Core Issue
After an atadefault.cfg file is created in the Trivial File Transfer Protocol (TFTP) root directory and the Cisco Analog Telephone Adapter (ATA) 186 is reset, when the Skinny Call Control Protocol (SCCP) parameter is changed to 0, it does not work. In the web page of the ATA in the SCCP parameters, the Endpoint ID (EPID) is still set to (.).
In addition, some of the ATAs fail to download the configuration from the TFTP server.
Resolution
In the older ATA load EPIDx specifies whether to enable the Phone 1 and/or Phone 2 ports on the Cisco ATA in order to register with Cisco CallManager. This EPID is replaced with EPID1orSID1 or SID1 in the new load. If EPID is shown in the parameters, it is recommended to upgrade the ATA load first. For Voice software Download
This issue also occurs when the ATA does not load the file properly, or it loads the wrong file from a TFTP server. It is suggested to use the tftpd32, which is used most often by Cisco in order to upload files.
If ATAs fail to download the configuration from the TFTP, use the ata.cfg file instead of the atadefault.cfg file. If there is one as ATA, take the configurations with its MAC address as well.
Refer to these documents for more information: