Abstract:
A document delivery network server having a set of integrated functions including sending, receiving, routing and filing of FAXes and e-mails to other users which achieves numerous advantages over the prior art. The document delivery system is based on a client/server model having both analog and digital Fax line capabilities. The server side provides very highly integrated systems functionality based on industry standard, commercially available hardware and a mix of industry standard and proprietary software components including integrated FAX/modem modules, an embedded OS, embedded plug-and-play driver sets, embedded e-mail gateways, an embedded FAX archive, embedded back-up/restore, proprietary high efficiency line utilization and highly efficient load balancing.

Description:
This application is a continuation of U.S. Patent Application No. 13/011,327, filed Jan. 21, 2011, now allowed now U.S. Pat. 7,982,899, which is a continuation of U.S. patent application Ser. No. 12/567,656, filed Sep. 25, 2009, now U.S. Pat. No. 7,876,468, which is a continuation of U.S. patent application Ser. No. 10/935,776, filed Sep. 7, 2004, now U.S. Pat. No. 7,612,903, which claims the benefit of U.S. Provisional Application No. 60/501,238, filed on Sep. 8, 2003, all of which are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates generally to electronic delivery of documents in a network environment, and more specifically to using a highly integrated plug-and-play system to deliver possibly differing types of documents over possibly differing types of electronic media to possibly differing types of target devices. 
     2. Discussion of Prior Art 
     Internet e-mail is suited for delivering various types of documents to a dispersed workforce, yet facsimile (FAX) continues to support a significant share of many business processes. Target devices ranging from full function computers to hand held Personal Digital Assistants (PDAs) and cell phones complicate communications. A user who needs to send one document to numerous recipients needs to know something about each of the target devices, which have their own conditions for the types of documents they can receive. Conventionally, these conditions are stored in the user&#39;s communication device and must be kept current by individual users, which is burdensome. 
     There exist several methods for separately sending different types of documents, but no current system can send diverse types of documents simultaneously. Moreover, no present system allows a user to send the same document simultaneously to different types of target devices. Conventional solutions require installation and integration of various hardware and software components such as a computer, fax modems, network interfaces, fax server software, e-mail server software, database and application interface code. 
     Current document delivery methods also restrict the format of documents that may be sent or received. For example, some systems can only send and receive Simple Mail Transfer Protocol (SMTP) documents, others only facsimile documents, and still others only graphical documents such as plot files or character delimited data. There are a number of current methods for analyzing an incoming document and converting it to a desired format before delivering it to a specific target device, but none have, from a single “plug-and-play” network device, the ability to simultaneously send the same document to multiple users with different target device types. 
     A further restriction on current methods is related to complexity. Providing document delivery service to multiple types of devices requires complex conversion processes that need to be loaded and run, which involves difficult initial installation and ongoing maintenance. Contemporary systems, when faced with new or changed input file types or target devices, do not have the ability to “plug-and-play.” 
     What is needed is a system and method for delivering a plurality of document types to a variety of target devices without the need to assemble the appropriate hardware components or to manually install or maintain software drivers and software applications. 
     Current systems maintain an acceptable number of lines idle by setting lines to “Receive Only,” “Send Only,” or “Bi-Directional.” It is common practice for Administrators to configure “Receive Only” lines as an assurance that they won&#39;t send a “busy” tone to incoming calls. This method does not allow a dynamic mix of send and receive jobs to fully utilize the lines and still maintain a dedicated number of lines idle for incoming calls. Instead, the administrator must predict and fix a static setting for the expected send and receive workload. 
     SUMMARY OF THE INVENTION 
     The present invention provides a document delivery network server which integrates functions preferably including sending, receiving, routing and filing of FAXes and e-mails to and from other users. The document delivery system is embodied in a client/server model having both analog and digital FAX line capabilities. The server side integrates conventional hardware with industry standard and proprietary software. The system&#39;s components include integrated FAX/modem modules, an embedded OS, embedded plug-and-play driver sets, embedded e-mail gateways, an embedded FAX archive, embedded back-up/restore, proprietary high efficiency line utilization and efficient load balancing. 
