For calculating QoS Score i saw this link
How latency is obtained from Asterisk server is RTT and latency same?
I have never heard of latency being included in an MOS score calculation, and the key part of MOS, the human judgement of the degradation caused by the chosen codec, seems to be missing from the formula
It is not possible to measure latency from within the system.
There is no mechanism to allow a SIP user agent to calculate RTP round trip time, and network prioritisation, and fast paths for RTP, may mean that the SIP round trip time measured, for example, by the response time for OPTIONS, may differ significantly.
As far as I know, the only valid way of getting a true MOS is by using a panel of humans and getting their opinions, as that is how it is defined. Any attempt to calculate one from engineering parameters can only be an approximation.
ITU T P.800 defines conversation and listener scores. I’m not sure which one is most used for VoIP, but only conversation scores could possibly be affected by latency.
In conversations, round trip time (of the media, not the signalling) will affect the ability to converse, no the one way latencies. Also conversations are end to end, so the conversation opinion score will reflect the whole system, not one component.
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