Abstract:
The present invention provides redundant, inverse multiplexing over ATM (R-IMA). An ATM control system may include line interface circuitry, transmission convergence logic, IMA logic, and a cross-connect coupling the IMA logic of the redundant ATM control systems to control activity. The line interface circuitry terminates n DSx lines and is adapted to receive n incoming ATM over DSx traffic streams and transmit n outgoing ATM over DSx traffic streams corresponding to the n DSx lines. The transmission convergence logic is adapted to recover incoming ATM cell streams from the incoming ATM over DSx streams and generate the outgoing ATM over DSx traffic streams to form n outgoing ATM cell streams. The IMA logic is adapted to combine the incoming n ATM cell streams to form an incoming combined ATM cell stream, and distribute ATM cells from an outgoing combined ATM cell stream to create the n outgoing ATM cell streams.

Description:
FIELD OF THE INVENTION 
     The present invention relates to incorporating inverse multiplexing over ATM (IMA) technology, and in particular, providing redundant IMA for supporting both voice and data transmission to customer premise equipment. 
     BACKGROUND OF THE INVENTION 
     With the growing number of remote local area networks (LANs) that require linking to central locations over wide area networks (WANs), and the ever-increasing demand for on-line services and data-intensive applications, there is a growing need for high bandwidth WAN access. Increasing bandwidth requirements and delay constraints imposed by real-time-interactive applications such as video conferencing, audio and video streaming, and basic telephony, dictate that WAN access maintain high levels of integrity. 
     To provide such integrity, asynchronous transfer mode (ATM) has become the technology of choice for maintaining integrity and reducing the complexity of WAN communications. ATM offers many benefits, including speed, scalability, traffic management, and the capability to combine LAN and WAN functions through a uniform protocol. Unfortunately, as enterprises require greater WAN access to support ever-increasing traffic loads, they are faced with either paying for very expensive T 3  or E 3  links that often go substantially unused, or adding additional T 1  or E 1  access lines, which often create multiple, parallel networks. 
     Inverse multiplexing over ATM (IMA) offers a solution to the above paradigm. IMA is a user-to-network interface standard approved by the ATM Forum in 1997, and specifies a transmission method in which ATM cells are distributed across multiple T 1  or E 1  lines, then reassembled at a terminating point while maintaining the original order of the ATM cells. By facilitating the transport of ATM cells over more cost-effective T 1  and E 1  lines, IMA facilitates the extension of ATM to areas having access to T 1  or E 1  lines. Thus, in situations where an application was limited to the 1.544 megabits per second provided by a T 1  line, multiple T 1  lines may be used to incrementally increase the unified traffic flow in a scalable fashion. 
     Unfortunately, IMA is data-focused, and does not incorporate the required redundancy for traditional telephone. Traditional telephone networks, such as the public switched telephone network (PSTN), require redundancy throughout the network and will not tolerate single points of failure. Thus, traditional telephony applications have not been able to take advantage of the bandwidth and scalability provided by IMA. Accordingly, there is a need for a way to provide redundancy in an IMA architecture to extend the benefits of IMA to voice telephony. 
     SUMMARY OF THE INVENTION 
     The present invention provides redundant, inverse multiplexing over ATM (R-IMA). An ATM control system may include line interface circuitry, transmission convergence logic, IMA logic, and a cross-connect coupling the IMA logic of the redundant ATM control systems to control activity. The line interface circuitry terminates n DSx lines and is adapted to receive n incoming ATM over DSx traffic streams and transmit n outgoing ATM over DSx traffic streams corresponding to the n DSx lines. The transmission convergence logic is adapted to recover incoming ATM cell streams from the incoming ATM over DSx streams and generate the outgoing ATM over DSx traffic streams to form n outgoing ATM cell streams. The IMA logic is adapted to combine the incoming n ATM cell streams to form an incoming combined ATM cell stream, and distribute ATM cells from an outgoing combined ATM cell stream to create the n outgoing ATM cell streams. 
