
Multiplexing is the process of combining two or more information channels into a single transmission medium. There are a number of different standards that can be applied to the process.
T-1 was the basic type of multiplexing scheme selected by Bell Labs for high capacity communication links. It is so pervasive in the world wide telephone network, that replacement protocols are just being introduced.
Source: FHWA
Digital Signal 0 (DS0)
The DS0 rate was introduced to carry a single digitized voice call. For a typical phone call, the audio sound is digitized at an 8 kHz sample rate, or 8000 samples per second, using 8-bit pulse-code modulation for each of the samples. This results in a data rate of 64 kbit/s.
Because of its fundamental role in carrying a single phone call, the DS0 rate forms the basis for the digital multiplex transmission hierarchy in telecommunications systems used in North America. To limit the number of wires required between two involved in exchanging voice calls, a system was built in which multiple DS0s are multiplexed together on higher capacity circuits. In this system, twenty-four (24) DS0s are multiplexed into a DS1 signal. Twenty-eight (28) DS1s are multiplexed into a DS3. When carried over copper wire, this is the well-known T-carrier system, with T1 and T3 corresponding to DS1 and DS3, respectively.
Source: WIkipedia
| Signal | Speed (mbits/s) | T1 | Voice Channels |
|---|---|---|---|
| DS0 | 0.064 | 1/24 | 1 |
| DS1 | 1.544 | 1 | 24 |
| DS1C | 3.152 | 2 | 48 |
| DS2 | 6.176 | 3 | 96 |
| DS3 | 44.736 | 28 | 672 |
| DS3C | 89.472 | 56 | 1344 |
| DS4 | 274.176 | 168 | 4032 |
Simplex, Half Duplex, and Full Duplex Transmission
| Basis for Comparison | Simplex | Half Duplex | Full Duplex |
| Direction of Communication | Unidirectional | Two-directional, one at a time | Two-directional, simultaneously |
| Send / Receive | The sender can only send data | The sender can send and receive data, but one a time | The sender can send and receive data simultaneously |
| Performance | Worst performing mode of transmission | Better than Simplex | Best performing mode of transmission |
| Example | Keyboard and monitor | Walkie-talkie | Telephone |
Reference
- Simplex, Half Duplex, Full Duplex
- Simplex communication
- Duplex (telecommunications)
- Multiplexing (Wikipedia)
- Multiplexing (telecomworld101)
- Chapter 2. Fundamentals of Telecommunications
- Chapter 4. Multiplexing and the T-carrier Hierarchy
- T1 Digital system
- T-carrier (Wikipedia)
- T1/E1 and fractional T1 connections
您的組織訂閱了一條連接到中央辦公室 (CO) 的 T1 線路，作為用於語音通信的專用交換機 (PBX) 中繼。 以下哪種機制最能描述 T1 線路的工作原理？ (Wentz QOTD)
A. 單工 (Simplex)
B. 半雙工 (HDX)
C. 全雙工 (FDX)
D. 多工 (Multiplex)
Half Duplex