There are a number of areas we need to consider when building our telephone system, such as the physical infrastructure for the stability and security of the system, the need to lock the PBX, the need to provide adequate heating control, and so on. Most of this is very specific to our environment and is covered well in the documentation on infrastructure and maintaining service-level agreements (SLAs). Besides these, the most important areas, on which this chapter focuses, are those relating to the configuration of the PBX system itself. We will need to consider the following:
Extensions
Ring groups
Call queues
Connectivity
PSTN
VoIP
ITSPs
DID Lines (Direct Inward Dial)
Telephones
Hard phones
Soft phones
IVR (Interactive Voice Response)
Fax requirements
These are the main, or most common, areas of concern when planning our deployment. We will cover each of these in detail and then look at case studies implementing these.