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Computer Science Paper 2 > Fundamentals of Communication and Networking > Flashcards

Fundamentals of Communication and Networking Flashcards

1
Q

Describe serial data transmission

A

Bits are sent one after another along a single wire from source to destination.

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2
Q

Describe parallel data transmission

A

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

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3
Q

What is the issue with using parallel transmission over long distances?

A

Each individual wire has slightly different properties, so bits may travel at slightly different speeds, causing skew (data arriving at slightly different times).

Serial transmission is reliable over much longer distances.

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4
Q

Where is parallel transmission used?

A

Over short distances, typically within integrated circuits and within random access memory (RAM).

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5
Q

As the strength of the signal increases, what issue becomes worse over parallel transmission?

A

Crosstalk
This is interference between different lines which can result in data corruption.

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6
Q

Why does serial transmission tend to be cheaper than parallel transmission?

A

There is much less complexity in the connections and the physical size of the cables is smaller.

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7
Q

Why does serial transmission result in higher net data transfer rates?

A

It suffers from little interference at high frequencies, allowing the signal frequency to be much higher.

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8
Q

Describe synchronous transmission.

A

Data is transferred at regular intervals, controlled by a clock signal.

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9
Q

Describe asynchronous transmission.

A

Each byte is sent separately, as soon as they are ready.

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10
Q

What type of communication makes use of synchronous transmission?

A

Parallel

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11
Q

How does a receiving computer differentiate between data sent with asynchronous transmission?

A

Each “character” is sent with a parity bit, and a start and stop bit.

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12
Q

Define latency

A

A time delay before some component in a computer system responds to an instruction.

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13
Q

What is a protocol?

A

A set of rules relating to communication between devices.

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14
Q

Define bitrate

A

The number of bits per second that can be transmitted between devices.

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15
Q

Define baud rate

A

The rate at which signals along a wire can change state.

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16
Q

What is bandwidth in relation to communication?

A

The range of signal frequencies a communications channel may transmit.

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17
Q

What does bandwidth have a direct relationship with?

A

Bit rate

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18
Q

What is a network topology?

A

The way a network and its connected devices are connected.

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19
Q

State an advantage of using a bus topology.

A

It is cheap to install as it does not require any additional hardware beyond the main cable.

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20
Q

State two disadvantages of using a bus topology.

A

If the main cable fails, no network data can be transmitted.
Performance degrades heavily with increased traffic.
Security is poor as all the computers on the network can see what is being transmitted.

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21
Q

What are the advantages of using a star topology?

A

Each computer has its own cable to the server, so there are no collisions and performance remains consistent, even with high traffic.

If a single cable fails, only the computer is affected. This makes it easier to isolate faults.

Easy to add new computers to the network.

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22
Q

What are the disadvantages of using a star topology?

A

Can be costly to install as lots of cabling is needed.
If the switch stops working, the entire network is unable to transmit data.

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23
Q

Describe the difference between physical and logical topology.

A

The physical topology is how the devices are physically connected.
The logical topology is placed onto the physical topology, it is how the data is transmitted.

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24
Q

What is a client-server network?

A

A centralised server receives and responds to requests for services and data from multiple clients. Here, the clients are server are differentiated.

