3. Communication services

Layer 2 communications are connectionless. It enables point-to-point (peer-to-peer), multicast and broadcast communications. The communication services supported by Profibus include station data access services, known as FDL (Fieldbus Data Link) services, and network management services, known as FMA1/2 (Fieldbus Management for layers 1 and 2) services.

All services provided by Layer 2 are executed at the LLI via Service Access Points (SAPs). These access points are used by Application Layer 7 for logical addressing and multiplexing of ongoing communications. All stations can thus serve several SAPs simultaneously. A distinction is made between SSAP source SAPs and DSAP destination SAPs.