2 Data Transmission Flashcards
How is data transmitted?
It is broken down into very small units called packets.
Can you describe the structure of a data packet?
Packet Header
Paylod
Trailer
What does the payload contain?
Contains the actual data from the file that you are sending.
What does the trailer contain?
- Marker to indicate end of packet
- Data for any error detection systems
Can you describe the process of packet switching?
- Data is broken down into packets
- Each packet is individually sent from one device to another
- Each data packet could take a different route.
- A router controls the route a packet takes.
- Packets may arrive out of order
- After all packets arrive, packets are reorderd.
What is serial data transmission?
Data is sent one bit at a time down a single wire.
What is parallel data transmission?
Data is sent multiple bits at a time down multiple wires.
What is simplex tranmission?
data is transmitted in a single direction only
What is half duplex transmission?
data is transmitted in both directions, but only one direction at a time.
What is full-duplex transmission?
data is transmitted in both directions at the same time.
What are the advantages of serial data tranmission?
- Less chance of data being skewed as it is sent one bit at a time.
- As data is sent along 1 wire, there are less chances of interference, therefore less chances of error in data
- only 1 wire is need, therefore it is cheaper to buy and cheaper to manufacteur.
What is a USB and how does it work to transmit data?
Universal Serial Bus is an industry standard that is used to transmit data.
A USB connection uses serial data transmission to transmit data between the devices. However it is a special type of serial data transmission connection that is designed to transmit data at high speeds.
What are the advantages of the USB interface?
- simple interface. The USB cable to device can only fit into the USB one way. Therefore means less errors in connecting devices are likely to be made.
- The speed of a USB connection is relatively high, so data transfer is quick
- USB interface is a universal standard so a USB port is included in many different devices.
What are the disadvantages of the USB interface?
- The length of the USB cable is limited, normally to 5 metres.
- Tranmission speed is relatively high but slower than other types of connection such as ethernet.
What are the methods of error detection for detecting errors in data after transmission?
- Parity check
- checksum
- echocheck
What is a parity check?
- type of error detection method that adds an additional bit to each byte to create an odd or even sum.
What is a checksum?
Type of error detection method. A checksum uses a calculated value to check for errors. A value is calculated from the data that will be transmitted, before transmission takes place. Checksum values are compared after transmission to see if they match.
What is echo check?
A type of error detection method that sends a copy of the transmitted data back to the sender to be compared with the original data sent.
What is a check digit?
A type of error detection method that is used for data entry. A calculation is performed on the data entered to create a value. Check digits values are compared to see if data entered is correct.
What are some examples of when a check digit is used?
- ISBN (international standard book numbers)
- bar codes
What is automatic repeat query (ARQ)?
A type of error detection method that uses acknowledgement and timeout to see if data has arrived correctly after transmission.
What is acknowledgement?
A message that is sent from one device to another to indicate whether data is recieved correctly.
What is a timeout?
A period of time that is set and used to wait for an acknowledegment to be recieved.
What is encription?
a method of securing data for storage or transmission that scrambles it and makes it meaningless.
What is plain text?
the name given to data before encryption.
What is cipher text?
the name given to data after encryption.
What is an encyrption key?
A type of algorithm that is used to encrypt data.
What is symmetric encryption?
A type of encryption that uses the same key to encrypt and decrypt data.
What is asymmetric encryption?
a type of encryption that uses two different keys to encrypt and decrypt the data.
