Tutorial on Synchronization Jean-Loup Ferrant Tim Frost Silvana

Tutorial on Synchronization Jean-Loup Ferrant, Tim Frost, Silvana Rodrigues, Stefano Ruffini 25 November 2014

Agenda Intro on need for sync (S. Ruffini) Time sync, basic concepts (T. Frost) Sync distribution (S. Rodrigues) Q 13 status and ITSF/WSTS (J-L Ferrant) 25 November 2014 2

Need for Sync 25 November 2014

Time and Frequency Aligning two time clocks (synchronization) implies: Make frequency B = frequency A (syntonization) Make phase B = phase A (e. g. roll-over instant of 10 7 counter) Make seconds B = seconds A (elapsed time equal; same time origin) Choose same formatting convention (and time-zone, etc. ) Clock A “Time” Clock B Time alignment (“local time”) “Time” Time alignment (UTC) Seconds Counter Time alignment (equal # of seconds) 1 Hz 10, 000 Counter 10 MHz Seconds Counter 1 Hz Phase alignment (roll-over coincident) (equality to within 1 clock cycle of 100 ns may suffice) Frequency alignment (syntonization) 10, 000 Counter 10 MHz

Timing Alignment in Wireless Df = frequency offset between BSs DT = time offset between BSs BS - B BS - A Mobile in motion; speed = X m/s When hand-over occurs, the mobile must reacquire carrier frequency Mobile in motion (X m/s) introduces a Doppler shift (X/c) Loop bandwidth wide enough to handle (Df + X/c +LO) (LO = local oscillator offset) Loop bandwidth should be small from a noise rejection viewpoint Large Df compromises the reliability of hand-over; 50 ppb typical requirement TDD networks require time/phase alignment between A & B To control interference between uplink and downlink Requirement in the microsecond range LTE-Advanced require DT to be small (microsec) for providing the more bandwidth intensive features 8

Current Timing Issues Networks are being migrated to packet switching as opposed to circuit-switched (i. e. based on TDM) Significant impact of variable delay (packet delay variation) Timing requirements remain Going “IP” does not mean that real-time services or mobile networks no longer need synchronization! Transition Phase: Hybrid Networks (IP/TDM islands) Circuit Emulation Timing over Packet Networks (packet-based methods) PTP, NTP, adaptive clock recovery Monitoring and Testing Metrics for packet-based timing methods (quantifying PDV) 9

Emerging Needs Increased need of time/phase sync in Mobile networks Time sync over various technologies (microwave, OTN, MPLS, etc. ) Financial Sector Io. T, Network of Sensors Power Networks. . . 25 November 2014 10

Power – the need for Sync “The Power Grid” is one of the world’s largest infrastructures High synchronization requirements due to distributed nature of the grid and the critical balance between power generation and consumption Power can’t be stored easily so Grids Generate according to Demand Need good Comms and Sync to correlate Demand Generation Has evolved from seconds to milliseconds and will evolve to microseconds → Greater Efficiencies Also enables the Greater Diversity of the Smart Grid Power Profile – IEEE C 37. 238 -2011 (target: 1 ms accuracy) Source: NIST

What is Time?

What is Time? Time is a fundamental physical dimension Allows ordering and scheduling of events Enables sharing of resources (e. g. time division muxing) Passage of time measured by counting a regularly repeating event Astronomical events, e. g. day/night, year Physical events, e. g. pendulum swing, quartz resonance or atomic transitions

Common Time Common time requires a reference point Time at an instant has no meaning without a reference Need to start counting from a common point, or epoch Example: the Gregorian calendar counts years from the birth of Christ A time reference clock counts at a constant frequency from a known epoch Sending time in a message. . . Need to know how long the message takes A letter – might be usable for setting the date A phone call – could use to set hour/minute/seconds A packet – millisecond level accuracy

What is Time Error?

Time Error The time error of a clock is the difference between the time indicated by that clock and a reference clock at the same instant in time Always relative: has no meaning without a reference Defined by ITU-T Recommendation G. 810: Time error Time at measured clock Time at reference clock

Direction of Time Error – clocks Reference Clock: Measured Clock: Time Error = 11. 55 – 12. 00 = – 5 minutes Time Error = 12. 05 – 12. 00 = + 5 minutes Clock lags reference (slow, delayed): negative time error Clock leads reference (fast, advanced): positive time error

Direction of Time Error – signals Reference Clock: Measured Clock: negative Time Error positive Time Error Signal lags reference (slow, delayed): negative time error Signal leads reference (fast, advanced): positive time error

