Apparatus and method of monitoring the status of a local area network

Claims

We claim:

1. Apparatus for monitoring the status of a star configured local area network having hubs, with a hub including a chassis for receiving a plurality of modules of varying type, each of the modules having at least one port for connecting a data terminal device to the hub, said apparatus comprising:

means for generating a topology of said network and for receiving topology data from a reporting hub wherein said topology data comprises addresses of other hubs which originated messages received by said reporting hub over a particular port of said reporting hub and an indentifier of said particular port;

location means for producing location data indicative of the location of each of the modules and each of the at least one port associated with the modules in the hub chassis;

type means for producing type data indicative of the type of each of the modules and each of the at least one port associated with the modules in the hub;

indicator means for indicating status information about each of said modules and for indicating status information about said at least one port associated with each of said modules, said indicator means also for isolating said status information for one particular module and associated at least one port, said indicator means coupled to said location means and also coupled to said type means;

modification means for modifying port status of each of said at least one port associated with each of said modules, said modification means responsive to a user input, said modification means coupled to said indicator means; and

display means for producing an image of the hub utilizing said location data, said status information and said type data, with the image depicting the location of the modules in the hub and the type of modules, said display means coupled to said indicator means.

2. The apparatus of claim 1 wherein said display means includes storage means for storing a set of graphic data representing a graphic image for display on said display means, for each of the types of modules, which represents the appearance of the modules.

3. The apparatus of claim 2 wherein said modules include a front panel which bears an indicia of the type of module and said set of graphic data, representing a graphic image for display on said display means, include data which represents said indicia.

4. The apparatus of claim 2 wherein said set of graphic data include data which represents an image of the at least one port of the modules.

5. The apparatus of claim 2 wherein one type of the modules has at least one port with an optical connector for receiving an optical cable and wherein said set of graphic data include data which represent an image of said optical connector.

6. The apparatus of claim 2 wherein one type of the modules has at least one port with an electrical connector for receiving an electrical cable and wherein said set of graphic data include data which represents an image of said electrical connector.

7. The apparatus of claim 2 wherein said indicator means of one type of the modules includes a front panel which has a light source which indicates the status of the module and the status of said at least one port associated with each of said modules and wherein said set of graphic data include data which represents an image of the light source.

8. The apparatus of claim 7 wherein said indicator means includes a light source status means for producing light source status data indicative of the state of the light source and wherein said display means utilizes said status data to control the image of the light source.

9. The apparatus of claim 1 wherein said location means, said indicator means and said type means are disposed at the hub.

10. The apparatus of claim 9 wherein said display means is disposed separate from the hub.

11. The apparatus of claim 2 wherein said set of graphic data include data which represents an image of the at least one port of the module and wherein said indicator means of said apparatus further includes:

pointer means for designating a particular location on the image selected by a user;

module status means for producing module status data indicative of the status of the modules;

port status means for producing port status data indicative of the status of the port of the modules; and

control means coupled to said modification means for selectively producing said module status data of a particular module when a user designates the image of said particular module utilizing said pointer means and for selectively producing said port status data of a particular port when a user designates the image of said particular port utilizing said pointer means.

12. A method of monitoring the status of a star configured network having hubs, with a hub including a chassis for receiving a plurality of modules of varying type, with each of the modules having at least one port for connecting a data terminal device to the hub, said method comprising the following steps:

generating a topology of said network by receiving topology data from a reporting hub wherein said topology data comprises addresses of other hubs which originated messages received by said reporting hub over a particular port of said reporting hub and an indentifier of said particular port;

generating and reporting by a hub location data indicative of the location of each of the modules and ports in the hub chassis;

generating and reporting by the hub type data indicative of the type data indicative of the type of each of the modules and ports in the hub; and

producing an image of the hub utilizing said location data and said type data, with the image depicting the location of the modules in the hub and the type of modules in the hub.

