Download Submarine to terrestrial networks

Submarine to terrestrial
networks
Integration with the Nokia 1830 PSS
Technical white paper
With recent enhancements in high-speed optics and advanced modulation
techniques, fiber optic systems used on terrestrial networks have caught up
with, and in many cases surpassed, the capabilities of submarine-specific
versions. Standard, terrestrial wave-division multiplexing (WDM) systems now
have the capability to operate directly over submarine networks, resulting
in significant cost savings. In addition, integrating terrestrial and submarine
networks enables reductions in equipment costs, space and power. This paper
discusses several new enhancements to the Nokia 1830 Photonic Service Switch
(PSS) that support submarine to terrestrial integration.
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Technical white paper
Submarine to terrestrial networks
Contents
Introduction
3
Traditional transponder boundaries
3
Nokia submarine to terrestrial integration
4
Conclusion7
Acronyms
2
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Technical white paper
Submarine to terrestrial networks
Introduction
Fiber optic submarine networks enable incredible advancements in global
communication services. Undersea networks provide seamless voice, highspeed data and video connections anywhere in the world, uniting businesses
and people across the planet.
Traditionally, submarine networks were constructed using custom-designed
systems for each undersea project, incorporating the latest technology
and performance advancements. The cost of these custom-built systems
was rationalized as necessary for networks spanning 4,000–8,000 km and
transporting up to 800G capacity. These specialized submarine networks
are justified by the tremendous capacity provided and the economic
value enabled.
With recent enhancements in high-speed optics and advanced modulation
techniques, fiber optic systems used on terrestrial networks have caught up
with, and in many cases surpassed, the capabilities of submarine-specific
versions. Standard terrestrial wave-division multiplexing (WDM) systems now
have the capability to operate directly over submarine networks, resulting
in significant cost savings. In addition, integrating terrestrial and submarine
networks enables reductions in equipment costs, space and power.
This paper discusses several new enhancements to the Nokia 1830 Photonic
Service Switch (PSS) to support submarine to terrestrial integration.
Traditional transponder boundaries
Submarine networks are constructed of undersea in-line amplifiers, referred
to as repeaters, on the “wet link” and submarine line terminating equipment
(SLTE) nodes deployed at the endpoints. As submarine cables are brought
onshore, they terminate at telecommunications buildings known as cable
landing stations, which house the SLTE nodes as well as additional equipment
to provide electrical power and network management.
Cable landing stations are typically located within a short distance from where the
undersea cable comes ashore, and they provide the first termination point for the
submarine network. Most cable landing points are in somewhat remote locations,
so terrestrial WDM networks are deployed to connect the landing station to the
nearest metro point of presence (POP) office, often 40–200 km away.
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Submarine to terrestrial networks
Unfortunately, each network segment utilizes a separate WDM system
with back-to back-transponders (O-E-O) at the interconnection points
(see Figure 1).
Figure 1. Typical submarine to terrestrial network
Submarine
wet link
Cable landing station
Metro POP
Longhaul
network
SLTE
WDM
WDM
Transponders
WDM
Transponders
Back-to-back transponders
Nokia submarine to terrestrial integration
Integrating terrestrial WDM nodes with the submarine wet link eliminates the
specialized SLTE nodes and also eliminates the back-to-back transponders
and terminals used to interconnect the cable landing station to the closest
metro POP (see Figure 2).
In some countries, termination of the submarine services at cable landing
stations is required by country-specific regulatory requirements. Where
permitted, eliminating the back-to-back transponders at multiple junction
points can save millions of dollars and also significantly reduce power
consumption and space requirements.
Figure 2. Nokia submarine terrestrial integration
Submarine
wet link
Cable landing station
Metro POP
Longhaul
network
1830 PSS
1830 PSS
Transponders
Comparing submarine termination and backhaul methods highlights the
potential cost, space and power savings with terrestrial integration. A network
model consisting of 60 x 100G channels compared a traditional submarine
terminated network with corresponding WDM backhaul to the metro POP, as
shown in Figure 1, to a terrestrial integrated network, as shown in Figure 2.
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Utilizing a terrestrial integrated network reduces the number of WDM nodes
from four to two and eliminates the costly and inefficient back-to-back
transponders. Of the 60 wavelengths from the submarine network, the study
estimated 30 channels terminating at the backbone POP for connection
to other systems and 30 channels passing through onto the long-haul
network. The vast majority of savings result from eliminating back-to-back
transponders at the multiple interconnection points.
Figure 3 shows the significant cost, space and power savings enabled by
the Nokia integration.
