synchronization protection and redundancy in next-generation networks
TRANSCRIPT
Synchronization Protection & Redundancy in NG Networks June 2016Nir Laufer , Director PLMWSTS 2016
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What Can Possibly Go Wrong? • GNSS failure
• Jamming (intentional and unintentional) • Antenna breakdown (lightning, cable cut)
• Equipment failure• HW failure
• Connectivity to GM is lost • Network outage or extreme overload
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GPS “Availability Issues” Feb 2016 According to the US Air Force (USAF), which manages the GPS satellite network, problems began when a satellite named SVN 23 was decommissioned.
A USAF spokeswoman confirmed that the error had been pushed to the satellites by "ground system software".
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GPS “Availability Issues” April 2016
“North Korea is using radio waves to jam GPS navigation systems near the border regions,” South Korean officials said.
“The broadcasts have reportedly affected 110 planes and ships, and can cause mobile phones to malfunction.”
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Protection and Redundancy Options • Protection at slave/BC side – switching to a standby GM based on the
relevant Best Master Clock Algorithm (BMCA) • May results in network rearrangement• Switching between GMs may results phase transience
• Protection at master side – GM switching to secondary source in case the primary source fails
• Might prevent network rearrangement if secondary source if sufficiently good
Both options can be combined in order to achieve best protection and redundancy
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Protection G.8265.1 – Multiple Masters
T-GM#2
GNSS
PTPGrandmaster
Packet-Based Backhaul Network
T-SC
First Aggregation Node
T-GM#1
GNSS
PTPGrandmaster
• Frequency delivery • IP Unicast – end to end
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Protection G.8275.1 – Multiple Masters
T-GM
GNSS
PRTC
PTPGrandmaster
& Sync-E
BC& Sync-E
BC& Sync-E
BC& Sync-E
BC& Sync-E
BC& Sync-E
BC& Sync-E
Ethernet Multicast
T-GM
PTPGrandmaster
& Sync-E
• Phase and Frequency Delivery • Eth’ Multicast – Hop to Hop
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Distributed Architecture Using Mini-GM
T-GM
GNSS
PTPGrandmaster
Packet-Based Backhaul Network
GNSS
T-SC
T-SC
T-SCFirst Aggregation Node
Mini-GM
GM are getting closer to network edge
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Distributed GM Protection Options • What if GNSS is locally in outage (e.g. jammed )
1. Physical layer input • Sync-E • BITS • Can be a good option – but not always available
2. PTP input (APTS) • Recovering both frequency and phase• Recovering only frequency which is used for phase holdover
3. Holdover based on local oscillator • Always available• Oscillators technology has come a long way since the first quartz clock (1927)
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Short-Term Holdover
±100ns
±200ns
±250ns
±250ns
±150ns
±550ns
PRTCT-GM
Random NetworkVariation
Node Asymmetry(±50ns per node)
Link AsymmetryCompensation
Short-TermHoldover
EndApplication
±1.1µs Network Equipment Budget±1.5µs End-to-End Budget
G.8271.1 Time Error Budget Example
• E.g. temporary GNSS jamming or poor line of sight • Duration: few seconds – few hours • Holdover budget – few hundred of nsec
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Long-Term Holdover • Antenna failure (e.g. lightening) • Few hours – three days • Depend on the available time error budget – but potentially can
be more than 1500nsec
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Oscillator Types – Aging and Temperature Stability Temperature Stability
Aging/Day
≤10ppb
≤1ppb
≤0.1ppb
≤0.01ppb
≤0.001ppb
≤0.0001ppb
≤1ppb≤0.1ppb≤0.01ppb≤0.001ppb≤0.0001ppb
OCXO
HQQOCXO
Rubidium
X10 better Temperature
Stability Vs Rb
X10 better Aging Vs HQQ
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It Can Be Very Cold …
HUAWEI BS China 2008 winter storm
Telenor base station or snow creature?
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Or Very Hot …
Telenor base station or snow creature?
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And It Can Swing in Between …• The greatest temperature change in 24 hours occurred in Loma, MT.
on January 15, 1972. The temperature rose 56 degrees, from -47C (-52.6F) degrees to 9C (48.2F).
