WO2001008338A9

WO2001008338A9 - Media converter for data communication on an extended twisted-pair network

Info

Publication number: WO2001008338A9
Application number: PCT/US2000/020179
Authority: WO
Inventors: David D Goodman
Original assignee: Cais Inc
Priority date: 1999-07-27
Filing date: 2000-07-26
Publication date: 2002-07-11
Also published as: CA2416068A1; TW484278B; WO2001008338A3; AU6492900A; WO2001008338A2

Abstract

A media adapter (110) for data communications over a twisted pair telephone network (150) has been invented. The media adapter has a first interface for receiving a first data signal and transmitting a second data signal. A second interface, which is coupled to the encoder and the decoder, transmits the first reduced band width signal to, and receives the second reduced bandwidth signal from a twisted pair telephone network at frequencies within the data band. The data band is at higher frequencies than a voice band used for voice transmission on the twisted pair network. A collision signal generator generates a collision signal when the the media adapter is transmitting the first reduced bandwidth signal to the twisted pair network. The collision signal is transmitted to the twisted pair network at frequencies within a collision band that is at higher frequencies than the voice band.

Description

MEDIA CONVERTER FOR DATA COMMUNICATION ON AN EXTENDED

TWISTED-PAIR NETWORK

Background

This invention relates to data communication over an extended twisted-pair telephone wiring network.

Systems have been designed for data communication over active telephone lines within a building, for example as described in International Patent Application US98/11197, "Techniques for high-speech distribution of data over ordinary twisted pair telephone wires." That patent describes a system in which devices communicate over active telephone lines using a collision detection/collision avoidance random access approach based on the Ethernet signaling standard. In another approach to data signaling on active telephone lines, Digital Subscriber Loop (DSL) standards address approaches to data communication between a telephone exchange and a residence over an active telephone local loop. In DSL, point-to-point communication between two DSL modems uses one of a number of signaling approaches, including Quadrature Amplitude Modulation (QAM), and carrierless amplitude/phase modulation (CAP).

Summary

In one aspect, in general, the invention is a media adapter. The media adapter has a first interface for receiving a first data signal and transmitting a second data signal. An encoder coupled to the first interface generates a first reduced bandwidth signal in a data band from the first data signal. The bandwidth of the reduced bandwidth signal is less than the bandwidth of the first data signal. A decoder coupled to the interface receives a second reduced bandwidth signal in the data band and generates the second data signal from the second reduced bandwidth signal. A second interface, which is coupled to the encoder and the decoder, transmits the first reduced bandwidth signal to and receiving the second reduced bandwidth signal from a twisted pair telephone network at frequencies within the data band. The data band is at higher frequencies than a voice band used for voice transmission on the twisted pair network. A collision signal generator generates a collision signal when the media adapter is transmitting the first reduced bandwidth signal to the twisted pair network. The collision signal is transmitted to the twisted pair network at frequencies within a collision band that is at higher frequencies than the voice band. The media adapter also includes a collision signal detector that detects signals within the collision band on the twisted pair network indicating that a device connected to the twisted pair network is transmitting a signal within the data band.

The media adapter can include one or more of the following features: A signal generator coupled to the collision signal detector and to the first interface for generating a signal indicating that another device is transmitting and transmitting the generated signal through the first interface.

The first data signal and the second data signal are Ethernet signals. The data rate of the first data signal and the second data is 10 Mb/s or greater and the bandwidth of the data band is 2.5 MHz or smaller.

The data rate of the first data signal and the second data signal is 100 Mb/s or greater and the bandwidth of the data band is 12 MHz or smaller.

The encoder includes a quadrature amplitude modulator for modulating the first data signal and the decoder includes a quadrature amplitude demodulator for demodulating the second reduced bandwidth signal.

The decoder further includes a signal pre-processor coupled to the quadrature amplitude demodulator for performing spectral equalization on the second reduced bandwidth signal prior to demodulation. In another aspect, in general, the invention is a method for passing data over an active telephone wiring network. The method includes receiving a first data signal and transmitting a second data signal over a first interface, generating a first reduced bandwidth signal in a data band from the first data signal, receiving a second reduced bandwidth signal in the data band, generating the second signal from the second reduced bandwidth signal, and transmitting the first reduced bandwidth signal to and receiving the second reduced bandwidth signal from a twisted pair network at frequencies within the data band . The method also includes generating a collision signal when the media adapter is transmitting the first reduced bandwidth signal to the twisted pair network, the collision signal being transmitted to the twisted pair network at frequencies within a collision band that is at higher frequencies than the voice band, and detecting signals within the collision band on the twisted pair network indicating that a device connected to the twisted pair network is transmitting a signal within the data band.