     Providing these components in a “Plug-n-Play” document delivery network server simplifies installation of hardware and software on the server side. Client side software installation is facilitated by offering many options for accessing the server. In the simplest “zero-install” case, a web browser can be used to access the document delivery server, and a word processor can be used as a cover page editor. Other access options include sending/receiving a plurality of documents through an e-mail gateway on the server, using regular application printouts with a proprietary FAX print driver to generate FAX jobs, copying files to a Drop Directory, and submitting jobs through an industry standard programming interface. Finally, a thick client can optionally be installed for a more fully featured interface to the document delivery server. The combination of a high level of functional integration, ease of installation and client flexibility provides a significant improvement over conventional solutions. 
     The document delivery server is preferably connectable to a plurality of delivery media including the Public Switched Telephone Network (PSTN), the Internet and one or more intranets including wired and wireless Local Area Networks (LANs) and Wide Area Networks (WANs). 
     The document server memory stores a set of software modules that provide functions including Queue Management, Document Conversion, FAX Scheduling, and a Document Delivery Database. These software modules work with an embedded operating system which includes a plurality of target device type drivers to enable a diverse set of users to simultaneously send and receive FAXes and e-mails. 
     In operation the document delivery server, which may or may not be in a remote location, receives input documents via network connections from users. For example, users may input documents of any file type via the Internet, the PSTN, an intranet or a wireless gateway. The invention examines the input, determines if the target device is compatible, if not, converts the document into a compatible format, and sends the document to the target device. The conversion process consists of rendering incoming files into multi-page Tagged Image File Format (TIFF) images for facsimile, a PDF (Portable Document Format) file for Internet viewing, or attaching the file to an e-mail. 
     The invention includes a method for better utilizing telephone facsimile lines and maintaining a configurable number of idle lines to service incoming calls. Rather than setting specific lines to “Receive Only” as current systems do, the invention frequently updates its count of idle lines. An outgoing send job is only allocated a line if there are more than a configurable minimum number of idle lines available. This simple algorithm allows a more dynamic mix of send and receive jobs to more fully utilize telephone FAX lines and still maintain a minimum number of lines idle to assure that incoming calls will be accepted rather than “busy-out.” 
     Multiple document delivery servers can be clustered together to scale the capacity of managed facsimile lines and the number of supported simultaneous users. The cluster configuration is a master-slave arrangement that allows for fail-over scenarios in the event that a server is unavailable. The master tracks the usage of all lines in the cluster. 
     One advantage of the invention is its ability to send the same input document to different target devices simultaneously. For example, a user may have a text document that must be sent to a FAX machine for one recipient but via e-mail for others. The text document is rendered as a TIFF file for the FAX machine or sent as text through e-mail. Advantageously, the invention accepts the input document, formats it correctly for all recipients regardless of the target device type(s), and then distributes the document in one session. These and other advantages of the invention are described below in conjunction with the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is physical block diagram showing a document delivery system that may implement the method of the invention; 
         FIG. 2  is a logical block diagram showing software modules involved in communicating with various sending and receiving devices; 
         FIG. 3  is a block diagram illustrating a global job queue and a plurality of Document Servers  12  arranged as a master and slaves for performing line utilization and load balancing; 
         FIG. 4  is a state diagram of the algorithm for performing line utilization; and 
         FIG. 5  is a flow chart illustrating a plug-and-play sequence for setting up the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a physical block diagram of the document delivery system  10  of the present invention which is comprised of a Document Server  12  including hardware  14  and software  16 . Server  12  communicates with numerous document sending and receiving devices including a conventional FAX machine  18  connected through the Public Switched Telephone Network (PSTN)  20 , and various other types of devices connected through a network  22  for example the Internet or an intranet such as Local Area Network (LAN) or Wide Area Network (WAN). The various types of sending and receiving devices include a Web browser thin client  24 , a User custom application  26 , a Microsoft Foundation Classes (MFC) thick client  28 , an E-mail server  30 , any Windows® print-capable application  32 , and a Drop directory  34 . Additional target devices, for example a cell phone or PDA, are also contemplated. 
     Hardware  14  comprises a conventional CPU  36  connected by a PCI bus  38  to (a) FAX/modem board(s)  40 A(,  40 B . . .  40   n ) which are in turn connected to PSTN  20 . In a preferred embodiment, the FAX/Modem board(s)  40 A,  40 B . . .  40   n  are CPi/2400-1T1 facsimile boards, each with twenty-four multiplexed channels, from Intel Corp., Santa Clara, Calif. Other types of board may be used. 
