Add-on server routes calls and manages voice traffic

Central routing mechanism from Cisco Systems, 3Com extends the traditional PBX

Voice over wireless requires more than wireless handsets and a wireless LAN. There also needs to be a telephony server to manage the voice traffic.

The telephony server can replace or be added to a PBX, the central routing mechanism for today’s phone systems. Most PBX makers — such as Avaya, Mitel Networks, Nortel Networks, and Siemens — provide IP telephony servers or switches that plug into their PBXes. This usually provides the same PBX features to VoIP users that PBX users get, including call forwarding, internal phone directories, internal extension-only quick dialing, and voice mail. The add-on server or switch connects to the enterprise’s network (wired or wireless) and routes calls within the network, as well as between the network, and the PBX.

In an all-IP telephony system, there is no PBX. It’s replaced completely by a telephony server that handles all the calls, both internally and externally. Cisco Systems, 3Com, and a raft of smaller companies offer such pure-play IP telephony servers. (Some are designed for small businesses, whereas others are for large enterprises.) They also offer typical PBX features such as internal directories and voice mail, but they usually also allow you to integrate faxes, calendars, and address books, because these are all available over the network. (Perhaps you recall the promise of unified messaging about six years ago? This is that same technology, but it has now found a more viable outlet, notes Gartner Analyst Ian Keene.) Such systems also let you program your call responses, so certain people (such as your boss or spouse) might be forwarded to your cell phone during staff meetings and others are routed to voice mail.

You can also set alerts, which are transmitted over e-mail or BlackBerry devices, based on who calls and when. For example, the on-duty overnight IT staffer would be sent the numbers of all help-desk callers only on his scheduled overnight periods.

Whichever type of hardware you use, it’s critical to upgrade your network to support VoIP, Keene says. “VoIP affects the whole network infrastructure,” requiring support for QoS for the streaming of voice traffic to ensure voice quality as well as sufficient bandwidth for the added traffic, he notes.

Furthermore, companies that deploy VoIP should be sure to have a backup power and a backup communications system that includes cell phones in the event of network or power outages, advises Scott Haugdahl, CTO of wireless LAN provider WildPackets. Unlike analog phones, VoIP requires both power and an operational network to handle calls.