Computer Science: 4.9 Fundamentals of Communication and Networking

4.9.1 Communication 4.9.2 Networking 4.9.3 Internet

Start and stop bits 1

The start bit synchronises the recievers clock to the transmitter

Start and stop bits 2

They are now locked in phase

Start and stop bits 3

The stop bit then indicates the end of the data being sent (usually one byte at a time)

Start and stop bits 4

This stop bit allows the receiver to process the received bits and allows the next start bit to be recognized

Start and stop bits 5

The is because of the change in voltage

CSMA/CA 1

Assemble data frame

CSMA/CA 2

Check if channel is idle if not wait random time

CSMA/CA 3

If RTS/CTS i s being used and RTS is sent if a CTS is not recieved the sender waits a random amount of time

CSMA/CA 4

Transmit data

CSMA/CA 5

If nothing is received there is a collision the sender waits a random time before trying again

DNS lookup 1

User requests a URL via a browser

DNS lookup 2

Browser extracrs FQDN and sends it to DNS server

DNS lookup 3

Local DNS server maps FQDN to an IP address and return it to the browser

DNS lookup 4

If local DNS doesn't have an entry it is passed onto a regional DNS

DNS lookup 5

If regional DNS doesn't have an entry it is passed onto a NSP. It will then be passed back

DNS lookup 6

A GET request is sent for the webpage or resource is sent to the web server using the IP address

DNS lookup 7

The file is returned to the web browser

Vernam cipher 1

Find the binary ASCII character code for each letter of the plaintext

Vernam cipher 2

Find the binary ASCII character code for each letter of the key

Vernam cipher 3

Carry out an XOR operation for each matching letter

Packet switching process 1

NIC receives a message to send out data

Packet switching process 2

NIC splits the message up into a number of equally sized packets and numbers them. A checksum is calculated for each packet.

Packet switching process 3