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DanielJB
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Posts: 82
Joined: Mon May 27, 2013 3:05 pm

cAP CAKE latency challenge

Mon Oct 10, 2022 4:20 pm

Are you up for the challenge?

On a cAP ac, netinstalled to RouterOS 7.5 then put into cAP mode (local forwarding, datapath.vlan-id=10), I have these adjustments:
/interface bridge settings
set use-ip-firewall=yes use-ip-firewall-for-vlan=yes

/ip firewall mangle
add action=set-priority chain=forward new-priority=from-dscp-high-3-bits out-bridge-port=all-wireless
add action=mark-packet chain=prerouting in-bridge-port=all-wireless new-packet-mark=upload
add action=mark-packet chain=postrouting new-packet-mark=download out-bridge-port=all-wireless

/queue type
add cake-diffserv=diffserv4 cake-flowmode=dual-srchost cake-memlimit=16.0MiB kind=cake name=upload-parent
add cake-diffserv=diffserv4 cake-flowmode=dual-dsthost cake-memlimit=16.0MiB kind=cake name=download-parent

/queue tree
add max-limit=40M name=upload-parent packet-mark=upload parent=global queue=upload-parent
add max-limit=60M name=download-parent packet-mark=download parent=global queue=download-parent

Without queues enabled, with laptop next to the cAP, I get ~100Mb/s (20MHz channels) [1]. With queues enabled, I get 37Mb/s download and 23Mb/s upload; this shows queue building is occurring in the tree rather than the AP or laptop WiFi MAC layer as expected.

The 95th percentile latency however is 107ms and 117ms respectively [2], not as well-controlled as expected for lower link utilisation; less importantly, the cAP single-core processor usage get to around 30%.

Bucket-size 1.0 doesn't help. Can anyone spot what I'm overlooking here to get better latency control with CAKE?

Thanks,
Dan

[1] https://www.waveform.com/tools/bufferbl ... a44b772c66
[2] https://www.waveform.com/tools/bufferbl ... b31004cc32
 
dtaht
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Posts: 226
Joined: Sat Aug 03, 2013 5:46 am

Re: cAP CAKE latency challenge

Tue Oct 11, 2022 6:35 am

That's pretty weird. Regrettably I reflashed my cAPs to openwrt and the latest wifi code and I don't see that, I can do 100mbit no problem.

Your baseline result, however, is pretty good in the first place.
 
Zoxc
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Posts: 21
Joined: Fri Aug 13, 2021 4:01 pm

Re: cAP CAKE latency challenge

Wed Oct 12, 2022 2:59 am

I'd give a CAKE queue with its own shaper as a total simple queue a try. That matches the half-duplex nature of Wi-Fi better.
 
anuser
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Posts: 603
Joined: Sat Nov 29, 2014 7:27 pm

Re: cAP CAKE latency challenge

Wed Oct 19, 2022 9:53 pm

So has anyone compared different queue types for wireless interfaces with RouterOS v7? Is there any benefits when 10, 20, 30 concurrent clients shares their airtime?