The invention has an advantage of allowing high rate data communication on an active telephone network over an extended range. By compressing the bandwidth of a data signal, such as a 10 Mb/s or a 100 Mb/s Ethernet signal, a lower range of frequencies can be used for the data band. These lower frequencies suffer less attenuation than do higher frequencies, thereby increasing the signal-to-noise ratio at a receiver. The same frequency range is used for all communication in a random access approach, thereby using a reduced bandwidth as compared to approaches in which different directions of communication use non-overlapping frequency ranges. Use of different frequencies for collision signals improves detection of transmissions of other media converters. Use of collision detection band that is above the voice band but at relatively low frequencies further improves detection of collisions on the network. Description of Drawings

FIG. 1 illustrates a system in which multiple computers are coupled to a twisted-pair telephone network through media converters; FIG. 2 is a diagram that illustrates a collision band and a data band at higher frequencies than the telephone voice band;

FIG. 3 is a block diagram of a media converter;

FIG. 4 is a block diagram of a decoder of a media converter; and

FIG. 5 is a block diagram of an encoder of a media converter. Description

Referring to FIG. 1, a number of computers 120 communicate with one another over an active twisted-pair telephone network 150. As illustrated in FIG. 1, twisted-pair network 150 carries voice signals between telephones 140 and a telephone exchange 170. Each computer 120 is coupled to twisted-pair network 150 through a media converter 110. Twisted pair network 150 has two conductors over which both voice and data signals are transmitted. In this embodiment, computers 120 communicate with their corresponding media converters 110 using a 10 Mb/s Ethernet standard, 10 Base-T, in which data link 122 includes two pairs of conductors, one pair for each direction of communication. In a second embodiment, the computers and media converters communicate using a 100 Mb/s Ethernet standard, 100 Base-T. Telephones 140 are coupled to twisted pair network 150 through low-pass filters 130. Low-pass filters 130 pass signals in the telephone voice band and presents a high impedance at higher frequencies to the twisted pair network. A terminator 160 is coupled at the end of twisted pair network 150 to reduce reflections at high frequencies.

Referring to FIG. 2, media converters 110 communicate with one another using a relatively small bandwidth as compared to the bandwidth of the signals passed between the media converters and computers 120 coupled to the media converters. Media converters 110 pass data between one another within a data band 230. Each media converter transmits data in the same range of frequencies. When transmitting data in data band 230, a media converter 110 also transmits a collision tone 220 within a collision band 220. Each media converter is assigned a different frequency for transmitting its collision tone. A receiving media converter 110 detects collision tones within collision band 220 at frequencies other than its own in order to detect collisions. In this way, a media converter does not have to simultaneously transmit in data band 230 and detect transmissions of other media converters in the data band. Collision band 220 and data band 230 are in different frequency ranges, both of which are at frequencies above the telephone voice band 210, which does not extend beyond 5 kHz.

Referring to FIG. 3, media converter 110 has a transmit section and a receive section that are each coupled to twisted pair network 150 through a junction 310. In the receive section, Ethernet signals from an inbound pair of wires 122b pass signal from computer 120 to the media converter. These signals pass to an encoder 360, which converts the Ethernet signals into a narrower bandwidth format for transmission to other media converters in data band 230 (FIG. 2). In addition to encoding the Ethernet signal into the data band, media converter 110 also generates a collision tone in tone generator 370 whenever it receives an Ethernet signal on wires 122b. The generated collision tone is at a different frequency than collision tones generated by tone generators 370 in the other media converters 110 coupled to twisted pair network 150. Both the collision tone generated by tone generator 370 and the data signal encoded by encoder 360 are coupled to twisted pair network 150 through junction 310.

In the receive section, signals from the twisted pair network are passed from twisted pair network 150 to a high-pass filter 320 and to a low-pass filter 322. High-pass filter 320 passes signals in data band 230 (FIG. 2), while low-pass filter 322 passes signals in collision band 220 (FIG. 2).

When media converter 110 is not transmitting a signal onto twisted pair network 150 and it receives a data signal in data band 230, that signal passes through junction 310 and high-pass filter 320 to decoder 330. Decoder 330 converts the signaling format used to communicate between the media converters into a standard Ethernet signal. The Ethernet signal is passed through a coupler 350 and over an outbound pair of wires 122a of data link 122, which couples media converter 110 and computer 120.

