What is a backup internet connection?
A backup internet connection is a second internet line — usually cellular — that kicks in automatically when the main connection goes down (failover). For an office that lives on the phone, it is the difference between an outage of hours and an outage of seconds.
Why the internet goes down, even a good one
Even the most stable fiber connection goes down sometimes. A cable cut by roadwork, a fault at the internet provider, overnight maintenance that runs into the morning, a modem burned out by a power surge, or just a router that freezes. Most of the time you won't notice. But when it happens on the day of a campaign, during a rush at a call center, or on the day all the registrations come in by phone — every minute is felt.
In an office that works with a cloud PBX, the internet is the line that connects the phones on the desks to the PBX. When it goes down, the phones in the office can't receive or make calls. The PBX itself keeps working — but you aren't connected to it from the office.
A backup connection gives a second way out. It doesn't prevent the fault in the main line; it simply lets you keep working while it is being fixed.
How the automatic switchover works
The heart of a backup internet connection is a router with two internet ports — what is called Dual WAN. The main line connects to one, the backup to the other. There are also routers with a built-in cellular modem, where you insert a SIM card and the backup is already inside.
- Monitoring. The router checks every few seconds whether the main line really reaches the internet — not just whether the cable is connected, but whether there is a response from outside addresses.
- Detecting the outage. After several failed checks in a row, it declares that the line is down. This usually takes anywhere from a few seconds to a minute, depending on the setting.
- Switchover. All traffic is redirected to the backup line. The phones re-register with the PBX through the new address.
- Switching back. When the main line returns and is stable, the router moves the traffic back to it.
What do you actually feel? A call that was in progress at the moment of the outage will usually be cut off, because the address the audio was coming from has changed. After the switchover, new calls come in and go out as usual. It's not a perfect experience — but it's an enormous difference compared to a whole morning without a phone.
Types of backup
| Type | Advantages | Disadvantages |
|---|---|---|
| Cellular (4G/5G) | Doesn't depend on cables in the street; quick to set up; relatively cheap | Depends on reception in the building; speed varies; sometimes a data cap |
| A second wired line, from a different provider and infrastructure | As stable and fast as the main one | More expensive; if both lines are in the same conduit in the street, one dig takes down both |
| A second line on the same infrastructure | Easy to order | Protects only against a fault in your equipment, not in the infrastructure |
The most important rule: a real backup has to be different from the main line. Two lines that pass through the same cable, the same neighborhood exchange or the same provider can go down together. That's why cellular backup is so popular: it travels a completely different way — through the air.
And in offices with two fast lines, you can consider load balancing: the router uses both at the same time, for example computers on one line and phones on the other. When one goes down, everything moves to the other.
Planning it right: what to check first
- Reception where the router sits. A communications cabinet in the basement is an excellent place for a cabinet and a poor place for cellular reception. Sometimes you need an external antenna or a modem in a different location.
- Upload speed on cellular. For calls it matters as much as download. Test it during a busy hour, not at one in the morning.
- What goes over the backup. If the backup is slow, you can set it so that during an outage only the phones and essential systems go through, and not cloud backups and updates.
- Data cap. A plan with a small cap will run out quickly if the whole office switches to it.
- The backup needs power too. A router and cellular modem without a UPS will shut off exactly when the power goes out.
- Test that it works. Disconnect the main line for a few minutes, once every few months, and make sure the phones come back.
Real-life examples
A nonprofit on a fundraising evening. Hundreds of callers within a few hours, and volunteers answering from the office. An internet outage in the middle of the evening means donations lost. Here a cellular backup in the router, together with a ready forwarding to the volunteers' mobile phones, is worth every shekel.
A service call center in Bnei Brak. Ten agents and a full queue all morning. A second connection from a different provider, with automatic switchover, gets the agents back to work within a minute.
An office of three employees. Usually it's enough that calls go to a mobile phone when the office isn't available, with no extra equipment.
And the plan for when both lines go down
This is the advantage of a cloud PBX: even without any internet backup, calls aren't lost. The PBX keeps receiving them, and the only question is where to send them when the office isn't available. Common options:
- Follow Me — calls ring on the mobile phone of the person in charge or of several employees.
- Another branch — a second office that keeps answering.
- SIM extensions — employees with a kosher mobile phone keep receiving calls as a regular extension, with no internet at all.
- Voicemail — messages are saved and sent to email.
For a small business, sometimes this is all that's needed: not a backup connection, but good forwarding. For a business where every minute is worth money — a call center, a campaign, customer service — combining both is the safest: internet backup for most faults, and forwarding from the cloud for the big ones.
Failure scenarios: what goes down, what keeps going, and what happens to a call in progress
"The internet is down" is really four different scenarios, and in each one the backup behaves differently. The table assumes an office with a cloud PBX, a router with a cellular line as backup, and a UPS in the cabinet:
| What happened | What goes down | What happens to calls in progress | What happens to new calls | How long |
|---|---|---|---|---|
| A fiber cable cut in the street | The main line only | Cut off at the moment of switchover | Go through the cellular line after the phones re-register | Seconds to a minute for the switchover; hours to days for the repair |
| A fault at the provider | The main line; sometimes partial — there is connectivity but it's slow | Depends: a full outage disconnects them, a slowdown just degrades them | Go over the backup only if the router detects the outage | Minutes to hours |
| A power outage | Everything — unless there is a UPS | With a UPS: continue; without: cut off | With a UPS: as usual, until the battery runs out | Minutes to hours |
| The router freezes | Everything, including the backup that sits inside it | Cut off | None, until it is restarted | minutes |
Two rows deserve an explanation. A slowdown at the provider is the most annoying scenario: the line "works," the router doesn't see an outage and doesn't switch to the backup, and calls sound bad all morning. Good routers can check not only "is there a response?" but also "how long did it take?" and "how many checks were lost?", and switch to the backup even when the line is alive but sick. It's worth looking for this setting.
