Cisco Systems IE 2000 IP SLAs Operation Threshold Monitoring , IP Service Levels by Using the UDP Jitter Operation

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Cisco IE 2000 Switch Software Configuration Guide
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Chapter 45 Configuring Cisco IOS IP SLAs Operations
Information About Configuring Cisco IOS IP SLAs Operations
The pending option is an internal state of the operation that is visible through SNMP. The pending state
is also used when an operation is a reaction (threshold) operation waiting to be triggered. You can
schedule a single IP SLAs operation or a group of operati ons at one time.
You can schedule several IP SLAs operations on a switch running the IP services image by using a single
command through the Cisco IOS CLI or the CISCO RTTMON-MIB. Scheduling the operations to run
at evenly distributed times allows you to control the amount of IP SLAs monitoring traffic. This
distribution of IP SLAs operations helps minimize the CPU utilization and thus improves network
scalability.
IP SLAs Operation Threshold Monitoring
To support successful service level agreement monitoring, you must have mechanisms that notify you
immediately of any possible violation. IP SLAs can send SNMP traps that are trigge red by events such
as these:
• Connection loss
• Timeout
• Round-trip time threshold
• Average jitter threshold
• One-way packet loss
• One-way jitter
• One-way mean opinion score (MOS)
• One-way latency
An IP SLAs threshold violation can also trigger another IP SLAs operation for further analysis. For
example, the frequency could be increased or an ICMP path echo or ICMP path jitter operation could be
initiated for troubleshooting.
Determining the type of threshold and the level to set can be comp lex, and depends on the type of IP
service being used in the network.
IP Service Levels by Using the UDP Jitter Operation
Jitter means interpacket delay variance. When multiple packets are sent consecutively 10 ms apart from
source to destination, if the network is behaving correctly, the destination should rec eive them 10 ms
apart. But if there are delays in the network (like queuing, arriving thro ugh alternate routes, and so on)
the arrival delay between packets might be more than or less than 10 ms with a positive jitter value
meaning that the packets arrived more than 10 ms apart. If the packets arrive 12 ms apart, positive jitter
is 2 ms; if the packets arrive 8 ms apart, negative jitter is 2 ms. For delay-sensitive networks, positive
jitter values are undesirable, and a jitter value of 0 is ideal.
In addition to monitoring jitter, the IP SLAs UDP jitter operation can be used as a multipurpose data
gathering operation. The packets IP SLAs generates carry packet sending and receiving sequence
information and sending and receiving time stamps from the source and the operational ta rget. Based on
these, UDP jitter operations measure this data:
• Per-direction jitter (source to destination and destination to source)
• Per-direction packet-loss
• Per-direction delay (one-way delay)