Black Box LBH2001A-H, Инструкция по установке и эксплуатации, Страница: 34 / 73

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Gigabit Media Converter Switch Installation & User Guide
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2.3 Frame Buffering and Latency
The LBH2001A Series Converter Switches are store-and-forward switches.
Each frame (or packet) is loaded into the Switch’s memory and inspected before
forwarding can occur. This technique ensures that all forwarded frames are of a valid
length and have the correct CRC, i.e. they are good packets. This eliminates propagation
of bad packets, enabling all of the available bandwidth to be used for valid information.
While other switching technologies such as "cut-through" or "express" impose
minimal frame latency, they will also permit bad frames to propagate out to the Ethernet
segments connected. The "cut-through" technique permits collision fragment frames,
which are a result of late collisions, to be forwarded to add to the network traffic. Since
there is no way to filter frames with a bad CRC (the entire frame must be present in order
for CRC to be calculated), the result of indiscriminate cut-through forwarding is greater
traffic congestion, especially at peak activity. Since collisions and bad packets are more
likely when traffic is heavy, the result of store-and-forward operation is that more
bandwidth is available for good packets when the traffic load is greatest.
To minimize the possibility of dropping frames on congested ports, each
LBH2001A Series Converter Switch dynamically allocates buffer space from 64Kb