Abstract:
A method of automatically selecting a mode of operation during an initialization sequence of a multi-mode signal controller includes selectively enabling and disabling signal reception and signal driving capabilities and includes monitoring the remaining signal traffic to determine the position of the controller along a communication path. In the preferred embodiment, the signal controller is one of at least two identical signal controllers along a single communication path. For example, the controllers may be components at opposite sides of a telecommunications link of a PBX or other telecommunication system. The structurally identical controllers perform mirror image operations when the controllers are properly initialized to restrict the controllers to different modes of operation. In the initialization sequence for a particular signal controller, the signal reception is monitored to determine whether the controller is receiving a known pattern of system control, such as a universally applied clock signal. Detection of the system control signal clearly identifies the controller as being on the same side of the telecommunications link as the source of the system control signals. On the other hand, the telecommunications link may be monitored for communication signals from the other signal controller. Detection of the communication signals identifies the initializing controller as being on the opposite side of the telecommunications link from the source of the system control signals.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to a device and method for automatic selective initialization of multi-mode signal controllers located at nodes of a communication system having different interface requirements and, more specifically, to a device and method for automatic selective initialization of a multi-mode signal controller connected to either a private branch exchange (PBX) shelf extension control or a PBX main switch control. 
     DESCRIPTION OF THE RELATED ART 
     A PBX serves as a miniature central office for a customer that requires sophisticated local telephony capabilities. For instance, a large business having a campus that includes multiple departments and numerous employees is likely to find it economical to install a PBX to provide intra-campus telephone service and external connections to a public switch telephone network (PSTN) central office. Station lines which connect the PBX switch to the phones of the employees are privately leased or owned and all internal calls are routed through the PBX switch. 
     In a typical installation of a PBX system, a cabinet houses a host of switching electronics, power supplies, and other computing components. For example, the switching electronics are organized within the cabinet into a number of shelves typically occupying the top portion of the cabinet. Below the switching electronics are the power supply components followed by computer components, including a common control which provides switching functions and system administration for the entire PBX system. A backplane interconnects the various parts of the system, providing data and access control between the switching electronics and the computer. 
     At times, it is desirable to separate one of the shelves containing switching electronics from the PBX main switch. If a PBX provides telephony for a business which expands to an adjacent building, it might be more cost effective to locate a peripheral shelf at the new building, rather than to equip the new building with an independent PBX system. The peripheral shelf and the main switch can be connected by a fiber optic cable. A first signal controller and a common control are on the main switch side of the fiber optic link, while a second signal controller and a peripheral shelf control are on the peripheral shelf side. The signal controllers perform conversions at the opposite ends of the fiber optic link in order to facilitate communication between the peripheral shelf and the main switch. For instance, the two controllers might communicate information over the fiber optic link in the form of Ethernet packets. The second signal controller at the peripheral shelf side of the link converts signals received from the peripheral shelf control into Ethernet packets to be transmitted to the first signal controller on the main switch side of the fiber optic link. The second signal controller also converts Ethernet packets received from the main switch side signal controller to a format compatible with the peripheral shelf control. The main switch side signal controller performs the opposite format conversions for the common control. 
     While the two signal controllers perform fundamentally the same functions, the controller operations are mirror images of each other when viewed from the fiber optic link. Each signal controller can be specifically designed to execute its packetizing and depacketizing operations, so that there are two different single-mode controllers that provide the necessary compatibility when connected at the correct ends of the fiber optic link. This requires some duplication of labor in the product design and product manufacture stages of the controllers, but works well for its intended purposes. 
     Alternatively, a multi-mode signal controller can be designed to allow the controller to be used on either side of the fiber optic link. If the controller is set in one mode, the controller functions as the main switch-side controller described above. On the other hand, the controller can be set in an opposite mode that enables performance of the functions of the peripheral shelf-side controller. Multi-mode signal controllers have the potential of providing significant cost savings. 
     Care must be taken to ensure that each multi-mode signal controller is properly initialized, based on the side of the fiber optic link on which it is located. Compatibility of switch-side and shelf-side operations is facilitated by providing a universal clock signal. Typically, the clock signal is generated by the common control and transmitted to the peripheral shelf via the fiber optic link. However, if the switch-side controller is improperly set in the second mode during initialization of the controller (i.e., power-up), the controller will be set to receive the clock signal in the fiber optic link, rather than being set to drive the dock signal over the link. At the least, this is likely to render the peripheral shelf inoperable. Moreover, signal conflicts may occur on some channels, as the first and second controllers are both initialized to drive signals over a particular channel. This may cause a system failure. 
