Broadcast messages on a C-Bus network

Discussion in 'General Discussion' started by dray, May 31, 2009.

  1. dray

    dray

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    Hi All,

    (Please excuse any incorrect terminology and bizarre assumptions. I have only ever seen C-Bus gear in a display home and am trying to plan my automated home based on what I can glean from web research and forum questions)

    I've read that certain devices broadcast information onto the C-Bus network - for example, the general input is able to broadcast information from an attached sensor onto the C-Bus network.

    Can someone explain if this is really a broadcast message, analogous to sending out a packet to a network broadcast or multicast address in an IP networking, or whether it needs to send this information to a specific device? I'm trying to understand how this works relating the terms and concepts back to IP networking.

    This question came about while researching how the C-Bus enabled homesafe alarm panel worked. It seems to 'broadcast' up to 16 configurable events onto the C-Bus network, but it does so by sending commands to a particular address group. I was hoping you could put a PAC on the network and have it monitor for something like 'zone 1 unsealed' and then based on the time of day do something exciting with a light... I suspect that you could probably make the homesafe panel send a bogus on/off/ramp whatever command to the PAC and have the logic engine do something based on the received event though...

    Cheers,
    Dray.
     
    dray, May 31, 2009
    #1
  2. dray

    ashleigh Moderator

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    Broadcasts really are broadcasts.

    Message are transmitted to an "Application Address" and anything subscribing to that application gets the message - to then further examine and process as it sees fit.

    This is analogous to an IP multicast, but with a significant difference: the messages in cbus ARE ACKNOWLEDGED even though broadcast. This is a rather difficult thing to do - but it is done, thus broadcasts in C-Bus are reliable (retransmitted in the event of a failure, etc) unlike other systems where multicasts are unable to be treated as a reliable transport mechanism.

    Things like the groups you see mentioned are to allow another dimension of segregation - once you have sent your message you need a method of allowing several such things to happen, and differentiating between them.

    You idea of having an alarm panel send events, and pick them up with a logic engine is exactly what you are allowed to do with all this neat stuff.
     
    ashleigh, May 31, 2009
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