OSI Layers
A quick and dirty on the seven layers of the OSI Model.
OSI Layers in Network Traffic
Layer 1: Physical
Represents the bit-level transmission between network nodes over the connection medium.
Data: Bits across the wire (1s and 0s) as pulse of electricity or light.
Layer 2: Data Link
Data Link Layer handles communications between adjacents network nodes via physical addressing (MAC).
Data: Frames.
Layer 3: Network
Handles routing messages (packets) via the best route to reach its destination based on IP address.
Data: Packets.
Layer 4: Transport
Defines how data will be sent providing validation and security.
Data: Segments.
Layer 5-7: Application, Presentation, Session
Layers 5-7 are typically managed by the application itself, providing the interface for the user to communicate.
Data: Data.
Data in a TCP/IP Example
- Data Link Layer (2): Frame = Frame Header + Frame Data
- Network Layer (3): Packet = IP Header + IP Data
- Transport Layer (4): Segment = TCP Header + Application Data
- Application Layer (5-7): Data = App Header + User Data
When dealing with subnetting, network masks etc, note that you are working in the Network Layer (layer 3).
Dennis O'Keeffe
Melbourne, Australia
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