What is network link flow control and how does it work in Red Hat Enterprise Linux ?

Issue

• What is network link flow control and how does it work in Red Hat Enterprise Linux?
• When I run the ethtool command, I receive the following output. Is Control flow enable ? What do the last 2 rows mean ?
• I'm seeing pause frames from ethtool -S what do these mean?

[root]# ethtool -a eth4
Pause parameters for eth4:
Autonegotiate:  on
RX:             on
TX:             on
RX negotiated:  off
TX negotiated:  off