![Cisco ASR 9000 Serie Скачать руководство пользователя страница 225](http://html.mh-extra.com/html/cisco/asr-9000-serie/asr-9000-serie_configuration-manuals_66679225.webp)
How to Implement IP Service Level Agreements
Configuring IP Service Levels Using the UDP Jitter Operation
The IP SLA UDP jitter monitoring operation is designed to diagnose network suitability for real-time traffic
applications such as VoIP, Video over IP, or real-time conferencing.
Jitter means interpacket delay variance. When multiple packets are sent consecutively from source to
destination
—
for example, 10 ms apart
—
and if the network is behaving ideally, the destination can receive
them 10 ms apart. But if there are delays in the network (for example, queuing, arriving through alternate
routes, and so on), the arrival delay between packets can be greater than or less than 10 ms. Using this example,
a positive jitter value indicates 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
like VoIP, positive jitter values are undesirable, and a jitter value of 0 is ideal.
However, the IP SLA UDP jitter operation does more than just monitor jitter. The packets that IP SLA generates
carry sending sequence and receiving sequence information for the packets, and sending and receiving time
stamps from the source and the operational target. Based on these, UDP jitter operations are capable of
measuring the following functions:
•
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)
As the paths for the sending and receiving of data may be different (asymmetric), the per-direction data allows
you to more readily identify where congestion or other problems are occurring in the network.
The UDP jitter operation functions by generating synthetic (simulated) UDP traffic. By default, ten
packet-frames (N), each with a payload size of 32 bytes (S) are generated every 20 ms (T), and the operation
is repeated every 60 seconds (F). Each of these parameters is user-configurable, so as to best simulate the IP
service you are providing, or want to provide.
This section contains these procedures:
Enabling the IP SLA Responder on the Destination Device
The IP SLA Responder must be enabled on the target device, which is the operational target.
By configuring the
ipsla responder
command, you make the IP SLA Responder open a UDP port 1967 and
wait for a control request (not for probes). You can open or close a port dynamically through the IP SLA
control protocol (through UDP port 1967). In addition, you can configure permanent ports.
Permanent ports are open until the configuration is removed. Agents can send IP SLA probe packets to the
permanent port directly without a control request packet because the port can be opened by the configuration.
If you do not use permanent ports, you have to configure only the
ipsla responder
command.
Cisco ASR 9000 Series Aggregation Services Router System Monitoring Configuration Guide, Release 4.2.x
209
Implementing IP Service Level Agreements
How to Implement IP Service Level Agreements