What is network services terminology?

The real function of every layer in the OSI model is to provide services to the layer above it. Understanding the terminology used in network services is essential for comprehending how different layers interact and communicate with each other.

Key Network Service Entities

Entities are active elements within each layer that can be either software-based (like processes) or hardware-based (like intelligent I/O chips). Peer entities are corresponding entities that exist in the same layer on different machines and communicate using the same protocol.

Service Access and Data Units

Service Access Points (SAPs) are specific locations where a layer can access services from the layer below. Each SAP has a unique address for identification. When layers exchange information, they use an Interface Data Unit (IDU) that contains both the actual data and control information.

• Service Data Unit (SDU) − The actual information passed across the network to the peer entity

• Protocol Data Unit (PDU) − Data fragments with headers used for transmission, such as packets

Types of Network Services

Data Flow in Network Services

When data moves between layers, the SDU from the upper layer becomes part of a PDU at the lower layer. The lower layer may fragment the SDU into multiple PDUs, each with its own header containing protocol information for peer communication.

Conclusion

Network services terminology defines how layers interact through entities, SAPs, and data units. Understanding these concepts is crucial for comprehending how the OSI model facilitates communication between different network components and layers.