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PTN Synchronization Subject V1.0

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  • PTN Synchronization SubjectV1.0

  • ContentsIntroduction to Synchronization PrincipleBasic Concepts of SynchronizationDifference between Time Synchronization and Frequency SynchronizationCommunication Network Requirements for SynchronizationHow to Achieve Synchronization TechnologyZXCTN Series Device Synchronization FunctionSynchronization Configuration Instance

  • Basic Concepts of Synchronization

  • Basic Concepts of SynchronizationFrequency synchronization (FS)FS refers to clock synchronization. It indicates that the frequencies or phases between signals are kept in a strict relation. Its corresponding instant appears at the same and equal rate to keep all devices in the communication network running at the same rate. Background information: The PCM (Pulse Code Modulation) discrete pulse which is obtained by encoding the information, is transmitted in the digital communication network. If the clock frequency between two digital switching devices are inconsistent, or the phase drift or jitter is overlapped because the digital bit stream is interfered and damaged in transmission, the element loss or repetition occurs in the buffer of the digital switching system, which causes the slide damage in the transmitted bit stream. For more details, refer to the ITU-T G.8261/8262 standards approved in June, 2007.

  • Basic Concepts of SynchronizationPhase synchronization (PS) (time synchronization)It means that not only the frequency between signals should be the same, but also the phase should be the same, so the time sychronization generally includes the clock synchronization. For more details, refer to the IEEE 1588V2 protocol. To synchronize time is to modulate the internal clock and time of the device according to the received time. The modulation principle of the time synchronization is similar to that of the frequency synchronization on clock. Both the clock frequency and the clock phase should be modulated. Meanwhile, the clock phase is indicated as a value, namely time. The differences from the FS are that the TS receives the non-consecutive time information and non-consecutively modulates the device clock, that the modulation of the device clock phase-lock loop is periodical; and that a clock in the TS can be a virutal clock.

  • ContentsIntroduction to Synchronization PrincipleBasic Concepts of SynchronizationDifference between Time Synchronization and Frequency SynchronizationCommunication Network Requirements for SynchronizationHow to Achieve Synchronization TechnologyZXCTN Series Device Synchronization FunctionSynchronization Configuration Instance

  • Difference between Time Synchronization and Frequency SynchronizationThe above figure provides the differences between TS and FS. If every minute on Watch 1 and Watch 2 are inconsistent, the status is called the TS.If the time on both watches is different, however, a constant difference is kept, such as 1 hour, this status is called the FS.If the frequencies on both watches are different, their time values are not in a fixed relation. Therefore, the prerequisite of the TS is the FS.

  • ContentsIntroduction to Synchronization PrincipleBasic Concepts of SynchronizationDifference between Time Synchronization and Frequency SynchronizationCommunication Network Requirements for SynchronizationHow to Achieve Synchronization TechnologyZXCTN Series Device Synchronization FunctionSynchronization Configuration Instance

  • Communication Network Requirements for SynchronizationTraditional fixed network TDM service requirements for clock synchronizationThe TDM service of the traditional fixed network is primarily voice service which requires a synchronization on both ends of service sending and receiving.If the clocks on both ends of the bearer network are inconsistent, the slide code may occur after a long-term accumulation. The ITUT defines the requirements and test standards, called the TRAFFIC Interface Standard, on the fixed network TDM service in G.823.

  • Communication Network Requirements for SynchronizationRadio IP RAN requirements on synchronizationCurrently, the TS is primarily applied in Call Charging, Inter-Network Account Settling, and NM Alarm. The strictest requirement that the communication network has on the clock frequency is embodied on the wireless application. Frequencies on different BSs must be synchronized in a certain precision, otherwise, disconnection may occurs during the BS switchover. Different from the fixed network TDM application previously mentioned, the clock here refers to the RF clock. In this application scenario, the requirment for the clock frequency is higher than the former one. Currently, the wireless technology exists in various forms. Requirements for clock bearing in different forms are much different.

  • Communication Network Requirements for SynchronizationDedicated Clock Synchronization Network DemandsIn the traditional communication network structure, besides the service bearer network, generally, an independent clock release network also exist, adopting PDH/SDH to distribute the clock.The ITU-T defines that, in this application scenario, the TIMING interface index in G.823 should be met.

  • ContentsIntroduction to Synchronization PrincipleHow to Achieve Synchronization TechnologySyncEthernet TechnologyTOP technologyIEEE1588V2PTPZXCTN Series Device Synchronization FunctionSynchronization Configuration Instance

  • Synchronized Ethernet (SyncE) technology uses Ethernet link code stream to restore clock.At the physical layer, the Ethernet adopts the serial code stream mode for transmission, just like SDH. 4B/5B (FE) and 8B/10B (GE) are adopted in coding. Every 4 bits is inserted an additional bit. In this way, no four consecutive 1s or 0s occur in the transmitted data bit stream, which can effectively include the clock information. Use highly precise clock to send data on Ethernet source port, restore and extract this clock at receiving end to keep accurate clock performance. SyncEthernet Technology

  • SyncEthernet TechnologySyncE Principle Diagram

    PHY

    High Precision Clock

  • Synchronous EthernetThe physical layer guarantees the clock performance of the SyncE, and has nothing to do with the load and packet-forwarding delay on the Ethernet link layer. The procedure to achieve this function is as follows: Devices, such as BITS, transmit the clock signal to the NE through the outer clock interface. The clock signal is transmitted between NEs through the SyncE. The NE clock processing module extracts the Ethernet link clock from the Ethernet port and selects the clock source. The system clock unit performs the clock locking and generates the system clock. The system clock unit provides the Etherenet port that supports the synchronization clock transmission, with the clock source used to transmit the clock to the downstream node when the Ethernet physical layer sends the data.DescriptionThe SyncE behaves the same as SDH on the networking application. The clock transmission is also based on the physical link. The SyncE requires all nodes on the clock transmission path to support the SyncE technology.

  • Synchronous EthernetThe ZXCTN PTN devices compose the SyncE network, supporting the SyncE interace to achieve the Ethernet synchronization at the physical layer. The typical application is shown in the figure below:

    In the SyncE environment, the clock signal of the devices, such as GPS, and BITS, passes the SyncE interface to achieve the clock synchronization for the ZXCTN PTN devices of the entire network. The ZXCTN device connected with BTS and NodeB, transmits the extracted clock signal to BTS or NodeB through the SyncE interface, and finally achieves Ethernet clock synchronization over the entire network.

  • SyncEthernet TechnologyEthernet SSM Frame Format a frame ESMC (Ethernet Synchronization Messaging Channel) that transmits the clock synchronization quality grade is defined in the SyncE.

  • SyncEthernet TechnologyEthernet SSM Frame Format The QL TLV frame where the SSM information is placed, resides in the information payload starting from No.25 in the ESMC frame.

  • ContentsIntroduction to Synchronization PrincipleHow to Achieve Synchronization TechnologySyncEthernet TechnologyTOP technologyIEEE1588V2PTPZXCTN Series Device Synchronization FunctionSynchronization Configuration Instance

  • TOP technologyTOP (Timing Over Packet) is a FS technology, namely, bearing the cock frequency in a specific TOP packet, and separating it from the packet when necessary, thus to achieve the transparent transmission of the clock frequency on PSN. It is only necessary to configure TOP Server and TOP Client nodes to support TOP packets which are forwarded like other service packets when passing the middle nodes. We refer to the device that translates clock frequency to packets as TOP Server, and the device that translates packets to clock frequency as TOP Client. TOP has two work modes: Differential Mode and Self-Adaptive Mode. The differential mode is applied when the network where TOP Server and TOP Client reside is synchronized or the node contains the shared clock, however the client's service clock should be transmitted transparently. The self-adaptive mode is applied in synchronization procedure of the service clock from TOP Server to TOP Client when the network where TOP Server and TOP Client reside, is asynchronized.

