Q.850 cause 28 Invalid number format (address incomplete)
Q.850 causeITU-T Q.850 Table 1
What it means
The dialed number's format was invalid or incomplete (Invalid number format).
Where you see it
In ISUP/BICC REL messages, 2G/3G DTAP Disconnect, and SIP Reason headers (Q.850;cause=…).
What to check
Confirm the dialed number is correctly formatted and complete.
Check the cause location (user, private or public network) to see which side released the call.
Got a trace with Q.850 cause 28 Invalid number format (address incomplete)? Drop it in the analyzer: it finds the step that really failed first, which node sent the code and what to ask the other side. Captures, test-system PDFs and vendor exports. 5 free analyses a month, no sign-up.