 within companies After proceeding with the adoption of SIP trunks is deemed a priority for the IT organi- zation, the technological steps toward implementation can begin. Phase III: Gather Information from the Local SPs An important early step in the transition to SIP trunks for PSTN access is to determine what services are available in your area and to your company and to plan the overall tran- sition to SIP trunking. This is best done by understanding the most formal process, the Request for Proposal (RFP), and to determine which of the steps of this formal process are essential to gather a complete and accurate understanding of the SP offerings. A complete RFP is provided in Chapter 9, "Questions to Ask of a Service Provider Offering and an SBC Vendor;" however, a formal RFP is not required in all cases in which a company considers utilizing or transitioning to SIP trunks. For example, internal appli- cations that might have previously used TDM or H.323 trunks can often easily be transi- tioned to SIP trunks without the help or hindrance of an external entity such as an SP. However, the outline and formality of an RFP is important to help frame the questions and understand the answers provided by SPs that look to offer SIP trunking services. Some of the important things to note are All the questions in an RFP might not be answered by the SP. Use of an arbitrary scoring system of an RFP is not the best method to determine which SP to use. Trials deployment can and should occur without or before completion of a formal RFP. An RFP and overall plan is an important and essential part of any large scale transition from TDM to SIP trunk for PSTN access at a company. However, the responses from an RFP alone are not enough to determine the architecture and plan required for a transition from TDM to SIP trunking. Phase IV: Conducting a Pilot Implementation of SIP Trunks for PSTN Access One of the key attractions to SIP trunking solutions is that they can easily scale up and down. One of the benefits that this offers is