VoIP vs SIP: What's the Difference?
VoIP is the call, SIP is the protocol that connects it. See exactly how they work together, with real examples from Telzio's platform.
VoIP vs SIP: What's the Difference?
VoIP and SIP both refer to internet telephony, but they're technically different things. VoIP describes the type of phone call, one that travels over the internet, while SIP is the industry-standard method used to actually set those calls up between devices.
Communicating online doesn't have to be complicated, but it can feel that way with an alphabet soup of acronyms floating around: VoIP, IP, SIP, ISDN, PSTN, IP-PBX. They sound similar enough that people mix them up constantly, and VoIP (Voice Over Internet Protocol) and SIP (Session Initiation Protocol) get used interchangeably more than almost any pair on that list, even though they're not quite the same thing.
| Category | VoIP | SIP |
|---|---|---|
| What it actually is | The type of phone call, made over the internet | The protocol used to set that call up |
| Scope | A broad umbrella term | One specific protocol within VoIP |
| What it covers | Any internet-based phone communication | Call signaling: setup, routing, and termination |
| Also used for | Voice calls specifically | Voice, video conferencing, messaging, media distribution |
| What connects to it | Softphones, mobile apps, WebRTC browsers | SIP-compatible IP phones, SIP accounts (Users) |
The simplest way to think about it: VoIP is the phone call itself, happening over the internet. SIP is the language two devices use to agree on how to start that call, keep it running, and end it. One is the "what," the other is the "how."
What Is a Protocol?
Before getting into the difference between VoIP and SIP, it helps to define "protocol," since that word shows up in both acronyms.
A protocol is a system of digital rules for exchanging messages within or between computers, smartphones, and other digital devices. Similar to how websites run on HTTP (Hypertext Transfer Protocol), a protocol is a well-defined format of syntax, semantics, and synchronization that lets different systems actually talk to each other.
Standardized protocols are what let different vendors build "endpoints" that can all communicate with each other, rather than everyone building incompatible systems in isolation.
IP telephony uses the Internet Protocol's packet-switched connections to move voice, fax, and other information that used to travel exclusively over the dedicated circuit-switched connections of the public switched telephone network (PSTN). Over the internet, calls travel as data packets on shared lines instead, skipping the tolls that came with the PSTN.
What Is VoIP?
Voice Over Internet Protocol is a broad term covering any phone communication that happens over the internet, as opposed to a traditional landline running on the PSTN.
Related: POTS vs VoIP: What's the Difference?
Terms often used interchangeably with VoIP include IP telephony, internet telephony, voice over broadband, broadband telephony, IP communications, and broadband phone service. They all point to the same underlying fact: the internet is the conduit carrying a digital voice signal to another phone or endpoint.
VoIP is really an umbrella term for a group of protocol technologies, both proprietary systems built by individual companies and open standards, of which SIP is the most widely adopted example, covered below.
VoIP is typically deployed alongside a mobile or browser-based app, through an Internet Telephony Service Provider like Telzio.
What Is SIP?
Session Initiation Protocol (SIP) is one of the specific protocols that makes VoIP possible.
While VoIP refers to the type of phone call, SIP refers to the protocol used to set that call up in the first place.
SIP is a communications protocol used for transmitting VoIP calls. It defines the messages sent between endpoints, and governs how a call gets established, terminated, and managed while it's happening.
SIP can connect just two endpoints, or many at once. Beyond voice, SIP also handles:
- Video conferencing
- Instant messaging
- Media distribution
- Other real-time applications
Related: Hosted PBX vs SIP Trunking: What's the Difference?
The IP phones you see in most offices are SIP-compatible phones, which is what enables them to make VoIP calls in the first place. IP phones are sometimes called VoIP phones or SIP phones, and a user's extension is often referred to as a SIP account. With a SIP account, a VoIP phone number connects to an IP phone to make calls. Setting that connection up used to require manually configuring each device, but Telzio's auto-provisioning handles it automatically, a phone just needs to be plugged in to register itself on the account.
That's exactly what made the difference for Matia Robotics, a Silicon Valley company building robotic mobility devices. "Telzio answered our need for a phone system. With Telzio's self-provisioning capabilities, we can manage everything in-house and haven't needed any IT or customer support at all," said Ayça Hacıkadiroğlu at the company. No telecom engineer required, just SIP devices that configure themselves.
At Telzio, SIP accounts are just called Users. By including unlimited users at no extra cost, Telzio offers genuinely disruptive, license-free pricing on business phone systems.
How VoIP and SIP Work Together
Now that SIP is the protocol and VoIP is the conduit, how do they actually work together?
VoIP encapsulates audio through a codec into data packets, transmits them across an IP network, and decodes them back into audio at the other end of the connection. VoIP endpoints include dedicated desktop VoIP phones, softphone apps running on computers and mobile devices, and WebRTC-enabled browsers, which is exactly how Telzio's Webphone works, no downloads, just a browser tab.
Over IP, those packets travel across the internet through nodes, the devices and routers along the path from source to destination.
That's a fundamentally different approach from traditional telephony, where a dedicated line or circuit between source and destination has to be reserved for the call, known as circuit switching, which is expensive to maintain. Packet switching instead uses existing shared networks, keeping overhead minimal.
This same infrastructure is also what's quietly powering most of the AI voice features showing up in business phone systems now. Telzio's Auto Attendant generates greetings from typed text and plays them back over the same SIP/VoIP connection as any other call, no separate system required.
So, Is VoIP vs SIP a Misnomer?
Not really, they're just two different layers of the same system. SIP is the industry-standard method for achieving VoIP. VoIP is the broader category, SIP is the specific protocol most providers, including Telzio, use to make it work.
Have more questions? Reach out to our team for straightforward, unbiased advice, or schedule a demo to see what Telzio's VoIP platform can do for your business.
