The OSI-Model (Open System Interconnection) is a reference model for how applications can communicate over a network and was developed by the International Standard Organization (ISO) is 1984. A reference model is a conceptual framework for understanding relationships. The TCP/IP protocols, which defines the internet, do not map cleanly to the OSI-Model.
This model breaks down data transmission over a series of seven layers. The layers 1-4 are considered the lower layers and mostly concern themselves with moving data around while layers 5-7 the upper layer, contain application-level data.
The Seven Layer OSI-Model with their functions and Protocol Examples.
| LAYER | NAME | FUNCTION | PROTOCOL EXAMPLE. |
| 7 | Application | It is a service that is used with end user applications. | SMTP, HTTP, FTP, DNS, TELNET, SNMP. |
| 6 | Presentation | It formats the data so that it can viewed by the user. It also encrypt and decrypt data. | HTTPS, GIF, JPG, SSL, TLS, MPEG. |
| 5 | Session | It establishes ends connection between two hosts. | Apple Talk, WinSock, NetBIOS, PPTP. |
| 4 | Transport | It is responsible for the transport protocol and error handling. | TCP,UDP, SPX. |
| 3 | Network | It reads the IP address from the packet. | Routers, Layer of the Switch, IP, ICMP, IPX. IPSec, ARP. |
| 2 | Data link | It reads the MAC address from the data packet. | Switches, Ethernet, ATM, Bridge, PPP. |
| 1 | Physical | Its sends data on to the physical wire to get access to media. | Hubs, NICs, Cable, Ethernet, Token Ring, repeater, USB, Bluetooth, IEEE802.11. |
Also read: 40 Network Protocols with Port numbers and examples
NOTE: The fact is that the OSI-Model isn’t much difficult to know and memories, so here are some enthusiastic tips of sayings to easily remind you of the seven layers of the OSI-Model.
SOME ADDITIONAL SAYINGS OF THE OSI-MODEL.
| Top to bottom | Bottom to Top | Top to bottom | Bottom to Top | Bottom to Top | ||
| 7 | Application | All | Away | All | Advice | Around |
| 6 | Presentation | People | Pizza | People | People’s | People |
| 5 | Session | Seem | Sausage | Should | Sales | Stupid |
| 4 | Transport | To | Throw | Try | Take | Tease |
| 3 | Network | Need | Not | New | Not | Not |
| 2 | Data Link | Data | Do | Diet | Do | Do |
| 1 | Physical | Processing | Please | Pepsi | Please | Please |
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