Reverse path allocation and contention resolution scheme for a broadband communications system

• US 5,581,555 A
• Filed: 06/07/1995
• Issued: 12/03/1996
• Est. Priority Date: 09/17/1993
• Status: Expired due to Fees

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Scientific-Atlanta Incorporated (Cisco Systems, Inc.)
• Inventors: Bohannon, Thomas A., Dubberly, Gregory T.
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): Patel, Ajit
• Application Number:
  US08/475,220
• Time in Patent Office: 545 Days
• Field of Search: 348/6, 348/8, 348/12, 348/13, 348/14, 348/15, 348/10, 348/7, 348/16, 348/17, 348/18, 455/3.1, 455/4.2, 455/5.1, 455/6.1, 455/4.1, 455/6.3, 370/69.1, 370/71, 370/73, 370/110.1, 370/94.1, 370/94.3, 370/94.2, 370/60, 370/85.2
• US Class Current: 370/487
• CPC Class Codes: H04H 20/78 CATV [Community Antenna Television] systems
• CPC Class Codes: H04H 20/79 using downlink of the CATV systems, e.g. audio broadcast via CATV network
• CPC Class Codes: H04H 20/81 combined with telephone network over which the broadcast is continuously available
• CPC Class Codes: H04H 60/94 Telephonic networks for accessing the Internet H04H60/84
• CPC Class Codes: H04H 60/97 using uplink of the CATV systems
• CPC Class Codes: H04J 1/12 Arrangements for reducing cross-talk between channels in line transmission systems H04B3/32; in cables or lines H04B3/26 - H04B3/30
• CPC Class Codes: H04J 2203/0041 Star, e.g. cross-connect, concentrator, subscriber group equipment, remote electronics
• CPC Class Codes: H04J 2203/0089 Multiplexing, e.g. coding, scrambling, SONET
• CPC Class Codes: H04J 3/1623 Plesiochronous digital hierarchy [PDH]
• CPC Class Codes: H04L 12/2801 Broadband local area networks
• CPC Class Codes: H04L 12/413 with random access, e.g. carrier-sense multiple-access with collision detection [CSMA-CD]
• CPC Class Codes: H04M 7/006 Networks other than PSTN/ISDN providing telephone service, e.g. Voice over Internet Protocol (VoIP) , including next generation networks with a packet-switched transport layer H04L65/00 takes precedence; aspects not specific to the type of network H04M3/00; special services in those networks H04M3/42
• CPC Class Codes: H04N 2007/1739 the upstream communication being transmitted via a separate link, e.g. telephone line
• CPC Class Codes: H04N 7/10 Adaptations for transmission by electrical cable H04N7/12 takes precedence
• CPC Class Codes: H04N 7/14 Systems for two-way working H04N7/12, H04N7/173 take precedence
• CPC Class Codes: H04N 7/17309 Transmission or handling of upstream communications
• CPC Class Codes: H04Q 11/0478 Provisions for broadband connections
• CPC Class Codes: H04Q 2213/13332 Broadband, CATV, dynamic bandwidth allocation

Abstract

A broadband communications system for coupling telephony or other digital networks to a CATV network. The system transmits a multiplex of telephony signals in the forward band of the CATV network. The forward telephony channels are demodulated and demultiplexed by a plurality of subscriber terminals into the individual telephony signals directed to an addressed subscriber. Signals returning from subscribers are digitized into standard telephony signals onto the reverse band of the CATV network, and demodulated and multiplexed into a standard telephony signal that is interfaced to the telephony network. A multiplicity of subscribers are initially assigned to a selected reverse band channel. If more than one subscriber contends for use of the reverse channel by transmitting in the channel, signals from the contending subscribers interfere and prevent any subscriber'"'"'s identity from being decoded and acknowledged. The contending subscribers wait for a random wait time and re-attempt to transmit. Upon transmission re-attempt, one of the subscribers (typically the one with the shortest wait time) will successfully gain access to the reverse channel, and the other subscribers are assigned to a different reverse channel.

Claims

1. A telephony system for communicating telephony signals between a telephony network and a broadband communication network including a headend communicating to a plurality of subscribers, comprising:

a modulator, coupled between the telephony network and the headend, for modulating the telephony signals from the telephony network on a carrier in a first band of the broadband communication network;

equipment for assigning a plurality of subscribers to a selected frequency subband in a second band of the subscription network;

reverse path contention resolution equipment for detecting contention by more than one subscriber for the selected frequency subband and reassigning at least one subscriber to a different frequency subband in the second band; and

a demodulator, coupled between the telephony network and the headend, for demodulating the telephony signals in the selected frequency subband and coupling them to the telephony network.

