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CS > Fundamentals of Communications & Networks > Flashcards

Fundamentals of Communications & Networks Flashcards

1
Q

How to calculate the Bit Rate?

A

Baud rate X No of bits per signal

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2
Q

What is a Network?

A

two or more communication devices connected together

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3
Q

What is the purpose of a Network?

A

for the purpose of exchanging (transmitting/receiving) data

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4
Q

How can one govern communication in a Network?

A

you require protocols that define how to handle data at various stages of data exchange

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5
Q

What is a Physical Topology?

A

The physical architecture of cabling between devices on a network

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6
Q

What is a Logical Topology?

A

How the data packets flow around a network

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7
Q

What is a Star Topology?

A

Each client has its own connection to the central device. The central device receives packets for all of the clients connected to it and is responsible for delivering them to the correct recipient.

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8
Q

What is a Hub Device?

A

A simple and cheap networking device that works under the physical layer of the OSI model and connects a bunch of computers in a LAN.
NOT intelligent as it is unable to identify unique machines.
It broadcasts to all devices hence wasting bandwidth (Data Collision)

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9
Q

What is a Switch?

A

A multicast networking device that works under the Datalink layer of the OSI model and connects a bunch of devices in a network.
Used to send private messages and does not waste bandwidth.
Switches can identify which device is connected to which port by using a MAC address giving it the ability to deliver the message to a particular machine

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10
Q

What is a MAC Address?

A

A MAC Address is a unique value that identifies the machine

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11
Q

Advantages of the Star Topology?

A
  • (When using a switch) packets are sent directly to recipient, other clients on the network cannot see packets that are not intended for them.
  • Easy to add and remove clients from the network.
  • Each cable has just one device communicating over it, eliminating possibility of collisions.
  • Failure of one cable does not effect the entire network.
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12
Q

Disadvantages of the Star Topology?

A
  • If the central hub/switch fails, all communication over the network is stopped.
  • Expensive to install due to all the cables needed (or switch)
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13
Q

What is Bus Topology?

A

A physical bus connects clients to a single cable called the backbone.
A terminator is placed at either end of the backbone.
A server can be connected to the backbone just like a client.

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14
Q

Advantages of the Bus Topology?

A
  • No central device which reduces the chance of a network failure and decreases the cost of installation.
  • Inexpensive to install as a minimum length of cable is required.
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15
Q

Disadvantages of the Bus Topology?

A
  • Packets are sent through the shared backbone therefore, every client on the server can see packets not meant for them.
  • used for communication by multiple clients increasing the risk of collision
  • if the backbone fails, the entire network becomes unusable.
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16
Q

What is a Host?

A

A device on a network that provides services.

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17
Q

What is a Server?

A

A computer that provides shared resources to network users.

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18
Q

What is a Client?

A

A computer that uses the services provided by a server.

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19
Q

Describe what happens between a Server and a Client:

A

The server will open a socket, this means it is now in ‘listen’ mode. Then the client can send a request to the server and it will be received. Finally, the server will send a response.

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20
Q

What is Client-Server Networking?

A

some computers (the clients), request services provided by other computers, the servers.

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21
Q

What is Peer-to-Peer Networking?

A

A network that has no dedicated servers. All computers are of equal status and can both share resources themselves and use resources from other computers, i.e. they are peers.

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22
Q

Advantages of Peer-to-Peer Networking?

A
  • Cost effective as there is no need for a powerful server to provide services.
  • easier to set up and maintain.
    (than client-server)
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23
Q

Disadvantages of Peer-to-Peer Networking?

A

All the clients that provide services must be running in order for the network to be fully operational.

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24
Q

What is Wireless Networking?

A

Any type of local area network (LAN) in which the nodes (computers or computing devices, often portable devices) are not connected by wires but use radio waves to transmit data between them.
Require Wireless Access Points.

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25
Q

How is Wireless Transmission and Wi-Fi protected?

A

encrypting transmitted data using WPA or WPA2 (Wi-Fi Protected Access) which requires that a new wireless client enters a password in order to connect to a network.

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26
Q

How to prevent people attempting to join your network?

A

Use WPA (Wi-Fi-protected access) - To encrypt transmission, so that if intercepted transmissions cannot be read by someone who does not have the key.
Encrypt transmissions - so that if intercepted cannot be understood/read by someone who does not have a key.
Disable broadcast of SSID (
Use a MAC address white list

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27
Q

What is the Internet?

A

A global wide area network that is formed from the interconnection of many other networks and that uses the TCP/IP protocol.

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28
Q

How is the Internet structured?

A

The structure of the internet is such that there is a network of interconnected computer networks and computers using IP addresses based on IP and TCP.

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29
Q

What is a router?

