Black Box LPH240A-H, Руководство по эксплуатации

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Chapter 2: Introduction
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There is no way to filter frames with a bad CRC (the entire frame must be
present in order for CRC to be calculated). Since collisions and bad
packets are more likely when traffic is heavy, store-and-forward switch
technology enables more bandwidth to be available for good packets
when the traffic load is greatest.
To minimize the possibility of dropping frames on congested
ports, each LPH240A Series Edge Switch dynamically allocates buffer
space from a 128KB memory pool, ensuring that heavily used ports
receive very large buffer space for packet storage. (Many other switches
have their packet buffer storage space divided evenly across all ports,
resulting in a small, fixed number of packets to be stored per port. When
the port buffer fills up, dropped packets result.) This dynamic buffer
allocation provides the capability for the maximum resources of the
LPH240A 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 LPH240A Series Edge 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.