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Chapter 41 Configuring Cisco IOS IP SLAs Operations
Configuring IP SLAs Operations
Analyzing 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 receive them 10 ms
apart. But if there are delays in the network (like queuing, arriving through 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 target. 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)
•
Round-trip delay (average round-trip time)
Because the paths for the sending and receiving of data can be different (asymmetric), you can use the
per-direction data to more readily identify where congestion or other problems are occurring in the
network.
The UDP jitter operation generates synthetic (simulated) UDP traffic and sends a number of UDP
packets, each of a specified size, sent a specified number of milliseconds apart, from a source router to
a target router, at a given frequency. By default, ten packet-frames, each with a payload size of 10 bytes
are generated every 10 ms, and the operation is repeated every 60 seconds. You can configure each of
these parameters to best simulate the IP service you want to provide.
To provide accurate one-way delay (latency) measurements, time synchronization, such as that provided
by NTP, is required between the source and the target device. Time synchronization is not required for
the one-way jitter and packet loss measurements. If the time is not synchronized between the source and
target devices, one-way jitter and packet loss data is returned, but values of
0
are returned for the
one-way delay measurements provided by the UDP jitter operation
Note
Before you configure a UDP jitter operation on the source device, you must enable the IP SLAs
responder on the target device (the operational target).
Beginning in privileged EXEC mode, follow these steps to configure UDP jitter operation on the source
device:
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
ip sla
operation-number
Create an IP SLAs operation, and enter IP SLAs configuration mode.
