What is VoIP and how does business VoIP work

On a traditional landline, a physical circuit connects two phones for the length of a call. VoIP works differently. When you speak, a phone or app turns your voice into digital audio, cuts it into small packets and sends them across the internet to the other side, where they are put back together and played. This happens many times per second in both directions, which is why a good connection sounds as natural as a landline.

• Your desk phone, mobile app or browser captures your voice and encodes it.
• The packets travel over your office or home internet to the provider's network.
• The provider routes the call to another VoIP user or hands it over to the public phone network, so you can call any regular number.
• On the way back, incoming calls to your business number reach the provider first, which then decides where they ring based on your rules.

That last point is the real advantage for a business. Because the provider sits in the middle, your number is no longer tied to a building. It can ring on a desk phone at the office, a laptop at home and a mobile in the car.

SIP, the Session Initiation Protocol, is the standard that VoIP devices use to start, manage and end calls. When you dial, your phone sends a SIP message that says who is calling and who should answer. The other side replies when it rings and when it is picked up, and both sides agree how the audio will be sent. SIP matters to a buyer for one practical reason: it is open. A SIP desk phone from a mainstream manufacturer can usually work with any provider that supports standard SIP, so you are not forced to replace hardware when you change service. SIP is also the basis of SIP trunking, which connects an existing office phone system to the internet instead of to copper lines.

A codec is the method used to compress and decompress voice. Some codecs keep the audio very close to the original and use more data; others compress more and use less. Modern wideband codecs, often called HD voice, carry a wider range of sound and make speech easier to understand than an old landline. Each call needs a steady stream of data in both directions. The exact amount depends on the codec, but a single voice call uses a small fraction of what a video meeting does. For planning, the questions that matter are simple:

• How many people may be on calls at the same time at your busiest moment.
• Whether your upload speed is stable, since calls need upload as much as download.
• Whether large backups, video uploads or cloud sync run during business hours on the same connection.

Most office connections handle voice easily. Problems usually come from other traffic competing with calls, not from the calls themselves.

Voice is sensitive to delay in a way that email or web pages are not. Three measures describe call quality:

• Latency is how long a packet takes to arrive. Too much delay makes people talk over each other.
• Jitter is variation in that delay. Packets arriving unevenly produce choppy audio.
• Packet loss is packets that never arrive. A little is hidden by the codec, more is heard as gaps.

QoS, Quality of Service, is a router setting that gives voice packets priority over other traffic. On a busy office network it is the single most effective fix for choppy calls. Many business routers support it, and your IT partner can set it up in minutes. On Wi-Fi, a strong signal and a less crowded channel help as much as raw speed. If you work from home, a wired connection for the laptop running the softphone removes most issues.

With a landline, emergency services know where you are because the line is fixed to an address. A VoIP number can be used anywhere, so the location has to be registered. E911 in the United States links each user or device to a registered address that is passed to emergency dispatchers. For a business this means two tasks: register the correct address for every user when you set up the service, and update it when someone moves to a different office or works from home. Also tell your team that a power or internet outage can affect the desk phone, and that a mobile phone is the backup for emergencies in that case. A good provider makes updating the address part of the normal user settings rather than a support ticket.

Consumer calling apps are built for one person talking to friends. A business phone system is built for a company number that many people share, and that difference shows up everywhere:

The business version also separates work from personal life. Employees call from the company number on their own mobile, and when someone leaves, the number and its history stay with the company.

The requirements are lighter than most people expect. You need a reliable internet connection, a way to make calls (the mobile and desktop apps, a browser, or SIP desk phones for people who prefer a handset), and a plan for your numbers. You can keep your existing numbers through number porting, and add a virtual phone number for a new region or campaign. If you are comparing services, read how to evaluate the best VoIP providers, and if you are still deciding whether to leave your copper line, our honest VoIP vs landline comparison covers reliability, power and cost.