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September 2007 | Volume 10 / Nuber 9
Feature Articles

When You Want to Transition to VoIP Follow These Simple Rules

By Ian Colville

Enterprise customers face a dilemma - they hear about the great reasons for moving to VoIP, but are mindful of the thousands, if not tens or hundreds of thousands, of dollars invested in their current PBX equipment. Should they trash that PBX (or, perhaps, sell it on eBay) in favour of new VoIP solutions, or is there a (relatively) pain free way of migrating to a VoIP capability? Just how easy is it to move to an all IP solution? This article looks at the steps involved in a practical migration strategy and advises those considering a transition to VoIP.

Three Steps to VoIP Heaven

“Now there are three steps to VoIP heaven; just follow the rules and you will see. The formula for VoIP heaven is very simply; just follow steps one, two and three.” First things first; I must apologise to Eddie Cochran for adapting his classic hit. Second things second, if you are looking for a VoIP transition strategy, you could do worse than heed Eddie’s words.

So, what are those steps?

Let’s start from the premise that you are an enterprise of reasonable vintage, which means you have traditional, TDM-based PBX equipment. Let’s also assume that, for the sake of the examples herein, you have a main headquarters building (HQ) and one or more satellite, branch offices. If this is not the case, the steps remain valid; you just have to adjust the scope of each step to suit your circumstance.

Step One - Get a Gateway.

There are alternatives to getting a gateway, such as asking your PBX vendor to upgrade or VoIP-enable your existing TDM switch with an ‘in the skins’ VoIP card. This means hardware and software upgrades, to provide a SIP or H.323 interface and an IP connection. However, there are at least a couple of issues with this approach, which can be pretty significant.




Firstly, consider the cost; is this likely to be a low cost option? I rather think not as most PBX vendors are not charitable organisations. Secondly, will the installation of the VoIP card mean you have to give up a TDM circuit card in its place? You may not have the spare capacity in your PBX to accommodate an additional line card. You can think up some more objections yourself.

A more cost-effective approach is the hybrid one involving a gateway.A gateway is an external device that connects to the legacy PBX equipment on one side and to an IP network on the other. Its job in essence is to convert call control and audio from the traditional format provided by the PBX (e.g., Q.931 call control, µ-law speech) to packet-based information for the IP network (e.g., SIP for call control, G.729A speech) and vice versa.

Why are gateways more cost-effective? Well, for one thing, the gateway vendors don’t have the same opportunity as the incumbent PBX vendor does to capitalise (prey) on your situation. They have to be competitive. However, they also need to differentiate between each another, and this applies to features as well as price.

There are off-the-shelf commodity gateways, to suit most needs, readily available. Be sure the ones you shortlist support the requisite protocols but, in particular, offer support for the supplementary services you make use of between your HQ and branch office(s).

You will need a gateway that offers transparent transit of essential features, such as call forward and call transfer, between your HQ PBX’s Q.931 protocol, via SIP (or H.323) and your satellite PBX’s protocol(s).

If you have inherited a number of disparate legacy PBXs in local branch offices, you will need to find a gateway that supports a range of protocols, perhaps even a few old (ancient by today’s standards) CAS protocols. The last thing you want to do is to be buying gateways from several vendors.

Figure 1 illustrates our first step.

Step Two - Migrate Your Peripherals and Branch Office(s) to IP-based Platforms

At some stage you are going to have to dispose of your legacy PBX platforms and where better to start than in your branch office(s). This approach is less risky, less disruptive to your organisation and has less negative impact on your cash flow - you can spread the cost by planning the roll out over time.

During this stage you should swap out your old PBX for a shiny new IP-PBX and get some of those SIP phones you’ve always wanted. This achieves an easy transition to VoIP, in premises where it causes least unrest, and is lighter on the pocket.

You will no longer need the gateways you purchased for each branch office, but you can always sell them on eBay, along with the PBXs (or your local museum may be open to a donation).

In conjunction with moving to an all-IP situation in your branches, now is also the time to consider converged applications. What does that mean?

No doubt you will have some additional applications serving your organisation. From simple voicemail, through IVR and ACD to contact centre platforms, for example. Of course, these will also be TDM-centric, but step two means they too must go.

As the objective is a transition to VoIP, you will need to replace these with IP-based application platforms. But, remember the term ‘converged’. This is important, as you have yet to replace the HQ PBX system (yes, you’ve guessed it - see step three) and so the application platform will need to number TDM connectivity amongst its attributes.

When sourcing an application platform, take a close look under the covers. Don’t let the vendor fob you off with a system that lacks platform architecture integrity. This refers to platforms that have been designed from the start with a core architecture based on IP. Many traditional equipment manufacturers have attempted to retrofit existing products with new IP interfaces. In most cases, these products are not as reliable or cost efficient. What you are seeking is an IP product that has TDM connectivity as an option; something you will need for the remainder of the transition period (wait for step three).

Your application platform will need media processing resources; the essential features needed for e.g., DTMF recognition and the recording of messages in a voicemail system, or the playback of prompts from an IVR platform. Viable systems will offer integrated and scalable converged functionality, based on multi-function resource boards from respected enabling technology vendors such as Aculab.

Look again for key attributes: designed from the ground up as an IP platform; provides media processing resources in both IP and TDM environments; can operate with a wide range of popular IP codecs (to allow you to readily interface with the IP world outside); offers TDM connectivity and a portfolio of circuit switched signalling protocols to choose from; has the density needed for your scale of operation; and the scalability to grow with your success.

Step Three - Replace the HQ Switch and Say Hello to St. Peter

This is the final step and no doubt the most expensive and disruptive, however, you’ve got to bite the bullet some time if you want to take advantage of all that VoIP has to offer.

In this phase you must finally dispose of your main legacy PBX platform and, as with the branch office(s) before, install a shiny new IP-PBX and some more of those SIP phones. The timing of each step is for you to determine, but don’t forget, the end goal back when we started was to move to an all IP infrastructure in three careful steps.

The remainder of your enterprise infrastructure is all IP by this stage, prepared and waiting for the cut-over at HQ. Here also, your IP-centric application platforms, with their media

processing resources, are by now entirely IP-based. You will have simply disconnected the TDM connections and reconfigured the IP-side connectivity inherent in these platforms. There is nothing to dispose of or trash here, as you continue to benefit from these applications just as you’ve been doing since step two. Your centrally located (or hosted) application platforms remain accessible by any of your users, from any location, in or out of the office.

So the final piece of the transition jigsaw falls into place when your switch over to an IP-PBX. Now you can enjoy the full benefits of enterprise wide mobility, presence, unified messaging, etc. Give yourself a pat on the back for a job well done.

By the way, you don’t have to throw out the gateway that was previously in use at HQ. You can reuse this gateway to provide a PSTN fallback capability, which is a good idea if you are of a nervous disposition.

That’s all there is to it; quite straightforward I’d say. But if you don’t believe me, just listen to Eddie. He said it was easy - just follow steps one, two and three. IT

Ian Colville is a Product Manager at Aculab. He can be reached at Ian.colville@aculab.com

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