Choosing Your New Phone System: PRI vs. SIP; Cloud vs. On-Premises

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Dec 7, 2018 by Russ Telford

When considering a new VOIP phone system for your office, among all the discussions surrounding requirements, usage cases and call flows, the question of how you get dial tone and how you host your system will come up. Depending on who you’re having this conversation with, you may find yourself a bit overwhelmed. Relax. It’s normal. Take a deep breath … that’s good … let it out … there we go. Now let’s discuss your options, their pros and cons, and maybe demystify some things.

No matter what phone system type you choose, you need to get your calls into it and out of your system. Some come with their own connectivity, some are bring-your-own-dial-tone. If you go with a phone system provided by your telco, they will usually take care of that connectivity for you. However, most telecom providers have the ability to provide that connectivity to any phone system you decide to go with.

Primary Rate Interface (PRI)

A PRI is a T-1 line supporting 23 voice channels, meaning it will support up to 23 concurrent calls. The telco brings in the PRI as a physical cable, and as such, if you want to add more lines than 23 they have to run another physical cable. A major benefit to having a PRI is that there is zero dependency on your internet bandwidth. It also allows for a high-quality voice experience, and if you add a second PRI, can be set up for circuit failover. Unfortunately, as this is a physical cable, there’s going to be some drawbacks. If you want to add lines, the telco has to physically run another PRI and will also have to implement changes on their side to support the additional PRI, so making changes may take longer.

There are a lot of folks out there still using PRI, and a lot of folks getting new PRIs installed. It’s not a bad technology but it can be cumbersome. I’ve also seen quite a few organizations who maintain their old PRI even after moving to a SIP trunk because it makes a great failover connection.

Session Initiation Protocol (SIP) Trunking

So now we’ve got PRI out of the way, lets move to SIP trunking. SIP is a set of standards for establishing calls between a voice over IP (VOIP) line and another phone number such as your cell phone or that old rotary dial at your grandparents’ house. A SIP trunk is how we refer to the connection that the SIP is being delivered over.

This can be a breakout to a Session Border Controller (SBC) from your telco or can be SIP over the Internet where the provider just points at your public IP and you set up your SBC to communicate. Concurrent sessions are generally provisioned on an as-needed basis, one line at a time, so if you’ve currently got it set up for 20 concurrent calls but you know you’ve got that big all-hands meeting coming up next weekend, you can bump it up to 25, 30, heck, go crazy, 50 concurrent calls, and then drop it back to 20 when everyone’s cleared out again. The max number of concurrent calls you can possibly have will be dictated by your SBC or PBX at this point.

SIP tends to be quite a bit less expensive than PRI. It is extremely flexible in that you can add call paths as needed. It allows for more than just voice, such as video. Yet, just as I have you thinking it’s all sunshine and unicorns with SIP, there are still considerations. SIP uses internet bandwidth. If you’ve got a five megabyte down / two megabyte up internet connection, your Quality of Service is going to be very poor. As such, you’ll want to have a high bandwidth reliable pipe to the internet.

You’ll also need to be concerned about toll fraud. I’m here to tell you that it’s real and it happens. Trust me, you don’t want to get that call from your carrier on a Monday morning saying they’ve shut down your international calling on your primary trunk because of suspicious calls to the Dominican Republic. This means that you will need to implement additional data security measures that you don’t have to worry about with a physical line such as a PRI.

Choosing Between SIP or PRI

When clients ask us to upgrade their phone system, we always begin with your dial tone delivery.

As we said before, if you have a single PRI, you’re capped at 23 concurrent calls. If you have a problem that sometimes you can’t dial out and people have stated that sometimes they can’t call in, your limited PRI could be the culprit. Your options are to have a second PRI installed (which may give you sticker shock) or you can switch to SIP. There’s a bit more flexibility and it costs less. As long as you’re okay with an internet-based dial tone or have a redundancy plan, SIP might be a great option.

Then, your dial tone delivery mechanism influences the rest of your phone system roll out.

Cloud vs On-Premises Phone System

You’ve got some different phone system options: cloud based and on-premises. Both have similar feature sets, so let’s just discuss the SIP trunking. Cloud-based phone systems usually provide their own SIP service. You port your numbers to them and you pay a monthly fee based on usage. The associated cost varies from one vendor to the next. Benefits? Oh yeah. If your building burns down, you can set up next day from nearly anywhere with an internet connection. Yes, really. Seriously. It’s an Internet-based PBX, so you can technically receive calls while you’re at the beach, McDonald’s, or even Starbucks.

An on-premises phone system means, well, on the premises. In house. Your system will be located inside your company where you have direct control. Dial tone is delivered to you and your phone system sends calls where they need to go. Yes, they can be setup for remote connectivity, so you’ve got phone calls at the beach and the bar, but now there’s single point of failure: your office. If the power goes out, your phones are down. If a plane crashes into your building, your phones are down.

Oh, and let’s not forget direct routing with Microsoft Teams!

The long and short of it is that there’s no easy answer to what’s the best way to get calls to your phones, have phones, use phones … It’s always some variation of, “Well it, depends”.

If you want something we like to call “set it and forget it” where you don’t have to worry about power requirements and redundancy and all that other stuff, go with a cloud-hosted service and just be done with it. You’ll pay a little extra, but you’ll get some extra usually in return, in its ease of use, ease of maintenance, or just plain lack of ever having to deal with anything more than adding a user.

If you want something that is more in your power, more under your control, go with an on-premises system. You’ll have the keys to the kingdom and be able to do number manipulations and failover routing and all sorts of fun things. Bear in mind that Microsoft is pushing hard to move everyone to Office 365 and Teams and Skype for Business 2019 is the last on-premises phone system they will be making.

Just remember: no matter what you go with, no matter what you choose, don’t be afraid to ask for help in deciding. We’re always happy to go down the rabbit hole with you and help you to make an informed decision on a phone system that’s going to last you for many years to come.

Have any questions or want to get started rolling out a new phone system? We’re here to help! Call us at 502-240-0404 or email us!

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