unit 2: data transmission

Question 1

data packets

Answer 1

small part of a data that is transmitted over a network

Question 2

data packet structure

Answer 2

• packet header
• payload
• trailer

Question 3

packet header

Answer 3

• IP address of source device
• IP address of destination device
• sequence no. of packet
• size of packet (in bytes)

Question 4

payload

Answer 4

actual data in the packet

Question 5

trailer

Answer 5

*method of identifying end of packet
*some form of error checking

Question 6

Cyclic redundancy checks (CRCs)

Answer 6

1. sending comp. adds up all 1-bits in payload and storing as hexa in trailer before sending
2. receiving comp. recalculates no. of 1-bits in payload
3. comp. checks this value against hexa in trailer
4. if matching, no transmission errors

Question 7

process of packet switching

Answer 7

1. each packet follows own path (route)
2. routers determine the route
3. routing selection depends on no. of packets waiting to be processed in a node
4. shortest possible path available is always selected
5. unfortunately, packets may reach destination in diff. order when sent

Question 8

benefits of packet switching

Answer 8

• no need to tie up a single communication line
• possible to overcome faulty lines: rerouting
• easy to expand package usage
• high data transmission rate

Question 9

drawbacks of packet switching

Answer 9

• lost: need to be resent
• more prone to errors with real-time streaming
• delay at destination

Question 10

hopping

Answer 10

method where a hop no. is added to the header and it reduces by 1 each time the packet leaves a router
there’s a max. no. of hop numbers and if the hop reaches 0, it will be deleted at next router
the receiving computer notices missing packet and then requests for the packet to be resent

Question 11

factors to consider in data transmission

Answer 11

1. direction
2. method
3. how data will be synchronised

they’re considered by communication protocol

Question 12

simplex

Answer 12

data is sent in ONE DIRECTION ONLY

Question 13

half- duplex

Answer 13

data is sent in BOTH DIRECTIONS but NOT AT SAME TIME

Question 14

full duplex

Answer 14

BOTH DIRECTIONS AT THE SAME TIME

Question 15

serial data transmission

Answer 15

data is sent ONE BIT AT A TIME over A SINGLE WIRE/ CHANNEL

Question 16

parallel data transmission

Answer 16

SEVERAL BITS OF DATA (usually 1 byte) are sent down SEVERAL CHANNELS/ WIRES all at the same time

Question 17

serial : features

Answer 17

1. less risk of external interference
2. reliable transmission: LONG distance
3. no risk of being out of synchronisation
4. used if amount is small
5. less expensive: fewer hardware requirements

Question 18

parallel : features

Answer 18

1. faster rate of data transmission
2. works wells over SHORTER DISTANCES
3. can arrive out of synchronisation
4. PREFERRED method WHEN SPEED IS IMPORTANT
5. if data TIME-SENSITIVE , better option
6. more hardware, more expensive
7. EASIER TO PROGRAM INPUT/OUTPUT OPERATIONS

Question 19

USB consists of:

Answer 19

1. Four-wire shielded cable
2. Two wires are used for power
3. Two wires are used in data transmission