Earlier, we wrote about radio-relay stations of the unlicensed millimeter-wave range, practically the only way to get a radio channel of gigabit capacity without a long and expensive receiving of frequency assignments.
In the comments, we were often asked how stable the connection would be in a middle band. After all, beautiful graphics and calculations of manufacturers is good, but how will things stand in practice?
We are glad to inform you that some of our channels have recently celebrated two years of work, and in this article we will look at almost annual statistics on channel performance and signal level.

Today we are reviewing statistics on the most sensitive to precipitation range of radio communications, 70-80 GHz.

The considered span on the Siklu 1200 equipment with two-foot (60 cm) antennas is built at a distance of 2560 meters.

The channel was installed in Bucharest, located in the rain zone K, where precipitation is significantly more intense than zone E, to which most of the territory of the Russian Federation belongs.
Recall that rain zones (in the original rain zone) reflect the probability of precipitation of varying intensity and their duration at the equipment installation site, which is reflected in the published ITU recommendations (Rec. ITU-R PN.837-1) dividing the planet into 15 regions.
For comparison, we present the tabular values ​​of the intensity of precipitation in the zone typical for the Russian Federation E.

When studying statistics on resistance to precipitation, it is important to take into account that precipitation is very unevenly distributed throughout the year, therefore, with a monitoring interval of less than a year, the availability of the channel is possible both for better and for worse.
So, we will make graphs for the observation period, fortunately, Siklu equipment allows you to capture the main parameters of the channel in several ways: via SNMP, or through the built-in statistics server.
The system allows you to take graphs of the signal level and the current modulation, for the most convenient viewing we have translated the modulation schedule into the channel bandwidth.

Measurement time 4656 hours. Date: 19.2-30.8 Days: 194
Channel availability, built on statistics provided by devices

Link length	Modulation, speed	Availability
		qpsk 1 4 0.5 ') 20 Mbit	qpsk 2 2 0.5 85 Mbit	qpsk 4 1 0.5 365 Mbit	qam16 4 1 0.5 700 Mbit	qam64 4 1 0.5 1000 Mbps
2560m		99.99359%	99.98918%	99.98775%	99.98205%	99.96892%

Expected availability, according to calculation (EH1200, 2ft antenna, 2560m, rain zone)

Channel length	Modulation, speed	Availability
		qpsk 1 4 0.5 20 Mbit	qpsk 2 2 0.5 85 Mbit	qpsk 4 1 0.5 365 Mbit	qam16 4 1 0.5 700 Mbit	qam64 4 1 0.5 1000 Mbps
2560m		99.993%	99.990%	99.985%	99.976%	99.962%

As you can see, the channel resisted and showed accessibility corresponding to the calculated one.
Please note that the test took place in the summer, respectively, the overall annual results will be better.
Combined with the QoS settings on the Siklu equipment, this allows for excellent accessibility for the highest priority traffic: telephony, network traffic, control and high-priority data.
If even greater network reliability is required, especially when building extended channels, EtherHaul can organize secure topologies.
You can connect a lower-frequency backup low-frequency radio channel (say, a short-range device with a 2.4 GHz band, which can also be used without a frequency assignment, and which are practically insensitive to rain) to the second port of the device. When enabled, Siklu will monitor the status of the main radio channel and, if communication is lost, redirect traffic to the reservation port.
Traffic is subject to processing and prioritization by the system, and switching is performed without breaking user data (hitless). When you resume communication, Siklu will switch traffic to the main radio channel.

findings
Several months of operation in the most difficult rainy seasons showed high stability of SIKLU radio channels .
Productivity has made Gigabit more than 99,9% of time
The reliability of the channels corresponds to the stated, adaptive modulation allows to ensure the maximum availability of the channel for high-priority traffic.