     CPU  36  is also connected through Address  42  and Data  44  busses and I/O circuits  46  to a Network Interface Controller (NIC)  48  and to other I/O Ports  50  interfacing to such I/O devices as monitors, keyboards and displays (not shown) typically used to communicate with the system, for example, to program it. Other conventional components of Server  12 , for example a power supply and chassis, are not shown. 
     CPU  36  is also connected through Address  42  and Data  44  busses to a Memory  52  made up of Read Only Memory (ROM), Random Access Memory (RAM), and a long term mass storage device such as a hard disk drive, not shown. The ROM and RAM store instructions and data for booting the Operating System (OS), setting initial system variables and storing transient data generated by routine operations of CPU  36 , while data files are stored on the hard disk. 
     The invention uses an embedded OS  54 , preferably Windows® 2003 Server Application Kit (SAK) from Microsoft Corporation of Redmond, Wash. Using an embedded OS provides a number of advantages including ease of portability, ease of programming, ease of interface and a large population of device drivers. Selecting a Windows based OS enables the broadest coverage of applications (and thus supported file types) that can be installed on the server for server-side rendering or document conversion. 
     Startup/Persistence Manager module  56  manages the startup and shutdown of Document Server  12  and provides required basic operational services including timer management, clock/time-of-day management, and memory management to ensure the integrity of data and an orderly transition of pending tasks during power up and down sequences. The persistence manager monitors and restarts hung or crashed services to improve availability of the document delivery services. These tasks are accomplished in a manner well known in the art. 
     Trace/Error Log module  58  tracks, and if possible assists in correcting, error conditions related to operation of Document Server  12 . For example, if a document was to be delivered to a particular target device, but that device was unavailable to receive, then after a predetermined number of attempts a “failure to deliver” error would be declared. Data associated with the error is then written to a log for later analysis. Other error conditions are handled in a similar manner. 
     Networked systems are susceptible to attack, and therefore certain security activities, for example, authentication, authorization, accounting, audit trails, and public key encryption, are required to ensure a high level of task/data integrity. Security module  60  contains instructions necessary to interpret and act upon tasks and data related to operating Document Server  12 , and uses data contained in the Document Delivery Database  74  as well as specific data generated by other functions within the system to monitor for, assess, and inform the system of, security threats. 
     Operating System  54 , Startup/Persistence Manager module  56 , Trace/Error Log module  58 , and Security module  60  operate in the background and interact with other modules that make up the software  16  of Document Server  12 . 
     In addition to the conventional general software/firmware components required by CPU  36 , memory  52  stores a number of specific purpose software function program modules. 
     Microsoft Internet Information Server (IIS™) with an Active Server Page (ASP)  62  is a standard Web Server. It is programmed with specific purpose ASP pages that provide the thin client Web Browser Interface  80  to the document delivery server. The specific purpose WSDL and SOAP files  86  provide a Web Services programming Interface to the document delivery server. 
     An e-mail Gateway module  64  accepts incoming documents as MIME attachments from networked e-mail servers including SMTP, Notes™, or Exchange™ represented as E-mail Server  30 . 
     A Document Delivery Printer module  66  accepts incoming documents from any application that is compatible with the Windows® Graphical Device Interface (GDI) and is capable of printing. 
     A FAX Board Scheduler module  68  determines and manages which of the channels in the several FAX/modem Boards  40  should be used for a particular document transaction. 
     An Administration module  70  manages the document delivery server configuration and user tables. The user tables include a mapping of fax numbers and email addresses for the routing of incoming jobs to users in the system. 
     A Queue Manager module  72  manages both the incoming and outgoing document queues. 
     A Document Delivery Database module  74  contains a number of tables for configuration of the document delivery server, user settings, incoming, outgoing, archival, and notice queues. 
     A Document Converter module  76  converts files in job groups to the set of file formats required by all destinations in the job group. For each type of input file, the associated application with the file type (for example MS Word for .doc files) is launched and a print command is issued to the document delivery printer that outputs appropriate file types for the target device. For example, the printer may output faxable TIFF files for a FAX target device or PDF files for a PDA device. 
     An Archiver module  78  creates and maintains a backup of documents processed by Document Server  12 . It may connect to any ODBC compliant database and Windows UNC networked mapped directory to store backups of the document delivery server jobs. 
