Here is a list of all documented files with brief descriptions:

sofia-sip
sip.h	SIP objects
sip_extra.h	Extension headers for SIP
sip_hclasses.h	Declarations of SIP header classes
sip_header.h	SIP parser library prototypes
sip_parser.h	SIP parser provider interface
sip_protos.h	SIP prototypes and macros for each header
sip_status.h	SIP status codes and standard phrases
sip_tag.h	Tag class for SIP headers
sip_tag_class.h	\ @{
sip_util.h	SIP utility functions