How do you get a solid connection?

RouterOS General
1

I have been using the Mikrotik equipment for almost a year now and started deploying a town wide connection. For Internet broadband server it works very well.

So my next step was to run Voice Over IP (VOIP) on the wireless service.

I have two mikrotik units. One on my office with a 802.11b for users, and 802.11a link to the other mikrotik unit on the cell tower.

When I run VOIP to the 802.11b to the unit on the office roof I can use voip with no problem. When I connect via 802.11b to the cell tower unit I can not because of latency.

Testing through the unit from a computer at the clients location it will usually start at 7ms. It will hit at 7ms for 20 times or so then creep up very quickly to about 30ms, then reset to 7ms. This is when voip crackels happen and customers complain.

I have tested from client to the mikrotik 802.11b card and I can see the small spikes. I can also test from mikrotik to mikrotik and also see a small splike. And when they combine they get up to 30ms. Which is where the problem lies.

Ok, for antani’s I am using 15.4db omni’s on the 802.11b Prisim. On the 802.11a I am using a 11db omni on the cell tower and the direction 28db dish (thats listed here on mikrotiks website).

I have also used the 28db dishes on both sides, also tried using flat panel antani’s on both sides as well.

on the 802.11a side of things there shows to be no one else using this frequency. Though 802.11b shows about 12 other access points across the town (most in office and home users, low signal strenths detected).

Thanks for your help and suggestions.

2

HI,
What is the configuration that you use? Routing or Bridging?

Regards
Xandor

3

I am routing.

I have a /23 on ethernet which goes to a /25 athlos link. The prisim has a /25 as well.

On the other end at the cell tower the athlos is on the same /25 as above, the prisim has it’s own /25. The ethernet of this unit just has a 192 public address on it since there is nothing atached to it.

Here is a simple ping:

time=13 ms
time=10 ms
time=12 ms
time=13 ms
time=9 ms
time=9 ms
time=9 ms
time=13 ms
time=10 ms
time=11 ms
time=11 ms
time=10 ms
time=9 ms
time=9 ms
time=9 ms
time=18 ms
time=10 ms
time=10 ms
time=21 ms
time=9 ms

Now, I am not unhappy with the pings, but i’d like to see them all the same or close. this is a 1 mile link. This ping is between the cell tower and office link, and I just turned netstream on (which made no difference in the ping).

The issue here is that clients that are on the prisim have a simular ping to the mikrotik unit and then once I say ping from client to our servers the ms compounds on both links and can get up to 40-60 spikes.

4

Followup:

I have truned on Netstream, set the framer policy to exact, and nailed the 802.11a link at 6Meg.

And I get pings of 13ms and 14ms consistant without any spikes.
On the AP i have ack of 25, overall tx ccq: 12.

On the other size the signal strenth is tx/rx: -74/-71. The tx/rc cqq jumps around anytinghing form 2/2 to 7/2, 5/4.

I have scanned the area for anyting int he 802.a band and It seems I am the have the only signal at all in this area.

5

I also had very inconsistent ping times, ranging from 40ms, to 4ms, and back up to 40ms, over and over again. I discovered that it was my Atheros card changing data rates on-the-fly that was causing the problem. I tried locking my links to 6Mbps, which helped alot, but I cannot get the devices to stop dropping down to 1Mbps sometimes, even with clear airspace and strong signals. What is even worse, is that I have to lock my AP at 6Mbps, so I cannot service any 2Mbps customers. Of course, I can lock each Routerboard CPE to only one data rate, depending on location and signal, but that would be a huge hassle, and would still only affect the CPE’s upstream, with the downstream still remaining a problem. The units should have better behaved auto-data-rate selection, and I understand that older 2.8.x versions of the RouterOS actually did behave better…

Hitek

6

Well I lost yet another voip customer today. This one is about 80 feet away across the street.

I have tried the linksys wet-11, a microsoft access point, then to the linksys gs routers (reflashed to linux). All three access points seem to do just fine but the pings jump around.

It goes 6ms then 12ms, 19ms, 19ms then back to 6ms. Sometimes on the second 19ms it times out.

They are connected to a prisim card and I updated the prisim card drivers before instaling on the roof.

Theres six access points connected to this prisim card.

No idea what to try next…

7

Did you try locking all of the data rates, on every radio being used, both 11a and 11b?

8

Varying ping times are generally b/c of interference. Only way to figure this out is with a spectrum analyzer. Scanning for other 802.11 networks won’t tell you the half of it, with Trango, Canopy, RedLine, AB, AV Senders, cordless phones, etc. polluting the airwaves.

We use a VoIP phone at home on the end of a two-hop Mikrotik link in a dense urban area. Quality for listeners is perfect on the far end, absolute rubbish on our end. :frowning: Likely has to do with the fact that the far end (where it terminates to PSTN) has the benefit of a jitter buffer, and our end doesn’t. (The phone we use is a cheap ZyXel WiFi connected to a D-Link AP in the flat, so there are really three wireless links involved) I guess if I switch to using a proper VoIP gateway at home and a stationary VoIP phone I could solve this problem.

As for the pings, since that’s your issue, on my link they look like this: 2,2,2,2,2,57,2,2,91,18,2,2,2,2,2,48,2,2,2,2,4,2,2,2,2,32,49,2,66,2,76,2,44,2,2,2,3,2,2,3,21,8,4,4,2,2,2,2 and so on. Average over 10,000 pings will give you 10ms, with low of 2ms and high of 90ms.

The reason for these times, I am convinced, is b/c 5GHz in the neighborhood is shared with all the devices I listed above, plus some I don’t even know about. And I think it’s a fact of life that you will have varying ping times in public spectrum. Overcoming them w/ jitter buffer is likely the only way to make VoIP work nicely.

9

If I set my “Data Rates” configuration to “Default” on a tower unit and on the client MT, my ping rates vary greatly every time. If I lock the data rates down in the “Data Rates” configuration by selecting “Configured”, then the ping times immediately fall straight into line…

“Data Rates” set to “Default”:
23 ms
4 ms
21 ms
4 ms
24 ms
4 ms

“Data Rates” set to “Configured” and locked to 6Mbps:
4 ms
4 ms
4 ms
4 ms
4 ms
4 ms

Maybe it’s interference causing it, but I cannot fix outside interference, while I can lock the data rates(even though the OS or radio should transparently handle this)…

Hitek

10

That’s very interesting.
I noticed differences between “default” and “configured” in various scenarios.

MT people, what is the difference?
I was guessing that “default” just leaves the card to do it’s own thing without intervention, in “configured”, routerOS is setting up some registers.
Would like to hear more on this -

Regards

11

correct, you can watch connection data rate jumping all around with default setting while it is solid with configured.

There is no rocket science about this :slight_smile:

12

The behaviour is definitely because of the frequent changing of data rates… Way too frequent… So frequent that they interfere with the quality of service…

I’ve read in past threads on this forum that some of the older version 2.8 wireless packages were much more reasonable about the frequency of data rate changes, and did not exhibit these problems. I would very much like to be able to add higher data rates(for subscribers with higher signal levels) to the AP’s configuration without watching the current data-rate and ping times bounce all over the place on the clients that can’t lock the higher rates…

13

Last time I tried to force a couple of links down to 6Mb, I saw a reduction in signal strength (both links different freqs, similar hardware). As much as 5dB of loss. Both of these links where constantly bouncing around between 54 and 48, but had about -65dB signals. These were with AR5212 cards. Anyone else see this happen?

14

I’ve seen slight changes in signal level changing from “configured” to “default” for the same air-side data rate… not more than 1dB though

Regards