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OCR A LEVEL COMPUTER SCIENCE > 1.3.3 - Networks > Flashcards

1.3.3 - Networks Flashcards

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1
Q

What are the advantages and disadvantages of a private network?

A

Advantages
1) Security
2) Control of access
3) Confidence of availability

Disadvantages
1) Need specialist staff, organised backups and security

Most companies use the cloud now

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2
Q

What are 3 network topologies?

A

Bus, Ring/mesh, Star

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3
Q

What is a star topology?

A

Where client machines are connected to a central switch or hub (which keeps a record of the MAC address), which is usually in turn connected to one or more servers.

Signals travel in either direction.

They are resilient.

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4
Q

What is the bus topology?

A

Where the computers and other devices are attached to a single backbone. A terminator is attached at each end to prevent reflection of signals. Signals travel in either direction.

Are vulnerable to breakages.

Bus topologies are prone to data collisions.

They are uncommon these days.

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5
Q

What is the ring/mesh topology?

A

Each node connects to exactly 2 other nodes.

Data frames are sent in one direction to minimise collisions.

Ring topologies are easily disrupted.

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6
Q

What are protocols?

A

A set of rules to control and govern data transmission between devices on a network.

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7
Q

What is a network?

A

A network is a set of interconnected devices (such as computers, printers, and servers) designed to share resources, exchange data and communicate with each other.

The main purposes of a network are to enable data sharing, resource sharing, communication, and collaboration

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8
Q

What is a standard?

A

A set of specifications for hardware or software, agreed upon by academic and industry contributors.

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9
Q

What is the difference between the internet and world wide web?

A

The World Wide Web is a collection of web pages that reside on computers connected to the internet. The Internet is a network of networks set up to allow computers to communicate with each other globally.

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10
Q

What is an ISP?

A

An organization that enables individuals and businesses to connect to the Internet by allowing users to connect to backbone cables.

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11
Q

What is a URL?

A

URL stands for Uniform Resource Locator and it points to resource files on the Internet.

URL has four components: http://www. address. com:80/index.html, where:
-http - protocol name
- address - IP address or host name
- 80 - port number
- index.html - file path.

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12
Q

What are internet registrars?

A

Hold records of all existing website names and the details of the those domains that are still available to purchase.

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13
Q

What are internet registries?

A

5 Organisations apart of ICANN (Internet Corporation for Assigned Names and Numbers) that hold records of all the domain names currently issued to users and their details. Such as the registrants name, type

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14
Q

What are domain names?

A

Identifies the area that an internet resource resides in. Its the unique name that appears after www (www.example.com).

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15
Q

Explain the process that allows people to access websites when they enter a domain name

A

1) The domain name is sent to the DNS Server
2) The DNS Server maps the domain name to an IP Address
3) If the DNS server cannot resolve it, it is passed onto another DNS Server.

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16
Q

What is a DNS Server?

A

Is a naming database which domain names are translated into IP addresses

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17
Q

What is a LAN and WAN?

A

Local Area Network - a network that connects computers within a limited area such as a school or office

Wide Area Network - uses long-range telecommunication, links across country or continent such as the Internet.

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18
Q

What is an IP address?

A

Each device on an IP network has a numerical address made of 4 numbers each between 0 and 255 i.e. 32
hexadecimal digits that uniquely identifies a device on a network. It is a logical identifier so can change on a physical device. Is used to route messages.

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19
Q

What is TCP/IP?

A

It is a suite of protocols developed for the internet that covers:
- data format
- addressing
- routing
- receiving.

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20
Q

What 4 layers does the TCP/IP stack use?

A

Application
Transport
Internet
Link

21
Q

What is the application layer in the TCP/IP stack?

A

-Capturing and delivering data, packaging.

-Uses protocols relating to the application being used to transmit data over a network, usually the internet.

-If this is a browser for example, it would select an appropriate higher-level protocol for the communication such as HTTP, POP3 or FTP.

22
Q

What is the transport layer in the TCP/IP stack?

A

-Establishment and termination of connections via routers.
- Uses the Transmission Control Protocol (TCP) to establish an end to end connection with the recipients computer.
-Data is split into packets, labelled with the packet number, total packets and the port number.

23
Q

What is the internet layer in the TCP/IP stack?

A

-Provides means of transmission across different types of network.
-Concerned with IP addressing and direction of datagrams.
-Adds the source and destination IP addresses.
-Adds the port number which tells the data which device the packet must be sent to
-Adds the application being used on that device to receive the data.

24
Q

What is the link layer in the TCP/IP stack?

A

-Concerned with passing datagrams to physical devices and media.
-Adds the MAC addresses identifying the NIC of the source and destination computers.
-This means that once the packet finds the correct network it can locate the hardware.

25
Q

What is layering?

A

Is a form of abstraction.

Division of a complex system into its component parts.

Allows work to be carried out piecemeal.

Each layer communicates only with adjacent layers.

Allows efficient problem solving – focusing on one part of the problem in isolation.

26
Q

What is a MAC address?

A

Are unique identifiers associated with a network interface. They:
- provide addressing capability in a network.
- are usually assigned by the manufacturer.
- are 48-bit (6-byte) addresses, i.e. 6 octets, e.g. DC-85-DE-4B-FB-3A

27
Q

What are packets?

A

File is divided or split into equal groups of bits of standard size made up of control bits and data.