2. The system of claim 1, wherein the broadband communication network includes a subscriber terminal for demodulating the telephony signals in the first band of broadband network and coupling them to the subscriber, and for modulating the telephony signals from the subscriber in the one or more selected frequency subbands in the second band of the broadband network for communication to the headend.

3. The system of claim 2, wherein the subscriber terminal includes a frequency agile modulator for modulating the telephony signals in the one or more selected frequency subband in the second band, and further comprising:

a noise monitor for monitoring the noise level in a selected frequency subband associated with a particular subscriber, and

equipment responsive to the noise monitor for communicating a frequency change signal to said particular subscriber when the noise level in the selected frequency subband exceeds a predetermined threshold,

whereby the subscriber terminal changes the frequency for communicating at least some of the telephony signals to a different selected frequency subband when a given channel becomes too noisy.

4. The system of claim 1, wherein the broadband communication network is a cable television (CATV) network, and further comprising equipment for providing television program signals in said first band of frequencies to subscribers.

5. The system of claim 1, wherein the assigning equipment comprises:

equipment for communicating a channel assignment message containing subscriber identification information and the identity of one or more selected frequency subbands in the second band associated with the subscriber identification information.

6. The system of claim 5, wherein said channel assignment message is transmitted in a directory channel in the first band.

7. The system of claim 1, further comprising:

a frequency agile modulator located at the subscriber operative to change the frequency at which telephony signals are being communicated to the headend from a first frequency subband to a second frequency subband in response to a command received from the headend.

8. The system of claim 7, wherein the frequency agile modulator comprises a quadrature phase shift keying (QPSK) modulator operative at selectable carrier frequencies varying in discrete increments of 128 kHz channels, beginning at a nominal initial carrier frequency of 5.12 MHz, with a nominal data rate of 144 kbps per channel.

9. The system of claim 8, wherein each said 144 kbps channel comprises two 64 kbps DS0 telephony channels and one 16 kbps overhead channel including data headers, address information, and CRC data.

10. The system of claim 8, wherein each 128 kHz channel comprises a 108 kHz bandwidth data channel and 20 kHz in guard bands.

11. The system of claim 1, further comprising:

a customer interface unit including a demodulator for demodulating said telephony signals in said first frequency band to obtain an incoming telephony signal directed to a particular subscriber and coupling said incoming telephony signal to a telephony port.

12. The system of claim 11, wherein said telephony signals are communicated to the customer interface unit via QPR modulation.

13. The system of claim 11, wherein said telephony signals communicated in the first frequency band comprise:

a plurality of incoming telephony signals arranged in a plurality of channels;

at least one directory channel containing channel assignment information; and

at least one signaling channel containing status information.

14. The system of claim 13, wherein said telephony signals comprise a 3.168 MHz QPR modulated signaling containing 96 DS0 digital incoming telephony signals, said directory channel, said signaling channel, and CRC data associated with a frame of digital signals.

15. A customer interface unit for connection to a broadband communication network, the customer interface unit operative for receiving first signals in a first frequency band from a headend associated with the broadband communication network, for receiving second signals from the headend, and for communicating telephony signals between a subscriber and the headend, said customer interface unit comprising:

a first demodulator for demodulating first signals in the first frequency band and for coupling them to an output port;

a second demodulator for receiving second signals and for determining, from said second signals, an acknowledge signal and one or more selected frequency subbands in a second band of frequencies in the broadband communication network for communicating telephony signals to the headend;

a frequency agile modulator responsive to the determined one or more selected frequency subbands in the second band of frequencies for modulating the telephony signals from the customer interface unit in the one or more selected frequency subbands; and

a timer for causing said frequency agile modulator to wait a predetermined time period before further transmission in response to failure to receive said acknowledge signal from the headend within a predetermined time period after an initial transmission.

16. The customer interface unit of claim 15, wherein the broadband communication network is a cable television (CATV) network.

17. The customer interface unit of claim 16, wherein said first signals include television program signals, and wherein said output port comprises a video signal port for connection to a CATV set top converter.

