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braxckloff | CompTIA Network+ | Module 1.1 - OSI and TCP/IP Models

By: braxckloff | Related Course: CompTIA Network+ | Published: April 2, 2018 | Modified: April 5, 2018
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NotepadOSI and TCP/ip Models

Networking = sending info from one computer to another computer anywhere in the world

Networking can be broken up into different layers using the OSI Model

OSI (Open System Interconnection) Model:

  • 1. Physical Layer
  • 2. Data Link Layer
  • 3. Network Layer
  • 4. Transport layer
  • 5. Session Layer
  • 6. Presentation Layer
  • 7. Application Layer

Similar to shipping process

Some times this can go from 7 to 1


  • Please
  • Do
  • Not
  • Throw
  • Sausage
  • Pizza
  • Away



NotepadOSI Model Layer 1 - Physical

OSI Model

Layer 1: Physical

  • Cables/BITS ( Binary Digits) 
  • Physical/Electrical stage
  • Starts the conversion between data to signals or vice versa 


– Pinouts, voltages, cable specifications, NIC (Network Interface Cards) 

This is the first point in the transfer of data using physical signals.

Using things that can be measured and be physically held



– Sends data from one computer to another but is not able to send specific data to specific computers

– Acts as a repeater

NotepadOSI Model Layer 2 - Data Link

OSI Model

Layer 2: Data Link

– Access to a computer or device

– Package physical bits and impulses into frames or data

– Transfer data from point to point

MAC addresses: ( media access control addresses) – Addresses that are hard encoded into network interface cards so that they have a globally worldwide unique set of numbers that identify them. 

If we had two computers with the same mac addresses we would end up with a lot of different problems with connectivity with those devices on our network.

– As if the truck is driving down the street and handing off the box to our particular house. 

NotepadOSI Model Layer 3 - Network

OSI Model

Layer 3: Network Layer

– Commonly referred to as the ”IP” layer because of it’s heavy use of IP addresses

IP (Internet Protocol) Address: The unique identifier for a computer

– Sending data to a single point while allowing us to route that data over different networks

– Translates logical addresses to Physical

– Functional means of transferring data through one or more networks

– Routers 


– Network routing functions

– Fragmentation/reassembly 

All computers with a network interface card (NIC) have a mac address and an IP address

Q. Why do you need both an IP address and a mac address?

A. We need to be able to take a computer’s mac address, assign a particular IP address to that mac address and then route data through mac addresses over our networks.

– You cannot transmit data to a computer on a different network using a mac address because you need to use an IP address

– Between us and the computer on that other network we have to go through a router and a router needs to have an IP address in order to transmit information



< All CompTIA Network+ Notes
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