Power and data redundancy in a single wiring closet

• US 20060078093A1
• Filed: 11/30/2004
• Published: 04/13/2006
• Est. Priority Date: 10/07/2004
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Cafiero, Luca, Karam, Roger A.
• Granted Patent: US 7,849,351 B2
• Time in Patent Office: Days
• US Class Current: 379/24
• CPC Class Codes: H04L 1/22 using redundant apparatus to increase reliability
• CPC Class Codes: H04L 12/10 Current supply arrangements
• CPC Class Codes: H04L 41/0604 using filtering, e.g. reduction of information by using priority, element types, position or time

Abstract

Redundancy of data and/or Inline Power in a wired data telecommunications network from a first network device and a second network device configured as power sourcing equipment (PSE) devices and coupled together and to a third network device (such as a PD) via a Y device is provided by providing redundant signaling to/from each of the pair of network devices, and coupling a port of each of the network devices to the Y device and from there to a third port where a third network device such as a PD may be coupled. Because the Y device is essentially passive, communications paths between the PSE devices and the PD are provided for negotiating master/slave status and other status and related information among the respective network devices. Dynamic impedance matching is provided to handle situations where not all devices are plugged in and as a communications technique among the devices.

Claims

1. A method for providing redundancy for communications and/or inline power between a first network node and a second network node in a wired data telecommunications network, the method comprising:

directing, from the first network node, redundant network communications to and from a first wired data telecommunications network device (first network device) and a second wired data telecommunications network device (second network device);

coupling a first port of a Y device to the second network node, the Y device having at least three ports with at least two pairs of conductors coupled across the at least three ports;

coupling a second port of the Y device to a first port of the first network device;

coupling a third port of the Y device to a first port of the second network device;

having the first network device initially act as master and thereby route communications between the network node and the first port of the wired data telecommunications network;

having the second data telecommunications network device initially act as slave;

monitoring at the second network device communications and/or inline power between the second network node and the first port of the first network device;

detecting a condition in the first network device with said monitoring; and

reconfiguring the slave as master and vice versa in response to said detecting.

2. The method of claim 1, further comprising:

dynamically adjusting wired data telecommunications network impedance at least one of the first and second network devices in response to measurements made at said first or second network devices.

3. The method of claim 1, further comprising:

sending a message to a network control point in response to said detecting.

4. The method of claim 3, wherein said sending is performed using the wired data telecommunications network to send a message from the second network device through the network node.

5. The method of claim 3, wherein said sending is performed using a wireless telecommunications link from the second network device to a wireless node coupled to the wired data telecommunications network, and from the wireless node to the network control point.

6. An apparatus for providing redundancy for communications and/or inline power between a first network node and a second network node in a wired data telecommunications network, the apparatus comprising:

means for directing, from the first network node, redundant network communications to and from a first wired data telecommunications network device (first network device) and a second wired data telecommunications network device (second network device);

means for coupling a first port of a Y device to the second network node, the Y device having at least three ports with at least two pairs of conductors coupled across the at least three ports;

means for coupling a second port of the Y device to a first port of the first network device;

means for coupling a third port of the Y device to a first port of the second network device;

means for having the first network device initially act as master and thereby route communications between the network node and the first port of the wired data telecommunications network;

means for having the second data telecommunications network device initially act as slave;

means for monitoring at the second network device communications and/or inline power between the second network node and the first port of the first network device;

means for detecting a condition in the first network device with said monitoring; and

means for having the slave take on the role of master in response to said detecting.

7. The apparatus of claim 6, further comprising:

means for dynamically adjusting wired data telecommunications network impedance at the second device in response to measurements made at the second network device.

8. The apparatus of claim 6, further comprising:

means for sending a message to a network control point in response to said detecting.

9. The apparatus of claim 8, wherein said means for sending utilizes the wired data telecommunications network to send a message from the second network device through the network node.

10. The apparatus of claim 8, wherein said means for sending utilizes a wireless telecommunications link to a wireless node coupled to the wired data telecommunications network, and from the wireless node to the network control point.

