Repeatered, multi-channel fiber optic communication network having fault isolation system

Abstract

A repeatered, multichannel fiber optic communication network includes a plurality of full duplex fiber optic channels and one or more auxiliary channels. In order to supervise and control the operation of the network, for both data transmission and fault/maintenance actions, each terminal station contains a processor-based subsystem capable of network monitoring, first level maintenance action, fault isolation, and remote network control and status reporting. This processor-based subsystem interfaces with each fiber optic channel, with an orderwire communication link, and with external input/output devices and surveillance equipment. Three substantially autonomous processor-based sections which are dedicated to performing specific functions within the overall network operation are employed for carrying out these separate interfacing tasks. Each section of the processor-based subsystem in a terminal station contains its own CPU and associated memory and is programmed to carry out specific functions identified with that section. Each section is interconnected with the other two so that, internally, the subsystem is fully integrated.

Claims

What is claimed is:

1. In a communication network wherein signals are conveyed between first and second stations over a first communication link having at least one repeater station disposed between said first and second stations, a method for isolating a fault occurring on said link comprising the steps of:

(a) transmitting a first prescribed encoded signal sequence over said communication link;

(b) selectively monitoring, at respective stations along said link, a prescribed signal transmission characteristic of the respectively monitored stations along said link; and

(c) in response to a prescribed change in the signal transmission characteristic of said link at one of said monitored stations, representative of the existence of a fault in said link at said one of said monitored stations, transmitting from said one of said monitored stations a signal representative of said change in signal transmission characteristic, so as to identify said fault as being associated with that monitored station along said link that introduces said prescribed change in said signal transmission characteristic.

2. A method according to claim 1, wherein step (a) comprises transmitting a pseudorandom code signal over said communication link.

3. A method according to claim 1, wherein step (b) comprises generating a second prescribed encoded signal sequence at a monitored station, comparing said first prescribed encoded signal sequence with said second prescribed encoded signal sequence, and generating an output signal indicative of the degree of comparison of said first and second prescribed encoded signal sequences.

4. A method according to claim 3, wherein each of said first and second prescribed encoded signal sequences is the same.

5. A method according to claim 3, wherein each of said first and second prescribed encoded signal sequences comprises a pseudorandom code signal.

6. A method according to claim 1, wherein said first prescribed encoded signal sequence is a digital signal and said prescribed signal transmission characteristic is the bit error rate of the throughput of said station.

7. In a communication network wherein signals are conveyed between first and second stations over a plurality of communication links having at least one repeater station disposed between said first and second stations, a method for isolating a fault occurring on one of said communication links comprising the steps of:

(a) replacing that one of said communication links on which a fault has been detected to have occurred with another of said communication links;

(b) transmitting a first prescribed encoded signal sequence over said one of said communication links;

(c) selectively monitoring, at respective stations along said one link, a prescribed signal transmission characteristic of said respective stations along said one link; and

(d) in response to a prescribed change in the signal transmission characteristic of said link at one of said monitored stations, representative of the existence of a fault in said link at said one of said monitored stations, transmitting from said one of said monitored stations a signal representative of said change in signal transmission characteristic, so as to identify said fault or being associated with that monitored station along said link that introduces said prescribed change in said signal transmission characteristic.

8. A method according to claim 7, wherein step (b) comprises generating a second prescribed encoded signal sequence at a monitored station, comparing said first prescribed encoded signal sequence with said second prescribed encoded signal sequence, and generating an output signal indicative of the degree of comparison of said first and second prescribed encoded signal sequences.

9. A method according to claim 7, wherein said communication links are fiber optic communication links.

10. A method according to claim 7, wherein step (a) comprises the steps of:

(a) causing the signals that are conveyed over said one of said communication links to be conveyed over said another of said communication links,

(b) synchronizing, at that one of said first and second stations to which said signals on said one link are conveyed, the signals that are conveyed on said one and another of said communication links with each other, and

(c) upon the signals on said one and other links becoming synchronized with each other, substituting said another of said communication links for said one communication link and inhibiting said communication link from transmitting said signals that would have otherwise been conveyed on said one communication link.

11. In a communication network having first and second terminal stations coupled to each other a plurality of communication links having at least one repeater station coupled in said links for regenerating information signals conveyed thereover between said first and second terminal stations, a system for controlling the operation of said network comprising:

first means, coupled to each of said communication links, for monitoring a prescribed characteristic of signals transmitted over said links, and producing a first output signal in response to a prescribed change in said characteristic on one of said links;

second means, coupled to said first means and coupled to each of said stations over a communication path exclusive of said communication links, for testing the operation of selected ones of said stations with respect to said one of said links;

third means, coupled to said second means and each of said communication links, for controllably modifying said prescribed characteristics of signals transmitted over a selected one of said links.

12. A system according to claim 11, further comprising fourth means, coupled to said first means and to said communication links, for replacing said one of said links with another of said links in response to said first output signal from said first means.

13. A system according to claim 11, wherein each of said communication links comprises an optical communication link.

14. A system according to claim 13, wherein said communication path comprises an electrical communication path.

15. A system according to claim 11, wherein said third means further includes means for monitoring the accuracy of the testing carried out by said second means with respect to said selected link at said selected ones of said stations.

16. In a communication network having first and second terminal stations coupled to each other over a plurality of communication links having at least one repeater station coupled in said links for regenerating information signals conveyed thereover between said first and second terminal stations, a system for controlling the operation of said network comprising:

first means, coupled to each of said communication links, for monitoring a prescribed characteristic of signals transmitted over said links and producing a first output signal in response to a prescribed change in said characteristic on one of said links;

second means, responsive to said first output signal produced by said first means, for replacing said one of said links with another of said links;

third means, responsive to the replacement of said one of said links with another of said links by said second means, for causing a prescribed encoded signal sequence to be transmitted over said one of said communication links;

fourth means, coupled to the stations along said one communication link, for monitoring a prescribed signal transmission characteristic of selected ones of said stations in response to the transmission of said prescribed encoded signal sequence over said one communication link; and

fifth means, coupled to said fourth means, for identifying that station, for which there occurs a prescribed change in the monitored prescribed signal transmission characteristic in response to the transmission of said prescribed encoded signal sequence, as being associated with the prescribed change in the signal characteristic monitored by said first means that has caused said first means to produce said first output signal.

17. A system according to claim 16, wherein said second means comprises:

means for causing the signals that are conveyed over said one of said communication links to be conveyed over said another of said communication links,

means for synchronizing the signals conveyed on said one and said another communication links with each other, and

means, responsive to the synchronization of said signals on said one and another communication links, for interrupting the flow of signals over said one link and enabling the flow of signals over said another link.

18. A system according to claim 16, wherein said prescribed encoded signal sequence comprises a PN signal sequence.

19. A system according to claim 16, wherein said fourth means is coupled to said fourth and fifth means stations over a communication path exclusive of said communication links.

20. A system according to claim 19, wherein said fourth means includes means for selectively communicating with each of the stations along said one communication link over said communication path and causing the selected station to monitor said prescribed signal transmission characteristic.

21. A system according to claim 16, wherein said communication links are fiber optic communication links.

22. A system according to claim 19, wherein said communication links are fiber optic communication links.

23. In a communication network having first and second terminal stations coupled to each other over a plurality of first communication links for conveying signals from said first terminal station to said second terminal station and a plurality of second communication links for conveying signals from said second terminal station to said first terminal station, and at least one repeater station coupled to said links for regenerating information signals conveyed over said links, a system for controlling the operation of said network comprising:

first means, located at said first terminal station, for monitoring a prescribed characteristic of signals transmitted from said second terminal station over said second communication links to said first terminal station and producing a first output signal in response to a prescribed change in said characteristic on one of said links;

second means, located at said first terminal station and responsive to said first output signal produced by said first means, for transmitting a first message to said second terminal station over each of said first communication links representative of the replacement of said one of of said first links by another of said first links;

third means, located at said second terminal station and responsive to said first message from said first means, for causing signals conveyed over said one of said second links to be conveyed over another of said second links;

fourth means, located at said first terminal station, for interrupting at said first terminal station the flow of signals conveyed over said one of said second links while enabling, at said first terminal station, the flow of said signals conveyed over said another of said second links;

fifth means, located at said second terminal station, for inhibiting the flow of signals, which would have otherwise been conveyed over said one of said second links, at said second terminal station and causing a prescribed encoded signal sequence to be transmitted in their place.

24. A system according to claim 23, wherein said prescribed encoded signal sequence is a PN signal sequence.

25. A system according to claim 23, further comprising sixth means, located at said first terminal station, for selectively communicating with each of the stations along said one of said first communication links over a communication path exclusive of said first and second communication links and causing a selected station to monitor a prescribed transmission characteristic of said one of said second links in response to said prescribed encoded signal sequence.

26. A system according to claim 25, wherein each of said stations includes means for comparing said prescribed encoded signal sequence with a prescribed code and producing an output signal indicative of the degree of mismatch between said prescribed encoded signal sequence and said prescribed code.

27. A system according to claim 26, further comprising seventh means, located at said first terminal station, for identifying that station, for which the degree of mismatch between said prescribed encoded signal sequence and said prescribed code exceeds a preselected value, as being associated with the prescribed change in said characteristic on said one of said second links.

28. In a communication network having first and second terminal stations coupled to each other over a plurality of communication links having at least one repeater station disposed between said first and second terminal stations, a system for controlling the operation of said network comprising:

first means, coupled to each of said communication links, for monitoring a prescribed characteristic of signals transmitted over said links and producing a first output signal in response to a prescribed change in said characteristic on one of said links;

second means, coupled to each of said stations, for monitoring at least one preselected operational or enviromental condition at said each station, and producing a second output signal in response to a prescribed change in said at least one preselected operational or environmental condition;

third means, coupled to said first and second means, for replacing said one of said links with another of said links in response to said first output signal or in response to said second output signal indicating a malfunction in a condition associated with said one of said links;

fourth means for causing a prescribed encoded signal sequence to be transmitted over said replaced one of said communication links; and

fifth means, coupled to each of said stations over a communication path exclusive of said communication links, for testing the operation of selected ones of said stations in response to said prescribed encoded signal sequence.

29. A system according to claim 28, wherein said encoded signal sequence includes a PN signal sequence.

30. A system according to claim 28, wherein said fifth means includes means for identifying that one of said selected stations that introduces a prescribed change in the signal transmission characteristic of said one link in response to said prescribed encoded signal sequence.

31. A system according to claim 30, wherein said second means includes means, coupled to each of said stations over said exclusive communication path, for interrogating said stations with respect to the production of said second output signals.

32. In a communication network having a first and second terminal stations coupled to each other over a plurality of communication links having at least one repeater station coupled in said links for regenerating information signals conveyed thereover between said first and second terminal stations, a system for controlling the operation of said network comprising:

first means, coupled to said communication links, for monitoring a prescribed content of said information signals transmitted over said links and producing a first output signal in response to errors in said prescribed content of said information signals; and

second means, responsive to said first output signal produced by said first means, for replacing said one of said links with another of said links, and wherein said second means includes means for replacing said one of said links with said another of said links irrespective of the degree of synchronization of information signals on said one and other links in response to said output signal being representative of at least a first preselected rate of errors in said prescribed content of said information signals.

33. In a communication network having a first and second terminal stations coupled to each other over a plurality of communication links having at least one repeater station coupled in said links for regenerating information signals conveyed thereover between said first and second terminal stations, a system for controlling the operation of said network comprising:

first means, coupled to said communication links, for monitoring a prescribed content of said information signals transmitted over said links and producing a first output signal in response to errors in said prescribed content of said information signals; and

second means, responsive to said first output signal produced by said first means, for replacing said one of said links with another of said links, and wherein said second means includes means for initially synchronizing the information signals on said one and another links and then causing the replacement of said one of said links with said another of said links in response to said first output signal being representative of no more than a first preselected rate of error in said prescribed content of said information signals.

