How to hang up the call?

We are talking about a really simple function. Hang up the call means ending an active phone or VoIP conversation by closing the session and releasing the resources used for it. In the Ozeki VoIP SIP SDK example, this is done by calling call.HangUp() and then setting the call object to null, which helps return the softphone to an idle state. 

if (call != null)
{
	call.HangUp();
	call = null;
}

If the call exists, we just need to use the call object's HangUp() method, and then to set the call object to "null".

Call flow diagram

The diagram below illustrates a full SIP Hang up call flow.

sequenceDiagram participant Softphone as Softphone Application participant Endpoint as Remote SIP Endpoint/PBX Softphone->>Softphone: User presses **Hangup** (call.HangUp) Softphone->>Endpoint: SIP BYE PDU (Terminate dialog) Endpoint-->>Softphone: 100 Trying (BYE Trying PDU) Endpoint-->>Softphone: 200 OK (BYE OK PDU) Softphone->>Endpoint: (No further SIP messages for this call) Softphone->>Softphone: Stop media devices (mic/speaker) Softphone->>Softphone: Detach media handlers Softphone->>Softphone: Unsubscribe from call events Softphone->>Softphone: Set call object to null (return to idle state)

Capture SIP hangup traffic with Wireshark

SIP Bye PDU

A SIP BYE PDU is the termination request sent by either party to end an established SIP call, signaling that the current dialog should be torn down. It reuses the existing Call-ID, To and From headers of the dialog and carries an appropriate CSeq value to ensure the BYE is processed in order within that session. When a BYE is sent or received, the softphone stops devices, detaches media handlers, unsubscribes from call events, and releases the call object to return to an idle state.

SIP Bye PDU
SIP Bye PDU

SIP OK Bye PDU

A SIP OK (BYE) PDU is the 200-class response confirming that the BYE request was successfully processed and that the call has now ended. It matches the BYE using the same Call-ID and CSeq, and includes standard To, From and Via headers to complete the transaction cleanly. After receiving this OK, both sides can safely release resources associated with the dialog, ensuring that media streams are stopped and no further signaling occurs for that call.

SIP OK Bye PDU
SIP OK Bye PDU

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