FORM 2

THE PATENTS ACT  1970
(39 of 1970)
&
THE PATENTS RULES  2003

COMPLETE SPECIFICATION
(See section 10  rule 13)

“A method and system for protection switching of clock synchronization during card switchover in a redundant transmission system”

Tejas Networks Limited
2nd floor  GNR Tech Park  46/4  Garbebhavi Palya 
Kudlu Gate  Hosur main road 
Bangalore 560 068  Karnataka  India

The following specification particularly describes the invention and the manner in which it is to be performed.

Field of the Invention

This invention relates to the field of telecommunications  and more particularly to clock synchronization and fault protection for a telecommunications device.

Background of the Invention

Many telecommunications devices include backplanes for transmitting digital information between components of the devices. For example  a telecommunications switching system might include a backplane for transmitting digital data representing voice signals or data between cards associated with incoming and outgoing ports. Typically  such a system would also include a mechanism to allow the system to detect a timing error  loss of clock synchronization  or other clock failure associated with the total or partial failure of one of the cards or of its clock generation functionality. Successful operation of the system in many instances will depend heavily upon the ability of this mechanism to detect and respond appropriately to such a failure to meet often stringent availability  flexibility  and other requirements placed on the system.

As the telecommunications industry continues to dominate the growth of the global economy  meeting availability  flexibility  and other requirements placed on switching and other systems has become increasingly important. High availability is generally considered as exceeding 99.999 percent availability  amounting to less than approximately five minutes of “down time” each year  and generally requires a system to be able to detect and to autonomously handle certain faults  such as a clock failure associated with a card or its clock generation functionality  without immediate human intervention. Providing high availability is often a de facto if not explicit competitive requirement for many telecommunications manufacturers.

Most of the client network equipment today supports multiple control cards for providing Card level redundancy to protect against any control card failures. Typically In such systems  one of the card acts as Primary Control card  and other control card acts as a backup standby control card. On failure of Primary card or manual Redundancy switchover  the backup control card becomes the new primary. All the control functionality is handled by the new Primary card  including the clock recovery functionality.

1588/NTP based clock recovery solutions pose a new challenge with redundant systems at the time of switchovers. Switchovers can be due to manual action or on card failures (software or hardware). Because of the continuous packet protocol exchange happening between the network Server and the client clock modules  whenever there is a switchover the new primary needs to restart its Clock recovery State machine to lock to the network Grand master clock. The locking times of the algorithm can typically vary between 30-45 minutes  depending on the network quality. This is not acceptable in most telecom system deployment as during this time  the clock provided to the line cards are not of good quality.

There is a need for a method and apparatus that overcomes at least the shortcomings of known clock synchronization architectures.

Summary of the Invention

The following presents a simplified summary of one or more embodiments in order to provide a basic understanding of such embodiments. This summary is not an extensive overview of all contemplated embodiments  and is intended to neither identify key or critical elements of all embodiments nor delineate the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later.

In accordance with one aspect of the present invention is a method for protection switching of clock synchronization during card switchover in a redundant transmission system  the method comprising: exchanging periodically timing information by a slave work card of a slave device with a master device clock to synchronize the time base reference clock  precisely  via first port on a line card  blocking transmission of work control card  upon detection of a fault  unblocking the transmission of protect control card  wherein the timing information to other slave devices are sent via second port on a line card and distributing the timing information within the slave device by transmission system  wherein the slave work card and the slave protect card are assigned same IP address  and during any time of the transmission only one of the slave work card or the slave protect card transmit the packets.

In accordance with another aspect of the present invention is a system for protection switching of clock synchronization during card switchover in a redundant transmission system  the system comprising: a master device and a plurality of slave device  wherein the slave device includes a first slave device and a second slave device  wherein each slave device comprising a work control card  a plurality of protect control card and a plurality of line cards  wherein the line cards include a first line card and a second line card  wherein the slave device and master device are configured for exchanging periodically timing information by a slave work card of a slave device with a master device clock to synchronize the time base reference clock  precisely  via first port on a line card  blocking transmission of work control card  upon detection of a fault  unblocking the transmission of protect control card  wherein the timing information to other slave devices are sent via second port on a line card and distributing the timing information within the slave device by transmission system  wherein the slave work card and the slave protect card are assigned same IP address  and during any time of the transmission only one of the slave work card or the slave protect card transmit the packets.

The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.

