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AQA A Level Computer Science - RSFC > 9 - Fundamentals of Communication and Networking > Flashcards

9 - Fundamentals of Communication and Networking Flashcards

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1
Q

What is the Internet?

A

The Internet is a network of interconnected computer networks using a globally unique address space using TCP/IP and supports a range of application protocols.

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2
Q

What is the difference between the Internet and an internet?

A

An internet is a collection of networks which are connected together. The Internet describes the specific worldwide internetwork that uses a standard set of Internet protocols for transmitting messages between devices.

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3
Q

What is a Domain Name Server?

A

A Domain Name Server is a server that contains domain names and the associated IP addresses.

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4
Q

What is an IP address?

A

An Internet Protocol (IP) address is a unique number that identifies devices on a network.

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5
Q

What is the link between a domain name and an IP address.

A

A domain name is the string that corresponds to an IP address.

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6
Q

What does a router do?

A

Routers receive packets on a network and forwards them to the correct destination based on the address in that packet. It uses a table and algorithm to determine the best route onwards.

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7
Q

What does a gateway do?

A

A gateway receives packets on a network and forwards them to the correct destination based on an address. They allow two or more networks that use different link or network protocols to be connected so that information can be passed from one system to another.

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8
Q

What are the similarities and differences between A Router and a Gateway?

A

Similarities:
• Routers and Gateways both route internet messages.
• They both use destination IP addresses to make routing decisions.
• They both forward packets from one network to another.
• They both store known data about the networks they connect (routing tables).

Differences:
• A Gateway forwards messages between different networks (or between LANs and WANS) that use different protocols.

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9
Q

What does ISP stand for?

A

ISP stands for Internet Service Provider.

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10
Q

What is a packet?

A

A packet is a unit of data used in a packet-switched network. They contain part of a network message (payload) and control information (header).

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11
Q

What are the main items in the packet header?

A
  • The IP address of the sender and receiver.
  • The MAC address of the sender and receiver.
  • Which protocol is being used.
  • The packet number.
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12
Q

What is a NIC?

A

A Network Interface Card (NIC) is a circuit board that enables the computer to transmit and receive data in the network using an Ethernet Port, WiFi aerial/s, or both. Each NIC is assigned a MAC address.

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13
Q

What are the steps in packet switching?

A

1) Data is split into chunks, also known as packets. Each packet has a source and destination address, and payload. If more than one chunk is required, then the sequence position of each packet is noted.
2) Packets are sent separately on the network. They move from router to router, potentially taking different paths.
3) Packets may arrive out of order and if any packets are missing, a request is sent for their re-delivery.
4) Once all the packets have arrived, they are reordered using the sequence numbers.
5) A message is sent from B to A indicating that the message has been received (acknowledgement).
6) If A receives no acknowledgement within a reasonable amount of time, A sends the data again.

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14
Q

What does NIC stand for and describe how it fits into the “three-box model” of computer architecture.

A

NIC stands for Network Interface Card. It comes under the I/O part of the three box model. The NIC would contain the network I/O controller.

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15
Q

What are the differences between IPv6 and IPv4?

A
  • IPv6 uses 128 bits to store the IP address whereas IPv4 only uses 32 bits.
  • Different packet headers.
  • Simpler allocation of addresses to countries.
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16
Q

Why was IPv6 created?

A

Mainly because of the larger address space. A shortage of IPv4 addresses lead to fewer directly addressable parts of the Internet. Solutions such as subnetworks became necessary.

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17
Q

What are the potential barriers to the adoption of IPv6 worldwide?

A
  • It is not backwards compatible with IPv4.
  • Existing hardware needs to be updated to work with IPv6.
  • Needs to work alongside IPv4.
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18
Q

What is a protocol?

A

A protocol is a set of agreed signals for data exchange between systems.

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19
Q

What does TCP/IP stand for?

A

Transmission Control Protocol / Internet Protocol.

