IEEE 1473-L to -T Gateway

Transportation Systems Design, Inc.

Updated 11/30/02


Introduction

This information is being provided to assist those who may be interested in building a gateway between IEEE 1473-L (EIA 709/LonWorks) and IEEE 1473-T (TCN). It is being provided by TSD in an effort to assist in development of open interoperable communications standards for the rail industry and is intended primarily to compliment efforts by IEEE, APTA, LonMark and others who desire to build standard interfaces between LonWorks and TCN and between LonWorks and other protocols. You input, updates, new links, and corrections to the information below is appreciated. 

Background

With ABB's June, 2002 announcement that its formerly proprietary TCN protocol stack is now available under General Public License (GPL) both TCN and LonWorks now appear to meet the generally accepted definition of an open protocol. LonWorks is a control protocol widely deployed in many industries around the world. On trains, LonWorks is used primarily in North America but it is also used by railcar builders in Europe (See: where used). TCN is a protocol used on some trains, mostly in Europe. There is one TCN project in the US (New Jersey Transit Comet V). This project also has developed a "double gateway" between LonWorks on Alstom trailer cars connected to Bombardier locomotives that use TCN. It is generally (perhaps universally) agreed that NJT's double gateway approach is not a good long-term technical solution and a simpler "single gateway"  is preferred. 

Technical Challenges

Neither IEEE-1473-L (LonWorks) nor IEEE-1473-T (TCN) protocols define a specific train architecture. Rather each is a communications protocols upon which  specific train applications must be developed. For example, in addition to many train systems, LonWorks applications control US Warships and European Nuclear Reactors. The TCN protocol is used on some trains but is also used to control printing presses at The Wall Street Journal.

For IEEE-1473-L based networks, interoperability is achieved using Standard Network Variable Types (SNVTs) in concert with LonMark Profiles. Perhaps the best example of this interoperability is the LonWorks propulsion control train lines used among three different rail car manufacturers at NYC Transit. In the case of IEEE-1473-T there are tabulations of data elements for many different rail cars listed in UIC Leaflet 556. These (mostly Boolean) data elements in 556 are somewhat analogous to simple LonMark SNVT's. A LonMark Profile for a train could be an Entry/Exit Device (i.e. a train door), a Propulsion System, or an HVAC unit. 

For IEEE 1473-T based networks there appears to be no concept directly equivalent to LonMark Profiles. Thus, it appears logical to craft object definitions of standard interoperable vehicle subsystems using TCN  based upon new LonMark Profiles. This appears to be what is happening today in IEEE RTVISC WG9. In addition, where existing LonMark SNVTs exist that are compatible with data elements that might be listed in UIC 556 they will be used. Where there are no apparent equivalents, new SNVTs will be created in cooperation with the LonMark Association. 

Passing information between nodes on a common network using routers is easy because routers need know nothing about the data they route. Routers are  like postal carriers who look only at the addresses on envelopes and care nothing about the contents -- to know where to forward a letter. But routers can be used only when the protocol on both sides is the same. 

When the protocols are different (as is the case with LonWorks and TCN) a gateway is required. The key issue with a gateway is the need to specifically translate every data element on one side of a gateway to its equivalent meaning on the other. It's as if the postal carrier must open every letter, refer to a dictionary, translate the contents to another language, put it back in another letter, and send it on its way.  

Thus, for a gateway to function at all, the data elements on BOTH sides of the gateway first must be completely defined. Further, a commercially viable IEEE-1473-T to IEEE 1473-L gateway must be inherently flexible to accommodate inevitable changes resulting when new devices are added to a train network or new functions are added to existing devices. When such changes occur, the data translation tables in all affected gateways must be updated. Likely this can be accomplished by providing electrically erasable flash memory in a manner similar to the way new Layer 7 application software can be downloaded into a Neuron on an IEEE-1473-L network -- to accommodate new functional requirements or revised parameter values.

Tunneling one protocol INSIDE another protocol is another preferred preferred alternative if it can be made to work. With a tunneling router, one protocol is used as the "conduit" for the other. This allows the protocol to be the same on both sides. Thus, the simplicity and benefits of a router are realized. For example General Electric and Safetran Systems tunnel vital, safety-critical train control ATCS packets through LonWorks networks that act as conduits for the ATCS protocol. Conversely, other firms use products that tunnel LonWorks through Internet Protocol. At NYC Transit today, all new  rail cars tunnel LonWorks through industry standard E1/T1 communications networks via Wabtec electric couplers. There has been some discussion about tunneling LonWorks through TCN. To the extent this may work it may be preferred to a gateway.

If you have additional comments or suggestions that may enhance this discussion please contact us. The table below attempts to highlight key LonWorks and TCN information as it may relate to a gateway effort. 

Relevant Links 

LonWorks   Description / Comment        TCN Description / Comment
IEEE-1473-L An overview of where, why and how LonWorks is used in rail transportation and related industries. Train Comm Following a predecessor project (ROSIN), TrainCom intends to go further deploying IT technologies in the railway field
IEEE-1544 This RTVISC Working Group is defining data elements, LonMark Profiles and new SNVT's  for rail car subsystems to be interoperable with UIC Leaflet 556 Same Same
LonMark The not for profit Association of LonWorks users certifies that products conform to interoperability definitions. These "exposed interfaces" are based upon LonMark Profiles. Profiles in turn make use of Standard Network Variable Types (SNVTs) defined by the LonMark Association.  ROSIN Data Representation This is a useful ABB document describing how TCN data might be represented in other protocols including LonWorks and FIP
SNVT List Revision 11 in Adobe PDF format for Standard Network Variable Types UIC Leaflet 556 A work in progress which lists data elements used on TCN-based passenger trains in Europe. This may be a proprietary document and thus is not listed here. 
LonMark Profiles A listing of Existing Profiles

?

No apparent equivalent concept in TCN
Reference Implementation The LonWorks reference implementation developed by Adept Systems TOSS TCN Open Source Set Released under General Public License in June 2002 (in zip format)
ShortStack MicroServer Code to add the LonWorks protocol specified in IEEE-1473-L to any 8, 16 or 32 bit CPU. Requires 4k Bytes of ROM and 200 Bytes of RAM

?

No apparent equivalent
ieee.fwsbcon.com A unofficial working group with a discussion board that compliments the activities of the RTVISC's IEEE RTVISC  Working Group #9 Same Same
 IEEE 1473 The IEEE's RTVISC Working Group that developed the IEEE 1473 standard defining LonWorks and TCN. Same Same

Papers

TSD papers and presentations section that includes some additional information related to train networking Same Same

LonWorks and Other Protocols

LonWorks is a general purpose communications protocol deployed worldwide in tens of millions of nodes by over 4,000 OEMS across many industries. A few of  these firms have also developed specific technologies that may be useful for train applications to permit interoperability between IEEE-1473-L (LonWorks) and other systems. If you know of additional products that may be of interest to visitors of this page please let us know and we will add them.

Product/Device/Tool Company Description
A190 Packet Tunnel Engine (PDF) MicroSym A general purpose tunneling router that appears useful when interfacing LonWorks with  other industry standard protocols such as E1/T1, E3/T3, WorldFIP, etc.
7805 Router SmooCom  Industrial grade router converts IEEE-1473-L to ANSI/EIA 709 Power Line. Designed to operate off a standard rail transit car batter. 
iLON 1000 Ethernet Adapter Echelon IEEE-1473-L to IEEE 802.11u router. Tunnels LonWorks through IP over Ethernet. Product not yet ruggedized for rail transit applications