Telecommunications Circuits, Channels, and Bandwidth

Circuits

A circuit is a communication path between two points, set as transmitter (TX) and receiver (RX).

Lines

A line is the local link connection that interconnects the telephone with the user terminal equipment.

Channels

An UNCA channel is a simple, logical connection for end communication. The channel may transmit voice and data signals.

Networks

A network is a set of interconnected telecommunications elements, properly working in coordination to make the transfer from the TX to the RX.

Dedicated Circuits

Dedicated circuits are unique physical circuits for a specific function, connected throughout a network.

Virtual Circuits

Virtual circuits are logical and physically independent circuits. The circuits are connected to perform physical transmission through multichannel, high-speed systems, such as optical fiber.

Bandwidth

Bandwidth is the measure of a circuit’s ability to transmit channel information.

Bandwidth of a Channel

The bandwidth of a channel is the range of frequencies that the channel can transmit with reasonable quality.

AW (Signal Bandwidth)

AW is the signal frequency range that contains the greatest signal strength.

Broadband

Broadband is a transmission technique in which one or more data signals can be simultaneously transmitted by the same means.

Hz (Hertz)

Hz is the frequency unit used in measuring the bandwidth of analog circuits, representing the number of transmission waves (N).

Period

Period is the time required for a signal event to take office or to develop a full course.

Frequency

Frequency represents the number of decibels or periods of a signal per unit of time.

Radio Electric Spectrum

The radio electric spectrum is the frequency range of all components that allow the propagation of electromagnetic waves.

Baud

Baud rate indicates the number of signal units per second necessary to represent the bits.

Bits per Second

Bits per second is a measure of bandwidth on digital systems and refers to the number of binary data units.

Narrow Bandwidth

Narrow bandwidth is one whose capacity is that of a single channel of 64k or less.

Wideband

Wideband examples:

  • T1 = 1.544M
  • E1 = 2.048M
  • T3 = 44.736M

Transmission Codes

Transmission codes include internal codes and interface codes.

Transmission System

A transmission system is a set of equipment parts and components, properly organized and structured to allow information transfer.

Transmission Stages

Transmission stages include the source, input transducer, transmitter, receiver, noise, output transducer, destination, and sink.

Line Codes

Line codes are techniques used to represent analog signals into sequences of bits and transmit power through a digital transmission system.

Internal Codes

Internal codes are those codes that are used internally in the entire digital transmission team, such as ADI, RZ, and NRZ.

Unipolar NRZ Code

Unipolar NRZ (Non-Return to Zero) code is binary and is provided by the encoder logic circuits so that any type of digital signal has NRZ, occupying each pulse or all of the time interval.

Cons of NRZ

The NRZ signal introduces a DC component in the transmission line, which prevents the use of coupling transformers required in regenerative circuits that are in the transmission line.

NRZ Polar Code

NRZ Polar code is a variant of unipolar NRZ code. The difference is that this signal makes the transmission link more efficient in terms of power, encoding binary data.

RZ Unipolar Code

In RZ (Return to Zero) unipolar code, the binary signal is reduced to half the allotted time interval for b1.

ADI Code

ADI (Alternate Digit Inversion) code is a unipolar NRZ code whose encoding is performed by inverting every other bit.

Interface Codes

Interface codes are those that are linked with two elements constituting a system of digital transmission. These are coded according to a signal pattern to be transmitted through a line, known as Line Coding (Bipolar RZ, AMI, mBnB, WCC).

IMC Code

In IMC (Inverted Mark Code), the signal level 0 is represented by a voltage or current with no signal.

mBnB Code

mBnB code is a binary code widely used in the transmission of fiber optics (FO). Versions include 5B60 (34M) and 7B8B (140M). In this code, it is necessary to enforce the inequality n > m, so that the mBnB encoder can be written with a sequential machine that transforms a word of m bits into another n-bit word.

Advantages of mBnB

  • Removal of long sequences of consecutive identical bits
  • Smooth operation of the light source
  • Possibility of recognition errors in line

Ternary Interface Codes

Ternary interface codes include Bipolar RZ, AMI, and HDB-3.

Bipolar RZ Code

Bipolar RZ code is a variation of RZ. The difference lies in having a pulse train with bit 1 alternating in position, sometimes positive and sometimes negative, thereby reducing the problem of the development of DC components.

Benefits of Bipolar RZ

This code reduces both the power required to carry the signal and the DC level, even though the latter remains.

Disadvantage of Bipolar RZ

For the same transmission signals, it requires increased AW, which should be twice as large.

AMI Code

AMI (Alternate Mark Inversion) code has two forms: AMI 1:1 and AMI 1:2. AMI 1:1 is from NRZ, and AMI 1:2 is from RZ. These codes assign alternation of values +v and -v to represent bit 1.

HDB-3 Code

HDB-3 (High-Density Bipolar of order 3) code is one of the most widely used codes. It is a high-density bipolar code with sequences of three zeros, meaning that this code avoids the succession of more than three 0 bits. AMI 1:2 is a modified code used in multiplexers at 2, 8, and 34 Mbps, mainly for cable transmission.