1588 V2 –                       Abstract:A New Paragon for               Ethernet continues to gain traction as a cost-   ...
Table of ContentsOverview of Historical Time Synchronization Technologies…………………….....3Evolution of 1588 V2………………………………………...
Acronyms & AbbreviationsBMC     Best Master ClockBMCA    Best Master Clock AlgorithmCDMA    Code division multiple accessG...
Overview of Historical Time Synchronization TechnologiesIn a data network, time synchronization allows all of the differen...
Evolution of 1588 V2The Precision Time Protocol (PTP) provides a standard method to synchronizedevices on a network with s...
Difference between version 1 and version 2 of IEEE 1588•   V1 does not support transparent clocks or profiles whereas V2 a...
Table 3 shows the major features of version 2 which were missing in version1.                   Table 3: Differences betwe...
Maintaining Synchronization using 1588 V2In a packet transport system, clocks communicate with each other over thecommunic...
Table 5 shows the different type of PTP messages.                                Table 5: PTP message typesThere are two m...
There are two parts to this synchronization method:1. Measurement of the propagation delay between Master and Slave usingt...
Application of 1588 V2•   GSM and UMTS Base station SynchronizationOne of the most common applications currently being cit...
•   Smart and Synchronized Electrical Substation AutomationThe latest buzzword in the power industry is “Smart Grid,” a re...
ConclusionSynchronization is an important part of today’s IP networks. By using 1588 V2protocol, carriers can achieve sync...
Tech Mahindra’s PlanTech Mahindra has vast experience in Optical, Ethernet & Wireless technologies.Leveraging these skills...
List of Figures and TablesFigures•   Figure 1: 1588 V2 in Wireless NetworkTables:•   Table   1:   Comparison of different ...
References•   Precision Time Protocol webpage on www.wikipedia.org -    www.en.wikipedia.org/wiki/Precision_Time_Protocol•...
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Packet synchronization

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Packet synchronization

  1. 1. 1588 V2 –   Abstract:A New Paragon for  Ethernet continues to gain traction as a cost- effective way to achieve higher bandwidth.Packet Synchronization  With the emergence of all Ethernet-based networks, packet-based timing synchronization is now of fundamentalA whitepaper importance to ensure maximum network performance as more demanding technologiesBy and applications are deployed. The transition to Ethernet from traditional Plesiochronous Digital Hierarchy (PDH) and Synchronous Optical Network (SONET)-based networksAnkur Rawat requires efficient timing synchronization & techniques in backhaul networks to synchronize base stations and avoid droppedSasindran M Prabhu calls as the call is handed off from one base station to the next. Similarly Data center networks & Electrical Sub Stations also require tighter synchronization to ensure the accuracy and performance.21st Mar, 2011 To address the synchronization needs, 1588 V2 came into existence. IEEE 1588 V2 is a protocol designed to synchronize real-time clocks in the nodes of a distributed system that communicate using a network. © Tech Mahindra Limited 2010 © Tech Mahindra Limited 2011
  2. 2. Table of ContentsOverview of Historical Time Synchronization Technologies…………………….....3Evolution of 1588 V2………………………………………………………………………..4Difference between version 1 and version 2 of IEEE 1588……………………......5Maintaining Synchronization using 1588 V2……………………………………….…7Application of 1588 V2……………………………………….……………………………10Conclusion……………………………………………………………………………………12Tech Mahindra’s Plan………………………………………....................................13List of tables……………………………………....................................................14References..................................................................................................15 1 © Tech Mahindra Limited 2011
  3. 3. Acronyms & AbbreviationsBMC Best Master ClockBMCA Best Master Clock AlgorithmCDMA Code division multiple accessGSM Global System for Mobile CommunicationsGPRS General packet radio service HFT High Frequency Trading IP Internet Protocol LTE Long Term Evolution PTP Precision Time ProtocolTEM Telecom Equipment Manufacturer TSP Telecom Service ProviderWiMAX Worldwide Interoperability for Microwave Access 2 © Tech Mahindra Limited 2011
