Extended and Miscellaneous Headers

This section covers a range of SIP headers that provide additional functionalities beyond the core and IMS-specific capabilities. These headers address various aspects of SIP communications, from enhancing user experience with customized alerting signals to supporting network functionality and service logic.

Alert-Info
This header specifies custom ring tones or alert signals for incoming calls, allowing for a personalized call experience.
Format Example: Alert-Info: <http://example.com/sounds/ring2.wav>;purpose=info

Reply-To
Indicates a return URI for responses, separate from the From URI, guiding where responses should be sent.
Format Example: Reply-To: <sip:bob@example.net>

Resource-Priority
The "Resource-Priority" header in SIP messages specifies the priority level of a communication, allowing network resources to be allocated based on the urgency or importance of the session. This header is crucial for services requiring differentiated handling, such as emergency calls or priority communications, ensuring they receive the appropriate network resources and handling precedence over less critical sessions.
Format Example: Resource-Priority: emergency

Diversion 
The "Diversion" header is used in Session Initiation Protocol (SIP) communications to indicate that a call or request has been diverted from its original destination to another. This header provides crucial information about the diversion, including the URI of the diverted-to destination and optionally, reasons for the diversion and a privacy indicator. The Diversion header enables both the originating and final receiving parties to understand the call flow, including any redirections that may have occurred, which is important for services like voicemail, call forwarding, and complex routing scenarios. It facilitates transparency in the signaling path and supports billing, call logging, and the application of user-specific call handling rules based on the history of the call's redirection.
Format Example: Diversion: <sip:12345@domain.com>;reason="busy";privacy="full"

Reason
Provides detailed reasons for a request, aiding in call flow analysis and troubleshooting.
Format Example: Reason: SIP; cause=200; text="Call completed elsewhere"