Communication and Internet Technologies Flashcards
(127 cards)
1
Q
Give examples of different transmission media
A
Cable, Wireless
2
Q
State the different options of cables
A
Twisted Pair, Coaxial, Fibre Optic
3
Q
Which cables use copper for data transmission?
A
Twisted Pair and Coaxial
4
Q
What factors need to be taken into account when looking at the suitability for choosing cable for an application
A
Cost, Bandwidth/Data Rate, Attenuation at high frequency, Interference, Need for Repeaters
5
Q
Which 2 factors of cabling can lead to poor performance?
A
THe likelihood of interference affecting transmitted signals and the extent of attenuation (deterioration of the signal) when high frequencies are transmitted.
6
Q
What can you do to combat the 2 factors that can lead to poor performance?
A
Repeaters/Amplifiers or transmission lines
7
Q
State the factors for Twisted Pair cabling
A
Cost - Lowest Bandwith - Lowest Attentuation at High Frequency - Affected Interference - Worst Affected Need for Repeaters - More Often
8
Q
State the factors for Coaxial cabling
A
Cost - Higher than twisted
Bandwith - higher than twisted
Attentuation at High Frequency - Most affected
Interference - Less Affected than Twisted
Need for Repeaters - More Often
9
Q
State the factors for Fibre Optic cabling
A
Cost - Highest Bandwith - Much higher Attenuation at High Frequency - Least affected Interference - Least Affected Need for Repeaters - Less Often
10
Q
Which cabling works best for new installations?
A
Fibre-Optic.
11
Q
Why would copper cabling be used?
A
Where copper cable is already installed the cost of replacement may not be justified
12
Q
Where is twisted pair cabling used?
A
Phone lines
13
Q
Where is coaxial cabling used?
A
Cable television companies.
14
Q
Where is fibre optic cabling used?
A
Long distance communication (replaced coaxial)
15
Q
State the 3 types of wireless transmission?
A
Radio, Microwave, Infrared
16
Q
What are the differences between the wireless transmissions?
A
The frequency of the waves
17
Q
What are the factors discussed when deciding on wireless media?
A
Bandwidth, attenuation, need for repeaters, directional focusing capability, penetration through a wall, interference
18
Q
State the factors for radio transmission
A
Bandwidth - lowest Attenuation - lowest Need for repeaters - lowest Directional focusing capability - lowest Penetration through the wall - best Interference - N/A
19
Q
State the factors for microwave transmission
A
Bandwidth - middle Attenuation - middle Need for repeaters - middle Directional focusing capability - middle Penetration through the wall - middle Interference - N/A
20
Q
State the factors for infrared transmission
A
Bandwidth - highest
Attenuation - highest
Need for repeaters - highest
Directional focusing capability - highest
Penetration through the wall - lowest (Worst)
Interference - N/A
21
Q
Give situations where infrared is most useful
A
Indoor applications due to the increased attenuation
22
Q
What is the most common form of data transmission
A
Microwave
23
Q
What is guided and unguided media
A
Guided - Cable
Unguided - Wireless
24
Q
What are the advantages of using transmission through a cable
A
- As wireless transmission frequencies is regulated by government agencies and so permission has to be obtained before wireless transmission is used
- Interference is much more significant for wireless transmission
25
What are the advantages of using wireless transmission
- You need permission to have cables put into the ground from the landowner
- Repeated are needed less often for wireless transmission
- Mobile phones dominate internet use - and these use wireless
26
Give examples of how wireless or wired transmission could be used for a scenario
Global communication where fibre optic cables are laid underground or on the sea bed whilst wireless use satellite transmission.
Home or small office
27
What is the difference between a WAN and the internet
Internet - a network of networks that allow computers to communicate using protocols.
WAN - A network over a large distance
28
What is a problem with the internet?
It has no design plan as it is evolving so has no defined structure.
29
What is the function of an ISP?
It is a hierarchical structure for the internet where it gives internet access to an individual or company (an access ISP).
30
How do ISPs work
```
Access ISP connects to
Middle Tier (Regional ISP) which is connected to Tier 1 ISPS (backbone ISPS - content providers)
```
31
State what is meant by an ISP
It is a network and connection between different ISPS which are handled by Internet exchange points.
32
State what is meant by a PSTN
Public switched telephone network - uses fibre optic cables to help people send and receive data
33
How has the introduction of fibre optic cables helped PSTNs?
Improved leased line services to ISPs but has also allowed PSTNs to provide their own ISP service.
34
State the two different services that PSTN ISPs can provide
1. Broadband network connection for traditional network access
2. WiFi hotspot technology which allows people to access the internet, t through their mobile device if they are are near a specified hotspot
35
How do users of mobile phones gain access to the internet?