  4. 4. Overview of Historical Time Synchronization TechnologiesIn a data network, time synchronization allows all of the different devices on thatnetwork to use a common clock to coordinate all of their activities. Networkintegrators currently have a number of different time synchronization optionsavailable. Each has its own advantages and disadvantages. Table 1 shows thecomparison of different synchronization techniques.Inter-range Instrumentation Group (IRIG): The IRIG standard defines a serialtime code format for use with serial communications networks. First standardizedin 1956, IRIG signals are a legacy technology used with older serial systems.IRIGB 205-87 is the latest update of this standard.Network Time Protocol (NTP): NTP is a time protocol for data networks; it wasfirst established in 1985. NTP relies on a hierarchical, layered system topromulgate the current time throughout the network. NTP imposes hierarchicaltree architecture on the network to avoid cyclical dependencies.Global Positioning System (GPS): GPS satellites orbiting the earth use highlyaccurate atomic clocks. Satellite signals carrying timekeeping information cantravel at the speed of light to receivers on the ground. These light-speed signalsare also corrected according to the principles of general relativity, which giveseach receiver on the ground highly accurate time information.IEEE 1588 V1: This standard defines a protocol enabling precise synchronizationof clocks in measurement and control systems implemented with technologiessuch as network communication, local computing and distributed objects. Theprotocol is applicable to systems communicating by local area networkssupporting multicast messaging including but not limited to Ethernet. Table 1: Comparison of different time synchronization techniques 3 © Tech Mahindra Limited 2011
  5. 5. Evolution of 1588 V2The Precision Time Protocol (PTP) provides a standard method to synchronizedevices on a network with sub microsecond precision. The protocol synchronizesslave clocks to a master clock ensuring that events and timestamps in all devicesuse the same time base. PTP is optimized for user-administered, distributedsystems, minimal use of network bandwidth and low processing overhead.PTP was originally defined in the IEEE 1588-2002 standard, officiallyentitled "Standard for a Precision Clock Synchronization Protocol for NetworkedMeasurement and Control Systems". In 2008 a revised standard, IEEE 1588-2008 was released. This new version, also known as PTP Version 2, improvesaccuracy, precision and robustness but is not backwards compatible with theoriginal 2002 version. Table 2 shows the list of major events during the evolutionof 1588 V2. Major Events during evolution of 1588 V2     Version 1 published as IEEE Std. 1588‐ 2002 – on November 8, 2002  Version  1  approved as IEC standard IEC 61588  on May 21, 2004  V1 products and installations began appearing in late 2003  Conferences on IEEE 1588 held, 2003 – 2007  Version 2  PAR approved March 20, 2005  Version 2  technical work completed February 9, 2007  Version 2  sponsor ballot opened July, 2007 and closed August 8, 2007 Version 2  sponsor ballot comment resolution and coordination with IEEE Registration Authority  Committee (RAC) occurred during August – December, 2007  Version 2  recirculation ballot occurred January 14 – 24, 2008  P1588 committee voted on January 31, 2008 to send version to IEEE RevCom  Version 2  approved by RevCom on March 26, 2008 and by IEEE Standards Board on March 27, 2008   Version 2  published as IEEE Std 1588TM – 2008 on July 24, 2008 (reference 1)  Table 2: Evolution of 1588 V2 4 © Tech Mahindra Limited 2011
  6. 6. Difference between version 1 and version 2 of IEEE 1588• V1 does not support transparent clocks or profiles whereas V2 allows for transparent clocks (including End-to-End and Peer-to-Peer delay options) and industry profiles. Store and forward Ethernet switches exhibit latency times that can vary depending on the data that the switch is currently processing. For instance if the device is transmitting a 1500-byte packet, the latency will be much greater than if the transmit queue was empty or transmitting a 500-byte packet. Transparent clock mode can account for the varying latency times; the switch timestamps the time packet as it enters, measures the residence time, and corrects the time packet either as it leaves (one-step mode), or with a follow-up message with the correction field in it (two-step mode). Accumulation of switch latency or jitter errors is eliminated with transparent clock mode.• V2 introduced the delay measurement mechanism. The propagation delay time is measured only between the switch and its upstream peer. This is an alternate method to measuring the total end-to-end path delay from the slave clock to the master clock that eliminates two likely problems with the previous scheme: In a large network the end-to-end method will traverse many switches, each with varying and unpredictable latency time that leads to timing inaccuracy and jitter, compounded by the possibility of asymmetric data paths, Secondly, all the end-to-end path delay request messages must be answered by the master clock that can cause a traffic and processing bottleneck at the master in a large network. In the peer-to-peer delay mechanism, path symmetry is guaranteed and there will never be processing or traffic overloading due to the one to one relationship.• V1 packets are larger, making more traffic whereas V2 packets are smaller. V1 is now completely redundant and is obsolete.• V2 introduced announce messages which improved the operation of the BMC (Best Master Clock) algorithm which made reconfiguration faster, so V2 is more fault tolerant 5 © Tech Mahindra Limited 2011
