Data processing system and method for transmission of a network packet specifying a group identifier identifying a selected plurality of clients

Information

  • Patent Grant
  • 6405259
  • Patent Number
    6,405,259
  • Date Filed
    Tuesday, December 8, 1998
    26 years ago
  • Date Issued
    Tuesday, June 11, 2002
    22 years ago
Abstract
A method and system are disclosed for transmitting a network packet which identifies only selected ones of a plurality of client computer systems. The client computer systems are coupled to a server computer system to form a network. A logical group is specified which includes only a first plurality of the plurality of client computer systems by specifying one of a plurality of group identifiers. A network packet is then transmitted utilizing the network to the logical group. The network packet includes the group identifier which identifies the logical group, wherein only the logical group are the intended recipients of the packet.
Description




BACKGROUND OF THE INVENTION




1. Field of the Invention




The present invention relates in general to data processing systems and, in particular, to a data processing system and method including a server and client computer system coupled together utilizing a local area network. Still more particularly, the present invention relates to a data processing system and method including a server and client computer system coupled together utilizing a local area network for transmitting a network packet having a group identifier which identifies only selected clients.




2. Description of the Related Art




Personal computer systems are well known in the art. They have attained widespread use for providing computer power to many segments of today's modern society. Personal computers (PCs) may be defined as a desktop, floor standing, or portable microcomputer that includes a system unit having a central processing unit (CPU) and associated volatile and non-volatile memory, including random access memory (RAM) and basic input/output system read only memory (BIOS ROM), a system monitor, a keyboard, one or more flexible diskette drives, a CD-ROM drive, a fixed disk storage drive (also known as a “hard drive”), a pointing device such as a mouse, and an optional network interface adapter. One of the distinguishing characteristics of these systems is the use of a motherboard or system planar to electrically connect these components together. Examples of such personal computer systems are IBM's PC series, Aptiva series, and Thinkpad series.




With PCs being increasingly connected into networks to allow transfers of data among computers to occur, more operations such as maintenance, updating of applications, and data collections are occurring over the network. Computer networks are also becoming essential to their user. It is desirable minimize loss of productivity by increasing availability of network resources.




Significant costs are associated with deploying and maintaining computer systems in large corporate environments. In particular, large costs may be involved in tracking and maintaining each computer system utilizing a particular network.




Computer systems which include a network controller have a particular network address. The network address is defined by the hardware included within the controller as it was configured during manufacturing. The controller addresses are randomly assigned. Although the address may be utilized to identify a particular controller, the address provides no information about the type of system, type of operating system, or other system characteristics.




It may be costly to maintain a typical network having a variety of system types coupled to the network. For example, a network administrator may need to transmit a particular network packet to only those computer systems which are a particular system type. The network administrator has no method for transmitting such a packet without manually checking each system's type, or querying each system.




Therefore a need exists for a data processing system and method for transmitting a network packet which includes a group identifier identifying only selected ones of a plurality of client computer systems.




SUMMARY OF THE INVENTION




A method and system are disclosed for transmitting a network packet which identifies only selected ones of a plurality of client computer systems. The client computer systems are coupled to a server computer system to form a network. A logical group is specified which includes only a first plurality of the plurality of client computer systems by specifying one of a plurality of group identifiers. A network packet is then transmitted utilizing the network to the logical group. The network packet includes the group identifier which identifies the logical group, wherein only the logical group are the intended recipients of the packet.




The above as well as additional objectives, features, and advantages of the present invention will become apparent in the following detailed written description.











BRIEF DESCRIPTION OF THE DRAWINGS




The novel features are set forth in the appended claims. The present invention itself, however, as well as a preferred mode of use, further objectives, and advantages thereof, will best be understood by reference to the following detailed description of a preferred embodiment when read in conjunction with the accompanying drawings, wherein:





FIG. 1

illustrates a pictorial representation of a data processing system including a plurality of client computer systems coupled to a server computer system utilizing a network and a hub in accordance with the method and system of the present invention;





FIG. 2

depicts a more detailed pictorial representation of a client computer system in accordance with the method and system of the present invention;





FIG. 3

illustrates a pictorial representation of a special purpose processing unit which is included within a network adapter included within a client computer system in accordance with the method and system of the present invention;





FIG. 4

illustrates a pictorial representation of a network packet, including a network header and a data packet, which may be transmitted by a server computer system over the network in accordance with the method and system of the present invention;





FIG. 5

depicts a high level flow chart which illustrates establishing logical workgroups, and establishing a modifies magic packet in accordance with the method and system of the present invention;





FIG. 6

illustrates a high level flow chart which depicts a client computer system receiving a network packet having a group identifier which identifies only selected clients in accordance with the present invention; and





FIG. 7

depicts a high level flow chart which illustrates a client processing a modified magic packet in accordance with the method and system of the present invention.











DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT




A preferred embodiment of the present invention and its advantages are better understood by referring to

FIGS. 1-7

of the drawings, like numerals being used for like and corresponding parts of the accompanying drawings.




The present invention is a method and system for transmitting a network packet including one of a plurality of group identifiers which identifies only selected ones of a plurality of client computer systems. The plurality of client computer systems are coupled to a server computer system utilizing a network.




A network packet is transmitted which includes a group identifier. The group identifier identifies a logical group of the plurality of client computer systems. The plurality of client computer systems may be grouped into logical groups. A single client computer system may be included within several or all of the logical groups. The logical groups may include a logical workgroup, a group of client computer systems which utilize a particular system type, a particular protocol type, or which utilize a particular operating system version.




In this manner, a subset of the plurality of client computer systems are identified as the intended recipients of a particular network packet. The subset is identified as a particular logical group of client computer systems. The network packet then includes the logical workgroup as the group identifier.




A filter included within each client computer is capable of being programmed to pass only selected network packets. For example, a filter included within a particular client computer system may be programmed to pass only those network packets which include group identifiers which identify the logical workgroup in which the client is included, the operating system or the protocol type the particular client utilizes, or the system type of the client.




When the network packet is transmitted, it is received by the network controller included within each client computer system. Thereafter, a filter included within the network controller filters the packet according to the manner in which the filter has been programmed. Packets which include a group identifier which identifies either this particular client, the logical workgroup in which the client is included, the operating system or the protocol type the particular client utilizes, or the system type of the client will be passed by the filter to the client computer system for further processing. All other packets will be ignored.





FIG. 1

illustrates a pictorial representation of a data processing system including a plurality of client computer systems


104


coupled to a server computer system


100


utilizing a hub


102


in accordance with the method and system of the present invention. Server computer system


100


is connected to a hub


102


utilizing a local area network (LAN) connector bus


106


. Respective client systems


104


also connect to hub


102


through respective LAN busses


106


. The preferred form of the network conforms to the Ethernet specification and uses such hubs. It will be appreciated, however, that other forms of networks may be utilized to implement the invention.




The term “network” includes any type of data communications channel, such as an Ethernet network, token ring, or X.10 or X.25. Those skilled in the art will recognize that the invention described herein may be implemented utilizing any type of data communications channel. However, the preferred embodiment is implemented utilizing an Ethernet network.





FIG. 2

illustrates a pictorial representation of a network adapter


230


included within a client computer system in accordance with the method and system of the present invention. A central processing unit (CPU)


200


is connected by address, control, and data busses


202


to a memory controller and peripheral component interconnect (PCI) bus bridge


204


which is coupled to system memory


206


. An integrated drive electronics (IDE) device controller


220


, and a PCI bus to Industry Standard Architecture (ISA) bus bridge


212


are connected to PCI bus bridge


204


utilizing PCI bus


208


. IDE controller


220


provides for the attachment of IDE compatible storage devices such as fixed disk drive


222


. PCI/ISA bridge


212


provides an interface between PCI bus


208


and an optional feature or expansion bus such as the ISA bus


214


. PCI/ISA bridge


212


includes power management logic. A PCI standard expansion bus with connector slots


210


is coupled to PCI bridge


204


. PCI connector slots


210


may receive PCI bus compatible peripheral cards. An ISA standard expansion bus with connector slots


216


is connected to PCI/ISA bridge


212


. ISA connector slots


216


may receive ISA compatible adapter cards (not shown). It will be appreciated that other expansion bus types may be used to permit expansion of the system with added devices. It should also be appreciated that two expansion busses are not required to implement the present invention.




