Patent Publication Number: US-8983288-B2

Title: Method and system for measuring latency

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This present patent application is a continuation of U.S. patent application Ser. No. 11/693,211, filed Mar. 29, 2007, entitled “METHOD AND SYSTEM FOR MEASURING LATENCY” to Michael B. Freiberger. The disclosure of this priority application is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     Communication networks of today often provide communication via digitally wrapped packet transmissions. There are many framed communication protocols in use and these protocols may be arbitrary or supported by an underlying function. A communication network may have one or more nodes which may transfer data streams over a communication channel. Many applications enabled by such a communication network may be latency sensitive and therefore may require a particular latency. However, latency measurement within a communication network may be disruptive of the transmission of data. Oftentimes, personnel may be required to test latency, thereby further complicating the process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to facilitate a fuller understanding of exemplary embodiments, reference is now made to the appended drawings. These drawings should not be construed as limiting, but are intended to be exemplary only. 
         FIG. 1  illustrates an exemplary optical transporting network system, according to an exemplary embodiment. 
         FIG. 2  illustrates an exemplary system to measure the latency of an optical transporting network system, according to an exemplary embodiment. 
         FIG. 3  illustrates an exemplary standard interface for an optical transporting network system, according to an exemplary embodiment. 
         FIG. 4  illustrates an exemplary overhead area of an interface for an optical transporting network system, according to an exemplary embodiment. 
         FIG. 5  illustrates an exemplary detailed overhead area of an interface for an optical transporting network system, according to an exemplary embodiment. 
         FIG. 6  is a flow chart illustrating an exemplary process of measuring the latency of an optical transporting network system, according to an exemplary embodiment. 
         FIG. 7  is a flow chart illustrating an exemplary process of measuring the latency of a synchronized optical transporting network system, according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     An exemplary embodiment of the present invention provides a system and process for monitoring delay within a network system. In one embodiment of the present invention, the network system may include synchronized network elements to facilitate measurement of latency of the network system. For example, latency of a network may refer to measurement of one-way latency which measures the time from a source transmitting data to a destination receiving the data. Latency of a network may also refer to the measurement of round-trip latency which measures one-way latency from a source to a destination plus one-way latency from the destination back to the source. 
     Latency measurement for an Optical Transport Network may have various applications. For example, a predetermined latency measure between two nodes may be established as a default latency measure between two nodes. A variance in latency measure from the default latency measure between the two nodes in an Optical Transport Network may indicate with a change in the length of telecommunication line linking the two nodes. Also, a variance in latency measure from between two nodes in an Optical Transport Network may indicate certain events. For example, an illegal tapping by an entity may cause a delay in the Optical Transport Network and thus may lead to a variance in the latency measure. Other various applications associated with latency measure for an Optical Transport Network may be implemented. 
       FIG. 1  is an exemplary network system, according to an exemplary embodiment. System  100  illustrates an exemplary system for an Optical Transport Network (OTN) which may implement a variety of standards of interface for managing optical wavelengths. For example, various standards of interface for managing the transmission of data within an Optical Transport Network may include a synchronous digital hierarchy standard (SDH) developed by the International Telecommunication Union (ITU), a synchronous optical networking (SONET) standard developed by Telcordia Technologies and/or other standards. A standard developed by the international Telecommunication Union is G.709 which may enable the use of optical switches without the optical/electrical/optical (O/E/O) conversions while compensating for data corruption due to impurities in optical equipments of the Optical Transport Network (OTN). In an exemplary embodiment, ITU-T G.709, a standard recommended by the International Telecommunication Union Telecommunication Standardization Sector may be used to enable the management of optical wavelength in an Optical Transport Network (OTN). Other Standards may also be implemented. 
     As illustrated, System  100  may include a plurality of Nodes  101  coupled by a network of Telecommunications Links  102 . A network of Nodes  101  and Telecommunication Links  102  may be arranged to enable transmission of data from a source node to a receiving node over a single or multiple telecommunication links. For example, a transmission of data from Node  1  to Node  2  as illustrated in  FIG. 1  may be enabled by transmission via plurality of intermediate Node  10  and Node  12  and/or Node  9  and Node  11 . Various different paths of transmission between a source node and a termination node may be enabled by different intermediate nodes within the Optical Transport Network (OTN). 
