The term SIP (Session Initiation Protocol) is slowly becoming more main stream. Mainly recognized in business context, it can be described in the most basic of terms, internet phone service for businesses. VoIP (Voice over Internet Protocol) is what makes internet phone calling possible and has grown in leaps and bounds with the likes of Majic Jack, SKYPE and Vonage to name a few.
SIP however is used to connect internet phone trunks to an end?s user PBX system using a set of specific protocols which are compatible with the phone system they are using. Many phone systems connect both to analog or SIP, but some are designed only for SIP, such as the Microsoft SIP trunking solution. In which case you would look for Microsoft Lync Most VoIP providers are hosted solutions while SIP can be on-premise.
Call Paths vs. Phone Lines
SIP providers charge based on the number of trunks while others will pay for usage with a cap on trunks. Each trunk can carry one call path, which means only 1 person can be making a call. However supposing there are 15 employees, this does not mean you need 15 trunks. If it were a plain old telephone service (POTS), then yes you would need 15 lines for the business.
However, with SIP trunks, you want to calculate the needs of the business in regards to call paths. How many people do you think will be on their phones at the same time? If you are an outbound call center, then the answer is obvious ? 15. However for a lawyer?s office the answer might be 7, in this case you would only need to order 7 trunks.
The second consideration for SIP growth is bandwidth capabilities. In the case of internet phone service, the greater the bandwidth, the better the call quality a user will experience. For example a G711 codec allows 80-85k per call path which means there is less jitter, dropped calls, and overall better clarity of voice. With a G729 however, there is less bandwidth allotted per call and that is no good.
Think of it in terms of mono and stereo, mono works fine, but isn?t nearly the same as stereo ? but stereo tracks mean larger files and that means larger space. If you don?t have enough space, you can?t use stereo. For people with restricted bandwidth, the G729 is what would be used allocating only 30-35k per call path less quality but the user will experience fewer issues too.
SIP trunks began gaining notoriety in the 90?s and more and more businesses have been able to jump on board migrating away from their POTS or even PRI?s (1 PRI allows for 24 lines) and began seeing the return on investment though ongoing savings. Users of SIP can save anywhere from 30% to 70% on their telephony expenses.
Additional advantages of SIP which influence popularity
Mobility: With a SIP based system, users can configure calls to ring to different places based on configuration settings. For example, if a client rings your office phone and no one answers, it can roll forward to any specified device such as a cell phone, home office, or another person in your department.
Easy Growth: As the company expands with new employees or employee turnover, SIP allows users to be easily added through the phone system, without having to install additional lines. You can add extensions as well where a business does not have to order direct dial numbers.
This means if you have someone who needs a phone, but not their own dedicated number, you can add them as an extension like x103. This saves a business company as direct inward dial (aka DID) numbers, can cause the monthly charges to add up. Although it is mainly the role of the phone system to input the configuration settings, it would not work if the sip trunking provider wasn?t capable of making it actually happen.
Virtual Numbers: Another advantage SIP has over traditional telephone lines is the ability to use a number with any area code. So if your business resides in Washington DC, but you want to run a marketing campaign in California advertising a 626 area code, you an order a 626 number and have it ring to your location?s IP address.
This is impossible to do with traditional phone service because the lines are physical, not virtual, however with VoIP or SIP it is one of the big advantages a company can benefit from ? especially those who want consistent numbers with the same area code for their telecommuting employees.
Traditional phone service is not going away anytime soon, however with the rise in SIP deployments for businesses large and small, it is getting a run for its money. Expect to see more internet phone usage over the next few years as more and more carriers and wholesale providers jump on board and invest in developing more advanced technologies.