Fix SIP Call Dropouts and Call Quality Issues

My SIP trunk is stable until a call is in progress—then the line suddenly drops, but only with certain callers. I need an engineer who can jump in quickly, pinpoint the root cause, and apply a clean, lasting fix.

Here’s what I can share right away:
• PBX and SIP provider details
• Sample call logs showing the drop pattern
• Remote access for packet captures (Wireshark or similar)

Your goals:
1. Analyse signalling and RTP flow to isolate why calls terminate mid-conversation.
2. Recommend and implement the configuration or network adjustment that stops the drops.
3. Provide a short report so I understand what was changed and why.

I’m looking for someone comfortable with Draytek Vigor Router configuration for use with our SIP phones. Uur SIP Provider is Telair and the handsets are Yealink. If you can tackle it promptly and keep me posted during the process, get in touch and I will arrange to be onsite and provide you remote access so that you can invetigate and implement a fix on the Draytek. I will be your eyes and ears and action the on-the-ground tasks.

Details

NBN Fiber 1000Mbs / 100Mbs connection
DrayTek Vigor2927ac Router with NBN connection into WAN1
3 Netgear Orbi Mesh Wifi into Darytek LAN P1
1 DLINK unmanaged 24 port switch into Draytek LAN P2
2 small 8 port switches in cabinet, unknown purposes.
10-11 Yealink (forget model) handsets
6 Yealink handsets upstairs - all ethernet connected via the DLINK switch and into Draytek
4-5 Yealink handsets downstairs, some using WiFi some ethernet
1 Epson MFC via Ethernet to DLINK Switch but having discovery issues but on Draytek gateway IP.

There is no specific VLAN or other configuration in Draytek router.
Workstation PCs and Laptops, some wifi some ethernet.