Abstract:
A service channel is used in a bi-directional communications network such as a DOCSIS cable modem system, fixed broadband wireless system, or other network to transmit in the upstream direction. The service channel communications do not require a properly functioning downstream communications link to operate. Remote devices may thusly be able to indicate to a central server various status related data that may assist in identifying problems with the network or aid in proper installation of devices on the network.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    a. Field of the Invention  
           [0002]    The present invention pertains to two-way communication networks and specifically to end-of-line status monitoring of the point-to-multipoint portion of a shared, two-way communication network.  
           [0003]    b. Description of the Background  
           [0004]    Shared communication networks with point-to-multipoint transmission in the downstream direction, and multipoint-to-point transmission in the upstream direction pose many problems for establishing communication protocols. For example, in a two-way hybrid fiber-coaxial (HFC) cable television distribution network, many cable modems may compete for communication bandwidth in both the upstream and downstream directions. A currently accepted standard protocol is Data-Over-Cable Service Interface Specification (DOCSIS) that uses the downstream path to indicate exactly when each modem is able to transmit in the upstream direction. Such protocols are used in many applications including wireless protocols such as IEEE 802.16 and other protocols.  
           [0005]    Such protocols require that the downstream communication path must be properly functioning for any upstream communication to happen. In cases where the downstream path may have a signal to noise ratio (SNR) too low for the cable modem to receive data, the downstream path may be unusable while the upstream path may function correctly. In the example of a cable television plant, causes of such low signal to noise ratio may be poor plant design, improperly functioning amplifiers and other network components, external environmental noise, damaged cables, or other factors.  
           [0006]    When a communication device is connected to a network that requires a good downstream connection to properly function, and the downstream connection has a low signal to noise ratio or is otherwise troublesome, that device may not be able to function at all. In such cases, a service call may require a service technician to respond to a subscriber&#39;s location. Such service calls are very expensive and time-consuming.  
           [0007]    It would therefore be advantageous to provide a system and method for end-of-line measuring and monitoring the signal quality of downstream communications and transmitting the measurements upstream without requiring the downstream channel to be fully functional. It would be further advantageous if the method could be performed automatically when a downstream channel is non-functional.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention overcomes the disadvantages and limitations of the prior art by providing a system and method for upstream-only communication for networks where the primary communication mechanism requires both upstream and downstream signals to properly function. The system and method utilizes an upstream service channel for periodic transmissions that may occur at random intervals so that collisions may be avoided. Alternatively, the system and method utilizes the upstream service channel for informing the central control management system only when signal quality of the downstream transmission path is determinated to be below a pre-determined threshold.  
           [0009]    The present invention may therefore comprise a method for upstream communications in a bi-directional communications network wherein the primary form of upstream communication requires properly functioning downstream communication wherein the network is characterized by a central station and a plurality of remote transceivers comprising: providing at least one service channel outside of the bandwidth allocated for the upstream communication; detecting at least one problem with the downstream communication by one of the remote transceivers; creating a status transmission comprising an identifier for the one of the remote transceivers; sending the transmission on the at least one of the service channels from the one of the remote transceiver to the central station using the service channel; repeating the step of sending the transmission after waiting a predetermined period of time; receiving the transmission by the central station; and identifying the one of the remote transceivers at the central station.  
           [0010]    The present invention may further comprise a bi-directional communications network wherein the primary form of upstream communication requires properly functioning downstream communication comprising: at least one service channel outside of the bandwidth allocated for the upstream communication; a central station capable of sending downstream transmissions and receiving upstream transmissions, the upstream transmissions being transmitted within a predetermined upstream bandwidth; and a plurality of remote transceivers capable of receiving the downstream transmissions and sending the upstream transmissions, at least one of the remote transceivers capable creating a status transmission comprising an identifier for the remote transceivers, sending the transmission on the at least one service channel outside of the pre-determined upstream bandwidth from the one of the remote transceiver to the central station using the service channel.  
           [0011]    The advantages of the present invention are that upstream communications from a remote device may occur even when downstream channels are not functioning. These communications may assist technicians in diagnosing problems with the network or with installation of various components of the network, thus drastically reducing the time and cost of sending service personnel to the customer premises. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    In the drawings,  
         [0013]    [0013]FIG. 1 is an illustration of an embodiment of the present invention of a cable television network with status monitoring cable modems.  
         [0014]    [0014]FIG. 2 is an illustration of an embodiment of the present invention of a status monitoring cable modem.  
         [0015]    [0015]FIG. 3 is an illustration of the frequency spectrum wherein the downstream channel, standard upstream channel, and service channel are located.  
         [0016]    [0016]FIG. 4 is an illustration of an embodiment of the present invention wherein three cable modems are transmitting their respective status at random intervals on the service channel.  
         [0017]    [0017]FIG. 5 is an illustration of an embodiment of a typical communication packet sent on the service channel.  
         [0018]    [0018]FIG. 6 is an illustration of an embodiment of the present invention of a method for transmitting on a service channel when the downstream communication is impaired.  
