ity of users in the enterprise is often aided by various call forwarding features. Calls between internal numbers can end up being forwarded externally due to a call for- warding mobility feature. Another call flow to consider is an external call that arrived via the SIP trunk into your enterprise, which, in turn, is forwarded from the internal endpoint to a second external destination via the same site's SIP trunk, or if you have distributed SIP trunking deployed, perhaps a different site's SIP trunk. This call flow consumes the bandwidth equivalent to two individual calls. Single-number reach call flows, where a single phone number is set up to ring a user's desk phone and an alternate mobile device such as a cell phone (which is often physically resident on an external network), should also be considered and tested. These call types have unique requirements for transfer, forwarding, voice mail. Network Demarcation Demarcation has to do with defining and protecting the borders between networks owned or managed by different entities while maintaining interconnectivity and interop- eration of traffic and features between the two networks. TDM PSTN gateways offered an implicit enterprise network demarcation point. Until recently VoIP has been deployed only in private enterprise and small business networks for on-net calls-calls that remain within the organization's own network. Off-net calls that went from the enterprise to (or from) the PSTN were converted between IP and TDM at the PSTN interconnect point (even though many service provider backbone net- works have also been VoIP for many years). With SIP trunking the provider-to-enterprise interconnect is now also migrating to using VoIP technology. This means you no longer need TDM PSTN gateways, but it also means you lose all the demarcation features TDM gateways implicitly provided to your network. These demarcation features include Compliance with service provider's User-to-Network Interface (UNI) Codec choice Fault isolation Statistics and voice quality repo