     Operation 
       FIG. 2  is a logical block diagram showing relationships between software modules involved in processing communications between various sending and receiving devices. 
     Document server  12  may be accessed in multiple ways. A first path into Document Server  12  is via a web browser interface  24 . This is referred to as a “thin client” or “zero install” method since no dedicated software need be loaded, and no software other than a web browser is required, on the user&#39;s system. A user sends a document via the Web Browser Thin Client  24  to Document Server  12  for delivery to a receiver. Since web browsers use the standard HTTP transport, and since the software of the Document Server  12  can receive documents of any registered file type, users may simply use their web browsers to send documents for delivery. The document sent by the user transits network  22  and arrives at NIC  48  in Document Server  12 . Web Browser Interface program  80  is part of the Microsoft Internet Information Server (IIS™)  62  which in turn is bundled with the Windows 2000® OS  54 . The document is passed to an Active Server Page (ASP) within the IIS  62  which in response generates HTML code. ASP IIS  62  passes the document via Queue Manager Application Program Interface (API)  84  to Queue Manager module  72 . The Queue Manager module  72  operates upon the incoming document to retrieve and analyze data fields. These data are used in cooperation with Document Delivery Database  74  to verify the user&#39;s sender information and determine what if any document conversion is required, and schedule the outgoing document. Once scheduled, the document is placed in the outgoing queue where it will be transmitted as described below. 
     A second path into Document Server  12  is through a User Custom Application  26 , which is identical to the thin client case except that the user must write Custom Application  26 , which can be in any language as long as the interface is Simple Object Access Protocol (SOAP) compliant. The SOAP-compliant application program must reside on the user&#39;s system. Soap interface  86  accepts SOAP messages over the HTTP transport protocol for further processing by MS IIS  62 . 
     A third path into Document Server  12  is via an MFC application  28 , a so-called “thick client,” running on a user&#39;s system. For this method a dedicated interface application resides on the user&#39;s system (not shown). The interface application is specifically written to interface with the Admin API  82  and the Queue Manager API  84  software. The interface application enables incoming documents to be presented directly via Queue Manager API  84  to the Queue Manager module  72 . Operations upon the incoming document are the same as for the zero install case. 
     Other inputs originating from web browser thin client  24 , user custom application  26  and MFC thick client  28  are routed through Admin API  82  to the Administration Manager which manages the document delivery server&#39;s configuration, user accounts, routing tables, fax line allocation, and other custom settings. 
     A fourth path for a document to be delivered to Document Server  12  is by e-mail using conventional protocols such as Simple Mail Transfer Protocol (SMTP), Lotus™ Notes™, or Microsoft Exchange™. Other e-mail protocols could be used as well. A sender&#39;s e-mail server  30  delivers an e-mail document via a network  22  such as the Internet to e-mail interface  88 , which passes the incoming document to e-mail gateway module  64 , which is capable of receiving, analyzing and acting upon incoming documents in a variety of formats. E-mail Gateway module  64  operates in a manner well understood in the art. E-mail gateway module  64  in turn sends the received document to Queue Manager module  72  for further handling. 
     A fifth path for a document to be delivered to Document Server  12  is from any Windows® Print Capable Application  32  such as Microsoft Word® which can format a document in a Graphical Device Interface (GDI) (bitmapped) file. The incoming document is received via Printer Interface  90  and passed to the Document Delivery Printer module  66  which extracts tag delimited commands embedded within the document text and parses the commands to evaluate such data as the source, destination, and delivery options, among other information. Printer module  66  converts the incoming document to a Tagged Image File Format (TIFF) format and passes it to Queue Manager  72  for further handling. Queue Manager  72  uses data retrieved from the embedded commands to look up target information contained in Document Delivery Database  74 . 
     A sixth path into Document Server  12  is by way of a Drop Directory  34 , which is a location in a sender&#39;s computer where a user may simply “drop” a file containing metadata about a delivery job. The metadata file may contain references to multiple documents also copied to the drop directory which will be included as the body of the delivery job. More than one (not shown) drop directory may be present. Queue Manager  72  continuously polls or checks the drop directory  34  to see if a new metadata job file or job group has appeared. If so Queue Manager  72  retrieves the job file, determines what actions are necessary from data fields contained within the document(s), and acts upon the document(s) as required. 