11. A system for providing redundancy for communications and/or inline power between a first network node and a second network node in a wired data telecommunications network, the system comprising:

circuitry for directing, from the first network node, redundant network communications to and from a first wired data telecommunications network device (first network device) and a second wired data telecommunications network device (second network device);

circuitry for coupling a first port of a Y device to the second network node, the Y device having at least three ports with at least two pairs of conductors coupled across the at least three ports;

circuitry for coupling a second port of the Y device to a first port of the first network device;

circuitry for coupling a third port of the Y device to a first port of the second network device;

circuitry for causing the first network device to initially act as master and thereby route communications between the first network node and the first port of the first network device;

circuitry for causing the second data telecommunications network device to initially act as slave;

circuitry for monitoring at the second network device communications and/or inline power communicated between the second network node and the first port of the first network device;

circuitry for detecting a condition in the first network device with said monitoring; and

circuitry responsive to said circuitry for detecting for enabling the slave to take over the role of master.

12. The system of claim 11, further comprising:

circuitry for dynamically adjusting wired data telecommunications network impedance at the first network device in response to measurements made at the first network device.

13. The system of claim 11, further comprising:

circuitry for sending a message to a network control point in response to said circuitry for detecting.

14. The system of claim 13, wherein said circuitry for sending utilizes the wired data telecommunications network to send a message from the second network device through the network node.

15. The system of claim 13, wherein said circuitry for sending utilizes a wireless telecommunications link to a wireless node coupled to the wired data telecommunications network, and from the wireless node to the network control point.

16. A redundant network device providing redundancy for communications and/or inline power between a first network node and a second network node in a wired data telecommunications network, the device comprising:

a router for directing, from the first network node, redundant wired data telecommunications network communications to and from a first wired data telecommunications network device (first network device) and a second wired data telecommunications network device (second network device);

wiring coupling a first port of a Y device to the second network node, the Y device having at least three ports with at least two pairs of conductors coupled across the at least three ports;

wiring coupling a second port of the Y device to a first port of the first network device;

wiring coupling a third port of the Y device to a first port of the second network device;

a processor internal to the first network device causing the first network device to initially act as master and thereby route communications from the router to the first port of the first network device;

a processor internal to the second network device causing the second network device to initially act as slave;

a monitor associated with the second network device monitoring communications and/or inline power between the first port of the first network device and the second network node;

a detector detecting a condition in the first network device with said monitoring; and

circuitry responsive to said detector for at least partially disabling the first network device so that the second network device may take over the role of master.

17. The device of claim 16, further comprising:

a dynamic impedance terminator for dynamically adjusting wired data telecommunications network impedance at the second device in response to measurements made at the second device.

18. The device of claim 16, further comprising:

a communicator for sending a message to a network control point in response to said detector.

19. The device of claim 18, wherein said communicator utilizes the wired data telecommunications network to send a message from the second network device through the first network node.

20. The device of claim 18, wherein said communicator utilizes a wireless telecommunications link to a wireless node coupled to the wired data telecommunications network, and from the wireless node to the network control point.

21. A circuit for dynamically terminating a transmission line, comprising:

a switch having at least a first state and a second state, wherein

the transmission line is terminated with a first impedance when said switch is in said first state; and

the transmission line is terminated with a second impedance when said switch is in said second state.

136. The circuit of claim 21, wherein:

the second impedance represents a combination of the first impedance with another impedance coupled in series through the switch with the first impedance.

22. A circuit for dynamically terminating a transmission line, comprising:

a switch having at least a first state and a second state;

a first termination resistance coupled to terminate the transmission line; and

a second termination resistance coupled through the switch so that when said switch is in the first state, the second termination resistance is coupled in parallel with the first termination resistance and when said switch is in the second state the second termination resistance is decoupled from the first termination resistance.

23. A system for communicating using termination modulation, comprising:

a transmission line having at least a first end and a second end;

the first end terminated with a first circuit having a selectable impedance; and

the second end adapted to sense a change in the impedance of the termination of the first end.

24. The system of claim 23, wherein said selectable impedance is selectable between a first impedance and a second impedance.

25. The system of claim 24, wherein the transmission line is a twisted pair transmission line.

26. The system of claim 25, wherein the transmission line includes a Y device so that in addition to the first end and the second end it has at least a third end.

27. The system of claim 26, wherein the impedance is selectable in response to a measurement made at the first end.

28. The system of claim 27, wherein the measurement is made with a time domain reflectometer.

29. The system of claim 26, wherein the second impedance is at least twice the first impedance.

30. A method for communicating using termination impedance modulation, comprising:

using a dynamic termination impedance circuit at one end of a transmission line to switch its termination impedance in a predetermined sequence between a first termination impedance and a second termination impedance;

sensing the changes in termination impedance at a location along the transmission line remote from the one end.