  • TOP Technology - Differential ModeThe differential mode is a typical mode specified in G.8261. The devices on both ends: TOP Server and TOP Client, share the FS clock. The PSN network that the TOP packet penetrates can both synchronized and asynchronized. At the TOP Server end, the difference: f, between the service clock frequencyand the common clock frequency is coded and borne in the TOP packet. At the TOP Client end, this common clock is used to restore the service clock at the remote end (receiving end) of the packet network. Because both TOP Server and TOP Client have a standard clock, as long as the frequency difference can be delivered to the Client end in a certain time, the service clock can be restored. The clock frequency is hardly affected by the delay jitter of the PSN network.

  • TOP Technology - Adaptive ModeThe adaptive mode is applied when the NE device clocks where TOP Server and TOP Client reside respectively are not in synchronous relation, so the clock frequency cannot be restored through the differential mode. Likewise, the problem of restoring the adaptive clock frequency is to find the PSN delay jitter variation rule between the two non-synchronization network (TOP Server and TOP Client), and remove it in order to synchronize the clock frequency.

  • ContentsIntroduction to Synchronization PrincipleHow to Achieve Synchronization TechnologySyncEthernet TechnologyTOP technologyIEEE1588V2PTPZXCTN Series Device Synchronization FunctionSynchronization Configuration Instance

  • IEEE1588V2PTPOverview IEEE 1588V2 is a precision time synchronization protocol, called PTP for short. It is active/standby synchronization system. Its core thought is to adopt the active/standby clock mode to code the time information, and use the network symmetry and delay measurement technology to achieve the active/standby synchronization.

  • IEEE1588V2PTPWork ProcedureDuring the system synchronization, the master clock periodically releases the PTP and the time stamp; and the slave clock port receives the time stamp sent from the master clock port. According to this time, the system calculates the time delay of the master and slave lines and the master/slave time difference, and uses this time difference to regulate the local time, keeping the consistent frequency and phase of the master/slave device time. The IEEE 1588 protocol supports the following work modes:Ordinary Clock: Only one port supports the 1588 protocol.Border Clock: Multiple ports support the 1588 protocol.Transparent Clock: The 1588 protocol does not run on the node, but the time stamp needs to be modified. When the time packet is forwarded, the time when the local node processes this packet should be filled in the modification position. Management node: The NM interface function is added on the basis of the above-mentioned mode.

  • IEEE1588V2PTPIntroduction to work modeThe IEEE 1588 divides the clock inside the network into two types: Ordinary Clock (OC) and Border Clock (BC). BC usually resides on the network (switch and router) whichis not stable. In terms of the communciation relation, the clock can be divided into master clock and slave clock. Theoretically, all clocks can act as the master clock and the slave clock. In the system, the optimal clock is the highest-level clock with the best stablity, precision and assurance. According to the clock precision, class and the traceability of the UTC on each node, the master clock inside each subnet shall be automatically selected by the Best Master Clock (BMC). In a system with only one subnet, the master clock is the Global Master Clock (GMC). Each system has only one GMC and each subnet has only one master clock. The slave clock is kept synchronized with the master clock.

  • IEEE1588V2PTP1588 Clock Networking Diagram

  • IEEE1588V2PTPTransmission Process of the IEEE 1588 Clock

  • IEEE1588V2PTPTransmission Process DetailsThe key point of IEEE 1588 lies in the delay measurement. To measure the network transmission delay, IEEE1588 defines a delay request information packet, Delay Request Packet (Delay_Req.). The slave clock sends a Delay Request at T3 after receiving the time information sent by the master clock. The master makes a time-stamp showing the accurate receiving time T4, on the Delay Request Packet Delay Response packet after receiving the Delay Request, and sends it to other slave clocks. Therefore, the slave clocks can accurately compute the delay in the network. For the detailed procedure, refer to the next page.

  • IEEE1588V2PTPDelay measurement in 1588 mode:Because:T2 T1 = Delay + OffsetT4 T3 = Delay Offsetwe can obtain:Delay= [ T2 T1 + T4 T3 ] /2Offset= [ T2 T1 T4 T3 ] /2According to Offset and Delay,The time information can be modified on the node. thus, to achieve the time synchronization between the master and slave nodes.

