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What is SIP trunking? | WhichVoIP

What is SIP trunking?

Session Initiation Protocol Trunking, or SIP trunking, is a relatively simple way of modifying your business' Private Branch Exchange (PBX) box and giving it the ability to make Voice over Internet Protocol (VoIP) phone calls. SIP trunking is similar to an at-home VoIP service like Vonage™ or Magic Jack™, SIP trunking allows you to 'overlay' your data connection to the Internet with a voice connection that acts simultaneously with the data connection.

The major advantage to SIP trunking is that it eliminates the need for Public Switched Telephone Network (PSTN) connections -- traditionally referred to as "phone lines" -- from the standard array of phone companies. By skipping out on the PSTN, you also skip out on the standard connection and per-minute fees charged by the phone companies.

The first major point to be aware of is that not all SIP trunking services are identical -- providers package (and price) their services quite differently, and the entire technology is just new enough that there is not yet a general industry standard. That means that each provider will have their own technical methodology, their own standard and optional services, and their own ideas of what your business can benefit from. Here are a list of questions that any competent SIP trunking service will ask you before making a decision on how to proceed with your installation:

What is the maximum number of calls (incoming plus outgoing) that you need to support?

This number could be limited by the PBX you have installed at your place of business, but it's more likely to be soft-capped by the size of your business in general. The amount of money you save with SIP trunking will be moderate if you need only 20 simultaneous calls -- but it will be much greater if you need to support 25. That's because your typical dedicated PSTN T1 voice line supports exactly 23 simultaneous calls -- break that hard limit, and you need to pay for a second T1 line; doubling your base expense. SIP trunking doesn't have that 'quantum leap' effect -- you pay for exactly the number of connections you need, no more or less, and you can expand the cap as your business grows.

Sidenote: Many modern PBXs have powerful features that might cause you to underestimate the number of phone lines you need. For example, the FindMe/FollowMe feature of your PBX might take an incoming call and simultaneously forward it to your cellphone, home phone, and off-site business phone -- using four connections (one incoming and three outgoing) at the same time. Obviously, if this should happen to multiple workers at once (say, the boss sends out a voice blast to his entire department at once), the effect can be profound.

How much bandwidth will you need?

This answer starts with knowing the answer to the previous question. SIP calls use your Internet connection, so you need to add your current maximum Internet bandwidth use (you can find out with a quick call to your ISP), plus enough to support the maximum number of simultaneous calls you have to support. There are quite a few factors that go into how much bandwidth each call will require, but you can generally estimate 92 Kbps each and be very safe. If you have a high call volume business, you might want to ask your ISP if they have a service that can dynamically allocate bandwidth, but either way, if you don't already have a lot of excess bandwidth going unused, you can expect to need to upgrade your bandwidth when you switch to SIP trunking for your phone service.

Business SIP Trunking Service

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Do you have an IP-PBX or a standard PBX?

If you've already upgraded to an IP-PBX, an SIP trunking service can connect directly to your PBX -- provided the two are interoperable; remember that there are not a lot of industry standards in this area as of yet. Each IP-PBX manufacturer and SIP trunking provider has their own mostly-unique take on the technology, so be prepared to give your IP-PBX's make and model number to your SIP trunking provider.

If you're still using a legacy PBX, SIP trunking is still an option. Many of the features that SIP trunking can support, particularly of the Unified Communications variety, won't work. You'll still get to make free phone calls and some of the Web-based features of your SIP trunking service, and you won't have to purchase any new equipment yet -- but you'll probably want to upgrade to an IP-PBX and IP phones as your current equipment needs replacing.

What do you want from your SIP trunking provider?

There is tremendous variety in SIP trunking providers today. Some may offer you an Internet connection, acting as both ISP and SIP provider. Some provide expansive call-quality and/or equipment-reliability guarantees. Some give you powerful diagnostic tools to help you address any call-quality issues on your own. You probably won't find it all under one roof, so deciding what your dealbreakers are ahead of time is critical.

Do you rely on faxes?

SIP trunking -- and IP telephony in general -- has one major weakness: faxes. Every SIP trunking provider has their own solution to this dilemma, ranging from "don't use them" to very elaborate Integrated Access Devices that they install on your premises with analog ports that can support fax machines. In many cases, it's actually wise to keep a single traditional PSTN line in order to run faxes and make emergency calls if for some reason your power goes out or your Internet connection is otherwise unavailable.

How many incoming phone numbers do you need?

Incoming phone numbers can be very useful to a business of any size -- for example, do you want each employee to have their own phone number? Or do you want to separate sales promotions by phone number so you can easily judge which are the most productive? Keep in mind that many companies only offers incoming phone lines that are locally available -- for example, you can only call into them from a specific city. This can be both a boon and a bane, for while your customers can only reach you from their homes on your local city line, if you purchase a line localized to another city, you can give your customers there the impression that you have a presence in their cities.

Submit a SIP Trunking VoIP quote request today for your business and save up to 80% on your monthly phone bills.

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