18. The customer interface unit of claim 15, further comprising a telephony port for receiving the telephony signals into the customer interface unit.

19. The customer interface unit claim 15, further comprising:

a video signal output port for coupling to a cable television set top terminal;

at least one telephony signal port for coupling to a subscriber'"'"'s home telephony network.

20. The customer interface unit of claim 19, further comprising:

a subscriber input port for receiving subscriber signals associated with an interactive consumer device selected from;

pay per view television, interactive television, video games, and shopping channel television selection.

21. The customer interface unit of claim 15, wherein the second signals are communicated in the first frequency band.

22. The customer interface unit of claim 15, wherein the second signals comprise a message including address information corresponding to a selected subscriber and frequency subband information corresponding to the one or more selected frequency subbands.

23. The customer interface unit of claim 15, wherein said second signals are transmitted in a directory channel.

24. The customer interface unit of claim 15, wherein said frequency agile modulator is operative to change the frequency at which telephony signals are being communicated to the headend from a first frequency subband to a second frequency subband in response to a command received via the second signals.

25. The customer interface unit of claim 15, wherein said frequency agile modulator comprises a quadrature phase shift keying (QPSK) modulator operative at selectable carrier frequencies varying in discrete increments of 128 kHz channels, beginning at a nominal initial carrier frequency of 5.12 MHz, with a nominal data rate of 144 kbps per channel.

26. The customer interface unit of claim 25, wherein each said 144 kbps channel comprises two 64 kbps DS0 telephony channels and one 16 kbps overhead channel including data headers, address information, and CRC data.

27. The customer interface unit of claim 25, wherein each 128 kHz channel comprises a 108 kHz bandwidth data channel and 20 kHz in guard bands.

28. The customer interface unit of claim 15, wherein telephony signals from the headend communicated to the subscriber are transmitted in said first frequency band, wherein said customer interface unit further comprises:

a third demodulator for demodulating said telephony signals in the first frequency band to obtain an incoming telephony signal directed to a particular subscriber and coupling said incoming telephony signal to a telephony port.

29. The customer interface unit of claim 28, wherein said telephony signals are communicated to the customer interface unit via QPR modulation.

30. The customer interface unit of claim 28, wherein said telephony signals communicated in the first frequency band comprise:

a plurality of incoming telephony signals arranged in a plurality of channels;

at least one directory channel containing said second signals; and

at least one signaling channel containing status information.

31. The customer interface unit of claim 30, wherein the telephony signals comprise a 3.168 MHz QPR modulated signaling containing 96 DS0 digital incoming telephony signals, said directory channel, said signaling channel, and CRC data associated with a frame of digital signals.

32. A method of operating a broadband communication network, including a telephony network interface for connection to a telephony network, for communicating signals between subscribers and the telephony network, comprising the steps of:

receiving a multiplexed incoming telephony signal from the telephony network comprising a plurality of telephony signals provided in a standard multiplexed telephony format;

demultiplexing the incoming multiplexed telephony signal to obtain at least one selected incoming telephony signal intended for a particular subscriber on the broadband communication network;

transmitting the selected incoming telephony signal to the particular subscriber in a first frequency band on the broadband communication network;

receiving the selected incoming telephony signal at a customer interface unit connected to the broadband communication network associated with the particular subscriber;

coupling the selected incoming telephony signal to a telephony port associated with the customer interface unit;

receiving an outgoing telephony signal from a particular subscriber at the telephony port;

assigning plural subscribers to a selected subband in a second frequency band on the broadband communication network;

transmitting said outgoing telephony signal on at least one assigned carrier in said selected subband;

resolving contention between plural subscribers assigned to said selected subband;

demodulating said outgoing telephony signal in the selected subband;

multiplexing said outgoing telephony signal from the particular subscriber with other telephony signals associated with other subscribers to obtain a multiplexed outgoing telephony signal comprising a plurality of telephony signals in a standard multiplexed telephony format to telephony network; and

coupling the multiplexed outgoing telephony signal to the telephony network.

33. The method of claim 32, wherein the step of resolving contention between plural subscribers assigned to a selected subband comprises the steps of:

transmitting a communication request signal from a requesting subscriber in said selected subband;

transmitting an acknowledge signal from the headend to the requesting subscriber;

in response to failure to receive the acknowledge signal from the headend in a predetermined first time period, causing the customer interface unit associated with the requesting subscriber to wait a predetermined second time period before transmitting a second communication request signal.

