Known as a Point to Point or a Wireless Bridge
Two Wireless radios are used, one as a transmitter and the other a receiver to link two destinations together. For a point to point (PtP) setup with Ubiquiti it is advised to use WDS. By using WDS you are creating a Layer-2 bridge, the equivalent of a Cat-5 cable.
WDS stands for ‘Wireless Distribution System”
Using WDS allows for OSI Layer 2 transparency.
WDS has two primary purposes:
- Layer 2 transparent bridging. Only one radio is in AP-WDS mode and all clients are Sta-WDS. No traffic is repeated, and all layer 2 traffic is visible to all devices as if they were physically wired together on the same switch. Because traffic isn’t repeated, it flows at full speed.
- Store and forward repeating. This allows for less radios to be used, and each is in AP-WDS mode. The access points are paired with each other by MAC address and forward a copy of everything they receive. Every hop reduces available throughput by half, so it’s only suggested in very rare situations.
Enabling WDS (or using AP-WDS <> Station-WDS) is always recommended when possible. Disabling WDS causes the station device to do IP > MAC lookups for every packet, which uses more CPU and may reduce performance.
The only reason to not use WDS in a bridged PTP link is if you have another vendor’s radio on one side of the link and WDS is not compatible.
Predominately Point to Point is used with 5.8GHz Radios to help eliminate interference issues using the standard 2.4GHz signal.
You need a good Line of Site (LOS) and a clear fresnel zone to get a perfect link between the two sites.
- 5.8GHz has a narrower Fresnel zone than 2.4GHz but needs perfect line of site without vegetation or trees
- 2.4GHz as mentioned is the standard wireless signal used by most wifi devices and therefore the choice for routers set as AP’s that connect to user devices, repeating and situations where line of site (LOS) is not perfect for 5.8GHz
- 900 MHz is used rarely but is less reliant on LOS so some situations are perfect for it, especially where there is vegetation and tree’s
EXAMPLES OF THESE TYPE OF SETUPS AT BOTTOM OF PAGE
Example Firmware Image
AP WDS Settings (nanoM2 5.5 firmware)
STATION WDS Settings
Set one router to AP-WDS and other to STATION-WDS
- Enter same SSID in both
- Disable auto ack and set the distance to 10% above actual
- Set both with same channel. Scan and pick a clean channel by clicking on TOOL’s (top right) and site survey, or by using Airview
- Set both to 20MHz
- Put WPA2-AES encryption on both
If you want to share the same Ubiquiti ‘M’ series WDS access point with both Ubiquiti and non-Ubiquiti radios, you must use 20MHz channel width. (This is true of any ‘M’ series access point). If you use 40MHz channel width, only another Ubiquiti radio will be able to connect in nearly all cases.
300 metres through a gap in the trees (7 metres across) using 5.8GHz
On this 5.8GHz example point to point -46 dBm was advised to be alittle bit too strong.
You should aim to make the signal strength no greater than -50 (-40 or -30 is greater/stronger). To do this you can do three things within the airOS firmware
- Back off your power at both ends
- Change the alignment of the radios alittle
- Change to use a wider Channel width, 10 MHz or 20 MHz.
Too hot a signal can effect MCS rates, latency, and transfer speed… and if it’s REALLY hot, potentially cause hardware problems down the line. Over time (months) an RX level better than -50 has been said to cause receiver desensitization.
Turning down the power in this example made things worse.. however switched to a 20mhz ch. width got the right result (below)
When signal was -46 dBm (stronger) the TX/RX (Transmitted/Received) was only 32.5Mbps on both.
After changing to 20mhz channel the signal dropped to -51 dBm, TX/RX improved to the maximum of 130Mbps and Airmax Qual/Cap both improved.
Overall a perfect link was achieved using two NanostationM5 (5.8MHz routers).
If you have a setup like this you would be advised to make sure the gap is keep clear and leaves do not grow over the hole. Water on leaves causes signal issues that can result in issues.
2.4Ghz and 900MHz could of been used also in this situation as it is less effected by the tree’s.
Sending internet from one building to a second building about 170 metres apart, then plugging in to a wireless router.
Two NanoStation M5’s where used to bridge two buildings and then an AirRouter (Standard AP) inside the second building to provide both Wifi and Wired Access inside the building.
There was good LOS between the buildings and distance was not an issue.
NSM5 AP-WDS Bridge ~> NSM5 ST-WDS Bridge -> AirRouter
With only 170 metres, NanoLoco’s would of been fine also.
~ > Wireless Link
– > Wired Link (Cable)
TREES IN THE WAY
Up to 800ft with trees in fresnel in most cases will be fine
With a few trees to consider, your odds of 2.4 Ghz working are much better than 5 Ghz. The denser the radio wave, the higher incidence of collision it encounters as it passes through objects, resulting in more attenuation and less signal for any given obstruction.
IS LINE OF SITE NEEDED FOR A POINT TO POINT?
Setups can have obstacles in the way and still provide a link between the radios, speed is the only thing that is effected and sometimes this is fine for the setup requirements.
2 NanostationM2’s with tree’s in the middle, 800ft can be fine.
An example had 600m (2000ft) links going through the guts of some thick trees using Nanostation M2’s. Signal was poor at -85 and only achieves about 1-1.5mbit throughput but it was reliable through all weather conditions… client says it’s a night and day difference over their previous high latency satellite ‘broadband’.
Also 1.2km link with Nanostation M2’s, one end completely obscured by trees, -75 signal
M5’s aren’t so forgiving of trees but again over that distance and with only fresnel zone obstacles they’ll work fine. It is advised going with the 5ghz to avoid every Tom, **** and Harry’s home wifi on 2.4.
- Loco M5’s are great from 50 feet up to a quarter mile (400 m).
- Turn the power down as necessary and configure them for a WDS (l2 transparent bridge).
Q1. Wireless signal levels received for each polarity should be the closest possible ?
A. They usually are about the same. If more than 3 dB difference, you have a bad radio or something unusual in the line of sight path.
Q2. The ideal signal level is between -55 and -65 ?
A. -50 to -70 is a good target, but…see Q3.
Q3. Is the ideal signal level affected by the noise floor ?
A. -70 is good if the RF landscape noise is around -95; but if the noise is at -70 to begin with, then a -50 signal should be considered.
Q4. If I have a very short link, less then 50m (across a street) the lowest signal level I can get is around -35. It is ok ? If not, what can I do ?
A. Degradation begins around -50. -45 is tolerable. -40 and you’ll see performance problems.