SIP Trunking Providers

An Introduction to SIP trunking

SIP (Session Initiation Protocol) is the protocol used by VoIP (Voice over Internet Telephony) systems to manage the VoIP phone calls. Because VoIP calls work differently from ordinary circuit-switched phone calls, different protocols are used to accomplish basic tasks such as establishing and terminating phone calls. SIP trunking is the method used when the VoIP network has to communicate with the Public Switched Telephone Network (PSTN).

If your VoIP system is used only internally, no SIP trunking is needed, because the PSTN is not a factor. But in reality, most VoIP installations are meant to seamlessly replace conventional telephony, and using it only for internal calls would not be taking full advantage of the power of VoIP. SIP trunking is what allows you to use your VoIP phone to make a phone call to someone outside of your enterprise, through the PSTN. You can think of SIP trunking as an adapter between VoIP and the PSTN.

SIP Trunking Service Basics

SIP trunking starts at the IP PBX. The PBX should include a trunking interface which is provided by the SIP provider. Although an IP PBX is preferred, an analog system can be used instead if an Integrated Access Device (IAD) is added. Through this interface, the PBX is attached to a firewall. The firewall must be one that supports SIP, to facilitate SIP traffic. Outside the firewall, the enterprise is then connected to the Internet via a VoIP service provider. On their end, the VoIP service provider will have an interface to the PSTN, although the enterprise need not be concerned with that. The end result is that the person using a VoIP phone is able to call any number, anywhere, whether it is on a VoIP service or not.

Ultimately, SIP trunking eliminates the need to deploy alternative technologies such as PSTN gateways or PRIs (Primary Rate Interfaces). In general, SIP trunking is a far less costly solution, highly efficient, and easier to manage, since fewer pieces of hardware are required. Since SIP trunks can be purchased incrementally, cost savings is increased compared to PRIs, which must be purchased by 23 channels at a time, but with option for unlimited SIP trunks.

If an enterprise is using a hosted VoIP solution, SIP trunking is unnecessary. Should an enterprise make the decision to use an on-premises VoIP solution, then SIP trunking should be considered.

Benefits of SIP Trunking Service

SIP trunking is the heart of what makes your VoIP system talk to the outside world, or the Public Switched Telephone Network (PSTN). There are alternatives, including using a hosted VoIP environment, and deploying PRIs (Primary Rate Interfaces), or of course, just using the Public Switched Telephone Network (PSTN) and not using VoIP at all. However, VoIP delivers so many advantages in terms of cost and extra features, many enterprises are finding it to be an essential component of their telecommunications environment. As such, SIP trunking is often a major consideration when an on-premises VoIP deployment is made.

When compared to a conventional analog circuit, SIP trunking affords the same level of quality at a much lower price per circuit. Further, when compared to PRIs, SIP trunking affords a similar price performance advantage. PRIs must be purchased in combinations of 23 channels, whereas SIP trunks are purchased incrementally, which gives the enterprise a great opportunity to purchase only as much as is needed. For more on SIP versus PRI check out this article.

Deploying SIP Trunking Service

When deploying SIP trunking, it is not necessary to purchase a SIP trunk channel from a SIP provider for every extension, rather, only enough to accommodate simultaneous calls. For example, if an enterprise has 100 telephone extensions, but at any given time only 25 people are on the phone, then only 25 SIP trunks are necessary to accommodate normal traffic. Some oversubscription to that figure would be a wise investment, but even with oversubscription, SIP trunking affords a much more efficient use of resources.

Scalability is also an issue with any telecommunications environment, and SIP trunking allows for easy additions. When additional extensions or higher phone traffic demand more trunks, they can be purchased incrementally, one at a time, on an as-needed basis. A PRI solution on the other hand, has a 23-channel incremental purchase requirement, which may mean that businesses would find themselves buying more channels than is really needed. Another comparative advantage between SIP trunking and a PRI solution is implementation time; a SIP provider may require as much as 30 days to provision PRI channels, and it requires an on-premises visit; whereas SIP trunking can usually be rolled out remotely within 24 hours with no truck roll required.

For more information on considerations for deploying SIP service check out our what is SIP trunking article.

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Author: Andy Forgrieve

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