And the frozen router is a reminder that a backup that sits inside the same box protects against the street, not against the box. In a call center where every minute counts, consider a separate cellular router that kicks in when the main one goes silent — or at least an automatic restart of the router when it stops responding.
Three backup options, side by side
| Cellular router (SIM in the router) | A second provider on a separate line | Hotspot from a mobile phone | |
|---|---|---|---|
| Switchover | Automatic, seconds to a minute | Automatic, seconds to a minute | Manual: someone has to turn it on and connect |
| Upload speed | Depends on reception; usually enough for dozens of calls | Like the main line | Low and variable; a few calls |
| What is backed up | The whole office | The whole office | One computer or one phone, whatever was connected |
| Monthly cost | Low (a SIM plan) | A full line | Zero, charged to the mobile plan |
| Resistant to | A cable cut, a provider fault | A provider fault; a cable cut only if the route is different | Everything — including a power outage, because the mobile phone runs on a battery |
| Not resistant to | Poor reception in a basement; a power outage without a UPS | A dig that damages both lines | Many users; the phone's battery |
| Best for | Most offices and institutions | Call centers, places where the backup has to carry everything | A small business, or an emergency plan for one person |
The mobile hotspot doesn't get much respect, but it has its place: in a business of three people, a softphone app on a laptop connected to the hotspot gets one station back to work in two minutes, with no equipment and no subscription. And when you have a SIM extension, you don't even need that.
One more setting worth asking for from whoever installs a router with two lines: voice always on one line. A router in load-balancing mode may send some of a call's packets through line A and some through line B, and then the PBX sees the same call from two addresses — and you get one-way audio with no fault anywhere. The rule: phones on the main line, switch to the second only on an outage, and switch back only when the main one has been stable for a few minutes.
What the cloud PBX does in any case, and a five-minute drill
Everything described so far concerns the office's connection. The PBX itself lives somewhere else, and what happens there doesn't depend on the fiber in your street:
- Calls keep arriving. Your number rings in the cloud, not in the cabinet. A caller who dials while the office is disconnected hears a ring or a menu, not "the number is unavailable."
- Forwarding works from the cloud. An extension that isn't currently registered is, to the PBX, like a busy extension: the call continues along the route you set — a mobile phone, a branch, voicemail.
- The queue keeps taking callers. Callers waiting in a queue sit in the cloud. If the agents in the office disappeared, agents at home or on mobile phones keep answering, and the callers feel nothing.
- SIM extensions and the app don't depend on the office. An agent with a SIM extension answers as usual, because they're on the cellular network, not on the cabinet's internet.
- Messages are saved. Voicemail sends the message to email, and the caller isn't lost.
And since all this works only if it was set up in advance, here is the drill. Once a quarter, at a quiet hour: unplug the fiber from the router (not the power) and time how long until the phones register again through the backup; call the main number from a mobile phone and check where the call arrives; disconnect the backup too and call again — now it should reach the mobile phone or voicemail, depending on the setting; connect everything back and check that the phones returned to the main line. Five minutes, four checks, and write down the date. A business that has done the drill once knows what will happen; a business that hasn't finds out on the least convenient day.
How it works with us at Kesher
Kesher's PBX is in the cloud, on servers in several countries with backup and redundancy at every layer. When the internet in the office goes down, the PBX keeps receiving calls and forwards them according to what was set in advance: to a mobile phone, another branch or voicemail.
It's worth setting this forwarding up before you need it. In the control panel, in the "Call Route" screen, you can see for each number where the call goes in every situation. And if you prefer, you can ask us to make the changes.
Should you get a backup internet connection? It depends on how critical the phone is for you, the cellular reception in the office and the existing equipment. For businesses where every minute without a phone is felt, we recommend considering it, and we'll check with you whether the existing router is suitable. A person answers every question.
And for someone who works outside, or with a kosher mobile phone: a SIM extension keeps working on the cellular network, regardless of what happens to the office internet.
While the office is disconnected, the Extensions screen in the control panel shows which extensions are currently registered and from which device — so you see immediately whether the phones came back through the backup, without lifting a handset in every room. And anyone who set up email or SMS alerts for missed calls gets an orderly list of who called during the outage, and calls them back when everything is up.
FAQ
What happens to calls when the internet in the office goes down?
With a cloud PBX, calls keep reaching the PBX. You can set in advance that they go to a mobile phone, another branch or voicemail, so no call is lost.
Does an active call continue when the system switches to the backup?
Usually not. A call that was in progress at the moment of the outage is cut off, and new calls go through the backup as normal.
Is a cellular backup enough for calls?
In most cases, yes, as long as there is good reception where the router sits. A call uses very little, but it is worth checking the upload speed at peak times.
What is Dual WAN?
A router with two internet ports. It can switch automatically to the second line when the main one goes down, or use both together.
The router does not switch to the backup even though the internet "isn't working." Why?
Probably the line is alive but slow, and the router only checks whether there is any response. Look in the monitoring settings for an option to fail over based on response time and the percentage of failed checks, not only on a full disconnection.
Can the phones work on both lines at the same time?
It is not recommended. Packets of the same call leaving from two addresses confuse the PBX and cause one-way audio. Keep the voice on one line, and the second one only for failover.
How do you test that the backup really works?
Disconnect the main line from the router for a few minutes during a quiet hour, and measure how long it takes for the phones to register again. Then call the main number from a mobile phone. Do this once a quarter.