Mobile phone companies act as an ISP.
The mobile phone is equipped with appropriate software that communicates with a cell tower to access the wireless telephone network which then provides a connection the internet
36
State the 3 different types of communication satellites
GEO (geostationary earth orbit - the highest over the equator); MEO (medium-Earth orbit); LEO (low earth orbit)
37
State how GEO satellites are used
Long distance telephone and computer network communication.
38
How many GEO satellites do you need?
3
39
State how MEO satellites are used
Provide our global positioning system (GPS)
40
How many MEO satellites do you need?
10
41
State how LEO satellites are used
Support mobile phone networks (like a constellation)
42
How many LEO satellites do you need?
50 but we have several hundred
43
What is the advantages of using satellites?
Due to being high above the ground it can act as a component in a network and can connect with other components that are separated by great geographical distances - something that ground components would find hard.
44
What are the disadvantages of using satellites?
The greater the distance = the greater the transmission delays which cause problems
45
What is meant by the world wide web (www)?
a distributed application which is available on the internet.
It consists of an enormous collection of websites and web pages which contain hyperlinks.
46
The internet is a mesh structure. What device acts as a node?
The router
47
What device is needed when networks of a different underlying technology need to communicate?
Gateway which provide the same function of a router
48
What is the definition of a server?
A specialised type of computer hardware designed to provide functionality when connected to a network. The server provides a service for the users
49
Give different examples of the different types of servers
```
Application Server
Web Server
Domain Name Server
File Server
Proxy Server
```
50
State what is meant by a server farm
File server functionality is often provided by a server farm - where a number of servers work together in a clustered configuration
51
Who provides server farms?
Tier 1 content providers and they are also used in the provision of cloud storage
52
Give an example of a proxy server
When a web server is overwhelmed by web page requests a proxy server is used
53
How do proxy servers work?
When a web page is used for the 1st time the proxy server saves a copy in a cache. When you get future requests, the server provides the web page without having to search through the filestore of the main server.
Proxy servers can also act as a firewall and provide security against malicious attacks on the server.
54
State what is meant by a client-server architecture
Originally was a distributed computer system where a client carries out part of the processing and the server carries out another part
55
How does the client and server cooperate in a client-server architecture?
Middleware
56
In modern times, explain what is meant by a client-server architecture?
The server is now a web server which is a suite of software that can be installed on any system.
57
State the function of a web server
To provide access to a web application
58
In modern times, explain what is meant by a client
The client is the web browser software
59
In modern times, explain what is meant by the middleware
The software the supports the transmission of data across a network together with provision of scripting
60
How have web pages evolved in modern times?
Web pages used to be downloaded on to the client screen and would be static. Modern web pages are dynamic meaning that what is displayed is determined by the request made the by client. It can be used for a lot of applications which have user interaction
61
Give examples of dynamic web applications
E-commerce - a customer buying a product online; e-business, email, searching video catalogues, online banking
62
What uses streaming media?
Watching a video/listening to music
63
How is data transmitted for streaming?
- Data prior to transmission is stored in bytes and it is possible to transmit this as a byte stream
- Streamed media is always compressed using techniques. Some compression techniques involve converting each byte into a representation with fewer bits.
- The decoding process at the receiver end, data must be transferred as a bit stream.
64
Explain how streaming media work
Option 1 Source is a website that has the media already stored. People can choose to download a file then listen to it or watch it at some future time
Option 2 viewing or listening on demand. The delivery and the playing of the media are 2 separate processes. The incoming media data are received into a buffer created on the users computer. The users machine has media player software that takes the media data from the buffer and plays it.
Option 3 is real time streaming/live transmission where the content is being generated as it is being delivered such as a live sporting event. At the receiver end the technology is the same as all the others
65
State what is the problem with real time data transmission
If a large number of users watching simultaneously - delivery issues
66
How can you improve real time data transmission to a large audience
Forward the content to a large number of content provider servers which then transmit onwards to individual users
67
What do you have to take into account when media streaming?
Whether the technology has sufficient power to provide a satisfactory user experience. When the media is created it needs to be delivered to the user at precisely the same speed as used for the creation i.e. a song that lasted 4 minutes when sung for the recording will sound different if it is received by a user, it lasts six minutes
68
What impacts the process of delivering content
The bit rate.. i.e. a poor quality video can be delivered at a bit rate of 300 kbps but a good quality audio file only needs delivery at 128 kbps.
