2. Communication and internet technologies Flashcards
What is half-duplex data transmission?
Both directions, one at a time
What is full-duplex data transmission?
Both directions at the same time
Example of simplex
Data being sent to a printer
Example of half-duplex
Walklie-talkies
Example of full-duplex
Phone conversation
What is serial data transmission?
Data is sent one bit at a time down a single channel
What is parallel data transmission?
Several bits of data are sent simultaneously down multiple channels
Example of serial
Between a computer and a modem; USB
Example of parallel
Buses within computer hardware
Advantages of serial
Works well over long distances
No issues with synchronisation
Disadvantages of serial
Slower
Advantages of parallel
Faster
Disadvantages of parallel
Can become skewed over long distances
What is asynchronous data transmission?
Data is grouped together and sent with control bits
What is simplex
One direction only
What is synchronous data transmission?
Data is sent in a continuous stream with timing signals
Advantages of asynchronous
Don’t have to worry about timing
Advantages of synchronous
Faster
What happens when a USB is plugged into a computer?
The computer detects that a device is connected and loads up the appropriate driver. If a new device is connected the computer will look for the appropriate driver to download.
Advantages of USB
Devices automatically detected
Very standard
Only fit one way - cant be broken in this way
How does a parity check work?
The sender and receiver decide to use either even or odd parity. A parity bit is allocated in the byte. The bit is either a 0 or 1 to give an even or odd number of 1s in the data. The receiver checks this is true and, if it is not, requests that the data is resent.
How does a parity table work?
Each byte is given a parity bit and a parity byte is attached as well.
Disadvantages of parity checks
Can’t locate error (unless in table)
If multiple bits are corrupted it wont be detected
How does an automatic repeat request work?
When the receiver receives the data correctly it sends an acknowledgement back to the sender. If the acknowledgement is not received before the timeout the data is automatically resent.
How does a checksum work?
Data is sent in blocks with an additional block for the checksum. Before the data is sent, the checksum for the bytes is calculated. When the data is receive, the checksum is calculated again using the same algorithm and compared to the checksum sent. If they are different, a request is sent for the data to be resent.
How does an echo check work?
When the data is received, it is automatically sent back to the sender and then compared to the original. If they are not the same the data is resent.
Disadvantage of echo check
Don’t know whether the error was made in the first or second time the data was sent.
What is an internet service provider?
A company that provides users with internet access for a monthly fee.
What is an IP address?
A 32 bit number assigned to a computer when it connects to the internet and is unique for that session.
Which IP addresses don’t change?
Those of web servers.
What is a MAC address?
A unique number that identifies a device connected to the internet.
What is the difference between HTML presentation and structure?
Structure includes the meaning and layout of the document, presentation is the style of the document.
What is http?
Hypertext transfer protocol is a set of rules that must be obeyed when data is transferred across the internet.
What is the function of a web browser?
Interpret HTML code from websites into something the user can view.
