VoIP and SIP both refer to internet telephony, but are technically different. VoIP describes the type of phone call (over internet), while SIP is the industry standard method used to enable VoIP calls between devices.
Communicating online in the 21st century doesn’t have to be complicated. With an alphabet soup of acronyms (VoIP, IP, SIP, ISDN, PSTN, IP, IP-PBX) — which sound as confusing as they are similar — certain telephony terms get misinterpreted and are used interchangeably. Such is the case with VoIP (Voice Over Internet Protocol) and SIP (Session Initiation Protocol) that sometimes are referred to interchangeably — even when they are technically different.
Before we can understand the difference between VoIP and SIP, it’s important to understand the meaning of ‘protocol’ since that term appears in both acronyms.
A protocol is a system of digital rules for message exchange within or between computers, smartphones and/or other digital devices.
Similar to how we find websites coded in HTTP [the Hypertext Transfer Protocol], protocols are well-defined formats of syntax, semantics, and synchronization used in order to be effective.
To be universally used, protocols have to be agreed upon by developers the world over. As such, they evolve into industry standards, making it easier for users to communicate with each other, without ‘reinventing the wheel’ again and again.
Standardized protocols make it easier for multiple vendors to create ‘endpoints,’ which allows for communication from device to device.
IP telephony (Internet Protocol telephony) uses Internet Protocol’s packet-switched connections to exchange voice, fax, and other forms of information that have traditionally been carried over the dedicated circuit-switched connections of the public switched telephone network (PSTN). Using the Internet, phone calls can now travel as packets of data on shared lines, avoiding the tolls of the PSTN.
Voice Over Internet Protocol is a broad term that covers any telephone communication over the Internet, as opposed to traditional landlines, otherwise known as the PSTN, noted above.
Terms used interchangeably with VoIP include IP telephony, Internet telephony, voice over broadband, broadband telephony, IP communications, and broadband phone service.
They all underscore the fact the Internet is the primary conduit to digitally transmit the voice signal to another telephone or endpoint.
This ubiquitous term covers a group of protocol technologies, including propitiatory ones like Skype Protocol and open standards, of which SIP is an example, discussed below.
VoIP is typically deployed in conjunction with a mobile or browser-based application, through an Internet Telephony Service Provider (ITSP).
Session Initiation Protocol (SIP) is one of the specific protocols that enable VoIP.
While VoIP refers to the type of phone call, SIP refers to the protocol used for setting up those calls.
SIP is a communications protocol that is used for transmitting VoIP calls. In so doing, it defines the messages, which are sent between endpoints and it governs establishment, termination and other essential elements of a phone call.
SIP can be used to transmit information between just two endpoints or many. In addition to voice, SIP can be used for video conferencing, instant messaging, media distribution and other applications.
The IP phones you see in offices and businesses are SIP-compatible phones, enabling you to make VoIP calls. IP phones are sometimes also referred to as VoIP phones or SIP phones, and user extensions often referred to as SIP accounts. With a SIP account, you can connect your VoIP phone number to an IP phone to make calls.
At Telzio, we simply refer to SIP accounts as Users.
By including unlimited users with all phone numbers, Telzio offers truly disruptive, license-free pricing on business phone systems.
The Workings of VoIP with SIP
Now that we know SIP is the protocol and VoIP is the conduit, how do they work?
VoIP actually encapsulates audio via a codec into data packets, and then transmits them across an IP network, where it unencapsulates them back into audio at the other end of the connection. VoIP endpoints include dedicated desktop VoIP phones, softphone applications running on PCs and mobile devices such as smartphones, and WebRTC-enabled browsers.
In the IP protocol, the IP packets travel over the Internet through nodes, which are devices and routers found on the way from the source to the destination.
This differs from traditional telephony where a line or circuit between the source and destination has to be dedicated and reserved (called circuit switching), which is cost-heavy. Packet switching, on the other hand uses existing networks for free, allowing users a service with minimal overhead.
Acronym Soup Solved?
Hopefully we’ve made some distinctions today that clear up the differentiation between VoIP and SIP. As you can see there is really no such thing as SIP vs VoIP.
SIP is the industry standard method of achieving VoIP.
Quick VoIP Terminology from A to Z will provide you with a quick and easy primer to understanding other commonly used terms related to your VoIP phone system.
Ron is part of the marketing team at Telzio, covering everything from tips and tech for growing businesses to customer success stories for the Telzio blog. Previously a Director of Advertising and Public Relations at Marriott International, Ron has published several books including the award-winning graphic novel Facebucks.