Network device with a distributed switch fabric timing system

• US 6,876,652 B1
• Filed: 07/11/2000
• Issued: 04/05/2005
• Est. Priority Date: 05/20/2000
• Status: Expired due to Term

• Current Assignee: Ciena Corporation
• Original Assignee: Ciena Corporation
• Inventors: Bell, Colin, Branscomb, Brian
• Primary Examiner(s): HO, DUC CHI
• Application Number:
  US09/614,187
• Time in Patent Office: 1,729 Days
• Field of Search: 370/352, 370/360, 370/386, 370/503, 375/294, 375/376, 375/362
• US Class Current: 370/386
• CPC Class Codes: G06F 1/14 Time supervision arrangements, e.g. real time clock
• CPC Class Codes: H04J 3/0685 Clock or time synchronisation in a node; Intranode synchronisation
• CPC Class Codes: H04L 41/0803 Configuration setting
• CPC Class Codes: H04L 41/085 Retrieval of network configuration; Tracking network configuration history
• CPC Class Codes: H04L 41/22 comprising specially adapted graphical user interfaces [GUI]
• CPC Class Codes: H04L 45/50 using label swapping, e.g. multi-protocol label switch [MPLS]
• CPC Class Codes: H04L 69/18 Multiprotocol handlers, e.g. single devices capable of handling multiple protocols
• CPC Class Codes: H04L 7/0008 Synchronisation information channels, e.g. clock distribution lines
• CPC Class Codes: H04L 9/40 Network security protocols

Abstract

The present invention provides a central switch fabric timing subsystem and distributed switch fabric timing subsystems. Distributed switch fabric subsystems reduce the cost of a minimally configured network device by providing a network device with a distributed switch fabric. Such a network device locates a portion of the switch fabric functionality on each forwarding card allowing the minimal network device configuration to include less than the entire switch fabric functionality. The cost of the minimal configuration is, therefore, reduced allowing network service providers to more quickly recover the initial cost of the network device. As new services are requested, additional functionality, including both forwarding cards and universal port cards may be added to the network device to handle the new requests, and the fees for the new services may be applied to the cost of the additional functionality. Consequently, the cost of the network device more closely tracks the service fees received by network providers.

Claims

1. A network device comprising

a central switch fabric subsystem including at least one local switch fabric timing subsystem:

a distributed switch fabric subsystem coupled to the central switch fabric subsystem and including at least one local switch fabric timing subsystem; and

a central switch fabric timing subsystem for providing a reference signal to each of the local switch fabric timing subsystems

wherein the reference signal is a segment demarcation signal and wherein each local switch fabric timing subsystem generates a reference clock signal from the received reference segment demarcation signal and passes the received reference segment demarcation signal and the generated reference clock signal to switch fabric components.

2. The network device of claim 1, wherein the reference clock signal comprises a first clock period and the reference segment demarcation signal comprises a second clock period.

3. The network device of claim 2, wherein the first clock period is substantially shorter than the second clock period.

4. A network device, comprising:

a central switch fabric subsystem including at least one local switch fabric timing subsystem;

a distributed switch fabric subsystem coupled to the central switch fabric subsystem and including at least one local switch fabric timing subsystem;

a first central switch fabric timing subsystem providing a plurality of first timing reference signals and at least one first master control signal, wherein one of the first timing reference signals is provided to each of the local switch fabric timing subsystems;

a second central switch fabric timing subsystem providing a plurality of second timing reference signals and at least one second master control signal, wherein one of the second timing reference signals is provided to each of the local switch fabric timing subsystems;

wherein the first central switch fabric timing subsystem receives one of the second timing reference signals and the second master control signal and the second central switch fabric timing subsystem receives one of the first timing reference signals and the first master control signal; and

wherein the first central switch fabric timing subsystem synchronizes the first timing reference signals to the received second timing reference signal in accordance with the second master control signal and the second central switch fabric timing subsystem synchronizes the second timing reference signals to the received first timing reference signal in accordance with the first master control signal.