13. A method of automatically determining the topology of a network of interconnected hubs which utilize contention control, with each of the hubs having modules and associated at least three data ports, each of which is for coupling the hub in a star configuration to either a data terminal device or another hub of the network, said method comprising the following steps:

transmitting from each of the hubs a message over the network which originates from the hub and which contains an address identifying an associated hub;

transmitting from each of the hubs a message over the network which was received by said associated hub from another hub on the network which originated the received message;

identifying, at each of the hubs, which of the data ports of said associated hub has received one of the messages transmitted by another hub of the network;

receiving topology data from each of the hubs, with the topology data identifying a particular one of the data ports of a particular reporting hub and receiving addresses of the other ones of the hubs which originated messages received by said particular reporting hub over the particular port;

determining the overall topology of the network utilizing said combining each of said received topology data; and

displaying said overall topology on a display device, said step of displaying including displaying multiple hubs, modules and associated ports on said display device at the same time.

14. Apparatus for automatically determining the topology of a local area network of interconnected hubs which utilize contention control, with each of the hubs having at least three data ports, each of which is for coupling the hub in a star configuration to either a data terminal device or another hub in the local area network, said apparatus also for monitoring the status of a hub of a star configured local area network, with the hub including a chassis for receiving a plurality of modules of varying type, each of the modules having at least one port for connecting a data terminal device to the hub, said apparatus comprising:

transmit means at each of the hubs for transmitting hub messages over the local area network, said transmit means including

(a) originate means for transmitting said hub messages which originate at an associated hub which contain an identifying address of said associated hub;

(b) repeat means for transmitting said hub messages received by said associated hub over the local area network which originated from other ones of said hubs of the network, said repeat means comprising a timing unit for retiming data to account for transmission distortion;

port identifying means at each of the hubs for identifying which of said data ports of said associated hub has received one of the said hub messages transmitted by another of said hubs of the local area network;

control means coupled to said local area network for receiving topology data reported from each of said hubs, said topology data reported for each data port of a particular reporting hub, said topology data identifying a particular one of said data ports of said particular reporting hub and said topology data identifying addresses associated with the the other ports of said hubs which originated network messages received by said particular reporting hub over said particular port;

processing means for determining the overall topology of the local area network utilizing and combining said received topology data;

location means for producing location data indicative of the location of each of the modules and ports in the hub chassis based on said overall topology;

type means for producing type data indicative of the type of each of the modules and ports in the hub; and

indicator means for indicating status information about each of said modules and for indicating status information about said at least one port associated with each of said modules, said indicator means also for isolating said status information for one particular module and associated at least one port, said indicator means coupled to said location means and also coupled to said type means;

modification means for modifying port status of each of said at least one port associated with each of said modules, said modification means responsive to a user input, said modification means coupled to said indicator means; and

display means for producing an image of the hub utilizing said overall topology, said location data, said status information and said type data, with the image depicting the location of the modules in the hub and the type of modules, said display means coupled to said indicator means.

15. The apparatus of claim 14 wherein said display means includes storage means for storing a set of graphic data representing a graphic image for display on said display means, for each of the types of modules, which represents the appearance of the modules and wherein said set of graphic data include data which represents an image of the at least one port of the modules.

16. The apparatus of claim 15 wherein said set of graphic data include data which represents an image of the at least one port of the module and said indicator means of said apparatus further includes:

pointer means for designating a particular location on the image selected by a user;

module status means for producing module status data indicative of the status of the modules;

port status means for producing port status data indicative of the status of the port of the modules; and

control means for selectively producing said module status data of a particular module when a user designates the image of said particular module utilizing said pointer means and for selectively producing said port status data of a particular port when a user designates the image of said particular port utilizing said pointer means.

17. Apparatus for automatically determining the topology of a local area network of interconnected hubs which utilize contention control, with each of the hubs having at least three data ports, each of which is for coupling the hub in a star configuration to either a data terminal device or another hub in the local area network, said apparatus also for modifying status information with associated with said ports of said interconnected hubs, said apparatus comprising:

transmit means at each of the hubs for transmitting hub messages over the local area network, said transmit means including

originate means for transmitting said hub messages which originate at an associated hub which contain an identifying address of said associated hub;

repeat means for transmitting said hub messages received by said associated hub over the local area network which originated from other ones of said hubs of the network, said repeat means comprising a timing unit for retiming data to account for transmission distortion,

port identifying means at each of the hubs for identifying which of said data ports of said associated hub has received one of the said hub messages transmitted by another of said hubs of the local area network;

control means coupled to said local area network for receiving topology data reported from each of said hubs, said topology data reported for each data port of a particular reporting hub, said topology data identifying a particular one of said data ports of said particular reporting hub and said topology data identifying addresses associated with the other data ports of said hubs which originated network messages received by said particular reporting hub over said particular one of said data ports;

processing means for determining the overall topology of the local area network by utilizing and combining said received topology data from each of said reporting hubs;

status indicator means for indicating status information of said data ports of each of said hubs in said overall topology, said status indicator means also for isolating a particular data port status information;

modification means for changing said status information of said data ports of each of said hubs, said modification means coupled to said status indicator means and responsive to a user input device; and

display means for displaying said overall topology in a graphic image format on a display device

18. The apparatus of claim 17 wherein said originate means periodically transmits one of said hub messages originating at said associated hub.

