Added OSI.

Author: luceCoding

system_design/osi_model.md

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+# 7 Layer OSI Model
+Acronym : "All People Seem To Need Data Processing"
+
+## 7. Application
+- Simple Mail Transfer Protocol(SMTP) File Transfer Protocol(FTP), Telnet, HyperText Transfer Protocol(HTTP), Secure Socket Layer(SSL),
+- "Language" that the applications and servers use to communicate with one another.
+
+## 6. Presentation
+- Format of data and character set conversion like ASCII, Encryption
+
+## 5. Session
+- Establishing and terminating connections.
+
+## 4. Transport
+- TCP, UDP, Ports
+- Data integrity checking, source and destination ports and specs for breaking application data into packets.
+
+## 3. Network
+- IPv4, IPv6, Routers
+- Defines how to move packets from a source host to a destination host.
+
+## 2. Data Link
+- MAC addresses, switches
+- How physical addresses are added to the data with the use of frames.
+
+## 1. Physical
+- Ethernet, modem
+- How to send raw data across a physical medium.
+
+### Other Resources
+- [OSI Model Youtube Video](https://www.youtube.com/watch?v=LANW3m7UgWs)