Paper 2 Theory Flashcards
Describe Serial Transmission
Bits are sent one at a time down a single wire
Describe Parallel Transmission
Several bits are sent simultaneously down several wire
Give the advantages of serial transmission over parallel transmission
Cost -> Only one wire is needed
No Crosstalk -> Interference between parallel wires can cause the corruption of bits, meaning data means to be transmitted
Distance -> Serial transmission is more reliable over long distances, as bits cannot come out of sync
Frequency -> Due to a lack of interference, signal frequencies can be higher, leading to a higher rate of data transfer
Explain Synchronous Transmission
Sender and receivers clocks are synchronised for the whole transmission, with the sender controlling the speed of transmission. Once they are in sync, the data may be transferred without the need for further information exchange
Explain asynchronous transmission
Sender and receivers clocks are not in permanent sync, but are instead only in sync for the duration of the transmission, with the data being sent with a start and stop bit
What is the purpose of the start bit in asynchronous transmission?
Sent at the beginning of transmission, causing the receiver to synchronise it’s clock with the senders
What is the purpose of the stop bit in asynchronous transmission?
Indicates that the data has arrived, giving the receiver time to process the information, and allowing the receiver to identify when the next start bit arrives
What is the Baud Rate?
The rate at which the signal changes, with each different signal coding for a bit pattern
What is the Bit Rate?
The speed at which data is transmitted, in bits per second
May be higher than the baud rate if multiple bits are encoding in each signal
Bit rate = ?
Baud Rate * Number of bits per signal
What is the Bandwidth?
The range of frequencies that the transmission medium can carry
The larger the bandwidth, the higher the bit rate, as more data can be sent across it in a given time
What is Latency?
The dealy between a packet being sent and the same packet arriving at its’ destination
What is a parity bit?
A bit that is added to a group of bits, used for error checking (To check if any of the bits have been flipped)
Explain Odd Parity
Parity bit is set to a 1 or 0 to make the total number of 1’s in the bit pattern an odd number
Explain Even Parity
Parity bit is set to a 1 or 0 to make the total number of 1’ in the bit pattern an even number
What is a protocol, and why are they used?
A set of rules relating to communication between devices
Allows equipment from different suppliers to be connected on the same network, and communicate with each other
What is the TCP/IP stack?
Transmission Control Protocol/Internet Protocol stack
A set of networking protocols for sending and receiving data packets across the internet
What are the four layers of the TCP/IP stack?
Application layer, Transport Layer, Network Layer and Link Layer
What is the function of the application layer
Uses protocols, relating to the application, to transmit data across the network
What is the function of the Transport Layer?
Establishes a connection between the sender and the receiver
If data is too large to be sent in one go, breaks it up into segments (Packets made up of only the data)
Adds source and destination port numbers (Identify which application the data relates to)
What is the function of the Network Layer?
Adds source and destination IP addresses, used to identify the two devices
What is the function of the Link Layer?
Adds source + destination Mac addresses, which are fixed on each device
What is encryption and what is a key?
The process of scrambling data, using a key, turning plain text into cipher text
A cryptographic algorithm used to encrypt or decrypt data
Explain the difference between symmetric and asymmetric encryption
Symmetric - The same key is used to encrypt and decrypt the data
Asymmetric - Two different but related keys are used, one to encrypt and the other to decrypt
What are sockets and what is their role in the TCP/IP stack?
A socket is the combination of the IP address and port number
It specifies which device the packet must be sent to, and the application being used on that device
What is a MAC address, and what are their role?
The Media Access Address is a unique number that is burned into the Network Interface Card of each machine
They identify specific devices, meaning that once the packet finds the correct network, the MAC address can be used to find the correct machine
What is an IP address?
A Internet Protocol address that is assigned to a network device, identifying it on the Internet
It indicates where a packet of data is to be sent or where it is sent from, allowing routers to direct the packet accordingly
What is packet switching?
A method of communicating data across a network
Data is split into manageable chunks, and is then sent across the Internet
What is usually contained in the header of a data packet, and what is the purpose of each?
Checksum - Used for error checking
Source IP address - Included if a response is needed, and/or to request packets be resent
Destination IP address - The packets final destination
Hop Limit - A limit to how many routers a packet may visit before it self-destructs
Sequence Number - Packets will arrive in the wrong order, so this is used to reassemble the data
How is routing achieved across the Internet?
Packets are split up and each sent along the least congested route to the recipient
What is the difference between a router and a gateway, and what is their purpose?
Router - Used to connect at least two networks using the same protocols
Gateway - Used to connect networks that use different protocols, and will translate between them
To move a data packet towards its’ final destination
How does a firewall work?
Packet filtering - Packets are rejected/accepted based on things like their source IP address or what ports they are trying to access
Stateful inspection - Firewall maintains information about current connections, and only allows packets relevant to these connections
Proxy Server - Intercepts all packets entering and leaving the network, hiding the true IP address of the source from the recipient
Explain how Public Key Private Key encryption works
First, the sender uses the receivers public key, made available to others, to encrypt the data they want to send
The public key cannot be used to decrypt the data
The data is then sent across the network to the receiver
The receiver then uses their private key, known only to them, to decrypt the data
Explain how a digital signature works
First, a value is calculated from the unencrypted message.
The sender then encodes this value using their own private key, and attaches it to the message (Encrypted with the recipients public key)
When the receiver receives the message, they can recalculate the value
The receiver then decrypts the senders value, and if the two values are the same, the message must be correct, and is genuinely from the sender
Explain the purpose of Domain Names, DNS and how it works
Domain Names are easier for humans to remember than IP addresses, and are ordered in a hierarchy of smaller domains
The Domain Name System catalogs all domain names and their corresponding IP addresses
When a web page is requested, the browser requests the corresponding IP address from the local DNS server
If it has it, it returns the IP address
If not, the DNS will send the request to a larger DNS database to try and find the IP address
Once the IP address is found, the user senders a request for the web page to that location
What is the difference between a worm and a virus?
A virus needs it’s host program to be run to begin self replicating, whereas a worm does not
