Thursday, May 31, 2007

Unlimited Cellular Data - Revisted

As I go around dealing with large utility customers and hear feedback from Digi salespeople who survive large accounts, I hear some interesting but disturbing trends rising.

First, there are the people (usually who are new to cellular) who claim any day now the age of cheap, unlimited cellular data plans means all my hard work to understand or offer reduced traffic are wasted effort. I especially hear this coming from European partners.

Then there are the other people ... people I know work with very large, very powerful end users who fail to get the cellular plans they desire. Things I hear:
  • I have heard of customers who pilot projects and hear promises of unlimited traffic, but when the time comes to sign the contract for 3000+ sites, the carrier decides that they cannot offer unlimited traffic ... period. Hmm, I guess this is the difference showing between the carrier's commissioned sales staff and the business managers who need to keep the cellular system profitable.
  • I have worked with large customers who do manage to get "unlimited deals" for a modest sized system - say 50 or 100 sites, but the carrier insists on adding the 2 clauses 1) the carrier has the right to artificially slow down the data communications (without detailing what this means) and 2) the carrier has the right to just stop all the customer's data traffic temporarily if the cell system gets busy (again, not details of this defined). Hmm, I have to kind of wonder what kind of control engineer agrees to such "clauses"? You'd think trying to get one's data under control to avoid the need for unlimited data is a wiser design.
  • I have heard that overall the cellular carriers are starting to rethink the value of machine-to-machine data plans. Unlike DSL or cable, this is NOT an issue of bandwidth; it is an issue of the % of the time the device "hogs" 1 of N slots or resources on the tower forever. Imagine having 10 or 20 such devices squatting there, locking up that tower resource. So it is not even so much an issue of talking once per few minutes verse flat out unlimited traffic. In either case 1 of N finite tower resources is used, so long-term the only "good" data plan may be for a data system using the cellular resource every few hours or a few times a day.

So overall it looks like my efforts to understand and reduce traffic is useful.

Tuesday, May 29, 2007

I will give Webinar 31-May-2007

31-May-2007 (Thursday) I'll be giving a webinar related to outdoor use of IP-to-serial devices. While not directly related to my blog theme of "Industrial Protocols over IP", remote devices frequently are in bad locations, where extended temperature ranges, conformal coating, and Class 1 Div 2 certs are desired.

Title: Connect Local and Remote Devices in Hazardous Environment SCADA Applications
Register here: WebEx Link

Date: May 31, 2007
Time: 11:00am CDT (central zone)
Duration: 1 hour
  • Lynn Linse - Engineer, Digi International
  • Deb Smith - Business Development, Digi International

What you will learn
This live webinar will illustrate the value of using TCP/IP & UDP/IP based communication over wired and wireless networks to monitor and manage local and remote devices. Topics include:

  • Overview of requirements for robust, remote, outdoor communication devices
  • Discussion of extended temperature, conformal coating, hazardous certs
  • Comparing features of IT-grade network devices to Digi's Haz product line
  • Extending IP networks to remote serial and Ethernet devices
  • Moving serial communications through TCP/IP and UDP/IP
  • Migrating from analog Telco/POTS lines to IP-based broadband
  • Real-world usage examples
  • Implementation benefits
    - Real-time access to remote sites and process data without site visits
    - Reduce repair/replacement costs due to less-than ideal environments
    - Options to reduce installation costs with wireless
Please register today and join us May 31st for this informative webinar!
Questions? Contact Deb Smith at or 952-912-3283.

Friday, May 04, 2007

ODVA, Rockwell, and Modbus Get Smart

Summary: next week an amazing joining of technologies will take place at ODVA in Ann Arbor MI as ODVA, Rockwell, and Schneider-Electric discuss how to integrate Modbus servers (slaves) into CIP Producer/Consumer systems

One of the fun things about being involved in "multi-vendor" solutions is when you recognize moments of amazing sanity as they occur. One such moment of amazing sanity is occurring next week when ODVA (aka Rockwell / Allen-Bradley) and Modbus supporters (aka Schneider-Electric / Modicon / SquareD / Telemecanique) sit down to discuss how to integrate Modbus devices into the ODVA Ethernet/IP and CIP network systems. Of course there must be some interesting hidden politics behind this move - and I somewhat light-heartedly believe that perhaps French Schneider-Electric sees joining with the Americans (Rockwell/ODVA) as the lesser of two evils when compared to joining with the Germans (Siemens/PNO).

