Abstract:
A digital communication trunk employing digital discrete multitone communication over twisted pair copper network segments to increase the effective bandwidth therethrough. Each central office includes an end unit to connect to the network segments and digital discrete multitone repeaters are employed throughout the trunk at defined distances to maintain signal quality. A multiplexer can be employed at the central offices to combine multiple baseband signals before transmission and to extract those multiple signals after reception. In one embodiment of the present invention, four T1 rate baseband signals are combined by the multiplexer into a single signal which is transmitted at T2 rates through the trunk.

Description:
FIELD OF THE INVENTION 
     The present invention relates to digital communication trunks. More specifically, the present invention relates to a system and apparatus for increasing the effective communication bandwidth through such trunks. 
     BACKGROUND OF THE INVENTION 
     Several factors, including the wide adoption of the Internet and the convergence of various communication media have lead to a phenomenal growth in the amount communications bandwidth that is required in the world. While much effort is being expended at establishing new networks to provide the needed bandwidth, the cost of constructing such networks can be very high. Further, right of ways, cable paths or other physical requirements may not be readily available for deploying such new networks in some locations. Also, the costs of earlier, lower bandwidth networks may not yet have been fully recouped and a telecommunications carrier may thus have a strong economic disincentive to commence construction of a new network. 
     It is therefore desired to have a system and apparatus which can work with at least some part of an existing networking infrastructure but which can provide an increased effective bandwidth through the network. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a novel system and apparatus for providing an increase in effective bandwidth in a digital communication trunk. 
     According to a first aspect of the present invention, there is provided a digital communication trunk for transmitting digital data between two distal central offices each connected to a network segment by a digital discrete multitone end unit, comprising: 
     a digital interface to receive baseband digital information to be transmitted through said network segment; 
     a digital discrete multitone transmitter to receive said baseband digital information and to convert said baseband digital information into digital multitone information; 
     digital discrete multitone code to convert said digital multitone information into encoded analog information in a plurality of frequency bands; 
     a transmit line driver to convert said encoded analog information to predefined signal transmission levels for transmission on said network segment; 
     a receive line driver to amplify tone information received from said network segment to a predefined signal level; 
     a digital discrete multitone code to convert said encoded analog information from said receive line driver into digital multitone information; and 
     a digital discrete multitone receiver to receive said digital multitone information and to form baseband digital information therefrom, said digital interface outputting said formed baseband digital information. 
     The present invention also provides, where two or more network segments of a digital trunk are employed to connect the central offices, a digital discrete multitone repeater unit to connect the network segments. The digital discrete multitone repeater unit includes a pair of repeater functions, each repeater function comprising: 
     a receive line driver to amplify encoded analog information received from a network segment to a predefined signal level; 
     a digital discrete multitone code to convert said encoded analog information to digital multitone information; 
     a digital discrete multitone receiver to receive said digital multitone information and to form baseband digital information therefrom; 
     a digital discrete multitone transmitter to receive said baseband digital information and to convert said baseband digital information into digital multitone information; 
     a digital discrete multitone codec to convert said digital multitone information into analog tone information; and 
     a transmit line driver to convert said analog tone information to a predefined signal transmission level for transmission on another network segment. 
     The present invention allows telecommunication carriers to increase the effective bandwidth of existing digital communication trunk lines, such as T1 or E1 trunks, by replacing the repeaters in such trunks with digital discrete multitone repeaters and by providing each central office with a digital discrete multitone end unit. In one embodiment of the invention, the effective bandwidth of an existing T1 trunk can be increased fourfold, to T2 transmission rates, allowing T2 transmissions or four mutliplexed T1 transmissions to be achieved without requiring the replacement of T1 standard copper twisted pair infrastructure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein: 
     FIG. 1 shows a schematic representation of a prior art T1 digital trunk; 
     FIG. 2 shows a schematic representation of a digital discrete multitone communication trunk in accordance with the present invention; 
     FIG. 3 shows a schematic representation of a digital discrete multitone end unit in accordance with the present invention for use in a central office; and 
     FIG. 4 shows a schematic representation of a digital discrete multitone repeater in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     One of the telecommunications standards for digital trunking of data is the T1 standard which provides bandwidth to transmit data at rates of 1.544 megabits per second (Mb/s). Another example of a digital trunking standard is the E1 standard, used mainly in Europe, which provides bandwidth to transmit 2.048 Mb/s. These and other digital trunk networks are widely used and are available throughout much of the industrialized world and the segments of such networks comprise twisted pair copper wiring. 
     FIG. 1 shows a conventional T1 network  20  connecting digital trunk controllers  24   a ,  24   b . For long haul T1 networks, the T1 standard requires that a digital repeater  28  be provided at least at every 6000 feet between network segments  32  to ensure that signal levels and characteristics are maintained along the network and other digital trunk standards have similar types of requirements. As used herein, the term segment is intended to comprise the run of cable/wire between a central office and a repeater or the run of cable/wire between pairs of repeaters. 
     A technique which is presently proposed to increase the effective bandwidth of existing subscriber networks is to employ discrete multitone modems to connect the telephone company central office to the subscriber premises with an Asynchronous Digital Subscriber Line (ADSL) system employing discrete multitone modems. These systems exploit the twisted pair copper lines between the central office and the subscriber premises and generally provide non-symmetric upstream and downstream channels, the latter of which can have a transmission speed exceeding one megabit per second (Mb/s). Such systems are generically know as xDSL systems and include ADSL, HDSL and other implementations. The present inventors have determined that the effective bandwidth through an existing twisted copper pair digital trunk network, such as a T1 network, can be significantly increased without requiring the replacement of existing network segments of twisted pair copper wires. 