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25
What is a peer-to-peer network?
A decentralised communications model where participants, called peers, interact directly with each other without the need for a server.
26
Why can wireless signals can be intercepted more easily than wired signals?
You don't have to be physically connected to the network, you can simply be in range.
27
How are wireless networks differentiated?
Through the use of a service set identifier (SSID).
28
Why might an SSID be hidden from broadcast? How can the network still be joined?
It is an added security measure. In order to join the network, the exact SSID must be known and entered.
29
What is the purpose of WIFI?
It allows a large number of users to move around freely (wireless network). It is easy to set up, less expensive, and convenient to use.
30
What are some of the challenges faced by Wireless Local Area Networks (WLANs)?
Speeds are slower compared to wired networks. Signals can easily be obstructed. Less secure then wired networks. Relies on signal strength coming from WAP.
31
What is the role of a network interface card (NIC)?
It is a hardware device used to connect a device to a network.
32
How does a NIC convert data to be sent into appropriate signals that can be carried across a medium?
In wired networks, the signal is a voltage through a wire, or pulses of light through a fibre. In wireless networks, it is a modulated radio wave.
33
What unique identifier does each NIC have?
A Media Access Control (MAC) address. This is allocated by the manufacturer and cannot be changed.
34
What does a hub do?
Repeats messages to all connected devices. This is inefficient because the data reaches places other than its intended destination.
35
What does a switch do?
Only sends a message to its intended destination device.
36
How does a switch work?
It builds up a table with MAC addresses of every connected device. When a signal is received, the data is analysed to determine the destination MAC address. The data is then sent to the port connected to the device with the destination MAC address.
37
What is required to allow communication between two separate networks?
A router
38
How are routers used in your home network?
It is incorporated into the hub provided by your ISP (Internet service provider). It connects your home network to that of the ISP.
39
What is the purpose of a modem?
It is used to change the signal so that it can be sent through a cable that uses different technology.
40
What are the main components of a network access device, i.e. home hub?
A WAP (Wireless access point), a router, a modem and a switch. The switch will usually have between two and four ports, labelled 'LAN' or 'Ethernet'.
41
How can network access devices be used to control access to a network?
Using the MAC addresses of the devices that are trying to connect to the network. A list of approved MAC addresses is kept, and if it isn't listed the connection will be denied.
42
What is the role of a gateway? How does it work?
Allow the transmission of data between networks that use different protocols. It strips off all of the header data from the incoming packet leaving just the raw data, and then adds a new header in the format required for the destination network before sending it on its way.
43
What is (CSMA/CA)?
Carrier Sense Multiple Access with Collision Avoidance. It is a protocol used in wireless networking that makes sure that network collisions (when two devices attempt to communicate at the same time) are avoided.
44
What are WIFI signals transmitted on?
Channels, these have a frequency range of around 22 MHz.
45
State the layers of the TCP/IP stack. Start from the first layer an outgoing data packet would would pass down.
Application Transport Network Physical
46
What is the role of the application layer? (TCP/IP)
It uses an appropriate protocol relating to whatever application is being used to transmit data. For example, a web browser might use HTTP.
47
What is the role of the transport layer? (TCP/IP)
It is responsible for establishing an end-to-end connection. Once the connection is made, it splits the data into packets ready to be transmitted.
48
Which layer of the TCP/IP stack uses the TCP?
Transport
49
When data to be transmitted is split into packets, what is added to each packet?
The total number of packets, the number of the packet (its sequence), and the port number the packet should use. This allows the receiving computer to reassemble the packets in the correct sequence.
50
What is meant by a socket?
The destination IP address + the port. It tells us where the packet is going along with which application requires the packet.
51
Which layer of the TCP/IP stack uses the IP?
Network
52
What is added to each packet at the network layer?
The source and destination IP addresses.
53
What layer of the TCP/IP stack do routers operate at?
Network layer, they use the IP address to know the destination of a packet.
54
What does the physical layer represent? (TCP/IP)
The physical connection between various network nodes.
55
What is the role of the physical layer? (TCP/IP)
It adds the source and destination MAC addresses.
56
What does MAC address stand for? How is it implemented? How is it used?
It is the Media Access Control address of each device. It is unique 12-digit hexadecimal code, hardcoded during the manufacturing stage to every single network interface card. It changes at each hop on the route, so each router will add its own MAC address and the MAC address of the next router until it reaches its destination device.
57
What is the purpose of a port?
It allows the TCP/IP protocol to determine which application should deal with a packet once it arrives.
58
Describe FTP, stating its role and where it operates.
File Transfer Protocol, It is an efficient way of transferring data across a network. It is a high level protocol, operating at the application layer.
59
State what SSH is, and describe its role.
Secure Shell, It is typically used to provide secure remote access to computers. It allows a network to be managed away from the office, giving great levels of control to offsite admins.
60
Describe how SSH works.