Check out: ODVA Call For Members: Modbus Integration JSIG The kick-off meeting for the Modbus JSIG runs from Thursday, May 10, 11:00 AM to Friday, May 11, 04:00 PM

Side-stepping the marketing fluff and platitudes of a brighter future such meetings evoke, small third-party suppliers and the folks on the plant floor can expect the following benefits. Regardless of the directly stated goals of ODVA, Rockwell, or Schneider-Electric, small vendors will implement solutions that include these abilities:
  • Vendors making Ethernet Modbus/TCP products will have a simpler "first step" to adding full ODVA/CIP support without the somewhat overwhelming task of 100% conversion of a word-array device model into hundreds (or thousands) of CIP objects.
  • ControlLogix PLC will be able to connect through Ethernet-to-Serial devices to multi-drops of Modbus/RTU slaves. For example a user with a dozen small Modbus/RTU PID loop controllers will be able to add an Ethernet-to-Serial device to read via Modbus and cyclically produce a small block of word data from each loop controller over Ethernet.
  • HART, Bluetooth, ZigBee and other new technologies which offer Modbus interfaces will find a instant place as sensors and I/O within CIP and Rockwell systems.
  • Since Siemens, GE-Fanuc, Omron, Mitsubishi and most major PLC brands offer some method to act as Modbus slaves, users with any of these PLC will be able to integrate them within the CIP Producer/Consumer system.
Looking forward a year or two, I also can foresee some other secondary benefits evolving from this JSIG's work:
  • I started working with ODVA Ethernet/IP almost 8 years ago and still as-of today the legacy PLC5E, SLC5, and serial MicroLogix (the old PCCC-based PLC) don't have effective inclusion within CIP Producer/Consumer systems. Since the device model of PCCC PLC shares much in common with Modbus PLC, it is a very small enhancement to add a similar support for AB PLC - perhaps AB will actually extend this to future firmware updates to Ethernet-based PLC. In fact, since my Digi One IAP code already allows Modbus masters to query DF1 and CSPv4 slaves as-if Modbus slaves, as soon as Digi adds Ethernet-to-Modbus support per this JSIG's output users of older AB PLC will gain access to CIP Producer/Consumer systems indirectly as honorary Modbus slaves.
  • Today legacy Modbus and Modbus/TCP systems lack any simple form of multicast producer/consumer exchange. While the IDA protocol offers this, IDA is so many orders of magnitude more complex (and resource hungry) than simple Modbus as to become really an "unrelated" protocol. Any specification that defines a "server interface" naturally implies a corresponding "client interface". So although this ODVA JSIG is not planning to define how Modbus "peers" could use multicast to exchange cyclic data, the end result will be a fairly natural and multi-vendor method to do this. So while I doubt many pure Modbus/TCP products would implement ODVA protocols just to gain this multicast exchange, any products which add the CIP support anyway will naturally add the last few bits of code required to enable pure Modbus-to-Modbus multicast via the ODVA mechanism.
  • Taking the above point to its natural conclusion means Modbus/TCP masters which implement the Modbus JSIG's "server" function will also gain a mechanism to access CIP Producer/Consumer systems. Even if the ODVA JSIG doesn't cover how to do this, natural methods will be inferred, produced, and copied by vendors to make this a fairly common new product feature.
And lastly, it will interesting to see what response PNO considers to likewise include Modbus slaves more formally into PROFINET. Personally, I have always felt that the simpler PROFINET IO protocol would fit very naturally with multi-drops of Modbus slaves acting like plug in I/O modules ... each slave would be a module within the IO device.