Question: In an IP Multimedia Subsystem (IMS), when terminating a session with a TEL URI, which network elements MUST support the TEL URI format for Public User Identity in a multi-HSS setup?
Option 1: Serving Call Session Control Function (S-CSCF) only
Option 2: Proxy Call Session Control Function (P-CSCF) and Serving Call Session Control Function (S-CSCF)
Option 3: Home Subscriber Server (HSS) but not Subscription Locator Function (SLF)
Option 4: Both Home Subscriber Server (HSS) and Subscription Locator Function (SLF)
Explanation: In a multi-HSS setup, both the HSS (for subscriber data management) and the SLF (for resolving the correct HSS) must support the TEL URI format for Public User Identity to ensure seamless session termination. This dual support is crucial for efficient routing and handling of calls in complex network architectures.