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Chapter 4
Cisco's Diagnostic Commands
F I G U R E 4 . 8
Overruns
An underrun is just the opposite of an overrun. When the transmitter runs
at a higher rate than the packets sent from the hardware buffer, an underrun
occurs. Look at Figure 4.9.
F I G U R E 4 . 9
Underruns
Interface Buffers
Interface buffers are intermediate storage. Packets from all of the hardware
buffers are copied to the interface buffers. The switch processor houses the
intermediate buffers by using 512KB for the SP board memory. This memory
is also shared with the autonomous switching cache. Other boards can have
up to 2MB of memory.
Hardware buffer
Overrun condition
Receiver
Hardware buffer
Underrun condition
Transmitter
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