data communications and networking cscs 311 lecture 7

Data Communications and NetworkingCSCS 311

Lecture 7

Lecture Focus:

Data Communications and Networking

Basic Concepts

Lecture 7

Data Communications and NetworkingForms of Data Transmission

There are two forms of data transmission:

1. Analog data transmission (Based upon Analog Signals)

2. Digital data transmission (Based upon Digital Signals)


ANALOG SIGNALS

Analog data transmission is the transmission of data in a continuous wave form. The public dial-up service supports analog signals. Analog signals are encountered by us every day of our life. Speech is an analog signal, and varies in amplitude (volume), frequency (pitch), and phase.


ANALOG SIGNALS

AMPLITUDEThis is the strength of the signal. It can be expressed a number of as volts. The higher the amplitude, the stronger (louder) the signal.

The decibel is a popular measure of signal strength. It has been discovered that sounds greater than 90db for a period exceeding 15 minutes causes permanent damage to hearing.

Our ability to hear high notes is affected. Speech is a very complex signal, and contains many thousands of different combinations of signals all mixed together.


ANALOG SIGNALS

The measurement of the two extremes is called the peak to peak measurement.


ANALOG SIGNALS


ANALOG SIGNALS

FREQUENCYThis is the rate of change of the signal in every second, expressed in Hertz (Hz), or cycles per second.

A cycle is one complete movement of the wave, from its original start position and back to the same point again.

The number of cycles (or waves) within a one second time interval is called cycles-per-second, or Hertz.

Humans can hear from reasonably low frequency tones about 100Hz to about 12KHz.


ANALOG SIGNALS

FREQUENCY


ANALOG SIGNALS

PHASE

This is the rate at which the signal changes its relationship to time. One complete cycle of a wave begins at a certain point, and continues till the same point is reached again.

Phase shift occurs when the cycle does not complete, and a new cycle begins before the previous one has fully completed.

The human ear is insensitive to phase shift, but data signals are severely affected by it. Phase shift is caused by imperfections in cable media, such as joins and imperfect terminations.


ANALOG SIGNALS

PHASE


DIGITAL SIGNALS

Digital data system is the transmission of data using distinct “on “ and “off” electrical states. These two states are represented by a 1 for “on “ and 0 for “off”.

Digital signals are the language of modern day computers. Digital signals comprise only two states. These are expressed as ON or OFF, 1 or 0 respectively.


DIGITAL SIGNALS


DATA TRANSMISSION TECHNIQUES

The process of converting digital pulses to an analog signal is called “MODULATION”.

The process of re-converting an analog signal to digital pluses is called “DEMODULATION”.


DATA TRANSMISSION TECHNIQUES

Modulation and Demodulation is done by a single device called MODEM.

Modem (modulator/demodulator) changes digital data signals to an analog frequency and allows transmission across an analog link. At the other end, another modem receives the signal and converts it back to digital.

The connections provided by telephone companies for the use of speech via dial up telephones is analog based.


DATA TRANSMISSION METHODS

In Asynchronous Transmission, one character is transmitted at a time. Start bits and stop bits control the transfer of data.

Asynchronous transmission is Serial and often used to low speed transmission of data, each character is packaged in an envelope, and sent across a single wire, bit by bit, to a receiver.

In Synchronous Transmission, block of characters are transmitted in timed sequences. The receiving device accepts data until it detects a special ending character. It is used when data transfer requirement exceed severalthousand bits per second.


DATA TRANSMISSION RATE

The speed at which data travel over a communication channel is called the communication rate. It is also known as the transmission speed.

The rate at which the data are transferred is the baud rate.

Baud rate is the number of bits per second that the signals being transmitted changes (modulation/demodulation).


COMMUNICATION CHANNEL BANDWIDTH

The bandwidth of a communication channel determines the rate or speed that data can be transmitted over a channel.

The term “bandwidth “ is often shortened to “band”.

The bandwidth of a cable is the difference between the highest and lowest frequencies that are carried over that cable.

For example the lowest frequency of telephone line is (300 Hz) and highest frequency is (3300 Hz). Its bandwidth is 3300-300=3000 HZ.



NARROW BANDThe narrow band channel is used where data volumes are relatively low and which transmit data at a rate between 40 to 100 bits per second (bps). Telegraph lines are an exampleof narrow band channels with slow transmission rate.

