Electrical computers and digital processing systems: multicomput – Computer-to-computer protocol implementing – Computer-to-computer data transfer regulating
Reexamination Certificate
1999-10-15
2004-08-10
Lim, Krisna (Department: 2153)
Electrical computers and digital processing systems: multicomput
Computer-to-computer protocol implementing
Computer-to-computer data transfer regulating
C370S395400, C370S395410, C370S468000
Reexamination Certificate
active
06775707
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to communication systems and, more specifically, to a communication technique that uses deferred acknowledgment of transmitted messages to increase data throughput in communication links that have a low bandwidth and/or a transmission time delay.
DESCRIPTION OF THE RELATED ART
Generally speaking, communication techniques provide a particular level of data throughput at a desired level of data integrity. Typically, a system designer selects an appropriate communication technique for an application by balancing the inherent tradeoffs between the data throughput and the data integrity provided by each of the available communication techniques against system cost objectives. In some applications, such as those involving communications between locally situated devices, like control devices, controllers, and workstations used in process control systems, a dedicated high speed databus (e.g., Ethernet) can be used to provide high levels of data throughput and integrity at a relatively low cost. In other applications, such as those involving communications between local and remotely situated devices, like control devices, controllers, and workstations used in process control systems, practical considerations and limitations compel system designers to use slow communication links, such as modem links, wireless cellular links, etc., that have a relatively low bandwidth or links that have a transmission time delay such as satellite communication links.
Using the above-mentioned slow communication links to accomplish communications between local and remote systems presents several significant problems. For example, slow communication links are typically highly susceptible to electromagnetic interferences that can result in the corruption of data transmitted through the link. Additionally, slow communication links are often associated with a purchased service such as telephone lines, cellular channels, or channel allocation within a satellite transponder bandwidth, which can result in a significant cost per unit of data sent through the link. Thus, communication techniques that “pack” the slow communication link with data in both the temporal and frequency dimensions of the link are highly desirable because they tend to increase data throughput and minimize cost per unit of data sent through the link.
For many applications, acceptable levels of data integrity and costs per unit of data sent can be achieved using conventional data encoding and channel modulation techniques within a one-way communication link. For instance, audio and video data is typically encoded prior to transmission using some type of forward error correction and/or convolutional encoding and may be effectively transmitted through the one-way communication link using a spread spectrum modulation technique. A receiving station may then demodulate and decode the transmitted data to generate audio and video signals having an acceptable integrity level. Because the receiving station does not communicate with the transmitting station, data that is severely corrupted or lost may not be recovered by the receiving station, thereby causing spurious errors within the video and audio signals provided to a user. While these spurious errors are undesirable, they do not have a significant impact on overall system performance because they are not easily perceived by the user. In this manner, conventional communication protocols for the transmission of audio and video data can eliminate the communication overhead that is normally associated with two-way communication techniques, which typically use a full-handshake communication protocol, without adversely affecting the qualitative performance of the system.
While the above-described approaches to transmitting data through a one-way communication link provide an acceptable level of data integrity for the reproduction of audio and video information, these approaches do not provide a level of integrity suitable for use in some other types of applications. For example, data associated with a process control system, such as data related to alarm conditions, may be of a highly critical nature because missing or corrupted alarm data may result in injury to personnel and/or damage to material, plant equipment, etc. Furthermore, one-way communication techniques are generally not suitable for use with process control systems because it is highly desirable (and often a requirement) for a local transmitting station to recognize that a remote receiving station is actually receiving and processing the data being sent to it by the transmitting station.
Traditionally, slow data communication links have used a two-way (i.e., full-duplex) communication technique that provides a full-handshake communication protocol requiring each transmitted message (which typically includes a plurality of data bytes) to be acknowledged by the receiving station before a subsequent message is sent. While these conventional full-handshake communication protocols provide an acceptable level of data integrity in, for example, process control systems, and allow the local transmitting station to ascertain whether or not the remote receiving station is receiving and processing the transmitted data, these protocols result in a low data throughput, which is highly disadvantageous where a great magnitude of critical data, such as alarm information on within a process control system is being transmitted.
The use of traditional full-handshake communication protocols is especially problematic when used in conjunction with satellite communication links because the round trip channel transmission time delay of these links may be several hundred milliseconds, which results in a significant amount of idle time for the communication link while the transmitting station waits for an acknowledgment of each message sent. Additionally, sending a large amount of information (e.g., from a local workstation operated by the user to a remotely situated workstation) may be perceptibly or even impractically slow for the user requesting the information. In any case, the inefficient use of the satellite communication link results in an unacceptably high cost per unit of data transmitted.
In addition to utilizing a full-handshake low level communication protocol to accomplish reliable communications via a slow communication link, many conventional process control systems use a full-handshake communication scheme at the application level so that each application message is acknowledged before a subsequent application message is transmitted through the slow communication link. For instance, conventional process control systems typically include alarm services in which alarms and alarm messages are sent to alarm subscribers that acknowledge receipt of the alarms. Thus, if alarm messages are sent through the slow communication link using a full-handshake communication protocol, the alarm will send application level acknowledgments for each of the particular alarm messages received. As a result, alarm messages sent through the slow communication link would actually be acknowledged twice (i.e., once by the low level full-handshake communication protocol and once at the application level). This redundant acknowledgment of alarm messages at the application level can significantly reduce the temporal efficiency of alarm communications through the slow communication
SUMMARY OF THE INVENTION
A communication technique is provided to enable the efficient transmission of data through a slow (i.e., low bandwidth and/or time delayed) communication link such as a satellite link, a cellular link, a wide area network, etc. Generally speaking, the communication technique minimizes the idle time of the communication link by using deferred acknowledgment of message bundles to temporally pack the communication link with multiple messages before receiving acknowledgments of any of the messages. More specifically, a message transmission portion of the communication technique sends messages over the communication link in me
Bennett William E.
Beoughter Ken J.
Havekost Robert B.
Jennings Dwight D.
Shepard John R.
Fisher-Rosemount Systems Inc.
Lim Krisna
Marshall & Gerstein & Borun LLP
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