This is almost certainly caused by interferences. It's not unusual that lags happen over wireless links; this always happens on each wireless link no matter which device. Much more important then ping round trip delays (RTD) is the overall throughput of the wireless link (well, except probably for gaming). I would not call high ping RTD a »drop-out«.

You can try to minimize lags by setting a fixed 20 MHz channel width and selecting a channel which isn't overcrowded. If there are too many nearby APs, changing to the 5 GHz band might help to improve the link quality and especially the throughput. But since WiFi is a half-duplex shared medium, you cannot avoid lags at all, thus you always will have a higher latency compared to a full-duplex medium such as Ethernet.

MAXtream TDMA (it's not MAXStream) makes sense only in PtMP setups – not so much in a PtP setup –, but even with MAXtream enabled your CPEs share the wireless channel with all other nearby APs visible to the CPEs, which use the same channel.

AndersG wrote

OK: Thanks. At this point are the dropouts my main concern and unfortunately would going 5GHz mean that I need to change devices, right? As for dropouts, what I mean is that the unit closest to me becomes totally unresponsive. It does not answer to pings on its own address, nor is the web UI responsive.

Yes, 5 GHz would require CPE510.

With »unit closest« to you do you mean the CPE wired to your local network? There should be no drop-outs at all over a cable and if they happen, it does not have to do with the wireless link. If the CPE's web UI becomes unresponsive, I would check IP settings (of the whole network, not only the CPE) and routing. Maybe you can run tcpdump or Wireshark to find out what happens in your local network when the CPE becomes unresponsive.

If this is not what you meant, please post a network diagram so that we know what we are talking about. In your opening post you wrote about pings to a computer on the remote site (over the WiFi link), so I'm not sure I understand what you mean with »unit closest« to you.

AndersG wrote

When the dropouts happen both stop responding.

Ah, I see, you run two pings simultaneously. Yes, you're right, if the ping to the remote CPE over WiFi lags or has drop-outs because of interferences, the ping to the local CPE should continue independently. So, there is probably another cause if both pings don't get a reply at the same time.

I once saw such a behavior (packet loss) even over Ethernet on a VLAN-aware switch where broadcasts from one VLAN leaked into another VLAN due to membership of switch access ports in an additional Default VLAN.

But from what I understand would 5GHz lead to a marked improvement in throghput?

Depends on the region and environmental parameters. In my country, the 5 GHz band was not much populated when we deployed the wireless link I described in the story. What's more, in Europe it's guaranted to have 20 MHz channel width (e.g. ch100 = 5490-5510 MHz, ch104 = 5510-5530 MHz etc.).

This avoids overlapping channels like they happen in the 2.4 GHz band (e.g. ch1 overlaps with ch2, 3 and partially 4 for 802.11b and ch2, 3 with 802.11g/n). There were only few foreign 5 GHz APs (~5) nearby, albeit nowadays there are considerably more (~35).

We did tests with two CPE210 on the same link and througput was as low as only 3-5 Mbps (~130 foreign APs visible to the CPE) compared to 80-90 Mbps with two CPE510.

Also, CPE510's antenna beam width is a bit narrower (45° H, 30° E) compared to the CPE210's beam wdith (65° H / 35° E) and they can have up to 23dBm transmit power yielding 30dBm (1W) EIRP in the U-NII-2C frequency band (channels 100 to 144).

One possible culprit would be if something else on the net had the same IP address as "CP210_Client", intermittently, but in that case would changing MAXtream not make a difference right?

Yes, MAXtream is just kind of a Time-Division Multiple Access protocol, where the base station WBS or CPE divides the available AirTime into smaller time slots to allow multiple remote CPEs share the same channel without too much collisions. It won't make a difference if two CPEs have the same IP.

When using CPEs in AP and Client modes, they must have different IPs, since they share the same broadcast domain.

@AndersG, with 30-50 Mbps throughput I would not consider changing a CPE210. The 2.4 GHz band has advantages, too, such as no requirement for DFS or better signal distribution when there are obstacles in-between both CPEs such as rain or snow.

Try to align the CPE's antennas more exactly, use 20 MHz channel width, set the distance to 0.4km for 300m, change the WiFi channels, preferably to channel 1 or 13. And of course, always use static IPs for stationary devices. But I still can't imagine what causes excessive packet losses (except probably wrong IP assignments, cable problems or a subtle hardware defect).