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20
Q

What are the four layers of the TCP/IP protocol?

A
  • Application Layer.
  • Transport Layer.
  • Network Layer.
  • Link Layer.
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21
Q

What does the application layer do?

A

The application layer uses protocols designed to work with specific types of applications. These handle the interaction with the user (eg. HTTP, IMAP, FTP).

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22
Q

What does the transport layer do?

A

The transport layer breaks application data down into packets and allocates sequence numbers, as well as source and destination port numbers to each packet. TCP also acknowledges the delivery of packets so that if it doesn’t receive an acknowledgement for a packet the packet is resent.

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23
Q

What does the network layer do?

A

The network layer prepares the packets for the Internet by adding source and destination IP address to each packet. All routers operate at this layer and look at the destination IP address to decide on the next appropriate hop. The network layer can also split, combine or resize packets if required.

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24
Q

What does the link layer do?

A

The link layer is responsible for the physical connection between various network nodes. It is responsible for adding the unique MAC address of the source device and the MAC address of the destination device for each hop. The MAC address is changed at each hop on the route.

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25
Q

For each of the layers in the TCP/IP protocol stack: state the name of the layer, the names of any relevant protocols at that layer and the important packet header fields that are dealt with at that layer.

A

• Application Layer.
- HTTP, HTTPS, FTP, SSH, IMAP, SMTP, POP3.
• Transport Layer.
- TCP.
- Header fields include source port, destination port and sequence number.
• Network Layer.
- IP.
- Header fields include source IP address and destination IP address.
• Link Layer.
- MAC, Ethernet, Wi-Fi.
- Header fields include source MAC address and Destination MAC address.

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26
Q

What is a MAC address?

A

A Media Access Control (MAC) address is a totally unique 12-digit hexadecimal code which is hardcoded during the manufacturing stage to every single NIC. The MAC address identifies the network adapter connected to the network so that the packet’s destination hardware address can be matched to a particular host with this adapter at its address.

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27
Q

Explain how MAC addresses change during the transmission of packets in the Internet.

A

The destination MAC address describes the exact computer for the packet’s next hop in the current network. The source and destination MAC addresses are stripped at each router and replaced with a new source (that of the router in the next network) and new destination (that of the new next hop).

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28
Q

What is a socket (in the context of TCP/IP and routing packets)?

A

A socket is the combination of an IP address and transport layer port number. It represents a particular process running on a particular Internet host.

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29
Q

What does a socket represent in Internet communication?

A

A socket represents a unique application on a logical device. It is the true source or destination of a TCP/IP message.

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30
Q

What is a port (in the context of TCP/IP and routing packets)?

A

A port is used to identify a particular process or application on a network.

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31
Q

What is the range of possible TCP port numbers?

A

0 to 65535 (16 bits of binary).

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32
Q 
What are the standard port numbers for:
• HTTP
• HTTPS
• SSH
• FTP
A

80
443
22
20 or 21 (or both)

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33
Q

Why might a traceroute show different hops when run a second time with the same destination address?

A

A link between routers might be busy and a different route is picked. Routers are determined dynamically as the packet moves from sender to receiver.

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34
Q

What is the World Wide Web?

A

A system of interlinked hypertext documents accessed via the Internet using HTTP protocol.

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35
Q

What is meant by the term packet switching?

A

A mode of data transmission in which a message is broken into packets which are each given a sequence number and are sent independently, over whatever route is optimum for each packet (which is determined by the routers), and reassembled at the destination.

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36
Q

What is encapsulation?

A

Encapsulation is where as each layer passes data down to the next, more information is added in a header. The total amount of information increases at each layer.

37
Q

What is the purpose of the protocol stack?

A

The purpose of the protocol stack is to transform the data from the application into a form suitable for transmitting “on the wire”.

38
Q

What happens to the data at the receiving end?

A

At the receiving end, the encoded data must work its way back up through the protocol stack until it is in a form that can be used by the application.

