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KB1055: Notes from the Engineer: What is an LNWI?

This article was last updated on Aug. 7, 2017, 4:42 p.m. | Print Article | Leave Feedback

What is an LnWi?

The Digitrax LnWi module is a 2.4GHz IEEE 802.11 b/g/n (Wifi) Wireless Access Point type of device that logically bridges access from compatible external throttle APP(s) running on mobile tablet or smart phones onto a Digitrax LocoNet. The LnWi is an independent method for Digitrax users to control locomotives, and can be used at the same time as e.g. Digitrax Duplex or Simplex Wireless, and IR/wired throttles and other Wifi LocoNet access devices on the same system it is wired to.

The design goal for the LnWi was to make it very easy for a Digitrax user to connect and run. It takes less than 60 seconds to setup and run, after you have downloaded a matching APP for your type of device i.e. Apple or Android.   LnWi is ‘Plug and Play’ and there is no user configuration required for most systems and no Networking knowledge is required. If you know how to connect to a web site with your mobile device, you can use an LnWi.

The LnWi does not transfer any TCP/IP packets to any other network such as other; Internet or wired Ethernet connections.  I.e. the LnWi is not a WAP or Router/Switch to; Internet or other non-LocoNet connections, and so does not require any other devices, PC’s or connections to allow compatible Wifi throttle APPS to be used.  The LnWi intrinsically understands and “speaks” native LocoNet commands and methods and performs a translating bridge function to another protocol over Wifi within the mappings possible.

Once a Wifi device is connected to an LnWi’s unique SSID, using its DHCP service, a dedicated point-to-point link from the mobile device to just the LnWi is set up.  Subsequently, an APP startup opens a socket to one of the four dedicated LocoNet access Servers, which then provide the required transfer of data and sequences to allow a portion of the public Hoffman Wifi Throttle Protocol to effect some locomotive control on the LocoNet system.

A Wifi link and the Hoffman Wifi protocol do not natively match the; LocoNet control methods, data rates and sequences, so the LnWi has to have separate input and output sequencing machines, task translation and control caches for each of the 32 possible throttles that a LnWi Server will support.  These Server logic components and timing methods complicate the software design because the Wifi data rates can be so much higher than the wired network, so a lot of state information must be cached and metered out to LocoNet. The LnWi itself embodies more than 20,000 source lines of high level language firmware, and to bound complexity and processing loads, four servers per LnWi were chosen in the design phase, and this is adequate for most basement layouts.  A single Wifi module can support up to 32 throttles and/or locomotives amongst the four APPs/Wifi devices that can connect to it. For larger layouts up to 8 LnWi’s can be added to a LocoNet, giving a very large and flexible expansion capability.

For future support the LnWi may be firmware updated using the free DigiIPL II application and the appropriate device IPL “.dmf” file on the LnWi support page, from the Digitrax web site. To allow secured Wifi access, the LnWi provides an Option Switch setting to enable WPA2 security with a user configurable password, or a convenient fixed password.  Since the LnWi does not route or provide Internet access, hacking cannot meaningfully pass through the dedicated-protocol LocoNet servers. Security is simply to control SSID access.

Digitrax worked with Brett Hoffman (the protocol developer) and Steve Todd another APP developer from mid-June 2017 to ensure the existing Apple and Android apps would work prior to LnWi release.  During this software collaboration a number of useful things were added to the; LnWi, Hoffman protocol and the APPS, such as automatic LocoNet Server setups and mapping the existing LocoNet throttle stealing protection back into the protocol. 


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