     Inputs originating from web browser thin client  24 , user custom application  26 , MFC thick client  28 , E-mail server  30 , Windows print-capable application  32 , and Drop directory  34  are routed through Queue Manager API  84 . The Queue Manager  72  schedules conversion for all documents to all required destination file formats. Cover pages may be rendered individually for each job or destination in the job group, where attachments will only be rendered once per job group per target file type. After conversion, Queue manager  72  checks “Castelle Internet Faxing” (CIF) routing tables to see if a job belongs in the local global job queue or needs to be forwarded to another master Queue Manager  72  on a document delivery server  12  in a different location. Once in the Global Ready Job Queue, and the delivery time has passed the job is available to the Fax Schedulers in the cluster on a FIFO basis. 
     A user may send a document on a seventh path from a traditional FAX machine  18  via PSTN  20  and through a FAX/modem interface board  40  and FAX Scheduler module  68 . FAX Board Scheduler module  68  receives instructions from, and passes received FAXes to, Queue Manager module  72 . Since the received document is already in a proper (TIFF) format for handling, Queue Manager module  72  is able to process the incoming document without a conversion step. 
     These seven input paths are not the only possible methods of document submission using this invention. Other input paths may be used without departing from the method of the invention. 
     Queue Manager module  72  generates and maintains the data contained in the Document Delivery Database module  74 , and works with Document Delivery. Database module  74  and Document Converter module  76  to ensure that a specific document is properly formatted and delivered to the appropriate user. For example, when an incoming document is received from E-mail Server  30  and destined for a Target Device  18  or  30 , Document Conversion module  76  uses the data contained in Document Delivery Database  74  to first determine whether the particular target device needs the document formatted for transmission and, if so, converts the document to the proper format. Queue Manager module  72  also operates in conjunction with Archiver module  78  and implements the invention&#39;s unique load balancing algorithm. Archiver module  78  is a scheduled task that backs up all transactions for a given period of time. Since this is a scheduled task, for example, every 24 hours at midnight, a run time may be selected that has the least impact on ordinary traffic. Archiver module  78  accomplishes the back-up task in a well known manner. While Archiver module  78  is resident on Document Server  12 , the actual storage of data may be either local or remote. 
     Once a document has been received by Document Server  12 , software  16  interprets incoming documents, determines what actions are required, identifies the target device(s) for the document(s), if necessary converts the incoming document to the format expected by the target device, performs the action(s) and deliver the document(s) to the indicated addressees. are destinations for documents processed by Document Server  12 . The Target Devices  18  and  30  may differ from each other. 
     Queue Manager module  72  stores the incoming and outgoing documents as files in queues in the Database  74  on the Document Delivery Server&#39;s hard disk (not shown). An incoming queue record includes identification fields for job number, user ID, origination ID as well as communication status and capability such as receive status, resolution, time, duration, baud rate, signal conditions such as noise and strength, page count and direct inward dialing data. Other fields may also be used. 
     An outgoing queue record includes identification data, outgoing queue data, document data, transmission channel data, and target device data. Identification data includes job ID, originating job ID and user ID. Outgoing queue data comprises queue status prior to any required document conversion, queue status after any required document conversion, job priority, job group ID if the document is part of a group job, and cover page data. Document data includes, among other fields, a file path, transmission type, number of pages to be sent, completed transmission attempts, timeout data, transmission attempt scheduling, number of pages sent and any error codes reported. 
     Transmission channel data includes such fields as line noise level, signal quality, signal strength, baud rate capability, baud rate used for transmission, and target device capabilities. Target device data is comprised of, among other fields, one or more user keys, sender&#39;s name, a comment field, a company name field, time the transmission actually started, sent resolution, number of transmission attempts, the retry delay, certain customer accounting data for billing, a telephone line number, telephone line group number, the target number to be dialed and the actual number dialed. There are a number of other data fields in the transmission channel data that are not presented since they do not directly impinge on the method of the invention. 
     Once an incoming document has been received and any initial processing has been completed, for example parsing embedded commands in the Document Delivery Printer module  66 , all documents are converted to the appropriate target destination format and henceforth processed in the same way, For example, if a sender has placed a file in their Drop Directory  34  and the document has been received, then a job number is assigned and target data collected and analyzed by Queue Manager module  72  cooperating with Administration module  70 . Data contained in the Document Database module  74  is used to identify sender and receiver, determine if the incoming file requires conversion for any of the designated target devices, and verify any security requirements. If the incoming document requires conversion for any of the target devices, the Queue Manager module  72  instructs the Document Converter module  76  to process the document. 