  • Comparison of Three Technologies

  • ContentsIntroduction to Synchronization PrincipleHow to Achieve SynchronizationZXCTN Series Device Synchronization FunctionZXCTN 6000 Series DevicesZXCTN 9000 Series DevicesSynchronization Configuration Instance

  • ZXCTN 6000 Synchronization FunctionOverviewAs a packet transmission device with the network-class clock synchronization, the ZXCTN6000 system is capable of selecting the synchronization clock source as the system clock through multiple ways to achieve the PTN network clock synchronization.

  • ZXCTN 6000 Synchronization FunctionSystem clock functionProviding BITS external clock input, output interface: Provides the external clock output interface (2.048 Mbit/s or 2.048 MHz) and clock input interface (2.048 Mbit/s or 2.048 MHz ) used to extract the clock and clock synchronization status information. Supporting the GPS (Global Positioning System) interface function: Provides 1 PPS (Pulse Per Second) + ToD signal. The device provides the GPS input or output. It also supports the GPS clock recovery and 1PPS lock phase loop.Supporting 1588 frequency recoverySupporting SyncE interface and the SyncE clock source settingSupporting extracting the clock signal from the E1 interface and providing the clock signal compliant with the ITU-T G.813 standardsSupporting the transparent transmission of customer clock on the circuit emulation E1 interfaceSupporting transmitting the SSM information, achieving the whole network clock synchronization according to the SSM information, supporting automatically selecting high-priority clock, and preventing timing looping.Supporting the work modes, such as the hyper snap mode, tracing mode, hold-on mode, and the free running modeSupporting monitoring and reporting the clock alarms on the system and cards

  • ZXCTN 6000 Synchronization FunctionTime Protection FunctionAdopts the basic SSM protocol and the extended SSM protocol to achieve the auto protection of the clock link and ensure the clock's reliable transmission. Selects an algorithm to compute the best clock information synchronization path and prevent the clock looping.Provides protection switchover function for the clock information according to the clock path algorithm, when the network fault occurs.Provides the functions of synchronization locking , suspension and free oscillation for the clock information.

  • ZXCTN 6000 Synchronization FunctionTime Transmission FunctionThe time SyncE constituted by ZXCTN 6000 has the following time transmission functions: Supporting PTP function on the Ethernet port and the SDH port The port supports one-step PTP protocol and the two-step PTP protocol.Supporting processing the link delay measurement protocolSupporting setting the clock node type which includes: Ordinary Clock, Border Clock, E2E Transparent Clock, and Ordinary Clock + E2E Transparent ClockSupporting setting the PTP port modeAccording to the NM setting, the device supports enabling or disabling the 1588 protocol time synchronization function on each Ethernet port.The system supports the Manual Mode, SSM Protocol Mode, or BMC Protocol Mode to determine the ports where the TS function is enabled to work in three work modes: on the Master Port, on the Slave Port, or Passive.Supporting TS management function: TS Configuration, Querying, and Alarm Performance Monitoring

  • ZXCTN 6000 Synchronization FunctionTime Protection FunctionAdopts the basic SSM protocol and the extended SSM protocol to achieve the auto protection of the clock link and ensure the clock's reliable transmission.Selects an algorithm to compute the best clock information synchronization path.Supports the TS protection switchover function. Provides protection switchover function for the clock information according to the clock path algorithm, when the network fault occurs.Supports delay compensation: Each time port of the device supports setting the time delay compensation.

  • ContentsIntroduction to Synchronization PrincipleHow to Achieve SynchronizationZXCTN Series Device Synchronization FunctionZXCTN 6000 Series DevicesZXCTN 9000 Series DevicesSynchronization Configuration Instance

  • ZXCTN 9000 Synchronization FunctionOverviewAs a packet transmission device with the network-class clock synchronization, the ZXCTN9000 system is capable of selecting the synchronization clock source as the system clock through multiple ways to achieve the PTN network clock synchronization.

