blake at pfankuch.me
Tue Mar 13 23:45:51 CDT 2012
Thanks very much to all of the useful on and off list releases.
I would like to also thank Ron Valdez of Vall Technologies for his very prompt sales contact as well. Very unprofessional, but nice try to cover up the contact with the excuse of "simple google searches while reaching out to local IT firms" to find my contact information and directly attempt to market a product which I just recently asked about here, and conveniently he happens to be a Xirrus Gold Partner.
Summary of what I have learned, including quotes from a few people who said it better than I can reword it. "Conceptually, it sounds like a good idea to increate spectral bandwidth, but I have a hunch that it falls down somewhat in practice." Several people have mentioned that only a limited number of radios within each device (3) can do 2.4ghz at the same time (which makes sense) due to signal conflict and the specified specs which say 120 degrees of broadcast per antenna. Several people have also stated (as well as math) that a single device can only handle about 90-120 2.4ghz clients before there is noticeable slowdown. 5ghz wise experience holds up to specs as far as client connections. Having 802.11b enabled anywhere has had a very negative on performance of the device as one could expect. In buildings with many smaller rooms, using a single device to cover so many rooms runs you into the problem of interference thanks to walls, refraction and material conflicts. Scaling them back becomes tough because each device with its large number of radios saturates the spectrum, allowing limited overlap... "Xirrus is overkill [...] when doing small gigs and won't scale [to] very big events, compared to a truckload of cisco APs. Mostly because our venues are not stadium sized." "Turn up the AP count, turn down the signal strength fill the building 'til it glows."
Thanks for all the input!
From: Pete Carah [mailto:pete at altadena.net]
Sent: Tuesday, March 13, 2012 4:46 PM
To: Blake Pfankuch; NANOG Mailing List
Subject: Re: Xirrus Wireless
On 03/13/2012 03:35 PM, Blake Pfankuch wrote:
> Thanks Pete, that does help. Now hopefully I can get someone who has experience with 500+ devices running on a single one in a fairly small area (High School Gym).
There was a thread about this a couple of months back, I'm pretty sure it was after last November (but not absolutely sure); lots of discussion about density and Xirrrus was mentioned. My personal experience with Xirrus is certainly not high-density, and the "real" hospital certainly copes with a bunch (though I'm guessing 20-30 users per AP from how many APs they have distributed among rooms. They seem to do a bunch of their device telemetry on 802.11 but there are also some more dedicated frequencies/protocols for medical devices. (even the IV pumps alarm at the nurse's station...)
I do have some experience with full-duplex RF transceiver design, though, and the Xirrus configuration can't be easy to make work well.
Not impossible, but difficult.
> -----Original Message-----
> From: Pete Carah [mailto:pete at altadena.net]
> Sent: Tuesday, March 13, 2012 4:32 PM
> To: nanog at nanog.org
> Subject: Re: Xirrus Wireless
> On 03/13/2012 02:34 PM, Blake Pfankuch wrote:
>> I know this is a little outside of the traditional NANOG realm but...
>> I have a customer looking at a fair number of Xirrus Wireless Arrays for 802.11a/b/g/n implementations and am looking for some real world insight into them. On the cover they look cool, the white papers look cool, but I am yet to find technical commentary from a real person on these devices. Looking at the XN line, and just curious if anyone has deployed these, supports these or knows anything about them.
> I can only speak from indirect experience; the rehab place where my
> wife is staying for a bit uses 4 or 5 of them (older, probably not
> current, flying-saucer-like boxes suspended from the ceiling at
> junctions) and there, at least, they appear to work pretty well. The particular ones don't appear to my laptop to do 11a. However, I don't think there is any significant user density just from watching the nifty directional light display, so this may not mean much (I'd guess 3 to 10 users over the whole building including smartphones and a couple of pieces of medical equipment that isn't used much). Also there is no IT (or any real technical maint) guy on-premises to talk to so I can't ask about any other aspect.
> The local real hospital uses a Cisco system (or at least Cisco APs; don't know about the AP manager box) which really does appear to work well; I'd guess several hundred APs with lots of full-time medical gear, and a "guest" network which is behind a rather draconian firewall (wouldn't let me ssh out to a non-standard port (65k range), for example; I had to fix myself a 443 ssh port for the time we spent there a couple of months ago... Blocked 25 outgoing; I don't blame them for that, however they also blocked 465 (but allowed 587)).
> I suspect if I wanted 2.4-only I'd go with ubiquiti, but I don't have any experience with them, and their "unifi" boxes don't (yet) come in 5gig. And they don't appear to have independent APs in each box, though I don't know how well the "directional" antennas in the Xirrus actually separate things; even a 100mw transmitter may well overwhelm all the other local receivers unless there is a bunch of shielding inside the enclosure (and maybe even then...) If 802.11 was frequency-split like the cell system it would help such systems a bunch.
> -- Pete
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