34. A system according to claim 32, wherein said second means includes means for initially synchronizing the information signals on said one and another links and then causing the replacement of said one of said links with said another of said links in response to said first output signal being representative of no more than a second preselected rate of errors in said prescribed content of said information signals.

35. In a communication network having a first and second terminal stations coupled to each other over a plurality of communication links having at least one repeater station coupled in said links for regenerating information signals conveyed thereover between said first and second terminal stations, a system for controlling the operation of said network comprising:

first means, coupled to said communication links, for monitoring a prescribed content of said information signals transmitted over said links and producing a first output signal in response to errors in said prescribed content of said information signals; and

second means, responsive to said first output signal produced by said first means, for replacing said one of said links with another of said links, and wherein said information signals comprise encoded digital data containing periodically located synchronization data signals, said synchronization data signals corresponding to said prescribed content of said information signals and being employed by the terminal station receiving the information signals that have been transmitted over a communication link for decoding said encoded digital data.

36. A communication network comprising:

a first terminal station;

a second terminal station;

at least one repeater station disposed between said first and second terminal stations;

a plurality of first communication links, coupled to each of said stations, for conveying data from said first terminal station to said second terminal station;

a plurality of second communication links, coupled to each of said stations, for conveying data from said second terminal station to said first terminal station;

a plurality of first means, located at said first terminal station and coupled to receive data to be transmitted over respective ones of said first communications links, each of said first means including

means for encoding data to be transmitted, and

means for transmitting said encoded data over a respective one of said first communication links;

a plurality of second means, located at said second terminal station and coupled to respective ones of said first communication links, for decoding encoded data that has been transmitted from said first terminal station to said second terminal station, each of said second means including

means for receiving encoded data transmitted over a respective one of said first communication links, and

means for decoding the received encoded data and outputting the original data;

a plurality of third means, located at said second terminal station and coupled to receive data to be transmitted over respective ones of said second communications links, each of said third means including

means for encoding data to be transmitted

means for transmitting said encoded data over a respective one of said second communication links;

a plurality of fourth means, located at said first terminal station and coupled to respective ones of said second communication links, for decoding encoded data that has been transmitted from said second terminal station to said first terminal station, each of said fourth means including

means for receiving encoded data transmitted over a respective one of said second communication links, and

means for decoding the received encoded data and outputting the original data;

fifth means, located at said first terminal station, for controlling the operation of each of said first and fourth means, and coupled to each of said first and fourth means for supplying information signals to be contained in the encoded data transmitted by each of said first means and for receiving information signals contained in the encoded data decoded by each of said fourth means; and

sixth means, located at said second terminal station, for controlling the operation of each of said second and third means, and coupled to each of said second and third means for supplying information signals to be contained in the encoded data transmitted by each of said third means, and for receiving information signals contained in the encoded data decoded by each of said second means; and wherein

each of said encoding means includes means for encoding data to be transferred to the form of a sequence of a selected number of data bits periodically separated by a prescribed control bit, information signals from said fifth and sixth means being encoded as first preselected ones of said control bits.

37. A communication network according to claim 36, wherein each of said transmitting means includes means for scrambling data to be transmitted.

38. A communication network according to claim 37, wherein each of said first and third means includes means for generating a prescribed synchronization data sequence individual signal portions of which are contained in the encoded data as second preselected ones of said control bits.

39. A communication network according to claim 37, wherein each of said first and second terminal stations further includes means for coupling further data signals, exclusive of said data to be transmitted, to said first and third means and encoding said further data signals as second preselected ones of said control bits.

40. A communication network according to claim 39, wherein each of said first and third means includes means for alternately inserting said information signals from said fifth and sixth means and said further data signals into said encoded data as said first preselected control bit.

41. A communication network according to claim 40, wherein each of said first and third means includes means for generating a prescribed synchronization data sequence individual signal portions of which are contained in the encoded data as third preselected ones of said control bits.

42. A communication network according to claim 38, wherein said prescribed synchronization data sequence comprises an N-bit maximal length pseudorandom digital sequence, where N is an integer.

43. A communication network according to claim 38, wherein each of said second and fourth means includes means for removing from said encoded data said prescribed synchronization data sequence.

44. A communication network according to claim 38, wherein each of said fifth and sixth means includes means for monitoring said prescribed synchronization data sequence contained in the encoded data received by said fourth and second means, respectively, and supplying information signals representative of the replacement of one communication link by another communication link to said first and third means respectively, upon the bit error rate in said monitored prescribed synchronization data sequence exceeding a prescribed value.

45. A communication network according to claim 44, further including a third communication link, exclusive of said first and second pluralities of communication links, coupled to said first and second repeater stations, and wherein each of said stations includes means, coupled to said first and second terminal stations and to said at least one pluralities of communication links, for monitoring the bit error rate of the throughput for that repeater station for a specified one of said first and second communication links in response to the transmission of said prescribed synchronization data sequence over said specified one of said first and second communication links and transmitting a message indicative of said bit error rate over said third communication link.

46. In a communication network having first and second terminal stations between which information signals are conveyed over a plurality of normally active communication channels, said network further including an auxiliary communication channel to be substituted in place of a normally active channel in the event of a signal transmission fault on the normally active channel, and including at least one repeater station for regenerating information signals along said communication channels, each of said terminal stations including a control apparatus for controlling the operation of said network, the improvement wherein each control apparatus is coupled to each of said communication channels for exchanging messages therebetween for controlling the substitution of said auxiliary channel in place of one of said normally active channels, and wherein said network further includes an additional communication channel, exclusive of said normally active and auxiliary channels coupled to each control apparatus and repeater station, over which interrogation messages for monitoring the operation of said normally active and protection channels are conveyed, the frequency of transmission of said interrogation messages being established in accordance with a prescribed relationship between the stations between which the messages are conveyed.

47. An improved communication network according to claim 46, wherein each control apparatus includes a first audio interface circuit for interfacing audio and voice signals generated at said terminal stations with the data signals that are transmitted over each of the active ones of said normally active and protection channels.

48. An improved communication network according to claim 47, wherein each control apparatus includes a second audio interface circuit, for interfacing audio and voice signals with the interrogation messages that are transmitted over said additional communication channel.

49. In a communication network having first and second terminal stations, a plurality of information carrying normally active channels and at least one auxiliary channel linking said first and second terminal stations through at least one repeater station, the improvement comprising:

first means for monitoring a prescribed characteristic of information signals received at the terminal station over each active one of said channels and producing a first output signal indicative of said prescribed characteristic;

second means, coupled to said ffirst means, for causing a substitution of an auxiliary channel for that one of said normally active channels for which said first output signal from said first means indicates an unacceptable prescribed characteristic of said information signals transmitted over said one of said normally active channels;

third means, for causing a prescribed portion of the information signals carried over said normally active channels to be conveyed through said substituted channel; and

fourth means, coupled to each of said stations, for monitoring a prescribed characteristic of the prescribed portion of the information signals carried over said substituted channel, at selected ones of said stations.

50. The improvement according to claim 49, further including fifth means, coupled to said fourth means, for identifying the location of a fault in said substituted channel as corresponding to that station the throughput of which causes an unacceptable change in said prescribed characteristic of the prescribed portion of the information signals carried over said substituted channel.

51. The improvement according to claim 50, wherein said information signals are comprised of digital data signals scrambled in accordance with a preselected scrambling code.

52. The improvement according to claim 51, wherein said digital data signals include a synchronization signal sequence periodically distributed among said data signals.

53. The improvement according to claim 52, wherein said synchronization signal sequence corresponds to said preselected scrambling code.

54. The improvement according to claim 53, wherein said preselected scrambling code is a maximal length N-bit PN sequence.

55. The improvement according to claim 49, wherein, for a respective information carrying channel, each terminal station includes

means, coupled to receive digital data information signals to be carried over said respective information carrying channel;

means, coupled to receive prescribed additional digital signals to be carried over said respective information carrying channel; and

means for combining said digital data information signals with said additional digital signals and causing said signals to be transmitted over said respective information carrying channel.

56. The improvement according to claim 55, wherein said combining means includes means for multiplexing a preselected plurality of said digital data information signals with a prescribed number of said additional digital signals.

57. The improvement according to claim 56, wherein prescribed ones of said additional digital signals correspond to said prescribed portion of said information signals.

58. The improvement according to claim 57, wherein said information signals are comprised of digital data signals scrambled in accordance with a preselected scrambling code.

59. The improvement according to claim 58, wherein said preselected scrambling code corresponds to said prescribed portion of said information signals.

60. The improvement according to claim 59, wherein said preselected scrambling code is a maximal length N-bit PN sequence.

61. The improvement according to claim 49, wherein said second means includes control means, associated with each of said terminal stations, for controlling the substitution of said auxiliary channel for said that one of said normally active channels in accordance with control signals transmitted between said terminal stations over at least one of said channels.

62. The improvement according to claim 61, wherein said control signals are transmitted between said terminal stations over each of the channels that is carrying information signals between the terminal stations.

63. The improvement according to claim 49, further including fifth means, associated with each of said stations, for monitoring prescribed operational or environmental conditions in said stations and generating a second output signal indicative thereof.

64. The improvement according to claim 63, wherein each of said fourth and fifth means includes local monitoring means, coupled in each said stations, for monitoring said prescribed characteristic and prescribed operational or environmental conditions, respectively.

65. The improvement according to claim 64, wherein said second means includes control means, associated with each of said terminal stations, for controlling the substitution of said auxiliary channel for said that one of said normally active channels in accordance with control signals transmitted between said terminal stations over at least one of said channels.

66. The improvement according to claim 65, wherein said control signals are transmitted between said terminal stations over each of the channels that is carrying information signals between the terminal stations.

67. The improvement according to claim 65, wherein said control means further includes means for controlling the substitution of said auxiliary channel for one of said normally active channels in accordance with said second output signal.

68. The improvement according to claim 64, further including an additional communication channel, exclusive of said normally active and auxiliary channels and over which said information signals are not carried, coupling the local monitoring means of each station to each terminal station.

69. The improvement according to claim 49, wherein said fourth means includes local monitoring means, coupled in each of said stations, for monitoring said prescribed characteristic of the prescribed portion of said information signals carried over said substituted channel.

70. The improvement according to claim 69, further including an additional communication channel, exclusive of said normally active and auxiliary channels and over which said information signals are not carried, coupling the local monitoring means of each station to each terminal station.

71. The improvement according to claim 70, wherein said second means is associated with each of said terminal stations and is coupled to said additional communication channel.

72. The improvement according to claim 70, wherein said local monitoring means includes means for responding to encoded interrogation signals transmitted from a terminal station over said additional communication channel and transmitting encoded reply signals to said terminal station representative of said monitored characteristics.

73. The improvement according to claim 72, wherein each of said terminal stations includes means for coupling voice signals onto and from said additional communication channel.

74. The improvement according to claim 73, wherein said encoded interrogation signals and said encoded reply signals are comprised of digitally encoded signals.

75. The improvement according to claim 74, wherein said digitally encoded signals are formed of digitally-on/off keyed tone signals.

76. The improvement according to claim 74, wherein at least one of said repeater stations includes means for coupling voice signals with respect to said additional communication channel.

77. The improvement according to claim 61, wherein, for a respective information carrying channel, each terminal station includes

means coupled to receive digital data information signals to be carried over said respective information carrying channel;

means coupled to receive prescribed additional digital signals to be carried over said respective information carrying channel; and

means for combining said digital data information signals with said additional digital signals and causing said signals to be transmitted over said respective information carrying channel.

