GarrettCom OSI User Manual

Industrial Network Track: Multi-Bus

GarrettCom, Inc.

47823 Westinghouse Drive

Fremont, CA 94539

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www.GarrettCom.com

Industrial Network Track: Multi-Bus

Author Jim W. Hammond – Technical Consultant, GarrettCom, Inc.

Keywords: Network integration, Ethernet, TCP/IP, field buses, topology

Last time I checked it was reasonably easy to get a bus transfer in NYC, but don’t expect that level
of ease when doing transfers from one industrial bus to another. More than likely you’ll get more
attitude than a rush hour bus driver. What you need is a good map to avoid the roadblocks along the
way, and a clear and logical itinerary that avoids the potholes. That is where this paper can help.

The interconnection and integration of existing heterogeneous sub-networks into a homogeneous
network has always presented challenges. Evolving and converging protocol standards along with
emerging multi-protocol components suggest that a clear understanding of the problems and solutions
has never been more important. These concerns include reliability, redundancy, robustness, and
security. Most importantly, the multi-bus points of integration should be as seamless as possible, and a
consistently high level of security should be maintained throughout.

Where legacy equipment is still performing as required, an efficient way to integrate these
components into the overall scheme while preserving security and reliability is vitally important. As
new equipment and processes evolve, a consistent strategy of deployment of Ethernet-supported
interfaces insures proper integration with a minimum of downtime and re-engineering delays. The
wide range and availability of Ethernet solutions and its support from standards groups, vendors,
OEMs, and industry provides the assurance that it will continue to evolve. From the early days of
10Mb coaxial cable products Ethernet has moved into the gigabit range and beyond. Bandwidth and
media support outstrip any other transmission and access control protocol set.

INDUSTRIAL NETWORKS AND BUSES

The range and types of industrial networks and buses are very broad as many evolved to handle
specific types of industries and related applications. Some lay claim to more universality and
interoperability. The focus will be on these network architectures since a prime pre-requisite for
choosing a common network platform must include its ability to work with other networks and be
standards-based. For convenience, the term network will be used to mean network or bus.

There are a number of ways to characterize the various networks, none that provide clear dividing
lines, but for our purposes they will be grouped into proprietary and open standard. Even proprietary
systems may provide gateway solutions for interconnectivity, but they require more configuration,
modification, and testing than an open standard system. In addition, some networks attempt to
standardize on the application and message syntax, or upper layers in Open System Interconnect (OSI)
terminology. To keep things relatively simple, this paper addresses the lower layers responsible for
getting the data to a destination device, user, or application.

Distributed with permission of author by ISA 2006

Presented at ISA EXPO 2006

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

7-Application

6-Presentation

5-Session

4-Transport

3-Network

2-Data Link

1-Physical

OSI MODEL

will spend most of our time in layers one and two, which is where Ethernet
operates.

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.

Layer four deals with end-to-end exchange of messages.

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.

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.

CC-Link is a Fieldbus network developed by Mitsubishi for real-time applications and is popular in

Asia. It uses a line topology with speeds up to 10Mbit/s.

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.

Modbus-IDA has three implementations, one using Token Bus at 2Mbit/s, another using a line

topology, and a third version running over Ethernet/TCP/IP is discussed later.

Distributed with permission of author by ISA 2006

Presented at ISA EXPO 2006