     One method of initializing the multi-mode controllers is to require manual configuration of the settings of the modes. This method requires the presence of a properly trained technician each time that one of the controllers is initialized. Otherwise, the process will be susceptible to error. As a result, the manual setting process may require a significant downtime period each time that initialization is required. 
     What is needed is a multi-mode signal controller capable of automatic initialization based on the location of the signal controller along a communication path, thereby providing automatic mode selection. 
     SUMMARY OF THE INVENTION 
     A method of automatically selecting a mode of operation during an initialization sequence of a multi-mode signal controller includes selectively enabling signal reception and disabling signal driving capabilities of the controller and further includes monitoring the remaining signal traffic to identify the position of the signal controller along a communication path. The identification of the position of the controller along the path is used to determine the desired mode of operation for the controller. 
     Signal reception at the initializing signal controller is monitored to identify whether the controller is receiving a known pattern of system control (e.g., a clock signal) or is receiving a signal that is indicative of a transmission from a second signal controller (e.g., packetized call information). For example, if the method is executed to first monitor traffic for a signal that is indicative of reception from the second signal controller, detection of the signal identifies the second controller as being operative and being on an end of a communication link opposite to the signal controller undergoing initialization. When this signal is detected, the signal controller undergoing initialization is configured to operate only within a first mode of operation. On the other hand, if the signal is undetected, the method moves to a step of monitoring for a known pattern of system control. For example, the known pattern may be a universal clock signal that synchronizes all the controllers along the communication path. When the known pattern is detected as being received from a source other than the second signal controller, the signal controller undergoing initialization is configured to operate only within a second mode of operation that is compatible with controller performance on a side of a communications link that is common with the source of the known pattern of system control. 
     In the preferred embodiment, one signal controller is on the same side of the communication link as a control device for generating the known pattern of system control, while the other signal controller is on the same side of the communication link as a controlled device. In the most preferred embodiment, the signal controllers are components of a telecommunications system, such as a PBX, and are structurally identical. However, the structurally identical controllers perform mirror image operations when the controllers are properly initialized to the correct modes. 
     In the embodiment in which the signal controllers are components of the telecommunications system, the control device may be a conventionally connected common control of a PBX. The controlled device may be a peripheral shelf control for extending the telecommunications capabilities of the system to a remote facility. The telecommunications link may be a fiber optic link, but other transmission media may be utilized. 
     Each signal controller includes circuitry for disabling all outgoing signals that jeopardize system performance when the controller is set in the incorrect mode. Preferably, all signal drivers are disabled during the initialization sequence. Each signal controller also includes recognition circuitry or software for detecting the incoming signals (e.g., clock signals or packetized call information) that identify the position of the controller along the communication path. A mode control switches the controller into the correct mode when the position is identified by detection of signals. 
     In the preferred embodiment, the initialization sequence begins with disabling at least selected signal driving capabilities and selectively enabling signal recognition capabilities. For example, the signal recognition capability for detecting packetized call information may be activated to determine if the signal controller undergoing initialization is receiving packets from an operating remote signal controller. If the packets are detected, the position of the controller is identified and the proper mode is implemented. On the other hand, if the packets are not detected, alternate signal recognition capability is activated to detect the presence or absence of known control signals, such as clock signals. If the known control signals are received independently from the telecommunications link, the position of the controller is identified and the proper mode is implemented. While not critical, the signal controller may be designed such that mode implementation is merely the activation of one of two mode interfaces and the deactivation of the other mode interface. The mode interfaces may be alternate sets of signal drivers and signal receivers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a telecommunications system, such as a PBX, having dual-mode signal controllers for supporting telecommunications via a remote peripheral shelf. 
     FIG. 2 is a block diagram of key operational components of one of the dual-mode signal controllers of FIG. 1, in accordance with the invention. 
     FIG. 3 is a block diagram of a telecommunications system having multiple dual-mode signal controllers in accordance with the invention. 
     FIG. 4 is a process flow of a method for automatically initializing one of the signal controllers of FIGS. 2 or  3 . 
    
    
     DETAILED DESCRIPTION 
     With reference to FIG. 1, a telecommunications system employs dual-mode signal controllers  10  and  12  to enable a main switch  14  to support telecommunications capability at a number of remotely located computers  16  and telephones  18 . The dual-mode signal controllers are located on opposite sides of a communication link  20 , such as a fiber optic link. The signal controllers provide signal conversions between a first format for transmitting information over the link  20  and a second format for processing at the main switch  14  and the shelf extension subsystem  22 . 