78. The improvement according to claim 77, wherein said control signals are transmitted between said terminal stations over each of the channels that is carrying information signals between the terminal stations.

79. The improvement according to claim 77, wherein first preselected ones of said additional digital signals comprise said control signals.

80. The improvement according to claim 79, wherein a terminal station further includes means for digitally encoding audio signals to be coupled to said combining means as second preselected ones of said additional digital signals.

81. The improvement according to claim 80, wherein third preselected ones of said additional digital signals correspond to said preselected portion of said information signals.

82. The improvement according to claim 81, wherein said preselected portion of said information signals corresponds to a prescribed scrambling signal sequence.

83. The improvement according to claim 81, wherein said combining means includes means for multiplexing a preselected plurality of said digital data information signals with a prescribed number of said additional digital signals.

84. The improvement according to claim 83, wherein said preselected portion of said information signals corresponds to a prescribed synchronization signal sequence in accordance with which the multiplexed signals carried over a normally active or auxiliary communication channel are demultiplexed.

85. The improvement according to claim 70, wherein each of said normally active and auxiliary communication channels is comprised of duplex fiber optic channel and said additional communication channel has a frequency spectrum characteristic different from that of a fiber optic communication channel.

86. A communication network comprising:

first and second terminal stations;

a plurality of information carrying normally active channels and an auxiliary channel linking said first and second terminal stations through at least one repeater station;

an additional communication channel, exclusive of said normally active and auxiliary channels and over which said information signals are not carried, coupled to each of said repeater and terminal stations;

first means for monitoring a prescribed characteristic of information signals received at a terminal station over an active one of said plurality of information carrying normally active channels and selectively causing, via one of said plurality of normally active and auxiliary channels, a substitution of said auxiliary channel for one of said normally active channels depending upon said monitored prescribed characteristic; and

second means, coupled to said first means, for causing a preselected portion of said information signals to be carried over said substituted channel and for monitoring, via said additional channel, a prescribed characteristic of said preselected portion of said information signals at at least one of said stations.

87. The improvement according to claim 86, wherein each of said terminal stations includes means for coupling voice signals onto and from said additional communication channel.

88. The improvement according to claim 87, wherein at least one of said repeater stations includes means for coupling voice signals with respect to said additional communication channel.

89. The improvement according to claim 87, wherein each of said terminal stations further includes means for coupling audio signals, exclusive of said information signals, with respect to each of the active ones of said plurality of normally active and auxiliary channels.

90. In a communication network having first and second terminal stations coupled to each other over a plurality of first communication links for conveying signals from said first terminal station to said second terminal station and a plurality of second communication links for conveying signals from said second terminal station to said first terminal station, and at least one repeater station coupled in said links for regenerating information signals conveyed over said links, a system for controlling the operation of said network comprising

first and second control apparatus, respectively located at said first and second terminal stations, each control apparatus comprising:

first means of monitoring a prescribed characteristic of signals transmitted over the communication links from the other terminal station and producing a first output signal in response to a prescribed change in said characteristic on one of said links;

second means, responsive to said first output signal produced by said first means, for transmitting messages to the control apparatus of the other terminal station over each of said communication links representative of the replacement of said one link which has caused the production of said first output signal by said first means; and

third means, for selectively communicating with each of the stations along said links over a communication path exclusive of said communication links for selectively testing the operation of the stations along said one link.

91. A system according to claim 90, wherein said first means includes means for controlling the replacement of said one link by another of said links in accordance with messages transmitted between the second means of each control apparatus.

92. A system according to claim 90, wherein said third means includes means for selectively testing the signal transmission capabilities of the stations along each link and producing a second output signal in response to the detection of an anomaly in the signal transmission capability of a tested station.

93. A system according to claim 90, wherein said third means includes means for selectively monitoring operational or environmental conditions of the stations along each link over said exclusive communication path.

94. A system according to claim 93 wherein said second means for transmitting messages to the control apparatus of the other station over each of said links representative of the replacement of that link for which said third means has monitored a prescribed defective operational or environmental condition.

95. In a communication network having first and second terminal stations coupled to each other over a plurality of first communication links for conveying signals from said first terminal station to said second terminal station and a plurality of second communication links for conveying signals from said second terminal station to said first terminal station, and at least one repeater station coupled in said links for regenerating information signals conveyed over said links, a system for controlling the operation of said network comprising:

first and second control apparatus, respectively located at said first and second terminal stations, each control apparatus comprising:

first means for monitoring a prescribed characteristic of signals transmitted over the communication links from the other terminal station;

second means for selectively testing the condition and operation of each station over a communication path exclusive of said communication links; and

third means, responsive to one of the detection of a prescribed change in the characteristic of monitored signals by said first means and the detection of a prescribed anomaly in the condition or operation of a selectively tested station by said second means, for communicating with the control apparatus of the other terminal station over each of said communication links and thereby causing the replacement of one of said communication links with an auxiliary communication link.

96. A system according to claim 95, wherein said second means includes means for transmitting and receiving prescribed encoded messages over said exclusive communication path with respect to each station along said communication links.

97. A system according to claim 96, wherein said second means further includes means for coupling voice signals with respect to said exclusive communication path.

98. A system according to claim 95, wherein said third means includes means for injecting and recovering prescribed control signals as part of the signals conveyed between said first and second terminal stations over said communication links, and wherein said first means includes means for controlling the replacement of said one of said communication links with said auxiliary communication link in accordance with said prescribed control signals.

99. A system according to claim 98, wherein said second means includes means for transmitting and receiving prescribed encoded messages over said exclusive communication path with respect to each station along said communication links.

100. A system according to claim 99, wherein said second means further includes means for coupling voice signals with respect to said exclusive communication path.

101. A system according to claim 95, wherein said first means includes means for controlling the replacement of said one of said communication links with said auxiliary communication link in accordance with predetermined control signals externally coupled to said control apparatus.

102. A system according to claim 101, wherein said third means includes means for injecting and recovering prescribed control signals as part of the signals conveyed between said first and second terminal stations over said communication links, and wherein said first means includes means for controlling the replacement of said one of said communication links with said auxiliary communication link in accordance with said prescribed control signals.

103. A system according to claim 101, wherein said first means includes

means for inhibiting the transmission of signals which would have otherwise been conveyed over said one of said communication links and causing a first prescribed sequence of signals to be transmitted in their place and wherein

said second means includes means, located at each of said stations for comparing said first prescribed sequence of signals with a prescribed code and producing an output signal indicative of the degree of mismatch between said first prescribed sequence of signals and said prescribed code.

104. A system according to claim 95, wherein each of said communication links is a fiber optic communication link and said exclusive communication path is a non-optical communication path.

Description

FIELD OF THE INVENTION

The present invention is directed to communication systems and relates particularly to a repeatered multichannel fiber optic communication network for transmitting high data rate digitally encoded signals between relatively geographically remote stations.

BACKGROUND OF THE INVENTION

With the recent development of and practical realization of electro-optic communication systems using fiber optic cables or high bandwidth signalling highways, applications of such systems to areas previously involving radio or copper wire cables have emerged. Auspiciously, fiber optic communication systems offer high density signalling traffic communication facilities, such as long distance telephone trunk lines, the ability to handle extremely high data rate digital data, permitting the telephone systems to service the increasing needs of a larger number of customers over a greater geographical area. Examples of fiber optic transmission networks that relate in general to repeatered communication systems are described in the Kach U.S. Pat. No. 4,027,153 and Maione et al, No. 4,019,048.

Within such systems, signalling integrity maintenance measures, such as repeaters and protection channel equipment, assist in permitting expansion of the system as the need arises. Of course, repeatered multi channel communication systems have been conventionally adopted for long range radio and copper cable environments and such systems typically include auxiliary or protection channels as an adjunct to the normally used communication highways in the event of a failure. Examples of such systems are described in the Farkas U.S. Pat. No. 3,111,624, Ferrar et al, No. 3,045,113, Miedama, No. 4,039,947 and Higo, No. 4,077,004. These systems typically employ signal monitoring and evaluation equipment separate from the signal transmission links themselves and take appropriate channel substitution action on the basis of the monitored inputs.

Unfortunately heretofore proposed multichannel communication networks, whether they be of the radio, copper wire, or fiber optic variety, as exemplified by the above-mentioned prior art schemes, do not offer a rapid and accurate approach to detecting the occurrence of a failure or a potential failure on a link together with a measure for isolating the cause of a failure on a link. Moreover, such systems do not offer the network subscriber a broad-based system capable of overall network monitoring, maintenance action, fault isolation, and remote system control and status reporting.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a new and improved repeatered, multichannel fiber optic communication system particularly suited for handling high data rate, high density digital data signals, e.g. T-4 data signals such as multiplexed voice and digital communications to be transmitted over long geographical distances. The fiber optic communication network of the present invention offers highly reliable telephone and data transmission capabilities and is suitable for inter-office trunk, digital microwave entrance, and special utility entrance links in both urban and rural installations.

For this purpose, and considering a communication scheme between a pair of relatively geographically remote stations with respect to which the digitized telephone traffic may be interfaced, the network of the present invention includes a plurality of full duplex fiber optic channels and one or more auxiliary channels to supplement a working channel in the event of a failure. While the number of channels, including both normally working and auxiliary or protection channels, is not limited to any particular number, for purposes of describing an exemplary embodiment of the invention, the configuration under consideration may contain five normally working channels and one protection or auxiliary channel. Each channel is comprised of a pair of fiber optic strands, one transmitting signals from a first station to a second station, the other transmitting signals from the second station to the first station, thereby providing full duplex capability over each channel.

Between the stations, between which the digitized voice and data traffic is to be transmitted over the fiber optic channels are one or more repeater stations. Each repeater station contains an individual repeater unit including a receiver and a transmitter, for each fiber optic strand, thereby providing six upstream and six downstream repeater units at each repeater station, for the six available channels. Every other repeater unit also contains a bit synchronizer, coupled between the receiver and the transmitter, for maintaining synchronization of data communications along the link. Transceiver components, similar to those employed in the repeater stations are contained at each terminal station so that the terminal stations may source or terminate data signals on the various channels. A transmitter portion of the transceiver accepts customer data to be transmitted as well as additional control and synchronization data, multiplexes the groups of data signals together and scrambles them for transmission to a distant terminal station. The scrambling of the data is effected using a maximal length PN sequence which serves to synchronize the descrambling and demultiplexing of data at the receiving terminal station.

A separate twisted pair copper wire link is coupled among the terminal stations and each repeater station along the network for the purpose of parameter monitoring and fault isolation in the event of a failure. Through the separate communication link termed an orderwire (OW) link, which carries no customer data but is dedicated exclusively to network operation, condition and bit error rate data from each station can be monitored. In addition, interface components associated with this additional orderwire cable permit supervisory and maintenance personnel to carry on audio communications with each other. Signalling over the orderwire cable for parameter monitoring and fault isolation is effected using digitally encoded tone pulses. These tone pulses are summed with any voice signals and both are transmitted simultaneously among the stations.

In order to supervise and control the operation, for both data transmission and fault/maintenance actions, of the network, each terminal station contains a processor-based subsystem capable of network monitoring, first level maintenance action, fault isolation, and remote network control and status reporting. This processor-based subsystem interfaces with each fiber optic channel, with the orderwire communication link, and with external input/output devices and surveillance equipment. To carry out these separate interfacing tasks, three substantially autonomous processor-based sections dedicated to performing specific functions within the overall network operation are employed.

