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Cisco Bug: CSCte57847 - PRE4: ATM VC throughput limitation in over-subscription with 64B frame

Last Modified

Feb 03, 2017

Products (1)

  • Cisco 10000 Series Routers

Known Affected Releases

12.2(33)SB7

Description (partial)

Symptom:
ESR10008 with PRE4 tail-drop packet on ESR-4OC3ATM LineCard when set 2,160VC with 64Byte Frame Length.
The total vc shaping rate is larger than total vp shaping rate.
It is over-subscription condition.
---------------------------------------------------------------------------------------------
One pvp shaping rate = 45Mbps
        The total vc rate within above one pvp is 12Mbps X 180vc = 2160Mbps
        45Mbps(pvp) << 2,160Mbps(vc total)
---------------------------------------------------------------------------------------------


Conditions:
[Topology in RTP Lab]
IXIA(XM-1202/10)-->(Gi6/0/0.100)ESR_PRE4(ATM5/0/0-3)==(ATM5/0/0-3)ESR_PRE2(Gi4/0/0)-->(XM-12 02/09)

ESR(c10008) have PRE4 or PRE2 with 12.2(33)SB7.
PRE4 and PRE2 are connected by 4 fiber cable.
The ATM interface is ESR-4OC3ATM-SM.
There are '4 atm-interface x 3vp x 180vc' = total 2,160vc
The total traffic load from IXIA is 64Byte Ethernet Frame, 510,339 frmae/sec, 261Mbps.

[Phenomenon]
On the above topology, the following phenomenon happen.
 - The PRE4 tail-drop packet on ESR-4OC3ATM LineCard when IXIA send 
    64Byte Ethernet Frame, 510,339 frmae/sec, 261Mbps..
   In case of IPLength is 200Byte, or 1500Byte, this phenomenon don't happen.

 - This phenomenon don't happen with '1 atm interface x 3vp x 180vc' = 540vc

 - This phenomenon don't happen with '4 atm interface x 1vp x 180vc' = 720vc

 - This phenomenon don't happen with '4 atm interface x 2vp x 180vc' = 1440vc

 - This phenomenon happen with '4 atm interface x 3vp x 180vc' = 2,160vc
   The 'Total output drops:' is counted on all 4 atm interface when this phenomenon happened.

 - This phenomenon don't happen on PRE2 for 46/200/1500Byte IPLength.
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