Abstract:
A system and method is designed for upgrading a digital PBX used with a pulse code modulation (PCM) telephone system by providing an interface card connected to the back plane of the PBX. The interface card acts as a replacement for the digital key set cards normally used with the back plane of such a PBX. The interface card is designed with circuitry to process voice-encoded packet data directly from a LAN to the PCM data used within the PBX network, and to process PCM data from the telephone network to voice coded packet data on the LAN to provide a voice-over Internet protocol and interface with the telephone system connected with and controlled by the PBX.

Description:
BACKGROUND OF THE INVENTION 
     Telecommunications switching systems typically are utilized by business users to place telephone calls within their offices, or to other users, by way of a network of telephone systems and communication devices. Currently, many businesses employ a combination of computer networks and telephone systems. Such businesses are faced with a never-ending series of complex decisions as the businesses grow and evolve. The reason for this is that the increasing demands on both the computer and telephone systems require both of these systems to undergo major upgrades over a period of time, generally with associated significant budgetary impacts. 
     The traditional recommendation for such business customers is to somehow integrate their voice and data traffic onto one network to simplify the planning and procurement process, especially when considering the impact that video and other wide band communications demands will have on their network transport requirements. This approach regards voice communications as a constantly decreasing percentage of data and video communications, and recommends that the network be designed for the most demanding traffic source to allow for the relatively low bandwidth voice traffic to ride along with it. 
     Systems also exist which allow off-site workers to access resources over the local area network (LAN); but expensive computer server and data routing arrangements are required to accomplish this. This complex arrangement also is expensive to maintain and continuously update. 
     Known systems generally propose one of two solutions. One is to utilize a private branch exchange (PBX) system which has a packet data network built into it, along with voice switching apparatus. Another is to upgrade the on-site LAN to a sufficient performance level that the LAN can act as a pathway for communications between multimedia devices and still maintain a reasonable quality of voice service. 
     Such prior art systems, however, lack an interim migration plan for smaller business customers who have relatively limited financial resources. The absence of such an interim plan begs for a more efficient mechanism to migrate a business to multimedia communications and e-commerce applications economically. The solutions which are provided by the known systems do not allow for a gradual migration to advanced networking techniques for customers with limited resources. 
     United States patents which are related to the technologies discussed above are Hunter U.S. Pat. No. 4,764,919; Beckner U.S. Pat. No. 4,592,048; Beckner U.S. Pat. No. 4,596,010; Tadamura U.S. Pat. No. 5,537,401; and Minakami U.S. Pat. No. 5,878,117. These patents cover interface and control arrangements to bridge between traditional telecommunications networks and packet data networks, for the purpose of combining the positive aspects of both network types, to provide improved communication solutions for customers. 
     Other prior art patents cover usage of various LAN protocol enhancements to make the quality of encoded voice messages better, so as to reduce user objections about choppy speech, audible delays and audio distortion. Such techniques include changes to the timing of sending LAN packets, as disclosed in the U.S. Pat. No. 6,064,673 to Anderson. Two other United States patents which are directed to techniques for assembling and disassembling voice packets more efficiently are the U.S. Pat. No. 5,923,655 to Veschi and U.S. Pat. No. 5,526,353 Henley. 
     Some systems are designed to establish direct links from digital telephone facilities normally used for voice to data network sources. These systems provide for data transmission over existing T-1 and PRI telephone trunks. Two such systems are disclosed in the U.S. Pat. Nos. 5,410,754 and 5,796,742 to Klotzbach. Essentially the disclosure of both of these patents is the same. The solution, however, is simply to take data and transmit it over a voice channel. There is no packetizing of voice information for transmitting that information over a LAN network. 
     Another solution is proposed in the U.S. Pat. No. 5,892,764 to Riemann. This patent discloses packet switching using the LAN to serve as a communication link for a complete PBX system, which does not use a central switching chassis. This is a solely digital system designed as a substitution for a pulse code modulated (PCM) PBX system. For a business customer having a digital PBX operating with PCM voice, the system of this patent offers no solution, other than removing the PBX and substituting the digital system of Riemann. 
     Product enhancements have been introduced for customers who desire to continue use of a PBX to transport multimedia information, such as voice data and video. Enhancement products of this type generally include function cards that combine audio and data from both a LAN and wide area network (WAN) interface for switching within the PBX. Three such United States patents for this type of a system are Guy U.S. Pat. No. 5,940,479; Chau U.S. Pat. No. 5,550,906; and Greaney U.S. Pat. No. 5,796,729. The Greaney patent employs cards which are plugged into the back plane bus of a digital PBX. The system, however, requires a variable bandwidth back plane to permit the back plane to be used for voice, data, and control signals. 
