SIP UA can't receive 500(Internal Server Error) after sending the REGISTER request with the equal CSeq header
field value to the last value of CSeq or lower than the number. The details can be seen as follows:
1 Test topology:
NUT(REG && PX) UA11 UA12 DNS
| | | |
IP : 3ffe:501:ffff:50::50 3ffe:501:ffff:1::1 3ffe:501:ffff:2::2 3ffe:501:ffff:4::1
aor-uri : ss.under.test.com UA11@under.test.com UA12@under.test.com
contact-uri : UA11@node.under.test.com UA12@node11.under.test.com
2 tcpdump file can be seen in "SIP Registrar- REGISTER request with the equal CSeq value to or lower than the last value of CSeq" attachment
3 openser configuration file can be seen in "openser.cfg" attachment
openser configuration file
As far as I know there are some CSeq checks. But I think there is a short time intervall were the same CSeq is allowed to handle retransmissions.