1)LocoNet bus
A standardized communication link that is used for communication between different electronic modules that together form a train control system. Used by e.g. Uhlenbrock (I think they developed the standard, but I'm not sure).
2)multiprotocol
Using different ways to communicate over the same physical link. For example using both Märklin/Motorola and DCC for signalling on the track, or sending both TCP/IP and NetBios over the same Ethernet line. A very wide term, as you see.
3)Digitrax
A company making digital control equipment for model railroads.
4)feedback module
A module that takes signals from sensors on the track (e.g. from contact tracks, reed switches or IR detectors), and sends them back into the train control system. The Märklin s88 is an example of a feedback module.

LocoNet is defined by Digitrax, and published as a standard, initially encouraging hobbyists and manufacturers to follow. Hobbyists may freely download the standard, and build for example computer programs sending and receiving info from and to throttles and other equipment connectted to this bus. Uhlenbrock uses this standard in all digital equipment since the Intellibox.

The bus itself is made by six-wire cable with phone-connectors, in any configuration. Throttles and the like may be placed anywhere, and also, when running, you may disconnect the throttle, move it to another connection, and continue running. I've collected info about LocoNet units in english and swedish at

http://home8.swipnet.se/~w-85672/emj_d.htm

Digitrax is one of the bigger digital firms in US I think. Among others they do throttles with IR-communication, radio, etc, with lots of functions on small area.

Uhlenbrock have feedback detectors that work as the s88, but report on LocoNet, they have Lissy that identifies locos, etc by IR, and through Switch Control buttons at a switch board may transmit events on the LocoNet. Such events may either transmit commands directly, or so called sensor events on the LocoNet. Such sensor events may be picked up on any unit, and used for any purpose. Examples are trigger a route setting by IB-switch, of sending info to a computer, or telling SwitchControl to turn on a indicator lamp on the switch board.

As you may understand, the LocoNet gives you many combinations that wasn't foreseen from the beginning, as opposed to the Central Station, which is a monolithic thing; it works as designed, but cannot be extended (except, after an upgrade of the software).

/Lars

LocoNet is a proprietary networking solution.
According to Digitrax it is a slowed down Ethernet.
Slowed down in order to prevent capacitance problems from ocurring in an extended length network with relatively cheap wiring components.
The network can be T-branched, linear or star shaped, any "topology"
is possible, mixed and matched.

To get full insight into the protocol, an NDA (=Non Disclosure Agreement) has to be signed by co-developpers.

Complying devices are awarded with the Digitrax LocoNet conformance
seal.

The main difference between LocoNet and other networking systems is its "event driven", "peer-to-peer" vs. "polled", "master-slave" nature.

In a LocoNet, all devices are created equal as communication partners, "peers", differing only in their respective capabilities and their relative prioritization. All devices can transmit and receive data on their own.

In a "polled" network, a master, mostly located in the command station
is asking/"polling" all peripheral devices in a rapid inalterable sequence for any changes that might or might not have occurred since the last poll.

In order to obtain a fast response rate in a polled network, the polls have to be performed at a very high speed, thus generating
the problems mentioned above.

Remember: The Lenz XpressNet initially allowed only for linear
component hook up at a moderate total network cable length and still requires a separate feedback bus.

Lenz found out, however, that their initial estimations were too conservative.

Digitrax is touting that LocoNet devices are acting like a normal piece of wire when confronted to new commands that they were not designed to "understand" and to process.
Hence the saying that LocoNet devices do not need to be updated.
This is in the commercial interest of Digitrax, as they want to sell
new equipment replacing older one.

As we all know from Uhlenbrock/Modeltreno, updatable IB`s have a long
and consumer friendly tradition to accommodate new and interesting features.

AFAIK, CAN-bus systems like the ones produced by ZIMO and the new Märklin systems "CS" are of the newer event driven/peer-to-peer type but not LocoNet compatible, except for the physical plugs and cables.

Regards,
Manfred