The Call Park & Retrieve service allows users to temporarily park an active call. The parked call can later be picked up from any phone by dialing a retrieve code. The typical use case is an assistant who picked up a call directed to an executive. The assistant then puts the call on park for the executive to pick it up when ready.

The sipX system allows as many park extensions to be created as you wish. The call park & retrieve service is provided by the Park Server. This is a stand-alone server component as part of the sipX system that effectively acts as a specialized user agent.

The sipX Call Park Server Implementation

The sipX Park Server implements park orbits with each orbit having its own extension number assigned. The idea of call park & retrieve in a SIP implementation is to have park orbits that are able to notify subscribed clients of their presence status. Similar to a bridged line appearance (BLA), phones can assign park orbits to line keys and then subscribe to the presence notification of the park orbit. This allows an indicator light on the phone to show the user whether the park extension is in use and gives information as to which park extension to pick up. Full presence enabled call park & retrieve services are not yet available as most phones and sipX need some additional capabilities.

While it would be possible in smaller deployments to assign an individual park orbit to every user, in most cases it is more practical to have one or two orbits per department or work group. The maximum number of park orbits that can be configured in sipX is 20 using one instance of the park server. Future releases of sipX will allow many independent park servers in a distributed system.

If two or more users try to park a call to the same park orbit calls will be retrieved in FIFO order. In this case park orbits behave like call queues, where calls can be queued / parked and then retrieved in a FIFO order. Each caller will be given his/her own background music and none of the callers are conferenced together while on park.

Using the Call Park Service

• An active call is parked by transferring the call to the park extension.
• A parked call is picked up by dialing *4 followed by the call park extension.

The user who wants to pick up a parked call has to know which park extension was used to park the call.

While a call is on park (i.e. transferred to a park extension) background music is played to the caller. This can either be the default music provided or the administrator can upload custom music files (.wav format).

Configuring the Call Park Service

The sipXconfig Call Park screen allows you to define additional call park service extensions. After clicking the Add Call Park Extension link you will see a configuration screen. Select the desired call park name and extension, where extensions have to be unique in the system.

It is a good strategy to reserve a special range of numbers in your dialing plan for the call park service. If you want the newly created call park extension to be active check the Enabled checkbox.

Note: You can dial the call park extension from any phone to verify that it is active and to listen to the music that will be played to callers.

All the defined Call Park extensions are listed as follows:

Custom music can be uploaded to be played as background music, and every call park extension can have its own background music file. The specification of the music files is identical to other prompts used by the sipX system.

Clicking on Listen will download the music file and start the default media player, which allows you to verify the content of the audio file.

Additional park extension capabilities

Starting with sipXconfig 3.6 you can configure additional parameters for your park extensions.

• You can now allow parked calls to time out. If Enable time-out is selected, calls that are not retrieved from the park orbit will be transferred back to the extension that was initially used to park the call. This prevents callers from being left in the park orbit forever. The default park timeout period is 2 minutes (120 seconds), but it can be changed in the Advanced section to any value between 30 seconds and 5 minutes (300 seconds).
• Park extensions are now by default restricted to accept only a single parked call. You can remove this restriction by clicking on Allow multiple calls checkbox.
• Callers can now be allowed to request transfer back to the parking extension at any time while the call is parked. This feature is disabled by default. If you check Allow transfer, callers will be able to press "0" to be transferred automatically back to whoever parked their call. The transfer key can be changed to any dial pad key (0 - 9, *, #) in the Advanced section of the configuration screen.

All parameters can be configured on a per extension bases or they can be set-up as defaults for all the park extensions. Click the Defaults link on the main Call Park configuration screen to change the defaults for all park extensions.

Presence Indication for Call Park Service Extensions

In release 3.0 of the sipX system it is not yet possible to subscribe to the call state of different extensions defined on the call park server. However, this is a clear goal of the project.

Use case: A phone should be able to visually display the state of a call park extension (busy, free). This allows a simplified workflow where the user can see which park extension a call is parked on. SIP subscribe / notify methods are used to implement such behavior.