- The document discusses business cases for new submarine cable and terrestrial fiber optic builds in Africa. It outlines the key components and design considerations for submarine cable systems, including repeaters, branching units, power feeding equipment, and cable armor. Challenges for submarine systems include high costs, difficulty of repairs, and reliability requirements. - Technological evolution, such as higher modulation formats and improved error correction, can increase submarine cable capacity over time to reduce costs. Terrestrial fiber may provide restoration alternatives and backhaul capacity for inland regions. The future requires maximizing capacity per fiber through longer spans, modular designs, and more efficient power systems.

1. © 2016 Xtera Communications, Inc. Proprietary & Confidential 1
Business Case for New SubSea and
Terrestrial Builds in Africa
Robert J Richardson
Xtera Communications
2-3 February 2016
NGON Africa 2016
Cape Town, South Africa

2. © 2016 Xtera Communications, Inc. Proprietary & Confidential 2
• Submarine system
• Technology evolution
• Can new terrestrial connectivity offer restoration alternatives to subsea
cable systems
• Challenges for the future
Business Case for New SubSea and
Terrestrial Builds in Africa

3. © 2016 Xtera Communications, Inc. Proprietary & Confidential 3
Not needed
if short enough
• SLTE Submarine Line Terminating Equipment
Specialised DWDM terminal
• PFE Power Feed Equipment
High voltage to feed long spans
• Repeater Protects Amplifier-pairs
• Cable Protects fibers
Provides power path
• BU Branching Unit
Routes fibers or wavelengths
• Marine Survey, installation, maintenance
What’s in a Submarine System?
Rep Rep Rep BU Rep
SLTE
SLTE
SLTE
SLTE
PFE

4. © 2016 Xtera Communications, Inc. Proprietary & Confidential 4
• More expensive than terrestrial!
• Targets longer spans
• Needs to withstand: water pressure
corrosion
anchors, fishing vessels
high-voltages
• Very high reliability repairs are difficult, expensive, take time
and cause outage on all fiber pairs
• Similar technology to terrestrial, but some important differences
What’s different? Submarine/Terrestrial

5. © 2016 Xtera Communications, Inc. Proprietary & Confidential 5
1 Command / response
– Access one repeater at a time
– Fast response
2 Loopback
– Use probe signal and get returns from all
amplifiers
– Signal average to get loop losses
– Simpler, but less information
Terminal Equipment and Submarine
monitoring
Rep Rep Rep

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• PFEs at each end for security – voltages up to 15,000 V
• Return current flows to ground – dedicated connection
• Tolerates shunt fault – cable insulation broken, fibers intact
creates a local ground connection
• PFE voltage adjusts automatically
• Reliability is critical – failure affects all traffic
Power Feeding
repeaters repeaters
PFE
repeaters
PFE
PFE
PFE

7. © 2016 Xtera Communications, Inc. Proprietary & Confidential 7
Repeater
Cable
Termination
Housing
Flexible
joint
Buffer
High reliability design with multiple pumps

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• Routes fibers
• Routes wavelengths
• Remote
box
Flexible
Better
sparing
Branching Unit
Filters
Fibres
Power
BU

9. © 2016 Xtera Communications, Inc. Proprietary & Confidential 9
• Several variants
– LW Light Weight
– LWP Light Weight Protected (includes aluminum tape)
– SA Single Armored
– DA Double Armored (shown below)
– ...
• Fibers protected in central steel tube
• Tensile wires form protective cage
• Seam-welded copper tube blocks hydrogen
• Polyethylene (high-voltage) insulation
• Repeaterless cable uses smaller diameter,
carbon-loaded polyethylene
Smaller, slightly cheaper
Cable for Repeatered Systems

10. © 2016 Xtera Communications, Inc. Proprietary & Confidential 10
• Survey to find best cable route
– Desktop
– Marine
• Install with correct vessel
– Clear route
– Lay cable
– Post lay inspection
– May include cable burial
– Shore ends
beach trench and manhole
articulated pipes
...
The Marine Element

11. © 2016 Xtera Communications, Inc. Proprietary & Confidential 11
• Industry standard typical numbers
• Shallow (<1000 m) repairs: 0.5 dB every 20 km
• Deep (>1000 m) repairs: 3.0 dB every 1000 km
• Fiber ageing: 0.005 dB/km
• Pump failures: 1 failure in 5% of amplifiers
at End Of Life
Depth Profile / Repairs / Ageing
-6000
-5000
-4000
-3000
-2000
-1000
0
0 200 400 600 800 1000 1200 1400
Depth (m) v. Length (km)Dania Beach GTMO
Depth (m)
A B
Burial limit