     After the telecommunications system of FIG. 1 has been properly initialized, the components operate in a conventional manner. That is, the invention relates to initializing the system, and particularly relates to initializing the dual-mode signal controllers  10  and  12  to establish the appropriate modes. 
     The dual-mode signal controllers  10  and  12  provide the telecommunications system with signal conversion capability. The signals generated by a common control  24  of the PBX main switch  14  can be converted into Ethernet packets, for example, which are transmitted over the fiber optic link  20  to a peripheral shelf control  26 . As is well known in the art, the extension shelf subsystem  22  having the peripheral shelf control  26  is functionally equivalent to the conventional shelves contained within a cabinet that houses the common control  24  of the main switch  14 . The shelf extension subsystem  22  is used to extend the capabilities of the PBX by a limited distance when some of the PBX-supported computers  16  and telephones  18  are not on the same site as the main switch  14 . Typically, the extension shelf subsystem  22  must be within twenty miles of the main switch  14 , but this is not critical to the invention to be described below. While the invention is illustrated and described as being used with a PBX system, the initialization sequence may be practiced with any communication system requiring two or more linked controllers that operate in different modes, depending upon the locations of the controllers along the communication path. 
     The interaction between the main switch  14  and the extension shelf subsystem  22  enables communication between the remotely located computers  16  and telephones  18 , as well as communication with local computers  28  and local telephones  30 . While not shown in FIG. 1, the switch is connected to other networks, such as a PSTN and/or the global Internet, to enable communication with computers, telephones and other devices that are not supported by the PBX. 
     In the preferred embodiment, the dual-mode signal controllers  10  and  12  are structurally identical. However, the controllers are initialized into different modes of operation. For a signal that is directed to one of the remote telephones  18  from the main switch  14 , the first signal controller  10  converts the signal from a first format that is compatible with processing within the main switch to a second format that is compatible with transmitting via the communication link  20 . For example, the signal may be packetized to an Ethernet format by the first signal controller. The second signal controller  12  then receives the packet or packets and reformats the signal to a format that is compatible with processing via the extension shelf subsystem  22  that is connected to the target telephone  18 . Thus, with respect to the signal, the second signal controller has the mode of operation that is the opposite of the first signal controller. 
     The modes of operation of the signal controllers  10  and  12  are set during initialization sequences of the controllers. For example, following installation at the local site that includes the first signal controller  10 , the controller must be initialized when power is available. Setting the controller in the proper mode is critical to operation of the main switch  14 . In fact, under some circumstances, improperly initializing the first signal controller can cause a full system failure. If the switch-side signal controller  10  is improperly initialized, the controller  10  might drive signals into the channel  34 . The resulting signal collisions would likely cause a system failure within the PBX. A limited number of other channels are shown in FIG.  1 . At the switch-side signal controller  10 , the controller is configured to receive time division multiplexed output (TDMO) signals over channel  36  and high level data link control output (HDLCO) signals over channel  40  and to transmit the signals via the fiber optic link  20  to the shelf-side signal controller  12 . The switch-side signal controller  10  is also initialized to drive time division multiplexed input (TDMI) signals and high level data link control input (HDLCI) signals received via the fiber optic link  20  to the common control  24  via channels  38  and  42 , respectively. 
     The shelf-side signal controller  12  is initialized to drive the SYSCLCK signals, the TDMO signals, and the HDLCO signals received from the switch-side signal controller  10  to the peripheral shelf control  26  via channels  32 ,  44  and  46 , respectively. In addition, the signal controller  12  receives TDMI signals and HDLCI signals via channels  48  and  50 , respectively. 
     If one of the signal controllers  10  and  12  is improperly initialized, “backdriving” may occur. Backdriving is the driving of input signals into output transmission channels. This will degrade the performance of the system and may cause a system failure. 
     With reference to FIG. 2, a dual-mode signal controller  52  is shown as including a shelf control interface  54  and a common control interface  56 . Both of the interfaces are included within the signal controller  52  to allow the controller to be used as either the switch-side controller  10  or the shelf-side controller  12  of FIG.  1 . That is, if the controller  52  is to be used in the location of controller  12  in FIG. 1, the shelf control interface  54  is activated and the common control interface  56  is disabled. On the other hand, if the controller  52  is to be used as the switch-side signal controller  10  of FIG. 1, the common control interface  56  is enabled and the shelf control interface  54  is disabled. 