34. The method of claim 33, wherein the predetermined second time period comprises a random time.

35. The method of claim 32, further comprising the step of:

allocating one or more selected frequency subbands in the second frequency band on the broadband communication network so as to provide selectably variable bandwidth service.

36. The method of claim 35, wherein said selectably variable bandwidth service comprises telephony service selected from a single line service, multiple line service, ISDN service and T1 service.

37. The method of claim 32, further comprising the step of:

changing the frequency from the selected subband in the second frequency band on the broadband communication network to another frequency subband during a communication session.

38. The method of claim 37, further comprising the step of:

monitoring the noise level in the selected subband, and wherein the step of changing the frequency of the selected subband is carried out in response to a determination in the monitoring step that the noise level in the selected subband exceeds a predetermined threshold.

39. The method of claim 38, wherein the step of monitoring the noise level in the selected subband comprises the steps of:

determining a cyclic redundancy check (CRC) value for each packet of digital data comprising the telephony signal prior to transmission of the signal;

receiving the CRC value at the headend;

in response to a determination that the CRC value is incorrect, incrementing an error count register;

comparing the error count register to a predetermined value;

when the error count register exceeds a predetermined threshold value, setting a noisy channel status flag; and

changing the frequency in response to setting the noisy channel status flag.

40. The method of claim 39, wherein the step of comparing the error count register to the predetermined threshold value is carried out on a periodic basis so as to determine the number of transmission errors associated with a predetermined number of packets transmitted in a predetermined time.

41. An apparatus for the communication of telephony signals to and from a telephony network and to and from a plurality of subscribers of a subscription system including a subscription network having a first band of frequencies for communicating signals to subscribers in the subscription network and a second band of frequencies for communicating signals from the subscribers, comprising:

a telephony network modulator for modulating the telephony signals from the telephony network on said first band of said subscription network;

a subscriber terminal including a subscriber terminal demodulator for demodulating the telephony signals in said first band from the subscription network and coupling them to a subscriber;

a frequency tunable second modulator associated with each of said plurality of subscribers for modulating telephony signals from each subscriber in a selected frequency subbands in said second band of the subscription network;

a telephony network demodulator for demodulating the telephony signals from said second band of the subscription network and coupling them to the telephony network; and

a device for detecting contention in said selected frequency subband and reassigning one or more of said second modulators to a different frequency subband in said second band.

42. The apparatus of claim 41, wherein said frequency tunable second modulator associated with each of said plurality of subscribers is initially assigned a predetermined frequency subband in said second band for communications, and the identity of said predetermined frequency subband is transmitted to each of said plurality of subscribers in said first band.

43. The apparatus of claim 41, further comprising an address and control unit (ACU) for associating frequency subbands in said second band of the subscription network with subscribers.

44. The apparatus of claim 43, wherein said ACU stores frequency subbands in said second band in association with subscriber identification information in a memory.

45. The apparatus of claim 43, wherein said ACU is operative for initially assigning each of said plurality of subscribers to a particular frequency subband in said second band, and wherein a given particular frequency subband may be initially assigned more than one subscriber.

46. The apparatus of claim 43, wherein said ACU is operative to detect a communication from a subscriber in a particular frequency subband in said second band, and is thereafter operative to reassign other subscribers assigned to that particular frequency subband to another frequency subband.

47. The apparatus of claim 43, wherein said ACU maintains an allocation table in memory storing subscriber identification and frequency subband assignment information in association.

48. The apparatus of claim 41, further comprising:

a broadcast message information source for generating second band frequency assignment information for broadcast to a selected group of subscribers on the subscription network; and

a device for coupling said broadcast message to a carrier in the first band of the subscription network for communication to said selected group of subscribers,

whereby second band frequency assignment information is generated at a single source and delivered to plural subscribers.

