[c-nsp] High drop rate with not much utilization

[Sergio D.]

Hello,
We currently have a DS3 with an outbound service policy prioritizing voice
traffic, some of this voice is not marked correctly (a different issue we
are working on) and it ends up on the class-default queue. The problem is
that we drop packets from that class-default queue even if our outbound
utilization is less than %50. Can someone explain why that happens? I
understand that it could possibly be top secret Cisco algorithm stuff.
Here is a snapshot of when it happens:
Cisco 3845 btw.

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3845-UT02#sh policy-map interface s1/0 output class class-default
 Serial1/0

  Service-policy output: Qos-Policy

    Class-map: class-default (match-any)
      1867364 packets, 271186963 bytes
      5 minute offered rate 13938000 bps, drop rate 15000 bps
      Match: any
      Queueing
        Flow Based Fair Queueing
        Maximum Number of Hashed Queues 256
        (total queued/total drops/no-buffer drops) 0/984/03845-UT02#sh
int s1/0 | in tx|rx
     reliability 255/255, txload 86/255, rxload 91/255



Thanks,
Sergio Danelli