  7. 7. Table 3 shows the major features of version 2 which were missing in version1. Table 3: Differences between 1588 V1 & V2 6 © Tech Mahindra Limited 2011
  8. 8. Maintaining Synchronization using 1588 V2In a packet transport system, clocks communicate with each other over thecommunication network using PTP. All clocks, whether master or slave, lead backto – and ultimately derive their time from – the ‘Grandmaster’ clock.There are 4 types of PTP clock devices. Table 3 lists all the 5 major type of PTPclock devices. Table 4: Different types of PTP devicesMaster and slave are kept in sync by exchange timestamps, which are sent withinPTP messages. There are two types of message in the PTP protocol – • Event Messages – Timed messages whereby an accurate timestamp is generated both at transmission and receipt of the message. • General Messages – Messages which do not require timestamps but may contain timestamps for their associated event message. 7 © Tech Mahindra Limited 2011
  9. 9. Table 5 shows the different type of PTP messages. Table 5: PTP message typesThere are two mechanisms used in PTP to measure the propagation delaybetween PTP ports:1. The Delay Request-Response Mechanism This mechanism uses the messages Sync, Delay_Req, Delay_Resp and Follow_Up.2. The Peer Delay Mechanism This mechanism uses the messages Pdelay_Req, Pdelay_Resp and Pdelay_Resp_Follow_Up. It is restricted to topologies where each peer-to-peer port communicates PTP messages with, at most, one other such port.There are two phases in the normal execution of the protocol:• Phase 1 - Master-Slave hierarchy establishment In each port of any Ordinary or Boundary clock there is a PTP state machine. These state machines use the ‘Best Master Clock Algorithm’ (or BMCA) to establish the Master for the path between two ports. The statistics of the remote end of a path are provided to each state machine by the Announce message. Since the local clocks statistics are already known by the state machine, a comparison can be made as to which is the best Master.• Phase 2 - Synchronizing Ordinary and Boundary Clocks (using the delay request-response mechanism or Peer delay mechanism) Method-1 Clock synchronization phase starts after the Master-Slave hierarchy has been established. This phase consists of the exchange of PTP timing messages on the communications path between the two clocks. 8 © Tech Mahindra Limited 2011
  10. 10. There are two parts to this synchronization method:1. Measurement of the propagation delay between Master and Slave usingthe delay request-response mechanism.2. Performing the clock offset correction. Once the propagation delay isknown the Master can send Sync and optional Follow_Up messagescontaining its master timestamp.Method-2After the Master-Slave hierarchy has been established the clocksynchronization phase can start.There are two parts to this synchronization method:1. Peer-to-peer ports maintain a measurement of the link propagation toeach peer by using the peer delay mechanism.2. Performing the clock offset correction. Once the link propagation isknown, the master sends Sync and optional Follow_Up messages containingits master timestamp. 9 © Tech Mahindra Limited 2011
  11. 11. Application of 1588 V2• GSM and UMTS Base station SynchronizationOne of the most common applications currently being cited for 1588 V2 is for thesynchronization of various wireless telephony and data services, e.g. GSM, UMTS,CDMA, WiMAX etc. These are gradually transitioning from a TDM-based backhaulnetwork to a packet-based network. The problem with eliminating the TDMinterface is that this is often used as a source of synchronization for the basestation itself. In order to permit correct handover between adjacent base stationsin the presence of Doppler shift generated by a moving mobile handset, the RFfrequency at a GSM or UMTS base station must be accurate to within 50ppb(parts per billion) of the nominal frequency at all times When the TDM backhaul isreplaced by a packet network, the synchronization requirement is fulfilled by 1588V2. Figure 1: 1588 V2 in Wireless Network 10 © Tech Mahindra Limited 2011
