epoc system level synchronization transport - r1a

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EPoC System Level Synchronization Transport - R1a 802.3bn Interim meeting - Phoenix

Bill Powell 23-25 January, 2013

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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

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Mobile BackHaul synchronization requirements

• 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

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 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]

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MEF-8 CES Synchronization requirements

• The External Timing Reference interface is required for Differential-mode or "network" CES timing

• MEF-8 TDM synchronization interface requirementsR47 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

Figure 6-7/MEF-8 - Synchronization Options for the TDM bound IWF

May be recovered from PON, EPoC, SyncE, or IEEE 1588v2 delivery

To MEN

Data

To TDM(or TSP)

Clock

Data

Clock

MEN-boundIWF

CESoETH IWF

Ext.

FreeRun

Data

TDMLine

External TimingReference

TDM-boundIWF

Eth.Line Clock

Recovery

Clock

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G.8261 CES Synchronization requirements

• Synchronization requirements from G.8261 are more stringent than MEF-8• Lower wander generation requirement• PDV tolerance test patterns

Figure 8/G.8261 - Network models for traffic and clock wander accumulation, Deployment Case 1 and Case 2

Case 2 for typical CES applications

0 . 01

1

10

2 . 1

0 . 45

4 . 5

0 . 01 0 . 1 0 . 47

1 1090 0 19 3 0

10 0 10 0 0

O b s e rv a t io n In t e rv a l τ (s )

M T I E (μ s )

10 0 00 10 0 00 0

Figure 10/G.8261 - Deployment Case 1: wander budget for 1544 kbit/s interface (also applies to Case 2)

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Synchronization delivery for Mobile BackHaul

• 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

IP

Transport

EPON OLT

USNO

GPS

GE10GE

GPS

IP Aggregation

Switch

GPS RX

Access CO

SyncE

NodeB

NodeB

NodeB

EPON OLTGE, 10GE

IEEE-1588

Slave Port

IEEE-1588 or SyncE+1588

S NodeB

NodeB

NodeBIP

Aggregation Switch

GPS RX + 1588GM

FE /

1588

Access CO

UTC

SyncEnet+1588

SyncE

SE+1588

SE+1588

DTI

ToD

Freq.

ToD

ToD

Freq.

ToD

D T I

1 5 8 8

1 5 8 8

FCU

CNU

CNUS

ONU

coax

S

IEEE-1588

Master PortDistributed IEEE-1588

Boundary Clock

CNU

CNU

ONUSyncE+1588

S

FCU

fiber

coaxfiber

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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

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EPON Frequency and Time Distribution Method

• 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]

OLT TQ Counter ONU TQ

CounterPHY

MAC

PHY

OLT ONUIEEE 1588v2

SlaveIEEE 1588v2

Master

ToD Input1588v2 pkts

ToD Logic

ToD & RTT Logic Ranging

Delay

ToD Correction

ToD Output

1588v2 pkts

Timestamps on MPCP Packets

OLT ToD

ONU ToD

Distributed 1588v2 Boundary Clock

(1)

(2)(3)

(4)

802.1as protocol

(5)Td4 Td3Td1 Td2

MAC

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EPON + EPoC Distributed Boundary Clock

• 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) OR, we need to know each delay explicitly to some precision

• Question: what level of performance is needed so the combination of EPON and EPoC meets current and emerging MBH time-sync requirements?

OLT TQ Counter MAC

PHY

OLTIEEE 1588v2

Slave

ToD Input1588v2 pkts

ToD & RTT Logic

OLT ToD

(1)

CNU TQ Counter

MAC

PHY

CNUIEEE 1588v2

Master

CNU ToD Logic

Ranging Delay

ToD Output

1588v2 pkts

CNU ToD

FCU

MAC

PHY

MAC

PHY

EPON TQ Counter

EPoC TQ Counter

Distributed 1588v2 Boundary Clock

FCU ToD & RTT Logic

(2)

(4)

TS on MPCP Packets TS on MPCP Packets

802.1as protocol 802.1as-like protocol?

