CS2 - Data transmission

What is a data packet?

What is a data packet?

Data broken up as they are sent over long distances

What is the structure of a packet?

Header:

• IP address of source and destination

• Sequence number of packet - to be able to be rearranged

• Size of packets

Payload - Actual data

Trailer

• Method of identifying the end of a packet

• Error-checking

What are Cyclic Redundancy checks?

Check data packets for errors by adding the number of 1 bits and storing this as a hex value. Then, the computer is sent the message and recounts the hex value. If they are the same, there are no errors

What is a router?

Stage in a route where the router receives a data packet and uses the header to see where the packet needs to be sent next

What is packet switching?

Method of data transmission where a message is broken into many packets and sent independently.

What is the entire process of sending data?

• Each packet is sent individually

• They go through nodes at each stage to tell them which was to take

• In the end, the packet is assembled in its correct order

What does router selection depend on?

The least number of packets waiting to be processed at each note

Why may the route taken not be the fastest?

The route taken may be busy or not suitable

What are the benefits of packet switching?

• No need to use only one communication line

• You can overcome failed/busy routes by rerouting

• Easy to expand package usage

• High data transmission rate

What are the drawbacks of packet switching?

• Packets can be lost and need to be re-sent

• Methods with real-time streaming (live videos) are prone to errors

• Delay at the destination while packages are reordered

What happens to packets that keep bouncing from router to router?

They are given a hopping number which reduces by one every time the packet leaves the router. If the hopping number reaches 0, the message is deleted and the missing packet is flagged by the destination and a request will be re-sent

What is a hop number?

Added to the header of a packet and reduced by 1 every time leaves a router

What are the three factors that are considered when sending data?

• Direction of data transfer

• Method of transmission

• How the data will be in its correct order

What are factors for sending data considered with?

By a communication protocol

What is simplex data transmission?

Data sent in one direction only

Half-duplex data transmission?

Data sent in both directions but not at the same time

What is full-duplex data transmission?

Data sent through both directions at the same time

What is serial transmission?

Data sent one bit at a time over a single wire

What is parallel transmission?

Several bits of data sent through several channels

What are comparisons between serial and parallel transmissions?

• Serial has a lower risk of interference due to having less wires

• Serial is better over long distance

• Serial has a lower chance of being skewed

• Serial is less expensive because it has less hardware

• Serial is slower than parallel

• It is easier to program input/output operations with parallel