When media converter 110 is transmitting onto twisted pair network 150 and it receives a collision tone from the network, a tone detector 340 at a frequency other than the frequency at which tone generator 370 generates collision tones, tone detector 340 sends a signal to signal generator 342, which in turn generates a signal that is passed through coupler 350 to computer 120 over wire pair 122a. This generated signal is an Ethernet format signal that computer 120 interprets as another computer transmitting, and the computer will thereby detect that a collision has occurred and stop transmitting.

Note that both the collision tones and data signals in this system are expressed at frequencies above the voice band. Separation of the voice signals from the signals related to data is achieved by passive low-pass and passive high-pass filters. Various arrangements for such separation, and for coupling signals above the voice band on branches of a twisted pair wiring network are described in patent application US98/11197 referenced above. Referring to FIGS. 4 and 5, encoder 360 and decoder 330 convert between Ethernet signals and narrower band signals used for transmission over twisted pair network 150. In this embodiment, encoder 360 and decoder 330 include a modulator and a demodulator, respectively, which uses quadrature amplitude modulation (QAM) for communication over twisted pair network 150. In this embodiment in which 10 Base-T Ethernet is used, a QAM-16 approach is used in which each transmitted symbol is chosen from a 16-point constellation, yielding a transmission of 4 bits per transmitted symbol. This results in data band 230 being approximately 2.5 MHz or less to carry the 10 Mb/s bit stream of 10 Base-T Ethernet. In the second embodiment in which 100 Base-T Ethernet is used, QAM- 128 is used, and data band 230 is approximately 12 Mhz wide or less. In alternative embodiments, other encoding approaches which reduce the bandwidth of Ethernet signals are used.

Referring to FIG. 4, decoder 330 includes a series of functional elements. An analog-to- digital converter (A/D) 410 converts the received signals in the data band into a digitized sampled waveform representation. This digitized representation is digitally filtered in equalizer 420. Equalizer 420 compensates for the frequency dependency of attenuation on twisted-pair network 150. In alternative embodiments, equalizer 420 adapts to the characteristics of the received signal. The equalized signal is passed to QAM decoder 430, which outputs a serial bit stream that was encoded in the received signal. The serial bit stream is converted by an Ethernet encoder 440 for transmission to the destination computer. In alternative embodiments, other implementations of this processing, for example performing some functions in an analog domain rather than a digitized domain, are used. Also, additional elements, for instance, providing error correction or echo cancellation mechanisms may be included in the encoder and decoder.

Referring to FIG. 5, encoder 360 essentially performs the inverse operations of decoder 330. An Ethernet decoder 510 receives an Ethernet signal from the computer and converts it into a serial bit stream. QAM encoder 520 converts the bit stream into a digitized sampled waveform representation of a QAM encoding of the bit stream. This digitized waveform is processed in signal pre-processor 530. In this embodiment, signal pre-processor pre-emphasizes the higher frequency component of the encoded signal in order to mitigate the greater attenuation of those higher frequency components. Finally, the processed digital waveform is passed through digital- to-analog converter 540 before transmission over the twisted pair network.

By reducing the bandwidth of the encoded data signals as compared to their original Ethernet representations and thereby allowing transmission at lower frequencies, the data signal suffers less overall attenuation on the twisted pair network than would the original Ethernet representation. This has the effect of increasing the signal-to-noise ratio (SNR) at the receiving media converter, or alternatively, increasing the transmission range of a media converter. In order to allow collision detection, which as described above makes use of collision tones 222 in collision band 220, the transmission path length is limited to allow detection of a collision at a sending media converter before the sending media converter has completed the transmission. In this system, the transmitted packets are at least 512 bits in length, as is prescribed by the Ethernet standard. At 10 Mb/s, 512 bits corresponds to 51.2 μs. If a transmission speed of 2x10 m/s is assumed, such a packet will be "stretched out" over to over 10 km. In the second embodiment in which 100 Mb/s signaling is used, the packet will be stretched out to over 1 km. In the case of 10 Mb/s signaling, if the maximum distance between media adapters is one half the length of a packet, or approximately 5 km, then if a second media adapter starts transmitting just before a packet transmitted from a first media adapter reaches it, then the first media adapter will detect the second media adapter's collision tone before it has finished sending the packet, thereby detecting the collision. Similarly, in the second embodiment with 100 Mb/s signaling, the maximum separation between media adapters is approximately 500 m. In alternative embodiments, other arrangements of signals in the frequency spectrum are used. In order to limit the upper frequency of the data band, the same band is used for transmission in both directions on the twisted pair network in a half duplex arrangement. In order to support robust collision detection, collision signals at different frequencies for each media adapter are used. In the embodiment described above, collision band 220 is at different frequencies than data band 230. In alternative embodiments, collision signals may be sent within the data band. For example, if a multi-tone signaling approach is used for transmission within data band 230 rather than QAM, collision tones could be interspersed with the signaling tones. Also, alternative collision signals rather than tones can alternatively be used. For example, orthogonal narrow-band signals or spread spectrum signals that are unique to each media adapter can be used in place of the collision tones.

