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Acronym Explosion: SIP Trunk FAQ

What is the big deal about SIP trunking? 

I get asked this a lot, especially after I have fallen down the acronym rabbit hole in a meeting with a customer and name-dropped ‘SIP trunks’ ten times in five minutes. I can usually tell that SIP has not become a household name yet by the blank look on everyone’s face.

The big deal is that phone lines will be dead soon. No, really. SIP is the future, and to sweeten the deal, SIP is cheaper than traditional phone lines. If you take away nothing else from this post, know that in the long run, you don’t have a ton of choice in the matter so dry your tears with your savings.

What is SIP?

SIP is Session Initiation Protocol, an open standard for transmitting media over the internet, including voice, but extensible to video, chat, and more. You can think of it as a common language devices from different manufacturers and developers use to get their products to talk to each other. Your phone system has to be new and hip enough to speak SIP to use SIP trunks.

What is a SIP trunk?

Think of it as an internet phone line (and we use “line” very loosely). It is actually termed a ‘call path’ that runs over an internet connection. Each call path supports one telephone call between two parties. Like a phone line, you pay a monthly fee per ‘line’.

So does a SIP trunk work different from a phone line?

Yes. For you geeks out there, its a different Layer 1 connection. For non-geeks, it is a different physical connection. Telephone lines connect to specialized FXO ports on a phone system. SIP Trunks are 1’s and 0’s inside an internet connection.

Phone numbers work different too with SIP. Traditional phone lines all have an individual phone number assigned that gets put in rotary or hunt around your main number. If your main line is busy, the second call goes to line 2, and a third call goes to line 3, and so on. With SIP, you don’t have a physical line that needs a phone number to be identified by ancient telephone company equipment. If you have 5 call paths, you can take 5 calls off the same number. You can also assign as many phone numbers as you can afford to your call paths, and the numbers do not have to match up. So, for example, you can have 10 call paths and 100 phone numbers that ring your office.

If you are used to ‘grabbing the call on line 2’ you will need to adjust how you use the phones a bit with SIP trunks – calls will hold on your extension, or be parked. It is a small change in behavior requiring a minimal amount of training, but old habits can die hard.

Can I keep my phone number if I get SIP trunks?

Yes. Keeping your numbers is the law unless you are renting space on someone else’s phone system and they are paying your phone bill.

What’s the catch?

Three catches. First, if your internet goes down, down goes your phone calls, unless you program in a backup, have a call forward option planned, or, as most business do these days, you have a second internet connection at the office. A backup DSL or cable connection is under $100/mo, and we urge companies to consider it, if only for SIP trunks. You will likely still save money.

Second, if your network is a mess, your calls will sound bad. Make sure you run a diagnostic test before going down this road and get your network certified for VoIP first. If your network has a lot of trouble, I would recommend not putting more strain on your network by moving to end-to-end VoIP. Similarly, if smoke is pouring out your car, don’t take it drag racing.

Third, you need enough bandwidth for phone calls. We recommend 100kbps upload and download per SIP call path. If you have a 5Mb DSL connection with 768kbps upload, do not get SIP trunks. If your internet is up and down all the time, do not get SIP trunks. If you are doing a ton of uploading and downloading and you have no spare bandwidth, consider a dedicated internet connection for your SIP trunks if you can’t throttle your internet traffic back to make room for voice calls.

How much can I save?

I’ve seen SIP trunks as cheap as $5 per line from reputable companies, and $25 per line if you want unlimited calling. Per minute charges are typically in the 1-2c per minute range for domestic calls. Locally in Los Angeles, we see phone lines starting to cost as much as $50 per line. The Public Utility Commission now allows AT&T and Verizon to set their own rates and prices have gone up every year since.

Anything other cool SIP trunk trick?

Glad you asked. Burstable SIP trunks allow you to pay a low fixed monthly in return for the ability to call huge numbers of people in a pinch – to send out ‘bursts’ of calls. This is perfect for seasonal businesses, emergency response systems, and businesses that have cyclical calling patterns with spikes in usage. With phone lines and PRIs, you have to rent circuits at your maximum capacity – with SIP you buy what you need.

Also, SIP carriers can get you numbers from anywhere – even other countries (though not all other countries) – without the onerous charges from traditional phone carriers.

My sales rep said my system supports SIP trunks – which trunks should I get?

Look for SIP validation first – see which carriers have tested their products on your system and can certify they work on your phone system. You should know better than to trust a sales rep – ask for a link or document showing which carriers work with your system. Most manufacturers test SIP carrier connections to make sure they work and require certification to get tech support on those connections.

Wait, wait, wait. Does that mean some carriers don’t work on my system?

The short answer is ‘kinda – buyer beware’ but the better answer is that if your carrier is not validated on your phone system, it can be time consuming to connect the two with no guarantee of success and very little support from the big companies involved. It will most likely be your phone vendor, your IT person and unsympathetic tech support folks hashing out a solution on your dime. Sometimes it takes minutes, and sometimes we are coming back day after day until it works.

Does my phone system support SIP trunks?

Our products from Mitel and Zultys are SIP compatible and validated on a whole slew of carriers.

I would argue that the Zultys SIP connection is bar none the best in the industry. Zultys is SIP at the core and can connect to SIP trunks without even a license. The Zultys premise-based products feature a built-in firewall and dual network connections, one on the scary Wild West of the WAN side and one on the trusted LAN side, so as to be able to connect to internet phone lines without jeopardizing your network’s integrity. So whether you buy the MX250, MXSE or MXvirtual, SIP integration is pretty easy and safe.

Mitel systems rightfully don’t trust the internet either. For SIP trunking, we deploy the Mitel Border Gateway to authenticate and encrypt SIP communications and off-site telephones. This provides the rock solid security that is a hallmark of Mitel engineering. Similar to the Zultys architecture, the Border Gateway will have one WAN and one LAN connection. The Border Gateway allows you to integrate the MiVoice Business and MiVoice Office 250 (the systems formerly known as the Mitel 3300 and Mitel 5000, respectively) with SIP trunks safely.

If you have an older system, we can use a SIP Gateway that converts SIP into an analog (phone line) or digital (T1 and PRI) signal. From an engineering standpoint, it isn’t ideal to introduce complexity and a point of failure, but sometimes the trade-off in savings and flexibility is worth it.

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