Communication system and method for interleaving or transmission of telephone rings and data

[0002] This document claims priority to and the benefit of the filing date of copending provisional application entitled INTERLEAVING TRANSMISSIONS OF TELEPHONE RINGS AND DATA, assigned Ser. No. 60/039,352, and filed on Mar. 18, 1997, and is hereby incorporated by reference.

[0003] The present invention generally relates to telephony and data communication and, in particular, to a system and method for concurrently communicating digital data and a telephone ringing cadence to facilitate the transfer of information within a telephone subscriber loop by interleaving the transmission of telephone rings and the transmission of digital data.

[0004] In data communications over a local telephone subscriber loop where simultaneous or alternating plain old telephone system (POTS) services are present, both digital data and ring signals are transmitted over the same transmission lines. Even though known methods attempt to make the data communications and the POTS communications independent via techniques such as frequency division multiplexing, reliable independence is impractical to achieve. The initiation of a ring signal is unpredictable and will typically cause data transmission errors and disrupt data transmission from the beginning of the ringing cadence, during the ringing cadence, and at least for some duration after cessation of the ringing cadence. Moreover, telephone ring interruption may cause loss of a digital data session due to the long communication interruption.

[0005] Some prior art systems have the capability of retransmitting data to a remote modem when communication errors occur. However, in these systems, the remote modem sends a notification to the transmitting modem to indicate that a reception has occurred and to request a retransmission. However, due to the largest and relatively long disturbance of a ringing signal, such notification is often not received by the transmitting modem when a ringing signal is causing the communication error.

[0006] Moreover, in some applications where telephone rings occur often, data operation may become impractical due to the frequency of telephone ring interruption. While it is possible to attempt to make the digital data path and the simultaneous POTS path mutually independent, for example, via POTS-splitter filters, this is often practically impossible due to the extremely large amplitude of the interfering signals with respect to the data signals. Therefore, for concurrent digital data communication and POTS communication (where digital data communication may be interrupted from time to time by ring signal requests for POTS service), sustained digital data communication is often not possible during the telephone ringing cadence associated with a request for POTS service.

[0007] Thus, a heretofore unaddressed need exists in the industry for providing a system and method for interleaving the transmission of telephone rings and digital data.

[0008] The present invention overcomes the inadequacies and deficiencies of the prior art as discussed herein. The present invention provides for a communication system and method for enabling the reliable concurrent transmission of POTS and digital data in the presence of disturbances such as telephone ringing signals.

[0009] The communication system and method utilize a data transmitter and a data receiver. The data transmitter is preferably configured to detect a ring signal, to stop the transmission of any digital data (if any such transmission exists), and to delay and store any desired transmission of digital data until the ring signal has ceased. After the cessation of the interrupting ring signal, the data transmitter preferably retransmits the digital data interrupted by the ring signal (if such interruption occurred) before resuming normal transmission operation. The data receiver is preferably configured to receive the transmitted data, to discard any data interrupted by the ring signal, and to process uninterrupted transmitted data.

[0010] In accordance with another feature of the present invention, the retransmitted data may include a header to indicate that the data being transmitted is a retransmission of a previously interrupted data signal. The transmission of this header may prompt the data receiver to discard the data signal received prior to the transmission of the header.

[0011] In accordance with another embodiment of the present invention, the data transmitter may be configured to delay the ring signal rather than to allow the ring signal to interrupt the data signal. In this regard, the data transmitter is configured to delay the ring signal when a ring request is received while the data transmitter is transmitting the data signal. The data transmitter ensures that the data signal is successfully transmitted by waiting until the data signal is reliably received by the data receiver before permitting the ring signal to occur.

[0012] The communication system and method of the present invention have many advantages, a few of which are delineated hereafter, as examples.

[0013] An advantage of the communication system and method is that they provide for the transmission of data signals during the intervals of silence in a ringing cadence. This provides faster and more efficient communications by allowing the concurrent transmission of a ringing cadence and data signals.

[0014] Another advantage of the telephone communication system and method is that they provide for elimination of digital data loss when a digital data communication session is interrupted by a ring signal. Such a scheme enhances the reliability of digital data communications over a subscriber loop.

[0015] Another advantage of the telephone communication system and method is that interruptions of a transmission of a data signal by a ring signal can be prevented, thereby ensuring the accuracy of the digital data signal.

[0016] Other features and advantages of the invention will become apparent to one skilled in the art upon examination of the following drawings in the detailed description. It is intended that all such additional features and advantages be included herein within the scope of the invention, as is defined by the claims.

