A call is preserved on a best effort basis. If the audio path is directly between two devices and there is no network issue between the two devices, the audio path is preserved. If the audio is anchored by a device in the middle, for example, a gateway or conference server and that device is affected by the network outage, there will not be any audio path. In a preserved call, the phone does not support call features, for example, conference call, call transfer, and call forward . The reason is loss of signaling between the phone and the SIP proxy that was used when the call was initially established.

The loss of signalling between the phone and the originating proxy also limits the call control between the preserved calling parties. For example,

• Calls cannot be transferred.
• Call conferencing cannot be initiated.

If a user disconnects a preserved call, the other end might not be disconnected because of the loss of signaling.