ypes of responses are detailed in Tables 2.7 to 2.13. Type of response Description Provisional response Definitive positive response Definitive redirect response Definitive negative response, error due to client Definitive negative response, error due to network Definitive negative response, global error Table 2.7. Types of respones 58 VoLTE and ViLTE Response Description The sender is informed that the SIP message has been 100 Trying received. The caller is informed that the callee is alerted to an 180 Ringing incoming call by a ringing tone. 181 Call Is Being The caller is informed that its call has been Forwarded transferred to a different recipient. 183 Session Progress The caller is informed that its call is being processed. Table 2.8. 1xx-type responses Response Description 200 OK The response acknowledges receipt of the request. The callee has received the request, requiring a 202 Accepted different treatment thereafter Table 2.9. 2xx-type responses Response Description The redirect indicates multiple contacts, the order of 300 Multiple Choices which is significant. 301 Moved Permanent ly The redirect is permanent. 302 Moved Temporarily The redirect is temporary. 305 Use Proxy The redirect is performed to a PROXY SERVER. 380 Alternative Service The redirect points to a different entity (e.g. voicemail service). Table 2.10. 3xx-type responses Signaling Protocols Response Description 401 Unauthorized The REGISTER request requires authentication 486 Busy Here The callee is busy 487 Request The response is transmitted by the UA when it receives Terminated a CANCEL request Table 2.11. 4xx-type responses Response Description An internal error has occurred on the PROXY 500 Server Internal SERVER or the REGISTRAR, SO the request has to Error be repeated later. The gateway to a different network has detected a 502 Bad Gateway fault. 503 Service Unavailable The service is temporarily unavailable. The gateway to a different network cannot relay the 504 Gateway Timeout request because a timer has run out. 505 Version 