Abstract:
Methods and apparatus for efficiently generating and updating screens representing device-status information. A management system that includes a Web browser is used to display device-status information transmitted to the management station in the form of an HTML file. An initial HTML file includes a complete description of the status screen to be displayed. Rather than generate and transmit a complete description of the status screen to the management station each time device status changes, a set of device state information in the form of an HTML file is transmitted, e.g., from a remotely located device monitor, to the management system. A JavaScript routine is used to update the displayed status information based on the received device state information. Use of a JavaScript routine allows portions of the displayed screen, e.g., the changed device-status portions, to be modified without having to alter or regenerate the fixed portions of the displayed status screen or the portions relating to device-status information which has not changed. The updating of device-status information is relatively efficient and is performed periodically or, alternatively, whenever a change in device status is detected.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to methods and apparatus for displaying information and, more particularly, to methods and apparatus for efficiently displaying and updating information, e.g., device-status information, at a location which is remote from the source of the information.  
         BACKGROUND OF THE INVENTION  
         [0002]    From a device or system management standpoint, it is often useful to know the status of one or more devices at any given time. In order to facilitate device and/or system management, monitoring devices are frequently used to collect device-status information. The collected information is then processed and, in many cases, transmitted to a physically remote management system for display to a human operator.  
           [0003]    Displayed images that indicate the status of one or more corresponding physical or logical devices are sometimes referred to as device mimics. Device mimics may be implemented as a graphical representation of one or more devices and the status of the device(s). For example, a device mimic may be used to represent a network router and to display the status of various ports included in the network router.  
           [0004]    The growing use of networked computers, i.e., intranets, and the growth of the now well known global Internet, provide a convenient infrastructure that can be used to transmit device-status information. Frequently, device-status information is transmitted using an intranet or the Internet to a management system so that it can be displayed to a human system administrator or other individual overseeing device and/or system operation.  
           [0005]    Web browsers, such as Microsoft Corporation&#39;s Internet Explorer, offer a convenient way to access and display information via an intranet or the Internet. Web-browser-based management systems can be intuitive and easy to use. This makes them well suited for use by novice and non-expert users.  
           [0006]    A typical Web browser enables a user to view, or “browse”, documents located on the World Wide Web, another network, or a user&#39;s computer. Documents on the World Wide Web, called pages or Web pages, are normally written in HTML (hypertext markup language). A typical Web page comprises one or more HTML documents that enable a user to follow hyperlinks, transfer files, display graphics, play audio and video files, and execute small programs, such as Java applets, embedded in the HTML documents. Thus, Web browsers are commonly used to display images, including mimics, transmitted as part of a Web page.  
           [0007]    As is known in the art, HTML documents contained in a Web page that represent a display are referred to as frames. Each frame generally comprises a rectangular section of a Web page that is a separate HTML document. Web pages usually have multiple frames, each of which is a separate HTML document. Each HTML document or frame typically contains HTML files that comprise image descriptions, image positioning information and instructions, e.g., routines for performing various operations. JavaScript routines may be included in these HTML files to perform various operations, including updating the visible contents of a frame that is displayed as part of a screen in which other frames are also displayed.  
           [0008]    In browser-based management systems, mimics are sometimes implemented as HTML documents that include a full description of the device mimic to be displayed. Activation of a hypertext link is one method used to initiate downloading, e.g., updating, of displayed HTML documents.  
           [0009]    In one known network management tool, a Web browser and a device mimic are used to display network device port status information to a user of a management system. In such a system, the device mimic is generated as part of a set of HTML documents that fully describe the device mimic. In addition to the device mimic, control information, e.g., optional commands, may be displayed. The device mimic is usually composed of a number of separate sub-images, some of which never change while others may change as a result of device-status update information.  
           [0010]    In the known system discussed above, HTML documents representing a device mimic are regenerated each time the status information is to be updated, e.g., in response to manual activation of a refresh hyperlink. The updated HTML documents containing the description of the entire mimic is then transferred as a Web page from the monitoring device to the management system where the mimic is to be displayed.  
           [0011]    Regenerating a new Web page with all of the necessary HTML documents needed to describe an entire mimic can entail significant device and network resources. The size of an HTML document representing an entire mimic may be significant, e.g., 30K bytes in some applications. It may take a monitoring device, e.g., 15 seconds of device processing time in some cases, to regenerate the HTML description of the entire mimic. The time needed to generate the HTML documents is in addition to the amount of time and network resources required to transmit the Web page containing the mimic from the monitoring device to the management system. These overheads are incurred regardless of the amount, if any, of a device&#39;s changes in status.  
           [0012]    Thus, to conserve network, monitoring device, and/or management system resources, mimic updating techniques of the type described above tend to find limited application in known monitoring systems. For example, device-status updates may be limited to points in time when a human operator of the management system that displays the mimic manually initiates a screen refresh by activating a refresh hyperlink, for example, by double clicking on a displayed text or an icon representing the hyperlink.  
           [0013]    When mimics, of the type discussed above, are initially generated or regenerated, the mimic accurately reflects the status of the device to which it corresponds. However as a result of the limited number of updates, the displayed mimic can lose synchronization with the device over time due to changes in device status. This is because changes that occur between the generation or regeneration of HTML documents used to implement the mimics will not be reflected in the displayed mimic until the refresh occurs.  