     In particular, the cross-connect facilitates direct or indirect communications between the IMA logic of each ATM control system to control switching between active and inactive states and provide limited information to help maintain synchronous operation of each ATM control system and its corresponding IMA logic. The ATM control systems operate regardless of being active or inactive, and operate synchronously to minimize the impact of switching activity in the event of a fault on the active ATM control system. 
     When a fault occurs on the active ATM control system, the IMA logic of the active control system will send a switch of activity message to the IMA logic of the inactive control system and transition from an active to an inactive state, preferably upon receiving confirmation of receipt of the switch of activity message from the inactive ATM control system. The inactive ATM control logic is configured to receive the switch of activity message from the active ATM control system and transition to the active state. As noted, the inactive ATM control system may send confirmation of receipt of the switch of activity message prior to transitioning to an active state. 
     Each ATM control system will preferably include control logic cooperating with the IMA logic to control activity of the ATM control system. Preferably, a transmit function in the line interface circuitry is selectively operable, and the control logic is adapted to activate the transmit function when the ATM control system is active and deactivate the transmit function when the ATM control system is inactive. Further, the DSx lines may be wire-ORed between the line interface circuitry of each ATM control system. 
     The ATM control system may also include ATM switch logic adapted to receive and combine voice-based ATM cells from a telephony processor and data-based ATM cells from a telephony interface to form the outgoing combined ATM cell stream. The switch logic will also receive the incoming combined ATM cell stream and send voice-based ATM cells contained therein to the telephony processor and data-based ATM cells contained therein to the telephony interface. The telephony processor is adapted to receive and convert the voice signals from the telephony interface to voice-based ATM cells for the switch logic of the ATM control system. The telephony processor is also adapted to receive and convert the voiced-based ATM cells from the switch logic of the ATM control system to voice signals for the telephony interface. 
     Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the invention, and together with the description serve to explain the principles of the invention. 
         FIG. 1  is a block representation of an access network according to one embodiment of the present invention. 
         FIG. 2  is a block representation of an ATM control card used in an access module of one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the invention and illustrate the best mode of practicing the invention. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the invention and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims. 
     With reference to  FIG. 1 , a communication environment  10  is illustrated wherein various customer premise equipment (CPE)  12  is provided access to an ATM network  14  via an access module  16 . Each CPE  12  is directly or indirectly coupled to a line card  18  via an analog-based telephone line  20 , which is typically copper-based twisted pair wire. The line cards  18  may support analog voice, modulated data, or a combination thereof, depending on the CPE  12 . For example, telephones  12 A may provide traditional voice and DTMF tones to facilitate bi-directional communications with the line cards  18 . Alternatively, the telephone lines  20  may support various data access technologies. A computer  12 B may be connected to a line card  18  via a modem  12 C, such as a digital subscriber line (DSL) modem  12 C, to facilitate a data connection between the computer  12 B and the corresponding line card  18 . Mixing or summation circuitry  12 E may be provided in association with the DSL modem  12 C to allow voice from another telephone  12 D to share bandwidth with the data provided by the computer  12 B. For the purposes of description, assume that each of the telephone lines  20  is a digital subscriber line. Those of ordinary skill in the art will recognize the various configurations the telephone lines  20  may take. 