Characterizing Time Error

Time Error Function Time error varies with time and can be expressed as a function*: Time error Frequency offset Constant time error Frequency drift Random variations (dynamic time error) If clocks are locked in phase, frequency offset and drift are eliminated, and time error reduces to two components: Constant time error or offset Dynamic time error or random variations * Equation defined in ITU-T Recommendation G. 810

Examples of Time Error Functions Time Error Clock frequency high; time error increasing 0 Time Periodic time corrections (not always accurate) Clock frequency low; time error decreasing Clock frequency high; time error increasing Time Error 0 Time Periodic frequency corrections

Measuring Time Error Max|TE| c. TE d. TE 0 Time Need an accurate time reference – time error has no meaning without a reference Maximum Absolute Time Error (Max|TE|) is the maximum distance from zero of the time error function Sign doesn’t matter: excursions may be positive or negative Constant Time Error (c. TE) is the mean of the time error fn. Period over it is measured is not specified; depends on signal Dynamic Time Error (d. TE) is the change of the time error fn. Phase or time wander, analyzed using MTIE and TDEV

Sync Distribution Slides for this section provided by Christian Farrow, Chronos Technology Ltd (except for the last slide) 25 November 2014

How Are “Bits” Represented. . ? The value of a Bit (0 or 1) can be represented by different modulations of a carrier signal examples are: 1 10101 Fibre Optics The presence or absence of a light pulse Different frequencies of light Radio/Microwaves - Mobile phone, satellite comms, Wi. Fi, etc. Changes in phase, frequency or amplitude of the electromagnetic waves Electrical Cabling - Coaxial, twisted pair, etc Voltage levels on the wire +2. 5 v 0 v -2. 5 v 24 The bits arrive at regular intervals, represented here

Sync Trail Architecture Rules • • PRC Level Standards • EN 300 462 -2 -1 • ITU G. 803 EN 300 462 -6 -1 ITU G. 811 PRC SEC • • SEC N x SECs (N<=20) N <= 60 for entire chain EN 300 462 -5 -1 ITU G. 813 SEC 1 st SSU-T SEC EN 300 462 -4 -1 ITU G. 812 SEC N x SECs (N<=20) SEC SSU-T • • SEC • • Kth SSU, (K<=10) N x SECs (N<=20) EN 300 462 -7 -1 ITU G. 812 SSU-L 26

Sync. E Overview How is Sync. E different from normal Ethernet? Existing Ethernet PHY (Physical Layer) TX RX IEEE 802. 3 defines Ethernet PHY Rx uses incoming line timing. Tx uses free-running 100 ppm oscillator. No relationship between the Rx & Tx. Sync. E PHY (Physical Layer) TX RX 100 ppm TX TX RX RX Rx disciplines the internal oscillator Tx uses the traceable clock reference, creating end-to-end scheme. PRC can provide the reference. SSUs filter jitter/wander. Sync. E and asynchronous switches cannot be mixed. TX Traceable TX TX 4. 6 ppm Inaccurate RX RX 100 ppm Ext. Sync 4. 6 ppm Sync. E Element TX Asynchronous Element

From clocks to packets Packet “clocks” can be thought of in the same way as physical layer clocks… CES Packets do have a regular rhythm – E 1 = 1 m. S NTP/PTP Packets may not arrive regularly, but timestamps within the packets themselves mean time information can be extracted Time and timing can be distributed from point A to point B Packets time (header, payload and footer) F Payload 4 H F Payload 3 H F Payload 2 Significant instants H F Payload 1 H 28

IEEE 1588 -2008 PTPv 2 Overview The Grandmaster “reference clock” sends a series of time-stamped messages to slaves. Slaves eliminate the round-trip delay & synchronize to the Grandmaster. Frequency is recovered from an accurate time of day reference. Accuracy is enhanced by: Frequent packet send rate (up to 128 per second) Hardware time-stamping (eliminate software processing delays) Best Master Clock Algorithm (optional, “best” master voted by nodes) Embedded Slave 1588 Grandmaster (Server) 1588 Packets External Slave PTPv 2 Slave clocks can be either standalone or embedded in network equipment 29

Combination Operation Sync. E as “frequency assistance” to 1588 PRC UTC 1588 GM PTP Sync. E Node Stream 1588 Packet Stream Sync. E Physical Layer PSN Sync. E Node PTP Stream 1588 Client PRC freq Gives immediate “frequency lock” to 1588 client Sync. E & 1588 functionality may be in the same node/element 31

