The subscriber is “hard to hear” over ip telephony, how does the connection worsen because of what?

Question

SIP

Such a situation:
Managers use ip telephony to call customers, some work from home. Some managers sometimes have two types of problems:
1) Quietly heard.
2) Communication "gurgles", is interrupted.
If we are struggling with the first problem with different headsets, sound card settings, and so on.
What to do with the second is not clear.
The call scheme is as follows:
The subscriber connects to our server, the server on Clodo.ru, on the Asterisk server to record calls.
For external calls we use sipmarket.net The
following chain is obtained:
Manager - Our server - Server sipmarket - Subscriber who is being called
How to check the quality at each stage? Where can gurgling, loss of communication come from?

Answer 1

1. Asterisk 2. Temporarily replace app MixMonitor
with Monitor, this will allow you to listen to each recording channel separately.

Answer 2

Call from two points, if one is good and the second gurgles, the channel lags, most likely to your asterisk from the subscriber.
If you do not trust the experiment, call from three.

Answer 3

90% of cases "gurgling" is a communication channel. Loss, jitter, ping. Check it very easily, includes a dump on the aster, see the traffic.