Question: What is the maximum number of digits allowed in an HSS-ID (Home Subscriber Server Identifier) as per 3GPP specifications, and what is a key constraint for its composition?
Option 1: Up to 15 digits, with the constraint that it cannot be identical to a complete IMSI (International Mobile Subscriber Identity) of a UE (User Equipment).
Option 2: Exactly 15 digits, with no specific constraints on its uniqueness in relation to IMSI.
Option 3: Up to 20 digits, with the requirement that it must match the first part of any UE's IMSI in the network.
Option 4: Exactly 10 digits, with the stipulation that it can only consist of the MCC (Mobile Country Code) and MNC (Mobile Network Code).
Explanation: The correct answer is Option 1 because, as per the specifications, an HSS-ID must not exceed 15 digits in length. Additionally, a crucial constraint for its composition is that it cannot be identical to the complete IMSI of any User Equipment (UE), ensuring uniqueness and avoiding potential conflicts in identification and routing processes within the telecom network.