Purpose of protocol models

• Standardise communication between heterogeneous systems and vendors.
• Divide complex networking into manageable, well-defined functional layers.
• Each layer provides services to the layer above and uses services from the layer below.

Benefits of modularity

• Changes in one layer do not require redesign of other layers (abstraction).
• Different vendors implement the same layer interface, promotes interoperability.
• Troubleshooting is simplified by isolating problems to a specific layer.

Two primary models

• OSI (Open Systems Interconnection): 7 layers, theoretical framework (ISO (International Organization for Standardization)/IEC (International Electrotechnical Commission) 7498).
• TCP/IP (Transmission Control Protocol and Internet Protocol) Model: 4 layers, practical model used on the Internet.
• Both describe the same communication process, with different granularity.