The signaling approach described above can be applied within a single building, in a campus of buildings, or between a telephone switching office and multiple residences. A centralized hub can couple computers on different branches twisted pair networks, and subject to the limitations of maximum total distance between computers, all the computers can function within a single collision domain.

It is to be understood that the foregoing description is intended to illustrate and not to limit the scope of the invention, which is defined by the scope of the appended claims. Other embodiments are within the scope of the following claims.

Claims

What is claimed is:

1. A media adapter comprising: a first interface (355) for receiving a first data signal and transmitting a second data signal; an encoder (360) coupled to said first interface for generating a first reduced bandwidth signal in a data band (230) from said first data signal, wherein the bandwidth of the said reduced bandwidth signal is less than the bandwidth of the first data signal; a decoder (330) coupled to said interface for receiving a second reduced bandwidth signal in the data band (230) and generating said second data signal from said second reduced bandwidth signal; a second interface (305) coupled to said encoder and said decoder for transmitting said first reduced bandwidth signal to and receiving said second reduced bandwidth signal from a twisted pair telephone network at frequencies within the data band (230), wherein the data band is at higher frequencies than a voice band (210) used for voice transmission on the twisted pair network; a collision signal generator (370) for generating a collision signal when said media adapter is transmitting said first reduced bandwidth signal to said twisted pair network, said collision signal being transmitted to said twisted pair network at frequencies within a collision band (220) that is at higher frequencies than the voice band (210); and a collision signal detector (340) for detecting signals within said collision band on said twisted pair network indicating that a device connected to said twisted pair network is transmitting a signal within said data band.

2. The media adapter of claim 1 further comprising: a signal generator (342) coupled to the collision signal detector and to the first interface for generating a signal indicating that an other device is transmitting and transmitting said generated signal through the first interface.

3. The media adapter of claim 1 wherein the first data signal and the second data signal are Ethernet signals.

4. The media adapter of claim 3 wherein the data rate of the first data signal and the second data is 10 Mb/s or greater and the bandwidth of the data band is 2.5 MHz or smaller.

5. The media adapter of claim 3 wherein the data rate of the first data signal and the second data signal is 100 Mb/s or greater and the bandwidth of the data band is 12 MHz or smaller.

6. The media adapter of claim 1, wherein said encoder includes a quadrature amplitude modulator (520) for modulating the first data signal and said decoder includes a quadrature amplitude demodulator (430) for demodulating the second reduced bandwidth signal.

7. The media adapter of claim 6 wherein the decoder further includes a signal pre- processor (420) coupled to said quadrature amplitude demodulator for performing spectral equalization on said second reduced bandwidth signal prior to demodulation.

8. A method for passing data over an active telephone wiring network comprising: receiving a first data signal and transmitting a second data signal over a first interface

(355); generating a first reduced bandwidth signal in a data band (230) from said first data signal, wherein the bandwidth of the said reduced bandwidth signal is less than the bandwidth of the first data signal; receiving a second reduced bandwidth signal in the data band (230) and generating said second signal from said second reduced bandwidth signal; transmitting said first reduced bandwidth signal to and receiving said second reduced bandwidth signal from a twisted pair network at frequencies within the data band (230), wherein the data band is at higher frequencies than a voice band (210) used for voice transmission on the twisted pair network; generating a collision signal when said media adapter is transmitting said first reduced bandwidth signal to said twisted pair network, said collision signal being transmitted to said twisted pair network at frequencies within a collision band (220) that is at higher frequencies than the voice band (210); and detecting signals within said collision band on said twisted pair network indicating that a device connected to said twisted pair network is transmitting a signal within said data band.

9. The method of claim 8 wherein: generating the first reduced bandwidth signal includes quadrature amplitude modulating the first data signal; generating the second data signal includes quadrature amplitude demodulating the second reduced bandwidth signal; generating a collision signal includes generating a tone at a first frequency in the collision band; and detecting signals with the collision band includes detecting tones at frequencies other than the first frequency within the collision band.