Abstract:
The invention relates to methods and apparatus for synchronously digital interfacing communications components. The apparatus includes a device configured to transmit and receive differential signals. One set of differential signals includes a transmit signal and a receive signal, and another set of differential signals includes a clock signal and a synchronization signal. The combination of clock signals and synchronization signals form other signals having a variable period. The other signals are used to modify the set of differential signals including transmit and receive signals.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to communications networks and, more particularly, to synchronous digital interfaces for connecting communications components in communications networks. 
     BACKGROUND 
     A communications system may be created by connecting various communication components such as servers, timeswitches, hubs, and data processing modules. Multiple communications systems connected together form a communications network. Many communications systems include a media services card (MSC); a personal computer (PC) card that performs call processing and media processing of voice channels in the network. The MSC can also be the central interconnect location of a communications network. It accomplishes this task by handling time switching of synchronous channels and interworking with other components in the communications network. 
     FIG. 1 shows a conventional communications network with a MSC  20  connected to a server  10 , and shows the MSC connected to other communications equipment via a synchronous interface  40 . A MSC can also include a hub  50 , timeswitch  60 , media service component  70 , and other modules  30 . In addition, a MSC can be connected to central units, such as servers  10 , via a slot in a PC (e.g. Peripheral Component Interconnect standard (PCI  2 . 1 ) slot). This allows interfacing with the server processor and other peripherals used in a communication system. Data packets may be transmitted between the MSC  20  and the server  10 , other internal modules  30 , or external modules and systems, thereby creating the communications network. 
     FIG. 1 also shows the MSC card connected to an expansion chassis  80  via an interconnection  40 . The interconnections between them can be used for trunk and line connections. Trunk and line interfaces provide access to telecommunications trunks and station set lines. Trunk and station set lines can include Caller ID Analog Trunk interfaces, T 1 /E 1 /PRI trunk with channel service unit interfaces, and Analog and Digital phone interfaces. These interfaces are the conduits that pass information throughout the network. 
     FIG. 2 shows a communications network architecture (with the servers not shown). The network is physically arranged as a branched tree, with a timeswitch  200  at the root and modules  210  as the end nodes. Intermediate nodes are called hubs  220 . This physical arrangement allows for point-to-point links at all interfaces. The systems and methods of interfacing between the devices are important components of communications systems and networks. As systems and networks grow, the interfaces handle greater amounts of data and connect to more devices. Present interfaces, however, are substantially limited in channel capacity, expansion capabilities, and the like. 
     There are many electrical synchronous interfaces available, however, these existing electrical synchronous interfaces are slow and limited in capacity. Those that are expandable are expensive, impractical (e.g. must cascade multiple interface cards), suffer from speed limitations, are electrically noisy, prone to interference from outside sources, and lack features such as maintenance signaling and automatic propagation delay calibration and compensation. Fiber-optic interfaces have been used as synchronous digital interfaces. However, fiber-optic interfaces are more expensive to implement and are much less common than electrical interfaces. 
     Accordingly there exists a need for systems and methods of synchronous digital interfacing that efficiently use existing wiring schemes. 
     There also exists a need for systems and methods of synchronous digital interfacing that do not require a clock source or sensitive clock recovery circuit in the peripherals in order to use the interface. 
     There also exists a need for systems and methods of synchronous digital interfacing that efficiently support multiple peripheral devices. 
     There also exists a need for systems and methods of synchronous digital interfacing that improve immunity to radio frequency interference (RFI). 
     There also exists a need for systems and methods of synchronous digital interfacing that reduce RF emissions. 
     There also exists a need for systems and methods of synchronous digital interfacing that allow for network synchronization control in the peripherals. 
     There also exists a need for systems and methods of synchronous digital interfacing that support automatic configuration. 
     There also exists a need for systems and methods of synchronous digital interfacing that support multiple cable lengths. 
     There also exists a need for systems and methods of synchronous digital interfacing that allow for insertion and removal of powered peripheral devices onto the network without disrupting the network. 
     There also exists a need for systems and methods of synchronous digital interfacing that interwork with an existing flow-controlled message transport without using any dedicated signaling bandwidth. 
     Accordingly, it is an object of the present invention to provide systems and methods of synchronous digital interfacing that efficiently uses existing wiring schemes. 
     It is also an object of the present invention to provide of synchronous digital interfacing that do not require a clock source or sensitive clock recovery circuit in the peripherals in order to use the interface. 
     It is also an object of the present invention to provide systems and methods of synchronous digital interfacing that efficiently support multiple peripheral devices. 
     It is also an object of the present invention to provide systems and methods of synchronous digital interfacing that improve immunity to RFI. 
