cascades: Vertical 5GHz-lock request letter (Poly handsets band-selection fix)

clients/cascades-tucson/docs/network/2026-06-19-vertical-5ghz-lock-request.md

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+# Cascades — request to Vertical (Richard Turner): set Poly handsets to 5 GHz-only
+
+- **Date:** 2026-06-19
+- **To:** Richard Turner <RTurner@vertical.com> (Vertical, VoIP vendor)
+- **From:** Howard Enos, Arizona Computer Guru
+- **Why:** After the RF optimization, the residual dropped-call/audio issues are handsets stuck on
+  saturated 2.4 GHz despite strong 5 GHz-capable signal (band-selection problem, not coverage).
+  Controller-side band steering is on but not holding the Poly fleet on 5 GHz -> need a phone-side
+  5 GHz band lock. Evidence: handsets on 2.4 at -50 to -60 dBm showing 36-96% retransmission vs <10%
+  for handsets on 5 GHz. Poly OUI 48:25:67.
+
+---
+
+To: Richard Turner <RTurner@vertical.com>
+Subject: Cascades — set Poly handsets to 5 GHz-only
+
+Richard,
+
+We've finished optimizing the WiFi at Cascades. 5 GHz is now clean (2-3% utilization); 2.4 GHz is
+saturated at 84-91% and isn't usable for voice at this site.
+
+The remaining dropped-call/audio issues are all handsets that are sitting on 2.4 GHz despite a strong
+5 GHz-capable signal — some at -50 dBm showing 36-96% packet retransmission, versus under 10% for the
+phones on 5 GHz. It's a band-selection problem, not coverage.
+
+Please set the Poly WiFi handsets at Cascades to 5 GHz only (disable the 2.4 GHz band in provisioning)
+so they can't fall back to 2.4.
+
+Let me know when it's pushed and I'll confirm they re-home to 5 GHz from our side.
+
+Thanks,
+Howard Enos
+Arizona Computer Guru