to the WAN backbone. Tip If you are considering centralized or aggregated SIP trunking, the bandwidth provi- sioning of all sites in your network must to be reviewed and likely changed. Latency Implications In the distributed model, the call path is direct between the remote site and the SP, and latency is similar to what it was for TDM trunking. For centralized or aggregated trunk- ing, the call path from a remote site hairpins through a central site that can be geographi- cally distant. When evaluating aggregated SIP trunking, be sure to consider the increased latency imposed on calls from remote sites and whether the resulting voice quality would be sufficient for your business needs. 92 SIP Trunking Tip If you are considering centralized or aggregated SIP trunking, the increase in latency of calls from all sites that do not have direct SIP trunk access needs to be reviewed. Operational and Equipment Implications A single, central SIP trunk is often attractive because that means equipment to terminate the trunk is required in one (or perhaps two for redundancy) site. The capital costs and management aspects of a gateway at each site goes away and is consolidated to a single or small number of sites in the network. However, each remote site still requires a router and a WAN connection, and it probably already has a PSTN voice gateway. That same Cisco router that is already present in the site and is the data router or the voice gateway, or both, can be upgraded to be your SIP trunk terminating Border Element (that is, add Session Border Controller [SBC] capabili- ties to the router). So new equipment might not be necessary; you might simply need a software upgrade and configuration change to the equipment you already have and already know how to manage. Tip Equipment can be consolidated by using a centralized trunk model. However, if a distributed model fits your network better, this might not necessarily mean more equip- ment. Cisco routing equipment already present in your remote sites can be upgraded to do S