US6852-V8-B EDITION 1
6852
NZQA LEVEL 4 | CREDIT 4 | VERSION 8
STUDENT NAME
STUDENT ID NUMBER

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Produced by Intueri Services Ltd, trading as Learntree
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13 | 01 | 2015
First edition January 2015
Written by Blair Woods
Edited by Virginia McClennan

OUTCOME 1 Describe past, current and emerging developments in data communications.
Range Signal characteristics, components, standards, protocols, media; a minimum of two past, current and emerging developments are required.
PC1.1 The description explains the origin and past developments of current data communications.
PC1.2 The description provides a classifi cation for current data communications.
Range May include but is not limited to – wireless, voice, data, digital, analogue, packet switching.
PC1.3 The description identifi es and projects trends from emerging developments in data communications.
Range A minimum of two trends.
OUTCOME 2 Describe synchronous and asynchronous data communications.
Range Physical interface, modes of operation.
PC2.1 The description outlines the characteristics of synchronous and asynchronous data communication.
Range Features, functions, standards, protocols.
PC2.2 The description explains the features of data communications equipment with respect to synchronous and asynchronous data communications.
Range Modem, network terminating unit, transmission equipment.
NZQA UNIT STANDARD
6852
Describe data communications
Level 4, Credits 4, Version 8
Learntree
31 Tongariro Street
Paraparaumu 5032
New Zealand
Phone: (04) 902 6742
Freephone: 0800 532 765
E-mail: publishing@learntree.co.nz
Web: www.learntree.co.nz
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1. The assessment context for this unit standard must be suitable to meet the criteria for level 4 in the NZQF
Level Descriptors, which are available by searching for
“level descriptors” at www.nzqa.govt.nz.
2. Legislation and guidelines relevant to this unit standard may include but are not limited to the:
ACC5637 Guidelines for Using Computers - preventing and managing discomfort, pain and injury. Accident
Compensation Corporation: Department of Labour
2010;
Copyright Act 1994;
Copyright (New Technologies) Amendment Act 2008;
Privacy Act 1993;
Unsolicited Electronic Messages Act 2007; and any subsequent amendments.
3. An assessment resource to support computing unit standards (levels 1 to 4) can be found on the NZQA website at www.nzqa.govt.nz/asm.
© Intueri Services Ltd, trading as Learntree 6852v8 Describe data communications

Welcome to the workbook for Unit Standard 6852. This workbook will help you to develop your knowledge of data communications. This workbook will also provide you with the knowledge that you require to complete the assessment for Unit Standard 6852. By successfully completing the assessment for Unit Standard 6852 you will be deemed competent in being able to “Describe data communications”.
In fact, even if you are not planning to complete the assessment for Unit Standard 6852 this workbook is still an excellent tool for learning about the different types of data communications that are in use today.
There are exercises at the end of each chapter which allow you to practise your knowledge of the topics that were covered in each chapter. The answers for each exercise are included in the Sample Answers section at the back of this workbook. You should complete each exercise and compare your answers against the answers in the Sample Answers section.
You will get the most out of this workbook if you already have a basic understanding of the following topics:
• Using a computer to carry out basic application-related tasks,
• Using a computer to connect to the internet,
• Basic networking concepts such as LAN, WAN, cables, hubs, switches, routers, and
• Files, folders, applications and system software.
The purpose of this workbook is to provide you with a general knowledge of data communications.
We’ll look at such topics as the past, present and emerging developments in data communication as well as synchronous and asynchronous data communications.
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© Intueri Services Ltd, trading as Learntree 6852v8 Describe data communications

6852
1 ::
2 ::
In the beginning - A history of electronic data communications ______ 1
What is Electronic Data communications? ___ 2
Where did it all begin? __________________ 4
Wired data communications _________ 15
The OSI (Open System Communication) model ______________________________ 16
Classifying data communications _________ 18
Baud rates & bps _____________________ 19
Wired data communications _____________ 21
EIA/TIA 568 Standard _________________ 27
Connections & Terminations _____________ 29
Common data communication protocols ___ 32
Internet Protocol _____________________ 32
Media ______________________________ 36
Data Compression ____________________ 38
Data Encryption Turning it into code _____ 39
Types of wired communications __________ 41
Dialup internet _______________________ 45
6852v8 Describe data communications © Intueri Services Ltd, trading as Learntree

