Cambridge AS Level Computer Science - Theory

This means that there is no defined infrastructure and network connections are created spontaneously.

"A bluetooth LAN is an ad hoc network" what does this mean?

If a frame was sent there would be a voltage which could be detected. The protocol would define a time period before attempting to send a frame again but as two end-systems could send

Describe the protocol CSMA/CD

Twisted pair, Coaxial, Fibre-optic

For transmitting data, state the three cable types from cheapest to most expensive.

Twisted pair or Coaxial, Fibre-optic

For transmitting data, state the three cable types from least need for repeaters to most need.

Coaxial, Twisted pair, Fibre-optic

For transmitting data, state the three cable types from most attenuation at high frequencies to least attenuation.

Twisted pair, Coaxial, Fibre-optic

For transmitting data, state the three cable types from most susceptible to interference to least susceptible.

Twisted pair, Coaxial, Fibre-optic

For transmitting data, state the three cable types from the lowest bandwidth to the highest bandwidth.

Bandwidth: increases as frequency increases Attenuation: increases as frequency increases Need for repeaters: increases as frequency increases Directional focussing capability: increases as frequency increases Penetration through wall: decreases as frequency increases Interference: no trend

For wireless data transmission, describe the systematic trends of bandwidth, attenuation, need for repeaters, directional focussing capability, penetration through walls and interference for wireless transmission (Radio, Microwave and Infrared)

Combing sound from different sources, fading in or fading out the sound, editing the sound to remove noise and other imperfections.

Give three typical features of a sound-editing software.

The system works because each cell has a defined frequency for transmission which is different from the frequencies used in adjacent cells.

How does a cellular network work in terms of the cells (the base station that provides wireless internet access + the area surrounding it)

about 3 MiB

If the resolution of an image is 1366 by 768 and the colour depth is 24 bits, what is the file size in mebi bytes?

-8

In 4 Bit two's compliment what is the value of the most significant bit?

The content providers provide a content description called a torrent that contains the name of the tracker (a server that leads peers to the content) and a list of chunks that make up the content.

In P2P file sharing, specifically BitTorrent, how do peers find others that have the content they want?

Peers simultaneously upload and download chunks. (Peers have to exchange lists of chunks and aim to download rare chunks making them less rare)

In P2P file sharing, specifically BitTorrent, how do peers replicate content to provide high-speed downloads for everyone?

CSMA/CD (Carrier Sense Multiple Access with Collision Detection)

In Standard Ethernet what method was adopted to avoid messages colliding?

A file that contains the name of the tracker (a server that leads peers to the content) and a list of chunks that make up the content.

In peer to peer (P2P) what is a torrent?

No (as each end-system is connected to the switch by a full-duplex link so no collision is possible along that link)

Is CSMA/CD needed today?

Application server, web server, domain name server, file server, proxy server.

List the 5 types of servers.

Connectionless

Was Standard Ethernet implemented in a connection oriented or connectionless service?

The software that supports the transmission of data across a network.

Define middleware.

The binary number obtained by subtracting each digit in a binary number from 1.

Define one's compliment.

The number of samples (of sound) taken per second

Define sampling rate.

the accuracy of the amplitude (loudness) of the digitised sound wave

Define sampling resolution.

The number of bits per pixel

Define the colour depth.

The one's compliment of a binary number plus 1. (for negatives only)

Define two's compliment.

Indirect transmission of data from the sender to receiver. This is referred to as wireless transmission as radio waves (most wireless connections) are unguided media.

Define unguided media.

These are used to provide long-distance telephone and computer network communication. Only three GEO satellites are need for full earth coverage.

Describe Geostationary Earth Orbit (GEO) satellites.

Huffman coding finds the most used characters and gives them shorter codes until the least used character is coded.

Describe Huffman coding.

LEO satellites supplement the mobile phone networks. 50 are needed to are needed for full global coverage.

Describe Low Earth Orbit (LEO) satellites.

Some of these provide the Global Positioning system (GPS). Only 10 are needed for full global coverage.

Describe Medium Earth Orbit (MEO) satellites.

Coding techniques that cause some information to be lost so the original cannot be recovered in subsequent decoding.

Define lossy compression.

No

Can text files have lossy compression?

Vector images are smaller than corresponding bitmap images.

Compare a Bitmap image to a Vector image.

Disadvantages Transmission frequencies are regulated by government agencies. Cables can only be laid in the ground with permission from landowners. Wireless interference is much more significant. Advantages Repeaters needed less often for wireless

Compare the disadvantages of wireless data transmission and cable data transmission.

13, 7, 14

Convert 110101111110 BCD (Two BCD Digits per Byte) to Decimal

1001

Convert Decimal -6 to 4 bit One's Compliment Binary

1001

Convert Decimal -7 to 4 bit Two's Compliment

0101

Convert Decimal 5 to 4 bit One's Compliment Binary

0111

Convert Decimal 7 to 4 bit Two's Compliment

176

Convert Denary 374 to Hexadecimal.

