[Serusers] NAT and protocol aware firewalls

Hi, I just want to dwell around a couple of things. Several vendors have "application awareness" for instance Cisco has <fixup protocol sip...> Hence the ser will not se the client as nat'ed and will not send nat-ping to the clients. If the client does not support some kind of keep-alives, I guess you will loose connectivity with the clients when standard register expiry is 3600 sec. (off course until the next register message is sent) The Cisco PIX, for instance, have a standard (however configurable) sip inactivity timer = 1800sec. What would actually be the best way of dealing with this? Best regards, hw