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What Is session initiation protocol (SIP)?


June 6, 2019


December 8, 2021


SIP trunking is one of our favorite subjects at Bandwidth. And while it’s a term that’s taking over the market place, “what is Session Initiation Protocol?” is still a fairly common question.

First, let’s make it clear that SIP trunking and Session Initiation Protocol aren’t the same thing. SIP trunking is a relatively complex system and something we’ve written about before, so take a look at our guide to SIP trunking if you’re interested in the bigger picture.

All you need to know for now is that instead of calls being carried across potentially thousands of miles of copper wiring to get to their destination as they do on the plain old telephone system, SIP allows voice traffic to be carried over data networks, including the internet.

So then, what is the Session Initiation Protocol (SIP)?

Session Initiation Protocol is simply a bunch of codecs (set of rules) that dictate how the packets of data that carry the sound of your voice travel through the data network of your choice.

There are lots of different protocols out there with lots of different codecs. And at every point on the data network that your voice data has to go through, they need to be able to communicate using the same codec.

Think of it like the children’s game of telephone, where you need to get a message across a line of people to the person on the end. If somewhere along the line of people someone speaks a different language to everyone else, it would be impossible to move past that person; the points on the network wouldn’t be able to communicate using the same set of rules (language).

What different Codecs are part of SIP?

G.711 – A codec that was introduced by ITU in 1972 for use in digital telephony.
G.729 – A codec with low bandwidth requirements and good audio quality.
G.723.1 – The result of a competition that ITU announced with the aim to design a codec that would allow calls with 28.8 and 33 kbit/s modems.
GSM 06.10 – A codec designed for mobile networks.
All of these codecs are available in a SIP trunk and so if a phone system is ‘SIP-enabled’ you can transfer your call using these sets of rules.

What does that mean for your business? Well, as SIP trunking has now become one of the main methods of transferring voice data across the world, if you have a SIP-enabled phone system in your building, you have the capability to potentially call anyone that your network allows.

At Bandwidth, we’ve got phone numbers in the countries you want to do business, thanks to our global network and VoIP infrastructure, with direct PSTN connections in 60+ countries covering more than 90% of the world’s economy.

Visit our Global Network page to learn more about how we connect businesses around the world and to see where we have coverage.