RFC 5626 may be of interest. > -----Original Message----- > From: Thomas Buono [mailto:tbu...@gmail.com] > Sent: Thursday, September 26, 2013 12:02 PM > To: Guan Xsun > Cc: sip-implementors > Subject: Re: [Sip-implementors] About SIP over TCP > > *"Does the SIP UAS can init a TCP connection to the SIP UAC if the UAC > is > behind the NAT?*" > > Not too sure. SIP/RTP with NAT usually is a source of quite a few > problems > so many avoid it. Investigate STUN or ICE, as they try to solve some > of > these problems. RTP over NAT usually causes a headache because ports > are > usually chosen on the fly for audio routing. > > e.g. during SDP Offer/Answer, a UAC might choose some high numbered > port > such as 50505. Since the UAC is behind NAT, it can listen all it wants > on > 50505, but since it's behind NAT, the UAS would not be able to send RTP > to > the UAC. > > One solution is to avoid NAT altogether and place the UAC in a DMZ > (Demilitarized Zone). Then you wouldn't have to mess with port > forwarding. > > *"And Does the SIP UAS needs keep the TCP connection alive all the time > with the UAC?"* > * > * > If the UAC (behind NAT) initiated the TCP connection to the UAS (public > network), the TCP protocol should handle keeping the connection alive, > and > NAT would be informed during keep alive messages to "keep the pathway > open". > > > > On Thu, Sep 26, 2013 at 11:39 AM, Guan Xsun <guanxian...@gmail.com> > wrote: > > > Hi, > > Does the SIP UAS can init a TCP connection to the SIP UAC if the > UAC > > is behind the NAT? > > And Does the SIP UAS needs keep the TCP connection alive all the > time > > with the UAC? > > > > Thanks > > Casey
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