[0017] The invention can be better understood with reference to the following drawings. The elements of the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating principals of the invention. Furthermore, like reference numerals designate corresponding parts throughout the several views.

[0018] FIG. 1 is a block diagram illustrating implementation of a subscriber loop communication system in accordance with the present invention;

[0019] FIG. 2 is a flow chart illustrating the preferred architecture, functionality, and operation of the data transmitter in accordance with a first embodiment of the present invention; and

[0020] FIG. 3 is a flow chart illustrating the preferred architecture, functionality, and operation of the data transmitter in accordance with a second embodiment of the present invention.

[0021] A telephone communication system 10 in accordance with the present invention is configured to operate over subscriber line 11 as depicted in FIG. 1. Telephone signals are communicated between a telephone 17 and a central office 18 associated with a telephone networking system such as the public switched telephone systems (POTS). Within central office 18 is a POTS switch 21 that transmits and receives the telephone signals which include ringing signals transmitted from POTS switch 21. Data is communicated over subscriber loop 11 between a remote digital subscriber line (DSL) modem 26 to DSL modem 29 located at central office 18. The data communications between DSL modems 26 and 29 may occur simultaneously (duplex), or may be alternating (halfduplex), and only one or the other may in fact be present (simplex). The data and telephone signals can occur concurrently on subscriber line 11, and independence between the data and telephony communications can be attempted by frequency division multiplexing wherein the telephony signals occupy the frequency band between 0 and 4000 Hertz (Hz) and the data signals occupy the frequency band above 8000 Hz, for example. The degree of achieved independence is dependent on controllable factors such as the filtering used to accomplish the frequency division multiplexing and uncontrollable factors such as the couplings between the POTS and the data at points where filtering cannot be effective. With regard to the description above, any combination of additional telephone devices 17 or similar terminating POTS devices such as dial modems are possible, and more than one DSL modem 26 also is possible.

[0022] As depicted by FIG. 1, DSL modem 26 includes a data transmitter to transmit digital data from DSL modem 26 and a data receiver to receive digital data from subscriber line 11. Furthermore, DSL modem 29 includes a data transmitter 42 to transmit digital data from DSL modem 29 and a data receiver 44 to receive digital data from subscriber line 11. For the purposes of the present invention, a “data transmitter” is any device or collection of devices in a modem which controls and implements the transmission of data from the modem, and a “data receiver” is any device or collection of devices in a modem which receives and processes the data transmitted from a data transmitter.

[0023] As can be further seen by reference to FIG. 1, POTS signals and data signals share the same communication channel 11. This sharing can cause problems due to the occurrence of very large amplitude POTS signals during POTS call establishments, examples being ringing and ring-trip (wherein the ringing signal is abruptly terminated by an off-hook termination). Such call establishment signals have amplitudes that may be one-hundred times larger than the POTS signals and DSL signals used during normal communication and may have frequency content that exceeds the normal POTS band and intrudes on the DSL band.

[0024] In particular, the occurrence of telephone rings can cause data errors when data is being communicated between DSL modems 26 and 29. Usually, the telephone rings occur as a part of a ringing cadence which is typically a repetitive cycle of about one second of ringing followed by about three seconds of silence which repeats until telephone 17 goes off hook or the ringing is terminated. The occurrence of a ringing cadence may result in the loss of data when the ringing cadence is allowed to interrupt a data session between DSL modems 26 and 29. In applications involving frequent telephone rings, data communication may be impractical if steps are not taken to ensure the reliability of the data communicated between DSL modems 26 and 29.

[0025] The data communication system 10 of the present invention enables the correction of any data erred by a ring or a ring-TRIP signal and enables the communication of data during the silent intervals of a ringing cadence, thereby allowing the communication of data during the occurrence of a ringing cadence. With reference to FIG. 1, the communication system 10 of the first embodiment of the present invention preferably provides for the detection of a ring signal or a ring request at data transmitter 42. A “ring request” is a signal transmitted from POTS switch 21 to modem 29 via connection 52 that indicates a ring is about to occur. DSL modem 29 is configured to detect the occurrence of a ring signal by detecting a ring request via line 52 and/or by detecting the ring signal via ring detector 54 which is any suitable device capable of detecting a ring signal. Therefore, it is possible for DSL modem 29 to detect a communications error due to the occurrence of a ring signal without receiving a notification from DSL modem 26.

