tion of the number of trunks; however, the complexity in the porting of a large number of DID at a HQ location should not be underestimated. Phase VIII: Transition to SIP Trunking of Branch Locations Large enterprise companies that have a large number of branches traditionally had to pay for TDM circuits at each of these branch locations. This can result in large charges from SPs and complex equipment requirements at the branch. This has resulted in the demand for transitioning branch locations from TDM to SIP trunking. There are at least two methods for transitioning branch locations to a SIP trunk- ing. These are distributed and centralized SIP trunking, and information about these dif- ferent architectures are discussed in Chapter 7, "Design and Implementation Considerations." Regardless of the method that you select, the transition of a branch infrastructure is a large and complex undertaking that requires a detailed analysis of the following: Branch IP addressing schemes: Is a high-quality IP network in place that will not have any topology issues (such as overlapping IP addresses, NAT, and SO on)? Branch phone numbers porting possibilities: Is the branch in a location that enables the porting of the phone number to a different location and different SP? Available branch bandwidth: Does the branch have enough high-quality IP band- width to transition to SIP trunks? The amount of bandwidth required changes based on the architecture utilized. Chapter 3: Transitioning to SIP Trunks 41 Branch equipment specifics: Does the branch have specialized equipment, such as teletext machines for the deaf and postal meters, or is colocation at a shared premise? The overall goal of porting the branch infrastructure to SIP trunks needs to maintain or improve the end user quality of experience by providing new features while reducing costs by lowering TDM trunking expenses. In summary, the complexity of transitioning a large branch infrastructure from TDM to SIP trunks is the most complex of any of the transitions but can res