     Node  101  may be a source node where transmission of data commences, a termination node where transmission of data terminates, and/or an intermediate node where transmission of data may traverse. Node  101  may implement various network elements to enable transmission of data between each node. 
     Telecommunication Link  102  may be a communication channel that may connect two or more network elements. Telecommunication Link  102  may be a physical telecommunication link or multiple of physical telecommunication links or a logical telecommunication link. Telecommunication Link  102  may be a point-to-point link, a multipoint link, a point-to multipoint link, or a combination of different types of links mentioned before. In an exemplary embodiment, an optical fiber may include glass and/or plastic fiber to guide light may be used for Telecommunication Link  102 . Various types of optical fiber may be used for Telecommunication Link  102  which may include, without limitation, multi-mode optical fibers, single-mode optical fibers, graded-index fibers, step-index optical fiber or a combination of the different types of optical fiber mentioned before. 
       FIG. 2  illustrates an exemplary system  200  for measuring the latency of an Optical Transporting Network (OTN), according to an exemplary embodiment. Latency measuring system  200  may include a Source Node  201  and/or one or more Intermediate/Termination Node  202 . Source Node  201  may represent a node sending a data packet. Intermediate/Termination Node  202  may represent a node receiving a data packet. In an exemplary embodiment, Source Node  201  may include a Time Stamp Module  210 , a Transmission/Receiving Module  212 , a Processing Module  214  and/or Other Module  216 . Source Node  201  may communicate with Intermediate/Termination Node  202  via one or more links, as shown by Telecommunication Link  102 . Intermediate/Termination Node  202  may include a Time Stamp Module  220 , a Transmission/Receiving Module  222 , a Processing Module  224  and/or Other Module  226 . Each node may include additional modules, as shown by Other Module  216  and  226 . In addition, the modules at each node may be combined, duplicated, separated and/or otherwise modified based on various applications and preferences. Other architectures and implementations may be realized. 
     In an exemplary embodiment, Source Node  201  may initiate a process for measuring latency of an Optical Transporting Network (OTN). Time Stamp Module  210  of Source Node  201  may generate a first time stamp such as a counter, trusted time stamp, digital postmark, digital time stamp and/or any signal or algorithms which may keep time. The first time stamp may be associated with a time tracking device at Source Node  201 . The time tracking device may include one or more various types of time tracking devices and/or a clock network which may enable time synchronization at each node of the Optical Transporting Network (OTN). 
     The first time stamp may be transmitted to Transmission/Receiving Module  212  where Transmission/Receiving Module  212  may associate the first time stamp with an Optical Transport Unit (OTU) frame. Further, Transmission/Receiving Module  212  of Source Node  201  may transmit the Optical Transport Unit (OTU) frame with the associated first time stamp to Transmission/Receiving Module  222  at Intermediate/Termination Node  202 . 
     Transmission/Receiving Module  222  may receive the Optical Transport Unit (OTU) frame with the associated first time stamp and extract the first time stamp from the Optical Transport Unit (OTU) frame. The extracted first time stamp may be transmitted to and/or stored in Processing Module  224 , Processing Module  224  may include a processing unit, a storage unit and/or other various network elements. Processing Module  224  may include various storage elements to store the first time stamp. In addition, Processing Module  224  may determine one-way latency of the Optical Transporting Network (OTN) based on the information associated with the first time stamp. Further, Processing Module  224  may include without limitation, software, hardware or a combination of software and hardware operable to determine the latency of an Optical Transport Network (OTN). In addition, the software may include, without limitation, algorithms determining latency in an Optical Transport Network (OTN). The hardware may include, without limitation, a processor and/or other similar integrated circuit. 
     Time Stamp Module  220  at Intermediate/Termination Node  202  may access the first time stamp stored in Processing Module  224  and generate a second time stamp such as a counter, trusted time stamp, digital postmark, digital time stamp and/or any signal or algorithms which may keep time. The second time stamp may be associated with the first time stamp. Also, the second time stamp may be associated with a time tracking device located at Intermediate/Termination Node  202 . The time tracking device may include one or more various types of time tracking devices and/or a clock network which may enable time synchronization at each node of the Optical Transporting Network (OTN). 
     Time Stamp Module  220  may transmit the second time stamp to Transmission/Receiving Module  222 . Transmission/Receiving Module  222  may associate the second time stamp in an Optical Transport Unit (OTU) frame and transmit the Optical Transport Unit (OTU) frame with the associated second time stamp to Transmission/Receiving Module  212  at Source Node  201 . 
     Transmission/Receiving Module  212  may receive the Optical Transport Unit (OTU) frame with the associated second time stamp and extract the second time stamp from the Optical Transport Unit (OTU) frame. The extracted second time stamp may be transmitted to and/or stored in Processing Module  214 . Processing Module  214  may include a processing unit, a storage unit and/or other various network elements. Processing Module  214  may include various storage elements to store the second time stamp. In addition, Processing Module  214  may determine latency of an Optical Transporting Network (OTN) based on the information associated with the second stamp. Further, Processing Module  214  may include without limitation, software, hardware or a combination of software and hardware operable to determine latency of an Optical Transport Network (OTN). In addition, the software may include, without limitation, algorithms determining latency in an Optical Transport Network (OTN). Further, the hardware may include, without limitation, a processor and/or other similar integrated circuit. 
     Furthermore, Other Module  216 ,  226  may include various types of network elements in cooperation with other modules at each node to enable a process to measure latency of an Optical Transporting Network (OTN). 
       FIG. 3  illustrates an exemplary Optical Transport Unit (OTU) frame, according to an exemplary embodiment. In this exemplary embodiment, the ITU-T G.709 standard may apply. The various embodiments of the present invention may apply to other standards as well. As illustrated in  FIG. 3 , an Optical Transport Unit (OTU) frame may include an Overhead  301  for operation, administration, and/or maintenance functions, a Payload  302  for data storage during a transmission and/or Forward Error Correction  303  which may reduce the number of transmission errors on noisy links while enabling the deployment of longer optical spans. Further, Forward Error Correction  303  may include a Reed-Solomon (RS) code to produce redundant information which may be concatenated with the signal to be transmitted. The redundant information generated by the Reed-Solomon (RS) code may enable a receive interface to identify and/or correct any transmission errors. 
     According to an exemplary embodiment, an Optical Transport Unit (OTU) frame for ITU-T G.709 network interface standard may include four rows of 4080 bytes. Data may be transmitted serially beginning at the top left, first row, and may be followed by the second row and so on. The ITU-T G.709 network interface standard may enable three rates of data transmission, for example, 2,666,057.413 kbit/s—Optical Channel Transport Unit 1 (OTU1) which may have a frame rate of 20.420 kHz or 48.971 ms, 10,709,225.316 kbit/s—Optical Channel Transport Unit 2 (OTU2) which may have a frame rate of 82.027 kHz or 12.191 ms, or 43,018,413.559 kbit/s—Optical Transport Channel Unit 3 (OTU3) which may have 329.489 kHz or 3.035 ms. 
       FIG. 4  illustrates details for an exemplary Overhead  301  of an Optical Transport Unit (OTU) frame, according to an exemplary embodiment. In this exemplary embodiment, the ITU-T G.709 standard may apply.  FIG. 4  illustrates general exemplary components for Overhead  301  of an Optical Transport Unit (OTU) frame for ITU-T G.709 network interface standard. Overhead  301  may include a Frame Alignment Overhead  401 , Optical Channel Transport Unit (OTU) Overhead  402 , Optical Channel Data Unit (ODU) Overhead  403  and/or Optical Channel Payload Unit (OPU) Overhead  404 . 
       FIG. 5  illustrates detailed exemplary components for Overhead  301  of an Optical Transport Unit (OTU) frame. Frame Alignment Overhead  401  may enable a receiving network element of an Optical Transport Network (OTN) frame to identify a starting point by framing bytes. Frame Alignment Overhead  301  may include a 6-bytes frame alignment signal (FAS) in row  1  columns  1 - 6 . A frame alignment signal (FAS) may enable a receiving network element to identify any out-of-frame (OOF), loss-of-frame (LOF) and/or a start of an Optical Transporting Unit (OTU) frame. In an exemplary embodiment, Overhead  301  may include signals which may span multiple Optical Transport Unit (OTU) frames therefore, Frame Alignment Overhead  401  may include a multi-frame alignment signal (MFAS) byte to identify signals that may span multiple Optical Transport Unit (OTU) frames. The multi-frame alignment signal (MFAS) for Frame Alignment Over head  301  may be defined in row  1  column  6  and/or  7 . 
