P-Asserted-Identity (PAI)

The P-Asserted-Identity (PAI) header is used to convey the asserted identity of the calling party in a SIP session. It allows the originating SIP server to indicate the identity (the ANI) of the user who initiated the call.

The PAI header is typically added by a SIP proxy or server within the caller's administrative domain. It helps to ensure that the recipient of the SIP message has accurate information about the caller's identity. This header can be useful in scenarios where the calling party's identity needs to be authenticated or verified.

By including the PAI header, the originating server asserts that the identity specified within the header corresponds to the caller. This information can be helpful for subsequent SIP entities in processing and routing the call properly.

The typical format of a PAI header is

P-Asserted-Identity: sip:caller@example.com