Abstract:
A system is described which provides bidirectional transport of data at different data rates for each direction over a shared medium. In one embodiment, the different data rates are accomplished using different modulation techniques. For example, in the downstream direction, quadrature amplitude modulation (QAM)  64  is used and in the upstream direction orthogonal frequency division multiplexing (OFDM) is used. The QAM  64  modulation provides for a higher number of bits per hertz in a transmission channel. By using QAM  64  modulation, down stream transmission rates on the order of 30 megabits per second (Mbps) in a 6 MHz channel can be achieved. A number of 6 MHz channels can be combined to provide for even higher data rates.

Description:
CROSS REFERENCE 
     This application is a continuation-in-part of U.S. application Ser. No. 09/397,374, filed Sep. 16, 1999 (abandoned), which is a divisional of U.S. application Ser. No. 08/673,002, filed Jun. 28, 1996 (now U.S. Pat. No. 6,334,219), which is a continuation-in-part of U.S. application Ser. No. 08/650,408 filed May 20, 1996 (abandoned). 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to the field of telecommunications and, in particular, to a system for the asymmetrical transport of data. 
     BACKGROUND 
     Telecommunications networks were developed to carry narrow bandwidth (low speed) voice communications between users at geographically dispersed locations. More recently, these networks have been used to transport data as well as voice communications. Conventionally, computers use modems to transmit data over a telecommunications network. Typically, these modems can transmit data with a rate up to approximately 56 kilobits per second (kbps) although modems with higher rates are available. 
     Telecommunications services are in high demand. And the demand continues to grow. Businesses, educational institutions, and individuals all have communications needs. These needs are met by an ever-widening field of service providers. For example, many cable companies have begun to offer telecommunications services, e.g., telephony, and data transmission, over their existing cable plant. 
     One problem with the transmission of data over existing telecommunications networks is the speed at which data is transmitted over the network. For example, some conventional modems can take up to an hour or more to download large files from the Internet. 
     For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a system for transporting data at high data rates. 
     SUMMARY 
     The above mentioned problems with telecommunications systems and other problems are addressed by the present invention and will be understood by reading and studying the following specification. A system is described which provides bidirectional transport of data at different data rates for each direction over a shared medium. In one embodiment, the different data rates are accomplished using different modulation techniques. For example, in the downstream direction, quadrature amplitude modulation (QAM)  64  is used and in the upstream direction orthogonal frequency division multiplexing (OFDM) is used. The QAM  64  modulation provides for a higher number of bits per hertz in a transmission channel. By using QAM  64  modulation, down stream transmission rates on the order of 30 Megabits per second (Mbps) in a 6 MHZ channel can be achieved. A number of 6 MHZ channels can be combined to provide for even higher data rates. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of one embodiment of a system for the asymmetrical communication of data according to the teachings of the present invention. 
         FIG. 2  is a block diagram of an embodiment of a data head end for the asymmetrical communication of data over a network. 
         FIG. 3  is a block diagram of an embodiment of a data portion of a service unit for the asymmetrical communication of data over a network. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description refers to the accompanying drawings which form a part of the specification. The drawings show, and the detailed description describes, by way of illustration specific illustrative embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be used and logical, mechanical and electrical changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense. 
       FIG. 1  is a block diagram of one embodiment of a system, indicated generally at  100 , for the asymmetrical communication of data according to the teachings of the present invention. System  100  includes head end  102  and at least one service unit  106 . For clarity in the Figures and description, system  100  is described in terms of a single service unit  106 . However, one of skill in the art will readily understand that system  100  can include any appropriate number of service units. 
     Head end  102  communicates with service unit  106  over network  104 . Network  104  comprises, for example, a hybrid fiber/coax network or other appropriate network that is capable of bidirectional communication between head end  102  and service unit Communication in system  100  is asymmetrical. Head end  102  transmits to service unit  106  over network  104  (“downstream transmission”). Further, service unit  106  also transmits to head end  102  (“upstream transmission”) over the same network  104 . This communication is asymmetrical because the downstream and upstream transmissions are accomplished with different data rates. For example, the data rate for downstream transmissions can be much higher than the data rates of the upstream transmissions. Advantageously, system  100  can more efficiently download large data files to a remote user, e.g., download large files from the Internet. A request for data is typically larger than the data requested. The request is thus easily transmitted from a user through service unit  106  to head end  102  over a low data rate connection without a large time delay. Then, head end  102  transmits the typically larger volume of data to the user at service unit  106  in a relatively short period of time due to the higher data rate in the downstream transmission. This arrangement more effectively uses the bandwidth resources of the network. 
     In one embodiment, head end  102  includes data head end  114  and telephony head end  116 . Data head end  114  includes quadrature amplitude modulation (QAM)  64  encoder  118  that modulates data for downstream transmission over network  104 . The use of QAM  64  encoding allows data to be transmitted at a rate of 30 Mbps in a 6 MHZ channel. Data head end  114  has access to a number of channels in network  104 . For example, data head end  114  may transmit on up to 28 of the 6 MHZ channels of network  104  in the downstream direction providing a maximum data capacity in this example of 840 Mbps. 
     Telephony head end  116  transmits telephony signals on, for example, three of the 6 MHZ channels of network  104  in the downstream direction such as described in co-pending application Ser. No. 08/673,002 (the &#39;002 application), which application is incorporated herein by reference. The downstream outputs of QAM  64  encoder  118  and telephony head end  116  are combined in combiner  120  and transmitted over network  104  to service unit  106 . 