         [0019]    [0019]FIG. 7 is an illustration of a wireless embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    [0020]FIG. 1 illustrates an embodiment  100  of the present invention of a two-way hybrid fiber-coax (HFC) cable television network with status monitoring cable modems. The cable modem termination system (CMTS) media access control (MAC)  102  is a system of hardware and software that co-ordinates the access of the upstream and downstream transmissions of a plurality of cable modems of the two-way cable television network. The CMTS  104  comprises the CMTS-MAC  102 , a downstream transmitter  106 , an upstream receiver  108 , and a service channel receiver  110 . The transmitter  106  and receivers  108  and  110  may be connected through a diplex filter  112  and a fiber optic cable  114  to a fiber node  116 . The fiber node  116  is connected to cable modems  118  via bi-directional distribution amplifier  117 , coaxial cable  120 , tap  122  and drop cable  124 .  
         [0021]    The CMTS-MAC  102  further comprises a DOCSIS-MAC  107  and status monitoring MAC  109 . The DOCSIS-MAC co-ordinates the transmissions of the downstream transmitter  106  and the upstream transmitters in cable modems  118  for normal cable modem operations. The status monitoring MAC  109  receives and decodes the status-monitoring packets from the service channel receiver  110 , and then relaying the status-monitoring packets to a network manager  111 . The network manager  111  provides diagnostic, alerting, and other information to service personnel as well as other functions.  
         [0022]    The embodiment  100  illustrates a separate service channel that is used by the CMTS  104  for receiving one-way communications from the cable modems  118 . The service channel  306  may be used by the cable modems  118  for various functions. For example, in cases where the downstream communication is impaired to the point where normal two-way communication is ineffective, a cable modem  118  may send a status message to the network manager  111  to indicate a problem with the particular downstream transmission path connected to the cable modem  118 . In such cases, a service call or other maintenance may be required. In another example, performance data may be collected by the modem and transmitted periodically to the network manager  11 .  
         [0023]    Many problems may occur during installation of the cable modem or other two-way communication device on the cable network. Such problems may prohibit proper functioning of the cable modem. For example, incorrectly attached cabling, malfunctioning cable modem, improper software installation, or even having the power disconnected to the cable modem may be problems with the installation. If a subscriber has a problem with the cable modem installation, the subscriber may call a service technician that can verify proper connections over the phone. If the subscriber can properly attach the cable modem, and the cable modem can sense, diagnose, and transmit downstream problems to the technician with the present embodiment, the technician can determine that a problem may exist with the downstream channel.  
         [0024]    The cable television network is illustrated only to demonstrate connectivity, and is not intended to show all of the various components that make up a complete network. Devices such as line-extender amplifiers, filters, splitters, electrical to optical converters, optical to electrical converters, upconverters, downconverters, and other devices may contribute to impairments in the transmission lines.  
         [0025]    Standard cable modems may require both upstream and downstream communication lines to be at least partially operational for communication between the cable modem  118  and the CMTS-MAC  102  to occur. In such situations, the downstream channel may have a timing synchronization and bandwidth allocation protocol that establishes a specific time and sequence when the cable modem  118  is to transmit upstream. When the downstream channel has a large amount of impairments and therefore a low signal to noise ratio, the cable modem  118  may be unable to transmit upstream, according the conventional DOCSIS-MAC protocol  
         [0026]    [0026]FIG. 2 illustrates an embodiment  200  of a status monitoring cable modem  202 . The cable modem  202  comprises a measuring device  204 , the cable modem media access control (MAC)  206 , and a transmitter  208 .  
         [0027]    The status monitoring cable modem  200  may collect status parameters and transmit the parameters upstream. Further, the cable modem  200  may transmit the status parameters upstream in a one-way fashion that does not require proper downstream communication. For example, the cable modem  200  may use the transmitter  208  to send a status packet upstream on a special service channel.  
         [0028]    The measurement device  204  may be a hardware component, software component, or combination of hardware and software that can detect and optionally measure data with the downstream signal. In some embodiments, the measurement device may measure signal to noise ratio, power level, or other performance measurements. In other embodiments, the device  204  may use software routines to monitor other factors that affect the performance of the cable modem  202 . Such parameters may include the software/firmware/hardware revisions of various components of the cable modem  202 , any status parameters including response to training signals, or other parameters. Those skilled in the arts will readily appreciate that the status parameters to be collected may be varied while still keeping within the spirit and intent of the present invention.  
         [0029]    [0029]FIG. 3 illustrates the frequency spectrum  300  wherein the downstream channel  302 , standard upstream channel  304 , and upstream service channel  306  are located. The service channel  306  may be located in a region unused for other purposes and may be considerably noisy for high-speed communications. Transmissions on the service channel  306  may be designed with a large tolerance for noise and other variables such as using a login symbol period, robust modulation schemes such as BPSK or QPSK, and suitable error protection and correction coding.  
         [0030]    In some embodiments, several service channels may be used so that one service channel is not overloaded by many cable modems transmitting simultaneously. In such embodiments, cable modems may be assigned different service channels as part of the firmware or software installed in the cable modem from the factory. In other embodiments, the cable modem may switch between service channels at random or based upon a user input.  