The bit rate for delivery to the user from the buffer must match the dfined rate for the specific media in use, but the planned transmission rate to the buffer must be higher to allow for unexpected delays. These rates are controlled by the media player by continuously monitoring the filling of the buffer in relation to the defined high and low watermarks which are a part of your buffer.
69
What influences the rate of transmission to the buffer
The bandwidth of the network connection.
70
What is the best requirements for streaming movies
2.5 Mbps
71
How does movie streaming occur so that all people can watch videos no matter their connection?
A video can be available at different levels of compression. The most highly compression version will be the poorest quality but the bit rate may be sufficiently low for low bandwidth internet connection.
72
State what is the purpose of IP addressing
Used to define from where and to where data is being transmitted
73
How many bits is IPv4 addressing scheme based on
32
74
What is the problem with IPv4 address scheme?
There are more users than available IP addresses
75
How is an IP address scheme structured?
The first group of bits are the netID and the other group of bits are the hostID. The aim is to assign a unique universally recognised address for each device on the internet.
The separation into two parts allows the initial transmission to be routed according to the netID.
76
How does an IP address work?
WHen packets arrive, the HostID is examined on arrival at the identified network.
77
How were IP address schemes allocated?
Based upon the different classes of networks.
78
State the different class types
Class A, Class B, Class C
79
State the class identifiers for each class
A - 0; B - 10; C - 110
80
State the number of bits for netID for each class
A - 7; B - 14; C - 21
81
State the number of bits for hostID
A - 24; B - 16; C - 8
82
In an IP address what do the most significant bits identify?
The class
83
In an IP address, the second group of most significant bits identify the?
NetID
84
In an IP address, what is the least significant bits representing?
HostID
85
Who would be allocated ClassA IP addresses?
Largest organisations - 128 of them with 224 hosts for each of them
86
How many organisations could be allocated ClassC?
2 million
87
What is the challenge for allocating organisations ClassC?
Each allocation could only support 256 hosts
88
What were the difficulties with the old IP address scheming?
Due to LANs being used a lot, the number of ClassB netIDs were not enough. If these organisations were given Class C the number of hostIDs were too small.
89
What is the representation used for an IP address?
32 bit binary code using dotted decimal notation. Each byte can be written as its denary equivelant i.e.
10000000 00001100 00000010 00011110 =
128.12.2.30
90
What is meant by classless inter-domain routing?
Developed to improve addressing schemes. It keeps the netID and hostID concept but makes it more flexible by allowing a split between the netID and hostID to be varied to suit individual needs
91
How does CIRD work?
It can create a split between netID and hostID by adding an 8-bit suffix to the address that specifies the number of bits for the netID.
if for example we have suffix as 21 = 21 bits for netID and 11 bits (2048 hosts) for hostID = 32 bits.
There is no need to use most significant bit to define the class
92
Give an example of a CIRD IP address
NetID(10000000 00001100 00000010) 00011110/00010101 - suffix
128.12.2.30/21
93
How does CIDR identify classes
Uses with with the suffixes - i.e. 8, 16, 24
94
State the purpose of sub-netting
To allow further structure in the addressing
95
State what is meant by Network address translation (NAT)
It doesn’t have every IP address that should be unique.
| Large organisations will have private networks (intranets) which use the same protocols as the internet
96
Why use a private network?
Extra security because of isolation from the internet.
97
What is the issue with private networks?
Extra security is what they want, but they also want access to the internet
98
How can we allow private networks access to the internet?
Using Network Address Translation
99
Explain how NAT works?
A NAT box has one IP address which is visible over the internet so it can be used as a sending address or as a receiving address. Internally IP addresses are chosen from 3 ranges of IP addresses (Lower Bound to Upper Bound).
Each address can be simultaneously used by any number of different private networks. It does not have any knowledge of the internet use or in any other private network.
The interface in the NAT box has software installed to examine each incoming or outgoing transmission. There can be a security check before an incoming transmission is directed to the correct internal address - network structures within the organisation could take many forms.
100
State what is meant by IPv6 addressing
It is an addressing scheme that uses 128-bit addressing scheme allowing 2128 different addresses
101
How is an IPv6 addressing system structured
16 bit parts represented by 4 hexadecimal characters
102
Give different examples on how IPv6 addresses can be structured
68E6:7C48:FFFF:3D20:1180:695A:FF01 = full address
72E6::CFFE:3D20:1180:295A:FF01 = where :0000:0000: has been replaced by just :: to make it shorter
6C48:23:FFFE:FFFF:3D20:1180:95A:FF01= Leading 0’s not put in
::192.31.20.46 = An IPv4 address used in IPv6
103
State what is meant by a domain name
It is plain text used to identify an IP address
104
State what is meant by a domain name system
A hierarchical distributed database installed on domain name servers that is responsible for mapping a domain name to an IP address
105
What is the purpose of a domain name system
The DNS system allocates a readable domain name for internet hosts and helps find IP addresses for an individual domain.
