2.1 & 2.3 Data Transmission and Encryption Flashcards
What is serial data transmission?
- Method of data transmission
- each bit is sent one after another …
- over a single wire (channel)
What is parallel data transmission?
- Method of data transmission
- Multiple bits (often 8 bits) sent at the same time …
- using multiple wires (lines)
Advantages and disadvantages of serial transmission are?
- more accurate/fewer errors over a longer distance
- less expensive wiring (single wire)
- less chance of data being skewed/out of synchronisation
- slower, less data sent at once dues to only one wire
Advantages and disadvantages of parallel transmission are?
- less accurate/more errors over a longer distance
- more expensive wiring (multiple wires)
- more chance of data being skewed/out of synchronisation
- faster, more data sent at once due to more wires
Uses of serial transmission?
- Medium to long distances e.g. Ethernet, Telephone Wire
- USB (Universal Serial Bus)
Uses of parallel transmission?
- Short distances
- Fast internal data transfer within a computer system (buses)
- IC’s (Integrated Circuits)
- Older printers
Explain duplex data transmission and give an example
- Direction of data transmission is both ways at the same time (simultaneously)
- Examples: Telephone call, broadband connections, video conferencing
Explain half-duplex data transmission and give an example
- Direction of data transmission is both ways but not at the same time (not simultaneously)
- Examples: Walkie Talkie, Intercom
Explain simplex data transmission and give an example
- Direction of data transmission is one way only (unidirectional)
- Examples: radio/tv broadcast, microphone to computer, computer to speaker
What are Integrated Circuits?
- self-contained circuits with many separate components (e.g. transistors, diodes) etched into a tiny silicon chip.
- Uses parallel transmission for …
- …sending data internally in computer systems
What are the drawbacks of integrated circuits?
- Less flexible - individual component or components cannot be removed or replaced – whole IC must be replaced
- Limited power rating
What are the benefits of integrated circuits?
- Small size – Thousands times smaller than discrete circuits
- Small weight due to miniaturised circuit
- Low cost due to mass production
- Low power consumption because of their smaller size
What is USB?
Universal Serial Bus
- Uses asynchronous serial transmission for …
- … sending data externally
- … (to and from peripherals / between devices)
Advantages of USB are?
- Devices plugged into the computer are automatically detected
- The connectors can only fit one way; this prevents incorrect connections being made
- Industry standard; this means that considerable support is available to users
- Supported by many operating systems
Explain what happens when a USB device is plugged into a computer
- The computer automatically detects a device (due to a small change in the voltage level)
- A known device is automatically recognised, and the appropriate device driver is loaded
- If a new device is detected, the computer will look for and install the device driver
- If this is not available, the user is prompted to download the device driver
Disadvantages of USB are?
- Limited distance: the maximum cable length is presently about 5 metres
- Current transmission rate is slower than Ethernet (although USB 3.0 is over 10 time faster than USB 2.0)
Data sent over long distances is broken up into data packets. State the 3 parts of a data packet.
- packet header
- payload
- trailer
The packet header of a data packet consists of …
- Ip address of the sending device
- IP address of the receiving device
- The sequence/packet number of the packet
- The protocol
- The packet size (in bytes)
The payload of a data packet consists of …
the actual data being sent
The trailer of a data packet consists of
- a way to identify the end of the packet
- error checking information (Checksum/CRC’s)
How are Cyclic Redundancy Checks (CRCs) used to check data packets:
- Sending computer adds up all the 1 bits in the payload and storing this as a hex value in the trailer before it is sent
- Once the packet arrives, the receiving computer recalculates the number of 1 bits in the payload
- The receiving computer then checks this value against the one sent in the trailer
- If the two values match, then no transmission errors have occurred;
Explain how packet switching works …
- Data is broken down into packets
- Each packet is given a sequence number and sent on its way.
- Each packet may take a different route to the next depending on the quickest route at the time.
- Routers control the route that a packet takes.
- Packets may arrive out of order
- Once the last packet has arrived, the sequence numbers are used to put them back into order.
State 3 benefits of packet switching
- There is no need to tie up a single communication line
- It is possible to overcome failed, busy or faulty lines by simply re-routing packets
- A high data transmission rate is possible.
State 3 drawbacks of packet switching
- Packets can be lost and need to be re-sent
- The method is more prone to errors with real-time streaming
- There is a delay at the destination whilst the packets are being re-ordered
Message data before it is encrypted is known as …
Plain Text
Message data after it has been encrypted is known as
Cipher Text
Describe the steps involved in encryption
- An encryption algorithm is used to scramble/encrypt the data
- The original data is called the plain text
- A key is used to encrypt the data
- The key is applied to the plain text
- Plain text is encrypted into cipher text
Describe the process of decryption
- An algorithm is used to decrypt the text
- The encrypted data is called the cipher text
- A key is used to decrypt the data
- The key is applied to the cypher text
- Cypher text is descrypted back into plain text
Encryption is used to …
- store information securely
- transmit messages securely.
Describe a disadvantage of symmetric encryption
- When sending symmetrically encrypted data …
- the key must be sent separately to the cipher text
- If the key is intercepted when being transmitted it is …
- easy to decrypt cipher text with the algorithm and the key
How can we improve encryption?
- Increase the length (number of bits) of the key e.g. 8 bit to 64 bit
- … which means there are more possible combinations for the key
- …and less chance of decryption by brute force
- Choose a more secure algorithm
How many keys do symmetric and asymmetric encryption use?
- Symmetric encryption uses an encryption algorithm and a single shared key
- Asymmetric encryption uses an encryption algorithm and 2 keys
- a public key and
- a private key
Explain how a symmetric key used to encrypt a message could be passed securely from User A to User B using asymmetric encryption
- The symmetric key is encrypted by User A using the public key of User B
- User A then sends the encrypted symmetric key to User B
- User B decrypts the symmetric key by applying their own private key
Magic!
Explain asymmetric encryption
- Everyone has their own public and private key
- Private key is kept secret
- Encryption algorithm and public keys are freely available
- To send a message securely the receivers public key is used to encrypt the message
- The receiver can then descrypt the message with their private key
Give a disadvantage of asymmetric encryption
It is slower than symetric encryption due to the longer key lengths and the complexity of the encryption algorithms