     It is also an object of the present invention to provide systems and methods of synchronous digital interfacing that reduce RF emissions. 
     It is also an object of the present invention to provide systems and methods of synchronous digital interfacing that allow for network synchronization control in the peripherals. 
     It is also an object of the present invention to provide systems and methods of synchronous digital interfacing that support automatic configuration. 
     It is also an object of the present invention to provide systems and methods of synchronous digital interfacing that are usable with different cable types. 
     It is also an object of the present invention to provide systems and methods of synchronous digital interfacing that support multiple cable lengths. 
     It is also an object of the present invention to provide systems and methods of synchronous digital interfacing that allow for insertion and removal of powered peripheral devices without disrupting a network. 
     It is also an object of the present invention to provide systems and methods of synchronous digital interfacing that interwork with an existing flow-controlled message transport without using any dedicated signaling bandwidth. 
     These and other objects of the invention will become apparent to those skilled in the art from the following description thereof. 
     SUMMARY OF THE INVENTION 
     In accordance with the teachings of the present invention, these and other objects may be accomplished by the present invention, which is a synchronous digital interface for connecting components in a communications network. 
     An embodiment of the invention includes a device configured to transmit and receive differential signals. One set of the differential signals includes a transmit signal and a receive signal. A second set of the differential signals includes a clock signal and a synchronization signal. Combinations of the clock signal and the synchronization signal form other signals having variable periods. The other signals can be used to modify the first set of differential signals. 
     Another embodiment of the present invention includes a method of synchronously digitally interfacing components in a communications network. This embodiment involves transmitting and receiving differential signals. A first set of differential signals includes a transmit signal and a receive signal. A second set of differential signals includes a clock signal and a synchronization signal. This embodiment also includes forming other signals having variable periods by combining the clock signal and the synchronization signal. This embodiment further includes modifying the first set of differential signals using the other signals. 
     Another embodiment of the present invention includes a transmission module for transmitting and receiving differential signals. A first set of differential signal includes a transmit signal and a receive signal. A second set of differential signals includes a clock signal and a synchronization signal. It includes a module for combining the clock signal and the synchronization signal to form other signals having variable periods. The other signals are used to modify the first set of differential signals. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The invention will be more clearly understood by reference to the following detailed description of an exemplary embodiment in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a block diagram of a conventional communications system. 
     FIG. 2 is a block diagram of a network physically arranged as a branched tree. 
     FIG. 3 is an embodiment of the mechanical aspect of the present invention. 
     FIG. 4 is a timing diagram of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This invention provides an interface between components in communications systems and/or networks. It provides a new method of signaling between the components in the network and provides added network maintenance messaging without interfering with the communications data. 
     FIG. 3 is an embodiment of the electro/mechanical aspect of the present invention showing the rear view of a communications module  310  with the present invention  300  connected to the module. The present invention can include a 2×5-pin connector  300  mounted on the rear edge of the module  310 , thereby permitting blind mating to a computer chassis. In addition, one pair of pins  340  on connector  300  may be shorted together, to provide an indication that a module is properly seated in a PC chassis. This indication may be used to control power soft-start circuitry and module initialization. Those skilled in the art will realize that logic signals may be used instead of the shorting link to provide the same indication. 
     A modular jack (not shown) can be included for connection to an expansion chassis. This provides a way of expanding the system via the front or rear plate of the PC. Additional jacks may be added, thus making the interfaces on an intermediate device electrically separate, operating as a point-to-point link to the next intermediate device or peripheral device. 
     The mechanical design of the present invention can also be made to support hot insertion and front-only installation and removal. Such aspects ease installation since it does not require disassembly of the chassis and system power-downs. 
     FIG. 4 is a timing diagram of the present invention. An embodiment of the present invention includes four signals which may be sent across twisted-pair, ribbon cable, and the like. One pair of signals may be used for encoding transmit (Tx)  460  and receive (Rx)  470  signals (i.e. data lines). And the other pair of signals (hereinafter called A signal  440  and B signal  450 ) may be used to encode other signals, such as a system clock, reset, synchronization and extra edges (i.e. extra bit transitions). By combining A signal  440  with B signal  450  this invention can extract a frame synchronization signal  410 , reset signal  420  and a system clock signal  400 . Each pair of signals may be transmitted using differential transmission. This will minimize electromagnetic interference (EMI) and maximize immunity to radio frequency interference (RFI). 