     Optical Channel Transporting Unit (OTU) Overhead  402  may be located at row  1  columns  8 - 14 , which may provide supervisory functions. Optical Channel Transport Unit (OTU) Overhead  402  may include three bytes section monitoring (SM), two-byte general communications channel (GCC 0 ), and two bytes reserved for future international standardization. The section monitoring (SM) of Optical Channel Transporting Unit (OTU) Overhead  402  may test and/or monitor Overhead Area  301  and/or Payload Area  302 . The general communications channel (GCC 0 ) may be defined in row  1  columns  11  and  12  which may provide control of a channel connection between Optical Transport Unit (OM) frame termination points and/or network management. Optical Channel Transporting Unit (OTU) Overhead  402  may further include a reserved (RES) field located in row  1  column  13  and  14  which may be set aside for future standardization. 
     Optical Channel Data Unit (ODU) Overhead  403  may reside in rows  2 ,  3  and  4  of column  1 - 14  of the Optical Transporting Network (OTN) frame. Optical Channel Data Unit (ODU) Overhead  403  may include multiple tandem connection monitoring (TCM), which may enable a network operator to monitor the transmission of a signal. Optical Channel Data Unit (ODU) Overhead  403  may also include TCM activation (TCM ACT) field which may enable the activation and/or deactivation of tandem connection monitoring (TCM) channels. Optical Channel Data Unit (ODU) Overhead  403  may further include path monitoring (PM) which may function in a similar manner as the section monitor in the Optical Channel Transporting Unit (OTU) Overhead  402  described above except the path monitoring (PM) may provide end-to-end monitoring. Furthermore, Optical Channel Data Unit (ODU) Overhead  403  may include a fault type and fault location (FTFL) which may monitor path level faults, transport both forward and backward fault information and/or a message structure. Moreover, Optical Channel Data Unit (ODU) Overhead  403  may include general communications channel fields GCC 1  and GCC 2  which may provide clear channel connection between Optical Channel Data Unit (ODU) termination points. In addition, Optical Channel Data Unit (ODU) Overhead  303  may include two reserved (RES) fields which may be used for future standardization and may be located in row  2  column  1 - 3  and row  4  columns  9 - 14 . 
     Optical Channel Payload Unit (OPU) Overhead  404  may include justification control (JC) located in column  15  row  1 ,  2  and  3 . The justification control (JC) byte provide for payload movements inside the Optical Transport Network (OTN) frame. Optical Channel Payload Unit (OPU) Overhead  404  may include three justification control bytes where two out of three justification controls may be sufficient to carry out justification events. Two types of justification control (JC) may determine a justification event, for example, a positive justification opportunity (PJO) and/or a negative justification opportunity (NJO). A positive justification opportunity (PJO) may cause one of payload bytes to not contain payload information as a justification event may occur. A negative justification opportunity (NJO) may cause one of payload bytes to temporarily maintain payload information as a justification even may occur. Optical Channel Payload Unit (OPU) Overhead  404  may include payload structure identifier (PSI) which may include payload type (PT) to identify the payload content. The payload structure identifier (PSI) may include one-byte located in row  4 , column  15  to transport a 256-byte payload structure identifier (PSI) signal. The payload type (PT) and/or virtual concatenation payload type (vcPT) may be each represented by one-byte in the 256-byte of payload structure identifier (PSI). The rest 254-bytes of payload structure identifier (PSI) may be reserved for future international standardization. 
