As companies migrate from traditional telephony to Voice over IP, there are more design decisions to make when choosing the most appropriate implementation type. The choices include variations of centralized or distributed architectures, as well as a choice of call control protocols. The design decision may be based on corporate policies (centralize control of infrastructure and services or providing autonomy to each site by distributing control), or the decision may be based on application and service requirements which may dictate one voice control protocol over another.

Common deployment models include:

• Single Site
• Multi-site Centralized
• Multi-site Distributed
• Distributed Single Cluster