As the way in which people communicate with each other continues to change, users can now be reached on multiple devices and via different technologies (voice calls, video calls, instant messages, emails, and so on). From an addressing point of view, these different devices and technologies can result in many different user addresses and address formats. SIP makes it possible to use the URI format for addressing an end user. This simple format consists of a user and host portion, such as an email address, and provides a simple, uniform way of identifying an end user.
When implementing SIP URI dialing in a multisite environment, you must route calls to other SIP call control systems by using SIP route patterns and SIP trunks. Certain SIP parameters may have to be tuned to ensure proper operation and interoperability between different SIP call control systems.