           [0014]    Unfortunately, users of such management systems often are not certain when the mimic needs to be updated, e.g., due to the monitored device changing status. In addition, the amount of time required to refresh the screen can be frustrating to users. Thus, the time required to refresh a device mimic may act as a deterrent to a user refreshing the mimic. As a result users may rely upon mimics that inaccurately display network device-status information.  
           [0015]    In view of the above, it is apparent that there is a need for new and improved methods and apparatus for implementing device mimics. It is desirable that at least some of the new methods be capable of updating device-status information included in a mimic without having to generate all of the HTML documents representing the entire mimic. It is also desirable that device-status updates occur without the need for a user to request that the displayed mimic be updated or refreshed. It is also desirable that device-status information be updated when a change in device status is detected or at least on a periodic basis so that the device-status information in a mimic be reasonably current.  
         SUMMARY OF THE INVENTION  
         [0016]    The present invention relates to methods and apparatus for efficiently displaying and updating information, e.g., device-status information, at a location which is remote from the source of the information.  
           [0017]    Specifically, the invention includes methods and apparatus for efficiently generating and updating screens representing device-status information. A management system that includes a Web browser is used to display device-status information transmitted to the management station in the form of an HTML file. The initial HTML file includes a complete description of the status screen to be displayed. Rather than generate and transmit a complete description of the status screen to the management station each time device status changes, a set of device state information in the form of an HTML file is transmitted, e.g., from a remotely located device monitor to the management system.  
           [0018]    A program, e.g., a JavaScript routine, is used to update the displayed status information based on the received device state information. Use of a JavaScript routine allows portions of the displayed screen to be modified without having to alter or regenerate the fixed portions of the displayed status screen or the portions relating to device-status information which have not changed. Because device state information is transmitted to update the displayed status information, as opposed to an HTML description of the entire device-status screen, the updating of device-status information is relatively efficient and can be done periodically or whenever a change in device status is detected.  
           [0019]    In accordance with the present invention, an image indicating status of a logical or physical device is displayed, e.g., on a computer screen. The displayed status information may be part of a device mimic which graphically represents a device and its status.  
           [0020]    Additional features of the present invention are discussed in the detailed description which follows. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:  
         [0022]    [0022]FIG. 1 depicts an overall high-level block diagram of one embodiment of the invention that displays status of a network device using a computer;  
         [0023]    [0023]FIG. 2 depicts a block diagram illustrating internal components contained within computer  111  of FIG. 1;  
         [0024]    [0024]FIG. 3 depicts a screen displaying device-status information in accordance with one embodiment of the present invention;  
         [0025]    [0025]FIG. 4 depicts the FIG. 3 device-status display after a plurality of status sub-images has been updated;  
         [0026]    [0026]FIG. 5 depicts a high-level flow diagram illustrating a mimic monitoring process in accordance with the present invention.  
         [0027]    [0027]FIG. 6 depicts a high-level flow diagram illustrating a portion of the mimic monitoring process of FIG. 5.  
         [0028]    [0028]FIG. 7 depicts a high-level flow diagram illustrating a portion of the process of FIG. 6.  
         [0029]    To facilitate understanding, the same reference numbers have been used in the figures, where possible, to refer to elements which are the same as, or similar to, one another. 
     
    
     DETAILED DESCRIPTION  
       [0030]    As discussed above, device mimics are displayed images that can indicate the status of one or more corresponding physical or logical devices. By using a device mimic, a user is presented with a graphical representation of a device that can be used to display device status in an intuitive format. In accordance with the present invention, display updates are depicted in the mimic upon detection of a change in device status or at periodic, e.g., pre-selected, intervals. By selecting the interval between device updates to be small, a change in device status is illustrated soon after it occurs. Display updates are accomplished in accordance with the present invention by changing those portions of the mimic display that correspond to a device having a status that changed since the last update. The other portions of the display are usually left unaltered.  
         [0031]    The present invention takes advantage of the fact that status sub-images that relate to device characteristics that have not changed their status since the last update, as well as fixed sub-images, need not be updated. One embodiment of the present invention involves monitoring the status of one or more physically remote devices from a management system including, e.g., a computer and a display device. In the exemplary embodiment, the management system is coupled to a monitoring system via the Internet and/or an intranet. In the exemplary embodiment, the monitored device is a network device, e.g., router. Though this exemplary embodiment is used to display information relating to a network device, it is envisioned that the device mimic described herein may be applied to display the status of any type of monitored device whether it be a logical or physical device.  
         [0032]    [0032]FIG. 1 illustrates system  100  implemented in accordance with the present invention. As illustrated, system  100  comprises management system  102 , monitoring system  118 , network device  104 , e.g., a router, computer  111 , digital camera  112 , for creating graphical data, and an information database, e.g., management information database (MID)  106 . Management system  102 , computer  111 , digital camera  112  and monitoring system  118  are coupled to network device  104  via network connections  108   a ,  108   b ,  108   c , and  108   d , respectively. Network device  104  and network connections  108   a - 108   d  may comprise part of an intranet or the Internet.  
         [0033]    MID  106 , which couples to monitoring system  118 , includes device-status information, such as port-status information about network device  104 . Monitoring system  118 , network device  104 , and management system  102  each include input/output (I/O) ports used for interfacing with network connections  108   a - 108   d.    
