well we had to ask...

Didn't we!


Insatiably curious souls that we are, we just had to ask.

Di,

I was just checking my email and noted that I had nothing since last week

from NMRANET NMRANETWG on Yahoo, so I checked, it seems to have disappeared...

Something happened?

at 7:57pm EST today, and the reply:

The sites have been closed.

Didrik

I have corrected my group naming error in the text above, what I crossed out is exactly what I sent to Didrik Voss.

So what do we make of this? Is Didrik basically saying that NMRAnet is dead in his mind? I mean if the working group nos no group to work in what are we supposed to do? Or is he telling us not so subtly that we can all go play in our own sandbox because he has taken control of the NMRAnet sandbox for himself? Or is he merely trying to remove the evidence? Just as well a few full mailboxes of those groups exist around the place then isn't it! At least we haven't lots years of work. Despite the fact that all of the files in those groups are gone now.

Vale NMRAnet

As of today, April 11, 2011 (and no this is not a late April fools piece) the two currently active NMRAnet discussion group on Yahoo Groups have disappeared! No notice to any of the members. Not even a word to the moderators. One of the moderators went to check why there was no email coming from the list, and guess what he found.

It's actually just a continuation of what has been a pretty torrid history for groups talking about NMRA. Back in mid-2005 David Harris established a group called MRR-LCB - to discuss layout control bus ideas! That group remained active, albeit sometimes sporadically, until mid-2010. Some discussion was entered into on the old NMRA DCC working group, but after the Detroit convention in 2007 a group known as NMRANET-WG-TECH was formed and operated from September 2007 until June 2010 - just before the NMRA convention in Milwaukee in July. Out of a discussion at Milwaukee with two gentlemen who agreed to try and moderate the discussion a new list, NMRANET was established about July 28th 2010 and continued in use until April 6th 2011.

NMRANET-WG-TECH was still alive on Yahoo today as was NMRANET but another group which had a transient life for a few weeks back in the first half of 2010, NMRANET-Applications, and NMRANETWG have now disappeared altogether.

Seems that our friend, one of the VossBros, has been trying to destroy the evidence out there! Or maybe he has decided that only the brothers can agree on what THEY actually want, and so they will handle it all themselves now? Who knows?

Not us! We are just the working group members, interested model railroaders and the interested manufacturers, we obviously don't matter.

Why? He asked...

Would Don want to change the heavily discussed and argued OpenLCB physical layer standard (already voted and accepted within the OpenLCB community) and modify it?

Several of my colleagues at work and elsewhere have been heavily involved with CAN bus for some little time now. So over the last few days a couple of us have used our break time to kick around some ideas in an attempt to figure out why Don was so insistent that these changes be included. All of the comments that I recall related to increasing the number of nodes allowable on a given length network.

Three factors influence the length of the network.

• The round trip propagation delay between the two most remote nodes.
• Voltage changes due to the intrinsic resistance of the cable and the Rdiff of the individual receivers
• Waveform distortion or signal level attenuation due to the effective distributed capacitance of the transmission line.

Cable: The specification as we established it calls for the use of CAT 5e cable, which according to the ISO11801 standard should have nominally 5.7ns/m delay. But this is purely for the cable, it does not include connectors, PCB's with their own intrinsic capacitance and the effects of any common mode chokes or ESD protection devices. Prudent manufacturers may choose to include common mode chokes, ESD clamping diodes or varistors for protection. All of these add capacitance which will increase Vp and reduce the maximum cable length as well as add waveform distortion as alluded to above.

Resistance: We are assuming, that despite their being no explanation of the derivation of the constant in the numerator of the equation, that the VossBros equation assumes a 90 ohm/kilometre resistance. And thats fine, but our concern here is that not only does the VossBros change actually not specify what Ri is, nor does it spell out how that constant was derived. That equation does not appear to take into account any parasitic or stray capacitance introduced by PCBs, connectors, ESD protection or whatever.

Waveforms: Anybody who knows anything about transmission lines knows that rise and fall times are a function of bandwidth. Compromising bandwidth with capacitance means that to get the performance we have to reduce capacitance, which means reducing cable length. If you are to allow users to calculate the maximum network length, or max number of nodes for a given length, then capacitive effects must be taken into account, but in the VossBros documents they are not.

The OpenLCB standard offered to the NMRA (but butchered by VossBros) specified the important maxima, length and number of nodes. Why was that so hard to understand? I have one possible hypothesis. At one point the concept of gateways and bridges was discussed with the S9.5/Voss group. It seems that in their own opinion bridges don't play well with their protocol. Of course we can't offer much more of an opinion because no details of their protocol have ever been published. But that could explain the obsession with maximising the number of nodes. So an S9.5/Voss based LCB could be limited to the 111 or 112 or whatever number of nodes. OpenLCB/S9.6 on the other hand can use bridges and gateways to create much larger LCB's.