Question: What is the format of a SIP URI for an Anonymous User Identity in a telecom network?
Option 1: sip:user@domain, where "user" is "anonymous" and "domain" is "anonymous.invalid"
Option 2: sip:anonymous@anydomain.com
Option 3: sip:user@anydomain.com, where "user" can be any string
Option 4: sip:anonymous@localhost
Explanation: In a telecom network, the Anonymous User Identity is used to conceal the identity of a user. The SIP URI for an Anonymous User Identity has a specific format, which is "sip:user@domain", where "user" must be "anonymous" and "domain" must be "anonymous.invalid". This ensures that the user's identity remains anonymous during communication.