A

A device that receives packets or from one host (computer) or router and uses the destination IP address that they contain to pass them correctly formatted, to another host (computer) or router.

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30
Q

What is a packet?

A

A packet is a container in which data is transmitted over networks

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31
Q

What is a Gateway?

A

A device used to connect networks using different protocols so that information can be successfully passed from one system to another.

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32
Q

What do routers do?

A

send packets to their recipients via the fastest possible route. this route might include the lowest amount of hops or the route that is least congested at the time.

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33
Q

How do routers work?

A

They hold tables with information relating to the fastest routes to certain devices which they update frequently as to enable maximum performance.

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34
Q

What do Gateways do?

A
  • Gateways strip away most of the packet’s details, leaving just the packets contents.
  • The gateways then give the packets new sender and receiver addresses which comply to the new protocol
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35
Q

Why are Gateways used?

A
  • Used to make packets comply with new protocols by stripping them down to just their contents and applying new sender/receiver addresses

(Where two networks use two different protocols, packets must be modified to conform to both protocols.

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36
Q

What is a Firewall?

A
  • Sits between a device and the internet and regulated the packets that pass through it.
  • can be either hardware or software and work as a proxy server which can perform both packet filtering and stateful inspection
37
Q

What is a Proxy Server?

A
  • A server that sits between a public network and a private network.
  • Manages every packet that passes between the two networks.
  • Firewalls can be said to act as proxy servers when they control the movement of packets between public and private networks.
  • Sometimes built into firewall.
38
Q

How does a proxy server work?

A
  • device in private network sends packet through firewall into public network
  • packets sender address replaced with one of the firewalls proxy servers rather than the device’s private IP
  • provides some degree of anonymity to devices on private networks as their address never leaves the private network
39
Q

What is a flaw of Symmetric Encryption?

A

vulnerable to interception (packet sniffing) if exchanged over a network

40
Q

What is Symmetric Encryption?

A
  • sender and receiver share the same private key.
  • used to encrypt and decrypt data sent between the two parties.
  • before sending any information, sender and receiver must partake in a key exchange to ensure they both have a copy of their shared key
41
Q

What is a Protocol?

A

A set of rules that allows for communication between devices

42
Q

What is Asymmetric Encryption?

A
  • four different keys used
  • each device has a pair of mathematically related keys, one which is kept secret (private key), one which is shared on the Internet (public key).
43
Q

What does Asymmetric Encryption do?

A

When a message is encrypted with a public key, only the corresponding private key can decrypt it (+ vice versa)

44
Q

How does Asymmetric Encryption work?

A
  • before message is sent, encrypted by sender using recipients public key.
  • message can only be decrypted by corresponding private key (recipients private key)
45
Q

What is the TCP/IP?

A

Used to enable different devices to communicate in all parts of the Internet.

4 Layer protocol.

46
Q

What are the four layers of TCP/IP?

A
  1. Application
  2. Transport
  3. Network
  4. Link (Physical)
47
Q

What does the Application Layer do in TCI/IP?

A

Selects and uses correct protocol to transmit data.
Interacts with the user with an application software.

48
Q

What does the Transport Layer do in TCI/IP?

A

Establishes a virtual path (end to end connection between sender and receiver).
Segments the data whilst sequence number and port numbers are allocated.

49
Q

What happens in the Internet/Network Layer in TCP/IP?

A

Prepares packets for the internet by adding source and destination addresses.
The routers work here by using the IP addresses on the packet to send it to its destination.

50
Q

What happens in the Link/Physical Layer of TCP/IP?

A

Controls physical connections between pieces of hardware in a network.
Adds MAC addresses to packets which it receives from the network
layer.
The MAC addresses identify the hardware to which a packet should be
sent. These MAC addresses change with every hop through a network.

51
Q

What happens at the Receiving End of the TCP/IP?

A

Link: Stripped of its extra
information by reversing the TCP / IP stack.
Network: Removes IP addresses
Transport: Uses the packet’s port number to determine correct application to send packet to. Also uses sequence number to ensure it is in the correct position.
Application: Receives packets and displays information accordingly

52
Q

What is a Socket Address?

A

Identifies which of the applications on the recipient device a packet should be sent to.
IP ADDRESS : PORT NUMBER

53
Q

What is the Protocol for ports 20 & 21?

A

FTP (File Transfer Protocol)

54
Q

What is the Protocol for port 80?

A

HTTP (Hypertext transfer protocol)

55
Q

What is the Protocol for port 443

A

HTTPS (Hypertext transfer protocol secure)

56
Q

What is the Protocol for port 22

A

SSH (Secure shell)

57
Q

What is the Protocol for ports 25, 587 & 465?

A

SMTP (Simple mail transfer protocol)

58
Q

What is the Protocol for ports 110 & 995?

