How A SIP Trunk Works

Organizations looking to upgrade their voice communication systems are quickly inundated with a barrage of technical terms, jargon and buzzwords. It is often difficult to distinguish between genuine product/service differentiation and what is just a marketing term. But for any company to realize the many advantages of VoIP, an understanding of the underlying technology and implementation practices will be immensely helpful.

Anyone who has started looking into the field will come across to phrases – hosted VoIP and SIP trunks. Both these configurations are used to deliver VoIP services to enterprises but the difference lies in the method of delivery. With hosted VoIP, all the equipment is owned operated and maintained by the external service vendor and the various phone services are delivered over the Internet for the company. SIP trunks are slightly different and come in many configurations.

What does SIP trunk mean?

To those working in the daily communication field, a trunk or trunking is a pretty familiar word. It is simply a physical connection between the switching equipment located in two places – the business and the phone operator. It is a dedicated circuit that allows concurrent calls to be placed, depending on the number of channels.

An SIP trunk is also connection between the client and the ITSP but this connection is IP-based, rather than being physical. With SIP trunks, companies are able to extend VoIP calls beyond the enterprise firewall. Normally this would require a PSTN gateway but utilizing SIP trunking eliminates that requirement. So instead of routing voice calls over dedicated TDM circuits, SIP trunks do so over data networks including the public Internet.

How a SIP trunk works

As the term itself hints, SIP trunks utilize the Session Initiation Protocol which is an IETF standard that dictates how VoIP sessions are initiated, handled and terminated. While there are other proprietary protocols available, SIP has become the most commonly utilized and implemented format. The benefit of using it is that most equipment and hardware that you purchase will be interoperable as long as it is compatible with SIP.

When a phone call is made over an SIP trunk, it may originate as an IP call or be converted into one at some point. This point maybe an ATA adapter, the IP PBX itself or even a SIP compatible router. Once it becomes an IP call, it is transmitted over the data network to the ITSP office and then on to its destination. The last leg of the journey may be over the PSTN which necessitates the payment of termination charges. Quite a few calls never land on the PSTN at any point which is how service providers are able to offer free calls and inexpensive international calling.

How is SIP trunking useful?

In many organizations, SIP trunking powers more than just voice calls through VoIP. It is also the basis for unified communication systems since SIP trunks can carry instant messages, different types of media including video and many other types of real-time communication services. SIP trunks can convey user presence information and offer an alternative to emergency dialing referred to as E911.

SIP trunks bring enterprise class communication within the reach of smaller organizations which previously could not afford dedicated, leased lines for their business. SIP trunks are easier to design, operate, develop and upgrade since it uses packet switching technology. It allows providers to deliver these services at low costs, which is a boon for businesses which have large call volumes.

From a business perspective, it allows consolidation of two different networks – voice and data into a single one. This reduces maintenance costs as well as the time spent in troubleshooting and bug fixing. If and when something was wrong, the company does not have to deal with multiple vendors and points of failure. SIP trunks and VoIP are also more suitable for modern business processes and offered a much wider range of communication services than traditional carriers.

Should you go for SIP trunks?

Whether or not SIP trunks are suitable for your business depends on a number of variables. The business requirements, external environment and even the comfort level of employees with new technology can influence the decision. Switching to VoIP does not require employees to relearn processes such as making or receiving calls but they will have to become familiar with the workflows/procedures for utilizing advanced features including visual voicemail, digital faxing etc.

In some cases, industry regulation and legislation can have an impact as well. Various nations around the world have different levels of VoIP adoption, legal frameworks and broadband penetration. So even if your business switches to SIP trunks, offices in certain regions may have to stick with PSTN services for security, privacy and legislative reasons.

Since on premise SIP trunking requires considerable investment, some organizations may choose to go with hosted VoIP as a sort of demo or trial before committing to the new technology. Larger organizations that have in-house expertise and personnel who can deploy the new systems will generally prefer to go with SIP trunks, as it is cheaper than hosted VoIP over the long-term.

If you do chose to go with SIP trunking, the choice of SIP trunk provider will greatly influence your experience with VoIP. Other than the price of the offered services, the portfolio, customer and technical support as well as the experience of the vendor are all aspects to be considered. SIP trunks enable companies to be agile, flexible and scale according to their needs, so it is no wonder its adoption is growing exponentially.