106
How does a domain name system work
The system is implemented as hierarchical distributed database which is installed on a large number of domain name servers covering the whole of the internet.
THe domain name servers are connected in a hierarchy, with powerful replicated root servers at the top of the hierarchy supporting the whole internet.
DNS name space is then divided into non-overlapping zones. Each zone has a primary name server with the database stored on it. Secondary servers get information from this primary server.
As a result the naming system is hierarchical. There are more than 250 top level domains which are like .com/.edu/.gov or present countries such as .uk and .n
107
State what is meant by a URL
It identifies a web page or an email address - and a domain name is included in it.
108
Show the structure of a URL
http:// (protocol)
www. or .cisco (subdomain)
bbc (domain name)
.co.uk (top level domain)
/image (path)
109
What is meant by name resolution?
Where it looks up a domain name to find an IP address
110
What are the outcomes of name resolution?
1. If the domain is under the jurisdiction of the server to which the query is sent then an authoritative and correct IP address is returned
2. If the domain is not under the jurisdiction of the server, an IP address can still be returned if it is stored in a cache of recently requested addresses but it might be out of date
3. If the domain in the query is remote then the query is sent to a root server which can provide an address for the name server of the appropriate top-level domain which in turn can provide the address for the name server in the next lower domain. This continues until the query reaches a name server that can provide an authoritative IP address
111
How would an individual create a client-server based web application for personal use?
They would need to download appropriate server software, installing the application and using their browser to access the application.
112
How does a developer create a web application for remote users?
The application developer makes the application as one or more web pages.
1. Each web page has a file which is written in HTML.
2. A domain name has to be obtained from a web-hosting organisation
3. HTML files have to be uploaded to the server provided by the web hosting organisation
113
How does a user access the application remotely?
1. The user opens up a browser on the client computer.
2. The user types in the URL of the web application or selects it from the bookmark list
3. The browser asks the DNS system for the IP address
4. The browser connects to the IP address and sends a request for the web page
5. The page is sent by the server to the browser
6.The browser displays the page
Users then can interact with the application by entering data or clicking a feature
114
State what is meant by HTML
It is a framework for using HTML. It is a text file which is made up of pairs of tags < >
115
Show the structure of an HTML file
...
...
116
What can be kept within the body tags?
Forms, videos, text, hyperlinks, icons, images, sound etc
117
What is meant by javascript?
It is written by the application developer into hTML text which allows the user at the client end to interact with the application and cause for processing to take place on the client computer
118
How does javascript work?
The browser must have javascript enabled
119
How do developers incorporate javascript into websites?
Javascript is normally written in a separate file which is then called from within the HTML
120
How is javascript added into an HTML file?
```
…
//javascript code
```
121
Why would you have javascript code into the html?
So that it can be accessed immediately - especially if it is in the section
122
Explain what this javascript - code does:
You can input a value in celsius and this will be converted to Fahrenheit
``` var tempC = prompt(“Please enter the Celsius value”, “”) var tempF = (tempC * 1.8) + 32; alert (“The Fahrenheit value is “ + tempF) ```
creates 2 variables - tempC and tempF.
TempC will give an input for a person to enter a celsius value.
TempF will calculate TempC multiplied by 1.8 and then plus 32.
Output the fahrenheit value
123
Why would a developer use javascript?
To carry out processing on the client computer which does not involve the software running on the server.
It is used for collecting data which is to be used by a program running on the server. The validation and verification can be handled using JavaScript
124
What is meant by PHP?
A programming language - not a scripting language
125
What is the difference between PHP and JavaScript?
The difference is that any PHP script is processed on the server. PHP can be contained in a separate file accessed by the HTML.
126
What does this PHP code do?
This is the PHP code kept as a separate file
This is the start of HTML
This is the start of PHP
This is a variable tempC which is getting an inputted value.
A variable called tempF will get the value of tempC and multiply it by 2 and add 30.
It will then print a string ‘The Fahrenheit value” and then print the variable value tempF.
The value for tempC is passed into the URL i.e. index.php?value=25
127
Why would a developer choose to use PHP script?
It speeds up the running of the application as it is not transmitting data back and forward between the client computer and the server.
It is used for database applications where it is essential that the database stays on the server and the the results of a query are displayed on the browser.
SQL used with the database needs to be running on the server not on the client.