An I/O controller


218


is coupled to PCI-ISA bridge controller


212


. I/O controller


218


controls communication between PCI-ISA bridge controller


212


and devices and peripherals such as floppy drive


224


, keyboard


226


, and mouse


228


so that these devices may communicate with CPU


200


.




PCI-ISA bridge controller


212


includes an interface for a flash memory


242


which includes microcode which client


104


executes upon power-on. Flash memory


242


is an electrically erasable programmable read only memory (EEPROM) module and includes BIOS that is used to interface between the I/O devices and operating system. PCI-ISA bridge controller


212


also includes storage


213


, which is preferably implemented utilizing CMOS storage, that holds the BIOS settings. Storage


213


includes values which describe the present configuration of client


104


. For example, storage


213


includes information describing the list of initial program load (IPL) devices set by a user and the sequence to be used for a particular power method, the type of display, the amount of memory, time date, etc. Furthermore, this data is stored in storage


213


whenever a special configuration program, such as configuration/setup is executed. PCI-ISA bridge controller


204


is supplied power from battery


244


to prevent loss of configuration data in storage


213


.




Client system


104


includes a video controller


246


which may, for example, be plugged into one of connector slots


210


. Video controller


246


is connected to video memory


248


. The image in video memory


248


is read by controller


246


and displayed on a monitor (not shown) which is connected to client


104


through connector


250


.




A client system


104


includes a network adapter


230


which may, for example, be plugged into one of the PCI connector slots


210


(as illustrated) or one of the ISA connector slots


216


in order to permit client


104


to communicate with a LAN via connector


236


to hub


102


.




Client computer system


104


includes a power supply


240


which supplies full normal system power, and has an auxiliary power main AUX


5


which supplies full time power to the power management logic


212


and to the network adapter


230


. This enables client


104


to respond to a wakeup signal from network adapter


230


. In response to a receipt of the wakeup signal, power supply


240


is turned on and then powers up client


104


.




Network adapter


230


includes a physical layer


234


and a media access controller (MAC)


232


connected together utilizing a Media Independent Interface (MII) bus


252


. The MII bus


252


is a specification of signals and protocols which define the interfacing of a {fraction (10/100)} Mbps Ethernet Media Access Controller (MAC)


232


to the underlying physical layer


234


.




MAC


232


processes digital network signals, and serves as an interface between a shared data path, i.e. the MII bus


252


, and the PCI bus


208


. MAC


232


performs a number of functions in the transmission and reception of data packets. For example, during the transmission of data, MAC


232


assembles the data to be transmitted into a packet with address and error detection fields. Conversely, during the reception of a packet, MAC


232


disassembles the packet and performs address checking and error detection. In addition, MAC


232


typically performs encoding/decoding of digital signals-transmitted over the shared path and performs preamble generation/removal, as well as bit transmission/reception. In a preferred embodiment, MAC


232


is an Intel 82557 chip. However, those skilled in the art will recognize that the functional blocks depicted in network adapter


230


may be manufactured utilizing a single piece of silicon.




Physical layer


234


conditions analog signals to go out to the network via an R


45


connector


236


. Physical layer


234


may be a fully integrated device supporting 10 and 100 Mb/s CSMA/CD Ethernet applications. Physical layer


234


receives parallel data from the MII local bus


252


and converts it to serial data for transmission through connector


236


and over the network. Physical layer


234


is also responsible for wave shaping and provides analog voltages to the network In a preferred embodiment, physical layer


234


is implemented utilizing an Integrated Services chip ICS-1890.




Physical layer


234


includes auto-negotiation logic that serves three primary purposes. First, it determines the capabilities of client computer


104


. Second, it advertises its own capabilities to server computer


100


. Third, it establishes a connection with server computer


100


using the highest performance connection technology.




Network adapter


230


includes a service processor, or logic module,


300


coupled to the MII bus


252


between physical layer


234


and MAC


232


. Service processor


300


may be a “hard wired” application specific integrated circuit (ASIC) or a programmed general-purpose processor which is programmed as more fully described below. By coupling ASIC


300


to the MII bus


252


, ASIC


300


may send and receive network packets using physical layer


234


.




