Question: When a Home Subscriber Server (HSS) receives a Send Routing Info for SM request with the GPRS indicator set, what are the possible serving node addresses that may be returned in the response?
Option 1: Only the Diameter address of the SGSN and its number.
Option 2: Either the MSC number or the MME's Diameter address and number for MT SMS, but not both.
Option 3: Up to two serving node addresses: the SGSN's Diameter address and number, and either the MSC number or the MME's Diameter address and number for MT SMS.
Option 4: The HSS will always return three addresses: SGSN, MSC, and MME for MT SMS.
Explanation: According to the detailed behavior of the HSS, when the GPRS indicator is set, two serving node addresses may be returned. These include the Diameter address of the SGSN (if available) along with its number, and either the number of the MSC or the Diameter address and the number of the MME for MT SMS, highlighting the flexibility in handling both circuit-switched and packet-switched domains.