I 1111111111111111 11111 111111111111111 IIIII 11111 11111 11111 111111111111111111
`US008121111B2
`
`c12) United States Patent
`Freiberger
`
`(IO) Patent No.:
`(45) Date of Patent:
`
`US 8,121,111 B2
`Feb.21,2012
`
`(54) METHOD AND SYSTEM FOR MEASURING
`LATENCY
`
`(75)
`
`Inventor: Michael B. Freiberger, Allen, TX (US)
`
`(73) Assignee: Verizon Patent and Licensing Inc.,
`Basking Ridge, NJ (US)
`
`( *) Notice:
`
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 418 days.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`6,330,236 Bl *
`12/2001
`Ofek et al.
`.................... 370/369
`6,477,181 Bl*
`11/2002
`Fujimori et al.
`.............. 370/476
`6,532,274 Bl *
`3/2003
`Ruffini .......................... 375/356
`2001/0002195 Al*
`5/2001
`Fellman et al ................ 370/420
`2002/0018475 Al*
`2/2002
`Ofek et al.
`.................... 370/400
`2002/0196801 Al*
`12/2002
`Haran et al.
`.................. 370/432
`2003/0115321 Al*
`6/2003
`Edmison et al. .............. 709/224
`* cited by examiner
`
`(21) Appl. No.: 11/693,211
`
`(22) Filed:
`
`Mar. 29, 2007
`
`(65)
`
`Prior Publication Data
`
`US 2008/0240077 Al
`
`Oct. 2, 2008
`
`(51)
`
`Int. Cl.
`(2006.01)
`H04L 12128
`(52) U.S. Cl. ........................................ 370/351; 370/252
`(58) Field of Classification Search ........................ None
`See application file for complete search history.
`
`Primary Examiner - Chi Pham
`Assistant Examiner - Kouroush Mohebbi
`
`(57)
`
`ABSTRACT
`
`A system and method for measuring latency of an optical
`transport network includes generating a time stamp, transmit(cid:173)
`ting the time stamp in an optical transport network, and pro(cid:173)
`cessing the time stamp to measure latency of the optical
`transport network.
`
`33 Claims, 7 Drawing Sheets
`
`100
`
`101
`
`NODES
`
`---102
`TELECOMMUNICATION
`LINKS
`
`Huawei Exhibit 1001
`Huawei Techs.Co. Ltd. v. Verizon Patent and Licensing Inc.
`IPR2021-00616
`Page 00001
`
`

`

`U.S. Patent
`
`Feb.21,2012
`
`Sheet 1 of 7
`
`US 8,121,111 B2
`
`100
`
`\
`
`101
`
`NODES
`
`---102
`TELECOMMUNICATION
`LINKS
`
`FIG. 1
`
`IPR2021-00616 Page 00002
`
`

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`
`IPR2021-00616 Page 00003
`
`

`

`U.S. Patent
`U.S. Patent
`
`Feb.21,2012
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`U.S. Patent
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`Feb.21,2012
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`IPR2021-00616 Page 00005
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`

`

`U.S. Patent
`U.S. Patent
`
`12b.eF
`Feb.21,2012
`10
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`US 8,121,111 B2
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`IPR2021-00616 Page 00006
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`

`

`U.S. Patent
`
`Feb.21,2012
`
`Sheet 6 of 7
`
`US 8,121,111 B2
`
`600
`
`~
`
`GENERATE TIME STAMP AT SOURCE NODE
`
`_;-601
`
`"
`IMPREGNATE AND TRANSMIT TIME STAMP TO
`INTERMEDIATE AND/OR TERMINATION NODE
`
`_J602
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`RECEIVE AND/OR EXTRACT TIME STAMP AT
`INTERMEDIATE AND/OR TERMINATION NODE
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`STORE TIME STAMP AT INTERMEDIATE AND/OR
`TERMINATION NODE
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`TIME STAMP AT INTERMEDIATE AND/OR TERMINATION
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`SOURCE NODE
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`NETWORK
`
`_J608
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`FIG. 6
`
`IPR2021-00616 Page 00007
`
`

`

`U.S. Patent
`
`Feb.21,2012
`
`Sheet 7 of 7
`
`US 8,121,111 B2
`
`700~
`
`SYNCHRONIZE NETWORK ELEMENTS
`
`_;-701
`
`GENERATE TIME STAMP AT SOURCE NODE
`
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`INTERMEDIATE AND/OR TERMINATION NODE
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`NODE
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`NETWORK
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`_;-709
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`FIG. 7
`
`IPR2021-00616 Page 00008
`
`