31. A method for communicating signals between a first port and a second port of a Y device so that the communications may be monitored at a third port of the Y device, the Y device configured so that at least two pairs of twisted-pair conductors are connected at each of the first, second and third ports so that first, second and third connectors correspondingly associated with said first, second and third ports have connection contacts connected so that a first connection contact of each of said first, second and third connectors are all connected together, a second connection contact of each of said first, second and third connectors are all connected together, a third connection contact of each of said first, second and third connectors are all connected together, and a fourth connection contact of each of said first, second and third connectors are all connected together, the method comprising:

coupling at least two pairs of conductors of a wired data telecommunications network in a Y device;

coupling the first port of the Y device to a first network device;

coupling the second port of the Y device to a second network device;

communicating between the first network device and the second network device; and

monitoring said communicating at the third port of the Y device with a third network device.

32. The method of claim 31, further comprising:

utilizing non-data packets to communicate status information among any two of the first network device, the second network device and the third network device.

33. The method of claim 31, further comprising:

utilizing non-data packets to communicate status information between the first network device and the second network device.

34. The method of claim 31, further comprising:

utilizing non-data packets to communicate status information between the second network device and the third network device.

35. The method of claim 31, further comprising:

utilizing non-packet signals to communicate status information between the first network device and the second network device.

36. The method of claim 31, further comprising:

utilizing non-packet signals to communicate status information between the first network device and the second network device.

37. The method of claim 31, further comprising:

utilizing non-packet signals to communicate status information between the second network device and the third network device.

38. A method for providing redundancy from a first network device and a second network device through a Y device having a first, second and third port in a wired data telecommunications network having at least two pairs of twisted pair conductors, the Y device configured so that at least two pairs of twisted-pair conductors are connected at each of its first, second and third ports so that first, second and third connectors correspondingly associated with said first, second and third ports have connection contacts connected so that a first connection contact of each of said first, second and third connectors are all connected together, a second connection contact of each of said first, second and third connectors are all connected together, a third connection contact of each of said first, second and third connectors are all connected together, and a fourth connection contact of each of said first, second and third connectors are all connected together, the method comprising:

coupling a first network device configured as power sourcing equipment (PSE) to a first port of the Y device;

coupling a second network device configured as PSE to a second port of the Y device; and

coupling a third network device configured as a powered device (PD) to a third port of the Y device.

39. The method of claim 38, further comprising:

Providing inline power from the first network device to the third network device while the first network device is fully operable.

40. The method of claim 39, further comprising:

providing inline power from the second network device to the third network device when the first network device is not fully operable in at least some respect.

41. The method of claim 38, further comprising:

utilizing a dynamic termination impedance at the first network device to terminate the wired data telecommunications network at the first network device with an impedance appropriate to conditions presented.

42. The method of claim 41, further comprising:

utilizing a dynamic termination impedance at the second network device to terminate the wired data telecommunications network at the second network device with an impedance appropriate to conditions presented.

43. The method of claim 42, further comprising:

communicating information between the first network device and the second network device over the wired data telecommunications network.

44. The method of claim 42, wherein:

said communicating utilizes common mode signaling between the first network device and the second network device.

45. The method of claim 42, wherein:

said communicating utilizes impedance modulation signaling between the first network device and the second network device.

46. The method of claim 42, further comprising:

utilizing the dynamic termination impedance of the first network device to discover that the Y device is coupled to the first network device.

47. The method of claim 38, further comprising:

sending a first test packet from the second network device to the first network device over the wired data telecommunications network;

receiving the first test packet at the first network device and, in response, sending a second test packet from the first network device to the third network device;

receiving the second test packet at the third network device and, in response, sending a third test packet from the third network device to the first network device; and

monitoring the transmission of the third test packet at the second network device.

48. The method of claim 47, further comprising:

configuring the first network device as a master and the second network device as a slave prior to sending the first test packet.

49. The method of claim 38, further comprising:

communicating information between the first network device and the second network device over a single pair of conductors of the wired data telecommunications network.

50. The method of claim 38, further comprising:

communicating information between the first network device and the third network device over a single pair of conductors of the wired data telecommunications network.

51. The method of claim 49, further comprising:

utilizing a single pair identity network to facilitate said communicating.

52. The method of claim 50, further comprising:

utilizing a single pair identity network to facilitate said communicating.

53. The method of claim 38, further comprising:

sending a communication from the first network device to the second network device, the communication telling the second network device to keep its link up for a period of time regardless of whether data packets are present on the wired data telecommunications network.

