Instead, we recommend limiting your VoIP implementations to a few key areas. Thanks to H.323's modularity, you can replace only select components on your network. For example, you might provide users in a new facility with VoIP equipment at the desktop, yet retain your existing PBX network at your corporate headquarters. Conversely, you could replace an outdated PBX cluster with IP-centric systems, while maintaining existing user-side equipment at the desktop.

Don't be hasty in your decision about where to implement VoIP, however. Every area of your network will be governed by individual factors that motivate (or discourage) the adoption of VoIP technologies. Each portion of your enterprise network has its own considerations and you have to treat each piece differently when planning your implementation. For instance, the opportunities to cut costs in remote offices are not the same as they are for local users. Similarly, bandwidth and infrastructure requirements for a large office or campus differ radically from those for a small office or a telecommuter. For more specific pointers in implementing VoIP, see the sidebars "VoIP at HQ" (page 56),
"VoIP at the Branch Office" (page 52)
and "VoIP for the Telecommuter" (page 48).