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My Comp Sci > 4.9 - Fundamentals of communication and networking > Flashcards

4.9 - Fundamentals of communication and networking Flashcards

1
Q

What is baud rate?

A

The number of signal changes per second.

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2
Q

What is bit rate?

A

Number of bits transmitted per second.

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3
Q

What is the formula for bit rate?

A

Baud rate x number of bits per signal

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4
Q

What is bandwidth?

A

The maximum rate of data transfer of a communication channel.

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5
Q

What is latency?

A

Difference in time between a signal being sent and it being received.

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6
Q

What is a protocol?

A

A set of rules that determine the communication between devices.

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7
Q

What is skew?

A

When the bits sent over a parallel medium are not received together, which in extreme cases can lead to bits from different pulses overlapping, causing corruption of data.

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8
Q

What is crosstalk?

A

When parallel communication lines are tightly packed, signals from one line can leak into another, causing data corruption.

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9
Q

What is synchronous transmission?

A

When data is sent at regular intervals determined by the common clock signal of the two devices.

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10
Q

What is asynchronous transmission?

A

Data is sent when it is available and transmissions use start and stop bits to indicate the duration of transmission. Both devices must have the same Baud rate, and clocks are only synchronised during the transmission.

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11
Q

What is physical network topology?

A

The actual architecture of the network, that describes how components are interconnected.

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12
Q

What is physical star network topology?

A

Each client has its own direct connection to the central hub. The hub receives packets for all clients and is responsible for delivering them to the correct recipient

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13
Q

What are the advantage of a physical star network?

A

Packets sent directly to recipient - other clients cannot see

Easy to add and remove clients

Each cable has one device communicating over it, reducing chance of collisions.

Failure of one cable does not affect performance of whole network.

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14
Q

What are the disadvantages of a physical star network?

A

All communication stopped if central hub fails

Expensive due to amount of cable

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15
Q

What is physical bus topology?

A

Connects clients to a single cable called a backbone. Device called a terminator placed at either end of backbone. No need for central hub.

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16
Q

What are the advantages of a physical bus network?

A

No central hub, reducing chances of network failure and decreasing cost of installation

Inexpensive as minimum length of cable required.

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17
Q

What are the disadvantages of a physical bus network?

A

All clients see all packets due to backbone

Backbone used for communication by multiple clients, increasing risk of collision.

All communication stopped if backbone fails.

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18
Q

What is logical network topology?

A

The flow of data packets within a network. A logical bus network delivers packets to all clients, whereas a logical star network delivers packets only to their recipient.

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19
Q

What is a host?

A

A device on a network that provides services, often a server which provides file storage, printer sharing and internet access.

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20
Q

What is client-server networking?

A

One or more central severs provide services to clients. Clients request services from servers, which respond to the client with the requested service. Allow for central management of clients on the network, improving security.

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21
Q

What is peer-to-peer networking?

A

Services provided by clients themselves and every client has equal status. Primary disadvantage is all clients providing services must be running for network to be fully operational. However, more cost effective since no need for powerful server, and easier to set up and maintain.

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22
Q

What are peer-to-peer networks often used for?

A

Large file-sharing networks and multimedia providers.

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23
Q

What do wireless networks require?

A

A wireless access point which connects to a wired network, and a wireless network adapter in the device that connects to the wireless network.

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24
Q

What are the three methods of securing a wireless network?

A

Encrypting transmitted data using WPA or WPA2

Disabling SSID broadcast

Set up a MAC address filter

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25
Q

How does WPA work?

A

Stands for WiFi protected access and requires that a new wireless client enters a password in order to connect to the network.

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26
Q

How does disabling SSID broadcast work?

A

SSID stands for service set identifier and is the name that identifies a wireless network. Disabling SSID broadcast means wireless devices within range cannot see the network is available, so only those who know the SSID can connect.

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27
Q

How does a MAC address filter work?

A

MAC address whitelists can be created to allow only specific devices to connect to a network. Likewise, MAC address blacklists can be created.

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28
Q

What is CSMA/CA?

A

Carrier sense multiple access with collision avoidance. A protocol used in wireless networks to avoid data collisions caused by multiple devices communicating simultaneously.