Data from client computer system


104


is accessed by ASIC


300


over a system management bus (SM)


238


. System management bus


238


is a two-wire, low-speed serial bus used to interconnect management and monitoring devices. With the trickle power supplied by signal AUX


5


from power supply


240


, ASIC


300


is preferably powered full time. Micro-controller


302


(shown in

FIG. 3

) included within ASIC


300


is coupled to bridge controller


212


via the System Management (SM) bus


238


through SM bus interface


316


. This provides a path to allow software running on client


104


to access ASIC and EEPROM


320


.





FIG. 3

illustrates a pictorial representation of management ASIC


300


which is included within a network adapter


230


included within a client computer system


104


in accordance with the method and system of the present invention. ASIC


300


includes a micro-controller


302


which includes several state machines to handle the following tasks: packet reception, SM bus interface, and EEPROM updates. Micro-controller


302


sends commands to FIFO control


308


to control data flow from TX FIFO


306


, RX FIFO


310


, and RX Buffer


318


. Micro-controller


302


also responds to SM bus requests from software running on client


104


to access register status


304


or access EEPROM


320


. Signals are received from the MII bus


252


by interface unit


312


and passed to RX FIFO


310


.




Micro-controller


302


accesses EEPROM


320


through EEPROM interface


314


to obtain values to create network packets such as source and destination MAC addresses, IP protocol information, authentication headers, and Universal Data Packet headers. Further, EEPROM


320


retains the Universal Unique Identifier (UUID). EEPROM


320


may also include a predefined data pattern


325


which is utilized as described herein to filter received network packets.




Micro-controller


302


also includes a filter


233


. Filter


233


is capable of being programmed to pass only selected network packets. Filter


233


compares a received packet to pattern


325


. Network packets which match pattern


325


will be passed by waking client


104


. Preferably, filter


233


is implemented utilizing a pattern match. Filter


233


may be programmed to pass only those network packets including a particular group identifier. The group identifier is a pattern identifying a particular logical group, such as a logical workgroup, a group of computer systems implemented utilizing a particular system type, a group of computer systems executing a particular version of an operating system, or a particular protocol.





FIG. 4

illustrates a pictorial representation of a network packet


400


, including a network header


402


and a data packet


404


, which may be transmitted by a server computer system over the network in accordance with the method and system of the present invention. Each network packet


400


includes a network header


402


and a data packet


404


.




Network header


402


includes a MAC header


406


, IP header


408


, authentication header


410


, and UDP header


412


which are all known in the art to provide addresses, identifiers, and other information for assuring correct transfer of the packet. In the present invention, MAC header


406


includes a destination MAC address which specifies all MACs on the network such that network packet


400


could, but not necessarily, be received by all clients. Data packet


404


includes the information content to be transferred.




Data packet


404


includes modified magic packet


414


and a group identifier


416


. Modified magic packet


414


is a specialized type of packet. The content of packet


414


is six bytes of “FF” followed by a global MAC address. Modified magic packet


414


is a management packet which does not include standard network data.




Group identifier


416


identifies the particular logical group which is the intended recipient of network packet


400


. For example, the intended recipient may be a particular group of clients which are associated with a particular logical workgroup such as an engineering workgroup, a group of clients which utilize a particular operating system version, a group of clients which utilize a particular protocol type, or a group of clients which a particular system type.




The global MAC address is an address which specifies all MACs which are coupled to the network. The global address may be implemented utilizing a default MAC address, a MAC address used for broadcast, or any predefined unique bit pattern.




Although the preferred embodiment utilizes a modified magic packet, the present invention could be implemented utilizing any predetermined data pattern as the “magic” packet portion, i.e. the six bytes of “FF”. Any predefined data pattern could be utilized to indicate to each client that the information following the “magic” packet portion of the network packet includes one of a plurality of group identifiers which is to be filtered as further described below.




When the modified magic packet includes a global MAC address, all MACs included in all client computer systems coupled to the network will process the network packet. When modified magic packet


414


is detected utilizing the six bytes of “FF”, or other predetermined data pattern, each MAC


232


included within each client will receive modified magic packet


414


.




For example, if a particular client's filter is programmed to pass only a particular group identifier associated with a particular logical group, the ASIC included within this client will determine, utilizing the filter, whether the packet includes a group identifier associated with the logical group. If the packet does include the particular group identifier associated with the particular logical group, the client will be powered-on. Thereafter the client may boot locally, or boot to the server. Alternatively, the server may stored a status in ASIC


300


which could be utilized by an application executing within the client which describes further action the client is to take. However, if the packet does not include a group identifier associated with the particular logical group, the packet will be ignored.