5. The network device of claim 4, wherein each of the local switch fabric timing subsystems comprise:

a phase locked loop circuit for providing a timing reference signal to local switch fabric components;

a selector circuit for receiving the first and second timing reference signals and coupled to the phase locked loop circuit; and

a control logic circuit coupled to the selector circuit for causing the selector circuit to send one of the first and second timing reference signals to the phase locked loop circuit.

6. The network device of claim 5, wherein the control logic circuit comprises a state machine.

7. The network device of claim 5, wherein each of the local switch fabric timing subsystems further comprises:

a status detector for receiving the first timing reference signal and for providing a signal to the control logic circuit indicating a status of the first timing reference signal; and

wherein, when the signal indicates that the status of the first timing reference signal is invalid, the control logic circuit causes the selector circuit to deselect the first timing reference signal.

8. The network device of claim 7, wherein when the signal indicates that the status of the first timing reference signal is invalid, the control logic circuit further causes the selector circuit to send the second timing reference signal to the phase locked loop circuit.

9. The network device of claim 7, wherein the status detector comprises an activity detector for providing an activity signal.

10. The network device of claim 7, wherein the control logic circuit causes the selector circuit to deselect the first timing reference signal without software interaction.

11. The network device of claim 4, wherein each of the local switch fabric timing subsystems further comprises:

a status detector for receiving the second timing reference signal and for providing a signal to the control logic circuit indicating a status of the second timing reference signal; and

wherein, when the signal indicates that the status of the second timing reference signal is invalid, the control logic circuit causes the selector circuit to deselect the second timing reference signal.

12. The network device of claim 11, wherein when the signal indicates that the status of the second timing reference signal is invalid, the control logic circuit further causes the selector circuit to send the first timing reference signal to the phase locked loop circuit.

13. The network device of claim 11, wherein the status detector comprises an activity detector for providing an activity signal.

14. The network device of claim 11, wherein the control logic circuit causes the selector circuit to deselect the second timing reference signal without software interaction.

15. The network device of claim 4, wherein the first and second timing reference signals comprise segment demarcation timing reference signals.

16. The network device of claim 15, wherein each local switch fabric timing subsystem generates a reference clock signal from the received reference segment demarcation signal and passes the received reference segment demarcation signal and the generated reference clock signal to switch fabric components.

17. The network device of claim 15, wherein the segment demarcation timing reference signals comprise start of segment timing reference signals.

18. A method of operating a network device comprising:

providing a reference signal from a central switch fabric timing subsystem;

synchronizing a first local switch fabric timing subsystem coupled with a central switch fabric subsystem to the reference signal;

synchronizing a second local switch fabric timing subsystem coupled with a distributed switch fabric subsystem to the reference signal; and

transferring network data between the central switch fabric subsystem and the distributed switch fabric subsystem in accordance with the reference signal

wherein the central switch fabric timing subsystem is a first central switch fabric timing subsystem and the reference signal is a first reference signal and further comprising;

providing a second reference signal from a second central switch fabric timing subsystem to the first and second local switch fabric timing subsystems.

19. The method of claim 18, further comprising:

detecting an error in the first reference signal;

synchronizing the first local switch fabric timing subsystem with the second reference signal;

synchronizing the second local switch fabric timing subsystem with the second reference signal; and

transferring network data between the central switch fabric subsystem and the distributed switch fabric subsystem in accordance with the second reference signal.

20. The method of claim 19, further comprising:

switching over from the first central switch fabric timing subsystem to the second central switch fabric timing subsystem.

21. The method of claim 20, wherein the central switch fabric subsystem and the first central switch fabric timing subsystem are located on the same printed circuit board and the second central switch fabric timing subsystem is located on a different printed circuit board and wherein switching over from the first central switch fabric timing subsystem to the second central switch fabric timing subsystem is transparent to the central switch fabric subsystem.

22. The method of claim 20, wherein the central switch fabric subsystem is a first central switch fabric subsystem and further comprising:

switching over from the first central switch fabric subsystem to a second central switch fabric subsystem; and

transferring network data between the second central switch fabric subsystem and the distributed switch fabric subsystem in accordance with the second reference signal.