Apparatus, method and computer program

A method, comprising:

• receiving, from a first client, a call request comprising address information for calling at least one second client, the address information being a Functional Alias, wherein the Functional Alias is activated by the at least one second client;
• in response to receiving the call request, sending, to a server, a request to resolve the Functional Alias to at least one Mission Critical Push to Talk Identifier of the at least one second client that has activated the Functional Alias;
• receiving, from the server, the at least one Mission Critical Push to Talk Identifier of the at least one second client;
• receiving, from the server, two or more Mission Critical Push to Talk Identifiers of the at least one second client;
• in response to receiving the two or more Mission Critical Push to Talk Identifiers of the at least one second client:
• determining, based on a policy, whether to send a call request to each Mission Critical Push to Talk Identifier of the two or more Mission Critical Push to Talk Identifiers, or to select one Mission Critical Push to Talk Identifier of the two or more Mission Critical Push to Talk Identifiers to send the call request;
• and
• based on the determining, sending the call request to the second client using the at least one Mission Critical Push to Talk Identifier of the at least one second client.

A non-transitory computer readable medium comprising program instructions that, when executed by an apparatus, cause the apparatus to perform at least:

• receiving, from a first client, a call request comprising address information for calling at least one second client, the address information being a Functional Alias, wherein the Functional Alias is activated by the at least one second client;
• in response to receiving the call request at the apparatus, sending, to a server, a request to resolve the Functional Alias to at least one Mission Critical Push to Talk Identifier of the at least one second client that has activated the Functional Alias;
• receiving, at the apparatus from the server, the at least one Mission Critical Push to Talk Identifier of the at least one second client;
• receiving, from the server, two or more Mission Critical Push to Talk Identifiers of the at least one second client;
• in response to receiving the two or more Mission Critical Push to Talk Identifiers of the at least one second client, determine, based on a policy, whether to:
• send a call request to each Mission Critical Push to Talk Identifier of the two or more Mission Critical Push to Talk Identifiers;
• or to select one Mission Critical Push to Talk Identifier of the two or more Mission Critical Push to Talk Identifiers to send the call request;
• and
• based on the determining, sending, from the apparatus, the call request to the at least one second client using the at least one Mission Critical Push to Talk Identifier of the at least one second client.