Electrical computers and digital processing systems: multicomput – Computer-to-computer session/connection establishing
Reexamination Certificate
1999-07-14
2003-09-30
Maung, Zarni (Department: 2154)
Electrical computers and digital processing systems: multicomput
Computer-to-computer session/connection establishing
C714S004110
Reexamination Certificate
active
06629144
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to dynamic directory services, and more particularly to the recovery of online sessions for such services.
BACKGROUND OF THE INVENTION
Current trends in computing suggest that computers are becoming networked to one another on a greater and greater scale. For example, computers that previously were connected to other computers in the same building over a local-area network (LAN) are now commonly connected to other computers all over the world over a wide-area network (WAN), an intranet, or the Internet. The rising prominence of the Internet in fact presages a future where all computers are able to connect with one another over a single vast global network.
With this rise in connectivity comes the need for easier recovery from the effects of client, server, and network crashes on directory services for such networks. One type of directory is similar to a phone book. The phone book permits a person to look up the phone number of another person so that the first person can communicate with the second person. Similarly, this type of directory for a computer network permits a computer user to look up the electronic address of another computer user (for example, the user's current dynamic Internet Protocol (IP) address in the case of a typical home Internet user), so that the first user can communicate with the second user. Although directory services may be used for a wide variety of different applications other than just to locate a user by looking up his or her electronic address, such user-location applications are nevertheless very common. For example, being able to determine the current IP address of a computer user is a very important feature for such diverse Internet applications as Internet telephony, whiteboarding, and videoconferencing.
However, unlike the phone book, which is a static directory, the directory for a computer network such as the Internet frequently must be dynamic in order to be useful. The phone book is a static directory in that it is not updated very often, typically only once a year when a new book is published. The phone book remains accurate, however, because each person's phone number generally also does not change very often. Conversely, in the case of the Internet, while every user may have a static electronic mail address (that is, an e-mail address that does not change often), every user typically does not have a static IP address. Dial-up users in particular are assigned a dynamic IP address by their Internet Service Provider (ISP) each time they initiate an online session. This lessens the accuracy and usefulness of a static directory for many Internet applications.
Static directory services nevertheless do exist for the Internet, and other Internetlike networks. One such static directory service is provided by the Lightweight Directory Access Protocol (LDAP). The LDAP is known within the art, and is specifically described in W. Yeong, et al., Request for Comments (RFC) 1777, March 1995, which is hereby incorporated by reference. The LDAP permits a server to maintain a static directory. Clients capable of communicating with the server are able to add entries to the directory by sending the server the appropriate request. These entries are static in that they persist until the client establishing them requests their removal from the server. If clients forget to make such requests, the server may maintain their entries in the directory indefinitely, which in time may result in the directory including outdated information. For example, if the server is maintaining a user-location directory of IP addresses, an entry containing the dynamic IP address of a client who has since logged off the Internet is inaccurate.
Dynamic directory services differ from static directory services in that entries must be periodically refreshed by their clients, or otherwise they automatically are removed by the server. Dynamic directory services also exist for the Internet, and other Internet-like networks. One such dynamic directory service is provided by the User Location Service (ULS). The ULS is known within the art, and is specifically described in R. Williams, Internet Draft “draft-uls-1.txt”, February 1996, which is hereby incorporated by reference. A server maintaining a dynamic directory as provided by the ULS is receptive to requests from clients to add entries to the directory that include a time-to-live value set by the client. If the client does not refresh its entry before the time-to-live value times out, the server is permitted to delete the entry. Thus, if the server is maintaining a user-location directory of IP addresses, an entry containing the dynamic IP address of a client who has since logged off will eventually be deleted by the server.
The time-to-live value is related to a period called the client refresh period. The client refresh period is how often the client refreshes its entry with the server. Ideally, the client refresh period could be set to the time-to-live value, since the client need only refresh its entry with the server before the time-to-live value times out in order to maintain the entry in the directory. However, because refresh requests may become lost, or even because of delays in transmitting the message to the server or delays in processing the message at the server, for practical reasons the client refresh period is usually set to a time period less than the time-to-live value. For example, a client refresh period of five minutes and a time-to-live value of ten minutes ensures that a client's entry will not be deleted by the server even if every other refresh request sent by the client does not get through to the server.
Another dynamic directory service is an extension to the LDAP as described in the U.S. patent application entitled “Server-Determined Client Refresh Periods for Dynamic Directory Services,” filed on Jul. 2, 1997, Ser. No. 08/886,796, now U.S. Pat. No. 6,016,508 issued on Dec. 21, 1999, which is hereby incorporated by reference. The dynamic directory service provided by this reference extends the capability of an LDAP directory to include dynamic entries. Thus, when a client sends a request to a server to create an entry for an LDAP directory maintained by the server, the client is able to specify whether the entry to be created is dynamic or static. If the entry is dynamic, the client must immediately send a refresh request to the server, in response to which the client will receive a response including a client-refresh period. If the client does not send another refresh request prior to the timing out of this period, the entry will eventually be deleted by the server.
Dynamic directories are useful in that they permit the servers maintaining them to periodically perform a garbage collection operation in a manner which does not affect the directories' accuracy. An entry in a dynamic directory is dynamic in that it lives for only a given period of time unless refreshed by its client. The server thus only deletes expired entries. By comparison, servers maintaining static directories perform garbage collections indiscriminately, because they do not know which entries have expired. The servers may delete only very old entries, which probably are outdated, but this means the entries will have persisted long enough to have rendered the directories inaccurate for a period of time. Alternatively, the servers may delete relatively younger entries, in which case the accuracy of the directory is maintained but some accurate entries will likely have been deleted.
Dynamic directories have their own flaws, however. A problem with dynamic directories is a client• s ability to recover from the client crashing, or automatically recover when the server or the network linking the client to the server crashes. For example, once a client has established an entry with a server maintaining a dynamic directory, the client may have difficulty reestablishing the entry upon rebooting after a crash. When attempting to reestablish the same entry with the
Chu Lon-Chan
Settle Kent F.
Yaacovi Yoram
Chang Jung-won
Leydig , Voit & Mayer, Ltd.
Maung Zarni
Microsoft Corporation
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