Installation guide

Network Infrastructure for EtherNet/IP™
B-5
Appendix B Overview of the OSI Model, EtherNet/IP and CIP
Physical Layer
The physical layer defines the electrical, mechanical, procedural, and functional specifications for
activating, maintaining, and deactivating the physical link between communicating network systems.
Physical layer specifications define characteristics, such as voltage levels, timing of voltage changes,
physical data rates, maximum transmission distances, and physical connectors. Physical layer
implementations can be categorized as either LAN or WAN specifications. Figure B-6 illustrates some
common LAN and WAN physical layer implementations.
Figure B-6 Physical Layer Implementations Can Be LAN or WAN Specifications.
Data Link Layer
The data link layer provides reliable transit of data across a physical network link. Different data link
layer specifications define different network and protocol characteristics, including physical addressing,
network topology, error notification, sequencing of frames, and flow control. Physical addressing (as
opposed to network addressing) defines how devices are addressed at the data link layer.
Network topology consists of the data link layer specifications that often define how devices are to be
physically connected, such as in a bus or a ring topology. Error notification alerts upper-layer protocols
that a transmission error has occurred, and the sequencing of data frames reorders frames that were
transmitted out of sequence. Finally, flow control moderates the transmission of data such that the
receiving device is not overwhelmed with more traffic than it can handle at one time.
IEEE has subdivided the data link layer into two sub-layers: Logical Link Control (LLC) and Media
Access Control (MAC). Figure B-7 illustrates the IEEE sub-layers of the data link layer.
Figure B-7 The Data link layer Contains Two Sub-layers.