39
Q

What does FTP stand for?

What is FTP responsible for?

A

FTP stands for File Transfer Protocol.

FTP is an application layer protocol that enables files on one host to be copied to another host.

40
Q

What does HTTP stand for?

What is HTTP responsible for?

A

HTTP stands for Hypertext Transfer Protocol.

HTTP is an application layer protocol that is used for accessing web pages.

41
Q

What does HTTPS stand for?

What is HTTPS responsible for?

A

HTTPS stands for Hypertext Transfer Protocol Secure.

HTTPS is a web protocol that encrypts and decrypts user page requests as well as the pages that are returned by the web server.

42
Q

What does POP3 stand for?

What is POP3 responsible for?

A

POP3 stands for Post Office Protocol (v3).

POP3 is used to check for new emails and fetch stored emails.

43
Q

What does SMTP stand for?

What is SMTP responsible for?

A

SMTP stands for Simple Mail Transfer Protocol.

SMTP is used by email clients to send email.

44
Q

What does SSH stand for?

What is SSH responsible for?

A

SSH stands for Secure Shell.

SSH is used for remotely accessing and managing a machine using public key encryption.

45
Q

Describe the roles of each layer of the TCP/IP protocol stack when two devices are communicating over the Internet.

A
  • When two devices are communicating over the Internet, data is passed down the layers of the TCP/IP protocol stack from the application layer, to the transport layer, to the network layer and the link layer and then passed back up the stack on the receiving end.
  • The application layer selects an appropriate protocol for the communication. It’s role is to interact with the user via appropriate application software or the users system.
  • The transport layer establishes end to end communication. The transport layer splits the communication into packets and numbers them. It allocates source and destination port numbers. As well as this, the transport layer also deals with error control by sending acknowledgements to the sender.
  • The network layer supplies appropriate IP addresses for the source and destination. Routers operate at this layer and use destination IP addresses to route packets to their destination.
  • The packets are received from the network layer by the link layer which deals with the physical connection and moves packets between 2 internet hosts. The link layer also adds source and destination MAC addresses which are changed from link to link.
46
Q

Describe the roles of routers in a packet switched network.

A
  • To examine the destination of each packet.
  • To forward packets from one network to another.
  • To manage congestion.
  • Choose an appropriate forwarding route.
  • Route packets according to destination IP address.
  • Store incoming packets temporarily.
  • Change link address in packet.
  • To make use of a routing table.
47
Q

What is a client port?

A

A port that is temporarily assigned where the port number is automatically allocated.

48
Q

Why must port numbers for web servers be well known?

A

Because the communication is initiated by the client, so the client must know which port number to connect to.

49
Q

Explain how the TCP/IP stack determines which application layer software on the server should deal with a received request.

A

The transport layer will use the port number to determine which software should deal with the request.

50
Q

Explain what the key exchange problem is, in relation to a symmetric cipher.

A

The problem is how to pass the key to the receiver without it being intercepted.

51
Q

Explain the difference between a symmetric and an asymmetric cipher system.

A

For symmetric, the same key is used to encrypt and decrypt, whereas for asymmetric different keys are used for encryption and decryption.

52
Q

What is encryption?

A

Using an algorithm to convert a message into a form that is not understandable without the key to decrypt it.

53
Q

What is Serial Data Transmission?

A

Data bits are sent in a sequence, one after the other, over a single wire from the source to the destination.

54
Q

What is Parallel Data Transmission?

A

Multiple bits are sent simultaneously over multiple parallel wires from the source to the destination.

55
Q

What is a problem with Parallel Data Transmission?

A

There is a possibility that data skew may occur as the bits could travel at slightly different speeds over each of the wires.

56
Q

What are the advantages of serial over parallel data transmission?

