ily imply that you have to choose centralized SIP trunking. Because SIP trunks are IP-based, you can have a SIP trunk in each branch office, but it does not have to be equivalent to the T1/E1 trunk currently there. If a remote office requires only 12 calls, get a SIP trunk with 12 calls into that office. How cost-effective this is again depends on what granularity of service you can get from your provider. Chapter 6: SIP Trunking Models 91 Tip TDM PSTN trunk oversubscription can be solved by SIP trunking in multiple ways, and both the centralized or distributed trunking models can provide this benefit. Quality of Service (QoS) Considerations Following are two considerations related to voice quality or QoS: Bandwidth provisioning: How is the WAN bandwidth provisioned for each site im- pacted by the SIP trunk model? Latency: How is the delay or latency of calls impacted by the SIP trunk model and call paths through the network? The following sections describe both considerations in greater detail. Bandwidth Provisioning Another bandwidth-related consideration is the call path VoIP calls take on your network after you implement SIP trunking. A call from a remote office to another site with a cen- tral SIP trunk impacts the bandwidth provisioning and QoS queue settings for both sites. First, the PSTN off-net call from the remote site now traverses your WAN where it did not for TDM PSTN trunking, SO the remote office's WAN connection requires more bandwidth than before. Second, the remote site's PSTN call traverses the WAN connec- tion of the central site with the SIP trunk twice: first, on the VoIP connection from the remote site to the central site, and second, from the central site to the SP. The physical connection for both legs of the call is most likely the same pipe SO that doubles the band- width required for all calls hairpinning from a remote site to a central SIP trunk. The distributed SIP trunking model follows the same call paths as the TDM trunking model and therefore does not put any extra VoIP calls on