A

POP3 (Post office protocol 3)

59
Q

What is the structure of an IP address?

A

2 parts: network identifier + host identifier

(computers in a network share the same network identifier but has its own host identifier)

60
Q

What is IPv4?

A

4 parts separated by dots. each part assigned one byte (8 bits) allowing numbers 0-225 to be represented.

61
Q

What is IPv6?

A

8 blocks separated by colons. Each block contains 4 hexadecimal characters. Uses 128 bits - allows for more unique permeations.

62
Q

What is a routable IP address?

A

A public IP address. Globally unique.

63
Q

What is an unroutable IP address?

A

A private IP address. Millions of devices can have the same one as long as they are not on the same network.

64
Q

What does the Dynamic Host Configuration Protocol do?

A

Used to assign IP addresses to devices as they join a network.

65
Q

How does the Dynamic Host Configuration Protocol work?

A

Uses a pool of available IP addresses to allocate IP addresses to new devices for the duration of their session.
Once a device leaves the network, the IP address that the device was using is returned to the pool for allocation to a new device.

66
Q

Why do we use the Dynamic Host Configuration Protocol?

A

The number of available private IP addresses within a private network is limited.
Assigning each device its own private address is wasteful as a device could leave and never join again.

67
Q

What is Port Forwarding?

A
  • client sends packets to the public IP address of the router attached to the servers private network.
  • packets sent by client contain port number of application running on the server the client wants to access.
  • private networks router forwards packet to the server using NA
68
Q

Why do we use/do Port Forwarding?

A

when a client needs to communicate with a server that is connected to a private network

69
Q

What is the Client Server Model?

A

Clients send request messages to servers, which reply to the clients with response messages.

messages may contain: request info, confirmation request has been completed, message explaining why action has not been completed

70
Q

What is an API?

A

Application Programming Inteference: name given to a set of protocols relating to how different applications communicate with each other

71
Q

What does an API do?

A

define how interactions between applications should be carried out: allowing applications to make use of other applications.

72
Q

What is the Web Socket protocol?

A

An example of an API. Operates in the application layer of the TCP/IP stack.

73
Q

What does the Web Socket protocol do?

A
  • Provides a constant stream of information between two devices
  • connection created by web socket protocol is full-duplex (data can be transmitted in both directions at the same time)
74
Q

What is the Web Socket Protocol used for?

A

allows for fast transmission of data by reducing the size of packet headers.

video streaming, online games, instant messaging

75
Q

What is a Standard?

A

Allows us to achieve compatibility between different systems.
Enables different hardware and code to work together and to communicate with each other.

Communication protocols establish the standards.

76
Q

What is a Network Protocol?

A

A set of rules that allow computers to communicate and exchange information over a network.

77
Q

What port do you use for FTP (File Transfer Protocol)?

A

20 & 21

78
Q

What is the Purpose of FTP (File Transfer Protocol)?

A
  • Used to send files between devices.
  • FTP client software can run on devices, allowing them to connect to FTP servers which send files requested by the client.
  • Clients can access FTP servers anonymously or non-anonymously by logging in with a username and password
79
Q

What port does HTTP (Hypertext transfer protocol) use?

A

80

80
Q

What is the purpose of HTTP (Hypertext Transfer Protocol)?

A
  • Web servers hold web pages in text form, which they can deliver to clients using HTTP.
  • Application software on the client received these text files and renders them as web pages.
81
Q

What port does HTTPS (Hypertext Transfer Protocol Secure) use?

A

443

82
Q

What is the purpose of HTTPS (Hypertext Transfer Protocol Secure)?

A

Used in e-commerce and online banking, performs the same function as HTTP but encrypts information during transmission.

  • Keeps information sent to clients secure and helps to prevent information being tampered with or modified during transmission.
83
Q

What port does the SMTP (Simple Mail Transfer Protocol) use?

A

25, 587 & 465

84
Q

What is the purpose of the SMTP (Simple Mail Transfer Protocol)?

A

Used for sending emails.

SMTP is used between a client and email server

85
Q

What port does POP3 (Post Office Protocol 3) use?

A

110 & 995

86
Q

What is the purpose of POP3 (Post Office Protocol 3)?

A
  • Used for retrieving emails from an email server.
  • Email servers are responsible for receiving and sending emails.
  • POP3 communicates with email servers to check for and download any new messages.
87
Q

What port does SSH (Secure Shell) use?

A

22

88
Q

What is the purpose of SSH (Secure Shell)?

A
  • Used for remote management of computers, allowing them to be accessed and controlled remotely.
  • In order to access a remote computer, SSH requires a username/password combination and encryption information during transmission.
  • SSH clients are pieces of software which can be used to make a TCP connection to a remote part.
  • Once a connection is established, commands for application level protocols can be sent to the remote computer.

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