Client initiates a connection by contacting server. Server sends a public key to client. Server and client agree communication rules and open a secure channel. User is able to login to the remote server host operating system.
61
How can SSH be used to tunnel through a company firewall?
The SSH client can establish a TCP connection on a remote port and send commands to that port using the appropriate protocol. This means other requests can be made (e.g. HTTP "GET" request) even if the normal firewall restrictions would block this.
62
What is the role of mail servers?
They act like a virtual online post office for all incoming and outgoing mail.
63
What are three main protocols an email server uses?
Post Office Protocol V3 (POP3) Internet Message Access Protocol (IMAP) Simple Mail Transfer Protocol (SMTP)
64
What does POP3 do?
Retrieves emails from a mail server by removing it from the server and transferring it to a device.
65
What does IMAP do?
Keeps email on a mail server, allowing synchronicity between devices.
66
What does SMTP do?
Transfers outgoing emails from one server to another (i.e. from a email client to a server).
67
What is the problem with POP3
By removing emails from the mail server on retrieval, it means a persons other devices will not be able to find the email on the mail server. This causes different emails to be stored on different devices.
68
Explain how a URL request by the browser from a user is handled.
Browser extracts Fully Qualified Domain Name (FQDM) and sends it to a DNS server. The DNS server maps the FQDN to an IP Address and returns it to the browser. Browser issues a "GET" request to the web server for the web resource specified by the URL. File is returned to the web browser. Browser renders contents according to HTML rules. If the file being rendered contains other URLs, then the browser issues additional requests to obtain these resources from the web server.
69
What is a routable IP address?
Unique IP addresses connected directly to the public internet. Routers store these in routing tables so they can send on packets.
70
What is a non-routable IP address? Why is it referred to as non-routable?
Assigned internally to devices on a private network. Non-routable because routers in the public internet will reject any data packets with source or destination IP addresses which are in the private ranges.
71
What is the role of DHCP server?
Dynamic Host Configuration Protocol, It is responsible for automatically assigning a dynamic IP address from a pool of available IP addresses to a computer which needs to operate on a public or private network.
72
How does DHCP help with the issue of a shortage of IPv4 addresses?
Active computers request addresses, and then eventually release them again back into the pool.
73
Describe the role of NAT.
Network Address Translation, It is responsible for converting IP addresses as they pass over the boundary for private and public address spaces.
74
Why does the NAT-enabled router assign a random port number and store it in a NAT translation table with its IP address.
This maps to a non-routable IP address inside the network. The NAT-enabled router pretends it is the source address, so the web server sends the information here. Then, the NAT-enabled router uses the socket attached to this information, and the NAT table, to determine where the information actually needs to be sent.
75
Describe the client-server model.
A client sends a request to a server, and if the information is available, the server responds with the data that was requested.
76
What is the websocket protocol?
A modern API used for communication, typically, but not limited to use with a web server.
77
What is an API?
Application Programming Interface, A set of protocols that define how two applications can interact with each other.
78
Why is the websocket protocol used?
It provides a modern, persistent (always open), bi-directional, fast, real-time, and interactive communication stream.
79
State an advantage of using the websocket protocol compared to traditional techniques.
Requires less hardware, saving: Transmission time Bandwidth Cost Space
80
State two applications for the websocket protocol.
Online gaming Instant messaging Remote cloud based document collaboration (e.g. Google Colab) (any real-time systems)
81
What is REST? What does it enable?
Representational State Transfer, It enables CRUD to be mapped to database (SQL) functions.
82
How does REST allow any client or server to be developed independently without breaking each other?
The REST API effectively allows JavaScript to talk to a database server through HTTP. This means the client computer needs no knowledge of how the database server works, it doesn't care how its requests are carried out.
83
What is JSON?
JavaScript Object Notation, It is (like XML) a standard for transferring data between a server and an application.
84
State two advantages of JSON over XML.
It is quicker and easier for humans to read and understand. The code is more compact, so it is quicker to transmit.
85
What is thick-client computing? What is the opposite of thick-client computing?
The majority of processing and storage is done on the client computer, with little done on the server-side. Thin-client computing.
86
State two advantages of thin-client computing.
Software updates can be done once on a server and automatically end up on every client. Much more secure than thick-client computing as all the data is stored in a central place, the server.
87
State two disadvantages of thin-client computing.
Reliant on the central server. If this goes down, most the functionality is lost. There is a much higher demand on bandwidth.
88
State two advantages of thick-client computing.
Can be operated without relying on a constant connection to a central server. Preferred solution for running resource hungry software applications.
89
State two disdvantages of thick-client computing.
Often more expensive as higher specification client computers are required. Every client needs its own software installed, increasing time and effort on the part of the network administration team.
90

Computer Science Paper 2 (7 decks)

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