FreeSWITCH simplifies SIP for us, with the concept of "gateway". That "gateway" in FreeSWITCH lingo is just a glorified automation provided to us, so we can use a simplified syntax meaning: "check whether this particular Internet Telephony Service Provider (ITSP) is up and reachable, send this call out to it, give the ITSP the login and password to authorize our call if needed, and wait for the ITSP to connect our call to the wide world".
All of those mechanisms and actions are performed transparently to us, and the monitoring of the ITSP availability is performed routinely even when we don't use it, so if ITSP is down we don't even try it, but we'll be able to use it when it is back.
By the way, ...
