EPoC System Level Synchronization Transport 802.3bn Interim meeting - Phoenix

Transcription

1 EPoC System Level Synchronization Transport 802.3bn Interim meeting - Phoenix Bill Powell January,

2 Agenda Mobile BackHaul (MBH) & Circuit Emulation Services (CES) sync requirements EPON & EPoC network architecture IEEE 1588v2 and EPON / EPoC Distributed 1588v2 boundary concept EPON frequency & time sync distribution method EPON + EPoC distributed boundary ITU sync distribution work, standards, and budget allocations Potential time/frequency error budgets for EPON & EPoC Summary 2

3 Mobile BackHaul synchronization requirements Wireless Technology Frequency Accuracy Time Accuracy GSM 50 ppb - UMTS FDD 50 ppb - UMTS TDD 50 ppb 2.5 us LTE FDD 50 ppb - LTE TDD 50 ppb 2.5 us TD-SCDMA 50 ppb 3 us CDMA ppb 3 us WiMAX FDD 2 ppm - WiMAX TDD 2 ppm 3 us [source: 3GPP, 3GPP2, IEEE e, ITU G987.1 specifications] Newer wireless technologies aiming for 500 ns accuracy at air interface (CoMP - Coordinated Multi-Point Transmission and Reception [1] ) FCC E911 emergency location services require ~100 ns/utc accuracy 3

4 MEF-8 CES Synchronization requirements CESoETH IWF External Timing Reference May be recovered from PON, EPoC, SyncE, or IEEE 1588v2 delivery To TDM (or TSP) Clock Data Clock Data MEN-bound IWF TDM-bound IWF TDM Line Clock Data Ext. Eth. Line Clock Recovery To MEN Free Run Figure 6-7/MEF-8 - Synchronization Options for the TDM bound IWF The External Timing Reference interface is required for Differential-mode or "network" CES timing MEF-8 TDM synchronization interface requirements R47 The method of synchronization MUST be such that the TDM-bound IWF meets the traffic interface requirements specified in ITU-T recommendations [G.823] for E1 and E3 circuits, and [G.824] for DS1 and DS3 circuits 4

5 G.8261 CES Synchronization requirements Case 2 for typical CES s Figure 8/G Network models for traffic and wander accumulation, Deployment Case 1 and Case MTIE (μ s) Synchronization requirements from G.8261 are more stringent than MEF-8 Lower wander generation requirement 0.47 PDV tolerance test patterns Ob s erv atio n In terv al τ (s ) Figure 10/G Deployment Case 1: wander budget for 1544 kbit/s interface (also applies to Case 2) 5

6 Synchronization delivery for Mobile BackHaul USNO UTC GPS IP Transport GPS Access CO IP Aggregation Switch Access CO IP Aggregation Switch GPS RX FE / 1588 GPS RX GM D T I GE 10GE DTI GE, 10GE IEEE-1588 or SyncE+1588 EPON OLT IEEE-1588 Slave Port EPON OLT EPoC core architecture & MBH NEs must meet FDD and TDD MBH requirements (15 ppb for Freq. & usec/utc for ToD delivery), in both FDD/TDD EPoC modes Should meet ITU SG15/Q13 error budget requirements for frequency (G ) and time/phase delivery (work in progress in Q13) Combination of EPON OLT + FCU + MBH CNU to look like a distributed IEEE 1588v2 BC (boundary ) CNUs for MBH time delivery to support SyncE + IEEE 1588v2 time delivery to MBH IEEE 1588v2 slave S fiber FCU S coax Distributed IEEE-1588 Boundary Clock CNU ONU S fiber SE+1588 CNU FCU SyncE NodeB S NodeB SyncE coax CNU ONU NodeB ToD CNU IEEE-1588 Master Port SyncEnet SE+1588 ToD SyncE Freq. NodeB Freq. NodeB NodeB ToD ToD 6

7 IEEE 1588v2 & EPON / EPoC Why can't native IEEE 1588v2 packets be transported through EPON? - They can, but the result is unusable for MBH time synchronization - IEEE 1588v2 assumes DS / US delay symmetry for time transport - EPON downstream TDM delay is minimal (typ. 10's of usec) - EPON upstream TDMA delay is much larger - polling, gate delays (typ msec) - Native 1588v2 packets also experience extra congestion-dependent delays (PDV, or packet delay variation) due to competing EPON traffic - IEEE 1588v2 assumes the 1-way link delay is ½ of the DS + US delays => msec-level time transfer errors through OLT/ONU for native Similar issues would be encountered for EPoC for native 1588 packet transport through PON and/or coax Solution? - Implement IEEE 802.1as protocol between OLT and ONU - OLT & ONU function as a distributed IEEE 1588v2 boundary 7

