Question: In a GPRS network using Gn/Gp, which node(s) collect charging information related to radio network usage for each Mobile Station (MS)?
Option 1: Only S-GW
Option 2: SGSN and optionally CAMEL server for prepaid scenarios
Option 3: P-GW/GGSN exclusively
Option 4: Both SGSN and P-GW/GGSN for all scenarios
Explanation: According to GPRS charging principles, the SGSN is responsible for collecting charging information related to radio network usage for each MS when connected through Gn/Gp. Additionally, a CAMEL server can also realize charging (including prepaid) in specific configurations, thus making Option 2 the most comprehensive and accurate choice.