What Is Communication Media? - Definition From Techopedia

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The bandwidth of the medium is shared between each connected device. For example, a home Wi-Fi network with one device would allocate 54 Mb per second to that device. The greater the number of devices connected to a network, the more important the choice of transmission medium becomes.This uses a normal telephone line to the local exchange that is monitored permanently for failures and The well-to-do more readily introduce new technologies and demand service. All this contributes to a The system that is used for domestic broadband is called ADSL (asymmetric digital subscriber...These transmission media have much more bandwidth available and can accommodate much more than just voice communications. The circuit-switched PSTN opens up a continuous connection between two phones, that begins with a dial tone and ends when the phone is hung up.Wired transmission media is media used to transfer information over a network, such as Twisted Pair cable. This is opposed to wireless transmission media which uses radio waves to transmit information. There are many types of wired transmission media such as coaxial cable, telephone...Telecommunications media, equipment and systems—metal wire, terrestrial and satellite radio, and optical fibre—employed in the transmission of Voice-grade twisted pair is used for local subscriber loops in the public switched telephone network, and flexible coaxial cable is commonly used for...

Telephone Line - an overview | ScienceDirect Topics

This is the Multiples Choice Questions Part 2 of the Series in Transmission Fundamentals as one of the Communications Engineering topic. MCQ in Signal and Noise Fundamentals. Continue Practice Exam Test Questions Part 2 of the Series. 51. If the grade of service of a telephone system indicated...One wire is used for transmission of the information. However, the end user may own the transmission facility (rather than lease it) such that it is exclusive to that user. This section talks about bandwidth and about where the various transmission media lie within the electromagnetic...Mass Media comprises a wide range of media technologies to disseminate or reach over a larger audience through mass communication. With the aim "driving home a message" transit media is significantly used for massive brand promotion to millions of people who travel the country's streets...For unguided media, transmission and reception are achieved by means of an antenna. For transmission, the antenna radiates electromagnetic energy into the medium (usually air), and for reception, the antenna picks up electromagnetic radiation waves from the surrounding medium.

How the Public Switched Telephone Network Works

Signals are usually transmitted over some transmission media that are broadly classified in to two categories.Guided Media:These are those that provide a conduit from one device to another that include twiste. 7 Answers are available for this question.Mass media is generally believed to influence people. But what is the media? And how it influences our minds? Mass media refers to communication devices, which can be used to communicate with a large number of people in different languages and influence what they do or think.Transmission media is a pathway that carries the information from sender to receiver. We use different types of cables or waves to transmit data. Data is transmitted normally through electrical or electromagnetic signals. An electrical signal is in the form of current. An electromagnetic signal is...What is Transmission Media? Definition: A communication channel that is used to carry the data from the transmitter to the receiver through the electromagnetic signals. The core is enclosed with less thick plastic or glass and it is known as the cladding, used for large volume data transmission.Transmission media used can be wired or wireless. In wired transmission, cables are used for transferring signals whereas in wireless transmission, electromagnetic waves are used to transmit data from one device CAT1 cables are used in telephone lines with small data rate whereas CAT6.

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Analog and Digital Transmission

There are a number of differences between analog and digital transmission, and it is important to understand how conversions between analog and digital occur. Let's look first at the older form of transmission, analog.

Analog Transmission

An analog wave form (or signal) is characterized by being continuously variable along amplitude and frequency. In the case of telephony, for instance, when you speak into a handset, there are changes in the air pressure around your mouth. Those changes in air pressure fall onto the handset, where they are amplified and then converted into current, or voltage fluctuations. Those fluctuations in current are an analog of the actual voice pattern—hence the use of the term analog to describe these signals (see Figure 2.9).

Figure 2.9 Analog transmission

When it comes to an analog circuit—what we also refer to as a voice-grade line—we need to also define the frequency band in which it operates. The human voice, for example, can typically generate frequencies from 100Hz to 10,000Hz, for a bandwidth of 9,900Hz. But the ear does not require a vast range of frequencies to elicit meaning from ordinary speech; the vast majority of sounds we make that constitute intelligible speech fall between 250Hz and 3,400Hz. So, the phone company typically allotted a total bandwidth of 4,000Hz for voice transmission. Remember that the total frequency spectrum of twisted-pair is 1MHz. To provision a voice-grade analog circuit, bandwidth-limiting filters are put on that circuit to filter out all frequencies above 4,000Hz. That's why analog circuits can conduct only fairly low-speed data communications. The maximum data rate over an analog facility is 33.6Kbps when there are analog loops at either end.

elicit meaning from ordinary speech; the vast majority of sounds we make that constitute intelligible speech fall between 250Hz and 3,400Hz. So, the phone company typically allotted a total bandwidth of 4,000Hz for voice transmission. Remember that the total frequency spectrum of twisted-pair is 1MHz. To provision a voice-grade analog circuit, bandwidth-limiting filters are put on that circuit to filter out all frequencies above 4,000Hz. That's why analog circuits can conduct only fairly low-speed data communications. The maximum data rate over an analog facility is 33.6Kbps when there are analog loops at either end.

How 56Kbps Modems Break the 33.6Kbps Barrier

With 56Kbps modems, only one end of the loop can be analog. The other end of the connection has to be digital. So, in other words, if you're using a 56Kbps modem to access your Internet service provider (ISP), you have an analog connection from your home to the local exchange. But the ISP has a digital subscriber line (DSL) or a digital termination facility from its location to its exchange.

