Multiplex communications – Communication over free space – Combining or distributing information via time channels
Reexamination Certificate
1999-09-10
2003-07-22
Le, Thanh Cong (Department: 2684)
Multiplex communications
Communication over free space
Combining or distributing information via time channels
C370S347000, C370S349000, C370S350000, C370S229000, C455S422100, C455S450000, C455S451000, C455S452200, C455S516000
Reexamination Certificate
active
06597683
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains generally to Medium Access Control protocol implementations. More particularly, the invention is a Medium Access Control protocol and method for use in a centrally managed network system at the Medium Access Control layer, which improves the throughput of protocol messages, reduces the latency of data transmissions and provides a set of failure management methods.
2. The Prior Art
Presently, there are numerous ways to provide communication algorithms between devices participating in a network offering various levels of reliability and effectiveness. Likewise, various protocol schemes have been developed to provide various networking services to such network devices.
In an effort to standardize protocols in network communication, the International Standards Organization (ISO) developed the Open Systems Interconnection (OSI) reference model. The OSI reference model deals with connecting systems that are open for communication with other systems and includes seven layers of network services including the Application or “highest” layer, the Presentation layer below the Application layer, the Session layer below the Application layer, the Transport layer below the Session layer, the Network layer below the Transport layer, the Data Link layer below the Network layer, and the Physical or “lowest” layer below the Data Link layer.
The Data Link Layer is designed to offer various services to the Network layer. The principal service that the Data Link layer provides to the Network layer is transferring data from the Network layer of a source device to the Network layer on the destination or target device. The usual approach is for the Data Link layer to break up the bit stream into discrete blocks of bits, compute a checksum for each block, transmit the block along with the checksum to the target device in the form of a packet. When a packet arrives at the target device, the checksum is recomputed for the received block. If the newly computed checksum is different from the checksum provided by the source device, the Data Link layer identifies that an error has occurred and an error-recovery process is invoked.
At the Medium Access Control (MAC) sublayer of the Data Link layer, protocols are used to solve the issue of which network device gets to use the broadcast channel when there is competition for it. The MAC layer is particularly important in Local Area Networks (LANs) where the number of network devices competing for the communication channel may comprise hundreds of devices.
One algorithm devised to provide MAC layer services is the ALOHA system which comprises a “regular” form and a “slotted” form. In the regular ALOHA framework packet transmissions can occur anytime, while the slotted ALOHA framework divides time into discrete time slots in which all packet transmissions must be synchronized, where the additional advantage provided is the increased throughput. A detailed treatment of slotted ALOHA protocols is provided by L. G. Roberts in “ALOHA packet system with and without slots and capture,” Computer Communication Review, vol. 5, pp. 28-42, April 1975 and is incorporated herein by reference. The simplest version of the two approaches share a common process where the corresponding receiver of the packet acknowledges the transmitter the integrity of the transmitted packet which will be destroyed when overlapping transmissions from more than one transmitter occurs.
Another MAC algorithm is called Carrier Sense Multiple Access (CSMA), with its two most common versions as discussed here. The first is called 1-persistent CSMA which allows a transmitting device to first listen to the channel to determine if another device is transmitting at that moment. If the channel is busy, the node device waits until the channel becomes idle. When the station detects an idle channel, it transmits its packet. However, due to signal propagation delay, collisions still occur, as a channel may seem to be idle from pending transmitters that will then transmit their packets at approximately about the same time.
The second version is nonpersistent CSMA. In this framework, before sending, a device senses the channel and if no other device is using the channel, the devices will begin to transmit as in 1-persistent CSMA. However, if the channel is already in use, the station will not seize the channel immediately upon detecting of the end of the previous transmission. Instead, it waits for a random period of time and then starts to transmit.
These and other present implementations of MAC layer protocols lack the capabilities to support low-latency as well as throughput of protocol and data transmissions all on the same broadcast channel. Accordingly, there is a need for a reliable Medium Access Control protocol and method suitable for use in a centralized managed network system which improves bandwidth usage, improves throughput as well as latency of both protocol and data transmissions, and provides a set of failure-recovery methods. The present invention satisfies these needs, as well as others, and generally overcomes the deficiencies found in the background art.
BRIEF DESCRIPTION OF THE INVENTION
The present invention is a Medium Access Control (MAC) protocol and method for use in a network system employing centralized management of a common channel which is shared for protocol messages as well as data transmissions. The invention employs a modified slotted-ALOHA mode and a regular TDMA mode within a single TDMA frame definition. The MAC protocol improves the throughput of protocol messages, reduces the latency of data transmissions and provides a set of failure management methods.
In general, the MAC layer protocol of the present invention operates in a network system having a master device and a plurality of slave devices. More particularly, the MAC layer protocol is a software protocol provided and executed in the MAC sublayer of the Data Link layer according to the Open System Interconnect (OSI) standard. The Logical Link Control (LLC) sublayer forms the “top” or “upper” half of the Data Link layer and provides virtual linking services. The MAC sublayer forms the “bottom” or “lower” half of the Data Link layer and provides the services described herein. The software protocol is executed and operates on circuitry or like hardware as is known in the art within the master and slave devices on the network at the MAC layer.
The software architecture of the present invention includes a protocol “engine” component and a protocol “microcode” component. The “engine” component, which consists of software and hardware parts, provides the execution of the microcode component and hardware-related routines and interfaces necessary at the MAC layer, including, for example, hardware set and reset routines, interfaces to the Physical (PHY) layer, and interfaces to the data transfer hardware.
The microcode component provides the actual software implementation for the protocol. The microcode component provides the engine component with the necessary software instructions, routines and other software definitions necessary to perform the protocol tasks of the present invention. This bifurcated protocol architecture allows updates to one component to be made independently of the other component, thereby streamlining the process of protocol updates. For example, updates to the microcode can be carried out by transferring the updated microcode software to a flash memory device. The engine component is then capable of executing the updated microcode by accessing the flash memory device. Similarly, the software part of the engine component is available for updates.
The invention employs centralized management of “connection-oriented service,” where the establishment of a connection between the source and destination device is achieved through a master device which carries out the operation of authorizing or otherwise managing all protocol communication between the source and destination slave devices.
The present invention also provides a Time
Gehring Stephan
Lynch William
Rahardja Krisnawan
Rogerson Gerald
Sparrell Carlton J.
D'Agosta Stephen
Luce Forward
Pulse-Link, Inc.
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