G. 8271. 1 Architecture G. 8273. 2 T-BC 1 Class A G. 8272 PRTC T-BC 2 Class A T-BC 9 Class A T-BC 10/ T-TSC Class A End App. T-GM 100 ns 50 ns 1. 5 us T-BC 1 Class B PRTC T-BC 2 Class B T-BC 19/ Class B End App. T-GM 100 ns T-BC 20/ T-TSC Class B 20 ns 1. 5 us Note: The network limit of 1. 5 us also accounts for other sources of noise (e. g. holdover, link asymmetries, sync. E rearrangements) PRTC = Primary Reference Time Clocks T-GM = Telecom Grand Master

Q 13 status transport of timing through telecom data networks -transport of frequency -Sync. E -1588 done for IP networks, through NEs not processing 1588 messages - Pure frequency T-GM ongoing: G. 8266 -transport of phase and time -ongoing - difficult as propagation delay corrupts time -need a two way transport -asymmetry of 2 directions -Testing sync transport over packets - Need for new metrics and news methods 33

Overview of recommendations Definitions / terminology Basics G. 8260 (Definition & metrics) Frequency: G. 826 x G. 8261 Agreed G. 8271 G. 8261. 1 G. 8262 (Sync. E) G. 8272 PRTC G. 8263 (slave clock) Clock Time/Phase: G. 827 x Full support assisted partial support G. 8271. 1 Netwk. PDV G. 8271. 2 Sync. E J & W Network requirements Ongoing G. 8273 73. 1 -GM 73. 2 BC & slave 73. 3 TC G. 8273. 4 A-PTS ck G. 8266 GM for F G. 8264 Methods G. 8265 () Profiles G. 8265. 1 G. 8265. m G. 8275. 1 PTPprofile 1 G. 8275. 2 34 PTPprofile 2

I-6 Time profiles First profile Full timing support from the network It means that all NEs process the PTP messages mapped in Ethernet (G. 8275. 1) Completed with G. 8272 (PRTC) G. 8273. 2 (BC and slave clock) Will be upgraded with Stand alone T-GM G. 8273. 1 Transparent clocks G. 8273. 3 35

I-7 Second time profile Partial Timing Support profile (PTS) Work item created in July 2013 General architectural view (G. 8275) PTP unaware networks separated by T-BCs PTP messages mapped in IP PRTC two-way packet timing signals time reference, Tin Packet Master Clock Boundary Clock Packet Slave Clock Tout + 36

I-8 Assisted PTS profile (A-PTS) New ideas brought in October 2013 e. Node B be synchronized with GPS receivers in priority PTP will be used only as a backup in case of GPS failure Operators request A-PTS for end 2014 Seemed difficult to achieve on time 37

new PTS profile- « non. A-PTS » New architecture agreed in September 2014 simple PTP over IP based distributed deployment model a grandmaster is deployed inside a building to provide frequency and time synchronization to the small cells within the building or to nearby buildings. Only a few PTP-unaware nodes between the local GM and the slaves on the small cells. 38

Partial Timing Support profile New recommendations required G. 8275 Add the « 1588 unaware » equipments in the network architectures for A-PTS & « non. A » -PTS G. 8271. 2(A-PTS), G. 8271. x(PTS)? Define the network limits and HRMs G. 8273. 2 Define a new Boundary Clock if needed G. 8273. 4(A-PTS), G. 8273. y(PTS)? Defines new clocks if needed G. 8275. 2, G. 8275. x? ? both A-PTS & PTS based on IP 39

Future of recommendations? Definitions / terminology G. 8260 (Definition & metrics) F Basics R G. 8271 E Network Time/Phase: G. 827 x Ongoing T B D Full support assisted partial support G. 8271. 1 Netwk. PDV Q Agreed G. 8271. 2 G. 8271. y requirements U E Clock N G. 8272 PRTC G. 8273 73. 1 -GM 73. 2 BC & slave Profiles ? G. 8273. 4 A-PTS ck Y : G. 8 2 6 X 73. y 73. 3 TC C Methods 73. 2 BC & slave G. 8275. 1 PTPprofile 1 G. 8275. 2 PTPprofile 2 G. 8275. y PTPprofile? 40 ?

Links between Q 13/15 and fora Operators, manufacturers, std organisations, universities and scientists meet once a year at WSTS in USA and at ITSF in Europe. During these events several sessions addresses: -the needs for synchronization -tutorials on synchronization -the requirements for synchronization -news from GNSS systems -alternative to GNSS: E Loran, . . -information on future technologies -information on deployments -information on sync standards: ITU Q 13/15, IEEE 1588 -etc… 25 November 2014 41