54. The method of claim 53, wherein

the communication comprises one of a flag pulse or a packet.

55. The method of claim 38, further comprising:

sending a communication from the first network device to the second network device, the communication telling the second network device to not utilize all four pairs of the wired data telecommunications network for communication for a period of time.

56. The method of claim 55, wherein

the communication comprises one of a flag pulse or a packet.

57. The method of claim 55, wherein the period of time ends upon receipt of another communication telling the second network device that it is permitted to use all four pairs for communication.

58. The method of claim 38, further comprising:

sending a communication from the first network device to the third network device, the communication telling the third network device to keep its link up for a period of time regardless of whether data packets are present on the wired data telecommunications network.

59. The method of claim 58, wherein

the communication comprises one of a flag pulse or a packet.

60. The method of claim 38, further comprising:

sending a communication from the first network device to the third network device, the communication telling the third network device to not utilize all four pairs of the wired data telecommunications network for communication for a period of time.

61. The method of claim 60, wherein

the communication comprises one of a flag pulse or a packet.

62. The method of claim 60, wherein the period of time ends upon receipt of another communication telling the third network device that it is permitted to use all four pairs for communication.

63. The method of claim 38, further comprising:

detecting the Y device at one of the first, second and third network devices in response to signals transmitted from that network device onto the wired data telecommunications network; and

causing at least one other device coupled to the wired data telecommunications network to initiate a link integrity check in response to said detecting.

64. The method of claim 38, further comprising:

detecting the second network device at the first network device and, in response, conducting a master-slave negotiation between the first network device and the second network device to select one of the first and second network devices to be master (original master) and the other to be slave.

65. The method of claim 64, wherein:

the master-slave negotiation takes place, at least in part, using pulses over the wired data telecommunications network that are not in the form or Internet Protocol packets.

66. The method of claim 65, further comprising:

monitoring the wired data telecommunications network with the slave; and

detecting a fault in another network device.

67. The method of claim 66, further comprising:

having the slave take over as master in response to said detecting.

68. The method of claim 66, further comprising:

shutting off power to circuitry in the original master in response to said detecting.

69. The method of claim 38, further comprising:

detecting the decoupling of the third network device from the Y device;

shutting down inline power provided from the first network device and the second network device in response to said detecting.

70. The method of claim 69, wherein:

said detecting includes using a TDR at the first network device to detect the decoupling.

71. The method of claim 70, wherein:

said detecting further includes communicating with the second network device, said communication causing it to shut down inline power provided from the second network device.

72. The method of claim 38, further comprising:

detecting a zero inline power current draw from the third network device at the first network device;

communicating the detection of zero current draw from the first network device to the second network device;

detecting a zero inline current draw from the third network device at the second network device;

communicating the detection of zero current draw from the second network device to the first network device; and

shutting down inline power provided from the first network device and the second network device in response to at least said detecting and communicating.

73. The method of claim 64, further comprising:

detecting the decoupling of the slave from the Y device; and

responsive to said detecting the decoupling, initiating a link integrity test at the master.

74. The method of claim 41, further comprising:

tuning the dynamic termination impedance to reduce ISI (inter symbol interference) received at one of the network devices.

75. The method of claim 38, further comprising:

signaling from the third network device to the first network device and the second network device a requirement that redundancy is required for at least a period of time.

76. The method of claim 64, further comprising:

initiating a communication at the third network device which can be monitored by the slave, the communication requesting the slave to conduct a conversation with the third network device.

77. The method of claim 76, further comprising:

having the master back off for at least a period of time in response to the communication.

78. The method of claim 77, wherein:

the master stops backing off when it detects the end of the conversation.

79. The method of claim 76, further comprising:

sending a communication from the slave to the master in response to the conversation, the communication requesting the master to become a slave.

80. The method of claim 38, further comprising:

providing a different single pair identity network across each pair of conductors of the Y device.

81. The method of claim 80, further comprising:

providing another single pair identity network on each pair of conductors coupled to the third network device.

114. The method of claim 38, further comprising:

detecting the presence of the Y device with the first network device.

115. The method of claim 114, wherein said detecting detects the Y device by sensing a single-pair identity network associated with a pair of the Y device.

116. The method of claim 114, wherein said detecting detects the Y device by sensing an impedance signature of the Y device.