8 EPON Frequency and Time Distribution Method Distributed 1588v2 Boundary Clock ToD Input 1588v2 pkts IEEE 1588v2 Slave OLT ToD OLT ONU IEEE 1588v2 Master ToD Output 1588v2 pkts (1) ToD & RTT Logic Ranging Delay ONU ToD ToD Logic OLT TQ Counter (2) MAC (4) PHY 802.1as protocol MAC PHY (3) ONU TQ Counter Td1 Td4 ToD Correction (5) Td3 Td2 Timestamps on MPCP s EPON time transport method defined in IEEE 802.1as, clause 13 The local 32b TQ counter in the OLT (1 TQ = 16ns) is timed from an external time source (1) MPCP messages sent to ONUs have OLT TQ counter value loaded into timestamp (TS) field at the OLT EPON MAC (2) At the ONU, the timestamp is recovered from RX MPCP messages and used to reset the local ONU TQ counter (3) OLT calculates RTT for a particular ONU from local TQ counter vs. return timestamps from the ONU (4) Important that (Td1 + Td2) = (Td3 + Td4) [Td1 & Td3 - MAC(TS)->PHYout; Td2, Td4 - PHYin-> TS extracted] ToD at ONU calculated from local TQ counter, ranging delay, & slow ToD correction (5) Range of current time error: OLT-to-ONU ~120 ns [6] [local ctr - 8ns, ½ RTT drift - 96ns, DS/US fiber -17ns] 8

9 EPON + EPoC Distributed Boundary Clock Distributed 1588v2 Boundary Clock ToD Input 1588v2 pkts IEEE 1588v2 Slave OLT OLT ToD FCU FCU ToD & RTT Logic CNU IEEE 1588v2 Master ToD Output 1588v2 pkts (1) OLT TQ Counter ToD & RTT Logic (2) (4) MAC EPON TQ Counter (3) MAC MAC EPoC TQ Counter Ranging Delay MAC CNU ToD CNU ToD Logic CNU TQ Counter PHY PHY PHY PHY Td4 Td1 Td2 Td3 TS on MPCP s 802.1as protocol TS on MPCP s 802.1as-like protocol? A similar method to 802.1as can be used to transfer synchronization and ToD corrections between the EPoC FCU and CNU Again important for EPoC time transport (and RTT calc) that (Td1 + Td2) = (Td3 + Td4) Question: what level of performance is needed so the combination of EPON and EPoC meets current and emerging MBH time-sync requirements? 9

10 ITU-T G Sync Distribution Model - Frequency master network N = 10 node (e.g., ethernet switch, IP router, MPLS router) slave G Y1361.1(12)_F01 10 Gbit/s fibre optical link 1 Gbit/s fibre optical link Figure 1/G HRM-1 for Delay Variation network limits DSLAM DSL modem HRM-2a EPON + EPoC Sync Distribution Error Allocation master network N = 5 OLT ONU HRM-2b slave HRM-2c node (e.g., Ethernet switch, IP router, MPLS router) G Y1361.1(12)_F02 10 Gbit/s fibre optical link 1 Gbit/s fibre optical link Microwave link Figure 2/G HRM-2 for Delay Variation network limits ITU-T requirements on frequency synchronization of MBH are contained in G.8261 [2] & G [7], both - consented & active ITU-T synchronization studies in performed in Q13/15 10

11 G Sync Distribution Model - Frequency PRC Physical layer based synchronization network master PNT-F Timing packets network C2 PNT-F E: requirements (e.g., frequency accuracy) A: PRC, EEC, SSU or SEC network limits PEC-M B: PEC-M output packet network limits C: PEC-S-F input packet network limits C1 PEC-S-F PNT-F D: PEC-S-F output network limits (deployment case 2) Figure 3/G Reference Points for network limits G Y (12)_F03 Network PDV limits that a 1588v2 slave has to tolerate are defined in G at the "C" interface for the PEC-S-F (packet equipment slave - frequency) MTIE and frequency accuracy requirements for the PEC-S-F are defined in G at the "D" interface 11

12 G Sync Distribution Model - Frequency MTIE 16 ppb 50 ppb ~1/3 of 50 ppb budget for MBH frequency sync s 18 μs 9 μs G Y (12)_F04 Observation interval τ (s) Figure 4/G Output wander network limit for case 3 based on G.823 The above MTIE interface specification has been consented in G [7] for MBH frequency synchronization s It is recommended that both EPON ONUs and EPoC CNUs used for MBH frequency sync s also meet the above MTIE requirement 12