     A signal  440  and B signal  450  are also encoded to reduce the maximum RF energy (i.e. RF emissions) by randomizing the distribution of transitions on the A signal  440  and B signal  450 . This reduces the RF spectrum in relation to a pure clock on either A signal  440  or B signal  450 . A signal  440  exclusive OR&#39;ed (XOR) with B signal  450  will yield a system clock signal  400  with edges centered in the Tx bit period. The Rx  470  bit period is clocked on an edge of the system clock signal  400 . If A signal  440  transitions high or low while B signal  450  is low, the resulting output of the XOR is a system clock signal  400 . When A signal  440  transitions high while B signal  450  is high the result is a system clock  400  and frame synchronization signal  410 . If A signal  440  transitions low, while B signal  450  is high then the resulting signals are a system clock  400  and a reset signal  420 . Those skilled in the art will realize that other logic devices can be used to combine the A signal  440  and B signal  450 , and still be within the scope of this invention. 
     Other simple codings of A signal  440  and B signal  450  are possible. The system clock signal is positioned to sample Tx  460 , but does not modify Tx bits being forwarded by a device (e.g. bits being forwarded downstream by a hub). It is desirable to modify some Tx data bits for the purpose of maintenance or other messaging. To correctly time changes to the Tx bits, additional clock transitions  430  (i.e. extra edges) can be added to the A signal  440  and/or B signal  450 . The extra transitions therefore allow a bit (or bits) in the Tx signal  460  to be modified before a receiver clocks the Rx  470  period. The Tx signal  460  can thus be used to carry a messaging signal which can be modified anywhere in the network. 
     Maintenance signals can include temperature monitoring, port monitoring, port identification, system identification, and the like. Intermediate devices can also arbitrate access to a common maintenance signaling channel using flow-control routing. 
     Since a frame sync  410  identifies the beginning of a data frame, this invention can distinguish the extra signaling transitions  430  from the rest of the system clock  400  transitions without compromising the data packets used for network communications. Thus, data signals  460  may originate from an upstream device (i.e. a device up higher in the hierarchy of the branched network) and seamlessly travel downstream to a hub or module. Conversely, this invention allows a downstream device (i.e. component located anywhere below the root device of the branched network) to alter the Tx  460  data at specific times and send the new data without affecting other data in the data frame. For example, intermediate devices, such as a primary hub (i.e. between the peripheral devices (modules) and the timeswitch) as shown in FIG. 2 can broadcast, via this invention, information from the timeswitch without sampling A signal  440 , B signal  450  or Tx signal  460  and send the information downstream with modified or unmodified messaging data. In addition, data moving upstream can come from downstream or be sourced within a device (e.g. hub) at any time. The intermediate device, via this invention, can also merge information from multiple peripheral devices and send the information upstream. 
     Maintenance signaling can be accomplished by encoding extra clock edges with the clock signals (e.g. temporarily speeding up the clock) by increasing the frequency and/or modifying the phase of B signal  450 . The clock can be recovered from the A signal  440  during the maintenance-signaling period when there are extra edges on B signal  450 . If the receiver is unsynchronized and therefore does not know when the maintenance-signaling period occurs, it can tolerate the (momentarily) faster clock resulting from A signal  440  XOR B signal  450 . Furthermore, reset signals can be ignored during the maintenance-signaling period when there are extra edges on the B signal. If the receiver is unsynchronized and therefore does not know when the maintenance-signaling period occurs, it can accept all resets. In other words, the extra transitions of B signal  450  are not necessary for synchronization indications. 
     Merging upstream data may include OR&#39;ing all of the downstream Rx signals  470  received by the intermediate device and forwarding the signals upstream. Merging can also be accomplished by determining which port is sending active Rx data  470  and forwarding more specific Rx data  470  upstream. 
     This invention can also insert delays to compensate for the propagation delays inherent in the communications network devices. In addition, this invention can calculate the propagation delay of a cable in the system using an adaptive cable measurement and data signal loop back. Accordingly, this invention can automatically insert corresponding delays. 
     This invention also provides a unique serial number for identifying the peripheral devices. This allows an upstream device to monitor all of the devices in the communications network. By using this circuitry, this invention can autonomously generate error messages as necessary, with sufficient information to allow stateless error handling. For example, the present invention may include interface circuitry for monitoring and controlling of devices such as a electronic thermometer and cooling fan, respectively. If a system component&#39;s temperature becomes too high, the device can send a maintenance alarm message. Those skilled in the art will realize that other more complex measurement and control situations can be handled, such as re-routing due to a downed device, security monitoring and counter measures that protect against system breach, etc. 
     In addition, the upstream device can monitor which ports of downstream devices are in use. This provides value by allowing for fast and automatic identification and service to peripherals. 
     It will be understood that changes may be made in the above construction and in the foregoing sequences of operation without departing from the scope of the invention. It is accordingly intended that all matter contained in the above description or shown in the accompanying drawings be interpreted as illustrative rather than in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention as described herein, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.