     An advantage of the invention is that a single incoming document may be delivered to a plurality of target devices simultaneously. Queue Manager module  72  instructs the Document Converter module  76  to produce a converted document for each target device. As a result, a single incoming document can yield multiple outgoing jobs, each with their particular document format requirement. The multiple jobs (one for each destination) become members of a single job group. 
     If the incoming document requires only a single outgoing job, which is a FAX job, then Queue Manager module  72  assembles the job and passes the outgoing document to the FAX Board Scheduler module  68  which, obeying line use and load balancing rules discussed below, analyzes the job, sets outgoing communication session characteristics such as baud rate, resolution and the like, and ultimately prompts the FAX Board Driver module  40 ( n ) to dial the number initiating the outgoing transmission. The reference designator  40 ( n ) indicates that there may be more than one instance of a FAX board in Document Server  12 . The FAX Board Driver  40 ( n ) establishes a connection with the target device, in this case traditional FAX machine  18 , and transacts the delivery, thereby completing the process. In this way the invention can receive one or more documents from a plurality of sources, analyze, process and deliver the one or more incoming documents to one or more target devices in a format capable of being used by the one or more target devices even if the format requirements of the target devices differ. 
     If the target device is local then the number dialed on PSTN  20  is not a long distance call. However, document transmissions can be very large in size and if the call is long distance it can be expensive. Therefore the invention preferably reduces that expense by using the less expensive Internet to pass the document to a remote location and then distribute the document via a local PSTN call to the ultimate target device. This process is denominated Castelle Internet Faxing (CIF), which requires multiple instances of Document Server  12 —one at each end. For example a company may have an office in Morgan Hill, Calif. and an office in New York, N.Y. Rather than use traditional FAX-to-FAX delivery over long distance PSTN lines, the company can install a Document Server  12  in both offices. A user in the New York office inputs a document, using any of the input cases described above, for several target devices in the Morgan Hill area. Document Server  12  in New York prepares the necessary documents, assembles the outgoing job and, using the proprietary CIF software over the more economical Internet communications medium, passes the entire job to Document Server  12  in Morgan Hill. Document Server  12  in Morgan Hill receives the job via NIC  48 . Since the same CIF software is resident on both servers, Document Server  12  in Morgan Hill simply processes the job as if it had originated locally. Documents destined for each designated target device have already been formatted, thus the server in Morgan Hill simply delivers the documents as it had processed the entire job locally. In this way the method of the invention provides a more economic method for simultaneously delivering properly formatted documents to a plurality of remote target devices. 
     Load Balancing 
     Multiple Document Delivery servers  12  may be clustered together in a Master/Slave(s) configuration. Each Slave is responsible only for the FAX lines connected to its respective slave node. The Master keeps track of the FAX lines connected to its own lines, and also tracks the status of each of the slave node lines and jobs. The entire set of lines for the master and all the slaves are presented as one set of “Virtual” lines to the clients of the Document Delivery Server Queue Manager clients. If three nodes have  48  lines each, the  144  physical lines are presented as one set of “Virtual” lines to all the client interfaces into the Master Document Delivery server. 
     The Master Document Delivery server runs all the software services in  FIG. 2 , where the Slave Document Delivery Server really only runs the FAX Scheduler service and Document Conversion services as slaves (clients) to the Master Document Delivery server&#39;s Queue Manager service. 
     Each FAX board Scheduler  68  on each node is responsible for maintaining an array of jobs ready to be sent. The size of the array is twice the number of lines on the node. This size assures that there will always be jobs “Ready” to be sent when a line is available. When a send job completes, the status (successful, busy tone, . . . ) is sent the Master Queue Manager, and the job is deleted from the local cache of “Ready” send jobs. 
