Abstract:
A timing interface module installs within a rack to increase bandwidth. The timing interface module receives a reference timing signal and outputs the reference timing signal to an optical multiplexer. The optical multiplexer also receives multiple data streams of different formats, and the optical multiplexer synchronizes the multiple data streams to the reference timing signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 12/251,348 filed Oct. 14, 2008, now issued as U.S. Pat. No. 8,233,796, and incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     The present invention relates to systems and methods for network communications. More particularly, the present invention relates to a timing interface module with daughter timing reference modules. 
     The increasing use and expansion of digital voice, TV and Internet services continue to apply pressure for increased bandwidth. In fact, even more bandwidth-intensive services are on the horizon. This increased demand means service providers need to add capacity to their networks as quickly as possible. Previously, that process required the integration of additional hardware or even the complete replacement of existing networks because a service provider&#39;s network typically only allows so much data traffic to travel through at any given time. 
     However, advancements in optical transport systems fully integrate additional bandwidth capability in easily expandable modules. Moreover, such advancements are allowing providers to increase the bandwidth available on their existing networks without extensive network redesign or reconfiguration. For example, rather than installing additional stand-alone hardware, an optical transport system may be used to integrate pure optical switching via wavelength selective switches, reconfigurable optical add-drop multiplexing, Ethernet switching, next-generation SONET/SDH add-drop multiplexers and dense wavelength division multiplexing (DWDM) into a single platform. Thus, traffic may be added or dropped into a DWDM network to easily increase bandwidth to offer HDTV, video-on-demand and high-speed Internet access. 
     A SONET multiplexer enables carriers to cost-effectively combine signals of multiple optical carrier levels onto one wavelength for transport. Further, SONET network equipment transports and/or multiplexes traffic that has originated from a variety of different clock sources. Thus, SONET requires timing sources to provide synchronization. External timing connections provide the timing signals to ensure synchronous accuracy of the network. In contrast, other types of networks do not require timing, e.g., Ethernet, ATM, SAN, etc. For example, legacy DWDM and other data systems do not have external timing connections. 
     It can be seen then that there is a need for a method and apparatus for providing external timing to systems for combining synchronous and data signals while complying with all relevant industry standards. 
     SUMMARY 
     Exemplary embodiments address these and other issues by providing a timing interface module with daughter timing reference modules. Timing modules are provided in a rack platform to eliminate routing problems and which is compliant with all relevant industry standards. 
     According to one embodiment, a timing reference module includes a face plate having a first and second substantially rectangular opening, the face plate further comprising mounting slots for receiving mounting hardware therein and a first and second timing module, the first and second timing module disposed within the first and second substantially rectangular openings, wherein the first and second timing modules provides timing terminations of timing reference signals for network elements of a synchronized optical network. 
     These and other features and advantages will be apparent from a reading of the following detailed description and a review of the associated drawings. It is to be understood that both foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a rack mounted optical transport system according to an embodiment; 
         FIG. 2  illustrates a multiplexer in a SONET network according to an embodiment; 
         FIG. 3  shows a system using an external timing source; and 
         FIG. 4  illustrates a timing interface module according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration exemplary embodiments. It is to be understood that embodiments are applicable to a timing interface module with daughter timing reference modules. 
       FIG. 1  illustrates a rack mounted optical transport system  100  according to an embodiment. In  FIG. 1 , a plurality of components  112 ,  114 ,  116  are mounted in a rack  110 . According to an exemplary embodiment, components  112 ,  114 ,  116  of the optical transport system  100  may include an optical transmission module, optical repeater module, optical reception module, etc. The optical transport system  100  conducts the processing, such as amplification, repeating, termination, add-drop, etc., with respect to optical signals. Moreover, a large number of optical cables (optical fibers) are brought into each optical transmission station that then carries out the processing, such as amplification, repeating, etc. A portion of the processed optical signal may be provided to an optical cable, while the remaining optical signal may be, for example, converted to an electric signal for transmission as a packet signal. 
     The amplification, repeating and other processing are conducted in the optical transport system  100 . A plurality of shelves  120  may be configured as one unit on one rack to provide for an increase in mounting density of these shelves. The entire equipment in which a desired device works (or operates) in a rack may be referred to as a rack mount apparatus. 
     In  FIG. 1 , a front view of the optical transport system  100  is shown. Slots  130  are formed in a front surface side of shelf rack  120  so that each of the slots  130  allows the insertion of a plug-in unit, printed board unit or package. Connectors  140  may be provided on the front or at the back of the rack. Components  116  may provide lighted indicators  150  on the front to provide an indication of a state for the components  114  or to a signal status. 
     Although the size of a rack is determined according to the industry standard, for non-standard shelving the size of the shelf  120  may be designed to match the size of the rack to achieve the high-density mounting in one rack. The optical transport system  100  may also include an internal fan unit  160  with a cooling fan, for example, at the base of the optical transport system  100 . 
