User`s guide

Full-Duplex Flow Control
2-8 Typical Configurations
Full-Duplex Flow Control
Normally, flow control is not available on full-duplex ports. This is because the switch
generates flow controls by sending a JAM signal whenever it is unable to forward a
frame. When the host NIC receives the JAM, it will retransmit the packet from
hardware buffers. This is faster than relying on higher level software transport layers,
which must first detect the dropped packet via a time-out mechanism, then regenerate
and re-queue it. Since there are no collisions in full-duplex mode, the traditional
method of generating a flow control will not work. However, the MultiSwitch 300
implements a proprietary flow control protocol on full-duplex ports by sending a
special frame that another MultiSwitch 300 interprets as a signal to briefly halt
transmission to the overloaded port; this will alleviate the over-bandwidth situation.
To gain the advantages of flow control when using full-duplex,
both
switches must be
MultiSwitch 300’s.
NOTE
Full-duplex MultiSwitch 300 flow control works only between MultiSwitch 300s.
Full-duplex flow control should NOT be enabled on a MultiSwitch 300 port if the
device on the other end is not a MultiSwitch 300 (that is, MultiSwitch 6xx,
VNswitch, other vendors’ switches).