         [0031]    [0031]FIG. 4 illustrates an embodiment  400  of the present invention wherein three cable modems are transmitting their respective status at random intervals on the service channel. The transmissions of cable modem A  402  is shown on a timeline. Similarly, cable modem B  404  and cable modem C  406  are shown. In the illustration, each cable modem is transmitting a status package on the service channel. Transmissions  408  and  410  occurred substantially simultaneously such that a collision occurred between the two transmissions. In such a case, neither transmission would have been received by the CMTS. Because the status of each cable modem is repeatedly sent and done so at random intervals, the CMTS has a high likelihood that at least one of the multiple transmissions from each of the cable modems would have been received.  
         [0032]    In a typical cable television distribution network, many cable modems may be transmitting on the service channel simultaneously. In some embodiments, every cable modem may be repeatedly sending status information on the service channel. In other embodiments, only those cable modems that have no downstream communication may be transmitting on the service channel. In still other embodiments, those cable modems with signal to noise ratios or other parameters that are below a certain threshold may be transmitting on the service channel.  
         [0033]    Those skilled in the art may utilize contention-based MAC protocol such as Aloha or slotted Aloha for transmitting the status-monitoring packets. To minimize collisions, a suitable back-off algorithm such as binary-exponential backoff or P-persistent back-off can be used. The slot time for slotted Aloha may be typically set to greater than the maximum loop delay for the upstream and downstream transmission paths, plus the time duration of the status-monitoring packet burst. Such techniques, as well as other techniques may be used by those skilled in the art while maintaining within the scope and intent of the present invention.  
         [0034]    [0034]FIG. 5 illustrates an embodiment  500  of a typical communication packet sent on the service channel. Block  502  is a preamble, block  504  is the MAC management header, which may contain a cable modem unique identifier such as its MAC address, block  506  is the downstream signal to noise ratio, status indicators, and/or other status information, block  512  is the cyclical redundancy check (CRC) information, and block  514  is the forward error correction (FEC) information. Those skilled in the art will appreciate that other transmission packet configurations may be used while maintaining within the spirit and intent of the present invention.  
         [0035]    [0035]FIG. 6 illustrates an embodiment  600  of a method for transmitting on a service channel when offline. The cable modem is connected to the network in block  202 , and the downstream signal is sensed in block  204 . If no downstream signal is present in block  204 , the cable modem transmits its status upstream on a service channel in block  206  before waiting a random period of time in block  208  and returning to check for a downstream signal in block  204 . If a downstream signal is present in block  204 , the normal, two-way communication handshaking is established in block  210 . The process returns to block  204  and, should any problem with the downstream signal occur, the process is repeated.  
         [0036]    The present embodiment illustrates a method whereby a cable modem transmits on the service channel only when a problem exists. Such an embodiment may keep the number of cable modems transmitting on the service channel to a minimum. The benefits are that the service channel may be monitored to identify problems with the network, as the only cable modems that are transmitting are those that are experiencing a problem with the downstream communication.  
         [0037]    In a network where multiple devices must communicate on a limited bandwidth, synchronized transmissions utilize the bandwidth efficiently so that hundreds if not thousands of devices may share the same medium. Such transmissions rely on proper functioning of both upstream and downstream paths. If the downstream path is not properly functioning, the device may be capable of communicating relevant and useful information to the network controller. This information may be used by service technicians in assisting the consumer in proper installation of the equipment as well as by maintenance engineers to identify problem areas of the network. The difficulty lies in having many devices transmit on the medium simultaneously. Thus, a separate service channel with an appropriate protocol may be used to tolerate multiple collisions while still transmitting the necessary and useful information.  
         [0038]    Other embodiments of the present invention may include different types of networks with network topologies similar to the two-way HFC. For example, wireless two-way networks such as cellular phone networks, IEEE 892.16 networks, and other wireless networks may benefit from having a dedicated upstream-only communication path for the network devices.  
         [0039]    [0039]FIG. 7 illustrates a wireless embodiment  700  of the present invention. A wireless server  702  contains a downstream transmitter  704 , a standard upstream receiver  706 , and a service channel receiver  708 . The server  702  is connected to one or more basestations  710  and  712  which transmit to wireless devices  714 ,  716 ,  718 , and  720 .  
         [0040]    The wireless devices may be any type of communication device that communicates through a radio signal. Examples include telephony devices, wireless data network devices, or any other wireless device arranged in a point to multipoint communication network.  
         [0041]    Within each wireless device, a status monitoring routine may monitor the downstream performance, similar to the status monitoring-MAC described above for a cable modem. Any impairments due to over-the-air interferences, device malfunctions, or other problems can be transmitted to the server  702  via a service channel and received by the service channel receiver  708 . The message may then be transmitted to a network manager for action. In this manner, critical information regarding the transmission network or the wireless device may be transmitted without requiring an active two-way communication path.  
         [0042]    The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and other modifications and variations may be possible in light of the above teachings. The embodiment was chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments of the invention except insofar as limited by the prior art.