3 :: Wireless & emerging data communication technologies ________ 55
Wireless solutions _____________________ 56
Wireless broadband ___________________ 56
Wi-Fi (IEEE 802.11) ___________________ 58
Bluetooth ___________________________ 62
Infrared _____________________________ 64
Mobile & cellular data communications ____ 66
Emerging trends ______________________ 69
Synchronous vs. Asynchronous data communications ______________________ 71
Protocols and standards ________________ 75
Sample Answers ___________________ 79
Index __________________________ 90
© Intueri Services Ltd, trading as Learntree 6852v8 Describe data communications

ONE
• Electronic data communications
• The history of electronic data communications
• The electric telegraph
• The modem
• The OSI model
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What is data?
For this Workbook you can think of data as the information that is sent during communication.
This might be a fi le, some text, a message or other types of information.
Data
At its simplest level, in computing, data is either a
1 or a 0.
What is electronic communication?
Electronic communication is the transmission of electronic information and data over an electronic system using electronic devices to send, guide and receive the information.
The fi rst computer (the
sender) sends a word processing fi le to the second computer (the receiver).
Electronic data communications refers to information digitised and transferred electronically between two external sources. These sources are referred to as a sender
(the electronic device that is sending the information) and a receiver (the electronic device that is receiving the information). A sender or receiver can be any electronic device that is capable of transmitting and/or receiving digital electronic signals. This could be a television, fax machine or a personal computer. In fact, there might even be more than one receiver – there might even be hundreds of receivers. For example, the sender might send the same data to multiple recipients.
Electronic signals can be transmitted over a range of distances, from almost touching (e.g. a wireless headset using Bluetooth) to into space (e.g. images broadcast from a probe sent to a distant planet).
Electronic data communications doesn’t just require special electronic devices able to send and receive electronic signals, the way these signals are sent, received and interpreted also require rules. These are called protocols and we’ll be looking at protocols later on in this workbook.
You can think of protocols as a series of rules, standards and regulations for sending and interpreting data. In order to successfully receive data the receiver of the data must meet the correct protocol/s.
This is a simple example that will help you to understand the basics of electronic data communications. Let’s assume that we have two completely different computers that are running two completely different operating systems and using completely different hardware. In this example the fi rst computer is your standard personal computer system and the second computer is a mobile device
(such as an Apple iPhone™).
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This communication doesn’t just “happen”. The receiver doesn’t just automatically receive the fi le that was sent by the sender.
There are a number of things that must happen for the receiver to successfully receive the correct data:
• There must be data to send – the sender must actually have some data to send to the receiver.
• There must be a way for the sender to connect to the receiver or send the information. In this example the sender must have the correct hardware (such as a modem, ADSL modem, local area network, wireless network or other form of communication) and the correct software to send the information.
• The sender must specify the protocol (the rules, regulations and standards) for sending and receiving the communication and the data.
• While the data is sent, the data must be intact and free from interference. If there is interference then the data might not reach the receiver or only part of the data might reach the receiver.
• The data must reach the receiver. If the receiver does not receive the data then the communication is unsuccessful” to “then the data must either be repaired or the communication is unsuccessful.
• The receiver must have a way of receiving the information.
Like the sender, the receiver must also have the correct hardware and software to receive the data that was sent by the sender.
• The receiver must be willing to receive the information.
The receiver doesn’t have to receive the data – they have a choice whether they can accept or reject the data sent by the sender.
• The receiver must understand and correctly interpret the protocols specifi ed by the sender for receiving and interpreting the data.
How the sender prepares the data that is to be sent and what the receiver does with the data once they have received it is not actually part of data communications. We are only concerned with how the data gets from the sender to the recipient. This is quite a simplistic look at electronic data communications and there are many more things that happen during the communications process. The purpose of this example was to give you an overview of how data communications work.
Receivers and
clients
In some cases you may hear the terms receivers and clients used interchangeably when talking about data communications.
Though not technically correct, the term client means the same thing as receiver – both refer to the electronic device that receives data.
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© Intueri Services Ltd, trading as Learntree
Now that you have an understanding of the concept of electronic data communications let’s have a brief look at the history of data communications. People have been exchanging information over great distances by the use of signals for thousands of years. Smoke, fi re and mirrors were used by many civilisations to communicate warnings, to ask for help or to extend invitations. The British Navy also used fl ag signals as a form of communication. We’re going to start by looking at something more recent – the telegraph.
Many people consider the telegraph to be the origin of modern data communications.
Samuel Morse was the inventor of the fi rst modern electronic telegraph. This was the fi rst device to use electrical signals to send messages. The telegraph was an important communication tool in sending messages over long distances. The telegraph could extend for many miles (right across the USA by the early 1860s and to every other continent by 1870) and was the fi rst true form of worldwide data communication.
It was primarily used by the army, law enforcement and newspapers; although any member of the public could pay to have a message (called a telegram) sent to any destination that the telegraph service reached.
Telegraph technology consisted of:
• Electro-magnetic sender/receivers at each telegraph station.
• The wires between these stations.
• The electrical current sent along the wires.
• The technology used to turn the electrical current into signals.
• The code used to make sense of the signals.
6852v8 Describe data communications

