At the NPL and BT webinar, Nir Laufer discussed timing for telecom networks. Providing an overview of Oscilloquartz's industry-leading portfolio of synchronization solutions, the presentation discussed new optical timing channel technology.

1. Optical timing channel (OTC):
Delivering sub-50ns over long-distance commercial WDM
networks
Nir Laufer, senior director, product line management, Oscilloquartz, ADVA
September 2020

2. © 2020 ADVA. All rights reserved.22
Oscilloquartz (OSA) at a glance
Innovation leader for timing distribution and assurance
• An ADVA company
• Focused on offering sync solutions for communications, government and
enterprise applications
• Longstanding relationship with customers worldwide since 1949!
• Around 100 sync-focused partners in about 80 countries around the globe
• State-of-the-art, end-to-end time, phase and frequency solutions
• Excellence in timing delivery and assurance

3. © 2020 ADVA. All rights reserved.33
Common synchronization challenges – sub-1usec
Mobile radio networks
1.1usec, 260nsec relative
Financial trading 1usec
Regulation (MIFID II), HFT
Power utilities
1usec – PMU, fault location
Data center infrastructure
1usec
Broadcast networks
1usec
How to make sync
delivery more accurate
and more resilient

4. © 2020 ADVA. All rights reserved.44
GNSS vulnerabilities and threats
GNSS for
timing
Jamming and
spoofing
Obstruction
Interference with
transmitters at
adjacent bands
Atmospheric
disturbance, solar
activity
GNSS segment errors

5. © 2020 ADVA. All rights reserved.55
Application area for OTC: aggregation network
Core time base network
Single-digit number of locations
for large operator
ePRTC-enabled, TE ≤ ±30ns
Aggregation network
Hundreds of locations for large
operator
PRTC-enabled, TE ≤ ±100ns
Feeders to end application
Thousands of locations for large
operator
TE ≤ ±1100ns
Optical timing
channel
Optical timing
channel
70ns budget
ePRTC

6. © 2020 ADVA. All rights reserved.66
Core time base sites – ePRTC
GNSS
Receiver
Clock
Combiner PPS/PPS+ToD
OSA 3230B ePRC cesium
clock
GNSS antennas
OSA 5440
10MHz
BITS
SyncE
PTP
NTP
Clock
combiner
GNSS
receiver
OSA 3350 ePRC+ cesium
clock
Carrier-grade,
fully redundant
HW
Multi-band, multi-
constellation GNSS
PTP+SyncE
Backup from
peer site
Peer core site
ePRTC with
cesium
backups
OSA 5405
Smart antenna
Syncjack and
GNSS
assurance
Advanced
jamming and
spoofing
detection

7. © 2020 ADVA. All rights reserved.77
OTC
Timing over ... Asymmetry is the biggest challenge!
Timing over ...
Optimization
methods
Time
error
Layer 3
(routed)
Small packet size
High
(ms/µs)
Layer 2
(switched)
VLAN with high
priority
Middle
(µs)
Layer 1
(OTN)
OTN buffer policing
or in-band
transmission
Low
(µs/ns)
Layer 1
(transparent
WDM)
Single fiber working
Lowest
(ns)
Asymmetry

8. © 2020 ADVA. All rights reserved.88
Timing device
OTC regen
ILA
ROADM
Terminal
Cross-connect
Terminal/ADM card
Optical timing channel (OTC)
The optical timing channel (OTC) achieves
high-accuracy time distribution by
PTP (IEEE 1588) via Gigabit Ethernet
over dedicated wavelengths on a single fiber
OTC has minimal constant link asymmetry
due to bidirectional transmission on a single
fiber; further compensation is supported
OTC is independent from other layers
(IP, Ethernet, OTN, reconfigurable optical layer)
practically eliminating dynamic time errors
OTC does not change optical network
engineering rules and is just an overbuild to
the optical transport layer

