A big part of initial planning should be devoted to how to manage the increased load of voice data. Voice data comes with a raft of additional requirements, such as increased bandwidth and packet prioritization, and several tactics must be employed to minimize voice disruptions.

"The biggest area of concern for IT managers is performance management," says Irwin Lazar, senior analyst at Burton Group. Managing a real-time application such as voice across a data network can be problematic, he notes, because IP networks were never designed for the strict latency and jitter requirements of voice. "Enterprises require not only a good QoS architecture, but the tools to manage voice performance in real-time, and to be able to both proactively and reactively troubleshoot problems as they occur."

Telecom vendors such as Alcatel, Avaya, Cisco Systems, Nortel Networks, and others provide management tools along with their VOIP product offerings while network management software vendors, including Brix, NetIQ, Qovia, and Telchemy, have licensing agreements with vendors or sell their products directly to end-users.

The software usually consists of a console that lets IT staff view how well voice traffic is moving across the network, and agent software, which gets embedded in equipment that sits in the VOIP calling path--gateways, routers, switches, vendor-supplied appliances, and, more recently, IP phones. The agent can report in real time on VOIP quality of service problems, such as packet loss, discard, latency, jitter and signaling issues. But VOIP management software alone is no substitute for expertise in telephony.

At what part of the network should you measure voice performance? There are several options: at switches, routers, and gateways, for example. The most crucial spot, however, is at the end point where problems are most noticeable to users.