Method for switching master/slave timing in a 1000Base-T link without traffic disruption

Abstract

A method switches master/slave timing in a communication network without traffic disruption. The method includes a master device informing a slave of timing loss. The master device additionally begins transmitting with timing from a local reference clock and begins receive timing recovery. The slave freezes its receive timing recovery and locks its transmit clock. The master device transitions its transmit timing to use the recovered receive clock. The slave gradually switches to transmitting using its local clock signal. The method may be used in synchronous Ethernet networks.

What is claimed is: 
     
       1. A method for reconfiguring a timing relationship in a network, the network comprising network nodes comprising at least one physical layer device, the physical layer devices pair-wise coupled between network nodes with a first node with a first physical layer device operating as a master and a second node with a second physical layer device operating as a slave, the method comprising:
 transmitting signals from the first physical layer device of the first node to the second physical layer device of the second node using a reference clock local to the first node;   transmitting signals from the second physical layer device of the second node to the first physical device of the first node using a clock signal recovered from signals received from the first physical layer device of the first node;   performing timing recovery, by the first node, on signals received from the second node;   freezing timing recovery, by the second node, of signals received from the first node;   switching the first physical layer device of the first node to transmit signals using a clock signal recovered from signals received from the second physical layer device of the second node; and   switching the second physical layer device of the second node to transmit signals using a clock signal local to the second node.   
     
     
       2. The method of  claim 1 , wherein switching the first physical layer device to transmit using a clock signal produced by the receiver of the first physical layer device and switching the second physical layer device to transmit using a clock signal local to the network node of the second physical layer device are performed substantially without bit errors in communication between the first physical layer device and the second physical layer device. 
     
     
       3. The method of claim  1  12, wherein additional configurational aspects are associated with a physical layer device operating as a master or as a slave, and wherein the reconfiguration of timing change of operation from the first configuration to the second configuration is performed without modifying the additional configurational aspects. 
     
     
       4. The method of  claim 3 , wherein the additional configurational aspects comprise a scrambling polynomial. 
     
     
       5. The method of claim  1  12, wherein said switching the first physical layer device to transmit using a clock recovered by the receiver of the first physical layer device  of the physical layer device of the third network node to transmit using the clock signal responsive to the local reference clock of the third network node comprises decaying a frequency term in a phase-locked loop used for timing of transmission from the first physical layer device of the second network node. 
     
     
       6. The method of  claim 1 , wherein switching the second physical layer device to transmit using a clock signal local to the network node of the second physical layer device comprises decaying a frequency term in a phase-locked loop used for timing of transmission from the second physical layer device. 
     
     
       7. The method of  claim 1 , further comprising transmitting a request to reconfigure timing from the first physical layer device to the second physical layer device. 
     
     
       8. The method of  claim 1 , further comprising transmitting a request to reconfigure timing from the second physical layer device to the first physical layer device. 
     
     
       9. The method of  claim 1 , wherein the network nodes further comprise phase-locked loop circuitry coupled to the physical layer devices of the network node and configured to supply the clock signal local to the network node sourced from clocks recovered by the physical layer devices of the network node, the method further comprising:
 determining the source of the clock signal local to the network node of the second physical layer device; and   when the source of the clock signal local to the network node of the second physical layer device is the second physical layer device, switching the source to a clock signal recovered from another physical layer device of the network node of the second physical layer device.   
     
     
       10. The method of  claim 1 , wherein switching the first physical layer device of the first node to transmit signals using the clock signal recovered from signals received from the second physical layer device of the second node is accomplished without performing an auto-negotiation between the first node and the second node. 
     
     
       11. The method of  claim 1 , wherein switching the first physical layer device of the first node to transmit signals using the clock signal recovered from signals received from the second physical layer device of the second node is accomplished without reinitializing a link between the first node and the second node. 
     
