So what is the difference between Quality of Experience (QoE) and Quality of Service (QoS)? It has to do with what is being measured. Quality of Service, although a pretty broadly defined term, usually means how well is the network delivering packets. We use QoS techniques like classification and DiffServ to differentiate packet streams in the network and to enhance the delivery of streams that are less tolerent of network impairments like packet loss and jitter. Usually at the highest priority are the voice and video streams we use for real-time communications. This is a very important and necessary function, and I have been writing (and will continue to write) about the details of QoS implementation on this blog.
Supporters of QoE measurement point out that just delivering packets to the far end does not necessarily guarantee a quality experience. Suppose for example that the voice signal reproduced by the VoIP system has a poor signal to noise ratio. Even if all the packets are delivered, if the resulting voice is hard to understand due to noise, the goal if simple and clear communications will not be met. There are a lot of reasons this might happen in a VoIP deployment.
In a typical VoIP deployment a voice stream may start in the PSTN, pass through a gateway into a VoIP environment, get carried across a SIP trunk to a remote site, have the compression type be recoded for compatibility with a second VoIP vendor's equipment and then finally be reconstructed on a VoIP handset. More transitions than this are both possible and probable. A number of problems can be introduced along this path including noise, poor recoding, echo due to a long end-to-end delay, and quality loss due to the type of compression used. The resulting voice quality experienced by the users may be quite low even as the network delivers 100% of the packets on time.
QoE measurement is about being able to reconstruct the voice signal in a measurement device, and to then run signal processing algorithms to determine the call quality. This type of QoE measurement will deliver a score that much more accurately reflects the true user experience than results by just watching the network packet characteristics.
On the panel with me at VoiceCon were Robert Blanton, Senior Sales Engineer with Shoretel, and Dr. Mike Hollier, CTO of Psytechnics. Robert emphasized the importance of monitoring voice qualtiy in the network in keeping a voice deployment tuned up and keeping users happy. Psytechnics offers tools to help with QoE monitoring, and Mike Hollier spoke about the effect of different types of impairment and how they can directly affect listening quality.
Now I know a lot of implementations are not yet measuring packet delivery quality end to end, so jumping to QoE might be a streatch. But the vendors will help here in the coming years. If knowing how well you are delivering voice quality is important to your enterprise, ask your vendors if they have the ability in their endpoints to measure QoE. When the endpoints are all making these measurements, managing the quality of communications delivery will get both better and easier.
