howto test/measure quality of a VoIP service?

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sbiddle

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#2054887 12-Jul-2018 11:15

Foiler:

The preferred Codec setting on the phones is G729a but an inbound call connects with G722 for both encode and decode, and an outbound call connects with G711a for both encode and decode.

Decode latency varies between 90 and 190 msec for the outbound/inbound calls respectively, but the round trip audio delay is measured roughly at 0.5 sec by one party saying stop to the other party counting one-and-two-and- ...

Unfortunately the Cisco SPA525G2 is reporting the R Factor, MOS-LQ and MOS-CQ fields as Not Available.

SPA series can only measure MOS stats in a CUCM environment.

You have all sorts of potential transcoding occuring, and if you haven't configured the SPA correctly (packet size needs to be changed to 20ms from the default 30ms for G.711) could be seeing some sort of issue with ptime mismatch depending on the SIP proxy.

If there is G.711 to G.722 transcoding occuring (since an inbound call from the Spark PSTN for example can't be native G.722) you could be getting audio issues as a result of the transcoding. Those Cisco phones don't seem to handle this sort of environment that well.

Who actually set this up? I would be configuring things correctly and ensuring they are set to G.711a and disabling G.722 for a start to see what impact that has.

Foiler

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#2055716 13-Jul-2018 13:29

Conversant have responded "You can change to G711a if you want to but it will not have any effect on the phone system"

I presume from that their network decides what coding system to use regardless of the preference set in the phone?

Interesting that we are seeing a mix of coding for different calls .. only one sample but we saw an inbound call connects with G722 and an outbound call connects with G711a.

Foiler

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#2100380 2-Oct-2018 22:47

The customer has now moved VoIP service to 2Talk and have changed all the Cisco phones to Yealink. Prior to the shift it was noted that when connected to Voyager the Yealink model T54S phones provided the same or markedly better voice quality than the Cisco; and both models of phones seemed to provide better quality when connected to 2Talk.

The corollary to this is that there a bunch of spare Cisco phones model 525 and model 504 - is there a second hand market for these or are they best for the dump?

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