What is a router?

What a router does

The word router comes from "route": the router decides which route each packet of data will take. In an office it has one main role — it is the gateway between the internal network and the internet. Everything that leaves the office or enters it passes through it.

In practice, an office router is several devices in one box:

• Routing — passes packets between the internal network and the internet connection.
• Address assignment (DHCP) — gives every phone and computer a private IP address when it connects.
• Address translation (NAT) — lets the whole office go out through one public address.
• Firewall — blocks unsolicited traffic from outside. See firewall and ports.
• Sometimes also — a Wi-Fi access point, a small switch with a few ports, and a modem.

Router, modem and switch — what's the difference

These three devices get confused all the time, because at home they are sometimes one box.

At home, one box from the provider does all three, plus Wi-Fi. In an office with more than a few seats, it's better to separate them: the router focuses on routing and protection, and a separate switch with enough ports, preferably with PoE, connects the phones and computers.

Types of routers

• An internet provider's router — comes with the connection, suitable for a home or a small office. Its advanced settings are sometimes locked, which makes it hard when you need to change something for telephony.
• A business router — more durable, with a stronger processor, a full management interface, support for traffic prioritization and network separation, and usually software updates over many years.
• A router with two internet inputs (Dual WAN) — connects two lines, for example fiber and cellular, and switches automatically to the second when the first goes down. See backup internet.
• A cellular router — works with a SIM card. Suitable for a temporary site, an event, or as a backup.

What matters in a router for telephony

A phone call uses very little bandwidth, but it is very sensitive to delays and dropouts. So for an office router working with a cloud PBX, "how many megabits" matters less, and these things matter more:

• Stability — a router that freezes once a week and needs to be turned off and on is a warning sign. Every such restart cuts off all calls.
• The ability to turn off SIP ALG — this setting causes audio problems more than anything else. See NAT.
• Support for QoS — priority for voice, so that someone's heavy download in the office doesn't disrupt calls.
• Enough processing power — a home router that handles ten devices can choke on fifty phones and computers. You notice this at peak hours.
• Keeping connections alive — a router that deletes its translation table too quickly causes incoming calls that don't ring.
• Access to settings — so that you, or whoever looks after the network, can change them without calling the provider for everything.

Where the router should sit

The natural place for the router is in the communications cabinet, next to the switch, the patch panel and the UPS. There it is ventilated, protected from accidental contact, and connected to backup power. A router sitting on the floor under a desk, next to a heater, or inside a closed drawer overheats — and a hot router tends to freeze.

If the router also serves as a Wi-Fi access point, placing it in a closed cabinet in the corner of the office will weaken the reception. The right solution isn't to take the router out of the cabinet, but to leave it there and add dedicated Wi-Fi access points in the rooms, which get network and power over a single cable from the switch.

Signs it's time to replace a router

• Calls sound good in the morning and start cutting out at noon, when everyone is in the office.
• Extensions disconnect and re-register several times a day, across the whole office at once.
• The router is very hot to the touch, or its lights blink abnormally.
• The manufacturer has stopped releasing software updates for the model.
• The office has grown: what suited five seats doesn't necessarily suit thirty.

Before replacing it, make sure the problem is really in the router and not in the internet connection itself. A simple test: connect a computer directly to the provider's cable, without the router, and see if the problem remains.

Common mistakes

• Two routers in a chain — a provider's router with a business router behind it, both translating addresses. It's better to put one of them in bridge mode.
• "A daily restart" as a solution — if the router needs a restart in order to work, the problem hasn't been solved, only postponed.
• The default admin password — a router with the factory password is an open door. Change it on installation day.
• No software updates — routers receive security updates. A router that hasn't been updated in years is exposed to known vulnerabilities.
• Opening ports "just in case" — with a cloud PBX this is usually unnecessary, and it only invites break-in attempts.
• Not documenting — the admin password, the public address and the provider's details should be written down in an organized place. On the day of a failure, nobody remembers them.

Diagnosis table: what happens, why, what to do

The first row is the most important check: browsing from a computer. If there's no browsing, there's no point checking phones. If browsing works and the phones are not registered — the problem is in the router's settings, not in the provider's line.

A full example: replacing a router in a 15-seat office without dropping the phones

An insurance agency with 15 seats decided to replace the provider's router with a business router, after months of restarts. Here is how it was done without a single customer noticing:

1. Documentation before. A screenshot of every setting on the old router: DHCP range, reserved addresses, the provider login details, port forwarding for cameras. Also: a list of the extensions registered in the PBX control panel, to compare against afterward.
2. Preparation outside of hours. The new router was configured on the desk, without connecting it to the network: the same address range and the same reservations, SIP ALG off, a new admin password, the latest software update.
3. The provider's unit to bridge mode. A call to the provider the day before: their router was switched to bridge mode, so the business router would be the only one translating addresses.
4. Replacement in five minutes. At seven in the morning, before the employees arrived: disconnect the old one, connect the new one to the fiber converter and to the switch in the cabinet, connect it to the UPS.
5. Testing. Browsing from a computer; then a look at the control panel: all 15 extensions were registered again within two minutes. An outgoing call from one seat, and then an incoming call after three minutes of silence — to make sure the new router doesn't delete connections too quickly.
6. Documentation after. The new password, the public address and the replacement date went into the office's infrastructure folder, plus a note on the cabinet door.

The whole process took an hour, of which five minutes were without phones — at an hour when nobody called. The difference between this and "let's replace it and see" is the second step: configure the new one before disconnecting the old one.

Checklist before buying a router for the office

• The type of connection to the provider — fiber with a converter, cable, or copper? The router needs a suitable WAN port, and if the connection uses a username and password (PPPoE), it must support that.
• How many devices — count phones, computers, mobiles, printers, cameras and Wi-Fi access points. A business router usually has a recommended number in its specifications.
• SIP ALG that can be turned off — and you can confirm this in the model's manual even before buying.
• Two internet inputs — if you're planning a cellular backup, a router that knows how to switch by itself is better.
• Network separation and prioritization — support for VLAN and QoS, even if you don't use them on the first day.
• Cabinet installation — a 19-inch model, or a suitable shelf.
• Updates — a manufacturer that releases security updates for the model over many years.
• Who manages it — an interface that someone in the office, or whoever looks after the network, is familiar with.

What to tell the internet provider when you bring your own router: "I'm connecting a business router. Please switch your router to bridge mode, and give me the login details." That's all that's needed.