Here's advice we wish we'd had up front: Study your voice and data network infrastructure before you start talking to VoIP vendors. We learned the hard way--but luckily early in the pilot--that our Syracuse network needed some key upgrades to support VoIP traffic.

Things started to get complicated when we moved pilot users from the TDM system to the IP network. Because voice can't tolerate normal traffic delays, we had to configure our switches and routers to handle the more sensitive IP voice. We also had to upgrade our LAN from half-duplex 10-Mbps Ethernet to full-duplex 100-Mbps with QoS (Quality of Service) on new Category 5E wiring. The old circuits were prone to voice no-no's--echos, dropped calls and other performance inconsistencies. The VoIP traffic needed new business rules, too, so we created rules that did tasks such as funneling IP phone problems in the pilot area to our own network engineers instead of to Verizon, our Centrex local telco.

We selected Cisco's AVVID VoIP architecture for the pilot mainly because Cisco had the most mature VoIP products and support at the time, and because Syracuse's backbone is built on Cisco switches and routers. It took us one year to build an IP voice design for our test (see Step by Step), with occasional help from Cisco.

In your initial VoIP analysis, consider whether your network can handle voice traffic. The rule of thumb is you need at least a QoS-capable 100-Mbps Ethernet backbone but ideally you'd have Gigabit Ethernet. If your infrastructure is built on professionally installed and certified Cat 5E or higher wiring, your network's physical layer meets the minimum VoIP requirements. If you're thinking about adding gigabit to your legacy Cat 5 wiring, you'll need to retest it to ensure it can support the upgrade.

Other things to consider: Does your data wiring exist everywhere you'd like to add a VoIP set? What vintage are your switches and routers? Does your network have the benefit of a reliable, balanced and backup-protected electrical power-distribution system that can sustain uptime during an outage? Do you have network management tools, such as NetIQ Corp.'s VoIP Manager or Brix Networks' VoIP Test Suite, that can analyze packet-level performance and detect jitter, delay and latency?

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A successful VoIP operation comes with a well-planned, modern and soundly implemented network. If your network is running on hubs or geriatric 10/100 switches and Cat 3 cables, replace them before you start setting up the VoIP call-processing hardware. In our case, we ditched our Cisco Catalyst 1900 switches in favor of new Catalyst 3500s to get the QoS, VLAN and power-over-Ethernet features we needed. If you have wireless networking, check whether your wireless access points support QoS parameters so the voice traffic gets priority when it hits the network's wireless segments. This may be tricky: Few of today's wireless devices come with QoS options.

Your network may need more than new switches and data wiring. Before you buy your VoIP equipment, build redundancy, failover and high-availability power distribution into the network. Uptime is crucial for voice: If you lose a segment of the data network, at the least it's inconvenient and at the worst you lose revenue and customers. But if that same segment carries your voice service and fails, you could face liability and would certainly lose clients. How you configure the Spanning Tree protocol and self-healing on the network and in the server farm can make or break the voice-call experience--and your VoIP infrastructure.

And don't forget your staff. If your helpdesk is divided into separate voice and data support staffs, be prepared for the sensitive process of merging them.