     In an exemplary embodiment, a time stamp may be associated with an Optical Transporting Unit (OTU) frame. The time stamp may be inserted within an Overhead  301  of an Optical Transporting Unit (OTU) frame. The size of a time stamp may vary. For example, amount, size or type of information associated with the time stamp may affect the size of the time stamp. In addition, other factors may be considered. Therefore, a time stamp may be inserted within different locations of Overhead  301  depending on the characteristics, size, amount, type, etc., of the time stamp. In an exemplary embodiment, a time stamp may be inserted in Frame Alignment Overhead  401 , Optical Channel Transporting Unit (OTU) Overhead  402 , Optical Channel Data Unit Overhead  403  and/or Optical Channel Payload Unit Overhead  404 . For example, a time stamp may be inserted within Frame Alignment Overhead  401 , wherein a reserved space may be available in a frame alignment signal (FAS) and/or a multi-frame alignment signal (MFAS). Also, a time stamp may be inserted within a reserved space in Optical Channel Transport Unit (OTU) Overhead  402  located at row  1  columns  13  and  14 . Further, a time stamp may be inserted within a reserved space in Optical Channel Data Unit (ODU) Overhead  403  located at row  2  columns  1 ,  2  and  3 , and/or row  4  columns  9 ,  10 ,  11 ,  12 ,  13  and  14 . Furthermore, a time stamp may be inserted within a reserved space in Optical Channel Payload Unit (OPU) Overhead  304  located at column  15  rows  1 ,  2 ,  3  and  4  and/or column  16  rows  1 ,  2 ,  3  and  4 . Moreover, a time stamp may be inserted in any reserved space located in column  17 . An Optical Transporting Unit (OTU) frame with inserted time stamp may be transmitted over an Optical Transporting Network (OPN) to an intermediate and/or termination node. In addition, information associated with the time stamp may be spread across multiple locations. Other various locations may be used for the time stamp. 
     In an exemplary embodiment, the ITU-T G.709 network interface standard may enable virtual concatenation which may enable a channel within a group to travel on different physical paths through an Optical Transport Network (OTN). Virtual concatenation (VOCH) overhead which may be specific in each individual Optical Transport Unit (OTU) frame. Optical Channel Payload Unit (OPU) Overhead  304  may include three-byte of virtual concatenation overhead (VCOH) which may be located at column  15 , row  1 ,  2  and  3 . Three bytes per individual Optical Channel Payload Unit (OPU) Overhead  304  may be utilized to transport a 3 byte×32 frame structure for virtual concatenation specific overhead. The virtual concatenation overhead (VCOH) for the Optical Channel Payload Unit (OPU) Overhead  404  may also include a reserved field for future international standardization. 
       FIG. 6  is a flow chart  600  which illustrates an exemplary method of measuring latency of an Optical Transporting Network (OTN). At block  601 , a time stamp module may generate a first time stamp. The first time stamp may correspond to a time tracking device associated with a source node. 
     At block  602 , the first time stamp may be associated with an Optical Transporting Unit (OTU) frame and transmitted to an intermediate/termination node. For example, the first time stamp may be inserted within an Overhead Area of an Optical Transport Unit (OTU) frame as mentioned above. 
     At block  603 , a transmission/receiving module at an intermediate/termination node may receive the Optical Transporting Unit (OTU) frame with the associated first time stamp. The transmission/receiving module at the intermediate/termination node may extract the first time stamp from an Overhead Area of the Optical Transporting Unit (OTU) frame. 
     At block  604 , the transmission/receiving module at the intermediate/termination node may transfer the extracted first time stamp to a processing module at the intermediate/termination node. The processing module may store the first time stamp in a storage unit. 
     At block  605 , a time stamp module at the intermediate/termination node may access a storage unit associated with the processing module to obtain information associated with the first time stamp. The time stamp module at the intermediate/termination node may generate a second time stamp associated with the information of the first time stamp. 
     At block  606 , the second time stamp generated at the intermediate/termination node may be associated with an Optical Transporting Unit (OTU) frame and transmitted back to the source node. For example, the second time stamp may be inserted within an Overhead Area of an Optical Transport Unit (OTU) frame as mentioned above. 
     At block  607 , the transmission/receiving module at the source node may receive the Optical Transporting Unit (OTU) frame with the associated second time stamp. For example, the transmission/receiving module at the source node may extract the second time stamp from an Overhead Area of the Optical Transporting Unit (OTU) frame. 
