SOURCEFORGE » RALF » 2014 Evaluation of videoconference and streaming

h1. Presentation of results VC

In VoIP, quality simply means being able to listen and speak in a clear and continuous voice, without unwanted noise. Quality depends on the following factors:

* data loss

* jitter

* latency, leading to echo

Latency:

Latency has the reputation of being the enemy of VoIP. It is also called lag.

Latency is the time between the moment a voice packet is transmitted and the moment it reaches its destination. It of course leads to delay. If the delay is too important our videoconference will be rambling, we will have to wait after each sentences the response of the other. 

Latency is caused by slow network links.

Consequences of the latency:

* Disturbs synchronization between voice and other data types, especially during video 

* Untimeliness can results in overlapping noises, with one speaker interrupting the other

!Latency.png!

T is the time that A has to wait before speaking again.

For the experience as we were in the same room, it was difficult to hear the latency. We put an important round trip time. 

What we notice, is that if the latency remains constant, the users may adapt their conversation. They will wait for the answer of the other a few time (each time the same) before speaking again. The conversation is not fluid but we can avoid overlapping noise.

But when we have jitter, problems increase.

Jitter

Jitter is defined as a variation in the delay of received packets. At the sending side, packets are sent in a continuous stream. Due to network congestion, improper queuing, or configuration errors the delay between each packet can vary instead of remaining constant. Jitter is an important problem during a video conference because people don’t know when the have to speak or not and it will introduce important overlapping noise and echo with people interrupting the other.

!jitter.png!

For the experience as we were in the same room, the delay was detectable only for important round trip time. We change the round trip time during our conversation but it was difficult to catch the impact of the changes as we were on the same room. It was difficult to find a good experiment which highlight the jitter.

To conclude, we saw the impact of the lag and the jitter during our experiments. We saw why it is very important to take them into account during a videoconference and to do everything we can to avoid them.