d monitoring equipment. This chapter also describes the differences in components for SIP trunks into large enterprises, medium-sized enterprises, and small-medium businesses. Chapter 6, "SIP Trunking Models": Explains the centralized, distributed, and hybrid network topology alternatives for connecting a SIP trunk from an SP into an enter- prise network for PSTN access. Chapter 7, "Design and Implementation Considerations": Focuses on network design and implementation considerations after a decision has been reached to connect to an SP via a SIP trunk, including geographic and regulatory considerations, IP connec- tivity options, dial plans and call routing, supplementary services, network demarca- tion and security, call traffic capacity and bandwidth control, and scalability and high availability. xxii SIP Trunking Chapter 8, "Interworking": Explores an additional set of interworking network design considerations, including dual-tone multi-frequency (DTMF) conversion, fax and modem traffic, and connecting different H.323 and SIP variations. Chapter 9, "Questions to Ask of a Service Provider Offering and an SBC Vendor": Explains the questions you should ask and appropriate answers you should seek from your SPs and SBC vendors before you deploy a SIP trunk into your network. Part III is for the network implementer. If you are familiar with the material in Part II, you can dive straight into this, but for most readers it would make more sense to cover Part II first before starting on Part III's chapters. Chapter 10, "Deployment Scenarios": Covers configurations for the typical SIP trunk deployment scenarios, including enterprise to SP deployments, SMB to SP deploy- ments, and configurations with SRST, transcoding, a collocated firewall, Tcl script- ing, and many more. Chapter 11, "Deployment Steps and Best Practices": Pulls together the detailed infor- mation from preceding chapters on network design considerations and deployment scenarios into an easy-to-use, step-by-step guide to implementing SIP trunking and a