[SIPForum-discussion] detect duplicate registration

[yy yy]

Hi,
I'm developing a SIP regsitrar server, and I endcountered the following problem:
2 User agents have the same configuration - same user ID, same authentication user, same password configured. Both of them try to register to the same registrar at about the same time. Since their configuration is correct by the registrar database, both of them can be accepted.

How can detect such a situation, and accept only one?
It is possible that there is only one UA, which reboots and sends me REGISTER messages again & again, possibly with a different ip address in contact (in case of DHCP) on each REGISTER message, 
in this case I should accept each REGISTER message, since this is a normal situation, which means that if one UA is already registered, and the expiration time has not passed, I should not reject another REGISTER message from the same UA.

Is there a way described in the SIP RFCs that overcomes this situation?

Regards,
Yuval

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