     Data head end  114  includes an interface for connection to a data source. For example, the interface may comprise a 100 BaseT or 10 BaseT Ethernet interface for connecting to a local area network or switched Ethernet network  124 . Further, this interface can provide a connection to the Internet  108 , local content  110 , management for telephony and data (SNMP)  112 , or other appropriate source of data. 
     Upstream data transmission is handled by telephony head end  116 . Telephony head end  116  is coupled to data head end over one or more communications links  122 , e.g., a T 1  or E 1  communications link. Thus, when upstream data is received at telephony head end, the data is switched over the communications link  122  to data head end  114 . 
     Service unit  106  includes QAM  64  decoder  128  that receives data transmissions from network  104 . Decoder  128  is coupled to downstream data service unit (“data service unit”)  130 . Data service unit  130  is coupled to, for example, terminal  126  over local area network  132 . Service unit  106  further includes telephony and upstream data service unit (“telephony service unit”)  134  that communicates both the telephony data and upstream data to head end  102 . 
     In operation, system  100  communicates data between a data source and a user. For example, a user requests data from Internet  108  using terminal  126 . The request is processed through service unit  106 . Data service unit  130  receives the request and passes it to telephony service unit  134 . The request is then passed to head end  102  in a frequency band designated for upstream transmission, e.g., 18 to 40 MHZ. The request is modulated using, for example, orthogonal frequency division multiplexing modulation as described in the &#39;002 application. 
     The request is received by telephony head end  116  and passed to data head end  114  over communications link  122 . Data head end  114  receives the data from Internet  108  and provides the data to QAM  64  encoder  118 . This data is modulated such that the data rate is as much as 30 Mbps in a 6 MHZ channel. This data is transmitted in a different frequency band from the upstream transmissions. 
     Service unit  106  receives the data at QAM  64  decoder  128 . This data is provided to terminal  126  over network  132  by data service unit  130 . 
       FIG. 2  is a block diagram of an embodiment of a data head end, indicated generally at  200 , for the asymmetrical communication of data over a network. Data head end  200  interfaces with data sources, a telephony head end, and a network. 
     Data head end  200  includes a T 1 /E 1  interface  202  for communicating with the telephony head end. In one embodiment, interface  202  provides an interface for a number of T 1  or E 1  lines, e.g., up to 4 lines. The number of lines coupled to data head end  200  depends on the number of users serviced by data head end  200 . If a small number of users is associated with the bandwidth of data head end  200 , then one T 1  or E 1  line may be sufficient. However, if the bandwidth of data head end  200  is to be shared by a large number of users, then more T 1  or E 1  lines may be necessary to communicate upstream information from the users to data head end  200 . An appropriate T 1 /E 1  interface is commercially available from LSI Logic or Motorola. 
     Data head end  200  also includes processor  204  and QAM  64  encoder  206 . Processor  204  provides interfaces to data sources through LAN interface (I/F)  208 . Further, processor  204  includes a high level data link control (HDLC) interface  210  that provides data to QAM  64  encoder  206 . QAM  64  encoder  206  comprises, for example, encoder part number L64767 from LSI Logic. An appropriate processor for data head end  200  is also available from LSI Logic. 
     Encoder  206  is coupled to transmitter  207  to transmit data over a network. This transmission is downstream transmission at high data rates, e.g., up to 30 Mbps in a 6 MHZ channel. Interface  202  receives upstream transmissions for data head end  200 . These transmissions are pulled off the incoming channels of the communications link and provided to processor  204 . Processor  204  then communicates with a data source through LAN interface  208 . 
       FIG. 3  is a block diagram of an embodiment of a data service unit, indicated generally at  300 , for the asymmetrical communication of data over a network. Data service unit  300  interfaces with a telephony service unit, a local data device or network, and the transport network. Data service unit  300  receives downstream data at a first data rate at receiver  312  and quadrature amplitude modulation (QAM)  64  decoder  310 . In one embodiment, QAM  64  decoder  310  comprises decoder part number L64768 from LSI Logic. Data head end  300  further transmits data with modulator  304  at a different, lower data rate in the upstream direction. Both downstream and upstream transmissions are accomplished over the same medium. 
     Data service unit  300  includes processor  302 . Processor  302  includes a LAN interface  306  that interfaces with a local data device or network, e.g., a computer. LAN interface  306  thus receives upstream data from and provides downstream data to a local device or network. Processor  302  also includes an interface  308  that receives high level data link control (HDLC) data from QAM  64  encoder  310 . Finally, processor  302  includes a modulator  304  that interfaces with a telephony/return data path service unit. The modulator  304  passes the upstream data out from data service unit  300  at a lower data rate compared to the data rate of the downstream transmissions. 
     In operation, data service unit  300  provides for asymmetrical transport of data over a network. Downstream data is received at receiver  312 . Receiver  312  provides the data to QAM  64  decoder  310  for demodulation. This data is presented to processor  302  at HDLC interface  308 . Processor  302  further provides the data to a local device or network through LAN interface  306 . 
     In the upstream, data is transmitted at a lower data rate. The upstream data is received at LAN interface  306 . Modulator  304  of processor  302  then provides this upstream data for transmission over the network in the same channel that is used to carry the return path for telephony signals over the network. 
     CONCLUSION 
     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement which is calculated to achieve the same purpose may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the present invention. For example, the network  104  of  FIG. 1  is not limited to a hybrid fiber/coax network. Other appropriate network configurations can also be used that provide for bidirectional transport of data. Further, other modulation techniques can be used so long as asymmetrical data rates are used to transport the data in upstream and downstream directions over a common network.