IP SLA Statistics Reliable?

Chuan Liu · ‎09-27-2010

Hi,

I have 2 routers configured with IP SLA udp jitter monitoring both as source and destination. They are connected over a private fiber link. But the statistics has never been of any similiarity. One constantly shows a large number of packet loss, while the other shows little. Can one IP SLA operation send that large number of packets? Can someone explain this please?

Thanks in advance.

3845 is configured as:

ip sla responder
ip sla 1
udp-jitter 192.168.176.50 17000 codec g729a
tos 184
ip sla schedule 1 life forever start-time now

1841 is configured as:

ip sla responder
ip sla 1
udp-jitter 192.168.176.51 17000 codec g729a
tos 184
ip sla schedule 1 life forever start-time now

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

on 3845:

sh ip sla stati 1

Round Trip Time (RTT) for       Index 1
        Latest RTT: 4 milliseconds
Latest operation start time: 13:33:54.880 NZDT Tue Sep 28 2010
Latest operation return code: OK
RTT Values:
        Number Of RTT: 999              RTT Min/Avg/Max: 3/4/37 milliseconds
Latency one-way time:
        Number of Latency one-way Samples: 999
        Source to Destination Latency one way Min/Avg/Max: 3/3/36 milliseconds
        Destination to Source Latency one way Min/Avg/Max: 1/0/2 milliseconds
Jitter Time:
        Number of Jitter Samples: 997
        Source to Destination Jitter Min/Avg/Max: 1/1/32 milliseconds
        Destination to Source Jitter Min/Avg/Max: 1/1/2 milliseconds
Packet Loss Values:
        Loss Source to Destination: 1           Loss Destination to Source: 0
        Out Of Sequence: 0      Tail Drop: 0    Packet Late Arrival: 0
Voice Score Values:
        Calculated Planning Impairment Factor (ICPIF): 11
MOS score: 4.06
Number of successes: 59
Number of failures: 0
Operation time to live: Forever

On 1841:

sh ip sla stati 1
IPSLAs Latest Operation Statistics

IPSLA operation id: 1
        Latest RTT: 4 milliseconds
Latest operation start time: 13:34:16.498 NZDT Tue Sep 28 2010
Latest operation return code: Over threshold
RTT Values:
        Number Of RTT: 999              RTT Min/Avg/Max: 3/4/7 milliseconds
Latency one-way time:
        Number of Latency one-way Samples: 510
        Source to Destination Latency one way Min/Avg/Max: 1/1/2 milliseconds
        Destination to Source Latency one way Min/Avg/Max: 3/3/6 milliseconds
Jitter Time:
        Number of SD Jitter Samples: 509
        Number of DS Jitter Samples: 508
        Source to Destination Jitter Min/Avg/Max: 0/122189/62193664 milliseconds
        Destination to Source Jitter Min/Avg/Max: 0/1/3 milliseconds
Packet Loss Values:
        Loss Source to Destination: 4294966376          Loss Destination to Source: 716
        Out Of Sequence: 233    Tail Drop: 4294966836
        Packet Late Arrival: 0 Packet Skipped: 0
Voice Score Values:
        Calculated Planning Impairment Factor (ICPIF): 11
MOS score: 4.06
Number of successes: 55
Number of failures: 0
Operation time to live: Forever

Chester Rieman · ‎10-05-2010

Looks like 2 different IOS version judging by the output differences, but output should be accurate.

Here is the white papaer for udp jitter:

http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6555/ps6602/prod_white_paper0900aecd804fb392.pdf

Looks like the 1841 is reporting a lot more drops to be sure.

However the MOS score and impairment factors are the same for both directions.

I would try clearing the counters and see if the drops reappear, if not, possibly some transient issue

led to this and the results are cumulitive.

Command refernce for this output is here:

http://www.cisco.com/en/US/partner/docs/ios/ipsla/command/reference/sla_04.html#wp1074642

Hope this helps.