     
       12. A method for reconfiguring a timing relationship in a network, the network comprising at least three network nodes each comprising a respective physical layer device, the physical layer devices pair-wise coupled between respective network nodes with a physical layer device of a first of each pair operating as a timing master and a physical layer device of a second of each pair operating as a timing slave, the method comprising:
 operating in a first configuration of synchronous operation wherein a first of the network nodes provides timing for a second of the network nodes over the respective pair-wise coupling of physical layer devices, and the second of the network nodes operates in a feedthrough timing mode thus providing timing to a third of the network nodes over the respective pair-wise coupling of physical layer devices from the timing provided by the first network node, wherein the physical layer device of the second of the network nodes operates as a timing master and the physical layer device of the third network node acts as a timing slave;   detecting at the second network node that a data link between the first network node and the second network node has been dropped;   informing, from the second network node to the third network node, responsive to said detection, that a configuration change is desired to a second configuration of synchronous operation;   transmitting signals from the physical layer device of the second network node to the physical layer device of the third network node using timing from a reference clock local to the second network node;   freezing timing recovery in a receiver of the physical layer device of the third network node thereby locking the timing of the physical layer device of the third network node to a local reference clock of the third network;   performing timing recovery in a receiver of the physical layer device of the second network node from a signal received from the physical layer device of the third network node;   switching the physical layer device of the second network node to transmit using timing locked to a clock signal recovered by the receiver of the physical layer device of the second network node; and   switching the physical layer device of the third network node to transmit signals using a clock signal responsive to the local reference clock of the third network node thereby operating in a second configuration wherein the third network node provides timing for the second network node over the respective pair-wise coupling of physical layer devices.   
     
     
       13. The method of claim 12, further comprising prior to said freezing timing recovery in the receiver of the physical layer device of the third network node,
 switching, in the event that the third network node was using a local reference clock recovered from the second network node, the local reference clock of the third network node to be responsive to an additional physical layer device of the third network node.   
     
     
       14. The method of claim 12, wherein said switching of the physical layer device of the second network node to transmit signals using timing locked to the clock signal recovered by the receiver of the physical layer device of the second network node is performed smoothly thus exhibiting timing characteristics that allow the physical layer device of the third network device to receive a signal transmitted from the physical layer device of the second network node substantially without bit errors. 
     
     
       15. The method of claim 12, wherein the network further comprises a fourth network node in communication with the first network node and arranged to receive timing therefrom, the method further comprising: receiving timing from said fourth network node at said additional physical layer device of the third network node. 
     
     
       16. A network arranged for reconfigurable timing, the network comprising:
 three network nodes each comprising a respective physical layer device, the physical layer devices pair-wise coupled between respective network nodes with a physical layer device of a first of each pair operating as a timing master and a physical layer device a second of each pair operating as a timing slave, the network nodes arranged to operate in a first configuration of synchronous operation wherein a first of the network nodes provides timing for a second of the network nodes over the respective pair-wise coupling of physical layer devices, and the second of the network nodes operates in a feedthrough timing mode thus providing timing to a third of the network nodes over the respective pair-wise coupling of physical layer devices from the timing provided by the first network node, wherein the physical layer device of the second of the network nodes operates as a timing master and the physical layer device of the third network node acts as a timing slave, the network further arranged to:   detect at the second network node that a data link between the first network node and the second network node has been dropped;   inform, from the second network node to the third network node, responsive to said detection, that a configuration change is desired to a second configuration of synchronous operation;   transmit signals from the physical layer device of the second network node to the physical layer device of the third network node using timing from a reference clock local to the second network node;   freeze timing recovery in a receiver of the physical layer device of the third network node so as to lock the timing of the physical layer device of the third network node to the local reference clock of the third network;   perform timing recovery in a receiver of the physical layer device of the second network node from a signal received from the physical layer device of the third network node;   switch the physical layer device of the second network node to transmit using timing locked to a clock signal recovered by the receiver of the physical layer device of the second network node: and   switch the physical layer device of the third network node to transmit signals using a clock signal responsive to the local reference clock of the third network node thereby operating in a second configuration wherein the third network node provides timing for the second network node over the respective pair-wise coupling of physical layer devices.   
     
     
       17. The network according to claim 16, wherein prior to said freezing timing recovery in the receiver of the physical layer device of the third network node,
 switching, in the event that the third network node was using a local reference clock recovered from the second network node, the local reference clock of the third network node to be responsive to an additional physical layer device of the third network node.   
     
     
       18. The network according to claim 16, further comprising a fourth network node arranged to provide timing to said additional physical layer device of the third network node. 
     
     
       19. The network of claim 16, further comprising a fourth network node in communication with the first network node and arranged to receive timing therefrom, said additional physical layer device of the third network node arranged to receive timing from said fourth network node.