====== esc ======
**C → S → C {type: 'esc'}**

esc – end call. Usually sent by client who wants to end or deny a call. Forwarded by server to other client.

**S → C {type: 'esc'}**

Server might also send esc message by itself.

optional arguments:
  * response - [[https://en.wikipedia.org/wiki/List_of_SIP_response_codes|SIP response code]]:
    * 404: address you attempted to call not found
    * 480: address you attempted to call temporarily unavailable
    * 486: call was denied, busy
    * 0 or missing: call ended normal ("hung up" by other side)
    * other [[https://en.wikipedia.org/wiki/List_of_SIP_response_codes|response codes]] may also occur
  * msg - response description in english

Message esc without optional arguments indicate normal call ending ("hung up" by other end).