# Mavlink protocol functionality

**URL:** <https://discuss.px4.io/t/mavlink-protocol-functionality/2699>\
**Category:** PX4 Autopilot\
**Created:** [March 9, 2017, 6:37pm UTC](https://discuss.px4.io/t/mavlink-protocol-functionality/2699 "2017-03-09T18:37:41Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Bernardo\_Sosa](https://discuss.px4.io/letter_avatar_proxy/v4/letter/b/13edae/32.png) [@Bernardo\_Sosa](https://discuss.px4.io/u/Bernardo_Sosa)\
**Post date:** [March 9, 2017, 6:37pm UTC](https://discuss.px4.io/t/mavlink-protocol-functionality/2699/1 "2017-03-09T18:37:41Z")

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Hello, I’ve read about MAVLINK, its format and everything, but I can’t clearly understand who sends the heart beat?

1. Is it the Quadcopter just because?
2. Is it QGC under normal conditions?
3. Is it a Question - Answer type of protocol?