     A thread in the FAX Board Scheduler  68  keeps the local cache of “Ready” send jobs full by requesting more jobs from the Master Queue Manager when there are empty slots in the local array. The Master just responds to requests from Slaves for “Ready” jobs. When responding to a request, the Master Queue Manager notes which slave has been assigned the jobs and will not allow the jobs to be assigned to multiple Slaves. Other load balancing schemes often try complex scheduling algorithms on a Master, but that creates a bottleneck on performance of the entire cluster in the Master Queue Manager. The distributed nature of this request/response architecture allows for efficient scaling out of the load, while presenting a unified view of the entire cluster&#39;s physical lines to users of the cluster. 
     Line Utilization 
     Line utilization occurs independently of load balancing. Once a FAX Scheduler has acquired a number of send jobs equal to 2× the number of lines it is scheduling for, the Line Utilization algorithms determine how to assign those jobs to a particular line. 
     Current systems maintain an acceptable number of idle lines by setting lines to “Receive Only”, “Send Only”, or “Bi-Directional”. It is common practice for Administrators to configure “Receive Only” lines as an assurance that they won&#39;t send a “busy” tone to incoming calls. This method does not allow a dynamic mix of send and receive jobs to fully utilize the lines and still maintain a dedicated number of idle lines for incoming calls. The administrator must predict a static setting for the expected send and receive workload. The invention&#39;s novel Line Utilization algorithm (numIdleLines&gt;minIdleLines) defines when a line is available for send jobs. If a line is available, one of the jobs in the local send “Ready” array is assigned a line by the node&#39;s FAX Scheduler  68 . This allows all lines to be set to “Bi-Directional” and a dynamic mix of send and receive jobs to be scheduled on the system while still maintaining a threshold of available lines reserved for incoming jobs that avoids sending a busy signal. 
     Any given Document Server  12  may contain a plurality of FAX boards  40  connected to PSTN  20 , and each FAX board  40  may contain as many as 30 separate channels. Since incoming documents may be arriving at any time, and since outgoing documents occupy channel space, the invention provides a line utilization method for ensuring that both incoming and outgoing activities may occur simultaneously. The FAXpress™ system administrator can reserve a default minimum number of channels (minIdleLines,  FIG. 4 ) for incoming documents. This insures that Document Server  12  will always be able to receive jobs. Consider that at some arbitrary point in time an incremental incoming job arrives. For this example, assume that there are 24 channels total available for use, and that 12 of these are sending traffic and 11 are receiving traffic. Assume further that the system administrator has reserved a minimum of three lines (minIdleLines=3 in  FIG. 4 ) to be for incoming traffic. Since one channel remains open, and since three is the minimum for receiving, the last open channel is reserved for an incremental incoming job. On the other hand, if three more receive jobs finish, there would now be 12 sending lines and 8 receiving lines with 4 idle lines. Because minIdleLines (3)&lt;numIdleLines (4), a send job is allocated to a line and there would now be 13 send jobs and 8 receive jobs. 
     Re-Capping Advantages 
     One advantage of the invention is the ability to deliver a single source document in multiple formats to multiple destinations simultaneously. This is accomplished by analyzing the incoming document to determine what target devices are intended, then operating upon the incoming document to create separate, properly formatted documents for each of the target devices. Once created, the documents are grouped as a job and simultaneously transmitted to all target devices. 
     A second advantage of the invention is enabling the economic use of transmission media. This is accomplished through both line utilization and load balancing. Line utilization occurs within each instance of a document server, while load balancing occurs over a cluster of master/slaved configured document servers  12 . The result is the physically and economically optimized use of document delivery resources. 
     A third advantage of the invention is level of integration of document delivery functions. This is accomplished by providing a plug-and-play solution where all necessary hardware and software are provided in a single, easily installed digital device. Users of the document server simply attach the server  12  to a source of power, insert PSTN  20  and network  22  connections, and turn the server on. A system administrator then sets initial preferences, such as minimum number of incoming channels, and the server is ready for use. 
     A fourth advantage of the invention is flexibility. A wide range of input paths may be used to simultaneously deliver a document to a plurality of target devices even though each of the designated target devices may require different formats. Users of the system may make use of document delivery without the need to install any dedicated software via a web browser interface. At the other end of the input spectrum, legacy devices such as traditional FAX machines may be used to input documents. 
     While the present invention is described in terms of a preferred embodiment, it will be appreciated by those skilled in the art that this embodiment may be modified without departing from the essence of the invention. It is therefore intended that the following claims be interpreted as covering any modifications falling within the true spirit and scope of the invention.