     Specifically, the present inventors have determined that the conventional digital repeaters employed with such networks can be replaced with novel digital discrete multitone repeaters, described herein, at the same or greater spacings and a digital discrete multitone end unit placed in each central office to achieve a greater effective bandwidth. In an embodiment of the present invention which employs ADSL strategies, an effective bandwidth of at least 6.312 Mb/s can be achieved, which is the bandwidth of a T2 standard trunk. It is contemplated that even greater bandwidths can be achieved by employing some of the more aggressive strategies such as VDSL. 
     FIG. 2 shows an embodiment of a digital communication trunk network  100 , in accordance with the present invention. As shown, network  100  includes two central offices  104   a ,  104   b  each of which has four 1.544 Mb/s (i.e.—T1 rate) connections  108  for data equipment  112  through network  100 . In this embodiment, connections  108  pass through a multiplexer  116  which converts the four connections to a 6.312 Mb/s T2-rate connection  120 . 
     Inputs and outputs of connection  120  are processed by a digital discrete multitone end unit (DDMEU)  124 , which is shown in more detail in FIG.  3 . DDMEU  124  includes a T2-rate digital discrete multitone modulated input  140 , a T2-rate digital discrete multitone output  144 , a T2 rate baseband digital input  148  and a T2 rate baseband digital output  152 . Input  140  is connected to a receive line driver  156  which amplifies modulated signals received from network segments  158  to predefined signal levels. The output of receive line driver  156  is supplied to digital discrete multitone decoder  160  which performs an analog to digital conversion and various filtering functions. The filtered digital information from decoder  160  is provided to a digital discrete multitone transceiver  164  which converts the digital information into T2 rate baseband information sent to output  152  via a digital interface  168 . 
     T2 rate baseband information supplied to DDMEU  124  at input  148  is provided to digital discrete multitone transceiver  164  via digital interface  168 . Transceiver  164  converts the baseband digital information to digital information for encoding by an encoder  172  to analog multi-frequency band tone information. The tone information output from encoder  172  is provided to a transmit line driver  176  which boosts the modulated signal levels to predefined levels for transmission through a network  158  via output  144 . 
     In a presently preferred embodiment of the invention, DDMEU  124  is implemented with the TNETD2000 series chipset for ADSL communications, available from Texas Instruments. Reference Sheets and other information on this chipset are available from a variety of sources, including the document “DSP Solutions for Voiceband and ADSL Modems”, the contents of which are incorporated herein by reference, When implemented with this chipset, receive line driver  156  and transmit line driver  176  are implemented in the THS6002 chip, decoder  160  and encoder  172  are implemented in the TNETD2011 chip, transceiver  164  is implemented in the TNETD2200 chip and digital interface  168  is implemented in the TNETD2100 chip. In this particular implementation, only the 8 Mb/s downstream portion of the chipset is employed and the TNETD2100 and TNETD2200 chips are operated in full-rate multi-line mode. The proper implementation and use of this chipset will be apparent to those of skill in the art, and will not be further discussed herein. As will also be apparent to those of skill in the art, the present invention is not limited to implementation with this chipset and can be implemented in a variety of manners, as will occur to those of skill in the art. Further, the present invention is not limited to ADSL-based implementations and any xDSL or similar scheme employing digital discrete multitone communications can be employed. In particular, the bandwidth allocation between upstream and downstream channels can be varied, with the upstream channel being very small and used for control or signaling purposes, or even omitted entirely. 
     Modulated input  140  and modulated output  144  are connected to a network segment  158 , such as an existing T1 standard copper twisted pair. Each end of a segment  158  is connected to an DDMEU  124  or an digital discrete multitone repeater  204 , which is shown in more detail in FIG.  4 . 
     As shown in FIG. 4, repeater  204  includes two repeater functions, each of which is similar to DDMEU  124 , with the exception that no baseband input or output need be provided at repeater  204  and that modulated communications received at repeater  204  are retransmitted as modulated communications. In fact, in a presently preferred embodiment of the invention, repeater  204  is essentially implemented as a pair of DDMEUs  124  with their respective baseband outputs  148  applied directly to their respective baseband inputs  152 . A modulated signal applied to input  208   a  is therefore repeated at modulated output  212   a  and a modulated signal applied to input  208   b  is repeated at modulated output  212   b.    
     As will be apparent to those of skill in the art, network  100  is not limited to use with four baseband T1 lines. For example, mutiplexer  116  can be omitted and a baseband T2 signal can be applied directly to DDMEU  124  at each central office. Similarly, other data channels and digital trunks, such as E1, with different data transmission rates can be multiplexed together to transmit a variety of data through network  100  at T2 data rates or higher. 
     The present invention allows telecommunications provides to increase the effective bandwidth of existing twisted pair copper digital communication trunk lines, such as T1 and E1 trunks, by replacing the repeaters in such trunks with digital discrete multitone repeaters and by providing each central office with a digital discrete multitone end unit. In one embodiment of the invention, the effective bandwidth of an existing T1 trunk can be increased fourfold, to T2 transmission rates, allowing T2 transmissions or four mutliplexed T1 transmissions to be achieved without requiring the replacement of T1 standard copper twisted pair segments. 
     The above-described embodiments of the invention are intended to be examples of the present invention and alterations and modifications may be effected thereto, by those of skill in the art, without departing from the scope of the invention which is defined solely by the claims appended hereto.