OSI MODEL
PROPRIETARY NETWORKS
The following networks provide their own proprietary layer one and two implementations, but some offer alternate access via an Ethernet interface. In some cases the media may also be unique to the network. Some define an architecture using layer concepts similar to the OSI model above.
CANopen is a proprietary system using speed below 1 Mbit/sec and a line topology with drops. The CIA (Can-in-Automation) international user and manufacturer group provides standardization.
ControlNet was developed by Rockwell Automation and is a Fieldbus using line, bus, tree, and star topologies at 5Mbit/s.
DeviceNet, also developed by Rockwell Automation, operates at speeds up to 500 Kbit/s using a bus line with trunkline/dropline topology.
Interbus was developed by Phoenix Contact and is popular in automobile production. It operates at speeds up to 2Mbit/s using a ring topology with a unique cable design.
Distributed with permission of author by ISA 2006
Presented at ISA EXPO 2006
The upper layers five to seven support the application and are beyond the scope of this paper. You can now breathe a sigh of relief.
Layer four deals with end-to-end exchange of messages.
To clarify terms, the physical layer deals with the transmission and synchronism of data and physical interface definition.
Layer two deals with the sending and receiving of data, validity of the data and retransmission, and access to the data link among other functions.
Layer three deals with network addresses, one example being an IP address, assembly and disassembly of messages, message sequencing, and routing.
If you’ve never seen the OSI model, avert your eyes from the following diagram. Too late. It’s not possible to read any book on data communications and networking and avoid seeing this conceptual view of a generic network architecture. Fortunately, we will spend most of our time in layers one and two, which is where Ethernet operates.