A first section, termed a terminal surveillance section, interfaces with the opto-electronic receiver and transmitter equipment at its end of the network for each of the available fiber optic channels and measures the channel quality (BER). The terminal surveillance section also monitors parameter conditions of the transceiver equipment in the terminal station itself. If either a fault in the terminal is sensed or channel quality falls below a prescribed threshold level, action is taken by the subsystem to cause the defective channel to be replaced by the protection channel.

A second section, termed a site surveillance section, forms that portion of the processor-based subsystem which communicates with the repeater stations over the orderwire cable. It is through this section that a fault isolation process to locate the cause of unacceptable channel quality as measured by the terminal surveillance section is implemented. Advantageously, through a separate channel quality monitoring unit associated with each repeater station, the site surveillance section measures the throughput of each repeater station for a specified channel in sequence, from the source of the channel data to the receiving terminal station and identifies the faulty repeater in response to an unacceptable change in measured BER. In carrying out the fault isolation process a prescribed psuedo random number digital data sequence corresponding to that used in scrambling and synchronizing data on the fiber optic links is injected into the faulty channel's fiber optic link at the transceiver equipment associated with the terminal station at the upstream end of the link. Via the local orderwire, each repeater station is individually addressed by a command message from the site surveillance section and a response meassage containing information as to the channel quality as monitored by the BER monitoring unit in the repeater is transmitted from the addressed repeater, thereby enabling the subsystem to identify the location of the data degradation on the channel of interest.

A third section, termed a control and status section, communicates with peripheral and I/O control devices, such as printer, CRT, operator display and control switches, etc., and also interfaces with the multiplexed data on each of the fiber optic channels through a prescribed overhead bit that is periodically inserted into the data stream transmitted over the fiber optic channels. Through this overhead bit, the processor based subsystems of the terminal stations at the opposite ends of the network communicate with each other exchanging control and status information.

Each of the three sections of the processor based subsystem in a terminal station contains its own CPU and associated memory and is programmed to carry out specific tasks identified with that section. Each of the sections is interconnected with the other two so that, internally, the subsystem is fully integrated.

As a further feature of the network, attendants or operators in the terminal stations may communicate directly with each other over any of the active fiber optic channels through an audio interface unit, termed an "express orderwire" subsystem which, like the control and status section of the microprocessor based subsystem, interfaces with the multiplexed data on each of the fiber optic channels through a preselected overhead bit that is periodically inserted in the data stream transmitted over the fiber optic channels. With respect to the inserted overhead bits in the active channels, it is to be observed that an overhead bit is coupled to each active channel in parallel so that even in the event of a complete failure of a channel (interruption of customer service) control and status information necessary for network operation will still get through over each of the remaining active channels. Facility is provided at each terminal station to either selectively monitor any desired channel or that channel having a preferred quality for the purpose of exchanging data via the "overhead bit highway" on the fiber optic channels.

In order to assist maintenance personnel in rapidly locating and identifying individual network components for which the processor based subsystem has determined a fault exists, individual fault indicators are provided in each module and associated housing components. In addition, operation mode and condition indicators and control switches are provided on the attendant's consoles in the terminal stations to facilitate supervisory action as necessary. In this respect programmed procedures stored in the various sections described above can be circumvented by direct operator control, thereby maximizing access to and control over all facets of the network's operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general block diagram of a repeatered multichannel fiber optic communication network;

FIG. 2 is a schematic block diagram of a terminal station of the network of FIG. 1;

FIG. 3 is a schematic block diagram of the protection switch configuration of a terminal station of FIG. 2;

FIG. 4 is a block diagram of the transmit protection switch of FIG. 3;

FIG. 5 is a schematic block diagram of the receive protection switch portion of FIG. 3.

FIG. 6 is a schematic block diagram of a data delay circuit shown in FIG. 5;

FIG. 7 is a block diagram of the components of the transmitter portion of a transceiver unit;

FIG. 8 is a block diagram of the components of the receiver portion of a transceiver unit;

FIG. 9 is a schematic block diagram of a transmit timing recovery module of FIG. 7;

FIG. 10 is a schematic block diagram of a transmit encoder module of FIG. 7;

FIG. 10A is a data timing diagram relating to the operation of the transmit encoder module of FIG. 10;

FIG. 10B is a detailed logic circuit diagram of the delay network 135 and multiplexer 131 of the transmit encoder module of FIG. 10;

FIGS. 10C-10E are data format diagrams showing the makeup of a subframe, frame and major frame, respectively of FIG. 10;

FIG. 11 is a schematic block diagram of an optical transmitter module of FIG. 7;

FIG. 12 is a schematic block diagram of an optical receiver module of FIG. 8;

FIG. 13 is a block diagram of a bit synchronizer module of FIG. 8;

FIG. 13A is a schematic diagram of the bit synchronization circuit portion of FIG. 13;

FIG. 13B is a schematic diagram of the clock generator circuit portion of FIG. 13;

FIG. 14 is a schematic block diagram of a receiver decoder module of FIG. 8;

FIG. 15 is a block diagram of an individual repeater unit of FIG. 1;

FIG. 16 shows the general network configuration of the local orderwire system;

FIGS. 17 and 17A are respective circuit diagrams of embodiments of the signal interface unit of a local orderwire interface module;

FIG. 18 is a block diagram of the encode/decode control unit of a local orderwire interface module;

FIGS. 19 and 20 show the data configurations of respective command and response messages transmitted over the local orderwire system;

FIG. 21 is a block diagram of a bit error rate module;

FIG. 22 is a schematic block diagram of the error counter portion of the bit error rate module shown in FIG. 21;

FIGS. 23 and 23A are respective schematic block diagrams of embodiments of the signal interface unit of a local orderwire control module;

FIGS. 24A and 24B show the components and configuration of an express orderwire interface module;

FIG. 25 is a general block diagram showing the auxiliary terminal equipment of a terminal station of FIG. 2;

FIG. 26 is a general block diagram of the makeup of an auxiliary terminal unit of FIG. 25;

FIG. 27 is a module block diagram of an auxiliary terminal unit of FIG. 25;

FIG. 28 is a functional block diagram of a microprocessor module of FIG. 27;

FIG. 29 is a functional block diagram of a PROM module of FIG. 27;

FIG. 30 is a block diagram of an alarm monitor and fault light module of FIG. 27;

FIG. 31 is a block diagram of a BER and fault locate module of FIG. 27;

FIG. 32 is a block diagram of the site command and response module of FIG. 27;

FIG. 33 is a block diagram of the section control and status module of FIG. 27;

FIG. 34 is a block diagram of the serial interface control module of FIG. 27;

FIG. 35 is a block diagram of the front panel display module of FIG. 27;

FIG. 36 is a block diagram of a front panel switch module of FIG. 27;

FIG. 37 shows an exemplary layout for an attendant's alarm panel;

FIG. 38 is a block diagram of an ATU address and fault light module of FIG. 27;

FIG. 39 is a block diagram of the interprocessor module of FIG. 27; and

FIG. 40 is a block diagram of the real time clock module of FIG. 27.

DETAILED DESCRIPTION

Referring to FIG. 1, there is shown a general block diagram of a fiber optic communication network in accordance with the present invention wherein information is to be conveyed between geographically separated locations identified in FIG. 1 as a West location and an East location. For purposes of facilitating the description and illustration of the invention, the network will be reduced to a simplified communication configuration containing only two spaced apart locations between which information is to be conveyed. It should be understood, however, that more than two separate locations may be interconnected with each other over respective network sections established between each pair of locations. FIG. 1 illustrates the configuration of an individual section of the network wherein a pair of terminal stations 10 and 12 geographically remote from each other at respective West and East locations are coupled together over the fiber optic transmission arrangement to be described in detail below. Where the overall network is comprised of more than only the two separate locations shown in FIG. 1, separate sections are associated with each pair of locations between which communications are to be conveyed, with the sections being linked together in a back-to-back chain configuration to complete the overall network. Since the network configuration will be assumed to be reduced to only a single section coupling a pair of locations geographically separated from each other, the terms network and section may be considered to be synonymous, except in a few isolated instances where reference to separate sections of a larger (more than two) network will be made. For purposes of the present description it will be assumed that the information to be conveyed over the network is in the form of digitized telephone traffic, although it should be understood that the particular type of information transmitted via the system is not critical. The digitized telephone signals may represent voice, data, etc., namely, whatever signals may be digitized into a suitable format for high speed, high density data communication.

Situated at one end of the network at a West location and coupled to a telephone signalling interface (not shown) is a first terminal station 10. Terminal station 10 provides full duplex transmission capability between a telephone interface, such as an interoffice trunk, or digital microwave interface and a multichannel fiber optic communication highway comprised of an N-channel fiber optic link 13 and a protection channel link 14. Each fiber optic channel is configured of a pair of optical fibers, one for transmitting signals in one direction (e.g. West-to-East) and the other for transmitting signals in the reverse direction (e.g. East-to-West). In the present description it will be assumed that six channels make up the system, including five normally active or used channels and one normally quiescent or protection channel. It should be understood, however, that the number of channels that may be employed is not limited to the particular number chosen in the example described, but may be any suitable number as the need demands. The protection channel 14 is normally not used but is provided in the event of a failure of one of the five active channels of link 13.

From terminal station 10 at the West end of the network, fiber optic links 13 and 14 are coupled to a repeater 11 which is further coupled to additonal fiber optic links 13 and 14 to terminal station 12 at the opposite (East) end of the network. Repeater 11 provides the necessary signal regeneration to ensure proper signal transmission, via the optical fiber channel links, reception and data recovery at the receiving terminal station 12. While only a single repeater 11 has been shown in FIG. 1 so as to simplify the drawing, it should be understood that more repeaters may be serially situated along the fiber optic link between terminal stations 10 and 12 as the distance between terminal statins at opposite ends of the network increases. With presently available optical fibers a cable length separation between units of up to approximately 3.8 km has been found to be acceptable at the data rates used in this system. In the T-4 embodiment described herein, the basic system frequencies are 274.176.+-.0.003 MHz and 301.594.+-.0.003 MHz. For purposes of the description to follow, these frequencies will be simplified as 274 MHz and 301 MHz, respectively.

Like terminal station 10, terminal station 12 provides full duplex transmission capability between an associated local telephone interface (not shown) and the multichannel fiber optic communication highway. Also coupled to each terminal and repeater is a supervisory link 17. Supervisory link 17 is used to convey status and control information between the separate portions of the network for monitoring the operation of the network. The supervisory signals that are conveyed over link 17 are produced by monitoring and control subsystems within the terminal stations and the repeater equipment, as will be described in detail below. Since the bandwidth of the status and control signals conveyed over link 17 is much lower than that of the high density signalling over the optical channel links, link 17 may be formed of a twisted copper wire pair. The details of the configuration and operation of the components of the communication network diagram shown in FIG. 1 will be explained more fully below.

TERMINAL STATION (FIG. 2)

A block diagram illustration of an individual terminal station, such as terminal station 10 of FIG. 1, is shown in FIG. 2. In the present example, for the assumed normally active five channel full duplex system, five sets of transmit/receive lines 31-1/33-1 to 31-5/33-5 are coupled between the telephone interface and a patch panel 21. Patch panel 21 consists of a set of ten pairs of jacks and associated jumpers or straps for coupling lines 31-1 to 33-5 to corresponding patch panel output lines 32-1 to 34-5 and an additional pair of jacks for coupling protection channel receive line 34-6 to line 26-6 and protection channel transmit line 32-6 to line 25-6. Lines 32-1 to 32-6 and 34-1 to 34-6 are coupled to a protection switch unit 22 which is controlled by a processor-based supervisory subsystem, hereafter referred to as auxiliary terminal equipment (ATE) 24, via link 28. As will be described in more detail below, ATE 24 is a processor-based network control unit that is coupled to the supervisory link 17 and which conducts necessary network monitoring and control functions which ensure proper network operation. In the event of a fault in one of the five channels, ATE 24 takes the requisite action to substitute the protection channel for the faulty channel. The intraterminal station connection substitution is effected through the use of protection switch unit 22 which normally couples transmit/receive lines 32-1/34-1 through 32-5/34-5 for respective channels one to five to lines 25-1/26-1 through 25-5/26-5 that are coupled to a set of transceiver units 23-1 to 23-5, respectively. The incoming data receive lines 26-1 to 26-5 are coupled through respective delay circuits 27-1 to 27-6.