Figure 3. Cost, space and power savings with Nokia integration
1.2
Price
Space
Power
1.0
0.8
78%
0.6
72%
72%
0.4
0.2
0
Submarine traditional
Submarine terrestrial integrated
Line loading
One of the key technologies enabling the integration of submarine networks
with terrestrial networks is line loading on unused channels. Submarine
networks operate with optical power transmitted on all channels. On unused
channels, optical noise power is transmitted in place of real, traffic-bearing
signals and is commonly referred to as “dummy light.” The dummy light fills all
unused wavelengths, ensuring the system operates with constant optical power.
Operating amplifiers in constant power mode improves the Optical Signal
to Noise Ratio (OSNR) and overall network performance, resulting in longer
optical reaches, which is critical when crossing 4,000–9,000 km of ocean.
In addition, operating in constant power mode simplifies the design of the
underwater repeaters, improving reliability.
Nokia developed a line loading unit for the 1830 PSS WDM system to support
direct integration to submarine networks. In addition to providing the dummy
light on all unused channels, the 1830 PSS line loading unit provides transient
suppression to reduce terrestrial network transients propagating over the
submarine wet link portion of the network (see Figure 4).
On terrestrial networks, optical transients occur as channels are added or
dropped on the network, either due to normal provision of services or due
to unexpected fiber cuts. The 1830 PSS terrestrial nodes are designed to
minimize network transients by rapidly adjusting the amplifier operating points.
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The 1830 PSS line loading unit further reduces these transients with perchannel power monitoring of both the inputs and outputs and automatic
adjustment of the optical dummy light power levels resulting from any
transient fluctuations.
The key line loading features are:
• Dummy light optical noise power on all unused channels
• Automatic, per-channel power monitoring and transient suppression
• Support for connection of additional multi-vendor systems
Figure 4. 1830 PSS line loading unit
Dummy light
Capacity upgrades
Due to the high cost of constructing new submarine networks, many carriers
upgrade existing submarine capacity by moving from 10G rates to 100G
per wavelength. Until recently, 100G optical rates were difficult to transmit
over the ultra-long haul distances (2,000–8,000 km) of most submarine
applications. Recent advancements in optical modulation formats are yielding
up to 60 percent longer optical reach with 100G coherent signals, allowing
100G wavelengths to be deployed over most submarine applications.
Traditionally, the industry has relied on Polarization Division Multiplexing
Quadrature Phase Shift Keying (PDM-QPSK) modulation for 100G coherent
signals along with Soft Decision Forward Error Correction (SD-FEC). These two
functions of modulation (optical layer) and error correction (electrical layer)
were separate functions.
New, advanced coded modulation techniques have been developed that improve
error performance of the optical symbols in the optical domain. The new coded,
optical modulation technique is called 100G Set Partition-QPSK (SP-QPSK).
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When combined with stronger, ultra SD-FEC algorithms, SP-QPSK can result
in significantly longer optical reach for 100G signals, suitable for use on most
submarine networks (see Figure 5).
Nokia is the industry leader with the first available 100G coherent optics
offering SP-QPSK as one of the provisioning options on the D5X500 500G
muxponder unit.
Figure 5. Performance improvements with 100G SP-QPSK
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Q factor (dB)
12
10
8
6
4
6
8
10
12
14
16
18
20
Number of loops (x 400 km)
43 Gbd 4D-SP-QPSK
32.5 Gbd SP-QPSK
Conclusion
With recent advancements in 100G coherent optics, terrestrial WDM systems
have caught up with, and in many cases surpassed, the performance of
specialized submarine terminals (SLTE). Carriers can take advantage of
significant cost savings by deploying terrestrial WDM systems at submarine
landing points and integrating those nodes directly with existing terrestrial
backbone networks, resulting in substantial cost, space and power savings.
New features, such as the Nokia 1830 PSS line loading unit and enhanced
100G coded modulation, enable ultra-long haul distances for submarine
applications.
Learn more about the Nokia 1830 PSS at:
http://networks.nokia.com/portfolio/products/1830-photonic-service-switch
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Acronyms
FEC
Forward Error Correction
O-E-O
optical-to electrical-to optical
PDM
Polarization Division Multiplexing
POP
point of presence
PSS
Nokia 1830 Photonic Service Switch
QPSK
Quadrature Phase Shift Keying
ROADM
reconfigurable optical add-drop multiplexer
SD-FEC
Soft Decision Forward Error Correction
SLTE
submarine line terminating equipment
SP-QPSK
Set Partition Quadrature Phase Shift Keying
WDM
wavelength division multiplexing
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