V6: Advanced - Advanced Network (Section): SIP T1 (ms)
V7/8: Advanced - SIP/RTP (Tab) - SIP(Section)__SIP T1 (ms)
Set the retry timer in milliseconds after which an unanswered request is resent. If it is set to 500, the phone will resend the unanswered request after 500, 1000, 2000, 4000, 6000 ... 31500 ms. If the request is still unanswered after this procedure, an error message will be shown on the display.
Integer values, e.g. 500, min value is 100