Before undertaking the detailed description of the invention below  it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise ” as well as derivatives thereof  mean inclusion without limitation; the term “or ” is inclusive  meaning and/or; the phrases “associated with” and “associated therewith ” as well as derivatives thereof  may mean to include  be included within  interconnect with  contain  be contained within  connect to or with  couple to or with  be communicable with  cooperate with  interleave  juxtapose  be proximate to  be bound to or with  have  have a property of  or the like; and the term “controller” means any device  system or part thereof that controls at least one operation  such a device may be implemented in hardware  firmware or software  or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed  whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document  those of ordinary skill in the art should understand that in many  if not most instances  such definitions apply to prior  as well as future uses of such defined words and phrases.

Brief description of the drawings

For a more complete understanding of the present invention  and the advantages thereof  reference is now made to the following descriptions taken in conjunction with the accompanying drawings  wherein like numbers designate like objects  and in which:

Figure 1 shows a system for protection switching of clock synchronization during card switchover in a redundant transmission system  in accordance with one embodiment of the present invention.

Figure 2 shows flow chart of a method for protection switching of clock synchronization during card switchover in a redundant transmission system  in accordance with one embodiment of the present invention.

Figure 3 is a diagrammatic block view of a processing system  according to various embodiments.

Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example  the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure.

Throughout the drawings  it should be noted that like reference numbers are used to depict the same or similar elements  features  and structures.

Detail description of the Invention

In the following description  for purposes of explanation and not limitation  specific details are set forth such as particular architectures  interfaces  techniques  etc. in order to provide a thorough understanding of the present invention. However  it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. That is  those skilled in the art will be able to devise various arrangements which  although not explicitly described or shown herein  embody the principles of the invention and are included within its spirit and scope. In some instances  detailed descriptions of well-known devices  circuits  and methods are omitted so as not to obscure the description of the present invention with unnecessary detail. All statements herein reciting principles  aspects  and embodiments of the invention  as well as specific examples thereof  are intended to encompass both structural and functional equivalents thereof. Additionally  it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future  i.e.  any elements developed that perform the same function  regardless of structure.

Thus  for example  it will be appreciated by those skilled in the art that block diagrams herein can represent conceptual views of illustrative circuitry embodying the principles of the technology. Similarly  it will be appreciated that any flow charts  state transition diagrams  pseudo code  and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor  whether or not such computer or processor is explicitly shown.

The functions of the various elements including functional blocks labeled or described as "computer"  "processor" or "controller" may be provided through the use of dedicated hardware as well as hardware capable of executing software in the form of coded instructions stored on computer readable medium. A computer is generally understood to comprise one or more processors  and the terms computer and processor may be employed interchangeably herein. When provided by a computer or processor  the functions may be provided by a single dedicated computer or processor  by a single shared computer or processor  or by a plurality of individual computers or processors  some of which may be shared or distributed. Such functions are to be understood as being computer-implemented and thus machine-implemented. Moreover  use of the term "processor" or "controller" shall also be construed to refer to other hardware capable of performing such functions and/or executing software  and may include  without limitation  digital signal processor (DSP) hardware  reduced instruction set processor  hardware (e.g.  digital or analog) circuitry  and (where appropriate) state machines capable of performing such functions.

Figure 1 shows a system for protection switching of clock synchronization during card switchover in a redundant transmission system according to one embodiment of the present invention. The system includes at least one master device and a plurality of slave devices (in figure only two slave devices are shown as an example). The slave device includes a first slave device and a second slave device  where each slave device comprising a work control card  a plurality of protect control card and a plurality of line cards. The slave device also includes a management card. In an example embodiment  the line cards include a first line card and a second line card  it is possible that transmission system may include more number of line cards  for sake of simplicity; here in figure 1 only two line cards are shown.

Initial configuration  primarily  first slave device is connected with master device and second slave device. Secondly  the first slave device synchronizes with master device and thirdly  first slave device synchronization to second slave device.

In an operation  when the work control card (slave device 1) exchanges timing information with a master device clock in order to synchronize the time base reference clock. This exchanging of information periodically between the master device and the work control card (slave device 1) in order to synchronize the timing information i.e. time stamp frame between them. The information exchanged by the work control card via first port on the line card.

Upon detecting a fault at the work control card (slave 1)  the system blocks the transmission of work control card and unblocks the transmission of protect control card (slave 1). The transmission of packets (sync) to other slave devices (example slave 2) is sent via second port on the line card. At any point of time only one of work control card or the protect control card transmits. Under normal condition  protect control card does not transmit. The work control card and the protect control card are so configured that both of them are capable of receiving the packets.

