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IP SLA: ICPIF always 1, MOS always 4.34

Hi there

Last week, a regional branch encountered echo in the Voice-Service and our VoIP-Provider saw a Problem with Jitter.

Amongst other things, we decided to monitor Jitter with IP SLA.

RTR-Responder: Catalyst 3560G with c3560-ipservicesk9-mz.122-25.SEE2

Sender: set up on a Catalyst 3560G with c3560-ipservicesk9-mz.122-46.SE

conf on sender:

ip sla 3

udp-jitter 10.144.202.16 32514 codec g711alaw

tos 46

frequency 30

ip sla schedule 3 life forever start-time now

this results to:

n91250-0280#sh ip sla conf 3

IP SLAs, Infrastructure Engine-II.

Entry number: 3

Owner:

Tag:

Type of operation to perform: udp-jitter

Target address/Source address: X.X.X.X/0.0.0.0

Target port/Source port: 32514/0

Type Of Service parameter: 0x2E

Operation timeout (milliseconds): 5000

Codec Type: g711alaw

Codec Number Of Packets: 1000

Codec Packet Size: 172

Codec Interval (milliseconds): 20

Advantage Factor: 0

Verify data: No

Vrf Name:

Control Packets: enabled

Schedule:

Operation frequency (seconds): 30

Next Scheduled Start Time: Start Time already passed

Group Scheduled : FALSE

Randomly Scheduled : FALSE

Life (seconds): Forever

Entry Ageout (seconds): never

Recurring (Starting Everyday): FALSE

Status of entry (SNMP RowStatus): Active

Threshold (milliseconds): 5000

Distribution Statistics:

Number of statistic hours kept: 2

Number of statistic distribution buckets kept: 1

Statistic distribution interval (milliseconds): 20

Enhanced History:

=====================

Now, the special thing are the results:

n91250-0280#sh ip sla stat agg 3

Round Trip Time (RTT) for Index 3

Start Time Index: 16:22:48.637 MET Thu Feb 26 2009

Type of operation: jitter

Voice Scores:

MinOfICPIF: 1 MaxOfICPIF: 1 MinOfMOS: 4.34 MaxOfMOS: 4.34

RTT Values

Number Of RTT: 65809

RTT Min/Avg/Max: 4/9/455 ms

Latency one-way time milliseconds

Number of Latency one-way Samples: 27487

Source to Destination Latency one way Min/Avg/Max: 0/3/288 ms

Destination to Source Latency one way Min/Avg/Max: 6/9/454 ms

Jitter time milliseconds

Number of SD Jitter Samples: 65741

Number of DS Jitter Samples: 65741

Source to Destination Jitter Min/Avg/Max: 0/2/277 ms

Destination to Source Jitter Min/Avg/Max: 0/3/414 ms

Packet Loss Values

Loss Source to Destination: 0 Loss Destination to Source: 0

Out Of Sequence: 0 Tail Drop: 2191 Packet Late Arrival: 0

Number of successes: 68

Number of failures: 0

Quite ugly Jitter-Times, but great values for ICPIF and MOS, without any variation. Of course I reported only the latter to management and dissed the guys from the branch office :)

joking apart: what went wrong with those values? did we miss something in the configuration, is this a bug or is a cat3560 simply not able to compute ICPIF or MOS?

On a side node: Is there any good guide, how to interpret IP SLA Jitter Values like what values in "Destination to Source negative jitter Number/Sum/Sum2" would be good/reasonable/catastrophic?

thx in advance and greetings from bern

stefan mueller

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