Have a structure defined by the protocol being used.

Each has an identity on the label attached stating the following. There are 3 basic parts:

Header:
- Sender’s/ transmitting IP address
- Receiver’s/destination IP address
- Protocol being used
- Packet number and order, i.e. the place of the packet in the complete message

Payload:
- The data file to be transmitted

Trailer:
- End of packet marker
- Error correcting code

28
Q

What is cirucit switching?

A

There are three phases:
- connection establishment
- data transmission
- connection termination.

Physically connects devices together - so-called ‘connection mode’.

Devices remain connected for the duration of data transmission.

Establishes a route before transmission between the two computers for the duration of the message.

Ties up large areas of network so no other data can use any part of the circuit until the transmission is complete.

Sends all packets on the same reserved route down the circuit in order.

Message can be interpreted if the route is tapped into.

Packets remain in correct order but must be reassembled at the destination.

29
Q

What is packet switching?

A

Central to the success of the internet.

Is connectionless mode, i.e. no permanent connection is established for the message.

Has no established route or pre-set path.

At each node on the network the destination address is read and the best available route is found from source to
destination

This means individual packets being sent on to the network on the most convenient or avoidable paths.

Transmission is safer from interception and avoids message failure if a route is disrupted because it is impossible
to intercept all packets as they use different routes so is more secure.

Packets arrive out of order at the receiving end and need to be reordered and message is reassembled to recreate
the data at its destination.

Only as fast as the slowest packet.

Maximises use of the available infrastructure very efficiently as each channel is only used for a short time so does
not tie up a proportion of the network.

Loss of part of the communication will not be fatal because if there is an error then only a small, identifiable, part
of the data or one packet is affected which can be retransmitted easily if the message does not arrive safely.

Error checking promotes successful transmission.

30
Q

What are firewalls?

A

Are anti-hacking applications (hardware and/or software) that sit between the system and external access to
control traffic signals and into and out of a network, ensure communications are restricted and attempt to limit or prevent access to the system by particular unauthorised sources, systems, users or external machines.

31
Q

What is a proxy?

A

Is a computer placed between a network and a remote resource that intercepts traffic and restricts the users
allowed access to individual machines on network from in the internet to isolate the network from the outside world.

32
Q

What is denial of service? (DOS)

A

Attacks send requests from multiple users, or bots, to disrupt the service for political reasons or
simply to blackmail the service owner/provider.

33
Q

What are 8 networks hardware’s?

A

Routers

Switches

Hubs

WAPs

NICs

Cables

Modems

Gateways

34
Q

What is a router?

A

Responsible for routing data between devices, connecting at least two networks together (like connecting a LAN to your ISP).

Works as the network layer.

35
Q

What is a modem?

A

Alters the signal between A and D to act as a gateway to the WAN

Works at the physical and data link layers.

(connect to the outside world, and to connect router via ethernet)

36
Q

What is a NIC?

A

A communications device that enables a computer or device that does not have built-in networking capability to access a network.

There is a wireless and a wired version.

Works at the physical and data link layers.

37
Q

What is WAP? (Wireless Access Point)

A

A switch that allows devices to connect wirelessly

Is usually connected to a router.

Works at the data link layer.

38
Q

What is a hub?

A

A hub is a networking device, that allows devices to connect to a network.

Broadcasts the signals they receive to all connected computers, unlike a switch, which only sends data to the intended recipient.

This greatly decreases network performance due to the amount of transmissions.

39
Q

What is a switch?

A

A switch is a network device which creates a separate collision domain on each port, while remaining within a single broadcast domain.

Much faster than hubs due to device having an individual port for a device.

40
Q

What are three types of cables used in netwrorks?

A

Fibre optic - Glass fibres, fastest bandwidth but are expensive, longest distant connections.

Twisted Pair - Copper wiring, but low bandwidth

Coaxial - 4 components, faster bandwidth but are more expensive than twisted pair

41
Q

What is FTP used for?

A

File transfer Protocol
Used to access, edit and move files between devices on a network (e.g. to access files on a server from a client computer)

42
Q

What is POP3 used for?

A

Post Office Protocol 3
Used to retrieve emails from a server. The server holds the email until you download it, at which point it is deleted from the server

43
Q

What is IMAP used for?

A

Internet Message Access Protocol
Stores the message on a server and synchronizes the message across multiple devices.

44
Q

What is SMTP used for?

A

Simple Mail Transfer Protocol
Used to send emails. Also used to transfer emails between servers.

45
Q

What is HTTP/HTTPS?

A

HyperText Transfer Protocol/ Secure.
Uses encryption for secure communication over a computer network, and is widely used on the Internet. In HTTPS, the communication protocol is encrypted using Transport Layer Security

46
Q

What is a Client-Server network?

A

A server controls:
-Access and security for a shared file store
-Manages access to the internet
-Manages printing jobs
-Provides email services
-Runs regular backups of data

A client makes requests to the server for data, connections and other services.

47
Q

What is a Peer-to-Peer server?

A

All computers are of equal status.

Computers can act as a client or server, or both.

Useful on the internet so traffic can avoid servers.

Is private so there isn’t a reliance on the company’s server and its connection to the Internet.

This means it hasn’t got to invest in lots of expensive hardware and bandwidth so is cheaper.

The system is likely to be more fault tolerant.

48
Q
A

OCR A LEVEL COMPUTER SCIENCE (20 decks)

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