Protocol Layers & Reference Models

Defining protocol layers helps in dealing with complex systems:

Explicit structure allows identification, relationship of complex system’s pieces.
- Layered reference model for discussion.
Modularisation eases maintenance, updating of system.
Change in layer’s service implementation is transparent to rest of system.

Internet Protocol Stack¹

Internet 5-layer model

The OSI reference model also includes:

Presentation - Allows the applications to interpret the meaning of data.
- Encryption, compression, machine specific conventions.
Session - Synchronisation, check-pointing and recovery of data exchange.

The internet stack is missing these layers. If they are need they must be implemented in the application.