The following table shows the characteristics of the telegraph:
Characteristics The Telegraph
The signal Signals were in the form of Morse code. This is a special type of code that uses a series of short and long beeps or sounds separated by silence to represent letters and words.
For example, ‘S’ is represented by
••• (three short beeps) and ‘O’ is represented by ––– (three long beeps).
Therefore ••• ––– ••• stands for SOS, which means someone is in trouble.
Components Components refer to the hardware and any software that is required for the communication to take place. For the telegraph each sender and receiver had electronic senders/receivers at each end. The signal was transferred over a wire.
Standards and protocols
Media
For the telegraph Morse code was used.
In order for the message to be successfully interpreted at the end the sender must use the correct Morse code alphabet in the message.
In some electric telegraphs the message (a series of dots and dashes) was embossed on paper.
In 1927, at the International Telegraph Conference, a proposal was put to the conference that a standard unit of measurement of current transfer be applied to all telegraph systems. This unit was the Baud (pronounced “board”) rate.
The Baud rate, which is still in use today, measures the number of symbol changes or signalling events (such as dot or dash) that can be transmitted per second. In the days of the telegraph an event was a signal change and there might be one or a few per second, depending on how profi cient the operator was.
Today there are three main methods of measuring data transmission: baud rate (signalling events per second) bps
(bits per second) and cps (characters per second). In fact, today the baud rate been replaced by a more accurate unit of measurement – bps. We’ll look at this in more detail later on in this workbook.
6852v8 Describe data communications
In terms of the telegraph, a signal is a changing electronic current that is used to move data from one place to another.
Essentially, the signal is the message that is being sent from the sender to the recipient.
Standards and
protocols are essentially the rules and regulations that the communication must follow in order for the message to be successfully sent and received.
Media is the way we communicate once we have the hardware, signal, standards and protocols in place. It covers how we transmit data and how we treat the data before we send it and after we receive it. It also covers how we store the data that is sent.
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The Baud rate is a unit of measurement that measures the number of symbol changes or signalling events (such as dot or dash) that can be transmitted per second.
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Analogue and digital
Computers and most other electronic devices use machine language. Also known as machine code or binary code, this is the most basic programming language.
Binary code consists of a combination of 1s and 0s.
(Sometimes described as a switch being on or off.)
Digital signals are where the signal has only two possible values. In computing these translate to 1’s and 0’s – the cornerstone of digital technology.
Analogue signals are different from digital signals in that they are continuously changing over a period of time and have a whole range of values. If you think of digital signals as a sound they will have only two sounds – a high sound and a low sound.
With analogue technology there will be a high and a low sound, but also all the sounds in between.
When we refer to something as being
digital we are describing something that uses
binary code – 1s and 0s.
Telephones are extremely common and are found in nearly all homes and organisations. Telephones originally worked using a PSTN
(Public Switched Telephone Network) system. This is where copper wires carry an analogue voice signal.
PSTN systems are still in use today but are increasingly becoming replaced by newer digital systems.
The word “Analogue” means a device or system in which the value of a data item (e.g. time) is represented by a continuously changing physical quantity which can be measured. Examples are a sundial (the device) in which shadows (the continuously changing physical quantity) move around the dial between marked hours (the measurement).
Another example is a watch that shows time with hands on a dial rather than numbers on an LCD screen.
In an analogue telephone system, the human voice (audio signal) is converted into electronic pulses. This creates vibrations in the handset’s speaker that can be heard by the listener.
In digital telephones, the audio signal is converted to into binary format. Remember, binary format consists of groups of 0’s and 1’s. The audio signal is ‘sampled’ thousands of times a second and these samples are digitised. This digital data is sent over the phone line and converted back into an audio signal at the receiver end. A digital telephone system is economical as it compresses the signal and is often clearer than an analogue system.
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The facsimile machine (or fax machine as it is commonly known) is a technology that is used to transfer data across a phone line to a receiver. Like the telegraph the receiver must have a special machine to receive the message – this is known as a fax machine.
The concept for the fax machine was conceived in 1842 by
Scottish electrical engineer Alexander Bain. Today the fax machine is found in almost all New Zealand organisations and is still used for communication of messages and documents. Variations of the fax machine include computerbased fax systems where a computer is actually the fax machine and is able to send and receive faxes. Many fax machines also double as a photocopier, scanner and telephone. However, the use of email has largely replaced fax communication as it is even faster and more cost effective than using a fax machine.
A fax machine works by electronically scanning a paper document (such as a letter). The electronic scan of the document is broken up into small pieces (called pixels).
These pieces are converted into an digital signal and transmitted over a phone line. At the end (the receiver) the message is decoded and interpreted by the receiving fax machine. The document (in this case a letter) is then printed onto paper so that it can be viewed.
