Unexpected low bandwidth

RouterOS Wireless Networking
1

CRS112_A—911G-5HPacD--------------911G-5HPacD—CRS112_B—911G-5HPacD-------------911G-5HPacD—CRS112_C

Bandwidth test from CRS112_A to CRS112_C says
120Mbps receive OR transmit UDP
70Mbps both UDP
12Mbps receive OR transmit TCP
6Mbps both TCP

Both radio links claim 300Mbps-40MHz/2S/SGI with 75 to 85% CCQ NV2 protocol
911 are eth/wlan bridged, as well CRS carrying tagged vlans

Any suggestion ?

2

UDP performance is about right to what both wireless hops can do.

TCP performance is a bit low … and you have to troubleshoot. Possible reasons for low TCP throughput are:

  1. lost packets and consequently retransmissions.
    Depending on test tool you may get information about retransmissions, iperf3 does report retransmission statistics
  2. high latency (even over otherwise idle link).
    Check both average latency as well as latency jitter.
  3. my experience is that sometimes TCP stack is excessively sensitive to some certain delay and throughput is better when delay is only slightly lower and also in case when delay is actually slightly longer. I guess that actually depends on processing rate of TCP packets on both sides of connection and is, in my experience, very hard both to debug and to replicate in another setup.
3

Thanks for reply,
Actually I’m doing A—C bandwidth test from inside CRS tool… being not powerful devices, cpus hits near 100% (middle CRS using HW offload hit nearly 10%) probably this is the bottleneck…
I’ll try locally with iperf outside both CRS

4

Well… changing wireless protocol from NV2 to 802.11 really does the trick…
Both link stabilized @ 866.6Mbps-80MHz/2S/SGI 95-98% CCQ.

Latency drops dramatically and bandwidth really increases.
One must forget to use CRS112 as bandwidth server , still 6Mbps@100%cpu
Tried from a RB3011 to latest opposite 911G , TCP bandwidth is about 60/60 both (with 911G cpu@100%)
UDP jumps to 220/220 both (almost all cpu at 911G)

Curious to try locally with iperf

5

Disable the short guard interval, this will increase the stability of the link. The bridge is outdoors, not indoors.
Without radio parameters and network settings, it is difficult to give advice. Only L3 traffic should be transmitted over the radio bridge.