GarrettCom Magnum Quad-Series Installation And User Manual page 16

Magnum Quad-Series Fiber Switches
Magnum Quad-Series unit to be applied to all traffic loads, even when the traffic activity
is unbalanced across the ports. Since the traffic on an operating network is constantly
varying in packet density per port and in aggregate density, the Magnum Quad-Series
Switches are constantly adapting internally to provide maximum network performance
with the least dropped packets.
When the Switch detects that its free buffer queue space is low, the Switch
sends industry standard (full-duplex only) PAUSE packets out to the devices sending
packets to cause "flow control". This tells the sending devices to temporarily stop
sending traffic, which allows a traffic catch-up to occur without dropping packets. Then,
normal packet buffering and processing resumes. This flow-control sequence occurs in a
small fraction of a second and is transparent to an observer. See Section 4.6 for
additional details.
Another feature implemented in Magnum Quad-Series Switches is a collision-
based flow-control mechanism (when operating at half-duplex only). When the Switch
detects that its free buffer queue space is low, the Switch prevents more frames from
entering by forcing a collision signal on all receiving half-duplex ports in order to stop
incoming traffic.
The latency (the time the frame spends in the Switch before it is sent along or
forwarded to its destination) of the Quad-Series Switches varies with the port-speed
types, and the length of the frame is a variable here as it is with all store-and-forward
switches. For 10 Mb-to-10 Mb or 10 Mb-to-100Mb or 100Mb-to-10 Mb forwarding, the
latency is 15 microseconds plus the packet time at 10 Mb. For 100Mb-to-100Mb
forwarding, the latency is 5 microseconds plus the packet time at 100Mb.
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Installation and User Guide (06/03)
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