Chapter 2 – Data Transmission
2.1 Types and methods of data transmission
Data Packets
What are packets?
● Information on the internet is broken down into data packets - also known as
datagrams and is created by TCP and transmitted over the internet.
○ Packets are small chunks of information/data.
○ TCP stands for Transmission Control Protocol and is used for organising data
transmission over networks.
○ TCP - When a web server sends an HTML file to a client, it uses the HTTP to
do so. The HTTP program layer asks the TCP layer to set up the connection
and send the file. The TCP stack divides the file into data packets, numbers
them and then forwards them individually to the IP layer for delivery.
● Small chunks of data are easier and quicker to route over the internet than big
chunks of data.
○ Routing involves finding the most optimal path over a network using a router.
○ Roles of a router: A router sends data to a specific destination on a network
A router can assign IP addresses
A router can connect a local network to the internet
● Data can include anything from text, images, audio, video, animations, etc, or any
combination of these.
What do packets contain?
● Packets are “chunks” of information. This information is called the “payload”
● Packets act like postage letters, each one has the following:
● a delivery address (destination IP address)
● a return address (source IP address)
● and a message (data payload)
, ● Packets are split into three parts:
● Packet header
● Payload (the actual data)
● Trailer
● The header contains:
● Source IP
● Destination IP
● Packet number
● Error checker e.g. a checksum or parity bit
● The trailer contains:
● Additional error checks
● End of packet notification
Figure 1: To transmit the message “This is a message :)” over the internet, the TCP might
break the message down into 4 packets
● Each packet in Figure 1 contains a source IP address, destination IP address,
payload (the data) and a packet number. Error checking and end-of-packet
notifications have not been included in this example.
2.1 Types and methods of data transmission
Data Packets
What are packets?
● Information on the internet is broken down into data packets - also known as
datagrams and is created by TCP and transmitted over the internet.
○ Packets are small chunks of information/data.
○ TCP stands for Transmission Control Protocol and is used for organising data
transmission over networks.
○ TCP - When a web server sends an HTML file to a client, it uses the HTTP to
do so. The HTTP program layer asks the TCP layer to set up the connection
and send the file. The TCP stack divides the file into data packets, numbers
them and then forwards them individually to the IP layer for delivery.
● Small chunks of data are easier and quicker to route over the internet than big
chunks of data.
○ Routing involves finding the most optimal path over a network using a router.
○ Roles of a router: A router sends data to a specific destination on a network
A router can assign IP addresses
A router can connect a local network to the internet
● Data can include anything from text, images, audio, video, animations, etc, or any
combination of these.
What do packets contain?
● Packets are “chunks” of information. This information is called the “payload”
● Packets act like postage letters, each one has the following:
● a delivery address (destination IP address)
● a return address (source IP address)
● and a message (data payload)
, ● Packets are split into three parts:
● Packet header
● Payload (the actual data)
● Trailer
● The header contains:
● Source IP
● Destination IP
● Packet number
● Error checker e.g. a checksum or parity bit
● The trailer contains:
● Additional error checks
● End of packet notification
Figure 1: To transmit the message “This is a message :)” over the internet, the TCP might
break the message down into 4 packets
● Each packet in Figure 1 contains a source IP address, destination IP address,
payload (the data) and a packet number. Error checking and end-of-packet
notifications have not been included in this example.