When a network packet


400


is received by client


104


, it is received by physical layer


234


and placed on the MII bus


252


. When network packet


400


includes modified magic packet


414


, MAC


232


detects that it includes modified magic packet


414


, and then MAC


232


ignores network packet


400


.




ASIC


300


also receives network packet


400


utilizing the MII interface


312


. Data packet


404


is transferred to RX FIFO


310


and then to RX buffer


318


.





FIG. 5

depicts a high level flow chart which illustrates establishing a modified magic packet and logical groups in accordance with the method and system of the present invention. The process starts as depicted by block


500


and thereafter passes to block


502


which illustrates establishing a plurality of different logical workgroups. For example, the engineering department could be divided into multiple logical workgroups, ENG


1


, ENG


2


, ENG


3


, etc., while the accounting department, finance department, and other departments each are a different logical workgroup. Next, block


504


depicts associating a plurality of client computer systems with one of the logical workgroups. For example, each client computer system within the first engineering workgroup would be associated with ENG


1


, while the accounting department's client computer systems are associated with another logical workgroup, ACNT. Thereafter, block


506


illustrates establishing a modified magic packet. The modified magic packet includes six bytes of “FF” hexadecimal, and either a system type, operating system version, protocol type, or an identification of one of the logical workgroups. The process then terminates as depicted by block


508


.





FIG. 6

illustrates a high level flow chart depicting a server computer system creating and transmitting a modified magic packet having a group identifier which identifies only selected client computer systems in accordance with the method and system of the present invention. The process starts as depicted by block


600


and thereafter passes to block


602


which illustrates a determination of whether or not the server will wake a selected logical workgroup. If a determination is made that the server will not wake a selected logical workgroup, the process passes to block


604


which depicts a determination of whether or not the server will wake all clients which utilize a particular operating system version. If a determination is made that the server will not wake all clients which utilize a particular operating system version, the process passes to block


606


which illustrates a determination of whether or not the server will wake all clients which are a particular system type. If a determination is made that the server will not wake all clients which are a particular system type, the process passes to block


608


which depicts a determination of whether or not the server will wake all clients which are utilizing a particular protocol type. If a determination is made that the server will not wake all clients which are utilizing a particular protocol type, the process passes to block


610


which illustrates a determination of whether or not the server will wake a particular client. If a determination is made that the server will not wake a particular client, the process terminates as depicted by block


612


.




Referring again to block


602


, if a determination is made that the server will wake a selected logical workgroup, the process passes to block


614


which depicts a creation and transmission of a modified magic packet having a group identifier which identifies a selected workgroup, and a global MAC address. The process then terminates as depicted by block


612


.




Referring again to block


604


, if a determination is made that the server will wake all clients which utilize a particular operating system version, the process passes to block


616


which depicts a creation and transmission of a modified magic packet having a group identifier which identifies a particular operating system version, and a global MAC address. The process then terminates as depicted by block


612


.




Referring again to block


606


, if a determination is made that the server will wake all clients which are a particular machine type, the process passes to block


618


which depicts a creation and transmission of a modified magic packet having a group identifier which identifies a particular system type, and a global MAC address. The process then terminates as depicted by block


612


.




Referring again to block


608


, if a determination is made that the server will wake all clients which are utilizing a particular protocol type, the process passes to block


620


which depicts a creation and transmission of a modified magic packet having a group identifier which identifies a particular protocol type, and a global MAC address. The process then terminates as depicted by block


612


.




Referring again to block


610


, if a determination is made that the server will wake a particular client, the process passes to block


622


which illustrates a creation and transmission of a standard magic packet. The MAC address included within the standard packet is the address of the particular client. The process then terminates as depicted by block


612


.





FIG. 7

depicts a high level flow chart which illustrates a client processing a modified magic packet in accordance with the method and system of the present invention. The process starts as illustrated by block


700


and then passes to block


702


which depicts programming the filter to pass only those packets having a group identifier identifying a particular system-type. Next, block


704


illustrates programming the filter to pass only those packets having a group identifier identifying a particular operating system version. Block


706


, then, depicts programming the filter to pass only those packets having a group identifier identifying a particular protocol type. The process then passes to block


708


which illustrates programming the filter to pass only those packets having a group identifier identifying a logical workgroup for the workgroup in which this client is included. Next, block


710


depicts the client waiting for a network packet.




