Odd Wireless Latency Issues

RouterOS Wireless Networking
1

Hi,

I have a 14.5km 5.x GHz link with perfect LoS. I can see the two sides on a clear day.

I am running a RB333 on one side, RouterOS v3.9 (was v3.3 upgraded in case problem was version specific) and a RB532 on the other side, RouterOS v3.9 (was v3.3 upgraded in case problem was version specific) Both sides have RB52H and 31dBi Grid antennas.

Signal strengths are similar (within 1-2dBm) in both directions and are at between -62 and -79 depending on the frequency used (5180-5825) and TX-Power. Ack Timeout is 121us to 252us depending on frequency used. Signal to Noise Ratio is 39dBm to 26dBm depending on frequency and TX-Power.

TX Power is set to ‘Default’, but has been tested at 15dBm and up.

My problem is this. My latency on that particular link is 1-3ms. As soon as any traffic occurs on the link (128kbps for instance) the latency goes above 2000ms and I have grumpy clients on the network and on the phone. :frowning:

I have changed frequencies (tried every channel allowable for ‘South Africa’ country code and even tested the ‘United States’ ones above 5700), tx-power (15-24dBm), antenna polarity (was horizontal, now vertical), software versions(3.3 changed to 3.9).

The only changes made to the system from when it was working, to now, is that the RB532 has a couple of EoIP tunnels and bridges configured. I also disabled all the interfaces not required for the test to see if it was perhaps a problem involving the tunnels and bridges. It made no difference.

The only thing I can think is that one or both sides has a lot more wireless inteference over a broad spectrum since we originally installed the site. The one site is pretty crowded, but I do not have this issue at any of my other crowded sites. However the fairly high SNR shows that the noise isn’t bad. The noise floor at some frequencies is sitting at -108dBm.

Has anyone got any ideas, as I am about to go postal with an axe on antenna and ethernet cables (my own, not anyone elses). :laughing:

WispZA

2

Do the math and figure out what the correct Ack Timeout for your distance is, then set it to that number and keep it static.

Turn on nstream w/ polling and exact size of 4000.
Also, try ANI on/off.

If none of that helps, you likely have a hardware problem. Your noise floor is too low to be realistic.
Replace your radios and check your power supply.

3
  1. Why would you poll on a point to point link?
  2. If the link is flaky why would use use a fixed size of 4000?
  3. If Nstream is enable you don’t use ACK.
  4. That noise floor could very well be realistic.

Now lets look at a fix.

  1. Enable Nstream, disable polling, disable CSMA, framer policy best fit, limit 3200. You only need to set the details on the AP side.
  2. Use HPOL antennas
  3. Leave the power settings at default - you may have already damaged the radios.

You need to get the signal in the -64 to -72 range. Use 10mhz channels if needed to accomplish this.