Universal Call ID (UCID) is a unique tag that Communication Manager assigns to a call. UCID is an 8-byte data element that displays as a 20-character number. Communication Manager that is configured to create UCIDs assigns one UCID to every call, not just to ACD calls.

With UCID, you can track calls across multiple Communication Manager and Voice Response Units (VRUs). Call centers use UCID to track call history since UCID can uniquely identify every call in a network of any size. For example, you can combine data from many locations and print reports to track a call throughout the life of the call.

In simple call scenarios, the tag stays with that call within a network that is based on communication servers connected by ISDN or SIP trunks. In complex call scenarios, the tag often merges with other tags.