# Multi-gigabit Point-to-Point going the extra mile

Wireless manufactures have been making multi-gigabit links for a while now, so the technology has matured significantly. Deploying a link across a two-mile stretch can easily achieve five nines availability. However, we come across customers needing to extend the stretch to five, sixth or more miles which when deploying E-band equipment creates a link between availability vs rain.

Availability is measured by how much time a link is up and transporting traffic. With this information know five nines availability would mean the expected downtime would be 5.26 minutes a year.

Availability % Downtime per year Downtime per month Downtime per week Downtime per day
99.9% ("three nines") 8.77 hours 43.83 minutes 10.08 minutes 1.44 minutes
99.99% ("four nines") 52.60 minutes 4.38 minutes 1.01 minutes 8.64 seconds
99.999% ("five nines") 5.26 minutes 26.30 seconds 6.05 seconds 864.00 milliseconds

E-band which operates in the 70/80GHz millimetre spectrum determines range by a combination of system gain or link budget and availability targets with statistical rain patterns for the site locations. Statistical rain patterns are gathered by organisations such as International Radio Telecommunications Union (ITU-R) and organised into prediction models for the calculations of their effect on radio links.

The availability needed is determined by a customer, led by their business case for implementation. Working towards a link with four nines availability is very common for our customers. A single link capable of a four or five-mile, with four nines availability in the E-band in the UK cannot achieve four nines availability on its own. So how do we make it work?

## Extending the range and availability

The answer to provide five nines availability is to install a backup link operating on a different frequency. Seems a simple answer, but the real implementation of this is not always simple, and the “backup radio” or “redundant radio” operation will maintain the links availability, but at the cost of capacity.

When we install E-band links, for customers wanting the higher availability we will implement a backup 5GHz solution. Some solutions come with dual band antennas, so if the link is going to be located on a tower, this will keep rental costs down allowing both 80GHz & 5GHz to broadcast from the single antenna.

For the backup link to work autonomously, high speed switching needs to occur. Some premium links come with built-in high-speed switching. Budget or more affordable links require additional configuration of a customer’s switch. An advantage of a premium link with a built-in switch includes a single cable run to the radio, with PoE out to the back-up radio.

Handling the lower traffic capability of the backup link requires forethought and design for the networks traffic to allow the radio to recognise traffic priority and apply quality of service to ensure timely delivery for the more important traffic such as voice, email and applications over fewer sensitive packets.

To conclude, with a good design, and professional installation, it is feasible to operate multi-gigabit links over moderate distances providing five nines availability which makes sense over traditional fibre lines in many situations. As a wireless professional we have integrated thousands of links across Europe and offer a range of services and solutions to meet the demands of today’s businesses. If you would like to discuss your network requirements, we have dedicated wireless backhaul account managers to assist.

Topic