SIP Trunking Providers

SIP (Session Initiation Protocol) is the protocol used by VoIP (Voice over Internet Protocol) systems to manage VoIP phone calls. Because these 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 providers offer a cheaper alternative to the Public Switched Telephone Network (PSTN), by instead routing calls to the outside world over SIP trunks.

To put it in basic terms, if you are running an on-premise PBX that is currently using the PSTN for external phone calls, there is a large saving opportunity by switching to a SIP trunking solution. To evaluate the cost savings, be prepared to answer these three questions:

1. How many concurrent calls does your company typically need?
2. How many phone numbers does your company need?
3. Is your existing PBX IP enabled? (Common IP enabled makes: Asterisk, 3CX, Cisco Callmanager, Allworks & Shoretel)

If your VoIP system is used only internally, no 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 trunks are 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 it as an adapter between VoIP and the PSTN.

Be Prepared to Answer These Important Questions

The first major point to be aware of is that not all 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. As we introduced above, there are 3 main questions that any competent service provider will ask. We expand on these below.

What is the maximum number of concurrent 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 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 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.

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

If you've already upgraded to an IP-PBX, a 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 service provider has their own mostly-unique take on the technology, so be prepared to give your IP-PBX's make and model number to the provider to verify interoperability.

If you're still using a legacy PBX, it is still an option. However, many of the features, 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 service, but you'll probably want to upgrade to an IP-PBX and IP phones as your current equipment needs replacing.

Other Questions to Consider

How much bandwidth will you need?

This answer starts with knowing the answer to the previous questions. 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 making teh switch over.

What do you want from your SIP trunking provider?

There is tremendous variety in service 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?

IP telephony in general has one major weakness: faxes. Every service provider has their own solution to this dilemma, ranging from "don't use them" to very elaborate Integrated Access Devices (IADs) 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. Alternatively, consider moving to an Internet Fax Service and say goodbye to that old fax machine!

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 Authorized sources :
www.google.com
www.voip-info.org/
http://whichvoip.com/
www.wikipedia.org