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comp sci > week4 > Flashcards

week4 Flashcards

1
Q

Network

A

A network is a collection of computers and peripheral devices connected together following agreed protocols.
Networks allow users to share resources.

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2
Q

Wireless Networking

A

Both Wi-Fi and Bluetooth offer wireless communication between devices. They both use electromagnetic radiation as the carrier of data transmission.

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3
Q

Bluetooth

A

Devices using Bluetooth automatically detect and connect to each other, but they do not interfere with other devices since each communicating pair uses a different channel (from the 79 options). When a device wants to communicate, it picks one of the 79 channels at random. If the channel is already being used, it randomly picks another channel. This is known as spread spectrum frequency hopping.

Bluetooth is useful when:
* transferring data between two or more devices which are less than 30 metres apart
* the speed of data transmission is not critical
* using low bandwidth applications (for example, sending music files from a mobile phone to a headset).

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4
Q

Wi-Fi

A
  • uses spread spectrum technology. However, Wi-Fi is best suited to operating full-scale networks because it offers
  • faster data transfer rates
  • better range
  • better security
    than Bluetooth.
    A Wi-Fi-enabled device can access, for example, the internet wirelessly at any wireless access point (WAP) or ‘hot spot’ up to 100 metres away.
    Wireless connectivity uses electromagnetic radiation: radio waves, microwaves or infrared.
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5
Q

Electromagnetic radiation comparison

A

Penetration measures the ability of the electromagnetic radiation to pass through different media.
Attenuation is the reduction in amplitude of a signal (infrared has low (?) attenuation because it can be affected by, for example, rain or internal walls). Thus, we would expect infrared to be suitable for indoor use only; the fact that it can be stopped by walls is seen as an advantage since this stops the signal causing interference elsewhere.
Microwaves seem to offer the best compromise, since they support reasonable bandwidth, and have reasonable penetration and attenuation.

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6
Q

Satellites

A
  • Microwaves and radio waves allow Wi-Fi connectivity in networks. The methods are perfectly satisfactory for short distances – the electromagnetic waves carry the signals.
  • The curvature of the Earth prevents such methods transmitting data globally.
  • The communication between antennae and satellites is carried out by radio waves or microwave frequencies.
  • Different frequency bands are used to prevent signal interference and to allow networks spread across the Earth to communicate through use of satellites (many satellites orbit the Earth)
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7
Q

Wired networking

cables

A

three main types of cable used in wired networks, only need to know about Copper and Fibre Optic cables for exams.

Coaxial (copper) cable
- Single copper wire with a plastic layer and metallic mesh to prevent interference

Fibre Optic cable
- Transmit data as light
- High performance and expensive
- Don’t suffer interference or loss of quality over long distances

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8
Q

Copper (Coaxial) cables

A

Coaxial cables are the most commonly used cables in M(w?)ANs and by cable television companies.
The cost of coaxial cables is higher than twisted pair cables but they offer a better data transfer rate and are affected less by external interference.
Coaxial cables also have about 80 times the transmission capacity of twisted pair. Coaxial suffers from the greatest signal attenuation, but offers the best anti-jamming
capabilities.

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9
Q

Fibre optic cables

A

Fibre optic cables are most commonly used to send data over long distances, because they offer the best data transfer rate, the smallest signal attenuation and have a very high resistance to external interference.
The main drawback is the high cost. Unlike the other two types of cable, fibre optics use pulses of light rather than pulses of electricity to transmit data. They have about 26 000 times the transmission capacity of twisted
pair cables.

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10
Q

Fibre optic cables

modes

A

Fibre optic cables can be single- or multi-mode.
Single-mode uses a **single mode light source and has a smaller central core, which results in less light reflection along the cable. This allows the data to travel faster and further, making them a good choice for CATV and telecommunications.
Multi core allows for a multi-mode light source; the construction causes higher light reflections in the core, so they work best over shorter distances (in a LAN, for example).

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11
Q

Wireless network

A
  1. It is easier to expand networks and is not necessary to connect devices using cables.
  2. Devices have increased mobility, provided they are within range of the WAPs.
  3. Increased chance of interference from external sources.
  4. Data is less secure than with wired systems; it is easier to intercept radio waves and microwaves than cables so it is essential to protect data transmissions using encryption.
  5. Signals can be stopped by thick walls (in old houses, for example) and signal strength can vary, or ‘drop out’.
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12
Q

Wired network

A
  1. More reliable and stable network (wireless connectivity is often subjected to interference).
  2. Data transfer rates tend to be faster with no ‘dead spots’.
  3. Tends to be cheaper overall, in spite of the need to buy and install cable.
  4. Devices are not mobile; they must be close enough to allow for cable connections.
  5. Lots of wires can lead to tripping hazards, overheating of connections (potential fire risk) and disconnection of cables during routine office cleaning.
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13
Q

Wired or wireless

A

There are also other considerations such as;
* If mobile phones and tablets are connected to the network, it will need to offer Wi-Fi or Bluetooth capability.
* There may be regulations in some countries regarding which wireless transmission frequencies can be used legally.
* Permission from authorities and land owners may be required before laying cables underground.
* There are numerous competing signals in the air around us; it is important to consider this when deciding whether to go for wired or wireless connectivity.

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14
Q

IP address

A
  • Each device on a network has a unique Internet Protocol (IP) address
  • Used to make sure that packets of data can be sent from a source IP to a destination IP
  • Home network IP addresses look like 192.168.0.12
  • The last number is different for each device
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15
Q

Switch

A
  • Controls sending packets from source to destination
  • It is a piece of hardware used to connect together a number of devices to form a LAN that directs incoming data packets to all devices on the network (LAN)

  • Connect devices on a LAN
  • Receive data from one device and transmit it to the destination device using its MAC address
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16
Q

Simple Wired Network

A

Device A (192.168.0.14) –switch – Device B (192.168.0.7)

There is a lot of detail missing from this diagram. However, there is enough here for us to get an idea of what is happening. Removing unneeded detail is called ‘abstracting.’ The result of ‘abstracting’ is called an ‘abstraction.’ This diagram is an abstraction of a home network.