  12. 12. • Smart and Synchronized Electrical Substation AutomationThe latest buzzword in the power industry is “Smart Grid,” a revolution thatpromises to make power distribution more efficient, sustainable, and cost-effectiveby applying information technology. The basic concept is simple: upgrade thepower grid to accomplish the same amount of work with less electricity by reactingintelligently to changes in power supply and demand with a more responsive,adaptable, and decentralized power distribution network.“Smart Grid” requires the electrical infrastructure to be smart & intelligent. This isachieved by means of front-ending computers connected to remote devices suchas switch gears, sensors, power generators, and circuit breakers throughintelligent electronic devices (IEDs). Other priority front-end computing tasks insubstations include data acquisition, data computing, and protocol conversionbetween the DNP, IEC, Modbus, and other proprietary protocols used insubstation communications.To create a “Smart Grid”, all the network nodes must work together seamlessly.That’s where time synchronization comes into picture. Accurate timekeepingallows the network to coordinate activity more effectively. For example, oneembedded computing task is to keep precise data logs of all the substationcomputers, switches, and IEDs. It’s important to keep accurate timestamps of allthe events in these data logs, which are often only milliseconds apart. Accuratetimekeeping ensures that these logs can be used to correctly manage anddiagnose any problems on the network.Electric utilities have recognized that 1588 V2 offers network-based precision timesynchronization that is reliable and accurate enough (i.e. sub-microsecond) foruse in electric power applications. IEEE 1588 V2 is currently being considered forinclusion within Edition 2 of the IEC 61850 standard for the design of electricalsubstation automation.In a network based on IEEE 1588 V2, the grandmaster clock determines thereference time for the entire substation automation system. The Ethernet switchacts as the boundary or transparent clock, and additional devices (such asmerging units, IEDs, and protection devices) are designated as ordinary clocks. Allof these devices are organized into a master-slave synchronization hierarchy withthe grandmaster clock at the top.• Capital Markets1588 V2 provides a foundation for accurate performance measurement andtransaction logging that is required for next generation electronic tradingplatforms, exchanges, and other trading venues. It provides accurate system clockand synchronization across server clusters required to measure applicationperformance in an ultra-low-latency environment such as HFT (High FrequencyTrading). Accurate measurement is the first step toward gaining advantage in acompetitive market where fast trading speed matters. 11 © Tech Mahindra Limited 2011
  13. 13. ConclusionSynchronization is an important part of today’s IP networks. By using 1588 V2protocol, carriers can achieve synchronization with accuracy matching that ofalternative solutions without the cost or need to build overlay networks requiredby those solutions. This standard provides an essential technology that allowscarriers to efficiently deploy IP networks with accurate synchronizationrequirements being met. Field trial showcasing excellent interoperability andperformance results, 1588 V2 is a proven solution for IP synchronization. 12 © Tech Mahindra Limited 2011
  14. 14. Tech Mahindra’s PlanTech Mahindra has vast experience in Optical, Ethernet & Wireless technologies.Leveraging these skills, Tech Mahindra will be able to contribute in the following1588 V2 areas.• 1588 V2 protocol stack development• System testing• Performance testing• Interoperability testing• EMS/NMS moduleBased on the opportunity from the vendors, we will be able to select among theseactivities:• Requirement Analysis• Product Design & Development• Testing & Validation• Interoperability Testing• Network Design, Deployment & Maintenance for Telecom Service Providers. 13 © Tech Mahindra Limited 2011
  15. 15. List of Figures and TablesFigures• Figure 1: 1588 V2 in Wireless NetworkTables:• Table 1: Comparison of different time synchronization techniques• Table 2: Evolution of 1588 V2• Table 3: Differences between 1588 V1 & V2• Table 4: Different types of PTP devices• Table 5: PTP message types 14 © Tech Mahindra Limited 2011
  16. 16. References• Precision Time Protocol webpage on www.wikipedia.org - www.en.wikipedia.org/wiki/Precision_Time_Protocol• www.metroethernetforum.org• Ixia solution for 1588 V2 testing – www.ixiacom.com/downloads/library/application_notes/ixnetwork/ieee1588_a pplication_note.pdf• IEEE 802 LAN/MAN Standards Committee www.ieee802.org/1/files/public/docs2008/as-garner-1588 V2-summary- 0908.pdf 15 © Tech Mahindra Limited 2011

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