Electrical computers and digital processing systems: multicomput – Multicomputer data transferring via shared memory
Reexamination Certificate
1999-01-21
2002-09-17
Eng, David Y. (Department: 2155)
Electrical computers and digital processing systems: multicomput
Multicomputer data transferring via shared memory
Reexamination Certificate
active
06453343
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to communications between host applications and terminals. More particularly, the present invention relates to multiple concurrent communication sessions over a low-speed or wireless communication link between a client application at a first computer and a server application at a second computer.
BACKGROUND OF THE INVENTION
Traditional mainframe computer configurations provided for user interface to the computer through computer terminals which were directly connected by wires to ports of the mainframe computer. An example of such a terminal is an IBM 3270 or IBM 5250 type terminal which may communicate with a mainframe (or host) using a Telnet protocol. A Telnet protocol for a terminal such as an IBM 3270 or an IBM 5250 typically provides for structured grouping of data stream transmissions with a series of control characters followed by a block of displayable characters with a data stream comprising a plurality of sequentially transmitted control character blocks followed by displayable character blocks.
As computing technology has evolved, processing power has typically moved from a more central computer model to a distributed environment with local area networks connecting individual work stations to wide area or internet networks linking a number of different local networks through devices such as, for example, routers. Furthermore, due to infrastructure limitations and cost, components of the “network” linking two devices wishing to communicate may include a low through-put component such as a wireless network link. Central mainframe computers continue to play a role in the networked environment. Accordingly, using structured protocols such as the Telnet protocol are still in use. These applications may communicate with users over the network to terminals such as an IBM 3270 or, alternatively, to microprocessor based work stations executing software applications which allow the computers to act as a terminal.
Communications from a terminal (or terminal emulator) to a host are typically disadvantaged particularly on lower through-put network legs, such as wireless legs (or highly congested legs which are effectively bandwidth limited), where bandwidth limitations result in slower response time for communications between the terminal emulators and the host application. In the extreme, protocol timeouts may even cause transmission errors and resulting retransmissions or even inability of the communication system to operate. Thus, utilizing wireless technology, or any low-speed communication technology, with terminal emulator or other structured type data protocols exacerbates the weaknesses of the wireless technology.
A further problem with terminal to host communications relates to session start up. Sessions may be intentionally discontinued and restarted later. Problems may also be encountered where random session failures occur; causing unplanned loss of connection to the host. Additional problems may be encountered with identification of sessions for start up where multiple sessions are active concurrently for a single client/server (terminal/host) pair.
OBJECTS AND SUMMARY OF THE INVENTION
In view of the above limitations, it is one object of the present invention to take advantage of the installed user base of terminal emulator applications and terminals in a low-speed communication environment such as wireless communications.
It is a further object of the present invention to use existing terminal emulator protocols in a low-speed or wireless communication system without requiring modification of the terminal emulator applications.
It is an additional object of the present invention to provide a method of communicating across an external communication link which can reduce the volume of data for transmittal and can thereby increase the performance of the communication system.
It is a further object of the present invention to provide a method of persistent cache synchronization for communications over an external communication link which allows for a reduced volume of data for transmittal and can thereby increase the performance of the communication system after breaks in communication sessions.
It is an additional object of the present invention to provide protocol cache start up synchronization for communications between a client and a server having multiple concurrent communication sessions to reduce the volume of data for transmittal on the network on start-up to thereby increase the performance of the communication system.
In view of these and other objects, the present invention provides methods, systems and computer program products for persistent synchronization for a first communication session and a concurrent second communication session over an external communication link between an application executing on a first computer and an application executing on a second computer located remote from the first computer. In accordance with the present invention, a checkpoint cache is provided for multiple concurrent sessions between a single client/server pair which overcomes the problem of a lack of a unique identifier which can be associated with the checkpoint cache and carried forward in a manner allowing restart of a session regardless of which of the concurrent sessions is being restarted. In particular, according to the present invention, each concurrent session between single client/server pair maintains a separate active protocol cache but all sessions share a common checkpoint cache which is thereby associated with all the sessions rather than any specific individual session. Checkpointing between sessions is courteous, i.e., while any one session is executing a checkpoint, other sessions do not attempt to create a checkpoint to avoid corrupting the shared checkpoint cache. As restarts occur over time, information from prior sessions is merged with information from new sessions. Alternatively, as checkpoints continue to be taken from the various sessions active protocol caches, over time, the checkpoint cache gradually obtains information reflecting traffic for all of the concurrently active sessions thereby providing a beneficial “hot” start up for a new session regardless of which of the concurrent sessions between the client/server pair is restarted.
In one embodiment of the present invention, a method of persistent cache synchronization for multiple concurrent sessions includes establishing a first cache operatively associated with the first session at the first computer and a corresponding second cache operatively associated with the first session at the second computer. A third cache operatively associated with the second session is established at the first computer and a corresponding fourth cache operatively associated with the second session is established at the second computer. A checkpoint request is transmitted to the second computer from the first computer indicating one of the first or the third cache to be used to provide a checkpoint. The checkpoint request is received at the second computer and the second computer copies the second cache responsive to the received checkpoint request if the checkpoint request indicates to the first cache it is to provide a checkpoint cache for the second computer. The fourth cache is copied responsive to the received checkpoint request if the request indicates that the third cache is to provide a checkpoint cache for the second computer. The provided checkpoint cache of the second computer is associated with both the first and the second session.
Responsive to copying a cache to the checkpoint cache of the second computer, a checkpoint confirmation message is transmitted to the first computer. The checkpoint confirmation message is received at the first computer and the first computer creates a checkpoint cache of the first computer as a copy of the indicated one of the first or the third cache responsive to the received checkpoint confirmation message. The checkpoint cache of the first computer is associated with both the first session and the second
Housel III Barron Cornelius
Shields Ian Beaumont
Eng David Y.
Myers Bigel & Sibley & Sajovec
Ray-Yarletts Jeanine S.
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