17
Q

WAP

A

Wireless access point - a hardware device that allows wireless devices to connect to the home network. It is wired into the switch.

18
Q

Router

A
  • It joins physical networks together.
  • A hardware device that enables data packets to be routed between different networks.
  • It can be used to join LANs to form a WAN.

-Transmit data between networks
-Connects a home/ office LAN to the Internet
-’Routers’ often actually contain a router, switch and WAP

19
Q

NIC

A

Network Interface Controller
- Used to connect to a network
- Available for both wired and wireless connections (wireless NIC)

20
Q

Bridge

A

A device that connects one LAN to another LAN that uses the same protocol (communication rules).
They are often used to connect together different parts of a LAN so that thy can function as a single LAN.

21
Q

Repeater

A

A device that boosts signals so they can travel greater distances. They amplify signals on both analogue (cooper cable) and digital (fibre optic cable) communication links.

22
Q

Ethernet

A

Ethernet: a protocol used by many wired LANs. A network using Ethernet is made up of:
1. A node (any device on the LAN).
2. Medium (the path used by the LAN devices such as an Ethernet cable.
3. Frames (data is transmitted in frames which are made up of source address and destination address).

23
Q

Conflicts

IP addresses

A

Devices on the same network may have been assigned the same IP addresses (if using dynamic IP addresses). Without a unique IP address it is not possible to connect to a network.
It can be resolved by restarting the router, as any dynamic IP addresses will be reassigned.

24
Q

Collision avoidance

Ethernet

A

Ethernet supports broadcast transmission (communications where pieces of data are sent from sender to receiver) and are used to send messages to all devices connected to a LAN.
A collision is where two messages are sent at the same time using the same data channel.
To resolve this issue Carrier sense multiple access with collision detection (CSMA/CD) was developed.

How this works:
1. When a frame is sent it causes a voltage change on the Ethernet cable.
2. If a collision is detected, a node stops transmitting a frame, and transmits a ‘jam’ signal instead.
3. It waits a random time period before trying again.

25
Q

Bit Streaming

A

Bit streaming is used in many areas including movie and music live streaming.
It is a contiguous sequence of digital bits sent over the internet/a network that requires a very fast data communication link.

It requires:
1. The files to have undergone some form of compression before transmission.
2. Buffering, to ensure smooth playback of the media files.
The data transmission rate from the file server to the buffer must be higher than the rate at which the data is transmitted from buffer to media player.
The larger the buffer, the better the control over the bit rate being sent to the media player.

26
Q

Internet

A

A network of networks, made up of computers and other electronic devices. It uses TCP/IP communication protocols.

27
Q

World Wide Web

A

A collection of multimedia web pages stored on a website. It uses the internet to access information from servers and other computers.

28
Q

Hardware used to support the internet

A
  1. A device (such as a computer, tablet or mobile phone)
  2. Telephone line/ mobile phone network connection/ wireless router
  3. A router
  4. An ISP (internet service provider)
  5. A web browser

The telephone network system (public switched telephone network/ PSTN) is used to connect devices and LANs between towns and cities.
Satellite technology is used to connect to other countries.

29
Q

Modem

A

Connects home network to the internet by converting digital signals from devices into analogue signals that can be transmitted over phone lines or cable networks.

30
Q

PSTN
Cell phone network
Dedicated lines

A
  1. PSTN - Public switched telephone network - network used by traditional telephones when making calls.
  2. Mobile phone providers act as the ISPs and the phones contain communication software which allow them to access the telephone network and internet connection.
  3. Dedicated lines - he development of technology such as WAPS, WLANs and fibre optic cables have enabled the growth of high speed broadband.
31
Q

IP address

A

Internet Protocol (IP): uses IPv4 or IPv6 to give addresses to devices connected to the Internet. The bits define the network (netID) and network host (hostID).
- netID allows for initial transmission to be routed.
- hostID is looked at by the receiving network.

IPv4 – IP address format which uses 32 bits such as 200.21.100.6

IPv6 – newer IP address format which uses 128 bits such as A8F0:3FFF:F0F1:F000:3DD0:256A:22FF:AA00

32
Q

Benefits of IPv6 over IPv4

A
  • Allows the internet to grow in terms of number of hosts
  • Has no need for NATs (network address translation)
  • Removed risk of private IP address collisions
  • Has built in authentication
  • Allows for more efficient routing
33
Q

Sub netting

A

Sub netting divides a LAN into two or more smaller networks. This helps to reduce network traffic and hide the complexity of the overall network

34
Q

Private IP addresses

A

Reserved for internal use behind a router. They allow for an entirely separate set of addresses within a network.
They allow access to the network without take up a public IP address space but devices using private IP addresses can’t be reached by internet users.

34
Q

Public IP addresses

A

These are allocated by a user’s ISP to identify the location of their device. Devices using these IP addresses are accessible from anybody using the internet.

35
Q

URL

A

Uniform resource locator

We use URLs to access websites. This is to make our life easier, as we remember words better than numbers

Each URL is made up of:
Domain host (www)
Domain name (name of website)
Domain type (.com, .org, .net etc)
A country code (.uk, .de, .br etc)

36
Q

DNS

A

URLs were only created to make it easier for us to remember websites. Computers can’t understand URLs, they can only work with the IP address.
The domain name service (DNS) converts a URL into an IP address the computer can understand

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