• The greatest temperature change in 12 hours happened on December 14, 1924. The temperature at Fairfield, Montana, dropped from 17C (62.6F) to -29 (-20.2) at midnight (Delta of 46C)
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Environmental Condition • Synchronization devices at the access networks are subject to
wider temperature variation!• ETSI environmental classes:
Class #
Class description Temp. change rate
Temp. change range
Delta
3.6 Control room locations 0.5°C / min [+25, +30°C] 5°C
3.1 Temp. controlled locations 0.5°C / min [+25, +40°C] 15
3.2 Partly temp. controlled locations 0.5°C / min [+25, +55°C] 303.3 Not temp. controlled locations 0.5°C / min [-5, +45°C] 504.1 Non-weatherprotected locations 0.5°C / min [-10, +40°C] 503.5 Sheltered locations 1°C / min [-40, +40°C] 80
Core
Access
Ethernet Access NE - typical operational temperature range
[-40, +65°C]
Higher temperatures are expected in other continents
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Oscillator TypesClock Type # Cost Operational
Temperature range of the clock
Typical Ambient Operational Temperature
range of the Sync Element
Temp Stability Aging/Day
OCXO Low(10%)
-40 to 85 C -40 to 65 C 1-10 ppb 1ppb
OCXO HQ Medium(100%)
-40 to 85 C -40 to 65 C 0.01 ppb 0.05 ppb
Rubidium High (300%)
-10 to +75 C -5 to +55 C 0.1 ppb 0.005 ppb
Aging seem to be the only advantage
of Rb
But aging can be
estimated with GNSS!
Rb high cost, limited operational temperature range and temperature instability make it less suitable for access
devices
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Comparing Leading Rubidium Suppliers: Clock Type # Cost Operational
Temperature range of the clock
Typical Ambient Operational Temperature
range of the Sync Element
Temp Stability
OCXO HQ Medium(100%)
-40 to 85 C -40 to 65 C 0.01 ppb
Rubidium Vendor A
(Market leader)
High (400%)
-10 to +75 C -5 to +55 C 0.1 ppb
Rubidium Vendor B
High (300%)
-30 to 65 -5 to +50 C 0.5 ppb
Rubidium Vendor C
High (300%)
-20 to 65 0 to +50 C 0.5 ppb
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Ideal Condition for Efficient Learning • Good teacher: GPS (long term accuracy is better than 1e-
12 )• No disturbances: temperature effects are isolated by
using very high quality quartz oscillator
Learn aging characteristics while
GPS available
GPS as referenceHQ oscillator
Use these characteristics while
in holdover
Combining OSC high temperature stability with GPS reference generate optimized solution in both performance and cost
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Oven
Test Setup
PRTC/GMDUT
1PPS Steered Clock Cs RefTester
1PPS
Free running Clock
TIEFFO
GPS
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Enter holdover
after locked to GPS for 2
days 2 days HQQ holdover
below 200 nsec !
Temperature effects are seen in the Rb TIE
0
2 4 6 8 10 12 14 16 xTime [sec]
0
2 4 6 8 10 12 14 16 xTime [sec]
-50
500
100150
200TI
E [n
sec]
Tem
pera
ture
[C]
252627282930
HQQ Vs Rb – Controlled Room (25-30C)
• Tested in the oven with controlled room profile • Phase holdover over 48 hours below 200nsec !
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120
HQQ Vs Rb – Temp’ Controlled Room (25-40C) Temperature effects are
seen in the Rb FFO
Temperature effects are
NOT seen in the HQQ FFO
Tem
pera
ture
[C]
25
30
35
40
0 20 40
Time [Hours]
60 80 100 120
0 20 40Time [Hours]
100
xFF
O
-0.50
0.511.52
2.53
12060 80
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HQQ Vs Rb – Temp’ Controlled Room (25-40C) Temperature effects are seen
in the Rb TIE
Enter holdoverafter locked to GPS
for 2 days 2 days HQQ holdover
below 1800nsec !
2 days Rb holdover are above 13500
nsec !
0 20 40Time [Hours]
60 80 100 120x
TIE
[nse
c]
-2000
02000
4000
6000
8000
100001200014000
16000
18000
Tem
pera
ture
[C]
25
30
35
40
0 20 40
Time [Hours]
60 80 100 120
Temperature effects are NOT seen in the HQQ TIE
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HQQ Vs Rb – Temp’ Controlled Room (25-40C)
Rb fails PRC G.811 mask
during holdover
HQQ meets PRC G.811
mask during holdover
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Best Rb Supplier Tested at 35-50C Te
mpe
ratu
re [C
]
35
40
45
50
0.1ppb pk2pk – worst case TE of 360nsec/hour!
FFO
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HQQ Holdover at +/- 20C (0-40C)
Enter holdover
24 Hours500ns
• Tested in the oven with temperature profile +/- 20C• Phase holdover over 24 hours below 500nsec !
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• Better operational temperature range and stability – guarantee better performance in the field
• Cost Effective Solution – ~one third of the cost • Superior holdover performance with the aging learning algorithm enabled for high
quality oscillator
Advantages of the High Quartz Oscillator Over Rubidium
400nsec 1.1usec 1.5usec 5usec 10usec
HQ Oscillator 15 hours ~1.3 days 2 days 4 days 6 days
Rubidium benchmark NA NA 1 day 3 days 5 days
Thank You!
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