When a SIP INVITE request is routed to a user which is not registered at the moment or there has not been any response for 3 seconds, the voipswitch looks up the callee instances from the aa_ue_instance table and checks if there is at least one token associated with any of the instances. If there is, a request is sent over http to the EMCI/emc.ashx. The request contains all relevant information about the call such as the caller login, display name, destination URI and callID of the pending call. From the moment the request is sent to the EMCI the voipswitch waits until timeout, meanwhile the call is placed on the parking. When the time elapses the voipswitch processes the call further i.e. proceeds with the answering rules action or just ends the call. At the same time it sends the “missed call” request to the EMCD.

The EMCI creates payload for PUSH notification which will carry the information received from voipswitch to the client’s device. Next it checks the destination PUSH service provider. If the provider is APNS the EMCI looks up for the api.contact_name associated with the calling login. If the caller is not in the destination user’s contacts the display name is used instead. Either of the names will be shown as the caller name in the iOS remote notification popup. This additional operation of obtaining a friendlier name than login is necessary as on the iOS the application is not woken up the moment when PUSH arrives and cannot influence the content of the notification’s window.

The EMCI sends the request to PUSH service for each user device.

On the client’s GUI push notifications are presented as incoming calls. On answering the application automatically sends an invite to pick up the call with the CallID received in the PUSH payload. The INVITE request contains the Replaces header with the call ID of the parked call.

If the calling party cancels the call before the timeout occurs and before the called party answers, the voipswitch will send the “missed call” request to the EMCI which will cause sending a notification to the client with a text informing that the call has been ended. The same will be happen when the timeout has occurred.

Voipswitch waits for the user to answer PUSH for 30 seconds which is the default timeout. After that time it proceeds further according to the user’s “answering rules” or if not set the call is ended.

The PUSH mechanism supports both video and audio calls.

Call forking

Each mobile device or desktop PC assigned to the same account has different SIP instance value. The instances are stored in the voipswitch.aa_ue_instance table. Each softphones sends its own SIP instance in the REGISTER request. On incoming call voipswitch checks which instances are registered at the moment and if there are more instances assigned to the account which are not registered. If there are not registered instances voipswitch will send PUSH request to the EMCI/emc.ashx and will pass the not registered instances as parameters. The EMCI will proceed with sending PUSH only to these instances. At the same time voipswitch will send the INVITE to the registered instances. In effect, it will ring on all the user devices, both registered and not registered.

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