I'm looking to try to find a difinitive answer in regard to registration of SIP end points on a PBX (Comdial MP5000) so that SIP to SIP calls can be made from one IP end points in one MP5000 to SIP end points in another MP5000 or from an MP5000 SIP end point to another manufacturer's SIP end point. I am not talking about the ability to call from one location to another. I am talking about true SIP calling. As I understand it there is no public registrar of SIP addresses like there are for email and domain names. Comdial tells me that at present a SIP call can only take place to another SIP device within the same switch. This allows the use of SIP features such as video soft phone and presence management and viewing. SO if I have three MP5000 systems, I have to register the SIP soft phones all in one switch (networked swtitches) to be able to do these things. Soon they say that this issue will be resolved so that any SIP end point on the network can register in it's own switch and all features will be available across the Comdial MP5000 network. Eventually there is supposed to be some sort of public registry server or servers, or at least a way for Comdial to register end points from another manufacturer's switch so SIP to SIP calling can take place.

For anyone who reads this that doesn't know exactly what I am talking about, You know, when you send an email to [email protected], he does not have to be residing (registered) in the same server you are in to get his email. He can be anywhere in the world. But with SIP he does have to reside in your server (registered SIP end point). I am not talking about Vonage or any of the other SIP IP phone companies. I'm interested in the advancement taking place within SIP based IP PBX systems. And I am using Comdial MP5000 only as an example. If someone else's system works differently, I would like to know about it.

Here are the implications of TRUE SIP to SIP calling as I understand the promise of it: I can use my SIP based end point (hard phone or soft phone) to call any SIP end point anywhere in the world and never really be concerned with the call going over the public telephone network. If I am calling from my office to Germany and the address of the SIP end point in Germany is [email protected], then my system looks to a registry server to identify where [email protected] is located and checks to see if he is available to take my call and if he is, we're connected. (I know there is more to the steps involved so don't pick that part to death). If I'm using a video soft phone and [email protected] is not, the call still goes through, I just do see him. In some applications the ability to do SIP to SIP calling would eliminate the need to set up networked switches, for instance if all the customer was looking for was a way to save on toll charges and call other individuals direct, this would work great. We have a need for this application where there is going to be multiple MP5000 switches throught the US and a number of Alcatel OmniPBX's in Europe. I'm out of breath so tell me what you think.

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