     While the various systems of the prior art discussed above provide a number of techniques for combining LAN data and PCM voice data, none of these systems are directed to the needs of customers who already own a PBX, but want a convenient and inexpensive means to switch (and convert) voice encoded packet data directly between a LAN and PCM data used within the PBX network. It is desirable to provide such a system, which is cost effective and which comprises a drop-in module to make existing PBX voice traffic available to network devices that are capable of sending voice over LANs. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide an improved voice-over Internet protocol system. 
     It is another object of this invention to provide an improved apparatus and method to create complete connectivity between devices on a LAN with communications and control channels within the existing telephone system while permitting communication over other wide area networks (WAN). 
     It is an additional object of this invention to cause an existing digital key or PBX system to be accessible by personal computers and other devices connected to a LAN without requiring changes in the software present in the existing PBX system. 
     It is a further object of this invention to provide an interface card to allow an owner of a digital PBX system to implement a drop-in replacement of existing telephones, with telephones directly connected to the LAN while continuing to permit operation of the PBX with standard digital key sets. 
     In accordance with a preferred embodiment of the invention, a system and method are disclosed for adapting a pulse code modulation (PCM) telephone system having a PBX with a back plane bus to transport information to and from an Ethernet data network or LAN. To do this, an Internet protocol card (IPC) is coupled to the back plane bus of a digital PBX system in the same manner as digital key set cards normally used with such a PBX. The IPC includes a plurality of digital signal processors and a digital cross point switch coupled in parallel with the digital signal processors, and with the PBX back plane, for routing PCM voice data to and from the digital signal processors. The digital signal processors are controlled by known algorithms to packetize the PCM voice data coming from the PBX and to de-packetize, into PCM voice data, packetized voice supplied to the IPC card from a port connected to the LAN. Power, timing and control interconnections for operating the Internet protocol card are obtained from the back plane. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram illustrating the major systems of the present invention and their connection to and through a standard digital PBX; and 
     FIG. 2 is a block diagram of a preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     Reference now should be made to the drawings, in which the same reference numbers are used in both figures to designate the same components. The system of the preferred embodiment of the invention is designed to function as an interface card with a conventional digital PCM voice PBX, such as those available through Inter-Tel Corporation for the AXXESS® key systems. Such a PBX has a number of digital key sets, shown as standard key sets  32  in FIG. 1; and these key sets are connected with the backplane  20  of the PBX  10  through digital key set cards  28  (three of which are shown in FIG.  1 ). The PBX  10  may be configured to handle a relatively small number of lines, up to several hundred. As shown in FIG. 1, the PBX  10  also is connected through the public switched telephone network (PSTN)  12 , through which connections may be made to any number of public telephones or public callers  14 , as indicated in FIG.  1 . In a conventional PCM PBX system of the type described thus far, the standard key sets  32  are linked with one another and to the public switched network  12 , through the operation of the PBX, and specifically, are linked through the backplane  20  of the PBX  10 . The PBX  10  functions as an interface between the public network and the business network using the digital key sets  32 . 
     To permit communication with, and interconnection of, the PBX  10 , along with the standard key sets  32 , to station apparatus on the Ethernet or LAN which use a TCP/IP data network, an Internet protocol card (IPC)  30  is plugged into or added to the back plane  20  of the PBX  10  in place of, or in addition to, one of the digital key set cards  28 . The manner in which this card  30  plugs into and interfaces with the back plane  20  is the same as the interconnections made by the digital key set cards  28 . It also should be noted that other cards are typically plugged into the back plane  20  of the PBX  10 , such as the (central processing unit) CPU  24 , (loon and around start controller) LGC  26 , power  22 , and the like. The back plane bus  20  of the PBX  10  serves to interconnect all of these functions and to synchronize the operation of the entire system to which it is connected. This includes the IPC  30 . 
     It should be noted that no changes whatsoever are made to the standard PBX back plane  20 , which has a bandwidth of 64 kilobit/second pulse code modulation (PCM) data streams present within the phone system. The Internet protocol card (IPC)  30  operates to convert this 64 kilobit/second data stream to TCP/IP Ethernet packets, which contain encoded voice at the rate of 8 kilobit/second. As a consequence, as indicated, in FIG. 1, packetized IP data is supplied from the IPC card  30  over a trunk  34  to a local area network (LAN)  36 , which may have connected to it application servers  40  and IP key sets and work stations  42 , which operate on packetized data in the LAN. In addition, the LAN  36  is connected through a conventional router/firewall  38  to the wide area network (WAN), shown as the Internet  44 , for communication with employee work stations  48  and IP key sets  46  operating in and through the WAN. 