ITSF (International Telecom Sync Forum) ITSF Website: www. telecom-sync. com Organiser’s Website: www. itsf-conference. com Meets every year since 2001 in November Last event: 4 -6 Nov 2014 in Budapest Next event: 3 -5 Nov 2015 location tbd WSTS (Workshop on Synchronization in Telecommunication Systems) Depends on NIST-ATIS http: //www. atis. org/wsts/cfp. asp Meets every year since 1992 in spring Last event: 4 -6 June 2014 in San Jose, Ca USA Next event: 9 -12 March 2015 in San Jose, Ca USA 25 November 2014 42

Backup slides List of main ITU-T recommendations related to synchronization (updated November 2014) 43

Where to get the recommendations? http: //www. itu. int/ITU-T/recommendations/index. aspx? ser=G 44

Recommendations for TDM hierarchies G. 803 (03/2000), Architecture of transport networks based on the synchronous digital hierarchy (SDH) G. 803 Amd 1(06/2005) G. 810 (08/1996), Definitions and terminology for synchronization networks G. 810 Corr 1(10/2001) G. 811 (09/1997), Timing requirements of primary reference clocks G. 812 (06/2004), Timing requirements of slave clocks suitable for use as node clocks in synchronization networks G. 813 (03/2003), Timing requirements of SDH equipment slave clocks (SEC) G. 813 Corr 1(06/2005) G. 822 (11/1988), Controlled slip rate objectives on an international digital Connection G. 823 (03/2000), The control of jitter and wander within digital networks which are based on the 2048 kbit/s hierarchy G. 824 (03/2000), The control of jitter and wander within digital networks which are based on the 1544 kbit/s hierarchy G. 825 (03/2000), The control of jitter and wander within digital networks which are based on the synchronous digital hierarchy (SDH ) G. 825 Amd 1 (05/2008) G. 781 (09/2008), Synchronization layer functions 45

Recommendations for timing over packet networks G. 8260 rev(02/2012), Definitions and terminology for synchronization in packet networks G. 8260 Amd 1 (8/2013), Amd 2 (5/2014) Recommendations for Synchronous Ethernet q q q G. 781 (09/2008), Synchronization layer functions G. 8261 rev(08/2013), Timing and Synchronization aspects in Packet Networks G. 8262 (07/2010), Timing characteristics of synchronous Ethernet Equipment slave clock • G. 8262 Amd 1 (02/2012), Amd 2 (10/2012) G. 8263 (02/2012), Timing characteristics of packet-based equipment clocks G. 8263 Amd 1 (08/2013), Amd 2 (05/2014) G. 8264 rev(05/2014), Distribution of timing information through packet networks 46

Recommendations for the telecom profile for time and phase q q q q G. 8271 (02/2012), Time and phase synchronization aspects of packet networks • G. 8271 Amd 1 (08/2013) G. 8271. 1(08/2013), Network Limits for Time Synchronization in Packet Networks • G. 8271. 1 Amd 1 (5/2014) G. 8272 (10/2012), Timing characteristics of primary reference time clocks • G. 8272 Amd 1 (8/2013) G. 8273 (08/2013), Framework of phase and time clocks • G. 8273 Corr 1 (5/2014) G. 8273. 2 (05/2014) Timing characteristics of telecom boundary clocks and telecom time slave clocks G. 8275 (11/2013), Architecture and requirements for packet-based time and phase distribution G. 8275. 1 (07/2014), Precision time protocol telecom profile for phase/time synchronization with full timing support from the network 47

Recommendations for OTN G. 8251 (09/2010), The control of jitter and wander within the optical transport network (OTN) G. 8251 Amd 1 (04/2011), Amd 2 (02/2012), Amd 3 (10/2012) G. 8251 Corr 1 (02/2012) Recommendations for the telecom profile for frequency only G. 8261 rev(08/2013), Timing and Synchronization aspects in Packet Networks G. 8261. 1 (02/2012), Packet Delay Variation Network Limits applicable to Packet Based Methods (Frequency Synchronization) G. 8261. 1 Amd 1 (5/2014) G. 8263 (02/2012), Timing characterisctics of packet based equipment clocks G. 8263 Amd 1 (8/2013), Amd 2 (5/2014) G. 8265 (10/2010), Architecture and requirements for packet based frequency delivery G. 8265. 1 rev(07/2014), Precision time protocol telecom profile for frequency synchronization 48

Future recommendations ( provisional titles) 49

Recommendation on Jitter and wander tests equipments O. 171 (04/1997), Timing jitter and wander measuring equipment for digital systems which are based on the plesiochronous digital hierarchy (PDH) O. 172 (04/2005) , Jitter and wander measuring equipment for digital systems which are based on the synchronous digital hierarchy (SDH) O. 173 (02/2012), Jitter measuring equipment for digital systems which are based on the Optical Transport Network O. 174 (11/2009), Jitter and wander measuring equipment for digital system based on synchronous Ethernet network 50