Digital T-Carriers and Multiplexing

Group Reporters:Bugayong, laurens Luis L.

Ramos, Romel R.Costiniano, Mariela

Garcia, GeraldAlarcon, Mariel Klaudine V.

Introduction

Multiplexing.

• Sometimes contracted to MUXING.

• is a method by which multiple analog message signals or digital data streams are combined into one signal over a shared medium.

• DEVICES THAT ARE USE FOR MULTIPLEXING:– Multiplexer (MUX), a device that perform a

multiplexing

– Demultiplexer (DEMUX), A device that perform the reverse function of the Multiplier.

Types of Multiplexing.

• Space Division Multiplexing

• Phase Division Multiplexing

• Time Division Multiplexing

• Frequency Division Multiplexing

• Wavelength Division Multiplexing

• Others..– Polarization Division Multiplexing

– Orbital Angular Momentum Multiplexing

– Code Division Multiplexing

Space Division Multiplexing.

• It implies different point-to-point wires for different channels.

Examples:

Phase Division Multiplexing

• It is a technique which allows two DSBSC (Double Sideband Suppressed carriers) channels sharing a common suppressed carrier to occupy the same spectrum space.

Frequency Division Multiplexing

• Frequency-division multiplexing (FDM) is inherently an analog technology. FDM achieves the combining of several signals into one medium by sending signals in several distinct frequency ranges over a single medium.

Wavelength Division Multiplexing

• Is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i.e., colors) of laser light. This technique enables bidirectional communications over one strand of fiber, as well as multiplication of capacity.

Time Division Multiplexing

• technology which uses time, instead of space or frequency, to separate the different data streams.

T1 Digital Carrier

T1 Digital Carrier

• 24 channels

• Sampled 800 times/second

• 1/24 total frame time

• 64 KBps

• 192 Bits per frame

• 1.536 Mbps

• Then later when an additional bits called the FRAMING BIT added to each frame now it became 1.544 Mbps

Channel Banks.

• A channel bank is a device that converts analog signals into digital signals to be carried over higher-speed lines between the central office and other exchanges. The analog signal is converted into a digital signal that transmits at a rate of 64 thousand bits per second ( Kbps ). This 64 Kbps signal is a standard known as a DS0 signal. The signal is multiplexed with other DS0 signals on the same line using time-division multiplexing ( TDM ) . Usually, the digital information is put on each DS0 signal using pulse code modulation ( PCM ).

Formats:

• Superframe TDM formats

• Extended Superframe Formats

Extended Superframes

• It not only provide frame synchronization but also error detection and a datachannel, all using the framing bit.

• The value in every 193 bits (in bits 193, 386 & so on) are used for three purpose:1. Every 4th bit of this 24 bit cycle (i.e. the framing bits for frames 4,8,12,16,20 and

24) goes through the pattern 001011.This provide frame synchronization.2. The framing bits for frames 2,6,10,……22 are used to send a 6 bit CRC,

generated from the data in previous 24 frames. This provide “Errordetection”.

3. The Channel Service Units (CSU) can then track the error rate and generate analarm if it gets too high. This error checking is done constantly while the links isin service and for any type of data.

4. The remaining framing bits(for frames 1,3,5,7,….,23) provide a 4 kbpssupervisory data channel that is used for other functions such as remoteconfiguration and monitoring of CSU.

5. The 8th bit in every channel of frames 6,12,18 & 24 is used for signalingbetween central offices.

Fractional T-Carrier Series.

• A Fractional T-carrier is one or more channels bundledtogether and sold to a customer as a set. However less thanthe full set of 24 channels is available to the customer.

• This allows a customer to purchase less than a full T1’s BWat lower cost.

• The individual channels can be voice or data and aCSU/DSU is used to split the channels.

• The fractional T-carrier emerged because standard T1carriers provide a higher capacity (higher bit rate) thanmost users require.

