nd should be taken into considera- tion when designing and connecting a SIP trunk into an enterprise network. IP Connectivity Options Several different types of service providers offer SIP trunks. Enterprises can find offers from service providers to transport just their data services or just their voice services, or both. When the data and voice services are delivered by different providers, each traffic type is typically delivered over a separate physical medium. Also, when the SIP trunk car- ries high traffic, for example 1000 sessions or more, a separate physical medium for the SIP trunk is often used. Chapter 7: Design and Implementation Considerations 103 Consider two aspects of IP connectivity when connecting to a SIP trunk: Physical medium of delivery IP addressing Physical Delivery and Connectivity A dedicated physical connection for a SIP trunk is not uncommon for larger enterprises. The physical delivery for these types of terminations is often optical fiber (OC-3 or high- er) and through a series of multiplexing, switching, and routing equipment eventually ter- minates as a gigabit Ethernet connection onto the enterprise's Session Border Controller (SBC). This connection model is shown in the left panel of Figure 7-1. Services (Presence, NMS and Media VM and so on) Softswitch Gateway SIP Trunk SP SBC Sonet Mux and Ethernet Media Converter SIP Trunk Voice Traffic NAT ALG Device Voice and Data Traffic Enterprise SBC Small Business Large Enterprise Figure 7-1 Physical Delivery of a SIP Trunk For smaller businesses this dedicated delivery model is not cost-effective and these organizations predominantly get their voice and data services from the same provider over the same physical connection. The connection in this case might be Digital Subscriber Loop (DSL), cable, Integrated Service Digital Network (ISDN), T1/E1, 3G wireless, or any other medium capable of carrying QoS-enabled IP traffic. This connec- tion might connect directly to the customer's routing equipment, or the provider might 104 SIP Trunkin