`

`US 8,121,111 B2
`
`1
`METHOD AND SYSTEM FOR MEASURING
`LATENCY
`
`BACKGROUND
`
`Communication networks of today often provide commu(cid:173)
`nication 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 communica(cid:173)
`tion 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
`
`2
`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
`5 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
`10 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 inter(cid:173)
`face for managing the transmission of data within an Optical
`Transport Network may include a synchronous digital hier-
`15 archy standard (SDH) developed by the International Tele(cid:173)
`communication Union (ITU), a synchronous optical net(cid:173)
`working
`(SONET) standard developed by Telcordia
`Technologies and/or other standards. A standard developed
`by the International Telecommunication Union is G.709
`20 which may enable the use of optical switches without the
`optical/electrical/optical (O/E/O) conversions while compen(cid:173)
`sating for data corruption due to impurities in optical equip(cid:173)
`ments of the Optical Transport Network (OTN). In an exem(cid:173)
`plary embodiment, ITU-T G.709, a standard recommended
`25 by the International Telecommunication Union Telecommu(cid:173)
`nication 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
`30 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 transmis-
`35 sion 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 net-
`45 work 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 telecommu-
`50 nication 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
`55 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,
`60 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
`65 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/
`
`In order to facilitate a fuller understanding of exemplary
`embodiments, reference is now made to the appended draw(cid:173)
`ings. These drawings should not be construed as limiting, but
`are intended to be exemplary only.
`FIG. 1 illustrates an exemplary optical transporting net(cid:173)
`work 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 exem(cid:173)
`plary embodiment.
`FIG. 4 illustrates an exemplary overhead area of an inter(cid:173)
`face 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, accord(cid:173)
`ing to an exemplary embodiment.
`FIG. 6 is a flow chart illustrating an exemplary process of
`measuring the latency of an optical transporting network 40
`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 pro(cid:173)
`vides 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 ele(cid:173)
`ments to facilitate measurement of latency of the network
`system. For example, latency of a network may refer to mea(cid:173)
`surement 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 desti(cid:173)
`nation 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
`
`IPR2021-00616 Page 00009
`
`

