It is interesting that you are getting a low ASR with cause code 16 as this is typically what you would want to see when the call ends.
As it says – Cause Code 16 is Normal Call Clearing – which is a good thing.
This is unless of course you are getting this back falsely from the far end, for example all the calls are clearing with a 16 but the call durations are all zero seconds. This can happen when sending to analogue lines or gsm gateways if the configuration is incorrect.
Typically cause codes like 34 – No channel available – are responsible for lowering your ASR levels so keep an eye out for these to.
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Hope this helps.