     Each of the interfaces  54  and  56  includes a set of signal drivers and receivers. For the shelf control interface  54 , the set includes a SYSCLCK signal driver  58 , a TDMO signal driver  60 , an HDLCO signal driver  62 , a TDMI signal receiver  64  and a HDLCI signal receiver  66 . On the other hand, the common control interface  56  includes a SYSCLCK signal receiver  68 , a TDMO signal receiver  70 , an HDLCO signal receiver  72 , a TDMI signal driver  74  and a HDLCI signal driver  76 . 
     A driver/mode control device  78  is used during the initialization of the controller  52 . At the outset of the initialization sequence the driver/mode control device  78  disables each of the drivers  58 ,  60 ,  62 ,  74  and  76 . However, the receivers  64 ,  66 ,  68 ,  70  and  72  may remain enabled during the initialization sequence. Signal inputs to the signal controller  52  are monitored to determine whether the controller is located on the shelf side or the switch side of a communications link  80 , such as a fiber optic link. If the signal controller is on the shelf side of the communications link, signals will be received from a signal controller on the opposite side of the communications link. Thus, the shelf control interface  54  must be activated in order to provide SYSCLCK signals to the extension shelf subsystem  22  of FIG.  1 . Simultaneously, the common control interface  56  must be disabled to prevent signals from being backdriven. 
     When the signal controller  52  is on the switch side of the communications link  80 , no signals will be received via the link, since the extension shelf system is without SYSCLCK signals. The fact that the signal controller is on the switch side of the telecommunications system can be confirmed by monitoring one or more connections with the common control  24  of FIG. 1 in order to detect known patterns of control signals that are unique to the common control. For example, the common control generates the SYSCLCK signals, so that for the receiver  68  of the common control interface  56  to receive SYSCLCK signals, the controller must be at the common control side of the communications link. Thus, the driver/mode controller  78  enables the common control interface  56  and fully disables the shelf control interface  54 . 
     A first signal recognition device  82  is connected to the SYSCLCK signal receiver  68  to monitor signal reception at the receiver. The first signal recognition device  82  is used to monitor SYSCLCK input during a portion of the initialization sequence of the controller  52 . A second signal recognition device  84  is connected to monitor traffic at a demultiplexer  86  connected to a fiber optic interface  88 . The combination of the interface  88  and the demultiplexer  86  is used to depacketize and reassemble data streams upon receiving Ethernet packets over the communications link  80 . This process is not critical to the invention and may be substituted with other techniques known in the art. A combination of a multiplexer  90  and the fiber optic interface  88  performs the opposite operations, i.e., receives data streams from receivers  64 ,  66 ,  68 ,  70  and  72  and provides format conversion into Ethernet packets that are transmitted over the communications link  80 . 
     The first and second signal recognition devices  82  and  84  may be implemented in computer hardware, software or a combination of hardware and software. The devices are activated and deactivated by a circuit control member  92 . In one possible initialization sequence, the driver/mode control device  78  disables signal drivers  58 ,  60 ,  62 ,  74  and  76 , while the circuit control member  92  activates the second signal recognition device  84  and deactivates the first signal recognition device  82 . Traffic from the communications link  80  is monitored by means of the connection of the second signal recognition device  84  to the demultiplexer  86 . If traffic indicates that the fiber optic interface  88  is receiving signals from a remote dual-mode signal control, the shelf control interface  54  is activated and the common control interface  56  is deactivated. On the other hand, if the second signal recognition device does not detect the appropriate packets, the device  84  is deactivated and the first signal recognition device  82  is activated. The first signal recognition device  82  monitors for SYSCLCK signals driven by the common control. If the SYSCLCK signals are recognized, the signal controller  52  must be at the switch side of the communications link  80 . Thus, the common control interface  56  is enabled and the shelf control interface  54  is disabled. 
     While the initialization sequence has been described as activating the second signal recognition device  84  for a preselected time interval before activation of the first signal recognition device  82 , the reverse may be executed. In fact, both of the signal recognition devices may be activated simultaneously. Referring briefly to FIG. 1, if both of the signal controllers  10  and  12  are initialized at the same time, fixed system control signals (e.g., SYSCLCK signals) driven by the common control  24  will be present, while no packets will be transmitted across the communications link  20 . Consequently, the switch-side controller  10  must complete its initialization sequence before the shelf-side controller  12  will receive signals. 
