Communication & Internet technologies

Question 1

Simplex

Answer 1

Data transmitted one way only

E.g. Computer to printer

Question 2

Duplex

Answer 2

Data transmitted both ways simultaneously

E.g. VOIP (Skype)

Question 3

Half Duplex

Answer 3

Data transmitted both ways but not at the same time

Question 4

Full Duplex

Answer 4

Data transmitted both ways at the same time

Question 5

Serial

Answer 5

One bit sent at a time over single wire
E.g. Computer to Printer
Sending data externally between devices
Advantages – fewer errors, cheaper wiring, less chance of data being out of order

Question 6

Parallel

Answer 6

Multiple bits sent at the same time using multiple wires
E.g. Computer to Modem
Sending data internally
Advantages- faster transmission

Question 7

Why serial is used to connect devices to PC

Answer 7

Single wire means less chance of corruption
Single wire reduces costs
More reliable over distances
Bits still synchronized after transmission

Question 8

Asynchronous Data Transmission

Answer 8

1. Data being transmitted in an agreed bit pattern.
2. Data bits (1s and 0s) are grouped together and sent with CONTROL BITS
3. Receiver of the data knows when the data starts and when it ends.
4. Prevents data becoming mixed up
5. Without these control bits, it would be impossible to separate groups of data as they arrived.

Question 9

Synchronous Data Transmission

Answer 9

1. Continuous stream of data
2. Data is accompanied by timing signals generated by an internal clock
3. The receiver counts how many bits (1s and 0s) were sent and then reassembles them into bytes of data.
4. faster data transfer method than asynchronous

Question 10

USB (Universal Serial Bus)

Answer 10

Data transmission method
Uses serial transmission – bits sent one at a time
Devices automatically detected
Only fits one way so can’t connect incorrectly
Industry-standard
Backward compatible

Question 11

Parity Check

Answer 11

Checks a byte of data
A parity bit is added
Counts number of 1s
Can be odd or even
If parity incorrect error detected

Question 12

When will parity Check not work

Answer 12

Two bits interchanged

Multiple errors in same byte

Question 13

Automatic Repeat Request (ARQ)

Answer 13

Uses acknowledgement
Check performed on receiving data
If an error is detected request is sent to resend the data
Resend request repeated until data is sent correctly
Send acknowledgement that data is received
If acknowledgement is not received in sent time data is resent

Question 14

Checksum

Answer 14

Value calculated form the data
It is added and transmitted with the data
Value recalculated after transmission
Values compared after transmission to check for error

Question 15

Check digit

Answer 15

A digit is calculated from the data
It is added to the data
Digit recalculated when data is entered
Digits are compared to check for error

Question 16

Requesting Web pages

Answer 16

Request
Web browser used
URL entered into a browser
HTTP/HTTPS protocol used
URL sent to DNS
DNS returns IP of the webserver
Request made to the webserver
Webserver returns HTML of the webpage

Sent
URL contains the domain name
The domain name used to locate the IP address
DNS server stores index of IP address and domain names
Web browser sends a request to the webserver

Received
Data stored on the webserver
Web server sends data to the browser
Browser translates HTML

Question 17

Browsers

Answer 17

Interprets and displays HTML
Provides functions such as bookmarks and history
Has forward, back and home buttons
Stores cookies and cached pages
Handles CSS and Javascript

Question 18

Drawbacks of duplex

Answer 18

Data more likely to be skewered

More expensive to install