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What to know before you buy an IP PBX

By Tim Greene and Phil Hochmuth

Before you get too far into interviewing vendors about their IP PBX products, you should have a good understanding of what you need and whether their products will work in your environment. Here are some points to consider:

1. Know what you want. When selecting IP-PBX software and hardware, decide early on whether you're going to do a complete replacement of your existing telephone system, or work out a gradual migration. This decision has a huge effect on the complexity of your deployment, because gateways that bridge old analog phones and PBXes to new VoIP telephones and IP-PBXes can be costly and difficult to program-especially if you think you're only going to have co-existence for a few weeks or months. If you can avoid or at least minimize the use of analog gateways to old phones or to your legacy PBX, you can reduce cost and complexity. However, this savings may come at a different cost: a more difficult and risky cutover to the new phone system.

2. Know what you've got. Businesses need to figure out exactly what hardware makes up their existing network infrastructure and, more important, whether it will support technology that can improve voice quality. For instance, routers and switches that support virtual LANs and traffic shaping go a long way toward carving out enough reliable bandwidth to prevent degradation of VoIP connections.

In addition, make sure all desktop deployments pass the PAS test. That is, desktop phones should have two things - power and switching (PAS). Make sure phones can be powered via standard Power over Ethernet (802.3af is the IEEE standard). Make sure the IP phones deployed have built-in LAN switch ports. This will allow for a single LAN cable to support a desktop PC and IP phone (the PC connects to a LAN port in the switch, which uplinks to the LAN).

3. Consider bandwidth. If audits reveal that bandwidth may be an issue, it could be time to consider an upgrade from, say, Fast Ethernet to Gigabit Ethernet. Even if such an upgrade seems like overkill now, it makes sense to project network-traffic increases from all applications over the next three years to determine whether such an upgrade is inevitable.

4. Use the right codec. To minimize bandwidth that VoIP requires, customers can choose from a variety of codecs that take the voice stream and encode it for transmission over network wires. This can be as little as 8Kbps or as much as 64Kbps, but businesses should listen to a variety of them to determine which ones produce acceptable quality. The ones to choose, especially if bandwidth is tight, are those that use the least bandwidth.

5. Remember 911. VoIP doesn't allow for easy 911 calling, because the voice server has no idea where the phone is; it knows only its IP address. The phone could be anywhere on any network segment, and its location could change if the user moves the phone to a different network jack. Emergency personnel could be sent to the wrong place.

6. Consider softphones as an alternative to desktop phones for certain types of employees. Tech-savvy users, or those who regularly work from different locations -- such as branch offices, home offices or on-site with customers -- are good candidates. It's also a less-expensive proposition for supporting remote workers. Cisco IP softphone license costs about $100 or less when bought in larger quantities. IP handsets with similar features as the softphones typically cost $300 to $400.

7. Find out how remote management applies to your IP PBX. Can you run on your IP PBX or call server the same tools you use to remotely manage, reboot and configure your regular mail/file/print servers? IP PBXs can run on platforms varying from Windows to embedded Linux and Unix, and each server type supports different remote-access/control applications.

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