A
  • Parallel communication requires more wires and hardware; therefore, serial transmission tends to be cheaper.
  • With parallel communication, there is a risk of data skew over long distances, whereas serial is reliable over much longer distances.
  • Parallel communication carries the risk of crosstalk between wires which results in more chance of errors. This is largely avoided with serial transmission.
  • Serial transmission suffers from little interference at high frequencies, so the serial frequency can be much higher than with parallel transmission. This results in higher net data transfer rates.
57
Q

What is the bit rate?

What unit is it measured in?

A

The number of bits that are transferred between devices in one second.

It’s measured in bits per second. (Typically megabits or gigabits per second).

58
Q

What is the baud rate?

What unit is it measured in?

A

Number of signal changes in a communications channel per second.

It’s measured in bauds.

59
Q

What is the relationship between bit rate and baud rate?

A

bit rate = baud rate × number of bits per signal

60
Q

What is bandwidth?

What unit is it measured in?

A

A measure of the maximum capacity of a given communication channel.
(Bandwidth and bit rate are directly proportional).

It is measured in hertz.

61
Q

What is latency?

A

Time delay between the moment an action is initiated and the moment its effect begins.

62
Q

What is synchronous transmission?

A

Data is transferred at regular intervals which are synchronised by a clock pulse signal.

63
Q

What is asynchronous transmission?

A

Each byte is sent separately and the receiver and transmitter do not need to be synchronised, as the bytes are sent as soon as they are ready. To control the communication start and stop bits are used.

64
Q

How are start and stop bits used in asynchronous transmission?

A

A start bit is sent at the beginning of the transmission so that the receiver can prepare for the incoming data, and a stop bit marks the end of the transmission.

65
Q

Why do you need both start and stop bits?

A

Because there is no common clock signal, start and stop bits have to be used to control the communication.

66
Q

What is a parity bit?

A

It’s a bit that is computed by counting the number of 1s and 0s in a data group which is appended to the data to allow errors to be detected.

67
Q

Define the term virus and explain briefly how it works.

A

A virus is a small computer program attached to another file or piece of software and is created to cause damage or harm to the target computer system. The first thing that will be done when the program is executed is it will copy itself to the local disk and
then hide itself to help prevent detection. After being copied to the local disk the virus can reside in memory and reconfigure the system so it carries out the intended disruption.

68
Q

Define the term worm and describe how it differs from a virus.

A

A worm is a program designed to replicate itself to spread across a computer network such as the Internet. A worm is a complete program as opposed to a virus which gets attached to a program. A worm can also run and travel without any human action.

69
Q

Define the term trojan and describe how it differs from a virus.

A

The Trojan will appear to be a useful software application but will actually do damage once installed or run on your computer. Trojans, therefore, are usually run because they trick the user into running it as it appears to be legitimate software or files from a trustworthy source. Trojans do not spread by infecting other files and they do not self-replicate.

70
Q

Some firewalls use stateful inspection. Why is this more effective than stateless inspection at stopping cyberattacks?

A

Dynamic filtering keeps track of open connections and checks the payload of a packet as well as its header, so unexpected packets can be blocked even after a connection is authorised.

71
Q

Explain how a thin-client network works.

A
  • Most processing is done by a central server
  • The user input is transmitted from the terminal to the server over the network
  • Data needed to produce image is transmitted from server to the terminal over the network
  • Applications are not installed on thin client workstations
  • Operating system is loaded by clients from server at boot
72
Q

Explain how the use of a thin-client network instead of a traditional rich-client (thick-client) network will affect the selection of the hardware of the system.

A
  • Higher bandwidth network connection required
  • Network must use switch not hub
  • Slower processor and reduced RAM
  • Server must have multiple processors and a lot of RAM
73
Q

What is the relationship between bit rate and bandwidth?

A

Bit rate is directly proportional to bandwidth.

74
Q

Explain how it is possible for the number of bits transmitted per second to be higher than the baud rate.

A

Each signal change represents more than one bit of data.

75
Q

What do start and stop bits do in asynchronous transmission?