9. © 2020 ADVA. All rights reserved.99
OpticallinesystemIntermediatesite
Node with timing access
Terminal west Terminal east
PTP over optical timing channel
Payload traffic
Timing device featuring
High-accuracy PTP
boundary clock type D
BiDi transceivers
OTC provides ample optical budget:
up to 30dB between two BiDi transceivers
Dispersion is irrelevant at GbE line rate
Line terminal

10. © 2020 ADVA. All rights reserved.1010
Impact of chromatic dispersion can be efficiently compensated
Same east-west wavelength
Asymmetric delay results in a deterministic time error
Chromatic dispersion creates asymmetric delay
100km of fiber with
dispersion of18ps/(nm km)
l1 = 1.605µm
l2 = 1.615µm
𝑐𝑇𝐸 ≈
100𝑘𝑚
2
10𝑛𝑚
18𝑝𝑠
𝑛𝑚 𝑘𝑚
= 9000𝑝𝑠 = 9𝑛𝑠
85km 65km70km 82km
Time error from chromatic dispersion: 27.2ns
Constant and
deterministic

11. © 2020 ADVA. All rights reserved.1111
50km_aOSC OSCOSC OSC OSC
Paragon Neo
OSA 5430 5WCAOTC
Patch-through
Master port Slave port
OSC
OTC accuracy measurment
3GU/1605LGBE/1615V 3GU/1605L
SFP/GBE/1605V
GBE/1615V GBE/1615V
MALPB-OSC-C MTP-OSC-C MTPB-OSC-C MTPB-OSC-C MTP-OSC-C MTPB-OSC-C
50km_b 65km_a 65km_b
OSA 5421
GBE/1310
GBE/1310
210 cm
𝑐𝑇𝐸 ≈
100𝑘𝑚
2
∗ −10𝑛𝑚
18𝑝𝑠
𝑛𝑚 𝑘𝑚
= − 9000𝑝𝑠 = − 9𝑛𝑠
𝑐𝑇𝐸 ≈
130𝑘𝑚
2
∗ −10𝑛𝑚
18𝑝𝑠
𝑛𝑚 𝑘𝑚
= 11700𝑝𝑠 = −11.7𝑛𝑠
TE within
15nsec

12. © 2020 ADVA. All rights reserved.1212
PTP
GM/BC type D / slave
NTP
server
SSUePRTC Sync probe
G.8265.1 EnterpriseG.8275.2 G.8275.1
2G/3G/
4G/5G
FDD BS
DOCSIS 3.1 MIFID ii
5G-NR/LTE
TDD/LTE-A BS
NTP61850-9-3/
C37.238
Smart grid
OSA 54XX – Synchronization “Swiss Army knife“
OSA 542X OSA 5430
OSA 5440

13. © 2020 ADVA. All rights reserved.1313
The challenge – transmission asymmetry
PTP (IEEE 1588) recovered time is affected by network asymmetry:
1) Forward and backward paths use different fibers and therefore have different lengths
(constant time error about 2.5ns/m)
2) Dynamically changing intermediate (Ethernet) processing on the paths
3) Forward and backward transmission use the same fiber but slightly different
wavelengths
(minor constant time error due to dispersion of about 0.09ns per km)
OTC eliminates (1) – (2).
The error according to (3) is small and constant and can be compensated

14. © 2020 ADVA. All rights reserved.1414
Two CWDM slots per bidirectional channel
Standard transceivers have two fiber
connectors (TX and RX)
One CWDM slot per bidirectional channel
BiDi transceivers have one fiber connector
with TX and RX pre-multiplexed in the
transceiver
BiDi transceiversStandard transceivers
Running on the same fiber, forward and backward paths
have exactly the same length; there is only marginal asymmetric delay
BiDi transceivers
CWDM
Slot
TX
CWDM
Slot
RX
CWDM
Slot
TX RX
OTC

15. Thank you
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nlaufer@adva.com