Td4 Td3Td1 Td2

(3)

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ITU-T G.8261.1 Sync Distribution Model - Frequency

Figure 1/G.8261.1 - HRM-1 for Packet Delay Variation network limits

G.8261.1-Y1361.1(12)_F01

Packetmasterclock

Packet network

N = 10

Packetslaveclock

Packet node (e.g., ethernet switch, IP router, MPLS router)

10 Gbit/s fibre optical link


G.8261.1-Y1361.1(12)_F02

Packetmasterclock

Packet network

N = 5

Packet node (e.g., Ethernet switch, IP router, MPLS router)



Microwave link

Packetslaveclock

DSLAM DSLmodem

HRM-2a

HRM-2b

HRM-2c

ONUOLT

Figure 2/G.8261.1 - HRM-2 for Packet Delay Variation network limits

EPON + EPoC Sync Distribution Error Allocation

• 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

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G.8261.1 Sync Distribution Model - Frequency

• 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

Figure 3/G.8261.1 -Reference Points for network limits

G.8261.1-Y.1361.1(12)_F03

PEC-S-F

PNT-F

PRC

Physical layer basedsynchronization network

Packet masterclock

PNT-F

PEC-M

A: PRC, EEC, SSUor SEC network limits

B: PEC-M outputpacket network limits

C: PEC-S-F inputpacket network limits

D: PEC-S-F outputnetwork limits(deployment case 2)

End applicationclock

E: End application requirements(e.g., frequency accuracy)

C1

Packetnetwork

Timing packets

C2 PNT-F

End applicationclock

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G.8261.1 Sync Distribution Model - Frequency

• 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

Figure 4/G.8261.1 -Output wander network limit for case 3 based on G.823

G.8261.1-Y.1361.1(12)_F04

MTIE

18 sμ

9 sμ

0.05 0.2 32 64 1125

16 ppb

Observationinterval (s)τ

~1/3 of 50 ppb budget for MBH frequency sync applications

50 ppb

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G.8271 Sync Distribution Model - Time

• 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

Figure 1/G.8271 -Example of a distributed PRTC synchronization network

G.8271-Y.1366(12)_F01

Endapplication

Endapplication

Endapplication

Radio distributed PRTC, e.g., GNSS ordistribution via cables

RxRx

PRTC limits PRTC limits

Endapplication

Time or phase synchronization distribution via cableTime or phase synchronization distribution via radio

PRTC limitsEnd

application

T-GM

T-BCT-BC

T-BC

End Application

PTP messages

T-GM

T-BCT-BC

T-BC

End Application

PTP messages

Figure 2/G.8271 -Example of packet-based method with support from network nodes

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• Another view of the G.8271 time distribution model currently being studied in Q13/15

Figure 3/G.8271 - Example of time synchronization distributed via packet based methods

G.8271-Y.1366(12)_F03

Endapplication

Packetmasterclock

Packetmasterclock

Radio distributed PRTC, e.g., GNSS ordistribution via cables

RxPRTC limits

Time or phase synchronization distribution via cableT-BC

Time or phase synchronization distribution via radio

PRTC limits

Transportnode

Packetslaveclock

Packetslaveclock

Packetslaveclock

Transportnode

Transportnode

Endapplication

Endapplication

EndapplicationEnd

applicationEnd

application

Endapplication

Packet timingdistribution network

Packet timingdistribution network

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• Current goal of Q13/15 is to meet 1.0 us time accuracy at point D relative to UTC

Figure 4/G.8271 -Network Reference Model

Figure 5/G.8271 -Possible locations of external phase/time interfaces in a chain of Telecom Boundary Clocks

G.8271-Y.1366(12)_F04

Network time reference(e.g., GNSS engine)

A

Packetmasterclock

PRTC Packetnetwork

B C D E

Packetslaveclock

End applicationtime clock

PRTC: Primary referencetime clock

Physical timing signal (for phase and/or time synchronization)Packet timing signal

A:B:C:D:E:

PRTC network limitsPacket master clock network limitsPacket slave clock input network limitsPacket slave clock output network limits (if applicable)End application requirements (e.g., phase accuracy)

T-GM

2

T-TSC

1

T-BC

PRTC

1

1

T-BC

1 1

T-BC

1

T-BC

1

End

applicationEPON OLT + EPoC FCU + EPoC CNU => Distributed 1588 BC

MBH base station

D

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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

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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]

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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 could 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

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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).

epoc system level synchronization transport - r1a

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