Thomas, are there any distance-limiting timing concerns using plain a/g
equipment for an outdoor link?
Norm
----- Original Message -----
From: "Thomas Giger TGC" <thomas.giger@tgc.de>
To: "'Karlnet Mailing List'" <karlnet@WISPNotes.com>
Sent: Friday, October 24, 2003 5:24 PM
Subject: RE: [KarlNet] 802.11a and SE-4505
> > I am afraid I must fall on my sword, so to speak, in this case. It
> > appears that bob is 100 percent correct about the compatibility issue.
> > I slap myself for not realizing that for a radio push 5 GHZ
> > it needs the extra voltage.
>
> Not only that. CardBus is the 32-bit successor of 16-bit PCMCIA. That is,
> these a and g cards use it for performance reasons. Same as with the
> transition from 10 Mbps (16-bit) ISA cards to 100 Mbps (32-bit) PCI cards
> ...
>
> > I am still trying to get my backbone shots off of b as
> > the noise floor around my neck of the woods is incredible, something
> > around -75 dbm!! I have yet to decide if this is directly
> > related to my own amount of presence in the area, or other 2.4GHZ
> equipment
>
> Maybe that the US has much more 2.4 GHz usage than Germany, but whenever
we
> have noise that high, it's usually one of two things:
>
> a) our own use of the spectrum: this is sometimes from near/same-channels
we
> use a few kilometers(!) away. It all depends on antenna gain, direction
and
> the amount of traffic - you will see a pattern that correlates to peaks in
> traffic in other segments (even if it is from competitors).
>
> b) TV/VCR equipment: Lately, we have had instances of someone using such
> stuff inhouse exactly in the focus of a narrow beam antenna or very close
to
> the CPE antenna. The pattern is usually: noise appears in the evening and
> disappears later in the night (except if they never turn it off again),
but
> it's never correlated to traffic peaks.
>
> To free 2.4 frequencies and to boost the backbone, which is typically made
> from PTP links, "normal" 802.11a/g equipment is usually much better than a
> polling (Karlnet, Proxim) solution because RTT is a stable 2-4 ms and
> performance is better. There is really no need to run TC on PTP links
> (except because the old Orinoco implemented bridging this way). Modern WDS
> featured bridges will do better if you stick to PTP.
>
> While this sounds like "just pick any 11a AP with WDS-bridging", we've
found
> that there are only a few devices which support something close enough to
> "management". The tendency being "hide signal/noise readings and the
> customer will be happy", there is only one device I've seen which has a
> "wireless link test" feature with signal, noise and SNR
readings/measurement
> like the Orinoco / Karlnet devices, combined with SNMP, WEB and TELNET
> configuration, PoE, etc.: The LANCOM L54ag from Germany. There may be
others
> in the US and it's not my intention to have you buy from Germany ;-)
> although this unit would support US regulatory requirements for 802.11a/g
as
> well and it supports 802.11h for the 5.475-5.725 GHz range which is being
> considered by the FCC (for 11 more channels).
>
> We have done measurements: 802.11a throughput is 24-28 Mbps on the LANCOM
> L54ag if you manage to keep an RSL better than -66 dBm and a SNR better
than
> 20 dB. With that many channels to choose from, you can even run Atheros
108
> Mbps mode and get 48 Mbps net throughput (also measured) but you need to
> have somewhat better SNR for 108 Mbps mode.
>
> Just in case some readers forgot what I said upfront: This is only for PTP
> links; doing PMP with the LANCOM will give you hidden node problems ...
that
> is still the domain of Karlnet, if Karlnet doesn't miss out while Proxim
is
> already shipping its MP.11a which uses the WORP polling mode on 5.x GHz
...
>
> --
> true global communications GmbH
> Thomas Giger
> In der Au 27, 61440 Oberursel, Germany
> fon +49.6171.6381-0, fax +49.6171.6381-19
> www.tgnet.de || www.megaspeed-internet.de
>
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