Question: Which of the following best describes the primary networks involved in an Inter System Change for a GPRS-attached mobile moving between cells of different systems like GSM and UMTS?
Option 1: Only UTRAN (Universal Terrestrial Radio Access Network)
Option 2: Only CN (Core Network)
Option 3: Both UTRAN (Universal Terrestrial Radio Access Network) and CN (Core Network)
Option 4: Neither UTRAN nor CN, only the mobile device
Explanation: During an Inter System Change between GSM and UMTS for a GPRS-attached mobile, both the radio access part (UTRAN) and the central part of the telecom network (CN) are involved to ensure seamless handover and maintenance of service. This is because such a change requires not just a physical layer adjustment (handled by UTRAN) but also updates in the logical connections and subscriber management handled by the Core Network (CN).