In an example embodiment  when the protect control card take over the transmission of the system  where the selection of protect control card after failure of work control card is based on priority.

The protect control card use the existing sessions with master device and with slave device i.e. the protection of clock synchronization by the protect control card is maintained in the existing session with the master device  wherein the existing session is the session of work control card with the master device. Further  the clock synchronization by the protect control card is maintained in the existing session with the slave device  wherein the existing session is the session of work control card with the slave device.

The distribution of the timing information to all cards including line cards  cross connects cards  management card  etc. within the slave device by transmission system. The time stamp frame includes at least an original time stamp about the time when the protect control card transmits and receives a synchronous (Sync) packet between the master device and the other slave devices (example slave 2). Further  the work control card and the protect control card are assigned same network identifier or IP address  and during any time of the transmission only one of the slave work card or the slave protect card transmit the packets.

One application of maintaining the clock synchronization improves the mobile deployment in redundant faults scenarios. The system of clock recovery and synchronization during card switchover in a redundant transmission supports layer 1 and or layer 2 and or layer 3 networking layer.

Figure 2 shows flow chart of a method for protection switching of clock synchronization during card switchover in a redundant transmission system  in accordance with one embodiment of the present invention.

At step 210  the method exchanges periodically timing information by a slave work card of a slave device with a master device clock to synchronize the time base reference clock  precisely  via first port on a line card. The exchanging periodically timing information is a time stamp frame  the time stamp frame comprises at least an original time stamp about the time when the slave work card clock side transmits and receives a synchronous (Sync) packet. During the normal operation  slave protect card does not transmit but receives packets by both the control cards.

At step 220  the method blocks the transmission of work control card  upon detection of a fault.

At step 230  the method unblocks the transmission of protect control card  wherein the sync packets to other slave devices are sent via second port on a line card. The protection of clock synchronization by the protect control card is maintained in the existing session with the master device  wherein the existing session is the session of work control card with the master device. The clock synchronization by the protect control card is maintained in the existing session with the slave device  wherein the existing session is the session of work control card with the slave device.

At step 240  the method distributes the timing information within the slave device by transmission system.

The slave work card and the slave protect card are assigned same IP address  and during any time of the transmission only one of the slave work card or the slave protect card transmit the packets. The selection of protect control card after failure of work control card is based on priority in order to use the existing sessions with master device and with slave device.

Although the flowchart 200 includes steps 210-240 that are arranged serially in the exemplary embodiments  other embodiments of the subject matter may execute two or more steps in parallel  using multiple processors or a single processor organized as two or more virtual machines or sub-processors. Moreover  still other embodiments may implement the steps as two or more specific interconnected hardware modules with related control and data signals communicated between and through the modules  or as portions of an application-specific integrated circuit. Thus  the exemplary process flow diagrams are applicable to software  firmware  and/or hardware implementations.

FIG. 3 is a diagrammatic block view of a processing system 300 according to various embodiments. The processing system 300 may include a central processing unit (CPU) 310  which may include any digital device capable of receiving data and programmed instructions  and processing the data according to the programmed instructions. Accordingly  the CPU 310 may include a microprocessor  such as a general purpose single-chip  or a multi-chip microprocessor. In particular  the multi-chip microprocessor may be structured as a three-dimensional multi-chip package  such as a system in package (SiP)  or a chip stack multi-chip module (MCM) the chip-stack multi-chip module  and may include one or more of the redundant signal transmission systems  according to one or more of the embodiments  such as  for example  the redundant transmission system of FIG. 1. The CPU 310 is generally configured to communicate with a memory unit 320 over a suitable communications bus 330. The memory unit 320 may also be structured as a three-dimensional multi-chip package  and may include one or more of the redundant signal transmission systems  according to one or more of the embodiments. The processing system 310 may also include various other devices that are operably coupled to the bus 330  which are configured to cooperatively interact with the CPU 310 and the memory unit 320. For example  the processing system 300 may include one or more input/output (I/O) devices 340  such as a printer  a display device  a keyboard  a mouse  or other known input/output devices. The processing system 300 may also include a mass storage device 350  which may include a hard disk drive  a floppy disk drive  an optical disk device (CD-ROM)  or other similar devices. It is understood that FIG. 3 provides a simplified representation of the processing system 300. Accordingly  it is understood that other devices not shown in FIG. 3  but known in the art (such as  for example  a memory controller  and other similar devices) may nevertheless be present in the processing system 300. As the various figures have shown  there may be multiple local paths and global paths in a memory system.

