Electrical computers and digital processing systems: multicomput – Distributed data processing – Client/server
Reexamination Certificate
2000-03-13
2004-11-09
Alam, Hosain (Department: 2155)
Electrical computers and digital processing systems: multicomput
Distributed data processing
Client/server
C709S200000, C709S245000, C455S414200
Reexamination Certificate
active
06816881
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of inter-application communications and, in particular, to methods and apparatus for enabling inter-application communication for devices that interact using wireless networks.
BACKGROUND OF THE INVENTION
For the purposes of this disclosure, we define a wireless network as a mobile network, characterized by wireless links, lack of central infrastructure (such as Domain Name Service), and frequent host mobility (resulting in changes in communication. capability between devices). An example of a wireless network is a network that uses radio signals for communication. By its nature, the strength of a radio signal determines the range within which the signal can be received. We define this range as the “radio-range” for a transmitting device. In a radio-based wireless network, two devices are able to communicate with each other, provided they are tuned for communication (use the same frequency), by virtue of being within radio-range of each other. Two devices cease to communicate if either device moves outside the radio-range of the other device. The radio-range for a device is a function of the strength of the radio transmitter on individual devices. The range could vary from tens of feet (in Bluetooth enabled devices) to several hundred feet (in wireless LAN enabled devices) to tens of miles (in a broadcast by radio stations). It is possible to extend the radio-range of a device by installing repeater nodes in the wireless network. Repeater nodes rebroadcast the transmitted signal, thereby increasing the radio-range for a single transmitting device. For the purposes of embodiments of this disclosure, two devices, in a wireless network, can communicate with each other provided they are within radio-range of each other and use the same radio frequency.
FIG. 1A
shows an example where two devices
102
are within radio-range
104
of each other, and thus can communicate with each other. As the two devices move apart, they cease communication as soon as they move outside each others radio-range. This is illustrated in FIG.
1
B.
Conventional inter-application communication paradigms either involve direct communication in which the communicating applications are directly aware of each other, or mediated communication in which the communicating applications use a commonly known and accessible mediator.
One flavor of direct communication is where a receiver “pulls” the data from a sender (e.g., Web browsing). Here, a receiver is explicitly aware of the sender and communicates with the sender using a well-known network name or address. Such a receiver “pull” model of direct communication is shown in FIG.
2
. In this paradigm, each application on the receiver
202
that is interested in receiving data from a sender
208
, sends a request message
204
to a particular port at the sender. The request message header identifies the type of the request along with the identity of the data (if any). The application at the sender processes the request and sends the requested data back as part of the reply
206
to the receiver application. The main weakness of this paradigm, when applied to wireless networks, is that each application on the receiver needs to know the location and address of the application at the sender.
Another flavor of direct communication is where a receiver first “registers” its intent to receive data items with a sender. Such a receiver “push” model of direct communication is shown in
FIGS. 3A and 3B
. During the registration phase (FIG.
3
A), a receiver
302
informs the sender
306
about the type of data that it would like to receive (registration step
304
). As and when the data becomes available, during the reply phase (FIG.
3
B), the sender
306
“pushes” the data (step
308
) to the receiver (e.g., Marimba channels—http://www.marimba.com; PointCast—http://www.pointcast.com). The main weakness of this approach, when applied to wireless networks, is that both the sender and receiver need to be aware of each other's location either by means of a network name or network address where they can send-to or receive-from.
An alternate means of direct communication proposed in the literature is based on the technique called Broadcast Disks (described in “Broadcast Disks: Data Management for Asymmetric Communication Environments” by S. Acharya, R. Alonso, M. Franklin and S. Zdonik, In Proceedings of ACM SIGMOD Conference, May 1995). This technique augments the memory hierarchy of clients in asymmetric communication environments by broadcasting data from a fixed server to clients with less powerful machines (who could be mobile). Clients interested in seeking data items missing in their local storage retrieve data from the broadcast channel when the data “goes by.” As the technique is intended primarily for information dissemination from a single source, its main weakness is that it does not support fine-grained arbitrary inter-application communication among mobile clients.
Mediated communications are used in tuple-based systems (e.g., Linda tuples as described in “Generative Communication in Linda,” David Gelernter, ACM Transactions on Programming Languages and Systems, Vol. 7, No. 1, Jan. 1985, pp. 80-112, and “Distributed Communication via Global Buffer,” David Gelernter and A. J. Bernstein, In Proceedings of the ACM Principles of Distributed Computing Conference, 1982, pp. 10-18; JavaSpaces as described in “JavaSpaces Specification,” http://java.sun.com/ products/javaspaces/specs/is.pdf, Sun Microsystems, Jul., 1998; and TSPaces as described in “TSpaces,” P. Wycoff, S. W. McLaugry, T. J. Lehman, D. A. Ford, The IBM Systems Journal, August 1998), or queue-based systems (e.g., MQSeries as described in “MQSeries,” http://www.software.ibm.com/mqseries, IBM). In these systems, two applications can communicate by depositing and withdrawing tagged data values in a tuplespace or a queue, without being explicitly aware of each other.
FIG. 4
shows an example of a queue-based model of mediated communication. The receiver
402
writes the request message to a queue (step
404
) with the Queue Manager
408
. The sender
414
retrieves the request message from the queue (step
412
). After processing the request, the sender writes the reply message (step
410
) to a queue with the Queue Manager. The receiver then reads the reply message from the queue (step
406
). The realization of a tuplespace or a queue is achieved by a third entity. This entity is independent of the communicating applications. The main weakness of this approach is that it relies on the constant presence of mediator (e.g., Queue Manager). If, for some reason, the mediator node disappears or fails, two applications cannot continue to communicate. The availability and accessibility of a mediating third party is unlikely in wireless networks which form (when devices come within communication range of each other) and dissolve dynamically (when devices move away).
SUMMARY OF THE INVENTION
This present invention combines the broadcast capabilities of the wireless networks with uniquely tagged data items to achieve ad-hoc inter-application communication without the above burdensome requirements set forth by conventional inter-application communication paradigms. That is, a sender of data items does not need to be aware of the presence of the recipients of the data items. Similarly, the recipient does not need to be aware of the presence of the sender. In this invention, the sender of a data item tags the data item with an identifier that is unique in the context of the intended communication, and then broadcasts the tagged data item in the wireless network. An application that intends to receive the data item, accepts the data item if the attached tag matches the tag expected by the receiving application. Therefore, two (or more) applications communicate simply by being in radio-range (physical proximity) of each other and agreeing on tag values. There are numerous means in which the sender and receiver applications can agree on the tag values.
Mohindra Ajay
Purakayastha Apratim
Alam Hosain
Herzberg Louis P.
Ryan & Mason & Lewis, LLP
Wang Liang-che Alex
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