How does WCNAM Work?

WCNAM relies on network technologies and capabilities including switch translations, SS7 signaling, addressing, and routing, storage of WCNAM data in a DB, and protocol translations.

The ANSI standards for CNAP (IS-764 and IS-771) establish two (2) methods or mechanisms for obtaining data using the Wireless Intelligent Network (WIN) triggers known as the Service Request (ServReq) and Facility Selected and Available (FAVAIL).

The first method, originally available with IS-764, establishes the home HLR as the controlling network element.  Upon receiving an incoming call, the MSC launches a Location Request query to the HLR, which triggers the ServReq once the HLR scans the data record to discover that the customer being called subscribes to CNAP.  The HLR then launches the ServReq request to an SCP acting as a CNAP DB containing the CNAP name data corresponding to the calling party number.

There is a lot that happens from point A to point B, including global title addressing, global title translation, routing the SS7/WIN message, etc.  Prior to the message being received by the SCP, the message must first be processed by a functional element whose role is to provide protocol conversion between the invoked protocol, ServReq, and the standard protocol for WCNAM, GR-1188, which is the standard data format for which the data is stored and the SCP expects queries.

Once the SCP obtains the message in GR-1188, it processes the request and provides a response in GR-1188 format containing the WCNAM information, which is converted back to a ServReq CNAP format and delivered to the HLR.

The HLR in turn delivers the CNAP data known as “Display Text” information along with the Route Request to the serving VLR.  This allows the VLR to provide the Display Text information necessary to send the information over the control channel to the called party, once the call is routed from home MSC to serving MSC and the RF system pages the target mobile.

Contrasting this method to the one using the IS-771 FAVAIL query, the serving MSC is the controlling network element.  In this method, a trigger profile is stored in the HLR, instructing the serving MSC/VLR to send the FAVAIL query to the proper SS7 alias point code for processing as described above.  The major difference between the two methods is the use of a trigger profile (shared in the HLR to VLR communications upon registration in the served area) and the query (from serving MSC to SCP) for the CNAP data occurs after the call has already been set-up (from home MSC to serving MSC).

Regarding the protocol conversion (from SerReq/FAVAIL to GR-1188), since GSM systems did not support the ANSI WIN standards, many manufacturers have simply decided to support the GR-1188 protocol directly.

For more details, see the book “Wireless Intelligent Networking”