Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1999-08-12
2004-08-10
Chin, Wellington (Department: 2664)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S219000
Reexamination Certificate
active
06775298
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a wireless communication link between handheld devices and network for accessing data and, more particularly, to a data transfer mechanism well suited for handheld devices with small memory sizes and restricted processor speeds.
2. Background Description
The past few years have seen a considerable reduction in the cost of computer systems. This coupled with the exponential decrease in size of microprocessors and memories along with rapid progress in VLSI (Very Large Scale Integrated) technology has resulted in a huge market for handheld devices. Smart-phones, palmtop computers, Personal Digital Assistants (PDAs) and automobile installed personal computers (Auto PCs) are becoming very popular. For example, one million Palm Pilots from US Robotics were sold in its first year. Orthogonal to the growth in popularity of handheld computers, Internet and networking applications have been growing at a rapid pace. The number of users who now want to remain connected even when they are mobile is growing. This, coupled with the rapid advances in wireless communication, has made it possible to browse the World Wide Web (WWW or the Web) in the Internet, check e-mail, transfer files, get information like stock quotes, flight arrival/departure information, and even do business transactions using a handheld device like a PDA.
However, the performance of current mobile applications is usually not acceptable. Traditional computing and networking paradigms do not give good performance on handheld devices communicating over a weakly connected link, e.g., a wireless link. Typical handheld devices do not have hard disks. Handheld devices typically use flash memory or battery backed Random Access Memory (RAM) to provide nonvolatile storage. Thus, traditional file systems and data access methods do not work well on handheld devices. Similarly, traditional network communication protocols like TCP/IP (Transfer Control Protocol/Internet Protocol) do not perform well on weakly connected links such as the links typifying handheld devices. It has been noted that TCP responds to all losses by invoking congestion control and avoidance algorithms, and that this results in degraded end-to-end performance in wireless and lossy systems. In addition, due to severe memory restrictions, not all handheld devices can implement the TCP/IP stack and satisfy runtime memory requirements. It is also important to realize, given the limited amount of memory and computing resources on handheld devices, that there is a need to provide a wide variety of services by having a simple integrated software structure and by eliminating functional duplication. See J. Kay and J. Pasquale, “The Importance of Non-Data Touching Processing Overheads in TCP/IP”,
Proceedings of SIGCOMM '
93, ACM, 1993.
There is considerable amount of work in providing a replicated, weakly consistent storage mechanism for mobile computing environments. The Coda project, described by J. J. Kistler and M. Satyanarayanan in “Disconnected Operation in the Coda File System”,
ACM Transactions on Computer Systems,
10:3-25, 1992, uses optimistic concurrency control and prefetching for supporting mobile computing. It logs all updates during disconnected mode and replays the log on reconnection. Later versions of Coda introduce certain adaptive mechanisms to support low bandwidth networks and intermittent communication.
The Bayou project, described by Douglas B. Terry, Marvin M. Theimer, Karin Peterson, Alan J. Demers, Mike J. Spreitzer and Carl H. Hauser in “Managing Update Conflicts in Bayou, A Weakly Connected Replicated Storage System”,
Proceedings of the Fifteenth ACM Symposium on Operating Systems Principles,
1995, defines an architecture for sharing data among mobile users and provides methods for detection and resolution of conflicts. It implements a mechanism for enabling client application to continue even if a conflict remains.
The Rover toolkit, described by Anthony D. Joseph, Alan F. deLespinasse, Joshua A. Tauber, David K. Gifford and M. Frans Kaashoek in “Rover: A Toolkit for Mobile Information Access”,
Proceedings of the Fifteenth ACM Symposium on Operating Systems Principles,
1995, provides mobile communication support on the basis of relocatable dynamic objects and queued remote procedure calls. Rover allows client operation and invocation of non-blocking remote procedure calls even when a host is disconnected.
The Cadmium project, described by Aline Baggio in “Design and Early Implementation of the Cadmium Mobile and Disconnectable Middleware Support”,
INRIA Research Report
3515, October 1998, uses a mechanism for referencing remote objects, a support station model, a mechanism for binding to objects and a dynamic replication, caching, and prefetching scheme to provide system level support for disconnected and mobile usage. It assumes the use of powerful laptop computers as the mobile clients.
The BNU project, described by T. Watson and B. Bershad in “Local Area Mobile Computing on Stock Hardware and Mostly Stock Software”,
Proceedings of USENIX Symposium on Mobile and Location
-
Independent Computing
, Cambridge, Mass., 1993, is also an RPC-driven application framework that includes proxies on stationary hosts for hiding the mobility of the system. Later versions of the project also includes support for disconnected operation like the queued RPC model.
The InfoPad project described by My T. Le, Fred Burghardt, Srinivasan Seshan and Jan Rabaey in “InfoNet: The Networking Infrastructure of InfoPad”,
Proceedings of Compcon,
1995, also has the proxy approach where the mobile device is dumb and the entire processing is offloaded to the server. They assume a permanent connection and there is no notion of disconnected operation on the client.
Xerox's PARCTAB system, described by R. Want, B. N. Schilit, N. I. Adams, R. Gold, K. Peterson, D. Goldberg, J. R. Ellis and M. Weiser in “An Overview of the PARCTAB Ubiquitous Computing Experiment”,
Personal Communications,
Vol. 2, No. 6, IEEE, 1995, also assumes a permanent connection and all services are off-loaded to the server by using the system's “Tab Agent” mechanism.
WebExpress, described by Barron C. Housel and David B. Lindquist in “WebExpress: A System for Optimizing Web Browsing in a Wireless Environment”,
Proceedings of the ACM/IEEE MOBICOM '
96
Conference,
1996, implements an HTML (HyperText Markup Language) cache and uses the concept of differencing as an original transfer mechanism to reduce network traffic and latency. In addition, they do HTTP (HyperText Transfer Protocol) reductions for connection overheads and verbose protocol inefficiencies.
However, most of this work in mobile computing and information access relates to operating system principles and adding weak consistency models along with caching, pre-fetching, etc., and with enabling remote procedure calls. The applicants' invention may be seen as a layer beneath these principles and can be used effectively for improving the performance of the above systems. The protocol described herein will improve the effective data transfer rate. It has been sufficiently demonstrated in literature that TCP and other wired network protocols do not perform well for wireless networks. Some work has been done to solve this problem by proposing modifications to TCP.
Hari Balakrishnan, Venkata N. Padmanabhan, Srinivasan Seshan and Randy H. Katz, in “A Comparison of Mechanisms for Improving TCP Performance over Wireless Links”,
IEEE/ACM Transactions on Networking,
December 1997, have a good comparison of several schemes designed to improve the performance of TCP in wireless networks. They classify these schemes into three broad categories: (1) end-to-end protocols, where loss recovery is performed by the sender; (2) link-layer protocols, that provide local reliability; and (3) split-connection protocols, that break the end-to-end connection into two parts at the base station.
Ajay Bakre and B. R. Badrinath in “I-TCP: Ind
Chin Wellington
Coca T. Rao
International Business Machines - Corporation
Pham Brenda
Whitham Curtis & Christofferson, P.C.
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