Application-Specific Scenario: VoIP

The goal of this example is to monitor a G.729a VOIP call, to the specific destination where the IP SLA Responder is configured (ip sla responder):

Router(config)# ip sla 1
Router(config-sla-monitorconfig-ip-sla)#type udp-jitter dest-ipaddr dest-port 1648 codec g729a
Router(config-ip-sla-jitter)# frequency 30
Router(config)# ip sla schedule 1 start-time now


The default settings of a 32-byte test packet size and an interpacket interval of 20 milliseconds are used in this example:

Router# show ip sla configuration 1
IP SLAs, Infrastructure Engine-II
Entry number: 1
Type of operation to perform: jitter
Target address:
Source address:
Target port: 1648
Source port: 0
Operation timeout (milliseconds): 5000
Codec Type: g729a
Codec Number Of Packets: 1000
Codec Packet Size: 32
Codec Interval (milliseconds): 20
Advantage Factor: 0
Type Of Service parameters: 0x0
Verify data: No
Vrf Name:
Control Packets: enabled
Operation frequency (seconds): 30
Next Scheduled Start Time: Start Time already passed
Group Scheduled : FALSE
Life (seconds): 3600
Entry Ageout (seconds): never
Recurring (Starting Everyday): FALSE
Status of entry (SNMP RowStatus): Active
Threshold (milliseconds): 5000
Number of statistic hours kept: 2
Number of statistic distribution buckets kept: 1
Statistic distribution interval (milliseconds): 20
Enhanced History:

Router# show ip sla statistics details 1
Entry number: 1
Modification time: 08:57:19.702 CET Mon Jul 11 2005
Number of Octets Used by this Entry: 14896
Number of operations attempted: 61
Number of operations skipped: 1
Current seconds left in Life: 1759
Operational state of entry: Active
Last time this entry was reset: Never
Connection loss occurred: FALSE
Timeout occurred: FALSE
Over thresholds occurred: FALSE
Latest RTT (milliseconds): 2
Latest operation start time: 09:27:19.709 CET Mon Jul 11 2005
Latest operation return code: OK
Voice Scores:
ICPIF Value: 11 MOS score: 4.06
RTT Values (milliseconds):
NumOfRTT: 992   RTTAvg: 2       RTTMin: 1       RTTMax: 5
RTTSum: 2761    RTTSum2: 8089
Packet Loss Values:
PacketLossSD: 6 PacketLossDS: 2
PacketOutOfSequence: 0  PacketMIA: 0    PacketLateArrival: 0
InternalError: 0        Busies: 0       PacketSkipped: 0
Jitter Values (milliseconds):
MinOfPositivesSD: 1     MaxOfPositivesSD: 2
NumOfPositivesSD: 192   SumOfPositivesSD: 194   Sum2PositivesSD: 198
MinOfNegativesSD: 1     MaxOfNegativesSD: 2
NumOfNegativesSD: 192   SumOfNegativesSD: 194   Sum2NegativesSD: 198
MinOfPositivesDS: 1     MaxOfPositivesDS: 2
NumOfPositivesDS: 233   SumOfPositivesDS: 256   Sum2PositivesDS: 302
MinOfNegativesDS: 1     MaxOfNegativesDS: 2
NumOfNegativesDS: 237   SumOfNegativesDS: 256   Sum2NegativesDS: 294
Jitter Avg: 1   JitterSD Avg: 1 JitterDS Avg: 1
Interarrival jitterout: 0       Interarrival jitterin: 0
One Way Values (milliseconds):
NumOfOW: 992
OWMinSD: 1      OWMaxSD: 3      OWSumSD: 1749   OWSum2SD: 3289
OWMinDS: 0      OWMaxDS: 3      OWSumDS: 1012   OWSum2DS: 1354
OWAvgSD: 1      OWAvgDS: 1


The convention in this output is that a term containing SD implies a direction from source to destination, and a term with DS implies the reverse direction. The output of this show command might not be intuitive; however, it is verbose. It contains the MOS score 4.06, the ICPIF value 11, the minimum/maximum/average RTT, the packet loss in each direction, the out-of-sequence packets, the Missing In Action packet (packetMIA), a lot of statistical jitter, and one-way values for both directions.

A new command, show ip sla statistics, and its variant, show ip sla statistics detail, have been introduced in the latest IOS version. The advantage is clear visualization of the most important parameters. That means the minimum/average/maximum values of the round-trip time, one-way delay, jitter, packet loss for both directions, and the MOS and ICPIF scores:

Router# show ip sla statistics 1
Round trip time (RTT) Index 1
Latest RTT: 1ms
Latest operation start time: *16:21:32.539 PST Wed Sep 27 2006
Latest operation return code: OK
Over thresholds occurred: FALSE
RTT Values
Number Of RTT: 6253
RTT Min/Avg/Max: 1/1/2 ms
Latency one-way time milliseconds
Number of one-way Samples: 0
Source to Destination one way Min/Avg/Max: 0/0/0 ms
Destination to Source one way Min/Avg/Max: 0/0/0 ms
Jitter time milliseconds
Number of Jitter Samples: 6253
Source to Destination Jitter Min/Avg/Max: 1/1/1 ms
Destination to Source Jitter Min/Avg/Max: 1/1/1 ms
Packet Loss Values
Loss Source to Destination: 0 Loss Destination to Source: 0
Out Of Sequence: 0 Tail Drop: 0 Packet Late Arrival: 0
Voice Score Values
Calculated Planning Impairment Factor (ICPIF): 0
Mean Opinion Score (MOS): 0
Number of successes: 23
Number of failures: 0
Operation time to live: 3496 sec



The new ip sla statistics detail command displays an extended version of ip sla statistics, with statistical information such as sum and square sum of the different metrics.

Finally, note that the information can be retrieved via SNMP with the RTTMON-MIB.

Part II: Implementations on the Cisco Devices