Digital communications
Opticalfibre communications became commercially viable in the 1970s and innovation continues today. This free course, Digital communications, will illustrate how very high data rates can be transmitted over long distances through optical fibres. You will learn how these fibres are linked, examine the technology used and assess the future direction of this continually developing area of communication.
Author(s):
This key skill develops your information technology (IT) skills in your studies, work or other activities over a period of time. To tackle all of this key skill, you will need to plan your work over at least 3–4 months to give yourself enough time to practise and improve your skills, to seek feedback from others, to monitor your progress and evaluate your strategy and present outcomes.
Skills in information technology cover a broad range, from using software unitages to developing a c
Managing complexity: A systems approach – introduction
Do you need to change the way you think when faced with a complex situation? This free course, Managing complexity: A systems approach introduction, examines how systemic thinking and practice enables you to cope with the connections between things, events and ideas. By taking a broader perspective complexity becomes manageable and it is easier to accept that gaps in knowledge can be acceptable.
Author(s):
Design thinking
Are you ever frustrated with something that you thought you could design better? Design thinking can structure your natural creativity to come up with solutions to all kinds of problems, and have fun in the process too! First published on Thu, 22 Dec 2011 as Author(s):
Many programming languages provide two functions associated with the character codes (see Table 2). We shall call these functions ASC and CHR. ASC takes a character as input, and returns the integer giving the ASCII code of the input character. CHR returns the character whose ASCII code is the input integ
A function is a process that, when given an input of a specified type, yields a unique output. This is a key idea in providing a precise, mathematical, description of processes in computing.
To describe a particular function, we first give the set from which the input will be drawn and the set from which the output is drawn. This information is called the signature of the function. An example will make this clearer. Author(s):
After studying this section you should be able to do the following.

Recognise and use the terminology: disjoint union; power set (of a set); representation (of a data abstraction).

Use and interpret the notation:

X

In Section 2, we introduced the notation SeqOfX for the set of all sequences whose members come from the set X. In Section 2, we looked only at sequences whose members were of one of the primitive forms of data (integers, characters or Booleans). We can have sequences whose members are themselves data with a more complicated form. For example, suppose that Jo is working at the till T1 and is replaced by Jessica. We might represent this handover by the 3tuple (Jo, T1, Jes
The T822 course team
David Reed (Chair and author)
Jill Alger (Editor)
Chris Bissell (Critical reader and author)
Philippa Broadbent (Print buyer)
David Chapman (Author)
Daphne Cross (Assistant print buyer)
Glen Darby (Graphic designer)
Donna Deacon (Course secretary)
Alan Dolan (Course manager)
Roger Jones (Author)
Jo Lambert (Learning projects manager)
Roy Lawrance (Gra
3.3 Hypertext transfer protocol (HTTP)
In this section, I shall look at one example of an application of the TCP/IP protocol suite – sending hypertext pages over the world wide web (WWW or simply the web). However, first I shall very briefly summarise the main features of the web that are relevant to this discussion. There are many sources of information about the web on the web itself for those who want to know more.
In very basic terms, the web is an application of the Internet for accessing resources where
3.1 What does TCP/IP protocol architecture do?
The Internet is a worldwide public internetwork, which allows computers to communicate with each other even though they may have different manufacturers and different operating systems. The origins of the Internet lie in a project of the US Defense Advanced Research Project Agency in the 1970s, where it was intended to foster communication between research institutions rather than operate for profit. However, a substantial amount of traffic carried by the Internet is now related to com
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 connectionoriented services, a connection must be established between peer entities. A connection has three phases: connection setup, 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
1.2 Protocols in multiservice networks: introduction
Early automatic telephone networks were built to carry only voice traffic and to provide a very simple telephone service – now called plain old telephone service (POTS). When computer networks started to appear, either they were separate from telephone networks or the data carried between computers was a small proportion of the traffic on the telephone network. There are various estimates for the growth of voice and data traffic, and various dates have been given for when data traffic will
3.1 Ghosts of departed quantities
They are neither finite quantities, or quantities infinitely small, nor yet nothing. May we not call them the ghosts of departed quantities?
(Bishop G. Berkeley, The Analyst)
This section follows up the ideas presented in and aims to:

define the terms analogue, discrete and digital;

look briefly at the human perceptual system, whic
Suppose I take a digital photograph of myself for my website. Horrified by my wrinkled, baggy appearance, what can I do? Actually, with the right software I can do more or less anything I like: I can smooth out the wrinkles; I can restore the grey hair to its former splendour; I can even put in a background of books to give me a scholarly appearance. In fact, I can so improve the picture that if you met the real me you probably wouldn't recognise me.
‘Massaging’ my photographic imag
The AND operation combines two binary words bit by bit according to the rules

0 AND 0 = 0

0 AND 1 = 0

1 AND 0 = 0

1 AND 1 = 1
In other words, only when both bits are 1 is the result 1. You may find it helpful to think of it this way: when one bit is one and the other bit is 1 the result is 1.
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 multiplelength representation may be needed to hold the result of a mu
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.
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
Generally, when we talk about communication between humans, we mean one person conveying information to another person. Figure 6 shows a basic model, or representation, of a communication system for getting a message from the sender to the recipient. The diagram shows the sender (User