To resolve this issue, install one of the following cumulative updates, as appropriate for the telephone that you use:
Note After you apply one of the cumulative updates, you must reregister Microsoft Lync Phone Edition for your telephone because Lync Phone Edition is disconnected from the Lync server. Get the cause of the issue in the "More Information" section in this article.
When an address resolution protocol (ARP) request that Lync Phone Edition sends is not responded, the number of the ARP request retry will be increased. Then, the SIP keep-alive interval time exceeds the time-out value. Therefore, a Lync server drops the connection to Lync Phone Edition.