Thereafter, block


712


illustrates the removal of the header from the network packet. Next, block


714


depicts a determination of whether or not the packet is a modified magic packet or a standard magic packet. If a determination is made that the packet is not either a standard or modified magic packet, the process passes to block


716


which illustrates checking the data included within the packet and sending it to the operating system. The process then passes back to block


702


.




Referring again to block


714


, if a determination is made that the packet is either a standard or modified magic packet, the process passes to block


722


which depicts the client being powered-on, i.e. waking the client. The process then passes back to block


702


.




While a preferred embodiment has been particularly shown and described, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the present invention.



Claims
  • 1. A method for efficient communication between a server and only selected client computer system types among a plurality of client computer system types coupled together utilizing a network, said method comprising the steps of:specifying a logical group identifier which includes only client computer systems of a first operating system among said plurality of client computer system types; transmitting a network packet throughout said network which includes said logical group identifiers; filtering said network packet at client computer systems within said network to identify said logical group identifier, and coupling said network packet to only those client computer systems of said first type wherein specific addresses of each client computer system of said first type within said network are not required prior to transmission.
  • 2. The method according to claim 1 wherein said step of specifying a logical group identifier which includes only client computer systems of a first type among said plurality of client computer system types further comprises specifying a logical group identifier which includes only client computer systems utilizing a first network protocol among said plurality of client computer system types.
  • 3. The method according to claim 1 wherein said step of specifying a logical group identifier which includes only client computer systems of a first type among said plurality of client computer system types further comprises the step of specifying a logical group identifier which includes only client computer systems within a first work group among said plurality of client computer system types.
  • 4. The method according to claim 1 wherein said step of filtering said network packet at client computer systems within said network to identify said logical group identifier further comprises the step of providing a network controller including a special purpose processor and a filter to filter said network packet at client computer systems within said network to identify said logical group identifier.
  • 5. The method according to claim 1 wherein said step of transmitting a network packet throughout said network which includes said logical group identifier further comprises the step of generating and transmitting a network packet including a modified magic packet and a data packet, said modified magic packet including a magic packet code identifying said network packet as a magic packet, a global network controller identifier, and said logical group identifier.
  • 6. A data processing system for efficient communication between a server and only selected client computer system types among a plurality of client computer system types coupled together utilizes a network, said system comprising;a server for specifying a logical group identifier which includes only client computer systems of a first operating system among said plurality of client computer system types; means for transmitting a network packet throughout said network which includes said logical group identifier; means for filtering said network packet at client computer systems within said network to identify said logical group identifier; and means for coupling said network packet to only those client computer systems of said first type wherein specific addresses of each client computer system of said first type within said network are not required prior to transmission.
  • 7. The system according to claim 6 wherein said means for specifying a logical group identifier which includes only client computer systems of a first type among said plurality of client computer system types further comprises means for specifying a logical group identifier which includes only client computer systems utilizing a first network protocol among said plurality of client computer system types.
  • 8. The system according to claim 6 wherein said means for specifying a logical group identifier which includes only client computer systems of a first type among said plurality of client computer system types further comprises the means for specifying a logical group identifier which includes only client computer systems within a first work group among said plurality of client computer system types.
  • 9. The system according to claim 6 wherein said means for filtering said network packet at client computer systems within said network to identify said logical group identifier further comprises a network controller including a special purpose processor and a filter to filter said network packet at client computer systems within said network to identify said logical group identifier.
  • 10. The system according to claim 6 wherein said means for transmitting a network packet throughout said network which includes a logical group identifier comprises means for generating a network packet which includes a modified magic packet and a data packet, said modified magic packet including a magic packet code identifying said network packet as a magic packet, a global network controller identifier and said logical group identifier.
CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention is related to the subject matter of co-pending patent application Ser. No. 09/024,231 entitled “FULL TIME NETWORK AUXILIARY PROCESSOR FOR A NETWORK CONNECTED PC” filed on Feb. 17, 1998, assigned to the assignee herein named and incorporated herein by reference, now U.S. Pat. No. 6,266,696.

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