         [0034]    Management system  102  includes computer  130  for performing various operations in response to routines, data, and information stored within computer  130  that relate to system management functions. Management system  102  also includes display device  134  and printer  110 . Various functions of computer  130  relate to the generation and updating of device mimic  140  which is displayed as part of Web browser screen  139 . Computer  130  displays Web browser screen  139  and mimic  140  on display device  134 .  
         [0035]    Monitoring system  118  is responsible for monitoring the status of network device  104  and the status of various other devices included in system  100 , e.g., computer  111  and digital camera  112 . A particular implementation may include monitoring system  118  as part of network device  104 . Network device  104  maintains and uses the information contained in MID  106  to provide status-update information and initial-device mimic description files to management system  102 .  
         [0036]    For purposes of explanation, network device  104 , which may be, e.g., a router, bridge, switch, repeater, hub, or any other similar type of device that transmits digital information or data between locations based on routing information, will be used as an exemplary monitored device.  
         [0037]    Display device  134 , which forms part of management system  102 , may be of any type including, but not limited to, a cathode ray tube display or a light emitting diode (“LED”) display. The internal structure of the computer  130  is illustrated in FIG. 2. FIG. 1 depicts mimic  140  being displayed on display  134 . Mimic  140  may be the same as, or similar to, the mimics shown in FIGS. 3 and 4. The manner in which mimic  140  is generated and refreshed by computer  130  in accordance with the present invention will be discussed below in detail with respect to FIGS. 5 and 6.  
         [0038]    [0038]FIG. 2 depicts an exemplary embodiment of those components associated with computer  130  for displaying a mimic  140 , e.g., of the type depicted in FIGS. 3 and 4, on the display  134 . Computer  130  may comprise a personal computer (PC), a workstation, a server, a mainframe computer, or any other type of computer.  
         [0039]    System memory  202 , included within computer  130 , comprises read only memory (ROM)  204  and random access memory (RAM)  206 . RAM  206  includes basic input/output system (BIOS)  208 , which contains basic routines to transfer information between the elements within computer  130 , such as during start-up. RAM  206  also includes an HTML document that includes visible frame  207   a  and hidden frame  207   b . ROM  204  may include operating system  209   a , applications  209   b , data  209   c , other program modules  209   d , and Web browser  209   e.    
         [0040]    Computer  130  further includes drive portion  220 , comprising hard disk drive interface  222 , hard disk drive  224 , magnetic disk drive interface  226 , magnetic disk drive  228 , optical disk drive interface  230 , and optical disk drive  232 . Magnetic disk drive  228  writes to or reads from a (e.g., removable) magnetic disk (not shown). Optical disk drive  232  reads from or writes to a removable optical disk (not shown) such as a compact disk or a digital video disk (DVD). Hard disk drive  224 , magnetic disk drive  228 , and optical disk drive  232  are coupled to system bus  280  by hard disk drive interface  222 , magnetic disk drive interface  226 , and optical drive interface  230 , respectively. The drives and their associated storage media may provide non-volatile storage of machine readable instructions, data structures, program modules, and other information that may be utilized by computer  130 .  
         [0041]    Some contents, such as operating system  209   a , which may be stored in hard disk drive  224 , may be written into ROM  204  during initial startup of computer  130 . Some contents of hard disk drive  224 , i.e., applications, may be written into corresponding locations in ROM  204  or RAM  206  as a result of user input of computer  130 . Thus, hard disk drive  224  (and its associated hard disk) may comprise the following copies: operating system  235   a , application programs  235   b , data  235   c , program modules  235   d , and Web browser  235   e . Copies in the hard disk drive correspond to locations in ROM  204 . Since the access space of the hard disk drive  224  is considerably larger than that of ROM  204 , only some of the data and programs contained in hard disk drive  224  may be stored in ROM  204  at any given time. Though FIG. 2 depicts a hard disk drive, a removable magnetic disk drive, and an optical disk drive, those skilled in the art will appreciate that other types of storage media may be used. These other types of storage media include, but are not limited to magnetic cassettes, flash memory cards, digital video disks, Bernouli cartridges, other types of RAM, and other types of ROM. In addition, a number of program modules may be stored on the hard disk, magnetic disk, optical disk, ROM, or RAM, such as an operating system, one or more application program, display driver, printer driver, and program data, for example.  
         [0042]    A user may enter commands and information into personal computer  130  through input devices, such as keyboard  270 , or a mouse, a joystick, or a microphone (not shown). Output devices, such as display  134 , display data output from computer  130 . Display device  134  connects to computer  130  via display interface  248  and system bus  280 .  
         [0043]    Computer  130  may operate in a networked environment, defined by logical connections between one or more remote computers, such as the management system  102  or an additional computer depicted in FIG. 2 as remote computer  250 . The connections depicted in FIG. 2 are intended to comprise local area network (LAN), wide area network WAN, intranet, Internet, and/or ISDN configurations. Remote computer  250  may be a PC, a server, a router, a network PC, or other common network node, or any other known computer. Remote computer  250  may include many or all of the elements described above relative to computer  130 . When used in a LAN, computer  250  may be connected to the LAN through network interface adapter  252 . Computer  130  may be connected to the remote computer  250  via modem  254  when used in a WAN, such as the Internet. Modem  240 , which may be internal or external to computer  130 , may connect to system bus  280  via a serial port interface (not shown). In a networked environment, some of the program modules depicted relative to computer  130  may be stored in a remote memory storage device. The network connections shown are exemplary and other means of establishing a communications link between the computers may be used.  