  • ZXCTN 9000 Synchronization FunctionSystem clock functionSupporting SyncE interface and the SyncE clock source settingSupporting extracting clock from the channelized STM-1/STM-4/STM-16/STM-64 interfacesSupporting extracting clock from the ATM STM-1 interface Supporting the SSM information transmission The clock unit achieves the whole network clock synchronization according to the SSM information, supporting automatically selecting high-priority clock, and preventing timing looping.Supporting the work modes, such as the hyper snap mode, tracing mode, hold-on mode, and the free running modeSupporting monitoring and reporting the clock alarms on the system and cards

  • ZXCTN 9000 Synchronization FunctionTime Protection FunctionZXCTN 9000 adopts the basic SSM protocol and the extended SSM protocol to achieve the auto protection of the clock link and ensure the clock's reliable transmission.Selects an algorithm to compute the best clock information synchronization path and prevent the clock looping.Provides protection switchover function for the clock information according to the clock path algorithm, when the network fault occurs.Provides the functions of synchronization locking , suspension and free oscillation for the clock information.

  • ZXCTN 9000 Synchronization FunctionTime Transmission FunctionThe time SyncE constituted by ZXCTN 9000 has the following time transmission functions: Supporting PTP function on the Ethernet port and the SDH port The port supports one-step PTP protocol and the two-step PTP protocol.Supporting processing the link delay measurement protocolSupporting setting the clock node type which includes: Ordinary Clock, Border Clock, E2E Transparent Clock, and Ordinary Clock + E2E Transparent ClockSupporting setting the PTP port modeAccording to the NM setting, the device supports enabling or disabling the 1588 protocol time synchronization function on each Ethernet port.The system supports the Manual Mode, SSM Protocol Mode, or BMC Protocol Mode to determine the ports where the TS function is enabled to work in three work modes: on the Master Port, on the Slave Port, or Passive.Supporting TS management function: TS Configuration, Querying, and Alarm Performance Monitoring

  • ZXCTN 9000 Synchronization FunctionTime Protection FunctionAdopts the basic SSM protocol and the extended SSM protocol to achieve the auto protection of the clock link and ensure the clock's reliable transmission. Selects an algorithm to compute the best clock information synchronization path.Supports the TS protection switchover function. Provides protection switchover function for the clock information according to the clock path algorithm, when the network fault occurs.Supports the delay compensation function. Each time port of the device supports setting the time delay compensation.

  • ContentsIntroduction to Synchronization PrincipleHow to Achieve SynchronizationZXCTN Series Device Synchronization FunctionSynchronization Configuration InstanceConfiguring Clock SourceSSM Mode ConfigurationExternal Clock Export1588 Time Node Configuration1588 Time Port ConfigurationGPS Parameter ConfigurationE1 Port Clock

  • Clock and 1588 Functional NM Configuration InstancesConfiguring Clock Source

  • Clock and 1588 Functional NM Configuration Instances SSM Mode Configuration

  • Clock and 1588 Functional NM Configuration Instances External Clock Export

  • Clock and 1588 Functional NM Configuration InstancesConfiguring 1588 Time Node

  • Clock and 1588 Functional NM Configuration InstancesConfiguring 1588 Time Port

  • Clock and 1588 Functional NM Configuration InstancesConfiguring GPS Parameter

  • Clock and 1588 Functional NM Configuration InstancesConfiguring E1 Port Clock

  • Problems and DiscussionsWhat is the difference between 2Mbit/s (2.048Mbit/s) and 2MHz?2Mbit/s: digital signal, square wave2MHz: analog signal, sine waveWhat do the system clocks 2.048, 19.44M, 25M, and 125M work as? 2.048M: used by the 2M external clock (supporting 2Mbits/s instead of 2MHz)19.44M: Used by TDM E1 and IMA E125M: Used for 8 FE interfaces of the master board and 8 FE interfaces of two FE subcards125M: Used for 2 GE interfaces on the master board

  • GSM/WCDMA0.05ppm50ppbCDMA/TD-SCDMA/WiMax/LTEGPSGPSGPSGPSSDH/MSTPIPTDMSDH/MSTPPTNIEEE1588V21588PTN The synchronous Ethernet injects the high-precision clock into the physical layer chip, PHY, on the sending side. The PHY chip uses this high-precision clock to send data. BPHY SDHSDH/SONETG.823TIMINGOctet Worker ATOP ServerWorker BBABTOP ClientBAAABABBSyncE is used currently. 1588 is not achieved.