For example, Alice and Bob are both registered so Alice can send a message to Bob and vice versa.
However, my use-case is slightly different. Only Alice is registered; Bob is a device at some unknown location on the internet on a NATed network behind a firewall/gateway.
Bob is able to send a SIP MESSAGE request to Alice@Domain.com and it will be received by FS then forwarded to Alice.
My question is how can Alice get a reply MESSAGE back to Bob when he hasn't registered? By default, if Alice tries to reply to Bob@Domain.com, FS will send back a 202/Accepted to Alice, but the message will go nowhere.
Given that when Bob sends his message to Alice, the source address of his message will be valid for a short period (therefore the source address is the return address), how can I ensure that when Alice sends a reply MESSAGE a second or two later, it gets
to Bob?
My initial thought was to somehow auto-register Bob in FS using the source address of his message. Then Alice's reply should get there. Is this possible? Or should Alice's reply be sent another way? I think the reply to Bob must come from the same address
to which he sent his message.
Some additional info: