Hello Reza,

happy new year.

Basically. flow control is a mechanism that enables congestion control between two connected Ethernet ports. If a port cannot receive any more traffic, with flow control enabled, it would send a pause frame to the device at the remote end, effectively telling the remote device to stop sending frames.

Does that make sense ?

Check this link for a more detailed explanation:

Configuring IEEE 802.3z Flow Control

http://www.cisco.com/univercd/cc/td/doc/product/lan/c3550/12225sec/3550scg/swint.htm#wp1138321

Regards,

GP