There are 2 types of transport protocols:

• TCP: Transmision Control Protocol
• UDP: User Datagram Protocol

TCP is a trusted protocol. Contrary to UDP.

UDP:

This protocol is called BEST EFFORT => i.e. it guarantees maximum use of Bandwidth.

UDP header:

Software port: These are virtual gates between the internal and external network. There are 65535 of them.

The most important:

• SSH: 22
• HTTP: 80
• HTTPS: 443
• DNS: 53
• DHCP: 67/68
• PROXY: 8080

A UDP data packet is cut into MAXIMUM 1500 bytes/packet.

Example: A 5KB packet = 5000 bytes. => 3 packets of 1500 bytes + 1 packet of 500 bytes.

TCP:

Handshake three way:

Popularized version :

1. Sender -> Receiver: I want to talk to you
2. Receiver -> Sender: I accept, but I also want to talk to you.
3. Sender -> Receiver: Let's talk together.

Technical version :

1. Sender -> Receiver: SYN ; SEQ=1
2. Receiver -> Sender: ACK=1 ; SYN, SEQ=100
3. Sender -> Receiver: SYN, ACK=2, SEQ=2

SYN = SYNCHRONIZATION SEQ = SEQUENCE ACK = ACKNOWLEGMENT => Acknowledgement of receipt.