Time Division Multiplexing

 

Introduction

DS-1 24 Channel System

SystemView Models

Student Assignments

 


 

Time Division Multiplexing

 

Introduction

The purpose of this report is to:

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High speed or high bandwidth transmission facilities are often used for inter-office trunks or in the long haul network. Multiple end-user channels are multiplexed onto these trunk facilities.

With the advent of large private networks and computer facilities, some of these transmission facilities are moving into the end-user market as well.

TDM is a convenient method for combining various digital signals. These signals may be interleaved at the bit, byte, or some other level. The resulting pattern may be transmitted directly, as in digital carrier systems, or passed through a modem to allow the data to pass over an analog network.

DS Hierarchy

Designation

# Voice

Channels

Bit Rate

[Mbps]

Comments

DS–0

1

.064

100% duty cycle, unipolar

DS–1

24

1.544

Media: 22 AWG cable

Repeater spacing: 6000 ft

Signal: bipolar RZ

DS–1C

48

3.152

Media: 22 AWG cable

Repeater spacing: 6000 ft

Signal: bipolar RZ

DS–2

96

6.312

media: low capacitance 22 AWG

Max repeater spacing: 14,800 ft

Signal: bipolar RZ, B6ZS

DS–3

672

44.736

Media: microwave, fiber

Signal: RZ, B3ZS

DS-3A

1344

91.04

 

DS–4

4032

274.176

Media: coax, microwave

Signal: bipolar NRZ

 

DS-1 24 Channel System

In North America, the basic digital channel format is known as DS-0. These are grouped into frames of 24 channels each.

A concatenation of 24 channels and a start bit is called a frame. Groups of 12 frames are called multiframes or superframes. These vary the start bit to aid in synchronizing the link and add signaling bits to pass control messages.

S Bit Synchronization

The S bit is used to identify the start of a DS-1 frame. There are 8 thousand S bits per second. They have an encoded pattern, to aid in locating channel position within the frame.

Frame

1

2

3

4

5

6

7

8

9

10

11

12

S Bit

1

0

0

0

1

1

0

1

1

1

0

0

 

This forms a regular pattern of 1 0 1 0 1 0 for the odd frames and 0 0 1 1 1 0 for the even frames.

Additional synchronization information is encoded in the DS-1 frame when it is used for digital data applications, so lock is more readily acquired and maintained.

SystemView Models

 Two channel digital multiplexer

 Four channel analog multiplexer

 Eight channel analog multiplexer

 Eight channel digital multiplexer

 Twenty channel analog multiplexer

 Twenty four channel analog multiplexer

 

 

 

Student Assignments

 

Ignoring the S-bit, create a 24-channel TDM multiplexer/demultiplexer SystemView model.

 



       Digital Signal type 0