Prepare an Extension for Plug and Play

From Pbxnsip Wiki

Binding to a MAC address

Whenever you want to use plug and play for an extension, you need to tell the PBX about that.

The PBX identifies a device by its MAC address (see for example http://en.wikipedia.org/wiki/MAC_address). When a device supports plug and play, it includes its MAC address in the request for configuration information. The PBX uses three ways to find the extension(s) that match this MAC address:

• If you explicitly specify a MAC address for an extension, then the PBX will associate that extension with that device. You can specify only one MAC address per extension. However, you can use the MAC address in more than one extension. Then the PBX will try to assign more than one extension to that device. It depends on the device if it supports more than one registration.

• In many cases it is inconvenient to enter the MAC addresses for devices. Therefore, the PBX accepts two wildcards for the provisioning. The star symbol ('*') is used for the permanent assignment mode. The PBX will wait until a user agent requests a configuration from the PBX. If that user agent has no configuration assigned to a specific account, it will search for permanent assignments and remember the MAC address of this user agent for this account. The next time when the same user agent boots up it will receive the same extension number and no other user agents will receive that extension number.

• The other mode is temporarily assignment. This mode is indicated by a question mark symbol ('?'). The PBX will search a "free parking slot". An extension is available for plug and play if no other user agent is registered to that extension. That means it will not remember that the user agents was assigned with the extension. The next time when the user agent boots up it might receive another extension number.

Password Provisioning

For complete plug and play, it is desirable to provide the passwords along with the other configuration data. However, this possibility may open a security hole. The PBX has practically not way to authenticate the device. For example, if another user in the network requests the same configuration information, the PBX would provide the same configuration again. The MAC address as key to the configuration data is a very weak protection – many devices use the MAC address in regular SIP requests.

Therefore, the PBX offers three modes:

• "Always" means that the PBX will always place the passwords into the provisioning files. That means everyone who know the MAC address in the network can get the configuration data for a device, including the password. This mode is acceptable in trusted environment, for example small offices or home offices.

• "Once" means that the PBX first checks if the password flag for the respective account is already set, and if not it sends the password; then sets the flag. This mode is useful, when the administrator sets the devices and has control over the time when the device is being provisioned. If the device uses https as protocol for transporting the configuration data, this mechanism is secure.

• "Never" means that the PBX does not provision passwords. This is obviously a safe mode. If the user has the possibility to enter the password on the device (e.g. on the keyboard), this will give the system a good security, while still being reasonable simple for end users.

If the administrator uses the "once" mode and the provisioning of a password fails, this is an indication that someone else retrieved the password by accident or by purpose. In this case the administrator should reset the flag for the extension and choose a new password.

Other relevant settings

There are some more relevant settings that you should consider when performing plug and play:

• The time zone is usually automatically provisioned on the devices. Make sure that you have chosen the right time zone for the system, domain or the extension.

• The dial plan can also be provisioned for some devices. Especially for customers in the North American Numbering Plan can benefit from this feature, as they (usually) don’t have press the "Send" button on the phone to start calls.

• Some profiles also provision star codes. For example, the code to retrieve the voicemail can be sent to the device. Make sure that the codes are set up correctly.

• The address book can also be provisioned for some devices. If you want to provide a domain or extension address book, you should set this up before starting the phones. If you do changes in the address book, you need to restart the devices so that they pick the changes up. Some devices support real-time access to the PBX, where a restart is not necessary.

• Some devices support provisioning of the busy lamp field (BLF). You can monitor other extensions, but you can also monitor the status of the hunt group, the agent groups, the CO-lines, conferences and other account types. In order to do this, you need to specify the "List of extensions to watch" in the user mode for an extension. Check the Dialog Permissions state of the account that you want to watch to make sure that the PBX allows the subscription.

• The PBX also supports the provisioning of the number of lines for an extension. Some phones use this information for defining the layout of the buttons.