- Range Extender - 2 Updates
| "pfjw@aol.com" <peterwieck33@gmail.com>: May 18 10:37AM -0700 On Friday, May 18, 2018 at 12:39:57 PM UTC-4, Jeff Liebermann wrote: > as much air-gap isolation from the lines as possible. That leaves > wireless, FSO (free space optics), and fiberoptics as the available > options. It was plugged into a high outlet just under the ceiling and line-of-sight, perhaps 30 feet from the node. 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. We are thinking that the main router has some means of blocking these things out. Is that possible? The nodes are all hard-wired. |
| Jeff Liebermann <jeffl@cruzio.com>: May 19 12:10AM -0700 On Fri, 18 May 2018 10:37:42 -0700 (PDT), "pfjw@aol.com" >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 jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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