2DF

Convert Denary 735 to Hexadecimal.

110110110111

Convert Hexadecimal DB7 to Binary.

64001

Convert Hexadecimal FA01 to Decimal.

A prefix representing the factor 2³⁰ written as the symbol Gi

Define Gibi. (Gibibyte)

A prefix representing the factor 2¹⁰ (1024) written as the symbol Ki

Define Kibi. (Kibibyte)

A prefix representing the factor 2²⁰ (1048576) written as the symbol Mi

Define Mebi. (Mebibyte)

A pixel (picture element) is the smallest identifiable component of a bitmap image, defined by just two properties: its position and its colour.

Define Pixel.

The world wide web is a distributed application available on the internet which contains websites which are collections of webpages.

Define WWW.

WiFi is a wireless LAN protocol which uses radio frequency transmission. Most often a WiFi LAN is centred on a wireless access point in an infrastructure network (no an ad hoc network).

Define WiFi

WiMAX is a protocol for MAN or WAN, it was designed for use by PSTNs (Public Switched Telephone Network) to provide broadband access to the internet without having to lay underground cables. Local subscribers connect to the antenna of a local base station using a microwave signal.

Define WiMAX.

A band-limiting filter removes high-frequency components as the human ear cannot detect these and they would cause problems for coding.

Define a band-limiting filter.

The area where there is cellular coverage with a base station at its centre.

Define a cell (the one used in cellular networks dummy!)

A device that connects networks of different underlying technologies.

Define a gateway.

A device that acts as a node on the internet.

Define a router.

A device that provides services via a network.

Define a server.

A graphic consisting of components defined by geometric formulae and associated properties, such as line colour and style.

Define a vector graphic.

A suite of software that can be installed virtually on a computer system.

Define a web server.

The reduction of power

Define attenuation.

Bluetooth is communication by short-range radio transmission in a confined area.

Define bluetooth

A direct transmission of data from the sender to receiver. (example: cables, infrared waves)

Define guided media.

Coding techniques allow subsequent decoding to recreate exactly the original file.

Define lossless compression.

1111

Show Decimal -7 as a 4 bit sign and magnitude binary.

0110

Show Decimal 6 as a 4 bit sign and magnitude binary.

Sampling must be done at a frequency at least twice the highest frequency in the given sample.

State Nyquist's theorem.

band-limiting filter and an analogue-to-digital converter (ADC)

What are the two components of a sound encoder?

One BCD digit per byte. Two BCD Digits per byte

What are two options for storing BCD?

Binary Coded Decimal

What does BCD stand for?

Public Switched Telephone Network

What does PSTN stand for?

public switched telephone network

What does PSTN stand for?

Worldwide Interoperability for Microwave Access

What does WiMAX stand for?

Huffman coding.

What is one compression method for text files?

-8

What is the Two's Compliment of the Binary 1000?

(need help pls)

What is the difference between an infrastructure network and an ad hoc network?

In connection oriented, one packet is sent and the rest of the packets aren't sent until the sender receives an acknowledgment. For connectionless, all the packets are sent in one go.

What is the difference between connectionless and connection oriented service?

IEEE 802.15

What is the formal name for Bluetooth?

IEEE 802.16

What is the formal name for WiMAX?

IEEE 802.11

What is the formal name for wireless ethernet/WiFi (WLAN in some countries)?

A.A = A

What is the idempotent law in AND form?

A + A = A

What is the idempotent law in OR form?

1.A = A

What is the identity law in AND Form?

0 + A = A

What is the identity law in OR Form?

A.NOT(A) = 0

What is the inverse law in AND form?

A+NOT(A) = 1

What is the inverse law in OR form?

Bit rate

What is the measurement for the process of delivering data through streaming?

0.A = A

What is the null law in AND Form?

1 + A = 1

What is the null law in OR Form?

802.3

What is the standard for a wired network (synonym for Ethernet) denoted as?

∧

What is the symbol for AND?

∨

What is the symbol for OR

A nibble

What is the term for 4 bits?

Standard Ethernet (either as a bus or star with a hub where the transmission was connection less)

What protocol was implemented on LANs back in the good days? (First generation)

For voice communication using analogue technology.

What were 1G cellular networks designed for?

The same as 1G but digital

What were 2G cellular networks designed for?

Multimedia transfer and serious internet connection capability

What were 3G cellular networks designed for?

The same as 3G but with high-bandwidth broadband connectivity.

What were 4G cellular networks designed for?

Sampling rate and sampling resolution

When coding for sound, what two factors make an impact on the file size?

Bit streaming

When transferring data over the Internet, which method is used?

In a buffer

Where is streamed data stored?