     Referring now to FIG. 3, a telecommunications system may include more than one extension shelf subsystem  94  and  96  that need to be individually addressable by the signal controller  10  at the main switch  14 . This may require more than two modes of operation by the signal controllers  10 ,  98  and  100 . Thus, if the three signal controllers are to be interchangeable, each controller must be capable of operating in any one of three modes. 
     The initialization sequence for the switch-side signal controller  10  may be implemented in the same manner as described with reference to FIGS. 1 and 2. Thus, a receiver of a known pattern of system control signals (e.g., SYSCLCK signals) may be monitored. Detecting the known pattern of control signals as having arrived independently of the communications link  20  is evidence that the initializing signal controller  10  is on the same side of the link  20  as the main switch  14 . 
     Initializing the remote multi-mode signal controllers  98  and  100  is more problematic. In some applications, the signal controller  98  that is connected to the first extension shelf subsystem  94  requires a mode of operation that is different than the mode of the signal controller  100  that is connected to the second extension shelf subsystem  96 . To provide additional information necessary for proper initialization, the common control  24  can be configured to transmit signals to both remotely located signal controllers  98  and  100 , such that the signals indicate the interface requirements of first and second peripheral shelf controls  102  and  104 , respectively. For example, the HDLCO signals which the common control directs to the first signal controller  98  can be modified to be distinguishable from the HDLCO signals directed to the second signal controller  100 . Upon recognizing a first modified HDLCO signal, the first signal controller  98  is programmed to initialize a proper one of three modes of operation. On the other hand, signal monitoring at the other signal controller  100  may be used to identify the position of the controller  100  for automatically initializing the controller into a third mode of operation. 
     With reference to FIGS. 1,  2  and  4 , a method for automatically initializing the multi-mode signal controller  52  for proper operation on one side of the communications link  20  of FIG. 1 includes the step  106  of disabling the drivers  58 ,  60 ,  62 ,  74  and  76 . Disabling the drivers prevents backdriving of signals along lines  108 ,  110 ,  112 ,  114  and  116 . The signal drivers may be disabled by the driver/mode controller  78  simply by providing a high impedance state at the drivers. 
     In step  118 , the recognition circuitry for monitoring activity is enabled. In one embodiment, the second signal recognition device  84  is activated for a preselected period of time to monitor traffic received via the communications link  80 . The monitoring process is shown as step  120  in FIG.  4 . However, in another embodiment the monitoring process of step  120  occurs simultaneously with the monitoring process of step  130  to be described below. 
     If traffic is detected along the communications link  80  by the second signal recognition device  84 , a positive response is generated at step  122  and the shelf control interface  54  is enabled, while the signal drivers and receivers  68 ,  70 ,  72 ,  74  and  76  of the common control interface  56  are disabled. Thus, the signal driver  52  operates in a mode of operation that is compatible with use of the controller in the position of the signal controller  12  of FIG.  1 . That is, the step  124  of enabling the shelf control interface allows the controller to be used with the extension shelf subsystem  22  of FIG.  1 . The controller can then be used to transmit signals between the peripheral shelf control  26  and the switch-side signal controller  10 , as shown at step  126 . 
     When no communication signals are detected by the second signal recognition device  84 , a negative response is generated at the decision step  122 . The circuit control member  92  of FIG. 2 executes step  128  of enabling the first signal recognition device  82 . This automatically implements the step  130  of monitoring a second link. In FIG. 2, the second link is the connection to SYSCLCK receiver  68  that is connected to the source of SYSCLCK signals when the signal controller  52  is on the same side of the communications link  80  as the main switch of a telecommunication system. Thus, in the decision step  132 , if the SYSCLCK signal is detected, the signal controller is in the position of the controller  10  of FIG.  1 . The common control interface  56  is then enabled at step  134 . On the other hand, if a negative response is generated at the decision step  122 , the process returns to the step  118  of enabling the second signal recognition device  84 . The process continues to loop until one of the two links provides a detectable signal for identifying the position of the signal controller  52  along the communication path that includes the controller. In a circumstance in which both of the signal controllers  10  and  12  of FIG. 1 are simultaneously initialized, the return of the process to step  118  from the decision step  132  is important, since the shelf-side controller  12  is unlikely to receive either communication signals at step  122  or control signals at step  132  until the switch-side signal controller  10  has been completely initialized. 
     While the process of FIG. 4 has been described as one in which the second signal recognition device  84  is utilized before the first signal recognition device  82 , this is not critical. In some applications, there may be benefits to monitoring the signal reception for the known pattern of control signals prior to monitoring the link to a remote signal controller for the reception of communication signals.