EPoC System Level Synchronization Transport,...
Transcript of EPoC System Level Synchronization Transport,...
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EPoC System Level Synchronization Transport 802.3bn Evaluation Criteria Ad Hoc Call
Bill Powell 9 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 field at the OLT EPON MAC (2)
• At the ONU, the timestamp is recovered from received 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)
• 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
Counter
MAC
PHY
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)
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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
• 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 Logic
(2)
(4)
TS on MPCP Packets TS on MPCP Packets
802.1as protocol 802.1as-like protocol?
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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
1 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)
10 Gbit/s fibre optical link
1 Gbit/s fibre optical link
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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G.8271 Sync Distribution Model - Time
• 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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G.8271 Sync Distribution Model - Time
• 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 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
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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).