117. The method of claim 38, further comprising:

securing the connection between the Y device and at least the coupled first and second network devices, said securing comprising at least one of;

(1) verifying the total cable length between the first network device and the second network device;

(2) providing a password-based security to verify that both the first network device and the second network device are permitted to be coupled together; and

(3) performing a link integrity test from each of the first network device and the second network device.

118. The method of claim 38, further comprising:

having one of the first network device and the second network device conduct a first link integrity test; and

having the other of the first network device and the second network device conduct a second link integrity test after completion of the first link integrity test.

119. The method of claim 118, further comprising:

selecting one of the first network device and the second network device to be a master network device; and

selecting the other of the first network device and the second network device to be a slave network device.

120. The method of claim 119, wherein said selecting one is based upon relative available inline power resources of the first network device and the second network device.

121. The method of claim 119, wherein said selecting one is based upon manual input of a user.

122. The method of claim 119, wherein said selecting one is based upon configured software/firmware.

123. The method of claim 38, further comprising:

implementing a back off algorithm at the first network device to not search for inline power via the connected Y device for a period of time selected by the back off algorithm.

124. The method of claim 123, further comprising:

detecting at the first network device, after the period of time selected by the back off algorithm, the presence of inline power via the connected Y device, the inline power being regular inline power, an inline power discovery signal, or an inline power classification signal.

125. The method of claim 124, wherein:

if said detecting detects inline power and if the detected inline power is an inline power discovery signal or an inline power classification signal, the first network device continues to back off, and if the detected inline power is regular inline power the first network conducts a communication with the second network device in order to negotiate the application of regular inline power from the first network device.

126. The method of claim 124, wherein:

if said detecting detects inline power and if the detected inline power is an inline power discovery signal or an inline power classification signal, the first network device monitors the conductors and waits until inline power is applied by the second network device and then conducts a communication with the second network device in order to negotiate the application of regular inline power from the first network device.

127. The method of claim 124, wherein:

if said detecting detects inline power and if the detected inline power is an inline power discovery signal or an inline power classification signal, the first network device monitors the conductors and waits until inline power is applied by the second network device and then initiates inline power discovery and classification on its own behalf.

128. The method of claim 38, further comprising:

detecting an event that eliminates redundancy between the third network device and the first and second network devices.

129. The method of claim 128, wherein the event includes a high bit error rate between the third network device and one or both of the first and second network devices.

130. The method of claim 128, wherein the event includes detecting a link down on one or both of the links between the third network device and the first and second network devices.

131. The method of claim 128, wherein the event includes detecting a system malfunction in one or more of the first, second and third network devices.

132. The method of claim 128, wherein the event includes detecting a drop in available inline power over one or both of the links between the third network device and the first and second network devices.

133. The method of claim 128, further comprising:

responding to said detecting by initiating a communication to a network control point, the communication describing the event.

134. The method of claim 128, further comprising:

responding to said detecting by initiating a communication to at least one of the first, second and third network devices, the communication describing the event.

135. The method of claim 134, further comprising:

taking at least one action to reconfigure at least one of the first, second and third network devices in response to said detecting.

82. A network device adapted for communicating using termination impedance modulation on a wired data telecommunications network, the device comprising:

a dynamic termination impedance circuit adapted to be coupled to a transmission line of the wired data telecommunications network, the dynamic termination impedance circuit capable of switching its termination impedance in a predetermined sequence among at least a first termination impedance and a second termination impedance.

83. Network equipment for a wired data telecommunications network, the equipment comprising:

a first network device;

a second network device;

a Y device having a first port coupled to the first network device, a second port coupled to the second network device and a third port for coupling to a third network device, the Y device including at least two pairs of twisted pair conductors coupled to each of its three ports; and

the network equipment adapted to communicate signals between the first port and the second port of the Y device so that the signals may be monitored at the third port of the Y device.

84. Network equipment for providing redundancy in a wired data telecommunications network, the equipment comprising:

a first network device configured as PSE;

a second network device configured as PSE, the first and the second network device providing redundant signals; and

a Y device having a first port coupled to the first network device, a second port coupled to the second network device and a third port for coupling to a third network device, the Y device including at least two pairs of twisted pair conductors coupled to each of its three ports;

85. The equipment of claim 84, further comprising:

a dynamic termination impedance circuit associated with the first network device to terminate the wired data telecommunications network at the first network device with an impedance appropriate to conditions presented.

