EPoC System Level Synchronization Transport 802.3bn Interim meeting - Phoenix
Bill Powell 23-25 January, 2013
1 Agenda
• Mobile BackHaul (MBH) & Circuit Emulation Services (CES) sync requirements • EPON & EPoC network architecture • IEEE 1588v2 and EPON / EPoC • Distributed 1588v2 boundary clock concept • EPON frequency & time sync distribution method • EPON + EPoC distributed boundary clock • ITU sync distribution work, standards, and budget allocations • Potential time/frequency error budgets for EPON & EPoC • Summary
2 Mobile BackHaul synchronization requirements
Wireless Frequency Time Accuracy Technology 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 2000 50 ppb 3 us
WiMAX FDD 2 ppm -
WiMAX TDD 2 ppm 3 us
[source: 3GPP, 3GPP2, IEEE 802.16e, 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 MEF-8 CES Synchronization requirements
May be recovered from PON, EPoC, SyncE, or IEEE 1588v2 delivery
External Timing Reference
CESoETH IWF
Clock MEN-bound Data IWF TDM Ext. To TDM Line To MEN (or TSP) Clock Clock Eth. TDM-bound Line Clock Data Recovery IWF Data 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 G.8261 CES Synchronization requirements
Case 2 for typical CES applications
Figure 8/G.8261 - Network models for traffic and clock wander accumulation, Deployment Case 1 and Case 2
10
4.5
2.1
MTIE (μ s) 1
0.45
0.01 0.01 0.1 110 100 1000 10000 100000 0.47 900 1930 Ob s erv atio n In terv al τ (s ) Figure 10/G.8261 - Deployment Case 1: wander budget for 1544 kbit/s interface (also applies to Case 2)
• Synchronization requirements from G.8261 are more stringent than MEF-8 • Lower wander generation requirement • PDV tolerance test patterns
5 Synchronization delivery for Mobile BackHaul
Distributed IEEE-1588 IEEE-1588 Boundary Clock Master Port Access CO CNU IP EPON OLT SyncEnet Aggregation GE, ToD 10GE +1588 NodeB GPS Switch IEE FCU E-1588 or S FE / yncE+1588 S CNU 1588 IEEE-1588 coax SyncE Slave Port Freq. 1 S NodeB GPS RX + 5 8 fiber ONU 1588GM 8 IP SE+1588 ToD NodeB Transport Access CO IP CNU Aggregation G FCU SE+1588 UTC Switch E EPON OLT ToD 10G NodeB E S CNU USNO I coax GPS DT S SyncE 1 D Freq. 5 fiber NodeB GPS RX T 8 ONU 8 I SyncE +158 ToD 8 NodeB • EPoC core architecture & MBH NEs must meet FDD and TDD MBH requirements (15 ppb for Freq. & 1-1.5 usec/UTC for ToD delivery), in both FDD/TDD EPoC modes • Should meet ITU SG15/Q13 error budget requirements for frequency (G.8261.1) 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 clock) • CNUs for MBH time delivery to support SyncE + IEEE 1588v2 time delivery to MBH IEEE 1588v2 slave
6 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 1588 - 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 clock
7 EPON Frequency and Time Distribution Method Distributed 1588v2 Boundary Clock
OLT ONU ToD Output ToD Input IEEE 1588v2 IEEE 1588v2 OLT ToD 1588v2 pkts Slave Master 1588v2 pkts ToD & RTT ONU ToD Logic Ranging (1) Delay ToD Logic
OLT TQ MAC MAC Counter (2) (4) ONU TQ (3) Counter PHY PHY 802.1as protocol Td1 Td4 ToD Correction (5) Td3 Td2 Timestamps on MPCP Packets
• 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 EPON + EPoC Distributed Boundary Clock Distributed 1588v2 Boundary Clock
OLT FCU CNU ToD Input ToD Output IEEE 1588v2 FCU ToD & IEEE 1588v2 1588v2 pkts Slave OLT ToD RTT Logic Master 1588v2 pkts CNU ToD ToD & RTT EPoC TQ Ranging EPON TQ CNU ToD (1) Logic Counter Counter Delay Logic (4) OLT TQ (3) Counter (2) MAC MAC MAC MAC CNU TQ Counter PHY PHY PHY PHY
Td4 Td1 Td2 Td3
TS on MPCP Packets TS on MPCP Packets
802.1as protocol 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 ITU-T G.8261.1 Sync Distribution Model - Frequency
Packet network Packet Packet master slave clock clock N = 10 G.8261.1-Y1361.1(12)_F01 Packet node (e.g., ethernet switch, IP router, MPLS router)
10 Gbit/s fibre optical link 1 Gbit/s fibre optical link Figure 1/G.8261.1 - HRM-1 for Packet Delay Variation network limits EPON + EPoC Sync Distribution Error Allocation DSLAM DSL modem Packet network Packet HRM-2a master clock Packet N = 5 slave OLT ONU clock HRM-2b
G.8261.1-Y1361.1(12)_F0 2 Packet node (e.g., Ethernet switch, IP router, MPLS router) HRM-2c 10 Gbit/s fibre optical link
1 Gbit/s fibre optical link
Figure 2/G.8261.1Microwave link - HRM-2 for Packet Delay Variation network limits • ITU-T requirements on frequency synchronization of MBH are contained in G.8261 [2] & G.8261.1 [7], both - consented & active • ITU-T synchronization studies in performed in Q13/15
10 G.8261.1 Sync Distribution Model - Frequency
End application clock
C2 PNT-F Packet master PRC clock Timing packets Physical layer based PNT-F Packet E: End application requirements synchronization network network (e.g., frequency accuracy)
PEC-M B: PEC-M output PEC-S-F packet network limits A: PRC, EEC, SSU or SEC network limits C1 C: PEC-S-F input PNT-F packet network limits End application D: PEC-S-F output clock network limits (deployment case 2)
G.8261.1-Y.1361.1(12)_F03 Figure 3/G.8261.1 -Reference Points for network limits