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29
Q

How does CSMA/CA work?

A

Transmitting device listens to its communication channel. If idle, transmits data. If not, waits random period of time and checks again.

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30
Q

Why is the RTS/CTS protocol added to CSMA/CA?

A

To get around the problem of hidden notes (when a transmitting device cannot see some parts of the network on which the communication may be occurring)

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31
Q

How does RTS/CTS work?

A

Once transmitting device has checked if channel idle, sends ‘request to send’ message to server. If server actually is idle, responds with ‘clear to send’ message, and communication can begin. If no ‘clear to send’ then server is busy and device must wait a random period of time and start the process all over again.

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32
Q

What is the Internet?

A

A network of interconnected computer networks which uses an end-to-end communication protocol (TCP/IP). It is mostly a wired network with cables that pass under oceans.

33
Q

What is an internet service provider (ISP)?

A

A company that provides its customers with access to the Internet.

34
Q

How is a national internet service provider different to a regular ISP?

A

They are the largest ISPs and provide internet access to smaller regional and local ISPs, from whom homes and businesses can then buy their internet access.

35
Q

What is a packet?

A

A container in which data is transmitted over networks.

36
Q

What are the primary components of a packet header?

A

Sequence number
Source and destination port numbers
Source and destination IP addresses
Checksum
Source and destination MAC addresses
Time to live

37
Q

What is a router?

A

A networking device that forwards data packets between networks.

38
Q

What is a gateway?

A

A router that converts between different protocols, which strips away everything other than the packet’s contents, and adds new sender and receiver addresses which comply with new protocol.

39
Q

What does the domain name server system do?

A

Maps fully qualified domain names to their corresponding IP addresses. It is a distributed database of mappings.

40
Q

What is a fully qualified domain name?

A

It describes the internet host and is made up of the host name and domain name.

41
Q

What is a domain name?

A

A name that identifies an organisation or individual on the internet.

42
Q

How does the domain name server system work?

A

A DNS stores a table of FQDNs and their corresponding IP addresses. If a DNS does not have a record of the FQDN you are trying to find, your request will be passed to another DNS.

43
Q

What are internet registries?

A

Organisations responsible for allocating IP addresses.

44
Q

What is a firewall?

A

Sits between device and internet, regulating packets that pass through it. Can either be software or hardware and work as a proxy server that can perform both packet filtering and stateful inspection.

45
Q

What is packet filtering?

A

Firewalls accept and block packets based on source IP address or the protocol they are using.

46
Q

What is stateful inspection?

A

Examining contents of packet before deciding if allowed through. Some firewalls keep record of current connections in network, and filter out packets that aren’t related to activity on network.

47
Q

What is a proxy server?

A

Server that sits between public network and private network. Manages every packet passing between. When device from private network sends packet into public network, IP address of server used as source address, providing some anonymity.

48
Q

What is symmetric encryption?

A

Both sender and receiver share same private key, used to encrypt and decrypt. Before sending info, must participate in key exchange. If key exchanged over network, vulnerable to interception.

49
Q

What is asymmetric encryption?

A

Four different keys used. Each device has private and public key, the two of which are mathematically related. When message encrypted with public key, only corresponding private key can decrypt it and vice versa. Before message sent, encrypted with recipient’s public key.

50
Q

What is a digital signature?

A

Used to verify sender of a message and verify message has not been tampered with.

51
Q

How do digital signatures work?

A
  1. Digest of message created by hashing algorithm. Value depends on contents so not the same if message changed.
  2. Digest encrypted with sender’s private key.
  3. Encrypted digest appended to message.
  4. Message and appended digest encrypted with recipient’s public key.
  5. When recipient receives, decrypt message with own private key, decrypt digest with sender’s public key, then same hashing algorithm on message and compares with digest.
52
Q

What is a digital certificate?

A

Verifies ownership of a key pair and can be used to check that fake key pair isn’t being used by imposter. Issued by certificate authorities and contains: serial number, owner’s name, expiry date, public key and certificate authority’s digital signature.

53
Q

What is a worm?

A

Piece of malicious software that can self-replicate between computers, either within network or by users downloading and running malicious file.

54
Q

What is a trojan?