86. The equipment of claim 85, further comprising:

a dynamic termination impedance circuit associated with the second network device to terminate the wired data telecommunications network at the second network device with an impedance appropriate to conditions presented.

87. The equipment of claim 86, further comprising:

circuitry for communicating information between the first network device and the second network device over the wired data telecommunications network.

88. The equipment of claim 86, wherein:

said communicating utilizes common mode signaling between the first network device and the second network device.

89. The equipment of claim 86, wherein:

said communicating utilizes impedance modulation signaling between the first network device and the second network device.

90. The equipment of claim 86, wherein:

the dynamic termination impedance circuit of the first network device is adapted to discover that the Y device is coupled to the first network device.

91. The equipment of claim 84, further comprising:

means for sending a first test, status or control packet from the second network device to the first network device over the wired data telecommunications network;

means for receiving the first test, status or control packet at the first network device;

means responsive to said means for receiving the first test packet for sending a second test packet from the first network device to the third network device;

means for receiving the second test packet at the third network device;

means responsive to said means for receiving the second test packet for sending a third test packet from the third network device to the first network device; and

means for monitoring the transmission of the third test packet at the second network device.

92. The equipment of claim 91, further comprising:

means for configuring the first network device as a master and the second network device as a slave prior to sending the first test packet.

93. The equipment of claim 84, further comprising:

means for communicating information between the first network device and the second network device over a single pair of conductors of the wired data telecommunications network.

94. The equipment of claim 84, further comprising:

means for communicating information between the first network device and the third network device over a single pair of conductors of the wired data telecommunications network.

95. The equipment of claim 93, further comprising:

means for utilizing a single pair identity network to facilitate said communicating.

96. The equipment of claim 94, further comprising:

means for utilizing a single pair identity network to facilitate said communicating.

97. The equipment of claim 84, further comprising:

means for sending a communication from the first network device to the second network device, the communication telling the second network device to keep its link up for a period of time regardless of whether data packets are present on the wired data telecommunications network.

98. The equipment of claim 97, wherein

the communication comprises one of a flag pulse or a packet.

99. The equipment of claim 84, further comprising:

means for sending a communication from the first network device to the second network device, the communication telling the second network device to not utilize all four pairs of the wired data telecommunications network for communication for a period of time.

100. The equipment of claim 99, wherein

the communication comprises one of a flag pulse or a packet.

101. The equipment of claim 99, wherein the period of time ends upon receipt of another communication telling the second network device that it is permitted to use all four pairs for communication.

102. The equipment of claim 84, further comprising:

means for sending a communication from the first network device to the third network device, the communication telling the third network device to keep its link up for a period of time regardless of whether data packets are present on the wired data telecommunications network.

103. The equipment of claim 84, further comprising:

means for sending a communication from the first network device to the third network device, the communication telling the third network device to not utilize all four pairs of the wired data telecommunications network for communication for a period of time.

104. The equipment of claim 103, wherein

the communication comprises one of a flag pulse or a packet.

105. The equipment of claim 103, wherein the period of time ends upon receipt of another communication telling the third network device that it is permitted to use all four pairs for communication.

106. The equipment of claim 84, further comprising:

means for detecting the Y device at one of the first, second and third network devices in response to signals transmitted from the that network device onto the wired data telecommunications network; and

means responsive to said means for detecting for causing at least one other device coupled to the wired data telecommunications network to initiate a link integrity check.

107. The equipment of claim 84, further comprising:

means for detecting the second network device at the first network device and, in response, conducting a master-slave negotiation between the first network device and the second network device to select one of the first and second network devices to be master (original master) and the other to be slave.

108. The equipment of claim 107, further comprising:

means for detecting the decoupling of the slave from the Y device; and

means responsive to said means for detecting the decoupling, for initiating a link integrity test at the master.

109. The equipment of claim 85, further comprising:

means for tuning the dynamic termination impedance to reduce ISI (inter symbol interference) received at one of the network devices.

110. The equipment of claim 84, further comprising:

means for signaling from the third network device to the first network device and the second network device a requirement that redundancy is required for at least a period of time.

111. The equipment of claim 107, further comprising:

means for initiating a communication at the third network device which can be monitored by the slave, the communication requesting the slave to conduct a conversation with the third network device.

112. The equipment of claim 111, further comprising:

means for sending a communication from the slave to the master in response to the conversation, the communication requesting the master to become a slave.

113. The equipment of claim 84, further comprising:

means for providing a different single pair identity network across each pair of conductors of the Y device.