Re: Dedicated Z-wave sites?

[nobody@xxxxxxxxxxxx (Dave Houston)]

"Dean Roddey" <droddey@xxxxxxxxxxxxxxxx> wrote:

>I think that the thing limiting Z-Wave is their choice for a very low speed
>network. It's going to be hard to achieve ubiquity when your system cannot
>ever be used to even transmit media metadata, much less media data. No
>powerline technology really could even be used for either of those things
>either I don't think. Zigbee seems to be the only one that could really have
>a chance at being a fairly ubiquitious wireless control technology that
>could move up out of the trivial amounts of data involved in turning some
>lights on and off.  It could not transmit media data, but it could transmit
>metadata and some other small stuff.

Dean,

I think there are other limitations.

As you have confirmed, getting timely ACKs from even a small Z-Wave
installation is problematic. The reason is explained in a Brian Dye post. He
got a Z-Wave engineer to answer some of the technical questions that I
raised.

http://groups.google.com/group/comp.home.automation/browse_frm/thread/b2586f0bd46213e1/e73f53b9a87d750b?lnk=st&q=&rnum=8&hl=en#e73f53b9a87d750b

"The Z-Wave Protocol supports 4 hops, so in a best case scenario it would
take some 250ms for the command to get there and a further 250ms for the
confirmation to get back. The actual time taken will depend on whether any
back-offs and retransmission were necessary along the way due to
collisions/lost frames (from other Z-Wave communication, or from other RF
noise or interference)."

The poor RF range plus the 4 hop limit means networks must be relatively
concentrated. And in a less than best case scenarion, the 1/2 second
round-trip time will be much longer.

Another problem is all Z-WAve devices are RF repeaters. Switches installed
in metal boxes are going to have limited range compared to the already low
range caused by the FCC 1mW limit on output power. Brian Dye also made note
of this.

http://groups.google.com/group/comp.home.automation/browse_frm/thread/b6af14c74920c47/71b1c727fc59d88b?lnk=st&q=&rnum=2&hl=en#71b1c727fc59d88b

"Metal boxes can be a real pain when working with Zwave."

People who do not understand how the mesh network and routing tables work
(or who are deliberately trying to confuse the issue) might propose adding
high power repeaters. They would violate FCC power limits and would totally
screw the network.

And people unfamiliar with Z-Wave (or who are deliberately trying to confuse
the issue) might see the limited range as a plus, arguing that it prevents
interference from neighbors. But, the fact is, Z-Wave already protects
against unintentional cross-talk by encrypting transmissions so that
neighboring systems cannot casually interfere (intentional interference is
another matter).

There is one thing that still mystifies me. You have said that a user of
your software reported very long range outdoors. Brian Dye has also reported
similar free air range. The thread that I cited from someone in the UK using
modules purchased in the US reported 30-40 feet _OUTDOORS_. I wonder whether
early modules sold here may have been quickly modified European designs
putting out 25mW as is allowed in Europe?

On the plus side (for you), many of the new Z-Wave products are little more
than glorified remote extenders, like those that have been around for years,
but they are HT and media oriented.

http://davehouston.net
http://tech.groups.yahoo.com/group/roZetta/
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