Next, a static route must be created for a particular matching SIP URI, and then pointed to the trusted application pool as a next hop. This URI is typically a separate SIP namespace, but there is nothing that prevents an organization from using the same SIP URI as used for Lync.
Figure 20.1 demonstrates the logical structure of this integration.
Lync operates similarly to Exchange’s Internal Relay method for an accepted domain with respect to a shared SIP domain. It first attempts to resolve a URI internally, and only if no match is found does it route the call to the third-party system.