     In the system shown in FIG. 1, information from the WAN and LAN to the standard key sets associated with the PBX  10 , as well as through the PBX  10  to stations  14  on the PSTN  12 , may be effected. As far as voice messages are concerned, the system is essentially transparent to the users, with the change over from PCM voice data to packetized TCP/IP voice, and vice versa, being effected automatically through the IPC which is simply plugged into the back plane  20  of a standard digital PBX  10 , which may be of any conventional configuration, including the one specifically mentioned above. 
     Reference now should be made to FIG. 2, which is a detailed block diagram of the IPC card  30 . The IPC card  30  is plugged into the back plane  20  of the PBX system  10 . As indicated in FIG. 2, the interconnections between the back plane  20  and the IPC card are through a back plane interface/decode logic  31 , which, in addition to the interface described above in conjunction with FIG. 1, also directly couples power, timing signals and call processor resources from the PBX back plane  20  to the interface card  30 . As a result, substantial savings in equipment costs are effected. In addition, this utilization of all of the internal facilities within the PBX telephone system results in a more reliable solution with fewer overall components, since the IPC card  30  and the other cards and operations of the PBX  10  are fully integrated with one another. 
     The interconnection to the Ethernet (LAN) is effected through an Ethernet port  60 , which is a ten-base-T Ethernet port. This port is coupled to a serial Ethernet IC network interface controller (ST-NIC)  62  in the form of an integrated media access controller (MAC), twisted pair transceiver (PHY), and an attachment unit interface (AIU) which provides ten Mbps throughput over various physical media. The ST-NIC  62  has a small sixteen-byte internal FIFO, but has the capability of being an address and data bus master to transport data to and from the host processor memory by way of the dual sixteen-bit DMA channels. 
     When it is in the bus/slave mode, the ST-NIC  62  allows the host processor  50  to read and write to the internal registers by way of normal peripheral access (non-latched timing mode). When a bus master (FIFO) is full, the ST-NIC  62  uses the sixteen-bit multiplexed address/data bus to access external memory shared by the host processor  50 . A latch is used to capture and hold the driven address while the ST-NIC  62  reads or writes to the addressed memory through an address data bus and control logic block  52 . 
     The controller  62  also provides status outputs through the data bus and control logic  52 , indicative of link, transmit and collision. The link and collision data are shown as combined into one LED indicator at  70 . Since the link status lights the LED constantly when a valid link is plugged into the Ethernet port  60 , the LED display is interrupted when a collision occurs. The transmit LED is illuminated during a transmit mode of operation through the Ethernet port  60 . 
     At this time, it should be noted that three other LED indicators in the group  70  are also shown in FIG.  2 . These are “halt”, “on-line” and “make busy”. The “halt” indication is supplied from the processor  50 ; whereas the “on-line” and “make busy” indicators are controlled by a DUART  68 . The status indicators  70  are provided to give the user a general idea as to the operational state of the IPC card  30 . There are also standard connectors to provide interfaces to the customer&#39;s network, installer programming terminal, and the telephone system&#39;s back plane signals. These standard connectors are not shown, since they are well known and widely used. 
     A control register in the address/data bus and control logic  52  is used to place the ST-NIC controller  62  in and out of reset. Using bit  0 , writing a zero places the ST-NIC  62  in reset. Reading the same register and bit, software is able to monitor the state of the ST-NIC  62  reset signal. Any on card (IPC card  30 ), system, or software generated reset causes the ST-NIC  62  to default to its reset state. 
     A key element to the interface provided by the IPC card  30  for converting PCM voice signals to packetized digital signals, and vice versa, is a number of digital signal processors (DSP)  56 . As indicated in FIG. 2, eight of the DSP&#39;s  56  are provided. This number, however, is arbitrary; and the number eight is a convenient number for many LAN systems. By using eight digital signal processors  56 , eight lines over the Ethernet may be employed. If additional lines are required, additional DSPs  56  may be added. It is apparent from an examination of FIG. 2 that the DSPs  56  are connected in parallel with a PCM highway  58 . The DSPs  56  are controlled by a digital cross point switch  54  and by the processor  50  through the address/data bus and control logic  52 . It should be noted that the DSP&#39;s  56  include memory for program RAM and memory for data RAM, along with connections for DMA channels and connections for serial ports. 
