Chapter 2 Data Transmission: Unit 2.1: Types and Methods of Data Transmission

Question 1

Define data packets

Answer 1

A small part of a message/data that is transmitted over a network; after transmission all the data packets are reassembled to form the original message/data

Question 2

Name the 3 parts of the packet structure.

Answer 2

Header
Payload
Trailer

Question 3

What is in the ‘Header’ of the packet structure?

Answer 3

IP address of the source (sender)
IP address of the destination (receiver)
Sequence number of the packet (allowing correct assembly)
Size of the packet (in bytes)

Question 4

What is in the ‘Payload’ of the packet structure?

Answer 4

The actual data in the packets (~64 KiB) - the payload

Question 5

What is in the ‘Trailer’ of the packet structure?

Answer 5

Method of identifying the end of the packet
Some form of error checking to ensure packet arrives error-free

Question 6

Define cyclic redundancy checks (CRC).

Answer 6

An error checking method in which all the 1-bits in the data packet payload are added and the total score in stored in the packet trailer; the same calculation is repeated at the receiving station

Question 7

Define router

Answer 7

Device that enables data packets to be moved between different networks

Question 8

Describe the process of packet switching.

Answer 8

Method of transmission in which a message is broken into many data packets which can then be sent along pathways independently from each other

Question 9

Define node

Answer 9

Stages in a network that can receive and transmit data packets; routers are nodes in communication networks

Question 10

Describe the benefits of packet switching

Answer 10

No need to tie up a single communication line
Possible to overcome failed, busy or faulty lines by simply re-routing packets
Relatively easy to expand package usage
High data transmission rate is possible

Question 11

Describe the drawbacks of packet switching

Answer 11

Packets can be lost and need to be re-sent
More prone to errors with real-time streaming
Delay at the destination whilst the packets are being re-ordered

Question 12

Describe the process of hopping.

Answer 12

A number in the data packet header used to stop data packets that never reach their destination from ‘clogging up’ the data paths/routes

Question 13

What 3 factors need to be considered when transmitting data?

Answer 13

Direction of data transmission
Method of data transmission
How the data will be synchronized

Question 14

What are the 3 transmission modes and describe them?

Answer 14

Simplex - Data that can be sent in one direction only
Half-duplex - Data that can be sent in both directions but not at the same time
Full-duplex - Data that can be sent in both directions at the same time (simultaneously)

Question 15

Define serial data transmission and its properties

Answer 15

Sending data down one channel/wire one bit at a time

Less risk of external interference than with parallel
More reliable transmission over longer distances
Transmitted bits won’t have the risk of being skewed
Used if the amount of data being sent is relatively small since the transmission rate is slower than parallel
Used to send data over long distances
Less expensive than parallel due to fewer hardware requirements

Question 16

Define parallel data transmission and its properties

Answer 16

Sending data down several channels/wires several bits at a time

Faster rate of data transmission than serial
Works well over short distances
Several channels/wires used to transmit data; bits can arrive out of synchronization
Preferred method when speed is important
If data is time-sensitive, parallel is the most appropriate transmission method
Parallel ports require more hardware, making them more expensive to implement than serial ports
Easier to program input/output operations when parallel used

Question 17

Define USB

Answer 17

Universal Serial Bus - form of serial transmission - most common type of input/output port
Consists of four-wired shielded cable

Question 18

What are the benefits of a USB?

Answer 18

Devices plugged into the computer are automatically detected and device drivers are automatically loaded up
Connections can only fit one way preventing incorrect connections being made
Has become industry standard, which means considerable support is available
Can support different transmission rates
No need for external power source
USB protocol notifies the transmitter to re-transmit data if any errors are detected; this leads to error-free data transmission
Relatively easy to add more USB ports if necessary, using USB hubs
USB is backward compatible

Question 19

What are the drawbacks of a USB?

Answer 19

Standard USB only supports a maximum cable length of 5m
Even though USB is backward compatible, very early USB standards may not always be supported by the latest computers