OSI Model

7 layers that standartize networks

Not used anymore - tcp / ip is used

Layers

• Physical - cable
• Data link - mac address
• Network - ip address, routing
• Transport - TCP / UDP
• Session - start / stop sessions
• Presentation - format data, encryption
• Application - SMTP (email)

TCP/IP model

Created to standartize computer networking

• Application - application protocols (http, smtp, ftp) - DATA

• Transport - TCP/UDP protocols - SEGMENT

• Network - IP - PACKET

• Data link - ETHERNET - FRAME

• Physical - Cable

TCP vs UDP

TCP

• Used when good and reliable connection is needed (for example to download files)

• Two computers ack the connection before it takes place. Three way handshake

  Syn -> Syn Ack -> Ack Received

• Tcp assigns numbers to data that being sent

• Receiver calculates checksum and sends to sender

• Tcp will re-send data if it wasn’t delivered

UDP

• It doesn’t establish a session

• Fire and forget protocol

• Udp is faster

• Live realtime connections - voice call, video calls, gaming

Mac Address

Unique address assigned to network interface card

DNS - domain name system

DNS translates domain name into ip address

• Check local cache first
• If it’s not found in local cache - dns resolver
• If it’s not found in dns resolver - root server
• Top level domain server

HTTP / HTTPS

HTTP - data transferred not encrypted

HTTPS - data transferred encrypted

• a client tries to access an https site

• a site returns a certificate with public key

• a client verifies certificate in the certificate authority

• a client create a new secret key and signs it with the public key in the certificate

• all communication is encrypted with this private key