Transceiver units 23-1 to 23-5 are coupled to respective pairs of optical fibers of which optical fiber channel link 13 is comprised. Similarly, a protection channel transceiver unit 23-6 is coupled to the optical fiber pair of protection channel link 14 and, via lines 25-6, patch panel 21 and lines 32-6, 34-6, to a protection switch unit 22. Each transceiver unit is coupled to ATE 24 via link 35. A further link 30 couples bit error rate (BER) data between the transceiver units 23-1 to 23-6 and an adjacent terminal-to-terminal network section, where the network contains more than the pair of stations shown in FIG. 1, as will be explained in detail below. Each transceiver unit 23-1 to 23-6 contains a transmitter section and a receiver section. The transmitter section receives incoming digital data to be transmitted from a telephone interface channel, derives appropriate clock signals, adds additional data (termed overhead bits) and then outputs optical data into an optical fiber. As will be described fully below in conjunction with the description of an individual transceiver unit, the overhead bits are used for synchronization and control purposes. The receiver section receives incoming optical data from an optical fiber, carries out timing recovery, separates the detected data into overhead and data bits, and then outputs the data to its associated telephone interface channel and the overhead bits to its associated auxiliary terminal equipment 24.

Under normal circumstances protection switch 22 couples incoming and outgoing serial data between lines 32-1 . . . 32-5 and lines 34-1 . . . 34-5 and transceiver units 23-1 to 23-5. In the event of a fault, ATE 24 causes the protection switch unit 22 to steer the communication through the protection channel, so that one of the lines of line pairs 32-1/34-1 will be coupled to a corresponding line of line pair 32-6/34-6, patch panel 21, one of lines 25-6/26-6 and transceiver 23-6. ATE 24 also places transceiver 23-6 into service for the protected channel and carries out diagnostic tests on the faulty link to locate the source of the failure. Communication over the optical fiber via the overhead bits sets up the distant terminal station to begin using the protection channel in place of the designated faulty channel.

PROTECTION SWITCH UNIT (FIG. 3)

A schematic block diagram of the protection switch unit 22 of the terminal station is shown in FIG. 3. Protection switch unit 22 includes a transmit protection switch section 22A and a receive protection switch section 22B, each operated under the supervisory control of auxiliary terminal equipment 24. The transmit protection switch section in one terminal station is used in corporation with a receive protection switch section in the other terminal station at the opposite end of the network to controllably carry out the substitution between the protection channel and a selected normally active channel. Advantageously, as is described in copending application Ser. No. 146,340, filed May 2, 1980, now abandoned but refiled as continuation application Ser. No. 319,999 on Nov. 10, 1981 by J. Toy, P. Casper, F. Orlando and R. Giri entitled "Synchronized Protection Switching Arrangement", assigned to the assignee of the present application, such a switching unit is capable of synchronizing a pair of signal paths between which the substitution is to be made, so that there is no loss or addition of data bits. Now although this synchronized or "hitless" switching arrangement is explained fully in the above reference copending application to which reference may be had for a description of the arrangement, it will be described here also in order to facilitate an understanding of its impact upon the overall network.

TRANSMIT PROTECTION SWITCH SECTION 22A

Within the transmit protection switch section 22A, respective lines 32-1 to 32-5 for incoming telephone data signals from patch panel 21 are coupled to respective signal splitters 44-1 to 44-5 of a signal divider 41. Each splitter has a first output line, corresponding to respective lines 25-1 to 25-5, coupled to one of transceiver units 23-1 to 23-5, and a second output line, corresponding to respective lines 45-1 to 45-5, coupled to a transmit protection switch unit 43. Transmit protection switch unit 43 (to be described in detail below in conjunction with the description of FIG. 4) has a data output coupled to transmit protection channel 32-6 and a control link 48 coupled to ATE 24 for controlling the action of unit 43. In the protection switching mode transmit protection switch unit 43 operates in response to a command on link 48 from ATE 24 to selectively couple one of lines 45-1 to 45-5 to output line 32-6 and thereby through patch panel 21 to the transmitter portion of transceiver 23-6. In this mode the data for the selected channel is applied simultaneously to two transceiver units--to the one of units 23-1 to 23-5 associated with the replaced normally active channel and also to transceiver unit 23-6 associated with the protection channel. However, as will be described in detail below, the data path through the replaced transceiver unit is interruptable by ATE 24 so that a fault isolation signal sequence may instead by transmitted out over the replaced fiber optic channel. Service to the users of the replaced channel is maintained via the action of transmit protection switch 43 and its associated protection channel transceiver unit 23-6 and fiber optic protection link 14.

The purpose of transmit switch control section 22A is to initially place the data that is being transmitted via the channel being substituted onto the protection channel at the upstream end of the communication link. Thus, taking as an example, the need to substitute the protection channel link that conveys data from terminal station 10 to terminal station 12 over channel-one with the corresponding link of the protection channel, the transmit switch control unit at terminal station 10 serves to connect the incoming data interface link for channel-one to two terminal-to-terminal channel links, that for channel-one and that for the protection channel. Downstream, at the receiving end of the link, namely, at terminal station 12, the switching between the protection channel and channel-one is controlled in a "hitless" or synchronized manner, in order to achieve the required data transfer between channels that connect to the outgoing data interface of interest.

In the channel substitution switching mode, transmit protection switch 43 (to be described in detail below with reference to FIG. 4) operates in response to a command on link 48 from ATE 24 to selectively couple one of lines 45-1 to 45-5 to output line 32-6 and thereby to the transmitter portion of a terminal-transceiver unit for the protection channel. In this mode, the data for the selected channel is applied from signal divider 41 to two transceiver units--over line 25-1 to the one associated with the replaced normally active channel (e.g. channel-one) and also over line 32-6 to the transceiver unit associated with the protection channel, so that both channels are initially active prior to the synchronized substitution at the receiving end of the link, i.e., at terminal station 12. Once the substitution has been completed, ATE 24 may supply a signal to the transceiver associated with channel-one to inhibit further transmission over the station 10-to station 12 link of channel-one or insert a predetermined signal onto channel-one for test/diagnostic purposes.

RECEIVE PROTECTION SWITCH SECTION 22B

Within the receive protection switch section 22B respective receive lines 26-1 to 26-5 for received signals from transceiver units 23-1 to 23-5 are coupled to respective receive protection switch units 61-1 to 61-5, only unit 61-1 being illustrated in detail, so as to simplify the drawing. Receive protection switch unit 61-1 includes a first signal divider 51 coupled to receive line 26-1. Divider 51 couples the data on line 26-1 over lines 53-A and 53-B to respective receive protection switch circuits 42-A and 42-B. These circuits are controlled via link 49 that is coupled to ATE 24. The circuits are identical and normally only one is operated at a time, the other providing a redundant back up capability. The outputs of receive protection switch circuits 42-A and 42-B are combined in adder 56 (although only one output is active at any given instant) and then coupled via signal splitter 57 to output line 34-1. Signal splitter 57 provides a pair of branched signals over lines 58A and 58B to a respective phase comparator contained within each of circuits 42A and 42B. The phase comparator is used to synchronize the switch-over operation between the protection channel and a normally active channel during a "hitless" switching mode of operation to be described below, thereby avoiding a loss of or addition of data, as will be explained more fully below in conjunction with the detailed description of the receive protection switch circuit illustrated in FIG. 5.

The protection switch unit 22 also includes a data delay unit 47, shown in FIG. 6 to be described in detail below, which adjusts the phase delay to .+-.1/4 bit between the protection channel and one of the normally active channels one to five. Briefly, this unit enables a "hitless" switchover between the protection channel and one of channels one to five to be effected without causing a bit insertion into or bit deletion from the traffic data stream. Control of the operation of data delay unit 47 is effected via link 64 which is coupled to ATE 24. The data output from data delay unit 47 is coupled over link 47A to each of receive protection units 61-1 to 61-5. In the detailed illustration of receive protection unit 61-1, the channel-one output of data delay unit 47 is separated by signal splitter 52 into respective signal branches 54A and 54B coupled to receive protection switch circuits 42A and 42B. That one of redundant receive protection switch circuits 42A and 42B which has been placed into operation will couple one of lines 53A (53B) or 54A (54B) to output channel line 34-1 under control of ATE 24. Assuming normal operation for channel-one and operation of circuit 42A, the output 53A from splitter 51 would be coupled through receive protection switch circuit 42A to channel-one output line 34-1. In the event of a failure of channel-one, ATE 24 will couple control signals over links 49 and 64 to cause the received signal on line 34-6 to be coupled through data delay circuit 47, link 47A to splitter 52, line 54B and circuit 42B to output line 34-1, while the output of receive switch circuit 42A is interrupted.

TRANSMIT PROTECTION SWITCH UNIT (FIG. 4)

As illustrated in FIG. 4, the five normally active communication channel lines for coupling data to be transmitted, branched from splitters 44-1 to 44-5 (FIG. 3), are supplied over lines 45-1 to 45-5 to a multiplexer 71. In the following description it will be assumed that channel-one is to be replaced by the protection channel, so that line 45-1 is to be coupled through multiplexer 71 to output line 32-6. From ATE 24 a binary code (001) indicative of channel-one is coupled over link 48-2 and is strobed into a register 72 in response to a strobe or store enable pulse on line 48-1 from ATE 24. This binary code is decoded into a multiplexer switch selection signal by decoder 74. The output of decoder 74 instructs multiplexer 71 to couple line 45-1 (channel-one) to output lead 32-6. With this coupling action having been taken, the data on the incoming link for channel-one is now coupled over a pair of fiber optic channels from terminal station 10 to terminal station 12, i.e. over the West-to-East fiber of channel-one and over the West-to-East fiber of the protection channel. As a result, as will be described in detail below, the receiver protection switch 22B of terminal station 12 can proceed to substitute the protection channel for channel-one.

Comparator 77 is coupled to the output 79 of multiplexer 71 which verifies that the channel coupled to output line 32-6 (here, channel-one), is the same channel selected by decoder 74. The output of comparator 77 is coupled to a fault detection circuit 78. Like the other fault detector circuits employed in the various modules of the network, fault detection circuit 78 may be comprised of a threshold detector which monitors the output state of comparator 77. For a change in state of the output of comparator 77 indicating an error in the operation of multiplexer 71, the fault detection threshold circuitry is triggered causing a fault signal to be applied to line 48-3. Namely, as long as the switched channel identifier output signal on line 79 corresponds to a signal indicative of the intended channel to be switched supplied by decoder 74, comparator 77 does not generate a fault identification signal. Should there be a fault or failure in the intended switching operation of multiplexer 71 as instructed by decoder 74, there will be a code mismatch signal supplied to fault detection circuit 78 and a fault alarm signal will be applied via line 48-3 to ATE 24 indicating that the defective channel was not replaced as intended. A fault indication signal is generated by ATE 24 and supplied to an attendant's control panel (FIG. 37) to advise operation personnel of the switching failure so that corrective action can be taken.