49. A method of operating a communication system to couple telephony signals to and from a telephony network and to and from a plurality of subscribers of a subscription system including a tree-and-branch type broadband subscription network extending from a headend to the subscribers, comprising the steps of:

providing an interface for telephony signals from the telephony network to the headend;

providing an interface for telephony signals from a subscriber to a subscriber terminal connected to the subscription network;

providing a first band of frequencies for communicating signals to subscribers from the headend;

modulating the telephony signals from the telephony network on the first band of the subscription network;

providing a second band of frequencies for communicating signals to the headend from subscribers;

subdividing the second band of frequencies into a plurality of selectable subbands;

initially assigning each of the plurality of subscribers to one of the plurality of selectable subbands, where more than one subscriber is assigned to any given selectable subband;

transmitting the subband assignments to the plurality of subscribers in the first band;

in response to a request for telephony service from a requesting subscriber, transmitting a signal in the selected subband comprising requesting subscriber identification information;

at the headend, in response to receipt of subscriber identification information, re-assigning other subscribers that were initially assigned to the selected subband in which the requesting subscriber transmitted to another selected subband; and

modulating telephony signals from the requesting subscriber in the selected subband.

50. A method of operating a communication system to couple telephony signals to and from a telephony network and to and from a plurality of subscribers of a subscription system including a tree-and-branch type broadband subscription network extending from a headend to the subscribers, comprising the steps of:

providing an interface for telephony signals from the telephony network to the headend;

providing an interface for telephony signals from a subscriber to a subscriber terminal connected to the subscription network;

providing a first band of frequencies for communicating signals to subscribers from the headend;

modulating the telephony signals from the telephony network on the first band of the subscription network;

providing a second band of frequencies for communicating signals to the headend from subscribers;

subdividing the second band of frequencies into a plurality of selectable subbands;

initially assigning each of the plurality of subscribers to one of the plurality of selectable subbands, where more than one subscriber is assigned to any given selectable subband;

transmitting the subband assignments to the plurality of subscribers in the first band;

in response to an incoming call to a selected subscriber, re-assigning other subscribers that were initially assigned to the subband associated with the called selected subscriber to another selected subband; and

modulating telephony signals from the called selected subscriber in the selected subband.

51. A method of operating a bidirectional communication system to couple telephony signals to and from a telephony network and to and from a plurality of subscribers of a subscription system including a broadband subscription network extending from a headend to the subscribers, comprising the steps of:

assigning a plurality of subscribers to a particular subband in a reverse frequency band in the subscription system for communication of signals from the plurality of subscribers;

receiving a multiplexed telephony signal containing a plurality of predetermined telephony signals in a plurality of telephony channels;

demultiplexing the multiplexed telephony signal to obtain a selected telephony signal from a selected telephony channel;

determining a selected subscriber for the selected telephony signal;

communicating the selected telephony signal from the headend to the selected subscriber in a forward frequency band in the subscription system;

in response to contention for use of the particular subband, reassigning other subscribers of the plurality of subscribers assigned to the particular subband in the reverse frequency band that included the selected subscriber to a different subband;

communicating subscriber telephony signals from the selected subscriber to the headend in the particular subband; and

coupling the subscriber telephony signals to the selected telephony channel.

52. The method of claim 51, further comprising the step of communicating information identifying the selected subband in the second frequency band to the selected subscriber from the headend so as to cause the subscriber terminal to transmit the subscriber'"'"'s telephony signals in the selected subband.

53. The method of claim 52, wherein the step of communicating information identifying the selected subband in the second frequency band to the selected subscriber comprises providing a signaling channel for communication of status signals between a subscriber and the headend.

54. The method of claim 53, wherein the status signals includes subband assignment information and subscriber identification information.

55. The method of claim 51, further comprising the step of changing the frequency from the selected subband in the second frequency band to another frequency subband during a communication session involving the selected subscriber.

56. The method of claim 55, further comprising the step of monitoring the noise level in the selected subband, and wherein the step of changing the frequency of the selected subband is carried out in response to a determination in the monitoring step that the noise level in the selected subband exceeds a predetermined threshold.

57. The method of claim 56, wherein the step of monitoring the noise level in the selected subband comprises the steps:

determining a cyclic redundancy check (CRC) value for each packet of digital data comprising the telephony signal prior to transmission of the signal;

receiving the CRC value at the headend;

in response to a determination that the CRC value is incorrect, incrementing an error count register;

comparing the error count register to a predetermined value;

when the error count register exceeds a predetermined threshold value, setting a noisy channel status flag; and

changing the frequency in response to setting the noisy channel status flag.

58. The method of claim 57, wherein the step of comparing the error count register to the predetermined threshold value is carried out on a periodic basis so as to determine the number of transmission errors associated with a predetermined number of packets transmitted in a predetermined time.