Question: Where is the GGSN Address in Use, which represents the IP address of the GGSN currently used by a certain PDP Address of the Mobile Station (MS), conditionally stored?
Option 1: Home Location Register (HLR) and Serving GPRS Support Node (SGSN)
Option 2: Gateway GPRS Support Node (GGSN) exclusively
Option 3: Mobile Switching Center (MSC) and Visitor Location Register (VLR)
Option 4: Gn/Gp-SGSN
Explanation: The GGSN Address in Use is considered temporary subscriber data. Given its temporary nature and direct relation to the serving network for a specific PDP context, it is logically stored in the Gn/Gp-SGSN, which manages the current session's context, rather than in more permanent storage like the HLR or exclusively on the GGSN itself. This ensures efficient access and updates as the MS moves or changes its PDP context.