Analog facilities have limited bandwidth, which means they cannot support high-speed data. Another characteristic of analog is that noise is accumulated as the signal traverses the network. As the signal moves across the distance, it loses power and becomes impaired by factors such as moisture in the cable, dirt on a contact, and critters chewing on the cable somewhere in the network. By the time the signal arrives at the amplifier, it is not only attenuated, it is also impaired and noisy. One of the problems with a basic amplifier is that it is a dumb device. All it knows how to do is to add power, so it takes a weak and impaired signal, adds power to it, and brings it back up to its original power level. But along with an increased signal, the amplifier passes along an increased noise level. So in an analog network, each time a signal goes through an amplifier, it accumulates noise. After you mix together coffee and cream, you can no longer separate them. The same concept applies in analog networks: After you mix the signal and the noise, you can no longer separate the two, and, as a result, you end up with very high error rates.

Digital Transmission

Digital transmission is quite different from analog transmission. For one thing, the signal is much simpler. Rather than being a continuously variable wave form, it is a series of discrete pulses, representing one bits and zero bits (see Figure 2.10). Each computer uses a coding scheme that defines what combinations of ones and zeros constitute all the characters in a character set (that is, lowercase letters, uppercase letters, punctuation marks, digits, keyboard control functions).

Figure 2.10 Digital transmission

How the ones and zeros are physically carried through the network depends on whether the network is electrical or optical. In electrical networks, one bits are represented as high voltage, and zero bits are represented as null, or low voltage. In optical networks, one bits are represented by the presence of light, and zero bits are represented by the absence of light. The ones and zeros—the on/off conditions—are carried through the network, and the receiving device repackages the ones and zeros to determine what character is being represented. Because a digital signal is easier to reproduce than an analog signal, we can treat it with a little less care in the network. Rather than use dumb amplifiers, digital networks use regenerative repeaters, also referred to as signal regenerators. As a strong, clean, digital pulse travels over a distance, it loses power, similar to an analog signal. The digital pulse, like an analog signal, is eroded by impairments in the network. But the weakened and impaired signal enters the regenerative repeater, where the repeater examines the signal to determine what was supposed to be a one and what was supposed to be a zero. The repeater regenerates a new signal to pass on to the next point in the network, in essence eliminating noise and thus vastly improving the error rate.

Analog Versus Digital Transmission

Table 2.1 summarizes the characteristics of analog and digital networks.

Table 2.1 Characteristics of Analog and Digital Networks

Feature

Analog Characteristics

Digital Characteristics

Signal

Continuously variable, in both amplitude and frequency

Discrete signal, represented as either changes in voltage or changes in light levels

Traffic measurement

Hz (for example, a telephone channel is 4KHz)

Bits per second (for example, a T-1 line carries 1.544Mbps, and an E-1 line transports 2.048Mbps)

Bandwidth

Low bandwidth (4KHz), which means low data transmission rates (up to 33.6Kbps) because of limited channel bandwidth

High bandwidth that can support high-speed data and emerging applications that involve video and multimedia

Network capacity

Low; one conversation per telephone channel

High; multiplexers enable multiple conversations to share a communications channel and hence to achieve greater transmission efficiencies

Network manageability

Poor; a lot of labor is needed for network maintenance and control because dumb analog devices do not provide management information streams that allow the device to be remotely managed

Good; smart devices produce alerts, alarms, traffic statistics, and performance measurements, and technicians at a network control center (NCC) or network operations center (NOC) can remotely monitor and manage the various network elements

Power requirement

High because the signal contains a wide range of frequencies and amplitudes

Low because only two discrete signals—the one and the zero—need to be transmitted

Security

Poor; when you tap into an analog circuit, you hear the voice stream in its native form, and it is difficult to detect an intrusion

Good; encryption can be used

Error rates

High; 10–5 bits (that is, 1 in 100,000 bits) is guaranteed to have an error

Low; with twisted-pair, 10–7 (that, is 1 in 10 million bits per second) will have an error, with satellite, 10–9 (that is, 1 in 1 billion per second) will have an error, and with fiber, 10–11 (that is only 1 in 10 trillion bits per second) will have an error

Conversion: Codecs and Modems

The fact is that today we don't have all-digital or all-analog networks; we have a mix of the two. Therefore, at various points in a network, it is necessary to convert between the two signal types. The devices that handle these conversions are codecs and modems (see Figure 2.11).

Figure 2.11 Codecs and modems

A codec (which is a contraction of coder-decoder) converts analog signals into digital signals. There are different codecs for different purposes. For the PSTN, for example, there are codecs that minimize the number of bits per second required to carry voice digitally through the PSTN. In cellular networks, because of the constraints and available spectrum, a codec needs to compress the voice further, to get the most efficient use of the spectrum. Codecs applied to video communication also require very specific compression techniques to be able to move those high-bandwidth signals over what may be somewhat limited channels today.

A modem (which is a contraction of modulator-demodulator) is used to infuse digital data onto transmission facilities. Some modems are designed specifically to work with analog voice-grade lines. There are also modems that are designed to work specifically with digital facilities (for example, ISDN modems, ADSL modems). A modem manipulates the variables of the electromagnetic wave to differentiate between the ones and zeros.

Although it is possible to convert between analog and digital networks, in general, conversions are a weak link in a network. A conversion is a point at which network troubles can occur, an opportunity for errors and distortions to be introduced. Therefore, ideally, we want to move toward an end-to-end digital and end-to-end optical environment. This means that nowhere between the transmitter and the receiver do signal conversions need to be done.