Cisco 8861 - Power Management

Cisco IP Phone 8861 and 8865 Wireless LAN Deployment Guide
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Power Management
Proxy ARP can optimize idle battery life, by answering any ARP requests on behalf of the phone.
To enable Proxy ARP, set Client ARP Caching to Enable.
Also ensure that Forward ARP Requests to Radio Interfaces When Not All Client IP Addresses Are Known is checked.