The OSI (Open Systems Interconnection) model, is a framework that breaks down how network communications work into **seven layers**. Each layer has a specific role and communicates with the layer above and below it:
1. **Physical (Layer 1):**
1. The actual hardware and media
2. Cables, switches, signals, raw bits over wire or fibre.
2. **Data Link (Layer 2):**
1. Responsible for point-to-point connections on the same network.
2. Defines the format of the data
3. Uses MAC addresses, switches, Ethernet
4. ARP, Frames, VLAN's
3. **Network (Layer 3):**
1. Handles addressing and routing between networks.
2. IP addresses and routers live here.
3. IPv4, IPv6, ICMP, IGMP, IPSec, OSPF
4. **Transport (Layer 4):**
1. End-to-end communication.
2. Protocols like TCP (reliable, connection-oriented) and UDP (fast, connectionless).
5. **Session (Layer 5):**
1. Manages sessions between applications
2. Establishes, maintains, and tears down connections.
3. NetBIOS, RPC, PPTP, SMB
6. **Presentation (Layer 6):**
1. Translates data formats (e.g. encryption, compression, character encoding) so different systems can understand each other.
2. TLS/SSL, JPEG, SSLVPN, ASCII
7. **Application (Layer 7):**
1. What the user interacts with
2. web browsers, email clients, file transfer apps.
3. HTTP/S, FTP, SMTP, POP3, IMAP, DNS, SNMP, Telnet, SSH, RDP, DHCP
## Pneumonic Device To Remember
```
Please
Do
Not
Throw
Sausage
Pizza
Away
```
```
P - Physical
D - Data Link
N - Network
T - Transport
S - Session
P - Presentation
A - Application
```