VOICE BANDThe voice band channels are able to speed up the transmission rate between 110 to 9600 bits per second. Telephone lines are an example of voice band channels.



BROAD BANDBroadband channels are used where data volumes are large and which transmit data at rate upped several megabits per second.

Broadband systems use analog signaling and a range of frequencies (300 MHZ to 450 MHZ).

With analog transmission, the signals are continuous and non discrete. Signal flows is unidirectional.

Microwaves, coaxial cables and communication satellites are examples of broadband channels, television cabling and telephone lines.



BASE BANDBase band systems use digital signaling over a single frequency.

Signals flow in the form of discrete pulses of electricity or light.

The digital signal uses the complete bandwidth of the cable. Each device on a base band network transmits bi-directional, and some can transmit and receive at the same time.

Examples are coaxial cable with 50-ohm and Fiber optics.


CHANNEL ORGANIZATION

In PARALLEL, each bit uses a separate wire. If there is eightbits sent at a time, this will require 8 wires, one for each data bit.

To transfer data on a parallel link, a separate line is used as a clock signal. This serves to inform the receiver when data is available.

In SERIAL, each bit is sent over a single wire, one after the one.


CHANNEL ORGANIZATION


TRANSMISSION MEDIA

The transmission media is the path between the transmitter and the receiver in a data transmission system.

A transmission medium can be defined as anything that can carry information from a source to a destination.

For example, the transmission medium for two people having a dinner conversation is the air.

For a written message, the transmission medium might be a mail carrier, a truck, or an airplane.


TRANSMISSION MEDIA

The transmission medium is usually free space, metallic cable, orfiber-optic cable.

The information is usually a signal that is the result of a conversionof data from another form.

The use of long-distance communication using electric signals started with the invention of the telegraph by Morse in the 19th century.

Communication by telegraph was slow and dependent on a metallicmedium.

Self study


TRANSMISSION MEDIA

Self study

Extending the range of the human voice became possible when the telephone was invented in 1869. Telephone communication at that time also needed a metallic medium to carry the electric signals that were the result of a conversion from the human voice.

Communication was, however, unreliable due to the poor quality of the wires. Lines were often noisy and the technology was unsophisticated.

Wireless communication started in 1895 when Hertz was able to send High frequency signals. Later, Marconi devised a method to send telegraph-type messages over the Atlantic Ocean.


TRANSMISSION MEDIA

Self study

We have come a long way. Better metallic media have been invented (twisted pair and coaxial cables, for example).

The use of optical fibers has increased the data rate incredibly.

Free space (air, vacuum, and water) is used more efficiently.


TRANSMISSION MEDIA

Self study

Computers and other telecommunication devices use signals to represent data. These signals are transmitted from one device to another in the form of electromagnetic energy, which is propagated through transmission media.

Electromagnetic energy, a combination of electric and magnetic fields, includes power, radio waves, infrared light, visible light, Ultraviolet light, and X, gamma, and cosmic rays.


TRANSMISSION MEDIA

Transmission media are actually located below the physical layer and are directly controlled by the physical layer. You could say that transmission media belong to layer zero.


TRANSMISSION MEDIA

Transmission media is commonly classified as:

1. BOUNDED or GUIDED 2. UNBOUNDED or UNGUIDED.


TRANSMISSION MEDIA

BOUNDED or GUIDED In Bounded or Guided media such as cable systems, the signal travels inside a physical conductor.

A signal traveling along any of these media is directed and contained by the physical limits of the medium.


TRANSMISSION MEDIA

UNBOUNDED or UNGUIDED.In Unbounded or Unguided media such as cable less systems, the signal is usually transmitted through air (free space).


TRANSMISSION MEDIA


TRANSMISSION MEDIA

CABLE MEDIACable is the medium through which information usually moves from one network device to another. There are several types of cable which are commonly used in networking.

In some cases, a network utilizes only one type of cable, but can use a variety of cable types also. The type of cable chosen for a network is related to the network's topology, protocol, and size.

Understanding the characteristics of different types of cable and how they relate to other aspects of a network is necessary for the development of a successful network.


TRANSMISSION MEDIA

TYPES OF CABLESCoaxial CableTwisted Pair CableFiber Optic Cable

Three primary types of physical media


TRANSMISSION MEDIA

Twisted-pair and coaxial cable use metallic (copper) conductors that accept and transport signals in the form of electric current.

Optical fiber is a cable that accepts and transports signals in the form of light.

