routed (routed via TDM versus IP, and SO on). One aspect that is distinct between Internet peering and SIP trunk peering is that with SIP trunk peering all traffic between SPs is measured and compensated for on a per-call basis. With Internet traffic exchange peering, traffic is usually exchanged at no cost between SPs without detailed examination of the specific destination of each traffic flow. Peering SBCs are usually deployed at shared central locations, such as large shared data center facilities. These shared facilities enable for the peering of traffic across a similar medium. This is usually done via an Ethernet connection between two providers. Each provider generally has its own peering SBC, and as such, the number of SBCs that a par- ticular call traverses from start to finish can be very large. Chapter 5: Components of SIP Trunks 73 Another important role of peering SBCs is to ensure that traffic that is both originated and terminated by IP endpoints-when they belong to the same SP-is not converted into TDM traffic unless required. (That is, if a call is tagged for Legal Intercept, conversion to TDM may be required.) This direct routing of calls over the IP link between customers of an SP is not always the method used to connect customers but is the ideal scenario. As SPs peer their SBCs and generate and terminate IP traffic, there is no reason that the traffic between two IP PBXs connected to two different SIP trunking networks from different but peered SPs should not stay IP end to end. Figure 5-7 shows how these connections occur most often today with a transition and interconnect over the PSTN network as they are converted to TDM traffic. However, the future deployment as connections over an end-to-end IP network is becoming more prevalent. Enterprise Domain 1 Enterprise Domain 2 Rich-Media Rich-Media Enabled Enabled Narrowband Voice Before all IP Peering SBC to Rich-Media Interconnect After all IP Peering SBC Rich-Media Enterprise Domain 1 Enabled Enterprise Domain 2 SP VolP Figure 5-7 Before and