Electrical computers and digital processing systems: multicomput – Computer-to-computer data routing – Least weight routing
Reexamination Certificate
1996-09-17
2001-01-16
Banankhah, Majid (Department: 2755)
Electrical computers and digital processing systems: multicomput
Computer-to-computer data routing
Least weight routing
C709S241000, C709S241000
Reexamination Certificate
active
06175853
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of collaborative computing and, more particularly, to the control of processes in a collaborative computing system.
BACKGROUND OF THE INVENTION
In desktop video conferencing and other desktop collaboration systems, it is often necessary that certain processes be implemented only by a single member of the collaborative session. For example, setting the global conference settings or adding a new member to a video conference generally should be performed only by a single member.
In conventional video conferencing systems, a lock is established for these processes by a central lock server. Under the T.120 standard, the top provider serves as the lock server.
With a central lock server, the video conferencing session is dependent upon successful communication with, and the non-failure of, the central lock server. Failure of that lock server can cause the video conferencing session to end.
The present invention overcomes this and other deficiencies, as will be shown in the remainder of the specification, referring to the attached drawings.
SUMMARY OF THE INVENTION
The present invention provides a robust locking system through the use of a distributed locking apparatus.
In a preferred embodiment, each member of a collaborative session has a separate lock engine for each lock. The collaborative session can be implemented, for example, through the collaborative computing system described in commonly-assigned U.S. patent application Ser. No. 08/401,922, entitled “Apparatus for Collaborative Computing,” which is incorporated herein by reference. With this implementation, the lock engine may be implemented as a lock plugin. Alternatively, other collaborative computing architectures can be used.
The lock engine can be in any of four states at any time during a collaborative session: AVAILABLE, PENDING, HELD, or LOCKED. The AVAILABLE state indicates that the session member is not aware of any member who holds the lock. Hence, the lock is available. The PENDING state indicates that the session member has sent a request for the lock to the other session members and is awaiting acknowledgment from the other members. The HELD state indicates that the session member currently holds the lock. The LOCKED state indicates that another session member currently holds the lock.
In order to obtain the lock, a member sends a Request for Lock message, which normally will be acknowledged by the other members. If another member has the lock, it will send a Negative Acknowledgment message back to the requesting member. If the lock is available, the requesting member will receive acknowledgments from each other member, and transition to the HELD state.
In order to release the lock, a member sends a Release Lock message to the other members, which will cause them to transition from the LOCKED state to the AVAILABLE state.
When a new member joins the collaborative session, a member that holds the lock will send a Claim message to the new member, informing the new member that the lock is held. The new member will then transition from its initial AVAILABLE state to the LOCKED state.
Preferably, conflicts between session member requests are resolved by giving preference to the member with the lower handle.
REFERENCES:
patent: 4480304 (1984-10-01), Carr et al.
patent: 5008853 (1991-04-01), Bly et al.
patent: 5129089 (1992-07-01), Nielsen
patent: 5220657 (1993-06-01), Bly et al.
patent: 5339427 (1994-08-01), Elko et al.
patent: 5515491 (1996-05-01), Bates et al.
patent: 5619726 (1997-04-01), Seconi et al.
patent: 5724508 (1998-03-01), Harple, Jr.
patent: 5802391 (1998-09-01), Chung-Shung
Banankhah Majid
Glenn Michael A.
Hendricks Don M.
Netscape Communications Corporation
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