13 G.8271 Sync Distribution Model - Time Radio distributed PRTC, e.g., GNSS or distribution via cables Rx PRTC limits Rx PRTC limits PRTC limits G.8271-Y.1366(12)_F01 Time or phase synchronization distribution via cable Time or phase synchronization distribution via radio Figure 1/G Example of a distributed PRTC synchronization network T-GM T-BC T-BC Application T-BC PTP messages Figure 2/G Example of packet-based method with support from network nodes The initial Q13/15 network models are contained in G.8271 Q13/15 is still working on defining network topologies, PDV, and wander (MTIE) limits 13

14 G.8271 Sync Distribution Model - Time Radio distributed PRTC, e.g., GNSS or distribution via cables timing distribution network Rx Transport node slave master PRTC limits Transport node slave master PRTC limits Transport node slave timing distribution network G.8271-Y.1366(12)_F03 T-BC Time or phase synchronization distribution via cable Time or phase synchronization distribution via radio Figure 3/G Example of time synchronization distributed via packet based methods Another view of the G.8271 time distribution model currently being studied in Q13/15 14

15 G.8271 Sync Distribution Model - Time Network time reference (e.g., GNSS engine) PRTC A master B C D E network slave PRTC: Primary reference time time Physical timing signal (for phase and/or time synchronization) timing signal G.8271-Y.1366(12)_F04 PRTC A: B: C: D: E: 1 PRTC network limits master network limits slave input network limits slave output network limits (if applicable) requirements (e.g., phase accuracy) Figure 4/G Network Reference Model EPON OLT + EPoC FCU + EPoC CNU => Distributed 1588 BC MBH base station 2 T-GM T-BC T-BC T-BC T-BC T-TSC D 1 Figure 5/G Possible locations of external phase/time interfaces in a chain of Telecom Boundary Clocks Current goal of Q13/15 is to meet 1.0 us time accuracy at point D relative to UTC 15

16 Example Error budgets for Time/Frequency distribution for EPON & EPoC For MBH FDD s, EPoC CNU & EPON ONU should meet MTIE requirements in Fig. 4, G (slide 12) For MBH TDD s, it is recommended that EPON and EPoC only consume a fraction of the current 1.0 us error allocation Possible error allocations - EPON: ~ ns - EPON + EPoC: ~250 ns Emerging MBH time sync requirements are getting tighter: CoMP air interface ~500ns => Would require access segment to drop to ~150ns error budget FCC E911 emergency services time sync requirements ~100ns (limit of GPS + time receiver) => Likely not possible to meet with added EPON/EPoC access segment 16

17 Proposed EPoC Synchronization Evaluation Criteria Reference Connection CLT -> CNU Error Criteria - Frequency transfer Error </= 15 ppb - Time-transfer (ToD) Error - EPoC Link: </= +/-120ns [Tentative] [Goal: EPON + EPoC combined (OLT->FCU->CNU): +/-250 ns or less] 17

18 Summary Current and emerging wireless standards require precise frequency and time synchronization to UTC Combination of EPON OLT and EPON ONU, or EPON OLT + EPoC FCU + EPoC CNU can be built to function like a single distributed IEEE 1588v2 boundary ToD time transfer at OCU/FCU (EPON to coax) should be done with digital methods relative to local OCU/FCU TQ counters Time transfer mechanism on EPoC should function similar to method described in 802.1as, clause 13 System level frequency and time transfer error budgets should guide choice of time transport protocol on the coax Proposed Eval criteria frequency/time error budget for EPoC link on previous slide 18

19 References [1] Impact of Synchronization Impairments on CoMP Joint Transmission Performance, Helmut Imlau, Heinz Droste, Samip Malla, Deutsche Telecom, presentation at ITSF [2] ITU-T G.8261/Y.1361, Timing and synchronization aspects in packet networks, April, 2008, [3] MEF-8, Implementation Agreement for the Emulation of PDH Circuits over Metro Ethernet Networks, October, [4] G.823, The control of jitter and wander within digital networks which are based on the 2048 kbit/s hierarchy, March, [5] G.824, The control of jitter and wander within digital networks which are based on the 1544 kbit/s hierarchy, March, [6] Time Synchronization over Ethernet Passive Optical Networks, Yuanqiu Luo, Frank Effenberger, Huawei, Nirwan Ansari, NJIT, IEEE Communications Magazine, Oct, [7] ITU-T G /Y , delay variation network limits applicable to packetbased methods (frequency synchronization), February, [8] ITU-T G.8271/Y.1366, Time and phase synchronization aspects of packet networks, February, 2012, [9] ITU-T Q13/15, WD8271, Helsinki, 4-8 June, 2012, Draft G Network limits for time synchronization in Networks, Stefano Ruffini, Ericsson (editor). 19

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