RECEIVE PROTECTION UNIT (FIG. 5)

As was described above in conjunction with the description of the protection switch unit shown generally in FIG. 3, the receive protection switch section 22B of protection switch unit 22 is comprised of a set of receive protection units 61-1 . . . 61-5, one for each normally active data channel, and a data delay unit 47. Each of the receive protection units serves two functions. In a first mode of operation, termed the static mode, it couples incoming data on either its associated channel (e.g. channel-one for receive protection unit 61-1) or the protection channel to its output coupling to patch panel 21. In a second mode of operation, termed the dynamic mode, the receive protection unit performs a switchover between the protection channel and its associated channel. Moreover in this second mode of operation the receive protection unit may be controlled in cooperation with data delay unit 47 (to be described below in conjunction with the description of FIG. 6) to effect a "hitless" mode of switching between the protection channel and the receive protection unit's associated channel, whereby no data bits are lost or added in the changeover process. This "hitless" switching capability can be omitted, if desired, by directly replacing the protection channel with the normally active channel subject, of course, to a possible loss of data bits.

Referring now to FIG. 5, there is illustrated a schematic block diagram of a portion of the protection switch unit 22 shown in FIG. 3, specifically the details of an individual receive protection unit (such as unit 61-1 taken as an example) and its associated data delay unit. Each receive protection unit is comprised of a pair of protection switch circuits 42A and 42B, one of which provides redundancy back-up capability during the static mode of operation of the unit, and both of which are used during the "hitless" dynamic mode of operation of the receive protection unit, with one protection switch circuit providing a data path for the normally active channel while the other switch circuit operates in conjunction with data delay circuit 47 to adjust the timing of the data to be coupled through the normally active channel, so that a changeover between the protection and normally active channels can be accomplished with no bit slips.

Again considering the circuitry associated with channel-one for purposes of providing an example, the configuration and operation of receive protection unit 61-1 will be described. Within the receive protection unit there are a pair of identically configured protection switch circuits 42A and 42B. As shown in FIG. 5, protection switch circuit 42A includes a multiplexer 81A the output of which is coupled to a switch 84A and a delay circuit 85A. The output of switch 84A is coupled through controlled gain amplifier 83A to adder 56. Switch 84A is controlled by a switch control circuit 82A. Switch control circuit 82A is coupled to ATE 24 via control lines 91, 94 and 95A. Line 91 coupled a channel strobe signal to the switch control circuit in each protection switch circuit to control the opening and closing of switches 84A and 84B. Line 94 couples a signal designating whether the switch control circuit is to open or close its associated switch circuit. Line 95A is used to advise ATE 24 of the state of switch control circuit 82A. Similarly line 95B coupled a signal to ATE from switch control circuit 82B indicating the state of the circuit.

Further control lines from ATE 24 are coupled to multiplexer 81A. In addition to channel strobe line 91 which controls the switching operation of multiplexer 81A, line 93A couples a signal to multiplexer 81A indicating which of input lines 53A and 54A is to be coupled to the output of the multiplexer. Line 92A couples a signal to ATE 24 from multiplexer 81A indicating the actual coupling state of the multiplexer. An additonal control signal line 96A is coupled to ATE 24 from the output of phase comparator 86A, to indicate the phase difference between the output of delay circuit 85A and divider 57 on line 58A. The output of phase comparator 86A is monitored by ATE 24 during "hitless" switching between the protection channel and the normally active channel, as will be explained in detail below in conjunction with the description of the data delay circuit shown in FIG. 6.

Since protection switch circuit 42B is configured identically as protection switch circuit 42A, a detailed description of the circuit will be omitted. Instead, reference will be made to the components of each circuit in the description of the operation below.

OPERATION

As was explained previously, each receive protection unit operates in either a static mode or a dynamic mode. In the static mode, one of the protection switch circuits 42A, 42B is quiescent or serves as a redundant backup for the other circuit in the event of a failure. Multiplexer 81A (81B) will have been strobed by line 91 and control line 93A (93B) to couple the output of splitter 52 to switch 84A (84B). Switch control circuit 82A will have received instructions from the ATE 24 to couple the output of the multiplexer 81A through switch 84A and amplifier 83A to summing circuit 56. The output of summing circuit or adder 56 is coupled through divider 57 and over output line 34-1 to the patch panel 21. With protection switch circuit 42B in the quiescent mode, switch 84B is open and there is no output supplied to adder 56 from swtch 84B, so that adder 56 and divider 57 couple the output of protection switch circuit 42A over line 34-1 and to the patch panel. In the normal operating mode, phase comparator 86A (86B) compares its active channel input to a sample of the output signal from divider 57. Thus, line 96A (96B) sends a signal to ATE 24 indicating the condition of the respective switching unit. In the event of a failure, auxiliary terminal equipment 24 takes the appropriate action to disengage protection switch circuit 42A and insert protection switch circuit 42B between the incoming channel and the output line 34-1. For this purpose, switch controls 82A and 82B are controlled to open switch 84A and close switch 84B, respectively, in order that service over the link will be maintained.

In the dynamic mode of operation, the receive protection unit operates to switch between the protection channel and a normally active channel. The dynamic mode of operation can be effected in either a "hitless" fashion, or a direct switching fashion (which may result in the loss of data bits). In the latter instance, ATE 24 simply switches the multiplexer (81A or 81B depending upon which protection switch circuit is being used) from the protection channel to the active channel, the data on which is then coupled through the protection switch circuit to adder 56, splitter 57 and out to the patch panel. Advantageously, however, switching between the protection channel and the normally active channel can be accomplished in a "hitless" fashion, so that the data stream on the protection channel and that on the active channel are brought into synchronization with one another within one-quarter of a bit at the time the multiplexer is switched, in order to prevent loss of or insertion of even one bit of data over the link.

In order to implement "hitless" switching in the dynamic mode of operation, data delay circuit 47 operates to delay the data stream on line 34-6 from the protection channel in a step-wise fashion until the output of the phase comparator (either phase comparator 86A or phase comparator 86B of the protection switch being utilized) indicates proper synchronization of the normally active channel data and the protection channel data.

More specifically, let it be assumed that protection switch circuit 42A is presently coupling the received data on normally active channel-one through multiplexer 81A, switch 84A and amplifier 83A to adder 56 and out to signal splitter 57 and output line 34-1. When it is desired to switch between the protection channel and normally active channel-one, again using channel-one for purposes of the example previously chosen, the data stream on channel-one must first be placed on the protection channel fiber optic link. As explained above in conjunction with the description of the transmit protection switch, this action is carried out at the upstream terminal station (i.e., terminal station 10 in the present example). It will be assumed here that this procedure has already taken place in the manner described above so that the data stream of interest on channel-one is also on the protection channel fiber optic link (although terminal station 12 is presently receiving only channel-one data since the protection channel substitution has not yet been carried out). Now, multiplexer 81B within protection switch circuit 42B will be instructed by the auxiliary terminal equipment 24 to switch its output to input line 54B over which the protection channel data is supplied. Switch control 82B will be controlled by the ATE to maintain switch circuit 84B in the open position so that only the normally active channel-one data continues to be applied to adder 56 and from there to the patch panel. The normally active channel-one data itself is split off from splitter 57 over line 58B to a phase comparator 86B which also receives the protection channel data by way of delay circuit 85B. Phase comparator 86B compares the phase of the protection channel data with that coupled from splitter 57 representative of the normally active channel-one data. A signal indicating an in-phase or out-of-phase condition is coupled over line 96B to the automatic terminal equipment 24. As long as the two signals are not within one-quarter bit of phase difference of each other, ATE 24 supplies a phase adjustment signal over line 64 in successive increments of one-quarter bit to the data delay circuit 47. As will be explained below, in conjunction with the description of FIG. 6, data delay circuit 47 operates to incrementally delay the data on the protection channel by one-quarter per bit until the protection channel and the normally active channel come within one-quarter bit of being synchronized with one another. Once the phase adjustment signals on line 64 have accomplished this proper synchronization, the output of phase comparator 86B will advise ATE 24 that switching between the normally active channel and the protection channel can take place. With the proper delay having been imparted to the protection channel to insure synchronization and switchover, the automatic terminal equipment 24 instructs each of switch controls 82A and 82B to change the operation of their respective switch circuits 84A and 84B. At this time, again using the example chosen, switch circuit 84A is opened so as to sever the link between the normally active channel-one and adder 56, while switch circuit 84B is closed so as to couple the protection channel through switch 84B to adder 56. As a result, there is no loss of even a single bit of data output over line 34-1 to the patch panel 21. Namely, the changeover between the protection and normally active channels is accomplished in a "hitless" fashion. The manner in which the data delay circuit accomplishes the incremental delay imparted to the protection channel data will be explained below in conjunction with the description of FIG. 6.

DATA DELAY UNIT (FIG. 6)

As was described above in conjunction with the operation of the receive protection unit (FIG. 5), in order to effect hitless switching between the protection channel and the normally active channel, a data delay unit 47, shown in detail in FIG. 6, is disposed in the data link between line 34-6 over which the protection channel data is supplied and each of the inputs to the receive protection units. The delay unit 47 operates to delay the data on the protection channel in quarter bit increments until synchronization between the normally active channel and the protection channel is achieved, namely, until there is no greater than one quarter bit offset between the two.

For this purpose, as shown in FIG. 6, the input protection channel data on line 34-6 is applied to the data input of a sixteen bit register 1201. Register 1201 is clocked by the 274 MHz clock B produced on line 217 from the receiver decoder module to be described below. Clock B is inverted in phase relative to the normal 274 MHz clock synchronously derived by the transmit timing recovery unit 101 to be described below. Suffice it to say for purposes of the description of the data delay unit that the clock on line 217 is synchronized with the incoming protection channel data. As input data is applied on line 34-6 to the sixteen bit register 1201, it is clocked in, one bit at a time, by the clock on line 217. Register 1201 is a serial in, serial out shift register with the spilled over bits from the last register being deleted. Each of the successive stages of register 1201 is coupled over parallel links 1202 to a multiplexer 1203. Multiplexer 1203 is controlled by a link 1223 from a "coarse" counter 1222 to selectively coupled one of the stages of sixteen bit register 1201 to output line 1204. Output line 1204 is coupled to a delay line 1205 which produces taps at quarter bit increments to provide, on output link 1206, successive delayed versions of the data bit output of multiplexer 1203. One of these delayed bits is coupled through multiplexer 1207 under the control of a switch signal on line 1218 from a "fine" counter 1217 to an output line 1208.

Counters 1222 and 1217 are controlled by an up/down controller 1222A which steers the direction in which the contents of counters 1222 and 1217 are operated. Up/down counters 1222 and 1217 are incremented for each count signal applied to line 64 until they reach positive capacity at which point they begin counting down to minimum value as controlled by up/down controller 1222A. Upon reaching its lower limit, controller 1222A causes counters 1222 and 1217 to begin sweeping back in the positive direction. This action on the part of up/down controller 1222A causes the control signal on link 1223 to switch multiplexer 1203 in such a fashion that it sweeps across the stages of register 1201 back-and-forth, rather than in onely on direction and then immediately back to the beginning. In this manner, counters 1222 and 1217 are prevented from rolling over, so that at the outputs of multiplexers 1203 and 1207 there is never a loss of the data bits that are applied to and shifted through register 1201. Output 1208 is coupled to the data input terminal of an output register 1209. Output register 1209 is clocked by a 274 MHz clock on line 1220 which is provided by a vernier delay 1219 that is clocked by the clock on line 217 but incrementally delayed in accordance with a control signal on link 1218 from counter 1217. The output of register 1209 is coupled over line 1210 through successive amplifiers 1211 through 1215 to link 47A which is coupled to the dividers 52 of each of the protection units 61-1-61-5, described above in conjunction with FIGS. 3 and 5.

