5-Layer Network Model

Defining OSI Model

1. Application Layer

   • Relevant Device: Browser/user application
   • Protocol: HTTP

2. Transport Layer

   • Relevant Device: Firewall
   • Protocol: TCP/UDP
   • Relevant Data Unit: TCP/UDP port number
   • Each computer's operating system manages its own TCP/UDP ports
   • A firewall device can blacklist (or whitelist) requests made to particular ports on a computer within its network

3. Internet Layer

   • Relevant Device: Router
   • Protocol: IPv4/IPv6
   • Relevant Data Unit: IP address
   • Each router has its own unique public IP address
   • A router maps each device on its network to one unique private IP address
   • The private IP address of a device (that has been assigned by the router) can change, but it must be unique within the private network

4. Data Link/Physical Layer

   • Relevant Device: Switch/Modem
   • Protocol: Ethernet
   • Relevant Data Unit: MAC address
   • Every computer has its own unique MAC address that can't be changed

Defining Processes

• A process is the instance of a computer program
• A process is made up of one or more threads
• Multiple threads can execute instructions concurrently
• The operating system manages a process

Defining Ports

• A port represents an endpoint used for outside communication
• At the software level, within an operating system, a port is a logical construct that identifies a specific process or a type of network service
• Specifically, it is an application-level construct representing an endpoint on a host
• The operating system manages any process bound to a port

References

• Defining Ports in Computer Networking
• Defining Processes in Computing