Posts Tagged ‘802.1p’

Jul
08

Generally, flow-control is a mechanics allowing the receiving party of a connection to control the rate of the sending party. You may see many different implementations of flow-control technologies at different levels of OSI model (e.g. XON/XOFF for RS232, TCP sliding window, B2B credits for Fibre Channel, FECN/BECN for Frame-Relay, ICMP source-quench message, etc). Flow-Control allows for explicit feedback loop and theoretically implementing loss-less networks that avoid congestion.

For the original Ethernet technology on half-duplex connections there was no possibility of implementing explicit flow control, since only one side could send frames at time. However, you may still remember the Cisco’s so-called “back-pressure” feature on some of the older switches, e.g. Cisco Catalyst 1924. The idea was that switch may send barrage of dummy frames on a half-duplex link, effectively preventing the attached station from transmitting information at given moments of time.

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