Terminology » LTE » VoLTE SIP Requests and Response Codes: A Detailed Guide

VoLTE SIP Requests and Response Codes: A Detailed Guide

volte sip requests response codes lte

This article outlines the various SIP requests and response codes used in Voice over LTE (VoLTE) communication. Understanding these elements is key to troubleshooting and comprehending the signaling process within VoLTE networks.

VoLTE SIP Requests

The following table details the common SIP requests used in VoLTE. These requests facilitate call setup, maintenance, and termination.

VoLTE SIP RequestDescription
INVITEThe client is invited to participate in a call session. This is the initial request to establish a call.
ACKConfirms the reception of the final response by the client for an INVITE request. It acknowledges that the INVITE was successfully processed (or that an error response was received and understood).
BYEIndicates the termination of a call. This message is sent by either the caller or the called party when one of them wishes to end the session.
CANCELIndicates the cancellation of any pending request. This is often used to stop a ringing phone before the call is answered.
OPTIONSThis message queries the capabilities of servers. It allows a client to discover what features and functionalities a server supports.
PRACKIndicates provisional acknowledgement. Used to reliably acknowledge provisional responses (1XX responses) in a SIP dialog.
SUBSCRIBEIndicates a subscription to event notification. A client can subscribe to receive notifications about certain events occurring on the server (e.g., presence status).
NOTIFYThis message notifies a subscriber if there are any new events. It’s the response to a SUBSCRIBE request, delivering the requested event information.
PUBLISHThis message publishes an event to the server. Used for updating the server about a certain event or status.
INFOCarries mid-session information which does not modify the session state. This can be used to convey supplementary information during a call.
REFERAsks the recipient to issue a SIP request (i.e., call transfer). This request initiates a call transfer process.
MESSAGETransports instant messages using SIP. This allows for sending text messages within the SIP framework.
UPDATEModifies the state of a session without changing the state of the dialog. This can be used to update session parameters during a call.

VoLTE SIP Codes

The following table provides a description of common SIP response codes used in VoLTE. These codes indicate the status of a SIP request and provide valuable information for debugging network issues.

VoLTE SIP CodeDescription
1XXProvisional Responses
100Trying
180Ringing
181Call is being forwarded
181Queued
183Session progress
199Early dialog terminated
2XXSuccessful response
200OK
202Accepted
204No notification
3XXRedirection response
300Multiple choices
301Moved permanently
302Moved temporarily
305Use proxy
380Alternative service
4XXClient Failure Response
400Bad Request
401Unauthorized
402Payment required
403Forbidden
404Not found
405Method not allowed
406Not acceptable
407Proxy Authentication Required
408Request Timeout
410Gone
412Conditional Request Failed
413Request Entity Too Large
414Request URI Too Long
415Unsupported Media Type
416Unsupported URI Scheme
417Unknown Resource Priority
420Bad Extension
421Extension required
422Session interval too small
423Interval too brief
428Use identity Header
429Provide Referer Identity
430Flow Failed
433Anonymity Disallowed
436Bad Identity Info
437Unsupported Certificate
438Invalid Identity Header
439First Hop Lacks Outbound Support
440Max Breadth Exceeded
469Bad Info Package
470Consent Needed
480Temporarily unavailable
481Call/Transaction does not exist
482Loop Detected
483Too Many Hops
484Address incomplete
485Ambiguous
486Busy here
487Request terminated
488Not acceptable here
489Bad Event
491Request Pending
493Undecipherable
494Security Agreement Required
5XXServer Failure Response
500Server Internal Error
501Not implemented
502Bad Gateway
503Service Unavailable
504Server Time Out
505Version Not Supported
513Message too large
580Precondition Failure
6XXGlobal Failure Response
600Busy Everywhere
603Decline
604Does not exist anywhere
606Not acceptable