Where to look for the source of problems on the network (voip)?

Question

SIP

good afternoon
equipment:
asterisk server, then a switch, clients are connected to it (one network segment), and a cable goes to another building. there are two tplink TL-SF1024D, to which clients are connected (second segment).
physically a network for a telephony - separate.
grandstream gxp1610 devices.
problems suddenly started in the second segment:
you pick up the phone - the ready signal does not immediately appear (and the indicator on the phone, accordingly, does not immediately light up).
a call comes in, you answer - the channels do not immediately connect (delay 1-5 seconds). while the call indicator on the phone continues to blink until a connection is made.
during a conversation, the sound may simply disappear.
after dialing the number, a long wait for the start of the call.
All this is absolutely sporadically manifested.
This problem has already appeared in the past year. decided by replacing the cable between the segments. I haven't looked at the dumps yet. last year - no crime was found there.
There are many assumptions, but in which direction to dig is not yet clear to me, I ask for advice on where to start, what to bet on. there are no problems in the first segment.

Answer 1

If the settings are the same on both segments, then check the connection between the buildings again. Watch errors on the port.