• Network PDV limits that a 1588v2 slave clock has to tolerate are defined in G.8261.1 at the "C" interface for the PEC-S-F (packet equipment clock slave - frequency) • MTIE and frequency accuracy requirements for the PEC-S-F are defined in G.8261.1 at the "D" interface
11 G.8261.1 Sync Distribution Model - Frequency
50 ppb ~1/3 of 50 ppb budget MTIE for MBH frequency
16 ppb sync applications
18 μs
9 μs
Observation 0.05 0.2 32 64 1125 interval τ (s) G.8261.1-Y.1361.1(12)_F04
Figure 4/G.8261.1 -Output wander network limit for case 3 based on G.823
• The above MTIE interface specification has been consented in G.8261.1 [7] for MBH frequency synchronization applications • It is recommended that both EPON ONUs and EPoC CNUs used for MBH frequency sync applications also meet the above MTIE requirement
12 G.8271 Sync Distribution Model - Time
Radio distributed PRTC, e.g., GNSS or distribution via cables
Rx Rx PRTC limits PRTC limits PRTC limits End End application End End End application application application application G.8271-Y.1366(12)_F01 Time or phase synchronization distribution via cable Time or phase synchronization distribution via radio Figure 1/G.8271 -Example of a distributed PRTC synchronization network
T-BC End T-GM T-BC Application
T-BC
PTP messages Figure 2/G.8271 -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 G.8271 Sync Distribution Model - Time
Radio distributed PRTC, e.g., GNSS or distribution via cables
Rx PRTC limits PRTC limits Packet End Packet master application master clock clock Packet timing distribution network Transport Packet timing Transport Transport node distribution network node node
Packet Packet Packet slave slave slave clock clock clock
End End End End End End application application application application application application G.8271-Y.1366(12)_F03
T-B C Time or phase synchronization distribution via cable Time or phase synchronization distribution via radio
Figure 3/G.8271 - 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 G.8271 Sync Distribution Model - Time
Network time reference A BCDE (e.g., GNSS engine) Packet Packet Packet PRTC master slave clock network clock
PRTC: Primary reference End application time clock time clock
Physical timing signal (for phase and/or time synchronization) Packet timing signal G.8271-Y.1366(12)_F04
A: PRTC network limits B: Packet master clock network limits C: Packet slave clock input network limits D: Packet slave clock output network limits (if applicable) E: End application requirements (e.g., phase accuracy) Figure 4/G.8271 -Network Reference Model PRTC End MBH base 1 EPON OLT + EPoC FCU + EPoC application CNU => Distributed 1588 BC station
2
T-GM T-BC T-BC T-BC T-BC T-TSC
1 1 1 1 1 D 1 Figure 5/G.8271 -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 Example Error budgets for Time/Frequency distribution for EPON & EPoC
• For MBH FDD applications, EPoC CNU & EPON ONU should meet MTIE requirements in Fig. 4, G.8261.1 (slide 12) • For MBH TDD applications, it is recommended that EPON and EPoC only consume a fraction of the current 1.0 us error allocation Possible error allocations - EPON: ~125-150ns - 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 Proposed EPoC Synchronization Evaluation Criteria
• Reference Connection CLT -> CNU
• Error Criteria - Frequency transfer Error
- Time-transfer (ToD) Error - EPoC Link: FCU->CNU): +/-250 ns or less]
17 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 clock
• 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 References [1] Impact of Synchronization Impairments on CoMP Joint Transmission Performance, Helmut Imlau, Heinz Droste, Samip Malla, Deutsche Telecom, presentation at ITSF 2012 http://www.itsf-conference.com/agenda_outline/s2627/ [2] ITU-T G.8261/Y.1361, Timing and synchronization aspects in packet networks, April, 2008, http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-G.8261-200804-I!!PDF-E&type=items [3] MEF-8, Implementation Agreement for the Emulation of PDH Circuits over Metro Ethernet Networks, October, 2004. [4] G.823, The control of jitter and wander within digital networks which are based on the 2048 kbit/s hierarchy, March, 2000 http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-G.823-200003-I!!PDF-E&type=items [5] G.824, The control of jitter and wander within digital networks which are based on the 1544 kbit/s hierarchy, March, 2000 http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-G.824-200003-I!!PDF-E&type=items [6] Time Synchronization over Ethernet Passive Optical Networks, Yuanqiu Luo, Frank Effenberger, Huawei, Nirwan Ansari, NJIT, IEEE Communications Magazine, Oct, 2012. [7] ITU-T G.8261.1/Y.1361.1, Packet delay variation network limits applicable to packet- based methods (frequency synchronization), February, 2012 http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-G.8261.1-201202-I!!PDF-E&type=items [8] ITU-T G.8271/Y.1366, Time and phase synchronization aspects of packet networks, February, 2012, http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-G.8271-201202-I!!PDF-E&type=items [9] ITU-T Q13/15, WD8271, Helsinki, 4-8 June, 2012, Draft G.8271.1 - Network limits for time synchronization in Packet Networks, Stefano Ruffini, Ericsson (editor).
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