`

`US 8,121,111 B2
`
`3
`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/ 5
`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 Trans(cid:173)
`mission/Receiving Module 222, a Processing Module 224
`and/or Other Module 226. Each node may include additional 10
`modules, as shown by Other Module 216 and 226. In addition,
`the modules at each node may be combined, duplicated, sepa(cid:173)
`rated and/or otherwise modified based on various applica(cid:173)
`tions and preferences. Other architectures and implementa(cid:173)
`tions may be realized.
`In an exemplary embodiment, Source Node 201 may ini(cid:173)
`tiate a process for measuring latency of an Optical Transport(cid:173)
`ing 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/ 20
`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 25
`of the Optical Transporting Network (OTN).
`The first time stamp may be transmitted to Transmission/
`Receiving Module 212 where Transmission/Receiving Mod(cid:173)
`ule 212 may associate the first time stamp with an Optical
`Transport Unit (OTU) frame. Further, Transmission/Receiv- 30
`ing 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 Intermedi(cid:173)
`ate/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. Process(cid:173)
`ing 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 Net(cid:173)
`work (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 soft(cid:173)
`ware may include, without limitation, algorithms determin- 50
`ing 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 55
`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 60
`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. Transmis-
`
`4
`sion/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 sec(cid:173)
`ond 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 process-
`ing unit, a storage unit and/or other various network elements.
`Processing Module 214 may include various storage ele-
`15 ments to store the second time stamp. In addition, Processing
`Module 214 may determine latency of an Optical Transport(cid:173)
`ing Network (OTN) based on the information associated with
`the second stamp. Further, Processing Module 214 may
`include without limitation, software, hardware or a combina(cid:173)
`tion of software and hardware operable to determine latency
`of an Optical Transport Network (OTN). In addition, the
`software may include, without limitation, algorithms deter(cid:173)
`mining latency in an Optical Transport Network (OTN). Fur(cid:173)
`ther, the hardware may include, without limitation, a proces(cid:173)
`sor 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
`35 Optical Transport Unit (OTU) frame may include an Over(cid:173)
`head 301 for operation, administration, and/or maintenance
`functions, a Payload 302 for data storage during a transmis(cid:173)
`sion and/or Forward Error Correction 303 which may reduce
`the number of transmission errors on noisy links while
`40 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
`45 enable a receive interface to identify and/or correct any trans-
`m1ss10n errors.
`According to an exemplary embodiment, an Optical Trans-
`port 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---Opti(cid:173)
`cal Channel Transport Unit 1 (OTUl) which may have a
`frame rate of20.420 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
`65 Transport Unit (OTU) frame for ITU-T G. 709 network inter(cid:173)
`face standard. Overhead 301 may include a Frame Alignment
`Overhead 401, Optical Channel Transport Unit (OTU) Over-
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`US 8,121,111 B2
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`5
`head 402, Optical Channel Data Unit (ODU) Overhead 403
`and/or Optical Channel Payload Unit (OPU) Overhead 404.
`FIG. 5 illustrates detailed exemplary components for Over(cid:173)
`head 301 of an Optical Transport Unit (OTU) frame. Frame
`Alignment Overhead 401 may enable a receiving network 5
`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 colunms 1-6.Aframe alignment signal (FAS)
`may enable a receiving network element to identify any out- 10
`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 there(cid:173)
`fore, Frame Alignment Overhead 401 may include a multi- 15
`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 colunm 6 and/or 7.
`Optical Channel Transporting Unit (OTU) Overhead 402 20
`may be located at row 1 colunms 8-14, which may provide
`supervisory functions. Optical Channel Transport Unit
`(OTU) Overhead 402 may include three bytes section moni(cid:173)
`toring (SM), two-byte general communications channel
`(GCC0), and two bytes reserved for future international stan- 25
`dardization. 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 (GCC0) may be defined in
`row 1 columns 11 and 12 which may provide control of a 30
`channel connection between Optical Transport Unit (OTU)
`frame termination points and/or network management. Opti-
`cal 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. 35
`Optical Channel Data Unit (ODU) Overhead 403 may
`reside in rows 2, 3 and 4 of colunm 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 40
`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 monitor(cid:173)
`ing (TCM) channels. Optical Channel Data Unit (ODU) 45
`Overhead 403 may further include path monitoring (PM)
`which may function in a similar manner as the section moni-
`tor in the Optical Channel Transporting Unit (OTU) Over(cid:173)
`head 402 described above except the path monitoring (PM)
`may provide end-to-end monitoring. Furthermore, Optical 50
`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 communica- 55
`tions channel fields GCCl and GCC2 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 60
`be located in row 2 colunm 1-3 and row 4 colunms 9-14.
`Optical Channel Payload Unit (OPU) Overhead 404 may
`include justification control (JC) located in colunm 15 row 1,
`2 and 3. The justification control (JC) byte provide for pay(cid:173)
`load movements inside the Optical Transport Network (OTN) 65
`frame. Optical Channel Payload Unit (OPU) Overhead 404
`may include three justification control bytes where two out of
`
`6
`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 infor(cid:173)
`mation as a justification event may occur. A negative justifi(cid:173)
`cation opportunity (NJO) may cause one of payload bytes to
`temporarily maintain payload information as a justification
`even may occur. Optical Channel Payload Unit (OPU) Over(cid:173)
`head 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 struc(cid:173)
`ture identifier (PSI) may be reserved for future international
`standardization.
`In an exemplary embodiment, a time stamp may be asso(cid:173)
`ciated 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 infor(cid:173)
`mation 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 Align(cid:173)
`ment 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 Align(cid:173)
`ment Overhead 401, wherein a reserved space may be avail(cid:173)
`able in a frame alignment signal (FAS) and/or a multi-frame
`alignment signal (MF AS). 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 colunms 1, 2 and 3, and/or row 4 colunms 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 colunm 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 colunm 17. An
`Optical Transporting Unit (OTU) frame with inserted time
`stamp may be transmitted over an Optical Transporting Net(cid:173)
`work (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 spe(cid:173)
`cific in each individual Optical Transport Unit (OTU) frame.
`Optical Channel Payload Unit (OPU) Overhead 304 may
`three-byte of virtual concatenation overhead
`include
`(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 bytex32
`frame structure for virtual concatenation specific overhead.
`The virtual concatenation overhead (VCOH) for the Optical
`
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`US 8,121,111 B2
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`5
`
`7
`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 Net(cid:173)
`work (OTN). At block 601, a time stamp module may gener-
`ate 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 10
`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 inter(cid:173)
`mediate/termination node may receive the Optical Transport(cid:173)
`ing Unit (OTU) frame with the associated first time stamp. 15
`The transmission/receiving module at the intermediate/termi(cid:173)
`nation node may extract the first time stamp from an Over(cid:173)
`head 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 20
`time stamp to a processing module at the intermediate/termi(cid:173)
`nation 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 25
`the processing module to obtain information associated with
`the first time stamp. The time stamp module at the interme(cid:173)
`diate/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 30
`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 40
`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 45
`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 50
`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 55
`(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 intermediat