VoIP Monitoring: Jitter, MOS, ICPIF and more
January 2010 by Keross
Every organization depends on technology as a provider to the business. IT Teams are required to manage and provide a safe, secure and realiable environment to help the business function. With the advancement of data, voice and video links, the need to stay on top of the quality of the links cannot be emphasized enough. At the end of the day, the reactivity of applications and devices to user requests will determine both the experience of the user, and the inherent stability of business operations.
It is crucial therefore, that users can verify service guarantees, validate network performance as well as proactively identify and deal with network issues stemming from poor links. Our Managed Services portfolio works with this motto every single day.
There are various metrics that are of interest when trying to understand voice and link quality:
For the purpose of networks and VoIP, jitter is expressed as a variation in the time between packets arriving, typically caused by network congestion or route changes. This means that the presence of jitter on a network is an issue. For example, data sent 5 ms apart should arrive at the destination 5 ms apart. If there are network problems, the data may arrive, say, 10 ms apart, leading to a jitter of 5 ms. It’s quite clear then, that in an ideal world, jitter should be 0. When monitoring jitter on a link, various aspects can be analysed: source-to-destination jitter vs destination-to-source, average, minimum and maximum jitter. Keeping jitter at all levels as close to zero will ensure your network is operating smoothly and your end-users aren’t complaining.
Latency, or simply, the delay (time) between a packet sent against it being received, is an important indicator of quality of the network. Lower the latency, better your functionality.
MOS Score Table
MOS Quality !Impairment
5 Excellent Imperceptible
4 Good Perceptible but not annoying
3 Fair Slightly annoying
2 Poor Annoying
1 Bad Very annoying
The mean opinion score (MOS) is a numerical indication of the perceived quality of received media after compression and/or transmission. This is expressed as a single number from 1 (lowest perceived audio quality) to 5 (highest).
The ICPIF, or Calculated Planning Impairment Factor loss/delay busyout threshold is an ITU-T G.113 standard to measure quality of service, or QoS. ICPIF represents predefined combinations of loss and delay on a VoIP call. ICPIF values for each call are generated by the gateways. Now that we understand what monitoring VoIP requires, it is important to consider visibility of this information on a network. This is the perfect juncture to announce our addition of Cisco IP Service Level Agreement (IP SLA). Built into every Cisco device, IP SLA enhances our performance collection systems, providing a thorough overview on end-to-end perfomance. Using IP SLA, synthetic transactions are sent between two end points (two network devices, or network device and a server).
As an integrated Managed Service offering, Vision 24/7 now reports on link metrics such as:
o Destination to Source and Source to Destination
o RTT Jitter
o Average Jitter
• Latency (one way, minimum, max)
• Packet Loss and Out of Sequence
Average Jitter Metrics
Along with providing regular connectivity checks on your network, and bandwidth monitoring for you links and tunnels, the IP SLA provides a greater analysis of the status of your networks and links. The integrated alert mechanisms ensure that you are notified by SMS and e-mail the second an issue is detected, allowing you to be proactive when tackling these issues. We are always interested in hearing your feedback in the comments.