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Online Rights and the Law
How does the law stand in relation to web privacy? Do we have the same rights online as we do in life? The online revolution has moved rapidly but has the law managed to keep up with it and what has been the impact on our legal rights? These two films touch upon issues that have emerged as a result of a growing online community like the complications that arise when attempting to reconcile how various countries use different laws to police an individual’s omnipresent profile on the net. It als
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Except for third party materials and otherwise stated (see http://www.open.ac.uk/conditions terms and conditions), this content is made available under a http://creativecommons.org/licenses/by-nc-sa/2

Introduction

This course provides an introduction to data and processes in software, and provides a basis that enables these fundamental ideas to be developed in a clear and precise way. It has two main aims. The first is to illustrate how we can describe ways in which data may be structured and processed. The second is to introduce you to some vocabulary and concepts that help us to do this. The material is accessible to anyone with a little experience of the use of symbols in presenting ideas.

Sec
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4.2.2 ATM layer

The primary functions of the ATM layer are associated with the routing and switching of ATM cells. Because ATM cells are packets, the switches are packet switches and the switching operation can be called forwarding, but by convention, because the ATM layer provides a connection-oriented service, the term ‘forwarding’ is generally not used.

The path cells take and the resources allocated to them depend on their service category. This is determined when a virtual connection is
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3.5.1 IPv4 Addresses

The allocation of addresses on the Internet is controlled by the Internet Assigned Numbers Authority (IANA), although authority is delegated to several local registries. IPv4 addresses may be interpreted in two ways. Initially, they were divided into distinct ranges of addresses called classes, but this proved to be inflexible and now a more flexible scheme, called classless addressing, dominates IPv4 internetworks. I shall describe both ways of interpreting IPv4 addresses because the limitat
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2.4 Examples of layer functions

There are several functions that can be performed at one or more of the OSI layers. Some of the more common ones are discussed below.

Connection control

For connection-oriented services, a connection must be established between peer entities. A connection has three phases: connection set-up, data transfer and connection clear. If the peer protocol supports connections, each protocol data unit type corresponds to a primitive type; for instance, a connection request primiti
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2.2 Vertical communication

Figure 6 shows the OSI view of adjacent layers. The interface between two layers in the same system is called a service access point (SAP). One of the features of a service access point is that it has an identifier, or an address, which allows each communication between adjacent layers to be uniquely identified. The processes that communicate across the interface are called entities. These are typically software routines, but may also be hardware components. The notation in Figu
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Learning outcomes

After studying this course, you should be able to:

  • evaluate technical descriptions of communication protocols and demonstrate an understanding of their operation

  • describe the characteristics of circuit-switched and packet-switched networks, and of connectionless and connection-oriented modes in packet-switched networks

  • describe the role played by primitives in the OSI reference model

  • explain how ‘vertical’ and ‘horizontal’ com
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5.5.5 Summary

In this section I've briefly considered the very contentious question of what digital representations mean, but this debate must be left to another course. I have also described some of the devices that take digital information back into the analogue world of sight and sound, presenting it in a form that is meaningful to human eyes and ears.


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5.5 Types of output devices

We can make a start by appealing to your own general knowledge.

Exercise 16

You have a computer; list the output devices that it uses.

Dis
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4.2.4 Keyboards

Every computer comes with a keyboard. They are still the main way of taking text across the boundary into the computer. The one I'm using to type this course has 109 keys. Under each key is a pressure sensor that detects when the key has been pressed and sends an electronic signal into the computer. There, a small program called the BIOS (Basic Input/Output System) translates the signal into the appropriate numeric code. Other software stores that code in a suitable place in the memory.


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7.5 Dividing 2's complement integers

Just as multiplication can be turned into repeated additions, so division can be turned into repeated subtractions. And just as shifting a binary integer one place to the left equates to multiplying by two, so shifting a binary integer one place to the right equates to dividing by two.

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7.4 Multiplying 2's complement integers

Multiplication can be thought of as repeated addition. For instance, in denary arithmetic

7 × 5

can be thought of as

7 + 7 + 7 + 7 + 7

There is therefore no need for a new process for the multiplication of binary integers; multiplication can be transformed into repeated addition.

In multiplication the result is very often much larger than either of the two integers being multiplied, and so a multiple-length representation may be needed to hold the result of a mu
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2.2.3 Positive integers: converting denary numbers to binary

If computers encode the denary numbers of the everyday world as binary numbers, then clearly there needs to be conversion from denary to binary and vice versa. You have just seen how to convert binary numbers to denary, because I did a couple of examples to show you how binary numbers ‘work’. But how can denary numbers be converted to binary? I'll show you by means of an example.

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2.2.2 Positive integers: binary numbers

Just as a denary number system uses ten different digits (0, 1, 2, 3, … 9), a binary number system uses two (0, 1).

Once again the idea of positional notation is important. You have just seen that the weightings which apply to the digits in a denary number are the exponents of ten. With binary numbers, where only two digits are used, the weightings applied to the digits are exponents of two.

The rightmost bit is given the weighting of 2°, which is 1. The ne
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4.2.3 Second computer (the FirstClass server)

The computer on the right of Figure 11 receives the data, manipulates it and then stores it. The computer then typically sends some kind of response back via the network, which may require the computer to retrieve some stored data.

The computer in this example is one of the Open University's FirstClass servers. A server
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13.4 Flash memory

Flash memory is an electronic form of memory which can be used, erased and reused. A flash memory card is a small storage device used to store data such as text, pictures, sound and video. These cards are used in portable devices such as digital cameras and in small portable computers, such as Personal Digital Assistants (PDAs).

A USB flash memory, sometimes called a 'memory stick', is a small storage device which is completely external and connects to the computer via a USB por
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13.3 Optical storage

A CD-ROM (Compact Disk Read Only Memory) uses a laser-based optical form of storage. This type of disk has been used for many years to distribute music and computer software. A CD-ROM drive is needed to read the disks. Data is locked into the disk during manufacture, and cannot afterwards be changed.

There are two other types of CD device for computers: CD-R (CD-recordable) and CD-RW (CD-rewritable). With the right sort of CD drive in your computer, you can 'burn' data (that is,
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4.1 Introduction

I'll now look at what these components do in the communication system, using the mobile phone system as an example.


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