nologies. Chapter 3 Transitioning to SIP Trunks This chapter covers the following topics: Phase I: Assessing the current state of trunking Phase II: Determining the priority of the project Phase III: Gathering information from the local service providers Phase IV: Conducting a pilot implementation of SIP trunks for PSTN access Phase V: Transitioning a live department to SIP trunks Phase VI: Transitioning to SIP trunking for call center locations Phase VII: Transitioning to SIP trunking at headquarters locations Phase VIII: Transitioning to SIP trunking of branch locations Phase IX: Transitioning any remaining trunk to SIP trunking Phase X: Posting project assessment This chapter explains the stages that an enterprise might want to plan or execute when transitioning its current Unified Communications (UC) systems from utilizing time division multiplexing (TDM) or H.323 trunks to a system that uses Session Initiation Protocol (SIP) trunks. The transition method can generally be applied to two distinct use cases for trunks that need to undergo transitions: Trunks used for interapplication connectivity: These are generally TDM trunks used between different Internet Protocol Public Branch Exchange (IP-PBX) solutions or UC applications within an enterprise. Typical examples of these trunks are connections from an IP-PBX to a voicemail system or connections from the IP-PBX to an Interactive Voice Response (IVR) system. Trunks used for Public Switched Telephone Network (PSTN) access: The method that is most widely deployed today to connect a UC system to the PSTN is the use of 32 SIP Trunking TDM trunks. These trunks can be in the form of digital T1/E1, analog Foreign Exchange Office (FXO) ports, or other types of TDM connections. This is the transi- tion methodology companies need to consider as they move to adopt SIP trunks as a replacement for TDM trunks. When transitioning from TDM to SIP trunking, a company needs to consider the current state of both the TDM and SIP trunking that exists within the enterprise. We dis