Like the telegraph, one of the advantages of the fax machine is that the communication is almost instant. Once the message has been sent, all the receiver needs to do is wait to receive and print the message. One of the biggest disadvantages of a fax machine is the cost of toner/ink and paper required to print receive messages. Fax machines can also take a long time to send a large numbers of pages.
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Characteristics
The signal
Components
Standards and protocols
Media
Because a fax machine operates over a phone line, the phone line is considered to be busy when a fax is being sent and received. For this reason many organisations that regularly use a fax machine have a separate phone line that is dedicated to sending and receiving fax messages.
These are the characteristics of the fax machine:
The Fax
The document to be transmitted is broken up into light and dark pixels (small dots) which are digitised. The signal is compressed, encoded and converted into audio tones which are sent over a phone line. The receiving fax machine receives and interprets these tones and converts them into an image which is then printed onto paper.
Both the sender and receiver require a fax machine (or a device that is capable of sending/receiving a fax). To receive a message the receiver will need suffi cient paper and toner/ink to print the message. The sending fax must be able to call the receiving fax over a phone network.
The standard protocol for nearly all fax machines today is known as Group 3.
This is a standard protocol that outlines how fax machines send and receive messages. This means that fax machines can receive messages that are sent from other fax machines in New Zealand and around the world. In many modern fax machines the data that is being sent is compressed so that it takes less time to send and receive.
Toner/ink and special fax paper (or normal paper with many fax machines) is required to receive a fax. The received fax is written to paper. With computerbased fax machines or internet-based fax services the fax can be viewed on the computer or as an email attachment.
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When the telephone was invented in the 1870s it produced a dilemma for later generations. The telegraph used an electrical current to send sound signals. Of course the problem didn’t become clear until we began using machines
(such as computers) to collect and manipulate information.
These machines used machine language (otherwise known as binary) to receive and deliver information. Machine language works on the On/Off principle.
But the telephone didn’t work that way. By the 1940s telephones were far more predominant than the telegraph, and they offered much quicker and more effi cient messaging. For a start, it didn’t take a trained clerk to receive or answer a telephone message. And it was much quicker to state a message than to spell it out in ‘dots and dashes’. But machines couldn’t talk into the telephone, so the information on them could not be transmitted via the most accessible method.
This is where the modem came in.
A modem (technically known as a modulator-demodulator) is a device that translates between digital signals or machine language ( binary) and sound (or analogue signals).
It converts 1011100011100 to streams of sound and silence that are transmitted via the telephone line to another modem that translates them back again (in fact all modems translate both ways) to send the information to a waiting machine or computer.
There are many different types of modems on the market today. In this section we are going to focus on “dialup” modems that send and receive data across a normal phone line.
Computers and most other electronic devices use
machine language. Also known as machine code or binary code, this is the most basic programming language.
Binary code consists of a combination of 1s and 0s.
(Sometimes described as a switch being on or off.)
This creates a challenge when data is sent as sound waves over a phone line.
This is because computers can’t interpret the sound waves – only 1s and 0s. To solve this problem, this is where modems come in.
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When two modems connect they go through a process called
“Handshaking”. This is the process by which two modems establish a connection by setting and agreeing on the rules and standards (the protocols) that are to be used for the connection.
Modems are commonly used for connecting computers to the internet and are still in use today in many homes. They are primarily used for connecting a home computer to the internet using what is called a “ dialup connection”. This is a type of internet connection where the user connects to the internet by using a modem and a phone line. However, as faster internet technologies have become available (and cheaper!) the use of traditional modems is declining.
A modem is connected to a computer system, such as a home personal computer. The computer uses the modem to dial up a connection to another computer or an ISP (internet service provider) – similar to how you make a phone call.
A modem takes the digital information on a computer and converts it to an analogue signal which is sent over a phone line. A modem also takes analogue signals that are received over a phone line (such as a web page) and converts them back into digital signals that the computer can read.
Here is a typical home modem:
PC
1 1
Modem
Receiver
0
Digital Analogue
The signal between the computer and the modem is a digital signal. Digital signals are where the signal has an exact high point and an exact low point. They don’t have any other values. In computing these translate to 1’s and 0’s – the cornerstone of digital technology.
The signal between the modem and the receiver (the device that is receiving the data) is sent over the phone line. In our diagram this is the signal on the right. This signal is an analogue signal which is transmitted as a wave. Analogue signals are different from digital signals in that they are continuously changing over a period of time and have a whole range of values.
© Intueri Services Ltd, trading as Learntree 6852v8 Describe data communications

