SCTP Events and Notifications

An event refers to a change in the network status, association startups, remote operational errors, or undeliverable messages. An SCTP application must understand and process these events, and resolve errors that occur on an SCTP stack.

If an SCTP application wants the SCTP stack to deliver notifications for a particular event, the SCTP application can set the appropriate socket option for notifications in the setsockopt()() call. You can configure an SCTP application to send notifications using the setsockoptg()() call. When an SCTP application sends a recvmsg()() call to another application at the peer endpoint, the SCTP application normally reads the data message from the peer endpoint. For information on recvmsg()(), see “The sendmsg() and recvmsg() Socket APIs”.

If the SCTP application reads a non-data message, the application sets the message notification flag in the recvmsg()() API. When the notification arrives, recvmsg()() returns the notification in the application-supplied data buffer in the msg_iov parameter, and sets the MSG_NOTIFICATION flag in the msg_flags parameter. A recvmsg()() call returns only one notification at a time. While the SCTP application is reading data, recvmsg()() returns a part of a notification if the msg_iov buffer is not sufficient. If a single read is not sufficient, MSG_EOR is not set in the msg_flags parameter. The SCTP application must finish reading the notification before the subsequent data arrives.

Following is the SCTP notification structure:

    union sctp_notification {
     struct {
       uint16_t sn_type;             /* Notification type. */
       uint16_t sn_flags;
       uint32_t sn_length;
       } sn_header;
       struct sctp_assoc_change   sn_assoc_change;
       struct sctp_paddr_change   sn_paddr_change;
       struct sctp_remote_error   sn_remote_error;
       struct sctp_send_failed    sn_send_failed;
       struct sctp_shutdown_event sn_shutdown_event;
       struct sctp_adaption_event sn_adaption_event;
       struct sctp_pdapi_event    sn_pdapi_event;
    };

For more information on the SCTP notification structure, see draft-ietf-tsvwg-sctpsocket-10.txt