A

The start bit is used to synchronise a clock in the receiving device. This means both devices are in step.
Once that has been received, timed periods will be used to receive the remaining bits in the transmission.
A stop bit indicates the end of the data.
The stop bit allows the receiver to identify when the next start bit arrives.

76
Q

What is an advantage of using synchronous transmission over asynchronous transmission?

A

Faster transmission because fewer bits have to be transmitted.

77
Q

What are the differences between a client and a server?

A
  • Client sends requests, server sends responses
  • Server can decide which data is sent, whereas client cannot
  • Servers are usually always on, whereas clients do not need to be
  • Clients are user facing, whereas servers are not
78
Q

Explain why it is common practice for servers to be always running and for clients to be sometimes running?

A
  • Clients should be able to connect at any time to the server
  • The client only needs to be running while the user is accessing the service
  • If the server is shut down, no one will be able to access the service
79
Q

An advantage of peer-to-peer networks over client-server models is that they are cheaper for the founder to run. Explain why this is the case.

A

Servers are more expensive to run because they are more powerful machines, they need more storage space and they need to be always powered on. In p2p, no one is responsible for a server. As more hosts connect to a p2p network, the resource supply increases, whereas when more hosts connect to a single server, the more powerful and expensive the server machines need to be.

80
Q

What are the advantages and disadvantages of thick client computers?

A

Advantages:
• Internet connection not needed to do useful stuff
• Can be used for storage of many files and large files
• More flexible in what can be done (whereas thin are limited to what cloud-based services exist and how they work)

Disadvantages:
• More expensive to buy and maintain
• Sometimes harder to use
• Sometimes less secure because the user is responsible for management of files and programs

81
Q

Explain why a client-server network is likely to be more appropriate than a peer-to-peer network in a situation where a system (for the administration of student courses to be used in an office in a college) must allow users at ten workstations to access and update a central database

A
  • System will be storing confidential data that must be kept securely
  • Administration will be easier
  • Centralised backup
  • Harder for users to change security settings
  • Running database from a server will avoid concurrency issues
  • Running database from server will ensure that it is always available
  • Server may allow more simultaneous connections than a workstation
82
Q

Explain the differences between client-server and peer-to-peer networking

A 
With client-server networking:
• Resources are stored on the server
• Clients access resources from server
• Centralised security management
• Configuration requires greater expertise

With peer-to-peer networking:
• Resources stored on each individual computer
• Any computer can access resources from any other
• Each computer has equal status
• Management of security could be more difficult
• There is no dependence on a server

83
Q

Describe the different parts of the URL http://www.aqa.org.uk/qual/gce/computing_new.php

  • http://
  • www.aqa.org.uk
  • /qual/gce/computing_new.php
A
  • http:// → the protocol used
  • www.aqa.org.uk → address of Aqa’s World Wide Web server
  • /qual/gce/computing_new.php → the path of the resource
84
Q

What is the purpose of a Domain Name Server on the Internet?

A

To resolve domain names into IP addresses

85
Q

Why do people prefer to use a fully qualified domain name (FQDN) rather than an IP address?

A

IP addresses are less memorable

86
Q

Explain what each of these parts of the URL http://www.aqa.org.uk mean

  • http://
  • www
  • uk
A
  • http:// → means Hypertext transfer protocol will be used
  • www → resource is on a web server
  • uk → country the site is registered in
87
Q

Describe how domain names are organised

A

Domain names follow a hierarchy. When forming a domain name, the leaf node appears first, then parents separated by dots. Each top level domain is managed by an internet registry.

88
Q

What is the purpose and function of the domain service, and describe its reliance on the Domain Name Server system

A

The domain service provides a mapping between domain names and IP addresses.
A registrar can help you find an authoritative name server. This name server must always have the most up-to-date record of your server’s IP address. A DNS lookup is used to find the IP address of the host before the web request is sent.

AQA A Level Computer Science - RSFC (12 decks)

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