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That directive, option boot-server, tells phones to contact the server http://server.example.com/proneprov/ for their configuration files and it w ill attempt to retrieve two files, a common configuration file, that contains settings that can apply to more than one phone, and a device configuration file, that contains settings that apply to only one phone, if the phone fails to retrieve the files, it will make 4 more attempts, and then stop. The successful retrieval of files will stop the process, as the phone will load the files and startup using the specified settings.
Common configuration file
Each phone model has a unique common configuration file, listed below.
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Please note that if you see the phone making multiple GET requests for a file, it is because the phone was not able to successfully retrieve or parse the first file. Also If the configuration file does not include a Version identifier in its first line, the phone will not parse it successfully.
Device configuration file
The device configuration file will be the MAC address of the phone with a .cfg extension at the end. The Phone will request the common file first and then the device configuration file second. As mentioned before you want to to populate the common file with settings that all phones will utilize while populating the device configuration file with device specific settings such as the phones pjsip account credentials.
A20, A22, and A25 TXT Configuration
A30 TXT Configuration
For a basic PJSIP line configuration to be added to your device configuration file you should review the SIP CONFIG MODULE Elements within the text configuration file at the link above.
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