SIP vs. VoIP – What’s the Difference?

Although SIP and VoIP Support IP Telephony, They are Not the Same Thing

What's the difference between SIP and VoIP?
SIP is a specific protocol that enables VoIP.

Every search for the right communications solution for business seems to come complete with a side of alphabet soup these days.  IP-PBX, PSTN, PRI, VoIP, SIP, ISDN – it’s no wonder buyers can become confused.  To make matters worse, those in the industry tend to use some terms interchangeably, even when they have very different technical meanings that matter.  VoIP and SIP are good examples, although they accomplish the same goal of connecting calls via the Internet, they are not the same thing.  So, let’s explore the differences between VoIP and SIP.

VoIP Defined

The term VoIP stands for Voice Over Internet Protocol.  It is a broad term that covers any phone calls made over the Internet, as opposed to traditional telephone lines, otherwise known as the PSTN (Public Switched Telephone Network). Other terms that are used interchangeably with VoIP include, IP telephony, Internet telephony, voice over broadband, broadband telephony, IP communications, and broadband phone service. They all describe the fact that the Internet is used to digitally transmit the voice signal to another telephone or endpoint.

The term encompasses a group of protocol technologies, including propitiatory ones like Skype Protocol and open standards, of which SIP is an example.  VoIP is typically deployed in conjunction with an application, such as Skype or Google Talk, with IP enabled PBX hardware or via a hosted VoIP service.

The Importance of Protocol

A protocol is a system of digital rules for message exchange within or between computers, phones or other digital devices. In order for one device to communicate with another, developers must use well-defined formats for exchanging messages. A protocol defines the syntax, semantics, and synchronization of communication. In order to be effective protocols have to be agreed upon and used by the developers of each connected device or application (often called endpoints).  For this reason, protocols tend to evolve into industry standards, making it easy for multiple vendors to create endpoints that can communicate with each other.

Understanding SIP

Session Initiation Protocol (SIP) is a communications protocol that is widely used for managing multimedia communication sessions such as voice and video calls.  SIP, therefore is one of the specific protocols that enable VoIP.   It defines the messages that are sent between endpoints and it governs establishment, termination and other essential elements of a 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.  SIP has been developed and standardized under the auspices of the Internet Engineering Task Force (IETF).

Deployment Examples

When most people hear the term VoIP, they imagine a hosted VoIP solution where the vendor hosts and operates the PBX functionality that manages call handling, voicemail and other applications.  The customer’s IP enabled phones connect to the Internet and ultimately to the vendor’s servers and software.  This, however is just one type of VoIP deployment.

SIP trunking delivers telephone services and unified communications to customers with SIP-enabled PBX and unified communications solutions.  In this case, call management, voicemail, auto attendants and other services are provided by the PBX.  The SIP trunks provide the connection between the PBX and the public telephone network, replacing the need for legacy telephone lines or PRIs (Primary Rate Interface).  This gives businesses the ability to select the IP-PBX hardware and software that works best for them, while freeing them from the expense and inflexibility of traditional phone lines and carrier relationships.

So there really is no such thing as SIP vs. VoIP.  SIP is an industry standard method of achieving VoIP.  Businesses looking to improve their communications and reduce cost by moving to VoIP should carefully consider each of the ways it can be deployed, including SIP trunking, and select the one that provides the greatest benefit for them.