Multiplex communications – Duplex
Reexamination Certificate
1997-10-31
2001-01-23
Patel, Ajit (Department: 2732)
Multiplex communications
Duplex
C370S445000
Reexamination Certificate
active
06178161
ABSTRACT:
This invention relates to communications methods and apparatus. The invention is particularly, but not exclusively, concerned with half duplex, or burst mode, communications systems, and with operation of such systems in a manner to reduce crosstalk or other interference of such systems between themselves and with other communicatons systems. The invention is particularly, but also not exclusively, applicable to communications via twisted pairs of wires in telephone cables used historically for providing telephone service to subscribers and now being used increasingly to provide additional communications services, for example for data communications and computer network connections.
BACKGROUND OF THE INVENTION
The communications arrangements and methods of the related applications provide a network access arrangement in which access to a CSMA/CD (Carrier Sense Multiple Access with Collision Detection) network, such as the Network using Ethernet frames, is provided via a telephone line by providing a master modem at the head end and a slave modem at the subscriber end of the line, and in which crosstalk with communications on other telephone lines can be reduced. The master modem provides a CSMA/CD interface to the Network and controls half duplex, or burst mode, communications with the slave modem via the line to avoid collisions of Ethernet frames on the line. The Ethernet frames are enveloped in frames on the line with error checking information; control information between the modems is contained in the same and/or in separate frames. Multiple Ethernet frames can be concatenated in a single frame on the line. The modulation method and signal bandwidth can be varied depending on errors to provide optimum conmmunications capacity via any particular line, and a ratio of upstream to downstream frames can be varied depending on buffer fills at the modems. The modulated signal frequencies are above telephone signal frequencies so that each telephone line can be frequency diplexed for simultaneous telephone communications.
In such communications arrangements, as in any communications system, it is desirable to provide, for the two directions of communication, an optimum, e.g. the greatest possible, capacity consistent with avoiding errors both in this communications arrangement and in other communications arrangements with which there may be crosstalk.
Object of this invention are to provide improved methods of transmitting information and improved communications apparatus.
SUMMARY OF THE INVENTION
According to one aspect of this invention there is provided a method of transmitting information comprising the steps of: buffering at least some information to be transmitted; selecting different ones of a plurality of communication modes depending upon amounts of buffered information to be transmitted; and transmitting information using the selected communication mode.
The information to be transmitted can comprise data packets and control or response packets, the data packets being buffered, and the selection of the communication mode can be dependent upon a number of buffered data packets to be transmitted. The plurality of communication modes can comprise different symbol transmission frequencies and/or different modulation methods and/or bits per symbol providing a plurality of different transmitted bit rates.
The step of selecting different ones of the plurality of communication modes can comprise selecting a communication mode providing a relatively lower transmitted bit rate in response to there being no buffered data packets to be transmitted and selecting a communication mode providing a relatively higher transmitted bit rate when there are buffered data packets to be transmitted, and in particular can comprise selecting a communication mode having a relatively low symbol transmission frequency in response to there being no buffered data packets to be transmitted and selecting a determined one of the communication modes when there is at least one buffered data packet to be transmitted. The use of a lower frequency reduces signal levels and coupling during relatively idle (no data tansmission) times, so that over many similar communications there is an aggregate reduction in interference and a consequent increase in aggregate communications capacity. The determined one of the communication modes can be adaptively determined in dependence upon at least one communication parameter, such as signal to noise ratio, for the transmitted information.
Another aspect of the invention provides a method of transmitting control information and data in a communications system having a plurality of communication modes providing different transmitted bit rates, comprising the steps of: buffering the data; selecting one of said communication modes providing a relatively low transmitted bit rate for transmission of control information in response to there being no buffered data for transmission; and selecting another of said communication modes providing a relatively higher transmitted bit rate for transmission of control information and data in response to there being buffered data for transmission.
This method can include the steps of defining signal to noise ratios for the communication modes and determining said another of said communication modes in dependence upon the determined signal to noise ratios.
A further aspect of the invention provides a method of communicating information in a communications system having a plurality of communication modes providing different transmitted bit rates using different symbol transmission frequencies and/or different modulation methods and/or bits per symbol, comprising the steps of: establishing communications using one of said communication modes providing a first transmitted bit rate; establishing communications using another of said communication modes providing a second transmitted bit rate greater than the first transmitted bit rate; communicating control information and data using said another of said communication modes; and in the absence of data to be communicated, communicating control information using said one of said communication modes. This method may include the steps of storing data to be communicated in a buffer, and selecting said communication modes in dependence upon data in the buffer.
The invention also provides communications apparatus comprising: a buffer for buffering data to be transmitted via a communications path; a transmitter for transmitting data from the buffer and control information via the communications path using any of a plurality of communication modes providing different transmission rates; and a control unit for monitoring an amount of data in the buffer, supplying the control information for transmission, and controlling the communication mode of the transmitter; wherein the control unit is arranged for controlling the transmitter to use one of the communication modes for transmitting control information in the absence of data to be transmitted from the buffer and at least one different communication mode for transmitting control information and data from the buffer, said one communication mode providing a lower transmission rate than said at least one different communication mode.
The apparatus preferably includes an Ethernet interface coupled to the control unit and to the buffer for supplying data to the buffer, and a digital-analog converter responsive to digital signals from the transmitter into analog signals for transmission via the communications path.
The invention further provides a modem for coupling between first and second communications paths, the first communications path providing for communication of data frames in a CSMA/CD (Carrier Sense Multiple Access with Collision Detection) network and the second communications path providing for communication of data of said frames and control information using half duplex communications with a complementary modem, the modem comprising: a first buffer for buffering information received via the first path for transmission via the second path; a contr
Foley & Lardner
Nguyen Brian
Nortel Networks Corporation
Patel Ajit
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