System and method for multiple timing masters in a network

• US 8,761,035 B2
• Filed: 08/20/2010
• Issued: 06/24/2014
• Est. Priority Date: 08/21/2009
• Status: Active Grant

• Current Assignee: SMSC Europe GmbH (Microchip Technology Incorporated)
• Original Assignee: SMSC Europe GmbH (Microchip Technology Incorporated)
• Inventors: Green, Christopher, Becker, Claudius, Ching, Eric Matthew
• Primary Examiner(s): Zhu, Alvin
• Application Number:
  US12/860,197
• Publication Number:
  US 20110044350A1
• Time in Patent Office: 1,404 Days
• Field of Search: 370/324, 370/503, 370/507, 370/509, 370/510, 370/511, 370/512, 370/513, 370/514
• US Class Current: 370/252
• CPC Class Codes: H04J 3/0641 Change of the master or reference, e.g. take-over or failure of the master
• CPC Class Codes: H04J 3/0661 using timestamps
• CPC Class Codes: H04L 12/422 Synchronisation for ring networks Time Division Multiplex ring networks, e.g. SDH/SONET H04J3/085

Abstract

A communication system, network, interface, and port architecture are provided for transporting data across a ring network. A network node operating as a first timing master generates a set of frames, each frame having a preamble, a data field and a time count field, which represents a portion of the time information associated with the set of frames. This time information may include counted time units, like seconds, or a number of generated and transmitted over the network. As the individual frames of a set of frames are generated and sent on the network, they pass other network nodes and are forwarded through the ring bus to the first timing master which receives at least a portion of the set it is still generating. This enables a received time count field to be compared with a transmitted time count field of the same set. If the fields are identical, there is no other timing master on the bus. If there is another timing master on the bus, the additional timing master would overwrite the contents of the time count field propagating through the network; therefore, the received time count field would not be equal to the time count field being transmitted by the first timing master.

Claims

1. A network node configured as a timing master in a ring bus network, the network node including:

a first communication port configured for generating at least one frame comprising at least a preamble, a data field, and a time count field containing time count information, and for transmitting said at least one frame onto the ring bus network;

a second communication port configured for receiving said at least one frame, comparing a received time count field with said time count field generated by the first communication port, and signaling the presence of at least another timing master on the ring bus network, if the compared time count fields are not equal; and

wherein a propagation delay associated with the at least one frame traveling around the ring bus network is less than a length of said frame, so that the second communication port receives at least parts of said frame while the first communication port is transmitting said frame.

2. The network node according to claim 1, wherein the first communication port comprises a time counter configured for generating the time count information for the time count field by counting one of frames, bytes, bits, or time intervals.

3. The network node according to claim 2, wherein the first communication port divides a bit value of the time counter into a predetermined number (n) of segments and places each segment into the time count field of n consecutive frames.

4. The network node according to claim 3, wherein said second communication port is configured for reassembling the bit value of the time counter by evaluating the time count fields of the n consecutive frames.

5. The network node according to claim 3, wherein at least one frame of the n consecutive frames contains a time count checksum for the time count fields contained therein.

6. The network node according to claim 3, wherein at least one frame of the n consecutive frames contains a unique ID value.

7. The network node according to claim 1, wherein the first communication port further comprises a stable clock for generating the at least one frame, and wherein the stable clock is synchronized to a reference clock source selected from a group comprising a crystal oscillator, an audio source and a video source.

8. A method for detecting multiple timing masters on a ring bus network including the steps of:

generating time count information associated with a set of frames, wherein the time count information is generated by counting time, bits, bytes or a number of generated frames;

generating the set of frames, wherein each frame in the set includes at least a preamble for marking the beginning of the frame, a data field and a time count field representing a portion of the time count information;

transmitting the generated frames on the ring bus network as the set of frames is being generated;

receiving the transmitted frames after each frame travels around the ring bus network;

comparing a time count field in a received frame with a time count field in a frame being transmitted; and

detecting multiple timing masters on the ring bus network if the received time count field and the transmitted time count field are different.

9. The method according to claim 8, wherein the step of generating the set of frames comprises dividing the time count information into a predetermined number (n) of segments, and placing the n segments into the time count fields of n consecutively generated frames, so that each time count field contains only 1/n of a total number of bits representing the time count information, while n consecutive time count fields represent the time count information.

10. The method according to claim 9, further comprising assembling n received time count fields into a received time counter value.

11. A communication system comprising a plurality of nodes interconnected by a transmission line to form a network, wherein each of the plurality of nodes comprises:

a first communication port configured for generating at least one frame comprising a preamble, a data field, and a time count field containing time count information, and for transmitting said at least one frame onto the transmission line for propagation through the network; and

a second communication port configured for receiving said at least one frame, comparing a received time count field with said time count field generated by the first communication port, and signaling a presence of at least two timing masters on the network, if the compared time count fields are not identical.

12. The communication system according to claim 11, wherein a propagation delay associated with the at least one frame propagating around the network is less than a length of said frame, so that the second communication port receives at least a portion of said frame while the first communication port is transmitting said frame.

13. The communication system according to claim 11, wherein the first communication port comprises:

a framer for generating a plurality of frames;

a clock generator for clocking said plurality of frames onto said transmission line;

a transmit time counter for generating time count information associated with a set of n consecutively generated frames; and

a transmit time count register for storing a value of the time counter for the set of n consecutively generated frames.

14. The communication system according to claim 13, wherein the framer is configured for assembling the plurality of frames, so that each frame in a set of frames includes at least a preamble, a time count field, and a data field, and wherein the time count field in each frame contains only a portion of the time count information generated by the time counter for each set of frames.

15. The communication system according to claim 14, wherein the second communication port comprises:

a frame buffer and decoder for buffering and decoding frames received from the transmission line;

a receive time counter register for assembling the time count information from each set of received frames; and

means for comparing a value of the assembled time count information with the value stored in the transmit time count register of the first communication port.

16. The communication system according to claim 15, wherein if the values stored in the transmit and receive time counter registers are identical, said means determines that there is only one timing master on the network.

17. The communication system according to claim 15, wherein if the values stored in the transmit and receive time counter registers are not identical, said means determines that at least two of the plurality of network nodes are operating as timing masters.