I recently discovered an interesting behavior of session expiration timer (pjsip_timer_setting) for iOS when app is in background. But I could not figure out why. So when I make a sip call there are 2 cases that will put my app into background, either I hit Home button or I receive an incoming phone call. From app point of view I thought they are the same, applicationWillResignActive: and applicationDidEnterBackground: will be called then app will be put into background and won't be executed anymore until it is waken up again (leave alone keepalive message for the time being). Then I find that if I answer a phone call what happens is what I just described, so when session timer expires my sip session is ended. But when I hit Home button, when session timer expires my app will send out UPDATE message to keep my session alive so my sip session won't die. But how come! When app is in background iOS won't run it anymore; how come it can continually send out UPDATE message ? And why that only happens in the case I hit Home button. Thanks! Qiulang
