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

Fundamentals of Communication and Networking Flashcards

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1
Q

Serial Transmission

Parallel Transmission

A

Data is transmitted one bit at a time down a single wire eg Keyboard or Mouse

Data is transmitted several bits at a time using multiple wires.

Parallel cables use more wires and are therefore more expensive to produce than serial cables. The signal will also degrade as distance or speed increases due to interference between the lines. Another problem is timing the signals so that the data sent down each wire arrive at the other end at the correct time and in sequence with data being transmitted through the other wires. This is known as synchronisation and this becomes more difficult as the number of wires increases.

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2
Q

Bandwidth

A

Bandwidth is the term used to describe the amount of data that can be transmitted along a communication channel. Measured in Hz and megahertz (mHz) The higher the frequency, the more data can be transmitted more quickly.

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3
Q

Bit Rate

A

The number of bits that are transferred between devices in one second.
Measured in bits per second (bps)

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4
Q

Baud Rate

A

Number of times a signal in a communications channel changes state.

Bit Rate of Channel = (baud rate) * (number of bits per signal)

https://youtu.be/I4dSIZM7Qdk?t=2m54s

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5
Q

Latency

A

The time delay that occurs when transmitting data between devices.

There are three general causes of latency when communicating data:
Propagation latency - The amount of time it takes for a logic gate within a circuit to transmit the data.
Transmission latency - The amount of time it takes to pass through a particular communication medium, for example, fibre optic would have a lower latency than copper cable.
Processing latency - The amount of time it takes data to pass around the network depending on how many servers or devices it has to pass through.

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6
Q

Asynchronous Data

A

Data is transmitted between two devices that do not share a common clock signal.

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7
Q

Start bit

A

A bit used to indicate the start of a unit of data in asynchronous data transmission

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8
Q

Stop bit

A

A bit used to indicate the end of a unit of data in asynchronous data transmission

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9
Q

Synchronous Data

A

Data is transmitted where the pulse of the clock of the sending and receiving device are in time with each other. The devices may share a common clock.

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10
Q

Protocols

A

A set of rules

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11
Q

4 Main Types of Protocols

A

TCP/IP (Regarded as 2 protocols): A set of protocols for all TCP/IP Network transmissions.

HTTP: Hypertext Transfer Protocol

FTP: File Transfer Protocol

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12
Q

Peer-to-peer

A

A network methodology where all devices in a network share resources between them rather than having a server.

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13
Q

Media Access Control (MAC)

A

A unique code that identifies a particular device on a network. EVERY device has its own unique MAC code.

The first half of a MAC address is the manufacturer code, and the second half is the unique device code allocated by the manufacturer.

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14
Q

Service Set Identifier (SSID)

A

A locally unique 32-character code that identifies a device on a wireless network.

One of the issues when using wireless network is ensuring that the various devices are connecting to the correct WLAN. as all of the data are being sent through radio waves rather than cables, each device needs a way of ensuring that it is connecting to the correct network. The standard method of doing this is using an Service Set Identifier (SSID) which is a 32-character code put into the header of each packet of data being sent.

Each code is locally unique to the particular WLAN that is being used and therefore acts as an identifier allowing that frame of data to be transmitted around the WLAN. The network interface card must also be programmed with the same 32 character code so that the device can connect to the WLAN in the first place.

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15
Q

Wifi Protected Access (WPA/WPA2)

A

A protocol for encrypting data and ensuring security on WiFi Networks.

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16
Q

Request to Send/Clear to Send (RTS/CTS)

A

A protocol to ensure data does not collide when being transmitted on wireless networks.

How it works
The RTS sends a message to the receiving node or access point and if a CTS message is received, it knows that the node is idle and that the data frame can be sent. If no CTS message is received, it will wait and send another RTS later.

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17
Q

Uniform Resource Locator (URL)

A

A method for identifying the location of resources (eg websites) on the internet.

http://www.awebsite.co.uk/index.html

http - indicates the protocol to be used

www - indicates which server is being accessed

awebsite - name of organisation

co - indicated the type of organsation

uk - country code

index.html - The name of the file being accessed. In this case an html file

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18
Q

IP Address

A

A unique number that identifies devices on a network.

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19
Q

Domain Name Server (DNS)

A

A server that contains domain names and associated IP addresses

When a person types in a URL, it makes a request to the DNS server for the IP address, the IP address is sent back to the computer which then establishes a connection using the IP address to the website server.

20
Q

Port

A

Used to identify a particular process or application on a network

Some well known ports:
21 - FTP
22 - SSH
80 - HTTP
110 - POP3
443 - HTTPS
21
Q

Secure Shell Protocol (SSH)

A

A protocol (set of rules) for remote access to computers

22
Q

Network Address Translation

A

NAT Is responsible for converting IP addresses as they pass over the boundary between public and private address spaces eg via a router

23
Q

Port forwarding

A

pg 331

https://www.youtube.com/watch?v=AkmQZx1ffKg

24
Q

Socket

A

An endpoint of a communication flow across a computer network

25
Q

Subnet Masking

A

A method of dividing a network into multiple smaller networks

26
Q

Dynamic Host Configuration Protocol (DHCP)

A

A set of rules for allocating locally unique IP addresses to devices as they connect to a network.