         [0044]    Computer  130  comprises computer processor  260  that controls operation of computer  130  through data communications via processor I/O  261  to and from the associated elements over system bus  280 . Operations of processors are well known, and will not be further detailed herein.  
         [0045]    In a preferred embodiment, a mimic is described to Web browser  209   e  as an HTML document that includes a JavaScript routine as described below in detail. In order to facilitate the implementation of mimics to a range of devices, a device mimic is typically composed of a plurality of separate sub-images. For instance, one embodiment of mimic  140  is illustrated in FIGS. 3 and 4, as it appears on display  134 .  
         [0046]    A mimic is usually formed from many different sub-images. The different sub-images may be classified as either fixed (invariant) or status (variant). Each status sub-image may indicate the status of a particular device status, say the statuses of port connections in the present example. A mimic usually comprises a variety of different status sub-images and fixed sub-images. Since a device status may vary during normal device operation, a mimic displaying corresponding status sub-images should be altered as quickly as practicable. For example, a status sub-image may illustrate one particular Ethernet port status. If there are twenty-four Ethernet ports in a specific device, correspondingly, there might be twenty-four Ethernet status sub-images. The same sub-image may be reused to generate each of the  24  status sub-images. Other status sub-images may include console port sub-images, data transfer rate of a port, etc.  
         [0047]    Fixed, or invariant, sub-images do not need to be updated, since they represent a characteristic of the device that does not change over time with normal device operation. Fixed sub-images may be used to make the graphical representation of a mimic to a user. Examples of fixed sub-images may include sub-image panels simulating device panels on a monitored device, advertising logos, and number sub-images corresponding to specific status sub-images.  
         [0048]    In FIGS. 3 and 4, examples of fixed sub-images include the permanent labels: “PORT STATUS INFORMATION” and “ETHERNET PORT STATUS.” Each of these fixed sub-images appears unchanged in mimic  140  regardless of updates. Panel  310  in mimic  140  defines a large pixel area that remains constant regardless of status changes in monitored network device  104 . In addition, numerals “1” to “24”, which identify the associated Ethernet port status sub-images, also do not change during the updating of mimic  140 , and thus are fixed sub-images. In addition, panel  310  in mimic  140  includes user activated poll-rate sub-image  311 . By clicking on poll-rate sub-image  311  a user can input a particular polling rate and, therefore, change the rate at which the Ethernet port statuses are polled and sub-images  302  are refreshed.  
         [0049]    Thus, a large portion of mimic  140  is formed from fixed sub-images. As such, a considerable amount of processing and refreshing time may be saved in accordance with the present invention by refreshing only portions of mimic  140  that represent the status sub-images corresponding to device characteristics that have a changed status since the last update, as opposed to regenerating the entire contents of mimic  140 . To render the refreshing of mimic  140  during status updates as quick and responsive as possible, it is desirable to limit the number of, and area of, status sub-images as much as practical. Limiting the refreshing to only those status sub-images corresponding to device states that have changed since the last update is also desirable.  
         [0050]    Status sub-images in FIGS. 3 and 4 include twenty-four bi-functional Ethernet port status sub-images  302 . Each Ethernet port sub-image  302  includes two status sub-image portions: a sign sub-image portion  306  and a color (striped) sub-image portion  308 . The sign sub-image portion  306  and the color sub-image portion  308  function in the same manner for each Ethernet port sub-image  302 .  
         [0051]    Color sub-image portion  308  takes on one of two color values represented herein by the presence or absence of striping. Color sub-image portions  308  indicate whether the associated Ethernet port is enabled or not. In FIGS. 3 and 4, a dark color, e.g., striped, in sub-image portion  308  indicates that the associated Ethernet port is not enabled, while a light color, e.g., non-striped, in sub-image portion  308  indicates that the associated Ethernet port is enabled. In FIG. 3, for example, the dark-colored (striped) sub-image portion  308  numbered “13” corresponds to a device port that is not enabled. In FIG. 4, the color sub-image numbered “13” corresponds to a device port that is enabled.  
         [0052]    In FIGS.  3 - 4 , sign sub-image portions  306  represent device state information, which indicates whether or not a link is connected to the corresponding port. A positive sign (+) in the sign sub-image portion  306  indicates that a link is connected to the corresponding device port; a negative sign (−) in the sign sub-image portion  306  indicates that no link is connected to the corresponding device port. In FIG. 3, for example, the sign sub-image for Ethernet port  12  is a “−” indicating that no link is connected to the corresponding device port. In FIG. 4, the sign sub-image for Ethernet port  12  is a “+” indicating that a link is connected to the corresponding device port. A console port sub-image (not shown) may similarly indicate whether a corresponding device console port is active or not. Accordingly, through the use of one of two color values (striping) and the use of either the “+” or “−” symbol, mimic  140  indicates the state of each port.  
         [0053]    The sign sub-image portion  306  and the color sub-image portion  308 , as depicted in FIGS.  3 - 4 , are illustrative and are not intended to be limiting in scope. For instance, sub-images appearing to be a link plugged into a port could indicate a link state, e.g., whether or not the link is connected to a port in the corresponding monitored device. A check-mark sub-image could indicate an active port in the corresponding monitored device. In addition, a port may be represented by two distinct sub-images, e.g., a first sub-image may indicate a link connected to the port and a second light may indicate that the port is active. The first sub-image might be on when the corresponding device port is active and off when the corresponding device port is inactive. The second sub-image might be on when a link is connected to the corresponding device port and off when no link is connected to the corresponding device port. Any readily comprehensible mimic sub-image convention is within the scope of the present invention.  
         [0054]    Mimic  140 , as illustrated in FIGS.  3 - 4 , provides status information relating to the monitored network device  104 . Web browser screen  139  includes additional images and information that may be used to control the device. Port setup portion  320  displays port status control sub-image  326 , which a user can activate to control network device  104 . A user can manually enable or disable a particular Ethernet port in network device  104  by, e.g., clicking on a corresponding button at the bottom of port setup portion  320 . In response, Web browser  209   e  transmits a request to network device  104 , which computer  111  executes, causing command data corresponding to the action suggested by the activated button in port setup portion  320  to be transmitted from monitoring system  118  to the monitored network device  104  via network connection  108   d . When command data are received by the monitored network device  104 , a processor portion of network device  104  processes the command data and responds by changing the state of the monitored network device  104 . A change in status of network device  104  is reflected by a change in a corresponding mimic sub-image  302  during the next update of sub-images  302 . Other device states of the monitored network device  104  may also be interactively controlled via management system  102 .  
         [0055]    In the known prior art discussed above, a full mimic description is used to generate each new mimic, which entirely replaces a previously displayed mimic. As discussed above, the periodic generation of entire mimics to replace similar mimics usually places considerable processing demands on a monitoring system. In addition, transmitting an entire mimic description each time a mimic is to be updated can place considerable demands on such network resources as bandwidth.  
         [0056]    In accordance with the present invention, mimic updates are accomplished by generating, transmitting, and using sets of HTML files that contain device state information, e.g., represented as a set of encoded values, as opposed to transmitting a description of an entire mimic. Such mimic update files may be hidden files, i.e., files the contents of which are not rendered directly visible to a user of the management system.  
         [0057]    The present invention also contemplates that mimic sub-images automatically update as a device status changes or at set periodic intervals without the need for intervention by a user of the management system. In accordance with the present invention, an HTML description of an entire mimic, including all of the status sub-images and all of the fixed sub-images, need only be generated at startup. Thus, the fixed sub-images and the status sub-images (which may subsequently be changed) are generated to form the complete mimic image at startup.  
         [0058]    Detected changes in the status, e.g., state, of a monitored device, for example, if an active port becomes inactive or if a new link is connected to a port, are transmitted from a monitor to a management system using a relatively simple encoding scheme. The encoded state information is included in an HTML file that is transmitted to a management system. The HTML file containing the device state information will usually be substantially smaller than the HTML documents needed to describe a typical mimic, e.g., less than one-twentieth or one-hundredth the size of a full mimic description. Use of this mimic update approach can greatly reduce the amount of network traffic associated with mimic updates. The method of the present invention also reduces the computational burden on a typical monitoring system.  
         [0059]    The state information files, e.g., hidden HTML files (sometimes called hidden frames), representing status updates are received by a Web browser. The hidden HTML files containing device state information normally include JavaScript commands that initiate a mimic update operation. The mimic update operation may be implemented using a separate update routine included as part of the full device mimic description file used to create an original mimic. An update routine compares each new status, e.g., state, value included in the received update state information with an existing status value associated or used to generate the existing mimic. If any new status value differs from a corresponding existing status value, the computer replaces the sub-image present in a mimic by a sub-image that accurately reflects the present state of the monitored devices or device. If no change in the state of the device is detected, the mimic is left unaltered.  
         [0060]    It is further noted that in a preferred embodiment, a management system and a monitoring device may be physically remote from each other. In addition, a monitored device may be physically remote from a monitoring system.  
         [0061]    Some of the various functions of the present technique may be summarized as follows:  
         [0062]    a. Tagging sub-images of a device mimic as either status sub-images, which can change, or fixed sub-images, which do not change. Normally, status sub-images may be used to illustrate device state information.  
         [0063]    b. Generating status update files including device state information. This function does not require generating a full HTML description of a mimic, and instead relies upon a simple encoding (discussed below) of device state or device-status information into a set of device state information which are included in a status update file.  
         [0064]    c. Processing of an encoded status or state information by a management system to detect changes in device states.  
         [0065]    d. Executing a JavaScript routine to allow sub-image replacement techniques to update portions of a mimic without having to regenerate an entire mimic.  
         [0066]    FIGS.  5 - 7  depict mimic monitoring process  500  in accordance with the present invention. In FIG. 5, Web browser  209   e  (see FIG. 2) performs a portion of process  500  (shown in the left side), while remote-monitoring system  118  (see FIG. 1) performs the steps located in the right side. In general, when a Web browser, e.g., Web browser  209   e , accesses an executable file, commonly known as a server script, from a Web server, e.g., monitoring system  118 , the Web server executes the file program and returns its output to the Web browser. Upon executing a file program, the Web server usually formats the output as an HTML document, commonly known as a script document.  
         [0067]    Process  500  begins with browse STEP  501 , wherein a user of management system  102  initially activates Web browser  209   e  (see FIG. 2) to “browse” into network device  104  (see FIG. 1) for remote-monitoring purposes via the Internet. In response, monitoring system  118 , which functions as a Web server, fetches frame-set document  502  from MID  106  and, via return STEP  505 , transmits frame-set document  502 , typically an HTML document, to Web browser  209   e.    
         [0068]    Frame-set document  502  includes frame-format data  503  and frame-files data  504 . Frame-format data  503  includes frame instructions that describe how Web browser  209   e  should divide screen  139  (see FIGS.  3 - 4 ) into several rectangular regions, commonly known as frames. Frame-files data  504  specifies the names and locations of executable frame files  524  located at monitoring system  118  that are capable of outputting HTML documents to be loaded into particular frames. Thus, while frame-set document  502  controls the number and size of the frames of mimic  140 , it also informs Web browser  209   e  where to obtain the contents of each of these frames.  
         [0069]    In particular, frame-set document  502  divides Web browser screen  139  into visible frame  207   a , and an invisible or hidden frame  207   b  (see FIG. 3). While the contents of hidden frame  207   b  are not visible in Web browser screen  139  (see FIGS. 3 and 4), the head of hidden frame  207   b  can contain data. In addition, frame-set document  502  may define other conventional frames, such as a second visible frame that holds port setup portion  320  (see FIGS.  3 - 4 ). Details related to the processing and displaying of port setup portion  320  and other conventional frames are well known and, therefore, are not described further.  
         [0070]    Thus, upon receiving frame-set document  502 , Web browser  209   e  performs frame-setup STEP  506 . In frame-setup STEP  506 , Web browser  209   e  initializes frames  207   a  and  207   b , and allocates a specific graphic area in Web browser screen  139  to be associated with visible frame  207   a . As described above, web browser  209   e  will allocate no graphic area for hidden frame  207   b  because there is nothing to display.  
         [0071]    In access STEP  507 , Web browser  209   e  essentially requests that monitoring system  118  execute frame files  504  and return specific frame-files data as, for example, a set of HTML documents. One such HTML document outputted by an execution of frame-files  504  is mimic document  509 , which is loaded into visible frame  207   a . Specifically, when executing frame files  504 , a server script located in monitoring system  118  generates mimic document  509 , which includes mimic description data  510  in the form of an HTML description of network device  104 . Mimic document  509  also includes the following JavaScript functions: poll-device function  511 , poll-rate function  512 , update function  513  and initialize function  514 . Finally, the execution of frame-files  504  also produces null document  515 .  
         [0072]    Monitoring system  118  returns mimic document  509  and null document  515  in return STEP  516 . Null document  515 , an HTML document with a null body, contains files to be loaded into the head of hidden frame  207   b . It is noted that the use of null document  515  and, therefore, hidden frame  207   b  is necessary to avoid potential sequencing errors. As will become apparent below, precise sequencing will ensure that mimic updates are not requested until after a mimic has been fully retrieved. After receiving mimic document  509  and null document  515 , Web browser  209   e  next renders these documents to produce device mimic  140 , via render STEP  517 . At this time, Web browser  209   e  displays an image of device mimic  140  that is similar to the image depicted in FIG. 3. However, at this point, monitoring system  118  has not yet informed Web browser  209   e  what the specific statuses are of the Ethernet ports of network device  104 . Thus, status sub-image  302  will not yet contain color sub-image portions  308  and sign sub-image portions  306 . Instead, status sub-image  302  could contain a set of twenty-four gray boxes. After rendering documents  509  and  515  in render STEP  517 , Web browser  209   e  performs periodic updates of the status-sub-images  302  in update STEP  518 .  
         [0073]    [0073]FIGS. 6 and 7 show the details of render STEP  517  and update STEP  518 . In FIG. 6, Web browser  209   e  performs the steps contained in the left side, while monitoring system  118  performs the steps located in the right side. The first step is to render null document  515 , which is trivial. Since frame  207   b  is invisible, there will be no place to display data from null document  515 . As such, null document  515  will have nothing to display and, therefore, will have no body. On the other hand, the head of null document  515  will contain a null value that Web browser  209   e  loads into the head of hidden frame  207   b , via load STEP  601 .  
         [0074]    Next, Web browser  209   e  renders mimic document  509 . The body of mimic document  509  contains references to a number of images that Web browser  209   e  automatically requests from monitoring system  118  as a result of rendering mimic document  509 . These images relate to the many fixed and changeable sub-images appearing in panel  310  of device mimic  140  (see FIGS. 3 and 4). Thus, the process of rendering mimic document  509  includes the act of requesting these images from monitoring system  118 , via request STEP  602 . In response, monitoring system  118  performs execute STEP  603 , which involves executing the requested image files to produce a set of image documents that monitoring system  118  returns to Web browser  209   e . Web browser  209   e  loads these documents into the body of mimic document  509 . Using the received image documents, Web browser  209   e  displays device mimic  140 , in display STEP  604 .  
         [0075]    After Web browser  209   e  displays device mimic  140 , a script engine in Web browser  209   e  executes initialize function  514  via execute STEP  605 . This causes poll device function  511  to periodically execute via periodic-trigger STEP  606 . In the present example, an updating or polling period might be, for example, a thirty-second period, meaning that management system  102  would be polled to update the status of status sub-images  302  in mimic  140  every thirty seconds.  