19. The apparatus of claim 17 wherein said control means receives said topology data in response to topology request messages which the control means transmits over the local area network to the hubs and wherein said control means transmits separate ones of said topology request messages to each of said hubs.

20. The apparatus of claim 19 wherein said control means monitors which of said hubs has responded to said topology request message and transmits additional topology request messages directed to any of the hubs for which a response in said topology data is not received by said control means.

21. The apparatus of claim 17 wherein each of said hubs includes a plurality of modules, with each of said modules having at least one of said data ports and wherein said hub includes monitoring means for identifying a particular one of said modules and a particular data port of said modules over which said hub has received said hub messages originating from other one of said hubs in the local area network.

22. The apparatus of claim 21 wherein said modules and data ports are of different types having varying capabilities and wherein said monitoring means is also a means for identifying said type of module and data port and wherein said topology data further includes type data indicative of the type of modules and data ports in said particular reporting hub.

23. The apparatus of claim 22 wherein said monitoring means identifies a particular one of said modules and a particular one of said data ports by determining a physical location of said module in said hub; wherein said status indicator means indicates the status of said data ports of said particular one of said data modules; and wherein said modification means allows modification of said ports of said particular one of said modules.

24. The apparatus of claim 23 wherein said hub includes a chassis having an electrical backplane for interconnecting said modules and said modules may be inserted in said chassis in any one of predetermined locations along said backplane, with said monitoring means determining said physical location by sensing the predetermined location where said modules are inserted.

25. A method of monitoring the status of a hub of a star configured network in accordance with claim 12 further comprising the step of providing modification to said ports of said modules based on said image of said hub and responsive to a user input

26. The method of claim 12 wherein said step of producing an image comprises the step of displaying a set of graphic data representing a graphic image for each of the types of modules, which represents the appearance of the modules.

27. The method of claim 26 wherein said modules comprise a front panel which bears an indicia of the type of module and said set of graphic data includes data which represents said indicia.

28. The method of claim 12 wherein said step of producing an image comprises the step of displaying a set of graphic data representing a graphic image for at least one port of the modules.

29. The method of claim 28 wherein one port comprises an optical connector for receiving an optical cable and wherein said set of graphic data include data which represent an image of said optical connector.

30. The method of claim 28 wherein one port comprises an electrical connector for receiving an electrical cable and wherein said set of graphic data include data which represent an image of said electrical connector.

31. The method of claim 12 further comprising the step of generating status data indicating status of the modules and ports of the hub and wherein said step of producing an image of said hub further comprises the steps of:

displaying a set of graphic data representing a front panel of a module of the hub which has a light source which indicates the status of the module; and

displaying a set of graphic data representing the status data of said at least one port associated with each module.

32. The method of claim 12 further comprising the steps of:

generating status data indicating status of the modules and ports of the hub;

providing pointer means for designating a particular location on the image for selection by a user;

selectively displaying a set of graphic data representing module status data of a particular module when a user designates the image of said particular module utilizing said pointer means; and

selectively displaying a set of graphic data representing port status data of a particular port when a user designates the image of said particular port utilizing said pointer means.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to local area networks and more particularly to apparatus and methods for monitoring the status of a local area network by producing a topology map of the network configuration and by producing a control console display image depicting the appearance of selected network hubs.

2. Background Art

Local area networks for interconnecting data terminal equipment such as computers are well known in the art. Such networks may include a large number of components which may be configured in a variety of ways.

