Question: In A/Gb mode, what entity besides the Mobile Station (MS) has knowledge of the relationship between a Temporary Logical Link Identity (TLLI) and an International Mobile Subscriber Identity (IMSI)?
Option 1: Serving Radio Network Controller (SRNC)
Option 2: Serving GPRS Support Node (SGSN)
Option 3: Gateway GPRS Support Node (GGSN)
Option 4: Mobile Switching Center (MSC)
Explanation: In the context of A/Gb mode for General Packet Radio Service (GPRS), maintaining user identity confidentiality is crucial. The Temporary Logical Link Identity (TLLI) is used to identify a user, and its relationship with the International Mobile Subscriber Identity (IMSI) is restricted to specific network elements for security reasons. Among the options provided, only the Serving GPRS Support Node (SGSN) is directly involved in managing the TLLI and its association with the IMSI, as it allocates the P-TMSI from which the TLLI can be derived. This limited knowledge distribution enhances user identity confidentiality.