Transmission rates supported on each of these physical media are measured in millions of bits per second (Mbps).


Coaxial (coax) Cable

Coaxial, or coax, cable looks like the cable used to bring the cable TV signal to your television. One strand (a solid-core wire) runs down the middle of the cable. Around that strand is insulation. Covering that insulation is braided wire and metal foil, which shield

against electromagnetic interference. A final layer of insulation covers the braided wire.



Coaxial cable is resistant to the interference and signal weakening that other cabling, such as unshielded twisted-pair (UTP) cable, can experience.

Coaxial cable carries signals of higher frequency ranges than those in twisted pair cable.

In general, coax is better than UTP cable at connecting longer distances and for reliably supporting higher data rates with less sophisticated equipment.



Instead of having two wires, coax has a central core conductor of solid or stranded wire (usually copper) enclosed in an insulating sheath, which is, in turn, encased in an outer conductor of metal foil, braid, or a combination of the two.

The outer metallic wrapping serves both as a shield against noise and as the second conductor, which completes the circuit.

This outer conductor is also enclosed in an insulating sheath, and the whole cable is protected by a plastic cover.

Self study



Just because TV cable is coax does not mean it will work with computer networks. Network coaxial cable has very specific requirements, such as gauge, impedance, and attenuation.

Self study



Coaxial cables are categorized by their radio government (RG) ratings.

Each RG number denotes a unique set of physical specifications, including the wire gauge of the inner conductor, the thickness and type of the inner insulator, the construction of the shield, and the size and type of the outer casing.

Each cable defined by an RG rating is adapted for a specialized function.

Coaxial Cable Standards / Categories



Coaxial Cable Standards / Categories

Category Impedance UseRG-59RG-59 75 Cable TVRG-58RG-58 50 Thin EthernetRG-11RG-11 50 Thick Ethernet



To connect coaxial cable to devices, we need coaxial connectors. The most commontype of connector used today is the Bayone-Neill-Concelman (BNC), connector.

Coaxial Cable Connectors



Performance

The attenuation is much higher in coaxial cables than in twisted-pair cable.

Although coaxial cable has a much higher bandwidth, the signal weakens rapidly and requires the frequent use of repeaters.



Applications

Coaxial cable was widely used in analog telephone networks where a single coaxial network could carry 10,000 voice signals.

Later it was used in digital telephone networks where a single coaxial cable could carry digital data up to 600 Mbps.

However, coaxial cable in telephone networks has largely been replaced today with fiber-optic cable.

Cable TV networks also use coaxial cables. In the traditional cable TV network, the entire network used coaxial cable.



Applications

Later, however, cable TV providers replaced most of the media with fiber-optic cable; hybrid networks use coaxial cable only at the network boundaries, near the consumer premises.

Cable TV uses RG-59 coaxial cable.

Another common application of coaxial cable is in traditional Ethernet LANs. Because of its high bandwidth, and consequently high data rate, coaxial cable was chosen for digital transmission in early Ethernet LANs.



Applications

The 10Base-2, or Thin Ethernet, uses RG-58 coaxial cable with BNC connectors to transmit data at 10 Mbps with a range of 185 m.

The 10Base5, or Thick Ethernet, uses RG-11 (thick coaxial cable) to transmit 10 Mbps with a range of 5000 m. Thick Ethernet has specialized connectors.

An adapter card provides connections to external devices called peripherals


Adapter Cards (expansion card)

An opening, or socket, on the motherboard that can hold an adapter card.With Plug and Play, the computer automatically configures cards and otherdevices as you install them

Expansion Slots

Types of Adapter Cards


Ports and Connectors Port connects external devices to system unit Connector joins cable to peripheral


What is a serial port?

Transmits one bit of data at a time Connects slow-speed devices,

such as mouse, keyboard, modem

Ports and Connectors


Connects devices that can transfer more than one bit at a time, such as a printer

What is a parallel port?

Ports and Connectors



Assignment

What do you mean the following?a) RG b) Ethernet c) Impedance

Marks: 5 Document: MS-WordCheating case(s): -5 marks Deadline: Very next same

daySubmission: Through email Address: ahzahid

@yahoo.com

Extra credit:1) Honesty 2) Effort 3) Excellent material and description4) Help from books and internet, but description in own words

Due Date: Date Assigned:

mailto:[email protected]

mailto:[email protected]

data communications and networking cscs 311 lecture 7

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