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parameter (MCS-rate, NV2-period size) setting wireless discussion

Wed Apr 13, 2016 5:17 pm

Let discuss experiences, knowledge and theoretical settings of wireless in Mikrotik products (and general)

First we have to make a difference between PtP and PtMP.
Then frequency band
Last, but not least, protocol. NV2, nstreame or plain 802.11a/b/g/n/c

Where in PtP throughput is important against low latency in AP to multi station environment latency is more important than throughput.
Since in PtP data is just send between 2 radio's the only factor that is 'cutting' the traffic flow is the switch-over between sending and receiving. If general internet traffic usually is 80/20 to 60/40 down/up ratio this might have effect on the connection rate setting for a PtP link.

In PtMP the access point need to communicate with several stations. Not all stations will have the same signal strength in both receive as send and not all station will generate/ask same amount of data to be send.
Although throughput is always a factor of signal and quality (CCQ) of a link between AP and station, the latency is important too. This latency is heavily influenced by the time the AP spends to communicate with other stations. During this no communication with the station of interest. Thus packages are held in waiting until AP 'talks' with station of interest again.
Now my first questions on the subject are; Is the 'rate' setting on the AP best left to 'auto' or should professional operator best set rates that find highest possible MCS rates all connected stations can achieve, with one rate lower for margin, and skip the higher ones?
Would it also preferred to skip the lower ones below a level all station can reach easy under even the worst circumstances? (By skipping the lower not used, rates the radio doesn't spill energy in these low but far traveling low rate waves. Noise outside the AP's working range (which we therefore set) is limited to the minimum and is better usable for other AP's.)

Eliminating the higher rates that the AP tries to set with station but cannot always sustain makes the AP to switch connection rates all the time which in fact creates pauses in the traffic flow?
If now other station cannot even work in certain mcs rate, it is best to skip these at all and only set that rate that all stations can sustain. Would that make life easier for the AP? And thus give better overall performance (lower latency) and due the higher CCQ's also possibly a better throughput?

The 'auto' setting versus 'manual' is interesting in this respect. The Mikrotik 'auto' setting is probably set to some algorithm of the OS (or chipset?) but will be a general one that give good results in all circumstances.
But since PtP or PtMP usage are inherent different for a 'master' radio I can understand that for both situation a manual setting after some fine tuning will give better results than the general 'auto'.

I leave it with this now. Hope we can start a nice discussion without becoming too theoretical with formulas etc. Let's keep it readable...
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Rudy R. Puister

WISP operator based on MT routerboard & ROS.

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