The Objective of Network Synchronization If the node clocks in a telecommunication network operate asynchronously then the transmit and receive rates of telecommunication systems in each node would be different to the other nodes. In this case causing data errors commonly referred to as “slips”. Slips per day = frequency difference x traffic frames/second x seconds/day (86400) The object of network synchronization is therefore to avoid and to minimize slips. This can only be achieved by synchronizing all the node clocks, and hence all the telecommunication systems, to the nearly master clock.
Overhead byte for synchronization in STM frame Fig. 8 Assignment of SSM bit patterns (TR3272EU00TR_0401 Synchronization, 10) S1 byte, the quality of Synchronization Message, indicates the type of clock source used to time the transmitted STM-n signal.
Assignment of SSM bit patterns SSM (Synchronization Status Message): Contains the timing quality of the reference timing of a received STM signal. It is 4 bits wide. Q6 DNU 1111 Q4 4.6x10℮-6 (lowest quality) SEC 1011 Q3 2x10℮-08 per day SSU Local 1000 Q2 1x10℮-09 per day SSU Transit 0100 Q1 1x10℮-11 PRC (highest quality) 0010 Q5 Quality unknown 0000 Q-level Accuracy Description S1 byte, bit 5-8
Reason: Timing loops occur, when a chain of slave-clocks forms a loop, so that the active reference input of any of the clocks is actually locked indirectly to the output of that same clock. Result: The clocks on the timing loop then are not locked to a PRC anymore, the loop’s clock frequency diverges, thus causing catastrophic degradation of traffic performance . Timing Loop
Better Design Priority 1 Signal, P1 Priority 2 Signal, P2 Holdover P2 selected P2 selected P2 selected P2 selected No Sync Loop for Every Possible Fiber Cut P1 selected
<ul><li>GPS Antenna. </li></ul><ul><li>Rubidium local oscillator. </li></ul><ul><li>Three weeks PRC Holdover performance. </li></ul><ul><li>Meets Stratum 1 performance with GPS lock 40% per day. </li></ul>The Goal: Get PRC/G8.11 reference at all nodes. Result: All network element internal oscillators elevated to the same level as the reference. TimeSource 3600
Hardware View Power Source B Power Source A IF Cable to roof antenna 2 MHz output (Wire wrap type) Ethernet port LCT port
The Antenna <ul><li>Functional Description </li></ul><ul><li>The GPS Receiver extracts a clock signal from the GPS satellite signals and process them. </li></ul><ul><li>2. An amplifier provides signal gain. </li></ul><ul><li>3. The downconverter converts the L1-band GPS signal to IF for long-distance transport on the coaxial antenna cable. The antenna cable provides current from the shelf to the antenna, and transports GPS satellite IF signals from the antenna to the shelf. </li></ul>The antenna type is roof antenna. It includes a GPS receiver, amplifier, and Intermediate-Frequency (IF) downconverter .
The TimeSource 3600 tracks all satellites within its field of view. The performance of each tracked satellite is observed and compared to the others, and available for use in the timing solution. A satellite with unacceptable performance data is dropped from the timing solution. GPS Tracking
Key features Power redundancy: Has two separate power sources A and B. Bit rate: 2.048 Mb/s Frequency accuracy: 1x10 GPS Holdover Stability: 1x10 for 72 hours. 1x10 for 30 days. Efficiency: Low installation cost and maintenance free. High Performing: BESTIME technology. -12 -11 -10
PRC PRC PRC PRC PRC PRC DHKJT DHLKB SYJGB CGPTL BSCOS BOBET Method of Distribution P1 P2 P3
LCT and NMS <ul><li>TimeScan Craft: </li></ul><ul><li>TimeScan Craft is designed as the complete LCT for TS 3600. It enables us </li></ul><ul><li>to monitor the behavior and performance of the clock in real time. Complete </li></ul><ul><li>Configuration coverage is provided by simple point and click controls making </li></ul><ul><li>configuration quick, easy and safe. </li></ul><ul><li>TimeScan NMS: </li></ul><ul><li>Monitor and manage all six PRS in real time. </li></ul><ul><li>Management and depiction of alarms. </li></ul><ul><li>Ensure up-to-date information. </li></ul>
1) Trouble shooting with Front panel alarms: Front panel alarms Alarm handling The system has been in holdover per the user alarm setting, or there is a hardware fault. n/a. Output signal is PRS. System is in warm-up mode or is not powered. OFF Status SYS A GPS event, which has existed per the user alarm setting, has escalated to a major alarm. A minor GPS event has occurred. GPS successfully tracking satellites. System is not powered. OFF Status GPS Description Status Name
Description Status Name Antenna failed. An event (GPS error, temperature error) escalated to a minor alarm. A software download is required. Power A or B has failed. There is no minor alarm OFF Alarms MIN The system has been in holdover per the user alarm setting. There is no major alarm OFF Alarms MAJ A major alarm has occurred due to any hardware fault. There is no critical alarm OFF Alarms CRIT Alarm handling
2) Trouble shooting with Error Messages: The system is in a power up state when it shouldn’t be. Perform the same action as stated in GPS ERROR message. Minor BT3 Warm-up <ul><li>If not accompanied by GPS ERROR message, none required. </li></ul><ul><li>If accompanied by GPS ERROR, follow the previous set of actions. </li></ul>Minor High/Low current fault <ul><li>Check cable connection between self and the antenna to find if it is short circuited. </li></ul><ul><li>If voltage and current ratings are OK, then replace the lightning suppressor or IF converter as necessary. </li></ul><ul><li>If the problem repeats, replace the antenna. </li></ul>Minor GPS Error Troubleshoot and repair the specified power input. Minor PWR Fail A/B Troubleshoot the GPS section. Major Holdover Download, and install, the GPS receiver (GPS) software Minor GPS download required Reset the plug-in card, if problem persists replace it. Critical Hardware Fault Action Category Message Alarm handling