     At block  608 , a processing module may store the second time stamp. The processing module may also determine the latency of an Optical Transporting Network. The second time stamp may include information associated with the first time stamp. For example, the information may include the time when the first time stamp may have been generated and/or transmitted. The processing module may determine the amount of time elapsed from the time the first time stamp may be generated and/or transmitted to determine the latency of the Optical Transporting Network (OTN). Also, the second time stamp may include a time counter or other time tracking device. The time counter may increment by a predetermined period of time. Accordingly, the processing module may determine latency of the Optical Transporting Network (OTN) based on the increment of the time counter. 
     In an exemplary embodiment, transmission between a source node and a termination node may traverse through one or more intermediate nodes along a transmission path. The one or more intermediate nodes may enable passage of an Optical Transport Unit (OTU) frame with the associated time stamp. Also, an intermediate node may generate one or more intermediate time stamps at each intermediate node according to the process mentioned above and transmit one or more intermediate time stamps to a subsequent intermediate node. 
       FIG. 7  depicts a flow chart  700  which illustrates an exemplary method of measuring the latency of a synchronized Optical Transporting Network (OTN). At block  701 , the time at a plurality of nodes in an Optical Transporting Network (OTN) may be synchronized. For example, a clock network may enable the plurality of nodes to display the same or synchronized time. Also, the time for the node at two end points of a transmission and/or any intermediate nodes along a transmission path may be synchronized. The plurality of nodes may be synchronized by setting the source node as a default/master clock while a termination node and/or one or more intermediate nodes may be a slave clock which may display the time of the master clock. Further, the nodes may be synchronized by setting an arbitrary node in the Optical Transport Network (OTN) as a master clock while a source, a termination, and/or an intermediate node may be a slave clock which may display the time of the master clock. 
     At block  702 , a time stamp module may generate a first time stamp. The first time stamp generate may correspond to a time tracking device associated with a source node. 
     At block  703 , the first time stamp may be associated with an Optical Transporting Unit (OTU) frame and transmitted to an intermediate/termination node. For example, the first time stamp may be inserted within an Overhead Area of an Optical Transport Unit (OTU) frame as mentioned above. 
     At block  704 , a transmission/receiving module at an intermediate/termination node may receive the Optical Transporting Unit (OTU) frame with the associated first time stamp. The transmission/receiving module at the intermediate/termination node may extract the first time stamp from an Overhead Area of the Optical Transporting Unit (OTU) frame. 
     At block  705 , the transmission/receiving module at the intermediate/termination node may transfer the extracted first time stamp to a processing module at the intermediate/termination node. The processing module may store the first time stamp in a storage unit. 
     At block  706 , a time stamp module at the intermediate/termination node may access a storage unit associated with the processing module to obtain information associated with the first time stamp. The time stamp module at the intermediate/termination node may generate a second time stamp associated with the information of the first time stamp. 
     At block  707 , the second time stamp generated at the intermediate/termination node may be associated with an Optical Transporting Unit (OTU) frame and transmitted back to the source node. For example, the second time stamp may be inserted within an Overhead Area of an Optical Transport Unit (OTU) frame as mentioned above. 
     At block  708 , the transmission/receiving module at the source node may receive the Optical Transporting Unit (OTU) frame with the associated second time stamp. For example, the transmission/receiving module at the source node may extract the second time stamp from an Overhead Area of the Optical Transporting Unit (OTU) frame. 
     At block  709 , a processing module may store the second time stamp. The processing module may also determine the latency of an Optical Transporting Network. The second time stamp may include information associated with the first time stamp. For example, the information may include the time when the first time stamp may have been generated and/or transmitted. The processing module may determine the amount of time elapsed from the time the first time stamp may be generated and/or transmitted to determine the latency of the Optical Transporting Network (OTN). Also, the second time stamp may include a time counter or other time tracking device. The time counter may increment by a predetermined period of time. Accordingly, the processing module may determine latency of the Optical Transporting Network (OTN) based on the increment of the time counter. 
     In the preceding specification, various preferred embodiments have been described with reference to the accompanying drawings. It will, however, be evident that various modifications and changes may be made thereto, and additional embodiments may be implemented, without departing from the broader scope of the invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense.