[SR-Users] What SIP stack does Kamailio or OpenIMSCore implements?

[天]

Hi, I am a rookie in SIP related area. 
I run into OpenIMSCore in recent days, and then I was introduced to Kamailio.
Now I am wondering what SIP stack does Kamailio or OpenIMSCore implements? Or neither of them use a SIP stack?
Can anybody help me on this? Thanks !
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