An output activity (fault) detector 1216 which is comprised of threshold detection circuitry is coupled to each of lines 1204 and 1210 to monitor the operation of the data delay unit and to provide an alarm signal on line 1224 to the auxiliary terminal equipment in the event of a failure (i.e., loss of activity). A phase adjust command signal on line 64 from the auxiliary terminal equipment 24 is coupled to the fine counter 1217 to control the incremental delay operation of the data delay unit.

OPERATION

In order to provide the desired synchronization between a normally active channel and the protection channel, the auxiliary terminal equipment monitors the output of one of the phase comparators 86A, 86B in the receive protection unit under consideration. As was explained above in conjunction with the description of FIG. 5, the output of the phase comparator indicates whether the data on the normally active channel is in-phase with the data on the protection channel. As long as there is a phase difference between the data on the two channels, the phase comparator delivers an output signal to the auxiliary terminal equipment which, in turn, delivers a phase adjust command signal to counter 1217. Counter 1217 is a count-to-four counter which produces an output on line 1221 at overflow for each four signals counted on line 64 from the ATE 24. Counter 1222 counts up to sixteen and then recycles in accordance with the count pulses produced on line 1221 from counter 1217. The state of counter 1222 governs which of the outputs of register 1201 will be coupled through multiplexer 1203 to delay line 1205.

Assuming that the protection channel and the normally active channel data bits are out of sync with one another, a phase comparison by one of the phase comparators in the receive protection unit will produce an output causing the auxiliary terminal equipment 24 to supply an increment signal to counter 1217. Beginning with the first stage of register 1201, assuming that counters 1222 and 1217 are cleared, multiplexer 1203 coupled the first bit stage to delay line 1205 which successively delays the data bit and applies it to multiplexer 1207, with four data bits identical to each other but each successively offset from the previous bit by one-quarter bit being applied to the inputs of the multiplexer. Counter 1217 initially addresses the first delay tap and causes the data bit to be coupled over line 1208 to the output register 1209. Delay 1219 effects a delay corresponding to that of the delay bit as addressed by counter 1217 so that the bit delivered through multiplexer 1207 is synchronously clocked into register 1209 and delivered over line 47 to divider 52 within each of the receive protection units 61-1 . . . 61-5. If the phase comparison circuit detects that the protection channel and the normally active channel are still out of sync, it delivers an output signal to the auxiliary terminal equipment 24. In turn, this equipment delivers a further pulse signal over line 64 to counter 1217 to increment its contents by one and to cause multiplexer 1207 to address the next successive input on link 1206 from microstrip delay 1205. Similarly, delay line 1219 responds to the new contents of counter 1217 provided on link 1218 to delay the clock on line 1217 by an amount to synchronously load the next successively delayed bit on line 1208 into register 1209.

The above process is repeated for each of the quarter bit delays of the presently addressed bit in register 1201 and then successively for each additional bit in the same manner, as necessary, for the successive stages of register 1201 until the output of the phase comparator within the receive protection unit indicates that the normally active channel and the protection channel are properly timed with one another. At that time, further phase adjust command signals from the ATE 24 are inhibited and the contents of counter 1217 and counter 1222 are no longer incremented. The delay provided by way of register 1201 and delay 1205 through the data delay unit is now fixed at the proper incremental offset between the normally active channel and the protection channel to insure a "hitless" switchover between the two channels. At this point, the operation described above in conjunction with the description of FIG. 5 for "hitless" switching between the channels may take place.

In the foregoing explanation of the operation of the hitless switching control arrangement of FIGS. 4-6, the description related to the substitution of the protection channel for one of the normally active channels (e.g., channel-one). With the data delay circuit being deposed in the communication path of the protection channel proper, rapid incremental delay adjustments to the phase of the protection channel data are carried out to bring the protection channel into synchronization with the normally active channel being replaced. When it is desired to switch back to the normally active channel, the adjustment of its incremental delay proceeds fairly slowly since the data output undergoes phase steps.

More specifically, it is common practice in commercial high data rate data communication networks of the type considered herein to couple communicaton channel outputs to timing recovery circuitry (usually including a phase-locked loop) to precisely regenerate the data being conveyed. Accordingly, assuming that there is a phase offset between the protection channel and that previously replaced normally active channel (although this is quite unlikely since the down time of the normally active channel should be reasonably brief while the channel should remain synchronized for a number of hours), ATE 24 causes a gradual incremental change in the protection channel delay. This gradual change (in increments of a quarter of a bit) is quite tolerable because of the action of the timing recovery circuitry which sees this quarter bit delay as jitter on the bit and properly reconstitutes the bit. Eventually, synchronization between the two channels is realized and return to the normally active channel can be effected.

TRANSCEIVER UNIT (FIG. 7 and 8)

Each of the transceiver units 23-1 to 23-6 depicted generally in FIG. 2, described above, contains a transmitter section comprised of a set of three intercoupled modules 101-103, shown in FIG. 7, and a receiver section comprised of another set of intercoupled modules 201-204, shown in FIG. 8. In keeping with the reference to channel-one for the purposes of the present description, the modules shown in FIGS. 7 and 8 are those which make up transcriver unit 23-1. Transceiver unit 23-2 to 23-6 are configured identically to unit 23-1.

TRANSMITTER SECTION (FIG. 7)

Within the transmitter section there is a transmit timing recovery module 101 (FIG. 9) which is coupled to receive an input data stream supplied from the protection switch unit 22 over line 25-1. This module couples the data to a transmit encoder module 102 over line 110 and also operates to derive a synchronous transmission clock at the frequency of the data and a further clock to be used for encoding and data transmission. Assuming a T-4 data rate of 274 Mb/s, transmit timing recovery module 101 generates a synchronous system clock signal at this 274 MHz frequency and an additional 301.6 MHz clock at 11/10 of the 274 MHz rate on line 112. Also, a 1/10 rate clock of 27.4 MHz is generated and output over line 111. Transmit timing and recovery module 101 is also coupled to ATE over line 101A for coupling fault alarm and indication signals therebetween.

Transmit encoder module 102 (FIG. 10) adds overhead bits to the 274 Mb/s data stream supplied over line 110 from transmit timing and recovery module 101, scrambles the resultant data and supplies a modified data output stream at the 301 MHz output frequency over line 113 to an optical transmitter module 103. Transmit encoder module 102 is also coupled to ATE 24 via link 102A for coupling control, fault alarm and indication signals between the two units. Lines 102B and 102C are coupled to respectively receive a system BER word from and transmit a BER clock to an adjacent terminal-to-terminal section if the network is of multi-section (more than two terminal stations) configuration.

The optical transmitter module 13 (FIG. 11) receives the modified serial data stream on line 113 and converts the incoming electrical signal into optical pulses for transmission over optical fiber 115. Optical transmitter module 103 is also connected to ATE 24 via link 103A for coupling parameter monitor and fault indication signals therebetween.

RECEIVER SECTION (FIG. 8)

The receiver section of the transceiver unit is shown in FIG. 8 as including an optical fiber receiver module 201 (FIG. 12) which includes an opto-electronic conversion unit, such as an avalanche photo diode circuit, for converting optical pulses making up the serial data stream supplied over fiber 210 into an electrical current signal. This signal is suitably filtered and gain-adjusted to produce a new raw received 301 MHz data signal that is coupled over line 211 to a bit synchronizer module 202. Optical receive module 201 is also coupled over link 201A to ATE 24 for coupling fault alarm and indication signals therebetween. A bias voltage supply module 204 provides -250 VDC via line 204A to the APD.

The bit synchronizer module 202 (FIG. 13) extracts a synchronous bit rate clock from the raw serial data and, with this clock, completely regenerates the data for subsequent logic processing. The detected data at the 301 Mb/s data rate is coupled over line 212 to a receiver decoder module 203. Also produced by bit synchronizer module 202 and coupled to receiver decoder module 203 over lines 213-215 are respective 301 MHz, 27.4 MHz and 274 MHz clocks. A feedback line 216 is coupled from receiver decoder module 203 for frame synchronization control. Fault alarm and indication signals are coupled between ATE 24 and bit synchronizer module 202 via link 202A.

Receiver decoder module 203 (FIG. 14) descrambles the 301 Mb/s data coupled from bit synchronizer module 202 over line 212, removes the overhead bits that were inserted during encoding by the transmit encoder module described previously, and delivers a replica of the original data stream over line 26-1 to protection switch unit 22 Receive decoder module 203 in the protection channel also produces a separate 274 clock signal on line 217 which is supplied to data delay unit 47 (FIG. 6). Fault indication and alarm signals and control signals are coupled over link 203A between ATE 24 and the receiver decoder module. Link 203B couples received system BER word produced by module 203 to the next section.

Each of the individual units of which a transceiver is configured will now be described in more detail below with reference to FIGS. 9-14.

TRANSMIT TIMING AND RECOVERY MODULE 101 (FIG. 9)

Transmit timing and recovery module 101 is shown in FIG. 9 as comprising a bit synchronizer 220 coupled to input data 25-1. Bit synchronizer 220 is configured essentially as the bit synchronization circuit of the bit synchronizer module 202, to be described below with reference to FIG. 13A. Bit synchronizer 220 derives a synchronous 274 MHz clock from the incoming 274 Mb/s data stream on line 25-1 and outputs this clock on line 221 to a divide-by-ten divider circuit 222. The 274 Mb/s NRZ data stream is coupled from bit synchronizer 220 to line 110. When phase lock is acquired, a signal is coupled over line 228 to OR gate 223. This signal is derived from a phase locked loop within the synchronizer 220 and indicates that the 274 MHz clock produced on line 221 is in sync with the data stream on line 25-1. The output of divide-by-ten divider 222 is a 27.4 MHz clock that is coupled over line 111 to transmit encoder module 102 and to a times-eleven phase lock loop 224. Loop 224 effectively multiples the frequency of the 27.4 clock by a factor of eleven and produces a synchronous higher frequency (.perspectiveto.301 MHz) clock over line 112 to be coupled to transmit encoder module 102. A phase lock indication signal for the higher clock rate (301 MHz) is coupled from loop 224 over line 229 to a second input of OR gate 223. The output of OR gate 223 is coupled to ATE 24 via line 230 and is used to advise ATE 24 of a fault in the timing circuitry of module 101. As long as the 274 and 301 phase lock loops are synchronously generating the 274 and 301 MHz signals, the output of OR gate 223 is low. An out-of-sync condition in either loop causes OR gate 223 to go high and thereby advise the ATE 24 of a fault condition.

Also contained within the transmit timing and recovery module is an input data activity detector 225, comprised essentially of a threshold detector, which is coupled to line 25-1 for monitoring data activity on the line. As long as there is data coming in on line 25-1, there is no change in state of the output of detector 225. Absence of data, however, causes a signal to be produced over line 226 to ATE 24 advising the supervisory subsystem of a loss of data. For either a loss of data signal on line 226 or a loss of sync signal on line 230, ATE 24 takes appropriate action and causes a fault light (not shown) on the module to be energized so that correction of the error condition can be rapidly carried out by service personnel.