Although equipment exists for monitoring the status of local area networks, such equipment is not capable of accurately monitoring and reporting network status in a manner which may be readily interpreted. For example, the network may include a large number of hubs or concentrators, each of which form the center of a star configuration. The concentrators may each be capable of servicing a large number of data terminal equipment such as personal computers. The network medium may be shielded twisted pair cable, unshielded twisted pair cable or fiber optic cable or a combination of all three. Further, each type of cabling may be supported by various types of modules located in each of the concentrators.

None of the conventional apparatus for monitoring and displaying the status of a network are capable of conveying the actual status of the network in a manner which can be easily comprehended by a user. The disclosed apparatus and method overcomes such limitations and allow the actual status of the network to be automatically monitored and displayed. The information displayed depicts in great detail the status of a network which can be easily comprehended by individuals with a minimum amount of training even if the network is relatively complex. Further, the status of the network is automatically updated. These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the Detailed Description of the Preferred Embodiment together with the drawings.

SUMMARY OF THE INVENTION

Apparatus and a method of monitoring the status of a local area network are disclosed. The network typically includes a plurality of hubs, such as concentrators, with each hub having data ports for coupling the hub in a star configuration to either data terminal equipment, such as personal computers, or for coupling the hub to another hub of the network. The network is of the type which utilizes network contention control such as the well known Carrier Sense Multiple Access With Collision Detection (CSMA/CD).

In one embodiment of the invention, the apparatus automatically determines the overall topology of the network, with the hubs having at least three data ports each. The apparatus includes a transmit means associated with each of the hubs having both originate and repeat means. The originate means functions to transmit messages over the network which originate at the associated hub and which contain an identifying address of the associated hub. The repeat means functions to transmit messages received by the associated hub over the network which originated from other hubs of the network.

Each of the hubs further includes port identifying means for identifying which of the data ports has received one of the messages transmitted by another hub of the network. In this manner, topology data regarding the connection of the various ports of the associated hub to other hubs of the network are obtained. The topology data from a single hub usually does not contain enough information to ascertain the overall network topology.

The apparatus further includes control means coupled to the network for receiving the topology data from each of the hubs in the network. The topology data identify a particular one of the data ports of the hub reporting the topology data and address of the other ones of the hubs which originated network messages received by the reporting hub over that particular port. Finally, the apparatus includes processing means for determining the overall topology of the network utilizing the received topology data.

In another embodiment of the invention, the apparatus monitors the status of each of the hubs of a star configured network by producing an image, on a control console display for example, which depicts the appearance of the actual hub.

Each hub of the network includes a chassis for receiving a plurality of modules. The modules have at least one port for connecting the data terminal equipment such as a computer to the hub, with the modules being of varying types. For example, some modules may be adapted for use with unshielded twisted pair cables and other modules may be adapted for use with optical cables.

The apparatus includes location means for producing location data indicative of the location of each of the modules in the hub chassis. An exemplary location means would include hard-wired slot identification bits located on the chassis which are transferred to any module inserted into the chassis slot associated with the hard-wired bits. Type means are further included for producing type data indicative of the type of each of the modules in the hub. An exemplary type means would include hard-wired bits on the module which indicate the type of module.

Finally, the apparatus includes display means for producing an image of the hub utilizing the location data and the type data, with the image depicting the location of the modules in the hub and the type of modules.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an exemplary local area network of the type in which the subject invention can be used and which includes three concentrators or hubs and associated data terminal equipment.

FIG. 2 is a schematic diagram of a local area network, having twenty-four concentrators, of the type in, which the subject invention can be used.

FIG. 3 is an exemplary display produced in accordance with the present invention depicting a selected portion of the topology of the network of FIG. 2.

FIG. 4 is a schematic diagram of a local area network with the upper level concentrators connected to a common coaxial cable.

FIG. 5 is an exemplary display produced in accordance with the present invention depicting a selected portion of the topology of the network of FIG. 4.

FIG. 6 is a section of a display menu showing a portion of a main menu bar and an exemplary selected submenu.

FIG. 7 is a section of a display showing a detailed view image which depicts the actual appearance of the front panel of a selected network concentrator, including the location of modules in the concentrator and the type of modules.

FIGS. 8A-8F are enlarged views of selected portions of the FIG. 7 image showing details of the various type of modules.

FIG. 9 is similar to FIG. 7 except that another style of concentrator is depicted.

FIG. 10 is a block diagram of one of the network concentrators showing the network management module and host modules all connected to a common concentrator backplane together with various data terminal equipment in the network management control console connected to the concentrator.

FIG. 11 is a block diagram showing the network management interface for the host modules for interfacing the modules to the concentrator backplane.

FIG. 12 is a block diagram of a further exemplary network showing the interconnection of the concentrators of the network.

FIG. 13 is a Network Management Module List showing the various ports of each of the concentrators and the addresses of the other concentrators which transmit messages received over the ports.

FIG. 14 is a flow chart depicting the process whereby the link data are obtained from the concentrators to construct the FIG. 13 List.

FIG. 15 is a flow chart depicting the process whereby the link data of the FIG. 13 List are processed, to form the Ancestor Table of FIG. 16.

FIG. 16 is a Ancestor Table constructed from the data contained in the FIG. 13 List.

FIG. 17 is a block diagram of a network where the up port of the highest level concentrators are connected together so that no concentrator will be assigned the Level 0 position of the topology display.

FIG. 18 is a simplified display image of the overall topology of a network based upon the data of the FIG. 16 Ancestor Table.

FIG. 19 is a functional block diagram of the network management module located in each of the network concentrators.

FIG. 20 is a functional block diagram of the control console adapter, the adapter being an expansion card used to convert a personal computer to a network management control console.

FIGS. 21A-21C are flow charts depicting the process for producing the detailed view of the concentrators such as depicted in FIGS. 7 and 9.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring to the drawings, FIG. 1 is a diagram showing the physical connection of a typical simplified local area network. The depicted network function to interconnect six personal computers or PCs 20a-f. The network includes three concentrators 22a, 22b and 22c. The concentrators function as a hub in the star network topology and provide basic Ethernet functions. Many of the details which will be provided regarding the network are exemplary only, it being understood that the present invention may be utilized in connection with a wide variety of communication networks.

Each of the concentrators includes several plug-in modules 26 which connect to a backplane (not depicted) of each concentrator 22. There are various types of modules including host modules which have ports for connecting the associated module to data terminal equipment (DTE). For example, concentrator 22b includes a host module 26c having a port (not designated) connected to personal computer 20a by way of an interface device 24a. Device 24a is a transceiver (transmitter/receiver) used to link the computer 20a (DTE) or node to the network cable. Module 26c will typically have several other ports (not depicted) for connecting to other DTEs.

One of the DTEs, such as personal computer 20d, is designated as the network management control console (NMCC). The designated computer 20d is provided with a control console adapter (CCA), which is an expansion board which adapts the computer for use as a control console. As will be explained, a user can perform various network monitoring and control functions at the NMCC. A pointer device, such as a mouse 23 having primary and secondary control buttons 23a and 23b, respectively, is used for carrying out these functions.

Each concentrator 22a, 22b and 22c is provided with a network management module (NMM). The network management module NMM gathers data received on a port of a host module and transmits the data to other modules in the concentrator. Further, the network management module NMM will forward the received data to other concentrators in the network that may be connected to the concentrator.

The foregoing can be further illustrated by way of example. Assume the personal computer 20e has a message for computer 20b. Each computer or node in the network has an associated address. Messages directed to a particular computer will be decoded by a conventional network controller card installed in the computer and, if the destination address in the message matches the computer address, the message will be processed by the computer. The message originating from computer 20e will include a destination address of computer 20b. The message will be transmitted to the associated transceiver 24e and will be received by a port (not designated) on host module 26g of concentrator 22c. Module 26g will transmit the received message to the network management module NMM in concentrator 22c by way of the concentrator backplane (not depicted).

The NMM will transmit the received message to each host module in concentrator 22c, including modules 26f, 26g and 26e. The message will exit each port of each module and will be received by transceiver 24d and 24f (but not 24e which received the message originating from computer 20e). However, since the destination address does not match the address of computers 20d and 20f, the network controller cards installed in computer 20d and 20f will not process the messages.

The NMM in concentrator 22c will also forward the received message to concentrator 22a by way of transceiver 24g. The message will be received by a port in module 26d and by the NMM in concentrator 22a. The NMM of concentrator 22a will transmit the message to the NMM of concentrator 22b. The NMM of concentrator 22b will transmit the message to each module in concentrator 22b so that the message will be received by transceivers 24a, 24b and 24c. Since transceiver 24b has an address which matches the destination address, transceiver 24b will forward the message to the associated computer 20b. The other two transceivers 24a and 24c connected to concentrator 22b will refrain from forwarding the message.

Since each message received by a concentrator is retransmitted, only a single message can be transmitted over the network at one time. In the event two computers attempt to transmit at the same time, the messages will interfere and cause a collision in the network. As is well known, when a collision on the network occurs, the concentrator connected to the two cables on which the collision occurred will detect the presence of the collision.

When a collision is detected by an NMM, a "jam" signal will be transmitted by the NMM of the concentrator over the network. The computers involved in the collision will detect the presence of the collided signals and will resort to statistical contention for the network. Other computers not involved in the collision will sense the carrier signal and refrain from transmitting on the network.

Eventually, the jam signal will disappear and the computers will contend for access to the network. A computer wishing to transmit first listens for message traffic on the network and transmits only if there is no traffic and only in the absence of any other carrier signal. This well known method of providing access to a common local area network medium is referred to as Carrier Sense Multiple Access with Collision Detection or CSMA/CD.

The network depicted in FIG. 1 is relatively small and includes two levels of concentrators. Concentrator 22a is at the top level (level "0") and concentrators 22b and 22c are at the next from top level (level "1"). It would be possible to connect several additional DTEs, including computers, work stations, servers, and the like to the concentrators 22a, 22b and 22c. Further, additional concentrators could be connected to the exiting concentrators.

FIG. 2 shows how a much larger network consisting of twenty three concentrators. None of the port connections to the individual host modules in the concentrators are shown. Concentrator 28 is the top level, or level "0" concentrator. Concentrator 28 is connected to the next from top level, or level "1" concentrators 30a-30f. The six level 1 concentrators are connected to a total of seventeen level 2 concentrators 32a-32g. Note that a lower level concentrator can be connected to a higher level concentrator by way of a connection to the network management module NMM of the lower level concentrator. It is also possible to connect the higher level concentrator to a host module port in the lower level concentrator.

The network management module NMM performs monitoring and controlling functions within the concentrator in which it is located. In addition, the NMM sends status and diagnostic reports to the network management control console NMCC. Further, the NMM executes commands issued by the control console.

One important function of the network management control console NMCC is to monitor the network topology. As previously noted, the NMCC is a designated computer of the network which includes a control console adapter CCA in the form of an expansion board which is installed in the computer. The designated computer uses a graphical user interface, such as a commercially-available software package called Microsoft Windows sold by Microsoft Corporation of Redmond, Wash. Other commercially available software packages which provide a window environment similar to Microsoft Windows could be used for the present application.

A principal function of the network management control console NMCC is to monitor the status of the network topology. An important feature of the present invention is the ability to automatically acquire information regarding the topology of the network so that a display of the topology can be generated and automatically updated to reflect changes in the network.

FIG. 3 is an image, generally designated by the numeral 36, which will be produced on the NMCC video display terminal showing the topology of the exemplary network depicted in FIG. 2. The display is a menu-driven graphics display which uses a pointing device such as a mouse, light pen or the like. Referring to FIG. 3, the rectangular boxes depicted in the display are concentrator icons 34a-34e 34e which represent the concentrators in the network. The screen is only capable of displaying a relatively limited number of concentrator icons at a time. Accordingly, it is necessary to scroll the display to depict all twenty four of the concentrators, as will be explained.

Concentrator icon 34a corresponds to concentrator 28 in FIG. 2. Icons 34b-34g represent concentrators 30a-30f of FIG. 2. The icons representing the remaining concentrators 32a-32g can be viewed only by scrolling the display both horizontally and vertically.

Display 36 is split between a "Level 0" and a "Level 1". Concentrator icon 34a is shown in the upper "level 0", with the remainder of the icons located in the lower half or "level 1" portion of the screen. The display can be scrolled vertically by placing the cursor icon or mouse pointer 38 over one of the triangle-shaped elements 40 and "clicking" on actuating the control button mouse. When the mouse is clicked, the display will replace the "Level 0" icon at the top with the level "1" icons and replace the "Level 1" icons at the bottom with "Level 2" icons. Since there are a total of seventeen "Level 2" concentrators 32a-32g (FIG. 2), it will be necessary to scroll the display horizontally to view all of these concentrators. Scrolling to the left is accom