I will add one point to this discussion; sometimes not sending out all the digits at once makes sense, but not with SIP.
Gateway protocols like MGCP will commonly send out digits one at a time. This allows a Gateway Controlled protocol to allow the controller to decide when enough digits have been entered instead of requiring the client process to figure this out. This in turn allows dumb clients at the edge of the network, while maintaining the intelligence in the core. SIP was made in direct opposition to that type of signalling protocol. It wants as much intelligence at the edge as possible. Because of this, it is much easier to implement nifty new features. At the same time, it makes interop more of a challenge ☺ Joel Gerber Network Administrator Network Operations Eastlink E: [email protected]<mailto:[email protected]> T: 519.786.1241 From: SIP Learner [mailto:[email protected]] Sent: July-15-13 7:28 PM To: Joel Gerber; Cary FitzGerald Cc: sip-implementors Subject: Re:RE: [Sip-implementors] Overlap signaling in a native SIP network A big THANK YOU to those guys who answered my questions! I Googled for overlapped signalling and did find RFC3578, and I do think using overlap signalling in SIP is weired. But one of my co-workers insists that overlapped signalling is useful in native SIP networks (not interfacing with any other networks using a separate signalling system, as the ones described in RFC3578 or RFC4497) . As I come from a PSTN background and are new to SIP (I am still reading RFC3261). I am not sure whether my idea about SIP overlap signalling was right, so I sent the original mail to look for help and, to some degree, confirmation! In my opinion, if only a SIP network is involved and no gateways are used, overlap signalling (e.g., the caller sends dialed digits to an outbound proxy in consecutive separate INVITEs for the outbound proxy to collect enough information and route the requests) is meaningless, because there are no physical connections to be established, am I right? Thank you again! ZHANG ------------------ Original ------------------ From: "Joel Gerber"<[email protected]<mailto:[email protected]>>; Date: Tue, Jul 16, 2013 01:24 AM To: "Cary FitzGerald"<[email protected]<mailto:[email protected]>>; "SIP Learner"<[email protected]<mailto:[email protected]>>; Cc: "sip-implementors"<[email protected]<mailto:[email protected]>>; Subject: RE: [Sip-implementors] Overlap signaling in a native SIP network Yeah, I’m aware of the methods used to support it in SIP, but I’ve never understood why you would want to. As RFC 3578 states, if there is some switch in the network the requires using the overlapping process to send out digits, your hand might be forced. I would think that the VoIP gateway interfacing with this element would try to buffer the full DN, but as 3578 also states, sometimes it’s not possible to know for sure if you’ve received the full DN or not. No matter what, it definitely isn’t something you want to choose to have happen, as there is no advantage that I can see in a modern trunking network of initially sending a subset of the total digits to be dialed. Joel Gerber Network Administrator Network Operations Eastlink E: [email protected]<mailto:[email protected]> T: 519.786.1241 From: Cary FitzGerald [mailto:[email protected]] Sent: July-15-13 1:12 PM To: Joel Gerber Cc: SIP Learner; sip-implementors Subject: Re: [Sip-implementors] Overlap signaling in a native SIP network Googling for overlap signaling leads you to http://tools.ietf.org/html/rfc3578 and other discussions. Cary. On Jul 15, 2013, at 9:51 AM, Joel Gerber wrote: That's an awesome question. To be honest; I'm not sure of when it's even a good idea in a TDM network. The time you save in routing lookups is negligible in an ISUP network. Maybe during the days when MF was king it made more sense? Joel Gerber Network Specialist Network Operations Eastlink E: [email protected]<mailto:[email protected]> T: 519.786.1241 -----Original Message----- From: SIP Learner [mailto:[email protected]] Sent: July-15-13 12:49 PM To: sip-implementors Subject: [Sip-implementors] Overlap signaling in a native SIP network Dear All! In PSTN networks, it's beneficial to try to establish a connection between the caller and the callee before the full phone number digits are collected. But SIP works over the connectionless IP network, is there any benefit to use overlap signalling in a native SIP network? Are there any official standards or technical materials that documents overlap signalling in a native SIP network? Thank you very much! ZHANG _______________________________________________ Sip-implementors mailing list [email protected]<mailto:[email protected]> https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors _______________________________________________ Sip-implementors mailing list [email protected]<mailto:[email protected]> https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
