Blog Entry of Friday, August 28 2009 in PRTG 7
New Features in PRTG 7.2: VoIP Monitoring Using Cisco IP SLA
During the
beta test of version 7.2 of PRTG Network Monitor I am posting a few posts about new features that we have built into this new version.
In
yesterdays blog entry I wrote about the new QoS sensor which measures various service quality parameters of a network connection by probing the connection with UDP packages.
Today I would like to introduce our second new monitoring solution for VoIP quality, the new IP SLA sensor.
What is IP SLA?
Wikipedia describes
IP SLA as "a feature included in the Cisco IOS Software that can allow administrators the ability to Analyze IP Service Levels for IP applications and services. IP SLA's uses active traffic-monitoring technology to monitor continuous traffic on the network. This is a reliable method in measuring over head network performance."
IP-SLA is mostly used to have a look at sound quality for VoIP traffic. VoIP related network traffic is especially sensitive to even slight problems in connectivity. Sound quality drops dramatically when UDP packets are not received in a timely fashion, if packets are lost or reordered.
Who Can Use This Sensor?
This feature is only available in the more expensive boxes from Cisco. If you don't have IP SLA capable routers/switches you can still get similar information with our
QoS sensor introduced yesterday which does not require any special hardware - just two PCs running Windows.
If you do own hardware which supports IP SLA then PRTG brings you probably the least-cost monitoring solution for IP SLA. Most vendors charge extra for IP SLA support (a thousand bucks and more). Following Paessler's long term policy we simply include this as one of our sensor types. With PRTG you can even use the Freeware Edition to monitor IP SLA!
What Parameters Are Monitored?
PRTG monitors the following parameters
- ICPIF (Calculated Planning Impairment Factor)
- MOS (Mean Opinion Score)
- Avg. Jitter
- Packets Lost
- Packets Out Of Sequence
- Packets Late
- Average Round Trip Time (RTT)
- DNS RTT
- TCP RTT
- Transaction RTT
Especially two of these parameters are interesting for VoIP: For MOS Cisco conducted a panel test where a wide range of listeners have judged the quality of voice samples sent using particular codecs, on a scale of 1 (poor quality) to 5 (excellent quality). The Cisco device calculated the corresponding value for the current network connection based on the network parameter measurements like jitter and packet loss. The values and their meanings are:
| MOS
|
Quality
|
Expected Quality Impairment
|
| 5
|
Excellent
|
Imperceptible
|
| 4
|
Good
|
Perceptible, but not annoying
|
| 3
|
Fair
|
Slightly annoying
|
| 2
|
Poor
|
Annoying
|
| 1
|
Bad
|
Very annoying |
The second parameter ICPIF "is the sum of measured impairment factors minus a user-defined access Advantage Factor that is intended to represent the user's expectations, based on how the call was placed (for example, a mobile call versus a land-line call)" (quoted from Cisco website).
| Upper Limit for ICPIF
|
VoIP Call Communication Quality
|
| 5
|
Very good
|
| 10
|
Good
|
| 20
|
Adequate
|
| 30
|
Limiting case
|
| 45
|
Exceptional limiting case
|
| 55
|
Customers likely to react strongly (complaints, change of network operator) |
For more information about these measurements see
P SLAs--Analyzing Service Levels Using the VoIP Jitter Operation on the Cisco Website.
How Can I Use PRTG's New IP SLA Sensor?
If you haven't done so already you must create a device for the Cisco device that you want to monitor. Remember to enter SNMP credentials because PRTG uses SNMP to get the data from the switch.
The second step is to create a new sensor on that device, choose "IP SLA" from the "VoIP and Infrastructure" section and follow the instructions on the screen. A few moments later you will see the current measurements in PRTG's user interface.
