You have a VoWLAN configured for platinum QoS, WMM, and CAC. IP phones for this VoWLAN include the Nokia and Cisco Unified Wireless IP Phones 7920G (pre-v2.0 firmware), 7921G, and 7925G. The…

Mandatory data rates affect association eligibility for all clients, not the ability to place calls after successful association.

Call Admission Control with WMM requires client devices to send a TSPEC (Traffic Specification) request before initiating a voice call so the WLC can evaluate available bandwidth. The Nokia IP phones and Cisco 7920G with pre-v2.0 firmware lack TSPEC support, so they can associate to the WLAN but are blocked from placing calls because they cannot complete the CAC negotiation. The 7921G and 7925G support TSPEC, which is why they function correctly under the same CAC policy.

EDCA (Enhanced Distributed Channel Access) is already implicitly active as part of WMM; enabling it separately would not resolve a TSPEC compatibility issue.

HCCA (Hybrid Coordination Function Controlled Channel Access) is a separate QoS mechanism not required for standard WMM voice calls and is rarely deployed in enterprise networks.

Reserved roaming bandwidth governs headroom for roaming clients, not the fundamental ability to initiate a call without TSPEC support.

Expedited bandwidth allows clients to exceed their TSPEC allocation but does not resolve the underlying problem of clients that cannot issue a TSPEC at all.