Recently I came across an issue with a new customer deployment where the 9951 SIP phones would drop call after 18s. All other SCCP phones were working fine but only these SIP phones would drop the call.
9951 -> SIP -> CUCM -> SIP -> CUBE
Bind commands were in place and the only way I could resolve the issue was forcing RTCP parameter “disabled” under Common phone profile and Enterprise Phone parameters.
System -> Enterprise Phone Configuration
Device -> Device Settings -> Common Phone Profile