 campus sites do not change. The distributed model has the following challenges: Manageability of a SIP trunk at each site. Chapter 6: SIP Trunking Models 99 Multiple SP SIP trunks entering different sites in the network-there may be feature or call operation differences between the SIP trunks; each provider's offering must be validated individually. No equipment consolidation. Hybrid SIP trunking has the following implementation characteristics: A Border Element at each regional location. A SIP Trunk IP address per regional site to the SP. Remote site calls hairpin through the regional site where SIP trunk terminates. The hybrid model has the following advantages: All the advantages of the centralized model for sites with a SIP trunk; all the advan- tages of the distributed model for sites not directly connected. More redundancy and disaster recovery options compared to centralized model. Easier DID migration than the fully centralized option. Flexibility to route calls through various trunk options. The hybrid model has the following challenges: All the challenges of the centralized model for sites with a SIP trunk. The challenges of the distributed model for sites not directly connected. This page intentionally left blank Chapter 7 Design and Implementation Considerations This chapter covers the following topics: Geographic and regulatory considerations IP connectivity options Dial plans and call routing Supplementary services Network demarcation Security considerations Session management, call traffic capacity, bandwidth control, and QoS Scalability and high availability SIP trunk monitoring This chapter focuses on network design and implementation considerations after a deci- sion has been reached to connect to a service provider via Session Initiation Protocol (SIP) trunking and the choice has been made regarding the appropriate network model (centralized, distributed, or hybrid) as discussed in Chapter 6, "SIP Trunking Models." Considerations about the network design and implementation of SIP trunking incl