SIP is a simple protocol in which requests to perform operations are sent over a connection, and responses are sent in return. The protocol explicitly does not define how a connection between the two devices is established; it is limited to specifying the format of the messages sent over the connection.[4] There are no "trial" transactions; each operation will be attempted immediately and will either be permitted or not.[5]
The protocol specifies messages to check books in and out, to manage fee payments, to request holds and renewals, and to carry out the other basic circulation operations of a library