On Fri, 18 May 2018 10:37:42 -0700 (PDT), "
wrote:
On Friday, May 18, 2018 at 12:39:57 PM UTC-4, Jeff Liebermann wrote:
It was plugged into a high outlet just under the ceiling and line-of-sight,
perhaps 30 feet from the node.
Altitude will help the signal clear all the ground level obstructions,
such as furniture and people. However, altitude tends to offer a
clear shot at windows, through which much interference from other
services on the same shared frequency band might enter the building.
You might consider moving the repeaters away from any windows with a
view of the city.
The basic problem is that the repeater will be a problem if there are
two paths between the source and destination of a packet. For
example, if the source and designation of a packet can both see each
other, as well as both see a repeater, then two identical packets will
arrive for every packet sent. One direct from the source to the
destination, and one from the source, to the repeater, and to the
destination, after a delay. The delay comes from most Wi-Fi device
being simplex and not full duplex. Simplex is when a device can only
transmit *OR* receive, but not both at the same time. Most Wi-Fi
devices are like that, including the repeater. If the repeater has to
store and forward a packet, there will be a 1 packet length delay
(which varies by packet size) switching from receive to transmit.
You can block the direct path between the source and destination by
making the path go around a corner. The corner obstruction blocks the
direct path. Since both the source and destination can both see the
repeater, the repeated path is not blocked and functional without self
interference. Unfortunately, that doesn't do much when the source is
a portable device, laptop, or smartphone, that can easily be moved
into a situation where there are 2 paths between endpoints.
It appears that you may have missed my first posting up-thread, where
I covered some of the problems with repeaters, mesh networks, and
self-interference. Should I repost it or email it to you?
Keep in mind that this is a hospital basement
built in the 1930s before any sort of computing of any nature. The
footprint is an entire city block.
I don't understand what that has to do with the initial connection
problem for a device.
We are thinking that the main router has some means of blocking
these things out. Is that possible? The nodes are all hard-wired.
Sure. You can filter by MAC address. All, and I do mean *ALL*, Wi-Fi
networking is done on Layer 2, the MAC address layer. The MAC
addresses of the source and destination of every packet are exposed
and not encrypted. There should be a MAC address filter in the router
that lets you block any Wi-Fi device by MAC address. Some of the less
disgusting wireless bridges and repeater also have MAC address
filters. However, I don't see what that buys you for eliminating what
I consider to be a designed in source of interference.
If the "nodes", which I presume means access points, are all wired to
a central router, then the system should have worked as expected,
although apparently with a few dead spots. Remove ALL the repeaters,
add some more hard wired access points in these dead spots, and it
should work.
If ripping out the repeaters doesn't improve the initial connections,
then something else is wrong. I've had to drag an SA (spectrum
analyzer) to the problem location to see what's happening. I've found
noise sources, non Wi-Fi devices, frequency hoppers, powerful inband
carriers, high power cordless phones, and such, none of which show up
on computing based Wi-Fi analyzers. The closest approximations that
might substitutes for a spectrum analyzer are either an SA dongle:
https://www.metageek.com/products/wi-spy/
or an AP (access point) with a built in spectrum analyzer such as the
various Ubiquiti products running Airview:
https://www.youtube.com/watch?v=NAuaSdzHwoo
https://dl.ubnt.com/datasheets/airmax/UBNT_DS_airView.pdf
https://help.ubnt.com/hc/en-us/articles/204950584-airMAX-How-to-Use-airView-to-Find-the-Best-Channel
or various low end portable SA's.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558