TRANSMIT ENCODER MODULE (TEN 102) FIG. 10

As was described briefly above in conjunction with the general description of a transceiver unit, transmit timing and recovery module 101 supplies timing (clock) and data signals to transmit encoder module (TEN) 102. TEN 102 adds overhead bits to the 274 Mb/s data stream, scrambles the modified data and produces a scrambled data stream at a higher frequency of 301 MHz at its output, the 301 MHZ scrambled data stream being applied to the optical transmitter module 103 (described in detail below in conjunction with the description of FIG. 11) for transmission out over the optical communication link. (In the receiving terminal station, a receiver decoder module (to be described below with reference to FIG. 14) descrambles and recovers the original data. Advantageously, the transmit encode module and the receiver decoder module employ a maximal length PN sequence for data scrambling and frame synchronization. The scheme for accomplishing these functions, per se, as applied to communication systems in general, is described in copending patent application Ser. No. 146,338, filed May 2, 1980, by Charles R. Patisaul, James W. Toy and Peter H. Halpern, entitled "Combined Use of PN Sequence for Data Scrambling and Frame Synchronization in Digital Communication Systems" and assigned to the assignee of the present application. Now although reference may be had to the above copending application for a detailed explanation of such a scheme, those components of such a system and their relationship with the remainder of a transceiver section of the network of the present invention will be described here in order to facilitate a full appreciation of the same. Overhead bits to be inserted into the data stream include synchronization bits made up of a maximal length PN thirty-one bit sequence, control and status bits, bit error rate bits and orderwire bits. The synchronization bits are used to enable the receiver section of a transceiver to which the scrambled data is sent to decode and recover the original data stream and to properly demultiplex all overhead bits. These bits are generated within the encoder module itself and one sync bit is multiplexed into each frame of data. If the network contains more than one terminal-to-terminal section, section BER bits are supplied from an adjacent section with one BER bit being inserted into each frame of data. The control and status bits and the orderwire bits are generated by ATE 24 and are inserted alternately into every other frame of data. The control and status bits convey command signals from the ATE while the orderwire bits carry digitized audio signals from one terminal station to another. The manner of generation, encoding, transmission and recovery of these various bits will be described subsequently in detail.

Referring now to FIG. 10, wherein a schematic block diagram of TEN 102 is illustrated, line 110 from transmitting and recovery module 101 couples the 274 Mb/s NRZ data to a delay network 135 which operates in conjunction with a multiplexer 131 and a timing signal generator 130 to increase the data rate of the incoming data stream and to insert overhead bits supplied by overhead bit multiplexer 133 at every eleventh bit position of the output of multiplexer 131. As shown in FIG. 10B delay network 135 may comprise a plurality of parallel delay channels 135a, 135b, 135c of different time delays to produce sequences of the 274 Mb/s data stream successively displaced in time with respect to one another over lines 157, 158 and 159, respectively. Thus, with reference to the data timing sequences illustrated in FIG. 10A and considering a sequence of ten successive data bits D1-D10, the action of delay network 135 serves to produce successively offset (in time) data sequences (a), (b) and (c). The period of time covering bits D1-D10 for a 274 mb/s rate is approximately 36.5 nanoseconds. With successive delays using parallel channels, the period of time from the beginning of one delayed sequence such as sequence (c) to the end of another sequence of a lesser or no delay such as sequence (a) (i.e. between instants of time t.sub.1 and t.sub.2 shown in FIG. 10A) is compressed to a length of time considerably shorter than the 36.5 nanosecond time span (for ten bits at 274 Mb/s) of each sequence. As was pointed out above, pursuant to the present invention the output data rate is 301 Mb/s. Since ten successive bits at 301 MHz rate cover a time span of only approximately 33 ns, then for the additional approximately 3.5 nanoseconds otherwise occupied by a data bit in the incoming data stream in line 110, it is possible to insert an overhead bit or auxiliary bit for synchronization and control purposes without loss of data by compressing the data using delay network 135 and multiplexer 131. For this purpose timing signal generator 130, which is comprised of suitable combinational logic and delay circuitry to generate timing signals in a straightforward manner, controls the multiplexing or switching action of multiplexer 131.

As is shown further in FIG. 10B, multiplexer 131 may comprise a set of gates 231-234 respectively coupled to each of data stream delay lines 157-159 and to line 137 which is coupled to the output of overhead bit multiplexer 133. The outputs of the gates 231 to 234 are coupled through OR gate 235 to one input of OR gate 236 the output of which is coupled to the D input of clocked flip-flop 217. A second input of OR gate 236 is coupled to data inhibit line 121. The clock input of flip-flop 217 is coupled to line 112 over which the 301 MHZ clock for reading out the compressed data and overhead bits is supplied from transmit timing recovery module 101. The selective enabling of the respective gates 231-234 of multiplexer 131 that are coupled to lines 157-159 and 137 is controlled by a set of timing signals supplied by timing signal generator 130 over link 138; these timing signals may be derived by appropriately delaying and logically operating on delayed ones of the 27.4 MHZ clock coupled to timing signal generator 130 over line 111. Thus, for example, and referring again to FIG. 10A, the selective control or timing signals supplied over link 138 to multiplexer 131 may be such as to couple data bits D1-D3 from sequence (c), data bits D4-D7 from sequence (b) and data bits D8-D10 from sequences (a) through multiplexer 131 with the 301 MHz signal applied over line 112 clocking out the values of these gates data bits from the Q output of flip-flop 217 at the 301 Mb/s readout rate over line 181. Between time instants t.sub.2 and t.sub.3 the timing or control signal on line 138 enables gates 234 (FIG. 10B), so that the overhead bit on line 137 can be clocked out at the 301 Mb/s data rate. Thus, the combined action of delay network 135, overhead bit multiplexer 133 and multiplexer 131 is to compress the incoming 274 Mb/s data rate to a 301 Mb/s data rate and then insert a selected overhead bit between each group of ten data bits. As a result, from multiplexer 131 there is produced a modified data sequence of the ten original data bits followed by one additional or overhead bit. Namely, by compressing the 274 Mb/s data to a rate of 301 Mb/s, then, for every ten input data bits there are produced eleven output bits.

Referring further to FIG. 10, the output of multiplexer 131 is coupled to one input of a modulo-two adder 171. A second input of modulo-two adder 171 is coupled to line 125 over which a prescribed transmit error control signal (TX ERRORS), the function of which will be explained below, from ATE 24 is supplied. A further input of modulo-two adder 171 is coupled to output line 167 from a scrambler 142. Scrambler 172 is comprised of five stage shift register 161 the output of selected ones of which are coupled to a modulo-two adder 166. The output of modulo-two adder 166 is coupled to the input of the first stage of shift register 161 and to the input of the first stage of a five stage shift register 140. Shift register 161 of scrambler 142 is clocked at the 301 MHZ clock rate via line 112. With five shift register stages, scrambler 142 is equipped to supply a 31-bit maximal length pseudorandom sequence that is modulo-two combined with the data and overhead bit sequence read out of multiplexer 131.

The PN scrambling sequence from scrambler 142 is clocked into shift register 140 at 1/33 times the scrambler clock rate. This is achieved by the provision of a divide-by-three divider 132 coupled to line 111 over which the 27.4 MHZ clock is supplied from transmit timing recovery module 101. The result is that every thirty-third bit from free-running scrambler 142 is loaded into shift register 140. It can be shown that taking every Kth bit from a cyclic 31-bit maximal length sequence generates another cyclic 31-bit maximal length PN sequence. For the scrambler 142 shown in FIG. 10, the sequence generated by taking every 33rd bit of the scrambling sequence on line 167 is a replica of the scrambling sequence and serves as a framing sequence.

FIGS. 10C-10E illustrate the data format as assembled by the transmit encoder module shown in FIG. 10. Each subframe illustrated in FIG. 10C is comprised of ten successive NRZ data bits followed by one overhead bit and is produced by the operation of multiplexer 131 as described previously. A frame, shown in FIG. 10D, consists of three successive subframes, differing from one another. A major frame is shown in FIG. 10E as containing thirty-one consecutive frames. Within a major frame, the frame sync bit sequence for the first five frames is termed a frame marker that is used to mark the beginning of a frame, namely, frame synchronization bits S.sub.1, S.sub.2, S.sub.3, S.sub.4 and S.sub.5. The marking of a beginning of a frame is effected by monitoring the state of the stages of shift register 140.

More particularly, the stages of shift register 140 are connected to a state decoder 141 which consists of combinational logic configured to decode one of the thirty-one possible states (all zeroes being forbidden for a maximal length sequence) of shift register 140 to mark the beginning of a frame. When the frame marker sequence is detected by state decoder 141 an output signal is supplied over line 143 to timing signal generator 130. Logic in timing signal generator 130 responds to the clock signal on line 178 from divider 132 and signal on line 143 to couple a signal over line 136 to multiplexer 133 causing multiplexer 133 to supply a zero over line 137 to multiplexer 131 to be inserted as an overhead bit at the intended frame synchronization bit position in synchronization with a timing signal on line 138. Thereafter, for each clock signal from divider 132 timing signal generator 130 couples a signal on line 136 causing a zero to be supplied over line 137 to multiplexer 131, thereby causing a zero to be inserted at every third overhead bit position. For the other two overhead bit positions of each frame, timing signal generator 130 responds to the 27.4 MHz clock on line 111 and supplies a signal over line 136 causing overhead bit multiplexer 133 to selectively couple one of the bits on links 122-124 to line 137 as the overhead bit.

Now, as the 301 Mb/s data and overhead bit stream is clocked out of multiplexer 131 and summed in modulo-two adder 171 with the scrambling sequence supplied over line 167, the zero bits occupying the framing bit positions S.sub.1 shown in FIG. 10E are replaced by every thirty-third bit of the scrambling sequence on line 167, thereby inserting the 31-bit PN framing sequence precisely where required in the major frame. Because each unique state of the framing sequence S.sub.1 . . . S.sub.31 contained within the major frame corresponds to only one state of the scrambling sequence produced by scrambler 142, synchronization of the descrambler contained within the receiver decoder module 203, to be described in detail below in conjunction with FIG. 14, can be achieved by observing the state of the recovered framing sequence.

As the scrambled sequence is generated by modulo-two adder 171 it is coupled to an output register 172 and, via a suitable delay (not shown), is clocked out of register 172 over line 113 at the 301 MHz clock rate supplied over line 112. Line 113 couples the scrambled 301 Mb/s data sequence to the optical transmitter module 103 to be described in detail below in conjunction with the description of FIG. 11.

Fault monitoring of transmit encoder module 102 is carried out by fault detection unit 191 which may be comprised of respective threshold detectors coupled to each of lines 113, 181 and 192, the outputs of the threshold detectors being logically ANDed and coupled to output line 293. Should there occur a lack of activity on scrambled data line 113, unscrambled data line 181 or the major frame timing derived by timing signal generator 130, the output of the corresponding threshold detector in fault detection unit 191 will change state so that a fault alarm signal will be delivered on line 193 to ATE 24. ATE 24 then activates the appropriate indicator 195 in TEN 102 via line 194 so that the location of the detective module can be readily identified.

The transmit encoder module shown in FIG. 10 also contains lines that are employed in conjunction with a repeater fault isolation process carried out under the direction of ATE 24. The purpose of the repeater fault isolation process is to locate and identify which unit in a communication link between stations is defective. Although the process will be described in detail below in conjunction with the description of the operation ATE 24, the control lines and their functions associated with the transmit encoder module shown in FIG. 10 will be explained briefly here.

The data inhibit line 121 is used to couple a signal from ATE 24 that prevents the coupling of data from multiplexer 131 over line 181 to modulo-two adder 171. As was described above in conjunction with the description of protection switch unit 22 (FIG. 3), the insertion of the protective channel via the operation of the transmit protection switch 43 (FIGS. 3 and 4) does not prevent incoming data from being applied over the corresponding one of lines 25-1 to 25-5 to its associated transceiver unit. Thus, data is still permitted to b