[0026] In response to the detection of an interrupting ring signal or ring request, data transmitter 42 is configured to cease any data transmission that may be occurring. If a data signal being transmitted is interrupted by the ring signal, then data transmitter 42 is designed to store the interrupted signal by techniques well known in the art. Data transmitter 42 is then designed to delay the transmission of any data signals until the interrupting ring signal has ceased. It may be necessary for data transmitter 42 to store data by methods well known in the art during this delay in order to prevent the loss or overrun of data. Once data transmitter 42 detects that the interruption has ceased, data transmitter 42 is designed to begin transmitting data again.

[0027] If a data signal was not interrupted by the occurrence of the ring signal (i.e., data transmitter 42 was not transmitting at the time of ring detection), then data transmitter 42 is preferably configured to continue normal transmission of data signals when necessary once the ring signal has ceased. However, if the ring signal interrupted the transmission of a data signal, then data transmitter 42 is preferably configured to retransmit the interrupted data signal upon the cessation of the ring signal before continuing the normal transmission of data signals. It is preferable to include a header on this retransmitted data to indicate to data receiver 32 that the transmitting signal is a retransmission of a previously interrupted data signal. As used herein, a header can be any sequence of particular data values recognizable by data receiver 32.

[0028] Data receiver 32 is designed to receive the data transmitted by data transmitter 42. If the occurrence of the ring signal did not interrupt a data transmission by data transmitter 42, then data receiver 32 is preferably designed to receive the transmitted data from data transmitter 42 and to process this data for use by DSL modem 26. However, if the occurrence of the ring signal interrupted a data transmission, then data receiver 32 is preferably designed to detect this interruption. Data receiver 32 can be configured to detect the interruption of a data signal either by having a ring detector 55 to detect the occurrence of a ring signal or by recognizing the header preferably attached to the first data signal transmitted after the cessation of the ring signal. When data receiver 32 recognizes that the interruption of a data signal has occurred, data receiver 32 discards the interrupted signal and anticipates the retransmission of the interrupted signal which it receives upon cessation of the interrupting ring signal.

[0029] When data receiver 32 detects the retransmission header to recognize an interruption, it is desirable for data receiver 32 to store received data before processing the received data until other data is received that does not contain a retransmission header. By doing so, data receiver 32 ensures that only valid data is processed.

[0030] It should be noted that the system 10 outlined hereinabove for data transmission during the occurrence of a ringing cadence is not limited to the situation where data transmitter 42 is a central office 18 transmitter and data receiver 32 is a remote modem 26 receiver. It should be obvious to one ordinarily skilled in the art that data transmitter 34 of remote DSL modem 26 and data receiver 42 of DSL modem 29 can be configured in the same way as data transmitter 42 and data receiver 32, respectively. By doing so, transmission from DSL modem 26 to DSL modem 29 during occurrence of a ringing cadence is enabled.

[0031] In a second embodiment of the present invention, modem 29 is preferably configured to notify, via signal 53, POTS switch 21 to delay ringing until such time that data communication has ceased. Unlike the first embodiment, modem 29 is preferably designed to delay the ring signal until data signals currently in the process of being transmitted have been completely and reliably received. In this regard, modem 29 may use any suitable conventional technique to determine whether all transmitted data has been reliably received. Once the current data signals have been successfully received, then POTS switch 21, in response to signal 53, allows the ring signal to occur. By delaying the occurrence of the ring signal until the current data signals have been reliably received, interference of ring signals and data signals is prevented. Accordingly, there is no need to retransmit data signals since all such signals have been reliably received by data receiver 32.

[0032] In the case when data transmitter 42 is not in the process of transmitting data upon the detection of the ring request, the ring signal is immediately allowed to occur. Once the ring signal has ceased, data transmitter 42 is preferably designed to begin data transmissions again until the detection of the next ring request. In this way, data communication and telephone ringing are interleaved across the same connections.

[0033] It should be noted that the second embodiment of the present invention may be used with communication between data transmitter 34 of modem 26 and data receiver 44 of modem 29. However, since modem 29 is preferably designed to control the ring request signal, modem 29 is preferably configured to detect when data transmitter 34 of modem 26 is transmitting. When modem 29 detects that data transmitter 34 of modem 26 is not transmitting at the occurrence of a ring request detection, then modem 29 merely allows the ring signal to proceed via signal 53. At this time, modem 26 detects the ring signal and waits for the ring signal to cease before transmitting any data.

