Contenu connexe Similaire à Sub-100ns accuracy at cell sites over commercial WDM networks (20) Sub-100ns accuracy at cell sites over commercial WDM networks1. Sub-100ns accuracy at cell sites over
commercial WDM networks
Nir Laufer, senior director, PLM, Oscilloquartz, ADVA
ITSF Nov 2020
2. © 2020 ADVA. All rights reserved.22
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?
3. © 2020 ADVA. All rights reserved.33
GNSS vulnerabilities and threats
GNSS for
timing
Jamming and
spoofing
Obstruction
Interference with
transmitters at
adjacent bands
Ionospheric
disturbance, solar
activity
GNSS segment errors
4. © 2020 ADVA. All rights reserved.44
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
?
30ns budget
5. © 2020 ADVA. All rights reserved.55
Core time base sites - ePRTC
GNSS
Receiver
Clock
Combiner PPS/PPS+ToD
GNSS antennas
Core redundent grandmaster
10 Mhz
BITS
Sync-E
PTP
NTP
Clock
combiner
GNSS
receiver
Carrier-grade
fully redundant
HW
Multi band, multi
constellation
GNSS
PTP+SyncE
Backup from
peer site
Peer core site
ePRTC with
cesium
backups
Smart antenna
Sync and GNSS
assurance
Advanced
jamming and
spoofing
detection
ePRTC
ePRC
cesium
clock
ePRC
cesium
clock
6. © 2020 ADVA. All rights reserved.66
WDM over long-distance routes
Typically long-distance WDM networks use C-band due to low attenuation
The “data” channels are sent over fiber pairs (RX/TX)
7. © 2020 ADVA. All rights reserved.77
OTC
Timing over ...
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 inband
transmission
Low
(µs/ns)
Layer 1
(transparent
WDM)
Single fiber working
Lowest
(ns)
Asymmetry
8. © 2020 ADVA. All rights reserved.88
OpticallinesystemIntermediatesiteNode without timing access
Terminal west Terminal east
Payload traffic
Line terminal
The extract length of each of
the fibers is unknown
The different between length of fibers can be a few
tens of meters over long-distance connections ->
creating significant asymmetry (~2.5nsec/m)
The inline amplifiers are
directional and add unknown
delay which varies between
generation of amplifiers,
types and suppliers
9. © 2020 ADVA. All rights reserved.99
Calibration of asymmetry with GNSS
Calibration with using GNSS is not sufficient
• One possible solution is to use GNSS on both sides of the link in order to
compensate the asymmetry
• GNSS might not be sufficiently accurate (typically ~ 40-100nsec)
• Installing GNSS antenna in a remote site might be challenging (e.g., indoor)
• Increase installation costs
• Initial calibration may not be valid when changes are made in the network
(replacing amplifier, fixing fiber, etc.)
Terminal TerminalROADM ROADM
GNSS
Master Probe
GNSS
10. © 2020 ADVA. All rights reserved.1010
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
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
11. © 2020 ADVA. All rights reserved.1111
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
12. © 2020 ADVA. All rights reserved.1212
OpticallinesystemIntermediatesite
Node with timing access
redundant OTC
Terminal west Terminal east
PTP over
optical timing channel
Anticlockwise
PTP over Optical Timing Channel
Clockwise
Two redundant
OTCs running on
two fibers
OTC
Regen
T-BC
T-BC
T-GM T-GM
Timing is handed over two
OTC. Best master clock
algorithm of client
equipment decides which
one to use.
Both OTCs are active all the
time thus avoiding
rearrangement transients
T-BC
T-BC
Redundant BC (type D)
13. © 2020 ADVA. All rights reserved.1313
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 of 18ps/(nm km)
l1 = 1.605µm
l2 = 1.615µm
𝑐𝑇𝐸 ≈
100𝑘𝑚
2
10𝑛𝑚
18𝑝𝑠
𝑛𝑚 𝑘𝑚
= 9000𝑝𝑠 = 9𝑛𝑠
50km 65km50km 65km
Time error from chromatic dispersion: 19ns
Constant and
deterministic
14. © 2020 ADVA. All rights reserved.1414
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| within15nsec. |cTE| within 5nsec.
Known (fixed)
asymmetry is
configured
on the BC
port
15. Thank you
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