Question: What is the purpose of the exclamation mark character ("!") in a wildcarded Public Service Identity (PSI) stored in the Home Subscriber Server (HSS)?
Option 1: To separate the user part from the domain part in a SIP URI or Tel URI.
Option 2: To delimit the Extended Regular Expression (ERE) in a wildcarded PSI, indicating the extent of the wildcarded part.
Option 3: To specify a port number for the application server in Inter Operator Network to Network Interface (II-NNI) communications.
Option 4: To distinguish between distinct PSIs and wildcarded PSIs in routing operations.
Explanation: The exclamation mark character ("!") is specifically used as a delimiter in wildcarded Public Service Identities (PSIs) to separate the regular expression (following the Extended Regular Expression syntax) from the fixed part of the PSI. This differentiation is crucial for the efficient operation and maintenance of nodes, as it allows for the matching of multiple specific PSIs to a single wildcarded PSI stored in the HSS.