         [0076]    In response to the execution of poll-device function  511 , via execute STEP  607 , Web browser  209   e  begins the process of retrieving the status of network device  104  from monitoring system  118 . Initially, Web browser  209   e  loads into the head of hidden frame  207   b  the name of a predetermined executable file located in MID  106  that, when executed, will retrieve and return the current status of network device  104 . In the present example, the value “EX” represents the name of that predetermined executable file located in MID  106 . Thus, in load STEP  608 , Web browser  209   e  loads the value “EX” in the head of hidden frame  207   b  causing the null value to change to the value “EX.” Web browser  209   e , responding to load STEP  608 , than performs request STEP  609 , which involves sending a message to monitoring system  118  to retrieve and execute file “EX.” Upon receiving the request, monitoring system  118  performs execute STEP  610 , which involves executing file “EX,” thereby obtaining the most-recent status of network device  104 . For instance, in execute STEP  610 , a JavaScript program that is part of file “EX” obtains the appropriate statuses of the twenty-four ports of network device  104 . That JavaScript program could do this by several means, including accessing a status look-up table stored in MID  106 . In this regard, monitoring system  118  could automatically maintain the status look-up table up-to-date by, for example, reading the current status of the twenty-four ports of network device  104  every second or so. The JavaScript program simply encodes each set of twenty-four port statuses into a status string of twenty-four characters, with each character representing the state of a corresponding port. Each character string would then be loaded into a look-up table in MID  106 .  
         [0077]    A typical encoding process will now be described using the port-status examples depicted by sub-images  302  in FIGS. 3 and 4. There are four possible states for each of the twenty-four sub-images numbered  1 - 24 . The four states may be encoded as: state 0=port disabled/no link; state 1=port disabled/link present; state 2=port enabled/no link; and state 3=port enabled/link present. As discussed above, a dark colored (stripped) image corresponds to a disabled port and a light colored image corresponds to an enabled port. A positive sign (+) corresponds to a link present and a negative sign (−) corresponds to no link. Thus, state 0 corresponds to a dark colored (stripped) image with a negative sign (−), such as shown in sub-image  2  in FIG. 3. State 1 corresponds to a dark colored (stripped) image with a positive sign (+), such as shown in sub-image  5  in FIG. 3. State 2 corresponds to a light colored image with a negative sign (−), such as shown in sub-image  3  in FIG. 3. Finally, state 3 corresponds to a light colored image with a positive sign (+), such as shown in sub-image  1  in FIG. 3.  
         [0078]    Using the above convention and the status example shown in FIG. 3, the encoded states of the twenty-four Ethernet ports would correspond to the following character string: “302312103030010301321021.”On the other hand, the following character string: “303312103031210301321021,” would represent the state situation represented in FIG. 4. Each of the twenty-four characters assumes one of only four different values, namely, 0, 1, 2 or 3. From comparison of the two character strings, it can be seen that only the corresponding third, twelfth and thirteenth characters differ.  
         [0079]    As explained above, monitoring system  118  would periodically read the state of each port in network device  104  and encode those states into a character string similar to those just described with respect to FIGS.  3 - 4 . In addition, monitoring system  118  loads the character strings into a look-up table in MID  106 .  
         [0080]    In execute STEP  610 , a JavaScript program located in file “EX” would retrieve the most recently encoded character string from MID  106  and return the output data to Web browser  209   e  as part of update HTML document  630 , in send STEP  611 . The update document  630  would also contain a function call to update function  513 , which was previously loaded into the head of visible frame  207   a  in render STEP  517 .  
         [0081]    Web browser  209   e  loads, in load STEP  612 , update document  630  into the head of hidden frame  207   b . Web browser  209   e  then renders update document  630 , via render STEP  613 . Since update document  630  has no body, there will be nothing for Web browser  209   e  to display. Thus, in render STEP  613 , Web browser  209   e  need only execute the script located in the head of update document  630 , which invokes a function call to update function  513 .  
         [0082]    When update function  513  executes, in execute STEP  614 , it accepts as a parameter the character string, which was part of update document  630 , as being a new device status. Using that new device status as a parameter, in update STEP  615 , Web browser  209   e  updates the twenty-four statuses in status sub-images  302 . After the update is complete, the process returns to periodic-trigger STEP  606  where the update cycle repeats.  
         [0083]    [0083]FIG. 7 illustrates the details of a process of updating the states of status sub-images  302  in update STEP  615 . In compare STEP  701 , Web browser  209   e  compares the old status to the new status. If, in decision STEP  702 , Web browser  209   e  finds that the old status equals the new status, signifying that there has been no change in the states of the Ethernet ports since the last update, the process exits the “Y” path of STEP  702  and returns to periodic trigger STEP  606 . If, however, Web browser  209   e  finds that the old status does not equal the new status, the process exits the “N” path of STEP  702  and makes a character-by-character comparison to find where the differences occur.  
         [0084]    That process begins in STEP  703  by initializing an index “i” to the value one (1), and a constant “n” to the value twenty-four (24). The index “i,” which varies from one to twenty-four, points to the twenty-four different sub-images  302 . The constant “n” represents the total number of sub-images  302 .  