     On the opposite side of the access module  16 , one or more gateways (GWs)  22 , which lead to the ATM network  14 , are redundantly coupled to ATM control cards (ACCs)  24  via DS 1  links  26 . The DS 1  links  26  support DS 1  or E 1  services, and in particular, support ATM over DS 1  or E 1 . When supporting voice and data, the traffic sent to and received from the ATM network  14  via the gateways  22  and the DS 1  links  26  will include both voice and data traffic, which is broken into voice over ATM traffic  28  and data over ATM traffic  30 . The data over ATM traffic  30  is switched to the appropriate line card  18 , which will recover the data and send it to the appropriate customer premise equipment  12  via the associated digital subscriber line  20 . The voice over ATM traffic  28  is sent over a redundant ACC  24  to an internet telephone processor (ITP)  32 , which will recover the voice signal, provide any signal processing required for the voice signal, and send the signals to the appropriate line card  18 , which will forward the voice signals to the CPE  12  via the associated digital subscriber line  20 . For traffic sent from the CPEs  12  to the ATM network  14 , the line cards  18  will send the voice signals to the ITP  32  for signal processing, and then multiplex the digitized voice into ATM cells, which are streamed to the ACC  24 . The ACC  24  will forward the cells to the ATM network  14  via the gateways  22  and the DS 1  links  26 . The line cards  18  will convert any data received from the CPEs  12  and forward the streams of ATM cells to the redundant ACCs  24 . The active one of the two redundant ACCs  24  will send the voice and data ATM cells to the ATM network  14  via the gateways  22  and the DS 1  links  26 . 
     Preferably, the ACCs  24  implement inverse multiplexing over ATM (IMA), wherein the ATM cells for any given application or combination of applications are fanned out across multiple DS 1  links, and then reassembled at the receiving end on the opposite side of the ATM network  14  in the original order in which they were transmitted. Thus, the bandwidth of multiple ones of the DS 1  links  26  can be shared to provide a fat ATM pipe, or gateway to the ATM network  14  and beyond. Thus, ATM access can be extended to the access module  16  to provide high bandwidth, high speed access to an ATM network  14  for customer premise equipment  12  in an efficient and effective manner. 
     In an effort to provide the redundancy required for voice telephony, the ACCs  24  operate in a redundant fashion, the details of which are disclosed in association with  FIG. 2 . The redundant ACCs  24  illustrated in  FIG. 2  each include a line interface unit (LIU)  36 , framer logic  38 , transmission convergence (TC) logic  40 , IMA logic  42 , and a switch matrix  44 . The LIUs  36  provide the physical interface to the DS 1  links  26 . Each DS 1  link  26  is “wire-ORed” to the LIUs  36  on both ACCs  24 . For transmission, only the LIU  36  of the active ACC  24  will transmit; however, for reception, ATM over DS 1  traffic is received simultaneously by the LIUs  36  on both the active and inactive ACCs  24 . During reception, the ATM over DS 1  traffic is received by the LIUs  36  and sent to the framer logic  38 , which will forward the ATM over DS 1  traffic to the transmission convergence logic  40 , which will recover the ATM traffic and forward the individual streams to the IMA logic  42 . The IMA logic  42  will effectively recombine the ATM cells recovered from each of the DS 1  links in the order in which they originated, and send the resultant ATM stream to the switch matrix  44 . Based on the type of information in the ATM cells and their respective destinations, the switch matrix  44  will direct the ATM cells either to the IPT  32  (for voice traffic  28 ) or directly to the corresponding line cards  18  (for data traffic  30 ). 
     For traffic destined for the ATM network  14  from the CPE  12 , voice over ATM traffic  28  will enter the switch matrix  44  from the ITP  32  and be directed over a high bandwidth ATM line to the IMA logic  42 , which will multiplex the incoming stream of ATM cells from the switch matrix  44  to the various channels in the transmission convergence logic  40  corresponding to the DS 1  links  26 . The transmission convergence logic  40  will layer the ATM cells on DS 1  signaling and send the resultant ATM over DS 1  signal to the framer logic  38 , which will synchronize the corresponding DS 1  frames and present the synchronized, ATM over DS 1  signal to the LIU  36 , which will forward the corresponding ATM over DS 1  signals to the respective DS 1  links  26 , if the LIU  36  is in an active ACC  24 . If the LIU  36  is in an inactive ACC  24 , the ATM over DS 1  signals are not transmitted over the DS 1  links  26 . Thus, the outgoing traffic originating from the CPEs  12  is combined over a wide bandwidth ATM link between the switch matrix  44  and the IMA  42  prior to being spread across multiple DS 1  links  26 . The ATM over DS 1  traffic will be sent across the ATM network  14  to a corresponding access module  16 , wherein the respective ATM over DS 1  signals will be recombined such that the ATM traffic can be recovered, and ultimately the voice and data carried therein can be recovered and directed to the appropriate networks or other CPEs  12 . 