IP addresses are defined as either static or dynamic. Static IP addresses are ones that are assigned and then never change. Dynamic IP addresses are allocated every time a device connects to a network and this is perhaps the most common approach. The allocation is done automatically by an application as you log on. For home users, this is typically assigned by your ISP.

What the DHCP does in simple terms, is when a user is attempting to log on, it is making a request and the server will then offer that device a particular IP address, which may be the last used address for that device, or the next available address within the pool. When the user logs off, the reserve process takes place, freeing up the IP address for the next user.

27
Q

Internet Registries

A

Organisations who allocate and administer domain names and IP addresses.

28
Q

Firewall

A

Hardware or software for protecting against unauthorised access to a network.

29
Q

Packet filtering

A

A technique for examining the contents of packets on a network and rejecting them if they do not conform to certain rules.

30
Q

Stateful inspection

A

A technique for examining the contents of packets on a network and rejecting them if they do not form part of a recognised communication

31
Q

Symmetric Encryption

A

Where the sender and receiver both use the same key ot encrypt and decrypt data

32
Q

Asymmetric Encryption

A

Where a public and private key are used to encrypt and decrypt data

33
Q

Private Key

A

A code used to encrypt/decrypt data that is only known by one user but is mathematically linked to a corresponding public key

Sender sends the data and the key SEPARATELY to the receiver, who decrypts it using the same key.

34
Q

Public Key

A

A code used to encrypt/decrypt data that can be made public and is linked to a corresponding private key

For this example, both the sender and the receiver have their own pair of public and private keys.

Person A will have a private key only known to A
Person A will also have a public key, which is mathematically related to the private key. It is called a public key because anyone can access it.
B will also have a private key and a related public key.
For A to send a secure message to B, A will first encrypt the message using B’s public key.
As the private and public keys are related, the message can only be decrypted by B using B’s private key
As no-one else knows B’s private key, even if the message were intercepted, it could not be decrypted.

35
Q

Digital Certificate

A

A method of ensuring that an encrypted message is from a trusted source as they have a certificate from the Certification Authority.

Certification Authority - A trusted organisation that provides digital certificates and signatures.

36
Q

Digital Signature

A

A method of ensuring that an encrypted message is from a trusted source as they have a unique, encrypted signature verified by a Certification Authority.

37
Q

Trojan

A

Malware that is hidden within another file on your computer

38
Q

Virus

A

A generic term for malware where the program attaches itself to another file in order to infect a computer.

39
Q

Worm

A

Malware or a type of virus that replicates itself and speeds around a computer system. It does not need to be attached to another file in order to infect a computer.

40
Q

TCP/IP

A

The TCP/IP stack defines the rules relating to transmission of data packets. IP controls the delivery of the packets and TCP keeps track of the packets and re-assembles them on receipt. TCP/IP is made up of a number of layers which are collectively referred to as a protocol stack.

41
Q

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

A

Layer 4. Application Layer - uses an appropriate protocol relating to whatever application is being used to transmit data. Protocols such as FTP, HTTP, HTTPS, POP3, SMTP and SSH. For example, if the application, then HTTP, HTTPS, FTP etc would be used.

Layer 3. Transport Layer - TCP Part. It is responsible for establishing an end-to-end connection. Once the connection is made, it splits the data to be transmitted into packets. It adds to each packet:

  • The number of the packet (its sequence)
  • The total number of packets
  • The port number the packet should use

Layer 2. Network or Internet Layer - The network layer uses the IP Part
It adds to each packet:
- Source IP address
- Destination IP address
Socket is also added to know what application the device needs for the packet. (port 80 for example)

Layer 1. Network Access Layer - The link layer represents the actual physical connection between various network nodes.
Responsible for adding:
- The unique MAC address of the source device
- The unique MAC address of the destination device

42
Q

The Client-Server Model

A

A client sends a request to a server, the server responds with the data that was requested. The easiest example to remember is that of a client sending an HTTP request for a webpage and a sever returning the webpage to the client to be rendered in its browser.

43
Q

Application Program Interface (API)

A

A set of protocols which define how two applications can interact with each other.
eg Facebook provides an API for other developers to use. For example to allow the news feed of your business page to appear embedded in your companies own website.

Websocket protocol: an example of a modern API used for communication, typically, but not limited to use with a webserver. This provides a modern, persistent (always open) bi-directional, fast, real-time and interaction communication steam.

44
Q

CRUD

A

Create, Retrieve, Update and Delete

45
Q

Thin vs Thick Client Computing

A

Thin Client - In a network where one computer contains the majority of resources, processing power and storage capacity, which it distributes to other clients.

Thick Client - In a network where resources, processing power and storage capacity are distributed between the server and the client computers

Computer Science Paper 2 (7 decks)

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