     As mentioned above, advancements in transponder modules have led to fully integrated bandwidth capability in easily expandable modules. Moreover, such advancements are allowing providers to increase the bandwidth available on their existing networks without extensive network redesign or reconfiguration. With reference to  FIG. 1 , an optical transponder module may be simply plugged into a slot for coupling to a network&#39;s existing switches of the optical transport system  100  to provide a dramatic increase in capacity. 
     A SONET multiplexer may be installed in the rack mount system to enable a carrier to cost-effectively combine signals of multiple optical carrier levels onto one wavelength for transport. A timing interface module as described below may be mounted in the shelf  120  to provide timing signals to enable the signals from different clock sources to be synchronized. 
       FIG. 2  illustrates a multiplexer in a SONET network  200  according to an embodiment. In  FIG. 2 , three datastreams  210 ,  212 ,  214  are shown as inputs to a SONET multiplexor  216 . SONET allows datastreams of different formats to be combined onto a single high-speed fiber optic synchronous datastream  220 . However, combining datastreams of different formats requires the connection of external timing source to synchronize the datastreams. Moreover, the timing source must be compliant with all relevant industry standards. 
       FIG. 3  shows a system using an external timing source  300 . In  FIG. 3 , a primary reference source (PRS)  310  provides signals to a synchronization supply unit (SSU)  320 . The synchronization supply unit  320  provides primary  322  and secondary  324  timing signals to equipment, such as an add/drop multiplexer  330  and telecommunications switch  340 . For example, the add/drop multiplexer  330  may be used to combine datastreams  332  of different formats as described above with reference to  FIG. 2 . The switch  340  may be coupled to a communications network  350 , such as a cellular network. 
       FIG. 4  illustrates a timing interface module  400  according to an embodiment. In  FIG. 4 , the timing interface module  400  is configured for mounting in a rack system, such as the rack mount system  100  illustrated in  FIG. 1 . The timing interface module  400  includes daughter timing reference modules  462 ,  464 . The timing interface module  400  is designed as a circuit pack-like device that is slotted in the shelves of the rack mount system  100  shown in  FIG. 1 . 
     The timing interface module  400  may be permanently mounted in the rack mount system  100  of  FIG. 1 , for example, with four screws through mounting slots  410 - 416  in the faceplate  418 . The timing interface module  400  provides timing terminations for any synchronous components that might be mounted in the rack. The timing interface module  400  may also include wire wrap pins  420  to physically tie down the synchronization signals. The wire-wrap pins are recessed and the cover provides strain relief for the timing cables that are terminated there. External cabling (other than the cables to the SSU) is not are not required. The two slots may be configured with redundant modules  462 ,  464  to provide copies of both the primary and secondary timing reference signals to the backplane  430 . Accordingly, the timing interface module  400  provides a solution that will not require any external cabling to make connections between T 1  timing reference termination points and distribution to the backplane of the rack mount system. 
     The timing interface module  400  according to an embodiment replaces the need for a previously required Timing Interface Bracket (TIB) and application of power for the timing interface module  400  is made simpler. In addition, the timing interface module  400  according to an embodiment eliminates the need for any special cables previously required to interconnect the TIB and timing reference modules (TRMs). The timing interface module  400  may therefore be installed so that an optical transport system may behave like a SONET NE with respect to timing connections, i.e., as if external timing were an option from the beginning. The dimensions of the timing interface module  400  may be configured to occupy two or more adjacent slots in a shelf of the rack mount system. Captive screws utilizing existing threaded holes in the chassis of the rack and threaded through the mounting slots  410 - 416  make the timing interface module  400  a semi-permanent extension of the shelf. 
     Sub-modules  462 ,  464  are the redundant Timing Reference Modules (TRM) that, as indicated above, provide copies of both the primary and secondary timing reference signals to the backplane  430 . In addition, the sub-modules  462 ,  464  are easily removable using, for example, thumb-latches  470 - 476 . An insulated metal cover  480  may be provided to protect wire-wrap pins  420  and provide mechanical strain relief for timing cables. Recessed wire-wrap pin fields  420  are provided for primary and secondary BITS clock connections. 
     Accordingly, the timing interface module  400  enables data and SONET services to be multiplexed onto a single wavelength. The combining of different services and data signals of different formats allows service providers to provide additional wavelength services. Additional advantages could be realized through cost savings for transport of IOF or other “internal” traffic. 
     The circuit pack-like device provided by the timing interface module  400  serves the same purpose as the backplane timing terminations found on all existing SONET network elements. Wire wrap pins physically tie down the synchronization signals. Thus, the timing interface module  400  eliminates the need for external cabling to make connections between the primary timing reference termination point and distribution to the backplane of the shelf. 
     The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.