Everything you need to know about SIP

You will have heard the term ‘SIP’ and perhaps wondered what it means and why it’s important. Frankly, if you are an everyday user of hosted VoIP services you don’t really need to know about SIP – which stands for Session Initiation Protocol – and SIP trunking.

But if you are part of a large organisation that needs to make to take scores or even hundreds of calls at the same time, have multiple locations, or you know that you’ll also need to connect directly to numbers that are running on analogue telephone networks, then you will need to at least have a working understanding of SIP trunking. And to do that, you really need to understand what SIP is and where it fits in.

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What is SIP?

SIP is a text-based protocol that is used by two or more systems to start, manage, and end a voice or multimedia connection. It can be used to set-up a simple person-to-person call, or calls involving several people. In other words, it’s the set of rules that are used at either end of the connection to make a voice call happen.

SIP is also be used to establish multimedia connections – that carry not only voice, but video and instant messages, for example. All these kinds of communication can be run over a single SIP connection.

SIP is commonly used as a core element of unified communications solutions. That said, don’t assume that all modern collaboration tools use SIP – they don’t need to as the connections are made directly over the Internet and many chose to use their own initiation methods. However, most do now support SIP as well. You have been able to use SIP handsets with Zoom for some time and Microsoft Teams was expected to start offering support popular SIP handsets from the first half of 2021.

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What’s the difference between VoIP and SIP?

Where a simple VoIP connection just establishes a links between two points on the Internet for a voice call, SIP can be used to connect other networks, so it would allow you to dial out to an old PBX line, for example, or to route incoming calls from analogue line to your VoIP phone. Whereas a VoIP call will always be between two (or more) computers or handsets that are connected to the Internet, you don’t necessarily need a PC or digital device to establish and run a SIP connection.

SIP was created at a time when there was a need to create a bridge between the old analogue and new digital voice worlds to allow connections between phones connected to the two different types of networks, rather than making the two mutually exclusive.

As digital voice was the newcomer, there was more of a need for the Internet world to make this happen. SIP was created by the new digital voice providers and as such it has developed as an Internet standard rather than one governed by the telecommunications authorities. It is governed and managed by the Internet Engineering Task Force (IETF) and while it is a recognised protocol in its own right, it actually makes use of a set of other protocols, operating at the application layer of the Open Standards Interconnect (OSI) standards model. You can think of SIP is a kind of unifying or umbrella protocol that makes use of other established rules to allow multimedia connections to be established, managed, and ended.

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SIP and SIP Trunking – what’s the difference?

SIP and SIP Trunking are not really anything to do with each other in practical terms. SIP is just a protocol for connecting calls; SIP Trunking is a way of putting multiple calls across digital connections and, if necessary, switching them over to be carried on other types of networks, although the latter is becoming less important as every business switches over to VoIP.  Prior to VoIP taking over much of the telephony world, a company would have used SIP trunking to switch calls made from existing analogue lines over to the Internet, thus reducing costs.

Of course, SIP trunking does use SIP to establish connections; essentially, SIP is a core technology that makes it possible to deliver digital voice services; SIP trunking is an actual, deliverable service.

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What is SIP Trunking?

You can think of a SIP trunk as a kind of backbone for all the digital connections you make to carry voice calls – and video and IM connections, if that’s what you need to do. It’s really a way of providing additional and reserved bandwidth for higher volumes of digital voice calls.

But you might need a SIP trunk service if you run scores or even hundreds of VoIP lines, as it would basically, reserve an amount of bandwidth for you and ensure that you would have the capacity to manage multiple incoming and outgoing VoIP calls. In such situations, having a SIP trunk is likely to be a more cost-effective option.

It is also a good option for business that have multiple locations and want to make it easier for staff to make ‘internal’ calls and for calls to be re-routed from one location to another. A direct connection over a SIP trunk will also be more secure than a standard VoIP call, which will be an important consideration for many organisations. You will also be able to apply additional security measures with a SIP trunk.

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SIP and SIP trunk suppliers

There is not really any such thing as a ‘SIP supplier’ as SIP is not ‘owned’ by anyone; it’s an industry standard protocol or set of rules that are used to establish, manage, and terminate voice and multimedia connections.

SIP trunks, however, can be and are offered as a ‘product’ or ‘service’. They are available from most established VoIP suppliers, who will be able to offer you a range of options, features, and cost models to support multiple digital voice connections and locations.

SIP trunking services are very scalable and secure and may provide you with significant cost-savings on simply using standard VoIP service for multiple users. As you would when choosing any business service, you need to examine your specific needs and make a decision that meets future as well as current requirements.

You would be best recommended to turn to recognised and reputable suppliers of VoIP services with a good track record when carrying out initial research into SIP trunking services.

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