[0034] When modem 29 detects that data transmitter 34 of modem 26 is transmitting when a ring request is detected, then modem 29 is preferably designed to inhibit the ring request until the transmitted data is reliably received by data receiver 44. Once modem 29 determines that the transmitted data is reliably received by data receiver 44, modem 29 is designed to allow the ring signal to occur, and data transmitter 34 is preferably designed to wait to transmit any further data until modem 26 detects the cessation of the ring signal. As a result, data communication and ring signaling are interleaved across a user subscriber line 11.

[0035] The preferred use and operation of the communication system 10 and associated methodology are described hereafter.

[0036] The operation and functionality of the first embodiment of the present invention are depicted in FIG. 2. Blocks 62-72 show that the present invention transmits data normally with the exception that data being transmitted is also being stored in transmitter 42 in anticipation of a need to retransmit this data in the event that it is determined that transmission was likely erred due to disrupting signals. Block 68 may detect an interfering signal by several means including the detection of the amplitudes of signals which exceed those normally transmitted or received by modem 29.

[0037] If a disrupting signal is detected in block 68, as noted in block 74, transmitter 42 stops transmission. Block 76 shows that modem 29, then continues to store incoming data. Although not necessary for implementation of the present invention, modem 29 (in block 76) also enables flow control on the incoming data in order to ensure that data overflow does not occur. As shown in block 78, modem 29 stays in the state of block 76 until the interfering signal ceases.

[0038] As noted in Block 82, when the interfering signal is absent, transmitter 42 retransmits the stored data and any data not flow controlled and preferably adds information suitable for receiver 32 to identify such data as a retransmission.

[0039] Note that most practical data transmission protocols limit the amount of data expected to be transferred by placing data into packets or cells. Thus, the amount of data stored above is not limitless when the present invention is utilized in the context of most current protocols.

[0040] It should be noted that the functionality of FIG. 2 is the same when DSL modem 26 is the transmitting device and DSL modem 29 is the receiving device.

[0041] The operation and functionality of the second embodiment of the present invention are depicted in FIG. 3. Blocks 104 and 106 show that the present invention initially determines if there is data to be transferred or if there is a ring request. As indicated in blocks 106-112, if a ring request is detected prior to the detection of data, the ring signal is generated. Although not shown in FIG. 3, it may be necessary to store requested data transmissions that occur during the ring signal in order to prevent the loss or overrun of data. Once the ring signal ceases, the process of checking for data and ring requests is repeated as shown by block 112.

[0042] If the present invention detects that there is data to be transmitted, blocks 114-118 show that the data is transmitted from transmitter 42 until a ring request is detected or the data is completely transferred. If a ring request is detected before the data transfer is completed, then block 122 shows that the data is allowed to finish transmitting before any more steps are taken. Once it is ensured that the current data signals have been reliably transferred, blocks 108 and 112 show that the ring signal is enabled.

[0043] It should be noted that the functionality of FIG. 3 is the same when modem 26 of is transmitting to modem 29. However, it is modem 29 that controls block 108 of FIG. 3, in such a case. Therefore, when data transmitter 34 is not transmitting at the occurrence of a ring request, modem 29, having determined that modem 26 has ceased transmission, permits any ring request to proceed.

[0044] It should be further noted that data transmitter 34 is preferably configured not to transmit any data until data transmitter 42 signals modem 26 to do so. Accordingly, a “yes” from block 104 in FIG. 3 is not only dependent upon there being data in modem 26, but it also is dependent on there being an enabling signal from data transmitter 42.

[0045] Furthermore, when modem 26 is transmitting at the occurrence of a ring request, data transmitter 42 inhibits any ring request until the data is reliably received. Accordingly, data transmitter 42 performs the functionality of block 111 and 108 of FIG. 3.

[0046] In either embodiment of the communication system 10 of the present invention, data communication and ring signals are interleaved on a subscriber line 11. Both embodiments achieve this by transmitting data only in the silent intervals of a ringing cadence and by either insuring no interruption of a data transmission or by retransmitting any data signal which is interrupted.

[0047] It should be noted that the implementation of the present invention has been illustrated with an occurrence of a ring signal. However, the ring signal can be replaced with a ring-trip or other relatively large disturbance without departing from the principles of the present invention.

[0048] In concluding the detailed description, it should be noted that it will be obvious to those skilled in the art that many variations and modifications may be made to the preferred embodiments without substantially departing from the principals of the present invention. All such variations and modifications are intended to be included herein within the scope of the present invention, as set forth in the following claims.