     As noted, the ACCs  24  are provided in pairs to provide redundancy in case one of the ACCs  24  fails. In an effort to minimize the impact of one of the ACCs  24  failing and the process of switching activity to the inactive ACC  24 , the IMAs  42  of both ACCs  24 , regardless of activity, are synchronized. In the event of a fault on the active ACC  24 , activity can be switched quickly and cleanly enough that the impact on voice or data is negligible, or at least minimized. Since the DS 1  links  26  are shared in a wired-OR configuration, incoming DS 1  frames arrive synchronously, which eliminates the need to separately synchronize the receiving side of the IMA  42 . At least one cross-connect  46  is provided between the IMAs  42  of the two ACCs  24  to allow the inactive IMA  42  to be synchronized in hardware to the active IMA  42 . Thus, the cross-connects  46  operate to synchronize the IMAs  42  for transmission across the DS 1 s  26  to the ATM network  14 . In this transmit direction, the IMAs  42  will cooperate with control logic  48  to disable the LIU  36  in the inactive ACC  24  to prevent it from transmitting information toward the ATM network  14 . 
     Further, each ACC  24  may include some form of synchronization logic  50  for the framer logic  38  to ensure outgoing frames to the DS 1 s  26  are internally synchronized, although the DS 1  frames would not be transmitted by the LIU  36  on the inactive ACC  24 . The synchronization logic  50  may run off of a highly accurate reference frequency, or may be tied to external signaling from the network or from a timing system, such as a GPS. 
     When a fault occurs on the active ACC  24  (A), the control logic  48  for the active ACC  24  (A) will request the control logic  48  of the inactive ACC  24  (B) to assume activity. When the inactive ACC&#39;s control logic  48  acknowledges the request, the active ACC&#39;s control logic  48  will disable the transmit side of its LIU  36 , and the inactive ACC&#39;s control logic  48  will activate the transmit function of its LIU  36 . As such, the formerly inactive ACC  24  (B) becomes active, and vice versa. The switch control signaling may take place and be initiated in software or hardware, depending on the nature of the failure. Those skilled in the art will recognize the various techniques for monitoring various types of faults throughout the ACCs  24  and providing signaling between the ACCs  24  in hardware or software to facilitate a switch of activity. 
     In an effort to keep the IMAs  42  synchronized, the amount of information necessary to swap between ACCs  24 , and in particular between the IMAs  42 , during a switch of activity is minimized. As such, state machines, counters, and the like implemented in the IMAs  42  and the control logic  48  independently run in a synchronous fashion, regardless of the state of activity. 
     During operation, certain information is provided between the IMAs  42 , and in particular from the active IMA  42  to the inactive IMA  42  to help in fault detection as well as maintaining synchronization. Various state information bearing on IMA frame sequence numbers and link transmit states, along with status control information, are provided to the inactive IMA  42  via the cross-connect  46 . The inactive IMA  42 , alone or in conjunction with the control logic  48 , processes the information provided by the active IMA  42 , and if errors are detected, the inactive IMA  42  or control logic  48  may signal the active ACC  24  to trigger a switch of activity or request information explaining any perceived errors. Thus, when an inactive IMA  42  switches to an active state, the active IMA  42  will switch from a receive mode to a transmit mode to provide the error detection and synchronization information, while the newly inactive IMA  42  will switch from a transmit mode to a receive mode over the cross-connect  46 . 
     Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present invention. For example, the line cards may support any digital services format, including DS 3 , and analog and digital telephony line types. Similarly, the present invention is described in relation to U.S. standards, but is equally applicable to European standards. Thus, the present invention is equally applicable to lines capable of providing E 1  services instead of T 1  services. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.