The processing system 300 may also form a part of other larger systems  such as a wireless device  which may include devices such as a wireless telephone  a personal digital assistant (PDA)  or another of a variety of known wireless devices.

FIGS. 1-3 are merely representational and are not drawn to scale. Certain portions thereof may be exaggerated  while others may be minimized. FIGS. 1-3 illustrate various embodiments of the invention that can be understood and appropriately carried out by those of ordinary skill in the art.

While various embodiments have been illustrated and described  as noted above  changes can be made without departing from the disclosure. The accompanying drawings that form a part hereof show by way of illustration  and not of limitation  various embodiments in which the subject matter may be practiced. The embodiments illustrated are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments may be utilized and derived therefrom.

This Detailed Description  therefore  is not to be taken in a limiting sense. Although specific embodiments have been illustrated and described herein  it should be appreciated that any arrangement calculated to achieve the same purpose may be substituted for the various embodiments shown. Furthermore  although the various embodiments have described redundant signal transmission systems  it is understood that the various embodiments may be employed in a variety of known electronic systems and devices without modification. This disclosure is intended to cover any and all adaptations or variations of various embodiments. Combinations of the above embodiments  and other embodiments not specifically described herein  will be apparent to those skilled in the art upon reviewing the above description.

We Claim:

1. A method for protection switching of clock synchronization during card switchover in a redundant transmission system  the method comprising:
exchanging periodically timing information by a slave work card of a slave device with a master device clock to synchronize the time base reference clock  precisely  via first port on a line card;
blocking transmission of work control card  upon detection of a fault;
unblocking the transmission of protect control card  wherein the timing information to other slave devices are sent via second port on a line card; and
distributing the timing information within the slave device by transmission system 
wherein the slave work card and the slave protect card are assigned same IP address  and during any time of the transmission only one of the slave work card or the slave protect card transmit the packets.

2. The method of claim 1  further comprising:
selection of protect control card after failure of work control card is based on priority in order to use the existing sessions with master device and with slave device.

3. The method of claim 1  wherein the protection of clock synchronization by the protect control card is maintained for the existing session with the master device  wherein the existing session is the session of work control card with the master device.

4. The method of claim 1  wherein the clock synchronization by the protect control card is maintained for the existing session with the slave device  wherein the existing session is the session of work control card with the slave device.

5. The method of claim 1  further including 
during the normal operation  slave protect card does not transmit but receives by both the control cards.

6. The method of claim 1  wherein the exchanging periodically timing information is a time stamp frame  the time stamp frame comprises at least an original time stamp about the time when the slave work card clock side transmits and receives a synchronous (Sync) packet.

7. The method of claim 1 supports layer 1 and or layer 2 and or layer 3 networking layer.

8. A system for protection switching of clock synchronization during card switchover in a redundant transmission system  the system comprising:
a master device; and
a plurality of slave device  wherein the slave device includes a first slave device and a second slave device  wherein each slave device comprising a work control card  a plurality of protect control card and a plurality of line cards  wherein the line cards include a first line card and a second line card;
wherein the slave device and master device are configured for
exchanging periodically timing information by a slave work card of a slave device with a master device clock to synchronize the time base reference clock  precisely  via first port on a line card;
blocking transmission of work control card  upon detection of a fault;
unblocking the transmission of protect control card  wherein the timing information to other slave devices are sent via second port on a line card; and
distributing the timing information within the slave device by transmission system 
wherein the slave work card and the slave protect card are assigned same IP address  and during any time of the transmission only one of the slave work card or the slave protect card transmit the packets.

9. The system of claim 8 supports layer 1 and or layer 2 and or layer 3 networking layer.

Abstract
A method and system for protection switching of clock synchronization during card switchover in a redundant transmission system

The present invention relates to a method and system for protection switching of clock synchronization during card switchover in a redundant transmission system. In one embodiment  this is accomplished by exchanging periodically timing information by a slave work card of a slave device with a master device clock to synchronize the time base reference clock  precisely  via first port on a line card  blocking transmission of work control card  upon detection of a fault  unblocking the transmission of protect control card  wherein the sync packets to other slave devices are sent via second port on a line card and distributing the timing information within the slave device by transmission system.

Figure 2 (for publication)