NethVoice CTI: Connection error when only Desktop Phone (NethLink) is enabled – malformed SIP packets from Janus

[mgarra]

Description:

When only the Desktop Phone device is enabled, therefore using NethLink only, a connection issue occurs on NethCTI.

After accessing NethCTI, after a few seconds a connection error appears (see attached screenshot).
At the same time, error messages are shown in the browser console (see attached screenshots).

In the Asterisk log, repeated SIP packet drop warnings are logged, for example:

[2026-01-28 15:26:26] WARNING[128]: pjproject: <?>: sip_transport.c Dropping 508 bytes packet from UDP 192.168.250.14:54020 :
PJSIP syntax error exception when parsing 'From' header on line 4 col 12:
PJSIP syntax error exception when parsing 'To' header on line 5 col 10:
PJSIP syntax error exception when parsing 'Contact' header on line 8 col 20

The same messages are repeated several times within a short time frame.

Analysis performed:

• From sngrep, it is possible to see REGISTER requests marked as malformed sent from the Janus client to NethVoice.
• Calls made through NethLink work correctly.
• The issue therefore seems to be limited to the NethCTI connection, not to call handling.

Alternative behavior:

When also enabling the Web Phone, in addition to the Desktop Phone:

• NethCTI works correctly
• No more disconnections occur
• No malformed SIP packets or Asterisk packet drops are observed

Expected behavior:

Even with only Desktop Phone / NethLink enabled, NethCTI should:

• Remain connected without errors
• Not generate malformed SIP packets
• Not cause SIP packet drops on the Asterisk side

See also:

Mattermost Chat: https://mattermost.nethesis.it/nethesis/pl/1uhqrfohgpnpdndghn55f8n3xw

Attachments:

• NethCTI connection error screenshot
• Browser console error screenshots

• Sngrep traces