topic 2 - communication and internet tech

Question 1

data transmission types (5)

Answer 1

• simplex
• duplex
• half-duplex
• full-duplex
• serial
• parallel

Question 2

simplex

Answer 2

data transmitted one way only

Question 3

duplex

Answer 3

data transmitted in both way

Question 4

half-duplex

Answer 4

data transmitted in both ways but not at the same time

Question 5

full-duplex

Answer 5

data transmitted in both ways at the same time

Question 6

serial(2)

Answer 6

• one bit sent at a time over a single wire (eg. computer to printer)
• used to send data externally between devices

Question 7

parallel (2)

Answer 7

• multiple bits sent at the same time using multiple wires

- used to send data internally

Question 8

why use serial instead of parallel when connecting device to PC

Answer 8

• single wire reduces the cost
• single wire means less chance of corruption
• more reliable over time
  bits still synchronised after transmission

Question 9

asynchronous transmission (2)

Answer 9

• Data is sent in form of byte or character

- time interval of transmission is random

Question 10

synchronous transmission (2)

Answer 10

• Data is sent in form of blocks or frames

- time interval of transmission is constant

Question 11

USB (7)

Answer 11

• universal serial bus
• data transmission method
• uses serial transmission
• device automatically detected
• only fits one way; it cant fit incorrectly
• industry-standard
• backwards-incompatible

Question 12

methods of error-checking (4)

Answer 12

• parity check
• checksum
• ARQ; automatic repeat request
• check digit

Question 13

how does parity check work (5)

Answer 13

1. checks byte of data
2. a parity bit is added
3. counts num of 1s
4. can be odd or even
5. if parity incorrect, error is detected

Question 14

when will parity check not work (2)

Answer 14

• multiple errors in same byte
• ## 2 bits interchanged

Question 15

how does ARQ (automatic repeat request) work (6)

Answer 15

1. uses acknowledgement
2. check performed on receiving data
3. if error detected request sent to respond data
4. resend request repeated until data sent correctly
5. send an acknowledgement that data is received
6. if acknowledgement not received in set time data is resent

Question 16

checksum (4)

Answer 16

1. values calculated from the data
2. it is transmitted with the data
3. value recalculated after transmission
4. values compared after transmission to check for error

Question 17

what is an IP address

Answer 17

location of a device on a network

Question 18

what is a MAC address

Answer 18

number that uniquely identifies a device

Question 19

what does https

Answer 19

hypertext transfer protocol secure

Question 20

describe what browsers do (3)

Answer 20

• interprets HTML
• URL entered into browser
  HTTP protocol used

Question 21

requesting web pages

Answer 21

1. request
   - web browser used
   - url entered into browser
   - http protocol used
2. sent
   - url contains domain name
   - domain name used to locate IP address
   - DNS server stores index of IP address and domain names
   - web browser sends request to web server
3. received
   - data stored on wbeserver
   - web server sends data to browser
   - browser translate html