Yealink SIP-T4X Administration Manual page 254

IP phones use the PoE preferentially.
Auto provisioning refers to the update of IP phones, including update on the
configuration parameters, local phonebook, firmware and so on. You can use auto
provisioning on a single phone, but it makes more sense in mass deployment.
Plug and Play (PnP) is a method for IP phones to acquire the provisioning server address.
With PnP enabled, the IP phone broadcasts the PNP SUBSCRIBE message to obtain a
provisioning server address during startup. Any SIP server recognizing the message will
respond with the preconfigured provisioning server address, so the IP phone will be
able to download the configuration files from the provisioning server. PnP depends on
support from a SIP server.
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Do one of the following:
Ensure that the configuration is set correctly.

Reboot the IP phone. Some configurations require a reboot to take effect.

Ensure that the configuration is applicable to the IP phone model.

The configuration may depend on support from a server.

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They are codes that the IP phone sends to the server when a certain action takes place.
On code is used to activate a feature on the server side, while off code is used to
deactivate a feature on the server side.
For example, if you set the Always Forward on code to be *78 (may vary on different
servers), and the target number to be 201. When you enable Always Forward on the IP
phone, the IP phone sends *78201 to the server, and then the server will enable the
Always Forward feature on the server side, hence being able to get the right status of
the extension.
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Troubleshooting
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