12. © 2016 Xtera Communications, Inc. Proprietary & Confidential 12
• More capacity = more repeaters (or more fiber pairs) = more cost
• Wider bandwidth repeaters = more capacity
• Technology evolution must be considered as alternative to initial CapEx
• System design
– Repeater spacing to maximize capacity & enable deployment of new
technology
– Optimize system powering design
– System architecture
• Open Line System (OLS) design
• Unrepeatered or OADM branches, where possible
– Power budget
• Optimize route design to minimize “OpEx”
– Direct routes
– Cable protection
– Deep water
Submarine System Cost / Capacity
Optimize capacity vs cost balance to maximize return
on “CapEx Investment”

13. © 2016 Xtera Communications, Inc. Proprietary & Confidential 13
Evolution

14. © 2016 Xtera Communications, Inc. Proprietary & Confidential 14
SubSea Network Evolution Example
Initial design: 1 x 2.5G
Upgrade with 100G technology: 4 x 100G  a 60 increase in capacity
Americas I North & Columbus 2B deployed in 1994

15. © 2016 Xtera Communications, Inc. Proprietary & Confidential 15
History
• WDM 4 to 100 wavelengths ...
• Line-rate 2.5, 10, 40, 100, 400 Gbit/s per fiber (2 WLs)...
• Networks Point-to-point , festoons, rings, multiple BUs...
Enablers
• Better optical filters
• More bandwidth and power in amplifiers – more fibers?
• Forward Error Correction (FEC)
• Coherent detection + Digital Signal Processing (DSP)
– More sensitivity + electronic dispersion compensation
– Support for multiple formats (e.g. QPSK, 8QAM, 16QAM)
• Multi-level modulation schemes
• ... More advanced repeaters?
Evolution (= More Capacity)

16. © 2016 Xtera Communications, Inc. Proprietary & Confidential 16
Q limit dB
1. No FEC 17
2. Soft decision FEC 5.5 (Second generation)
• Rapid progress, but now nearing the limit set by Shannon’s law
Improved FEC
5 FEC overhead (%)
Hard-decision
theoretical limit
10 15 20 25 30
5
6
7
8
9
10
11
Netcodinggain(dB)
12
13
Soft-decision decoding
RS (239,255)

17. © 2016 Xtera Communications, Inc. Proprietary & Confidential 17
Benefit of Different Modulation Formats
QPSK 16 QAM
7 dB 10 dB
2 bit/symbol
100G
3 bit/symbol
150G/300G
4 bit/symbol
200G/400G
More power / OSNR than BPSK
BPSK
1 bit/symbol
100G
3 dB0 dB
8 QAM
0
1
2
3
4
5
6
7
8
BPSK QPSK 8QAM 16QAM 32QAM 64QAM
Power per bit
Higher line-rates need
significantly higher OSNR

18. © 2016 Xtera Communications, Inc. Proprietary & Confidential 18
• QPSK
• 16QAM +7 dB OSNR
2x capacity
• QPSK More bandwidth
2x capacity
+3 dB repeater power
• Bandwidth: the better solution for difficult systems
Higher Level Modulation or More
Bandwidth?

19. © 2016 Xtera Communications, Inc. Proprietary & Confidential 19
Terrestrial Systems as Restorations
Alternatives for SubSea Systems

20. © 2016 Xtera Communications, Inc. Proprietary & Confidential 20
• To backhaul traffic to land-locked countries
and inland PoPs / DCs
• To offer restoration
alternatives for
subsea cable
systems
Need For More Light Into Africa

21. © 2016 Xtera Communications, Inc. Proprietary & Confidential 21
January 2016:
• Three subsea cable cuts
off Alexandria
• Cuts on two independent
terrestrial segments
across Egypt
 74% of internet
connectivity lost in Gulf
countries, and 100% in
South Africa for few hours
Need For More Diversity

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Direct PoP to PoP
• Traditional
• Better?
• Eliminates two TTEs
• Needs ILAs compatible with submarine amplifiers
• Needs good terrestrial protection scheme
Integrating the Terrestrial Part
SLTE TTE TTE
SLTEAMP

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Protected Backhaul
CLS
DC
ROADM
68.2km
68km 83km 70km80km 75km 45km 63km 53km 77km 60km 69km 92km
51km
66km
37km80km66km49km91km50km64km74km75km65km70km63km
75km
Working
Protect
ILA
73km
DC

24. © 2016 Xtera Communications, Inc. Proprietary & Confidential 24
Challenges for Future

25. © 2016 Xtera Communications, Inc. Proprietary & Confidential 25
OBJECTIVE
• Maximum capacity per fiber
80 nm = 25/50T
• Longer spans
• More pairs with modest capacity
• Other features
– Environmental sensors
– Turn-down unused pairs
– …
• Anything else?
• Faster implementation
POTENTIAL ISSUE
• Will need extra pumps
More power
• Lower loss, more Raman gain
• Takes space in housing
– Complex mechanics
– How does one monitor?
SOLUTION
• More compact design
• More efficient powering
Possible scheme
• More modular system design
Next Gen System: Which Technology
Will Enable the Next Step?

26. 26
Any Questions?
Thank you for listening