A

Malware disguised as benign file that tricks users into opening. Often spread as email attachments or downloaded from malicious websites.

55
Q

What is a virus?

A

Malware that requires host file. Usually executable files, so viruses dormant until host file opened or run. Can spread between computers over private network, the internet or even physical media like hard drives.

56
Q

How can you prevent malware?

A

Good code quality: malware often exploits bugs in code, small oversights can have devastating consequences.

Anti-virus software: scan files and remove any suspicious files.

Employee training: in organisations, train employees about risks of opening suspicious email attachments.

57
Q

What does the application layer do?

A

Selects and uses the correct protocol to transmit data, and interacts with user with application software.

58
Q

What does the transport layer do?

A

Establishes a virtual path and splits the transmission into packets. Adds sequence number to each packet, as well as port number.

(Also sends and receives acknowledgements)

59
Q

What does the network layer do?

A

Attaches source and destination IP addresses for each packet.

60
Q

What does the link layer do?

A

Attaches source and destination MAC addresses, which change at each hop through the network.

61
Q

What is a socket?

A

A combination of an IP address and port number, in the format IP:Port

62
Q

What are the two parts of an IP address?

A

Network identifier and host identifier. Each computer in a network shares same network identifier but has own host identifier.

63
Q

What is a subnet?

A

A subdivision of a network, where each subnet has a different network identifier. The network identifier can be determined with a subnet mask.

64
Q

How do you use a subnet mask?

A

AND the binary IP address and binary subnet mask.

65
Q

What is a host ID with all 0s reserved for?

A

Network identifier

66
Q

What is a host ID with all 1s reserved for?

A

Broadcast address for a subnet

67
Q

What is a host ID of 1 reserved for?

A

Default address of a router

68
Q

Why was IPv6 introduced?

A

We are running out of IPv4 addresses and IPv6 allow for far more permutations.

69
Q

What is a routable IP address?

A

A globally unique address, where every network in the world has its own routable IP address.

70
Q

What is dynamic host configuration protocol?

A

Protocol used to assign IP addresses to devices as they join a network, from a pool of available addresses, for the duration of their session. Once the device leaves the address is returned to the pool.

71
Q

How does network address translation work?

A

When a device on a private network needs to communicate to a device on the internet, it sends a packet through the router, which makes a record of the packet before replacing the private IP address of the computer with its own routable IP address. When response received, it is sent to router’s public IP address, which then forwards the response to the correct private IP address.

72
Q

What is port forwarding?

A

Used when client needs to communicate with server connected to a private network.

Client sends packets to public IP address of router belonging to server’s private network. Packets sent by client contain port number of application running on server that client wishes to access.

Private network’s router then forwards the packets to the server using NAT.

73
Q

What is an application programming interface (API)?

A

Set of protocols relating to how different applications communicate with each other. Define how interaction between applications should be carried out, allowing applications to make use of other applications.

74
Q

What is the websocket protocol?

A

API which operates in application layer. Provides constant stream of info between two devices, usually client’s web browser and a server.

Connection is full-duplex - data can be transmitted in both directions at the same time.

Fast transmission of data by reducing size of packet headers, used for video streaming, online games and instant messaging.

75
Q

What is CRUD?

A

Acronym for create, retrieve, update, delete: four commands used to query online databases.

76
Q

What is REST?

A

Acronym for representational state transfer. Design methodology for online database applications that are queried with web browser.

Uses four HTTP request methods POST, GET, PUT and DELETE.

77
Q

How does REST work?

A
  1. Request by client to web browser
  2. Browser responds with web page as text file
  3. File contains JavaScript which loads API that uses rest to enable database server to be queried by client
  4. Client sends HTTP requests to server
  5. Server responds to request using JSON or XML
  6. Browser processes JSON or XML and displays response to user
78
Q

How do XML and JSON compare?

A

JSON is more compact, easier to read, easier to create and faster to process. XML sometimes seen as more flexible.

79
Q

What is a thin-client network?

A

Majority of network’s processing power belongs to server which provide services and resources including storage and processing.

Easy to add new clients, and clients are inexpensive machines.

Greater centralised control of network.

Require powerful server which is expensive and complex to set up and maintain.

My Comp Sci (7 decks)

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