         [0085]    In compare STEP  704 , Web browser  209   e  compares the corresponding characters numbered “i” in those character strings representing the new status and the old status. For example, since “i” will initially have a value one (1), the first characters in the new and old status strings are compared. For purposes of illustration, assume that the twenty-four states depicted in FIG. 3 represent an old status, and that those depicted in FIG. 4 represent a corresponding new status as follows:  
         [0086]    old status: 302312103030010301321021;  
         [0087]    new status: 303312103031210301321021.  
         [0088]    Thus, when “i” equals one (1), Web browser  209   e  will find, in decision STEP  705 , that the first characters are both “3” and, therefore, are equal to each other. Thus, the process exits the “Y” path of STEP  705  to decision STEP  706 . In decision STEP  706 , the index “i” is compared to the constant “n.” In the present example, “i” equals one and “n” equals  24 . Since at this point “i” does not equal “n,” the process exits the “N” path of STEP  706  to increment STEP  707 , where “i” is set equal to “i+1.” With “i” now equal to two (2), the corresponding second characters are compared, in compare STEP  704 . Since the second characters both equal “0,” the process advances to increment step  707  via the “Y” path of STEP  705  and the “N” path of STEP  706 . Index “i” is now incremented to three (3) in STEP  707 , causing comparison of the corresponding third characters, in compare STEP  704 . Since the corresponding third characters are unequal (the old equals two and the new equals three), the process will exit the “N” path of decision STEP  705 . Next, the Web browser  209   e  proceeds to a process of replacing the image of the third status sub-image, i.e., the sub-image numbered  3  in FIGS.  3 - 4 , to reflect the new state of the corresponding Ethernet port. Specifically, Web browser  209   e  replaces the negative sign (−) in the third status-sub-image  302  with a positive sign (+) (see FIGS.  3 - 4 ).  
         [0089]    To effect this change, Web browser  209   e  first changes the source (SRC) attribute for status sub-image “i,” where “i” equals three (3). Specifically, assume that the SRC attribute has the following format:  
         [0090]    http://&lt;ip address&gt;/&lt;directory  
         [0091]    path&gt;/&lt;name&gt;-&lt;state&gt;.gif  
         [0092]    where:  
         [0093]    &lt;ip address&gt; is the Internet protocol address of monitoring system  118 ;  
         [0094]    &lt;directory path&gt; is a path to the image&#39;s directory in MID  106 ;  
         [0095]    &lt;name&gt; is an arbitrary symbolic or descriptive name of a particular image;  
         [0096]    &lt;state&gt; is a numeric code representing a discrete state; and  
         [0097]    gif is a file extension that identifies a particular commercial bit map image format.  
         [0098]    Since, in the present case, only the state of the image has changed, only the numeric code corresponding to the state in SRC attribute needs to be changed. With respect to the corresponding third characters, the old state is represented by the character “2” and the new state is represented by the character “3.” Consequently, the corresponding SRC attributes are as follows:  
         [0099]    Old SRC attribute:  
         [0100]    http://&lt;ip address&gt;/&lt;directory path&gt;/&lt;name&gt;-&lt;2&gt;.gif  
         [0101]    New SRC attribute:  
         [0102]    http://&lt;ip address&gt;/&lt;directory path&gt;/&lt;name&gt;-&lt;3&gt;.gif.  
         [0103]    Web browser  209   e  now retrieves the appropriate image data for updating the corresponding third sub-image  302  in mimic  140 . Using the new SRC attribute (shown above) in retrieve STEP  711 , Web browser  209   e  first looks in a cache memory to see if the corresponding image data had recently been downloaded from the network so that the image data can be redisplayed quickly in update STEP  712 . If the appropriate image data is not located in cache memory, web browser  209   e  accesses the appropriate image data from monitoring system  118 . In either case, Web browser  209   e  uses the new SRC attribute to obtain the image data corresponding to the new state. In the present example, Web browser  209   e , in update STEP  712 , displays the new image (a light color with a positive sign) for the third status sub-image  302  to reflect the new state of the corresponding Ethernet port.  
         [0104]    The process then proceeds to decision STEP  706 , where index “i” is compared to constant “n.” The process continues as described above, changing only those status sub-images  302  that have a new state. In the present example, in addition to changing the third status sub-image, status sub-images  12  and  13  will be the only other sub-images that need to be changed. Finally, when Web browser  209   e  finds “i” to be equal to  24  in decision STEP  706 , the process exits the “Y” path, thereby returning to periodic trigger STEP  606 .  
         [0105]    While the process of updating a displayed mimic has generally been described as being performed in response to an update request generated by management system  102 , it is to be understood that such updates may be initiated by monitoring system  118 . Indeed, those update requests that monitoring system  118  initiates may take place only when an actual change in state of an Ethernet port occurs. For example, after the initial generation and display of device mimic  140 , management system  102  may generate a hidden frame of the type discussed above and transmit it each time the monitoring system detects that a change in the state of the monitored device has occurred. Management system  102  would update the displayed mimic  140  in the manner discussed above when responding to the reception of a hidden frame that included a set of device state information and an appropriate JavaScript program. In addition, it is to be understood that device mimic  140  can be output to a printer in addition to, or instead of, being displayed on display device  134 . Obviously many other modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.