What is VoIP, and how is it different from a regular phone line?
Summary
VoIP, short for Voice over Internet Protocol, turns your voice into digital data and sends it over an internet connection, where a regular phone line carries it over the phone company's analog network. You can still call any landline or cell phone, because the provider hands those calls to the public phone network. The differences show up in three places: call quality depends on your connection, a power or internet outage can take the service down, and 911 relies on an address you register and keep current.
A method, not a product
The FCC describes VoIP as a technology for communicating using Internet protocol instead of traditional analog systems. A "VoIP phone system" on a product page almost always means more than that: numbers, extensions, call routing, an auto attendant, voicemail, and an admin portal, all delivered over VoIP. Two services can both call themselves VoIP and include very different things.
What happens during a call
Your phone or app converts your voice into digital audio, chops it into packets, and sends them across the network, where the other end puts them back together. Two protocols usually share the work. SIP, the Session Initiation Protocol, sets calls up, changes them, and ends them. RTP, the Real-time Transport Protocol, carries the audio itself. If the other person is on the same service, the call can stay on the internet end to end. If they are on a landline or a cell phone, your provider passes the call to the public switched telephone network.
What the FCC calls interconnected VoIP
Federal rules define interconnected VoIP as real-time, two-way voice that needs a broadband connection and IP-compatible equipment, and that lets users generally receive calls from and place calls to the regular phone network. The 911 obligations are written for this category, and most business cloud phone services belong to it. For 911 purposes, a service that can only place calls to the phone network is treated the same way.
Depending on the service, the FCC says VoIP calls can be made from a computer, a special VoIP phone, a traditional phone with or without an adapter, or a wireless phone. Business setups tend to mix mobile and desktop apps with IP desk phones.
How 911 finds you
A landline's address is fixed to the line. A VoIP phone can move, so the rules split services in two. Fixed services must send an automatic dispatchable location with every 911 call. Services that can be used from more than one place must do the same if it is technically feasible; otherwise they can rely on a registered location, among other options. You must be able to update that registered location at will, and the provider has to notice when 911 is dialed from somewhere else and either prompt you for a new address or update it itself.
Providers also have to tell every subscriber, in plain language, when 911 may be limited, listing situations such as moving the equipment, a broadband failure, or a loss of power, and keep a record that each subscriber acknowledged it.
Why VoIP alone does not set the price
Microsoft sells Teams Phone Standard at $10 per user per month and Teams Phone with Calling Plan at $17, both paid yearly. The $7 difference buys a phone number from Microsoft and 3,000 outbound domestic minutes in the US. The technology is identical. Standard users who want to reach outside numbers connect through another route, such as a carrier contract under Operator Connect.
Sources
- fcc.gov/consumers/guides/voice-over-internet-protocol-voip
- fcc.gov/consumers/guides/voip-and-911-service
- ecfr.gov/current/title-47/chapter-I/subchapter-A/part-9/subpart-A/section-9.3
- ecfr.gov/current/title-47/chapter-I/subchapter-A/part-9/subpart-D/section-9.11
- rfc-editor.org/rfc/rfc3261
- rfc-editor.org/rfc/rfc3550
- microsoft.com/en-us/microsoft-teams/microsoft-teams-phone
- learn.microsoft.com/en-us/microsoftteams/pstn-connectivity
Related on this site
- How far apart are business VoIP prices, from entry plans to the top tiers?
- What does a business phone system actually do for a small company?
- Should you own your phone system's PBX or let a cloud provider run it?
- Is SIP just another word for VoIP?
- How much internet speed do VoIP calls actually need?
- Will 911 know where you are if you call from a VoIP phone?
Written by Kaz (pen name). Figures are copied from providers' published pricing pages on the dates shown. We have not used these products. Corrections: contact form.