Update, 2 November 2026: added how to choose between 4G and 5G, and what to keep running in a shop or restaurant.
Most businesses run on a single internet connection. When it fails, everything that depends on it fails too: email, Microsoft 365, the accounts system, card payments and, increasingly, the phones.
And at some point it will fail, usually because the cable outside your building is shared with the rest of the street.
Why lines go down
The most common causes of a long outage have nothing to do with your provider’s network:
Third-party damage. A contractor digs through a duct, or a vehicle hits a roadside cabinet.
Weather. Flooding gets into underground chambers; storms bring down overhead cables.
Faults in the local network. A failed component in a cabinet or exchange can take out a whole area.
Theft and vandalism. Cable theft still happens.
Repairs that need civil works, permits or traffic management can take days.
How the backup router and failover work
A backup router with a 4G or 5G SIM sits alongside your main connection. When the main line drops, traffic switches over to mobile data automatically, usually within moments, and switches back when the line is restored. That automatic switch is the failover, and it is what separates a backup from a dongle in a drawer.
For most offices, the switch is barely noticeable. Email keeps arriving, cloud applications stay connected, and staff carry on working.
Hosted phones keep ringing. If your phones run over the internet, they move to the backup connection too, so customers can still reach you.
Card terminals stay up. Payment terminals, tills and booking systems that use your internet connection keep working. For a shop, café or restaurant, that is usually the reason to have one.
It is a different route. Mobile data does not share the cable in the street, so it is not affected by the same problem.
4G or 5G?
Either will do the job for most offices. A backup only has to carry what the business cannot do without: phones, card payments, email and cloud applications. 4G handles all of that, and its coverage is wider.
5G gives more speed and lower latency where there is a good 5G signal. That matters if the backup has to carry video calls or large files for days at a time, or stand in for a fast fibre line without anyone noticing. A 5G router drops back to 4G where there is no 5G, so choosing 5G rarely costs you coverage. The survey decides: which network, which generation, and whether an external antenna is worth fitting.
What to think about
Signal. 4G and 5G coverage varies building by building. A survey tells you which network performs best where your router will sit, and whether an external antenna would help.
Data allowance. A backup connection is idle most of the time, but when it is needed it carries everything. Choose a plan sized for a few days of full use.
What runs on it. If the backup is smaller than your main line, decide what takes priority: phones and payments first, large uploads and updates later. In a shop or restaurant that means the card terminals, the till and the bookings; in an office, the phones and Microsoft 365.
Testing. A backup that has never been tested may not work when you need it. Test the failover, and test it again after any change.
Backup or a second fixed line?
For businesses that cannot tolerate any downtime, a second fixed connection via a different route, or a leased line with a guaranteed fix time, may be the right answer. For most small and medium businesses, mobile backup gives most of the protection for a fraction of the cost.
Set up and supported by our own team
We supply the SIMs, the routers and the failover set-up, and our own engineers handle faults and changes. See our mobile and 4G and 5G data services, talk to us or call 01642 661888.