• It distributes the channels (i.e bits) in a standard T1 systemamong more than one user, allowing several subscribers toshare one T1 line.

• Bit rates offered with fractional T1-carriersystem are 64 kbps(1-channel), 128 kbps(2-channels), 256 kbps(4-channels), 384 kbps(6-channels),512kbps(8-channels) and 768kbps(12-channels) with 384 kbps(1/4T1) and(1/2T1) being the most common.

• The minimum required data rate required topropagate video information is 384 kbps.

Digital Signal Service• Telephone companies implement TDM through a hierarchy of digital

signal, known as Digital Signal (DS) service.

DS Line Rate(Mbps) Voice Channels

Services

DS-0 (Single Digital Channel)

T-1

64Kbps 1 Voice & Data

DS-1 T-1 1.544 24 DS-0 Voice & Data

DS-2 T-2 6.312 4 DS-196 DS-0

Voice or Data, Picture Phone

DS-3 T-3 44.736 7 DS-2 or 28 DS-1 or 672DS-0

Voice or Data, Picture Phone, Broadcast

DS-4 T-4 274.176 4032 DS-0 Voice or Data, Picture Phone, Broadcast

DS-5 T-5 560.160 8064 Voice or Data, Picture Phone, Broadcast

TDM Hierarchy

4.25

MASTER GROUP &

COMMERCIAL TELEVISION

• The master group terminal receives voice band

channels which are multiplexed using FDM.

• The signal processor, shifts the master group signals

frequencies, from a 564 KHz to 3084 KHz bandwidth

to a 0 KHz to 2520 KHz BW.

• DC restoration is also provided to TV signals.

• The master group band is sampled at 5.1 MHz rate

& for commercial TV signal sampling rate is 10.2

MHz, i.e twice of master group rate.

4.26

Block Diagram of Master group & Commercial TV Digital Terminal

4.27

Signal Process

or

Encoder(9-bit)

Sampler

Signal Process

or &

Sampler

Digital Process

or

TV Cahnnel

Master GrouporTV Signal

Digital Process

or

Framer

PAM Signa

l

12

9

T-3 Signal

T3 Signal

o/p

(46 Mbps)

Channel

for TV

(46 Mbps)

Decoder

(9-bit)

2

9

1Recovered Master Group

Or

TV Signal

• A 9-bit PCM code is used to digitize each sample of the master

group or television signal.

• The output of digital processor is approx 46 Mbps for master

group and 92 Mbps for TV signal.

As there is no 92 Mbps line speed in the digital hierarchy, the

92 Mbps digital output must be split into two 46 Mbps signals

for TV terminal.

The digital terminal has three main functions:

1. Conversion of the parallel data from the output of the

encoder to the serial data.

2. Frame synchronizing bits are inserted.

3. It converts the serial binary signal to form more suitable for

transmission.

4.28

Picture Phone Terminal

1. Used to transmit the low quality video signals for the

use of non dedicated subscribers.

2. This picture phone signal is encoded into T2 capacity

of 6.312 Mbps, which is less than that for commercial

network broadcast signals.

3. Thus, reduced cost and affordability are achieved.

4. It allows adequate details and contrast resolution to

satisfy the average picture phone subscriber.

5. Picture phone service is ideally suited to a DPCM.

4.29

DATA TERMINAL

• These are designed to transmit the signals other than voice.

• In most of the cases, the data rate generated by each individual

subscriber are substantially less than the data rate capacities of

digital lines.

• Therefore, it seems only logical that terminals be designed that

transmit data signal from several sources over the same digital

line.

• Data coding method is more efficient & it codes the

transition time . The coding format is as follows:

1. It uses 3 bit code to indentify when transition occurs on the

data and whether the transition is from ‘1’ to ‘0’ or vice versa.

First bit is referred as “Address bit”.

Second bit indicate “Transition bit”

Third bit indicate “Direction of transition or sign bit”4.30