/*** Structure for osip handling.* In order to use osip, you have to manage at least one global instance* of an osip_t element. Then, you'll register a set of required callbacks* and a set of optional ones.* @var osip_t*/typedef struct osip osip_t;/*** Structure for osip handling.* @struct osip*/struct osip {void *application_context;/**< User defined Pointer *//* list of transactions for ict, ist, nict, nist */osip_list_t osip_ict_transactions;/**< list of ict transactions */osip_list_t osip_ist_transactions;/**< list of ist transactions */osip_list_t osip_nict_transactions;/**< list of nict transactions */osip_list_t osip_nist_transactions;/**< list of nist transactions */osip_list_t ixt_retransmissions;/**< list of ixt elements */osip_message_cb_t msg_callbacks[OSIP_MESSAGE_CALLBACK_COUNT];     /**@internal */osip_kill_transaction_cb_t kill_callbacks[OSIP_KILL_CALLBACK_COUNT];/**@internal */osip_transport_error_cb_ttp_error_callbacks[OSIP_TRANSPORT_ERROR_CALLBACK_COUNT];/**@internal */int (*cb_send_message) (osip_transaction_t *, osip_message_t *, char *,int, int);/**@internal */#if defined(HAVE_DICT_DICT_H)dict *osip_ict_hastable;          /**< htable of ict transactions */dict *osip_ist_hastable;          /**< htable of ist transactions */dict *osip_nict_hastable;          /**< htable of nict transactions */dict *osip_nist_hastable;          /**< htable of nist transactions */
#endif};注意：
1、ict, ist, nict, nist是osip的四种状态机

/*** Enumeration for transaction type.* A transaction can be either of:*  ICT,*  IST,*  NICT,*  NIST,*/typedef enum osip_fsm_type_t {ICT,/**< Invite Client (outgoing) Transaction */IST,/**< Invite Server (incoming) Transaction */NICT,/**< Non-Invite Client (outgoing) Transaction */NIST/**< Non-Invite Server (incoming) Transaction */} osip_fsm_type_t;

/*** Consume ALL pending osip_event_t previously added in the fifos of ict transactions.* @param osip The element to work on.*/int osip_ict_execute(osip_t * osip);
/*** Consume ALL pending osip_event_t previously added in the fifos of ist transactions.* @param osip The element to work on.*/int osip_ist_execute(osip_t * osip);
/*** Consume ALL pending osip_event_t previously added in the fifos of nict transactions.* @param osip The element to work on.*/int osip_nict_execute(osip_t * osip);
/*** Consume ALL pending osip_event_t previously added in the fifos of nist transactions.* @param osip The element to work on.*/int osip_nist_execute(osip_t * osip);

/*** Retreive the minimum timer value to be used by an application* so that the osip_timer_*_execute method don't have to be called* often.* * @param osip The element to work on.* @param lower_tv The minimum timer when the application should wake up.*/void osip_timers_gettimeout(osip_t * osip, struct timeval *lower_tv);

/*** Check if an ict transactions needs a timer event.* @param osip The element to work on.*/void osip_timers_ict_execute(osip_t * osip);
/*** Check if an ist transactions needs a timer event.* @param osip The element to work on.*/void osip_timers_ist_execute(osip_t * osip);
/*** Check if a nict transactions needs a timer event.* @param osip The element to work on.*/void osip_timers_nict_execute(osip_t * osip);
/*** Check if a nist transactions needs a timer event.* @param osip The element to work on.*/void osip_timers_nist_execute(osip_t * osip);