The Backup That Only Works on Paper: Rehearsing Your 4G Failover in Half an Hour

Most UK small businesses already own some form of mobile-data backup. It might be a 4G router left by the previous IT supplier, a dual-SIM box in the comms cabinet, or a PAYG SIM in a drawer with a note that says emergency. The trouble is that a backup nobody has switched on is less of a plan and more of a rumour.

A proper failover rehearsal takes about half an hour. You do not need a change window, a consultant or a windswept visit from Openreach. You need a quiet moment, a stopwatch and the willingness to unplug the main line while everyone is watching.

Pick a quiet half-hour and tell people

Choose a time when a 10-minute wobble will not ruin a client demo or a card payment rush. Mid-afternoon on a Tuesday is often kinder than Monday morning. Tell the team what you are doing and why. Ask them to carry on as normal, but note anything that stops working.

Have the following to hand: the main router, the 4G router or hotspot, the SIM PIN if there is one, the admin password for the mobile router, and a notepad. If you use a managed IT provider, tell them too. You want them watching the monitoring graph, not raising a ticket because the office has vanished.

Find out what your backup actually is

There are three common setups. First, a router with a second WAN port and a 4G stick or SIM that fails over automatically. Second, a standalone 4G router that someone has to plug into the switch by hand. Third, a phone hotspot, which is a backup for one laptop and not for the office.

Each needs a different test. Automatic failover should be left to do its thing. Manual failover needs a human to practise the cable move. A hotspot needs an honest conversation about whether it can carry card payments, VoIP calls and the finance team's month-end.

Also check where the mobile kit lives. A 4G router in a metal comms cabinet in the basement is not the same as one on a windowsill. Signal strength in the room where the kit actually sits is the only number that matters. Test with a phone on the same network before you start.

Pull the plug and start the clock

For an automatic setup, unplug the main WAN cable from the router or switch off the fibre ONT. For a manual setup, do exactly what a colleague would do: unplug the main router, power up the 4G router, connect the switch cable. Start the stopwatch when the main line goes down.

Time how long it takes before a laptop can load a fresh web page. Under two minutes is a decent automatic failover. Five to ten minutes is normal for a manual change. If it takes twenty minutes, a phone call and a hunt for a password, the backup is not ready.

Do not stop at Google. A web page proves that data is flowing. It does not prove that your business is trading.

Test the services that make money

Work through the things that actually matter, one at a time:

• VoIP calls. Ring a desk phone from a mobile. Ring in from outside. Check that voicemail or the auto-attendant still answers. If calls divert to a mobile, note how long that takes.
• Card terminal. Run a small test transaction and refund it. Check whether the terminal is on Wi-Fi or Ethernet, and whether that route goes through the main router. A backup line is no help if the card machine is plugged into the wrong box.
• Cloud email. Send and receive a message from Microsoft 365 or Google Workspace. Open an attachment. Check that shared mailboxes still load.
• Teams, Zoom or Google Meet. Start a two-minute call with one colleague. Video is a good stress test, but it also eats data.
• Line-of-business apps. Open Xero, QuickBooks, your CRM, the practice management system or the payroll portal. Log in properly. A cached page is not a working app.
• Files. Open a SharePoint or OneDrive file, and a file on the office NAS if you have one. Check whether remote access or the VPN still works.
• Phones and CCTV. If your door entry, CCTV or alarm uses the internet, check the app. These are often forgotten until someone needs footage.

Write down pass or fail for each one. Be specific. Email works is less useful than Outlook sent and received, but the shared accounts mailbox took two minutes to load.

Make the fallback human-sized

The drill is only useful if the next person can repeat it. Write a one-page sheet: a photo of the kit, which cable goes where, the SIM PIN, the data cap, the router admin address and who to ring if it fails. Put it in the shared drive and print a copy for the comms cabinet. Label the cables with tape and a marker. WAN and 4G LAN are good labels. Thing 2 is not.

Then walk a non-technical colleague through it. Not to make them a network engineer, but to prove that the instructions work without you. If they get stuck, the sheet is wrong, not the colleague. Rewrite it.

Check the cap and the signal before you need them

A 4G backup with 1GB left on the plan is a decoration. Look up the monthly data allowance, what happens when it runs out, and whether the SIM is on a contract or PAYG. A few VoIP calls and some email will fit in a small allowance. Ten people on video calls will not. If the router can prioritise traffic or block video, set that up now, not during an outage.

Signal is the other half. Test in the room where the router lives, not in the car park. Run a speed test on a phone using the same network. If the signal is weak, try a window, a longer cable or an external antenna. Also check which network the SIM uses. A spare SIM on a network with no indoor coverage is a lucky charm, not a failover.

Plug back in, fix one thing, diarise the next go

Reconnect the main line. Confirm that everything has returned to normal, including card payments and calls. Then pick one improvement from the drill: label the cables, move the router, top up the SIM, write the instructions or add a reminder to test again in three months.

The point of the exercise is not to prove that you have a backup. It is to find the gap while the coffee is still warm and nobody is losing money. A backup that has been unplugged, timed and tested is worth ten that sit in a cupboard with a hopeful label.