The fi rst commercial modems (in the 1950s) used baud rates (signalling rates) of 110 baud (meaning 110 signals per second). They also only sent one data bit per signal, so their data transfer rate was no more than 110 bps. As computers got more powerful, and were asked to perform more tasks, the commercial demand for faster data transfer increased.
At fi rst, this demand was satisfi ed by increasing the signalling rate, with the data rate remaining at one bit per signal, and the baud rate reaching 1200 baud. By the end of the 1970s, commercial modems had reached only 1200bps.
In the early 1980s, modems were released which could send two data bits per signal change, so although they operated at 600 baud, they could send or receive data at 1200bps.
From there the process advanced, on to the modern V.90 modem which (if the telephone line will support it) can receive 56kbps (57,600bps) at a signal rate of only 8000 baud.”
This table helps to summarise the characteristics of the common household modem.
The speed of a modem is measures in bits per
second (or ‘bps’ for short).
Characteristics The Modem
The signal Modems take digital data from a computer or other digital device and translate it into sounds, which are transmitted over the phone line as an analogue signal (electronic pulses). The modem that receives the analogue signal translates it back into a digital signal that the receiving device can understand.
Components To send and receive information both the sending and receiving machines require a modem and a phone line that is free of distortion.
Standards and protocols
Media
The International Telecommunication Union (ITU) is one of the key organisations that are responsible for setting and developing the standards for the dialup phone- line modem.
The most recent standards are V.90 and V.92.
V.92 is a modem standard allowing near 56 kbit/s download rates and 48 kbit/s upload rates.
The information is sent as sound waves. It is usually viewed on the electronic device that receives it, for example a computer that receives an email.
Because digital data can be only one of two values
(a 1 or a 0), it is easy for a communications device to determine which value is which. Because analogue signals essentially use a constantly changing range of values (a stream of sound in the case of a modem), any unexpected noise or distortion on the phone line can interrupt the signal. This can reduce the accuracy and even the speed of the communication. It can even cause the connection to be lost.
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You may notice that with modems people talk about
“ theoretical maximum
speeds”.
While a manufacturer might specify that a
56kbps modem can send and receive data at a rate of 56kbps, in reality this is not the case. The actual speed of the connection will depend on a whole range of factors including the quality of the phone line, the distance from the exchange and any interference that may occur.
Routing is a method of sending ‘packets’ of information over a network via different routes to the same destination.
Today many people confuse modems and routers.
Routing didn’t develop until the 1970s-1980s and it is a method of directing ‘packets’ of information between networks via different routes to the same destination. The confusion comes because users of broadband internet connections require a router/modem (a router with a modem installed in it), or a separate router and modem, to connect, whereas dialup users require only a modem.
So, from components being a code-tapping instrument
(such as the telegraph), an electromagnetic send/receive instrument and thousands of kilometres of wiring, they became computers, modems, routers, telephone lines and network cards/chips and cabling.
© Intueri Services Ltd, trading as Learntree 6852v8 Describe data communications

This exercise will give you the opportunity to practice the knowledge that you have learnt in this Chapter. Answer all of the following questions. Once you have completed these questions then you should check your answers against the sample answers in the Sample Answers section at the back of this Workbook.
1. Complete the following table by describing the signals, components, protocols and standards and the media for each of the communication technologies that were discussed in this chapter:
Characteristics The Telegraph
The signal
The Fax The Modem
Components
Standards and protocols
Media
2. What does the baud rate measure?
3. What are three disadvantages of a fax machine?
4. What is the difference between an analogue and a digital signal?
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