     Voice data from the PBX back plane  20  is transferred through the back plane interface decode logic  31  to the digital cross point switch  54 , from which it is routed to the serial port of the DSP&#39;s  56 . The selected one of the DSP&#39;s  56 , as chosen by the control logic  52 , compresses the PCM voice data using an algorithm downloaded from the host processor  50 . The algorithm may be any suitable compression algorithm. Currently, a suitable conversion between PCM voice data and TCP/IP follows the G.729 standard to produce TCP/IP Ethernet packets which contain encoded voice at the rate of eight kilobit/second. Although this is a current conversion algorithm which is widely used, this conversion format is expected to change in accordance with a customer&#39;s network requirements. The particular conversion algorithm is not important. The significance, however, is that the digital signal processors  56  convert PCM information into packetized voice information for communication with IP key sets on the LAN and the WAN. 
     Conversely, when packetized information is supplied to the IPC from the Ethernet port  60 , this information again is supplied under the control of the processor  50  through the address/data bus and control logic  52  to the digital signal processors  56  by way of the cross point switch  54 , where the packetized data is converted to standard PCM voice on the PCM highway  58 . This decoded PCM voice data then is supplied through the cross point switch  54  and the back plane interface decode logic  31  to the PBX back plane for utilization through the PBX with the PSTN or standard key sets  32  associated with the PBX. The DSP&#39;s  56  operate to convert data in both directions to provide a seamless interface between the packetized Ethernet (LAN/WAN) voice data and PCM voice data, essentially operating as a bridge between these two different protocols. 
     It should be noted that synchronization is provided by a modified frame sync which is activated at the start of the standard PBX back plane time slots. This modified frame sync is activated at the start of time slot  31 , instead of between time slots  31  and  0  (62.5 microseconds before normal frame sync). This allows the DSP&#39;s  56  ample time to prepare for the start of a new frame. 
     Each DSP  56  obtains program data (the operating algorithm) from the processor  50  through its IDMA port. The processor  50  first generates a DSP chip select at an address indicating that the chip  56  is available. The address, in the form of data, is latched when the bus cycle of the PBX back plane  20  is complete, after which data is then written or read from the DSP. Internal registers are accessed using this method as well. The system also may be designed with each of the DSP&#39;s  56  having their own chip select in conjunction with address location, which selects all the DSPs  56  at once. Resets then are controlled through a register which can be used to assert or de-assert resets on any combination of DSP&#39;s  56 . This feature allows multiple DSP&#39;s  56  to be loaded with the same program code, at the same time. 
     It should be noted that the RS/232 serial port  64 , connected through a serial transceiver  66  to the address/data bus and control logic  52 , is used only for maintenance and to initially program the data mapping for the system to set up the addresses for the DSP&#39;s, as described above. At all other times, this port is unconnected and unused in the normal operation of the system. 
     As indicated in FIG. 2, non-volatile memory consists of a flash memory  76 , which has a portion in it reserved for the boot sector. A static RAM  74  consists of a static memory with a portion shared with the host processor  50  and with the Ethernet controller  62  DMA memory space. Programming the flash memory  76  is accomplished with the use of the boot block programming connector (BBPC) which contains a storage in EPROM or flash. When installed, the EPROM base address of the BBPC is defined to be separate from the flash memory base address where vectors and code then can be programmed. The BBPC with flash memory can be programmed while it is installed. When it is in the program mode, the BBPC utilizes a pre-defined address range. The primary flash and RAM address remain unchanged, allowing the BBPC to be programmed by the primary flash. 
     The DUART  68  provides an interface between the host processor  50  and an external terminal by way of the RS-232 driver configured for the DCE mode. As noted above, this port  64  is only used during maintenance and initial programming of the DSP&#39;s  56  on the card  30 . As stated previously, the DUART also provides status and/or control registers for the LED&#39;s indicative of “on-line” and “make busy”, cross point, card ID, flash, and back plane interface control. 
     Data transfer within the interface card  30  is provided by the address/data bus control logic  52 , as mentioned throughout the foregoing description. This also includes processor interrupt control for both the processor  50  that is resident on the interface card, and the processor of the system, which is coupled to the CPU card  24  shown in FIG.  1 . Also included is a data/address bus with associated control logic to decode and route information to the appropriate device memory location assignment. 
     The foregoing description of the preferred embodiment of the invention is to be considered as illustrative and not as limiting. Other versions of the system envision the extension of data network protocols to allow a wider variety of data devices to communicate with the telephone systems. This includes gateway capabilities as defined H.323 and related standards. Because multimedia data protocols are in a constant state of flux, the design has taken into account the need for relatively frequent changes in the firmware contained in the flash memory, as well as future increases in DSP processing power. For that reason, the processing power of the individual DSP blocks  56  has not been addressed. These are standard components currently available for effecting the digital signal processing required of the system and described above. Various other modifications and changes will occur to those skilled in the art for performing substantially the same function, in substantially the same way, to achieve substantially the same result without departing from the true scope of the invention as defined in the appended claims.