Abstract: A method and apparatus for a paging service to automatically respond to a paging acknowledgment. The pager server receives an initial pager request from an originating user. The initial paging request is sent to a target user by the paging server. An acknowledgment to the initial pager request is received at the paging server from the target user. If the acknowledgment is not positive, alternate users are paged until a positive acknowledgment is received.

Abstract: A compact representation of a tree data structure and techniques for navigating the compact representation. The compact representation is a list. Each element of the list represents a node of the tree and the list is organized according to a preorder traversal of the tree. Each list element contains only the index of a data dictionary entry for the kind of item represented by the node corresponding to the list element. The navigation techniques permit the location of the list element for the sibling of the node corresponding to the given list element, the location of the list element for that node's parent, and in the case of a parent node, the location of the list element for any child of the parent. The navigation techniques work by finding the list elements for subtrees. The subtrees are found by techniques based on the fact that the number of children of all of the nodes in a subtree minus the number of nodes in the subtree always equals -1.

Abstract: A system which employs a pair of encryption functions f and g in the "log on" protocol of a computer dial-up arrangement. The functions are inverses of each other and, hence, a random sequence when encrypted with f and then with g results in the original sequence. When a user wishes to "log on", the computer selects a random sequence and forms a challenge sequence. The user encrypts the challenge sequence with the function g and thus forms a response sequence. Encryption with the function f by the computer permits verification of the response sequence.The secrecy of the user's function is maintained by providing the user with an authenticating device having only two ports: a power port and an I/O port. The I/O port is connected to a microprocessor which accesses a memory that contains the secret encryption function g.