Optical Network Evolution The first and second generation of optical systems were single wavelength systems where all switching and other higher order network functions were done in electronic equipment. Examples of typical first and sec-ond generation optical systems are the PDH and SDH networks deployed in Europe and SONET networks deployed in North America.

The third generation came with the introduc-tion of WDM technology using fixed/static filters enabling optical bypass. All traffic no longer needed to pass through an electronic switch fabric to enable local add/drop. This could now be achieved in the optical domain.

The introduction of ROADM technology represents the fourth generation where opti-cal wavelengths can be dynamically switched within an optical network.

Service providers have many new revenue opportunities now as IT and networking increasingly merge. New high bandwidth networked multimedia applications, services and video content are changing the way we live our business and personal lives. But despite the revenue potential these services create, they generate far more traffic at less revenue per bit, while increasing operational challenges. Service providers will need to attain new levels of operational efficiency if they are to maintain and grow their profitability.

WDM and ROADM technology, planning tools and network management software are tightly integrated in Transmode’s Flexible Optical Network to simplify the entire life cycle of planning, provisioning, commissioning, monitoring and troubleshooting the network. It gives operators an intuitive and flexible view and complete control of network resources and services that they need, and enables remote provisioning and automation to streamline operations.

Transmode’s Flexible Optical Networks4th generation optical networks provide the most cost efficient and flexible way of delivering new and existing transport services

The Transmode Flexible Optical Network leverages a design that is the product of Transmode’s extensive experience building WDM and ROADM networks around the globe. Based on the state of the art in proven commercially viable ROADM technology, it incorporates innovative concepts in planning and management tool design and automation.

The Transmode Flexible Optical Network enables service operators to reduce time to market, simplify planning and management, and leverage automation to streamline operations.

The result: an unprecedented level of operational efficiency and flexibility that enables service providers to overcome cost challenges, grow revenues, and ensure future profitability.

This Application Note describes the changing market environment, the new opportunities and challenges that this environment creates for service operators and how Transmode’s Flexible Optical Network creates unprecedented operational efficiency in the network to ensure a bright future for service providers.

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Transmode’s Flexible Optical Networks provide key functionality for cost efficient & flexible handling and management of wavelengths in an optical network.

Application Note

Challenges to profitability demand a new operations modelThe telecoms networking business is undergoing a rapid transformation. A wide variety of new bandwidth-intensive applications and services are driving many of the revenue opportunities that service operators must increasingly rely on for growth. A phenomenal number of new applications are already changing the way consumers interact with their world, and such applications also change the way an increasingly mobile work force does its job. This new environment creates many new challenges to the service operators’ operations model in addition to the revenue opportunity.

The figure below illustrates the kind of changes in network utilization patterns that a service provider might encounter during a day, comparing a view of past years to a more recent scenario. Note that spikes in bandwidth demand have increased and peak-to-average traffic ratio has soared, and more traffic is being generated at all hours of the day.

Fig 1. Typical bandwidth utilization during a day – before and now. Bandwidth in general has increased over time, but traffic peaks have increased even more resulting in higher peak-to-average traffic ratio.

Bandwidth demand, scalability challenges, and unpredictable traf-fic patterns are not the only problems associated with the rapid growth in high bandwidth multimedia services. As businesses and consumers increasingly rely on the network, they demand shorter provisioning intervals, and their patience with service degradation or “down time” has decreased dramatically due to the rising cost of such events. These costs have also created some demand for temporary network services to maintain operations during office

construction or moves, services that can be difficult to support at the pricing and within the timeframes that enterprise customers want. The desire to leverage the network for real-time marketing wherever and whenever large crowds gather has even begun to create a bit of demand for event-based services, which can be very difficult to offer profitably.

So the good news is that there is very strong demand for a variety of new services that have an increasing reliance on the network, giving service operators many new revenue streams while allow-ing them to diversify their service portfolios. The bad news is that although these new services are driving growth for operators, they not only generate far less revenue per bit, but are also placing extreme new demands on planning, network performance and availability, bandwidth resources, and the complexity and cost of operations.

Operators have two scenarios to contemplate. They can either try to accommodate the demand for new bandwidth hungry services with the current cost model and suffer the consequences, or find a new way to maximize operational efficiency to cut cost per man-aged bit to the level required to make these new high bandwidth services profitable – as shown in figure 2.

Fig 2. The impact of operational efficiency on making high bandwidth services profitable.

Here is the dilemma. Operators must offer new services unless they are happy with the stagnating margins and increasing com-moditization of legacy revenue streams. On the other hand, they cannot afford to offer new services if they do not find a way to offer them profitably. Simply lowering prices without changing network costs dramatically is untenable. Is there an answer?

The need for more flexible optical networksThere is an answer: operators need more flexible optical networks. The changes in the market environment are causing the traditional business model to break if service operators rely on historic operations procedures. An innovative new model that redefines the benchmark of operational efficiency is needed in order to make new revenue opportunities profitable. Static networks cannot be used to attain that goal. A new approach to operations that is more simple, flexible, and agile is required. Making that flexible and agile network a reality requires integrating planning with management oversight and control of the network, eliminating redundant efforts, and leveraging automation wherever possible to streamline operations.

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Application Note

WDM provides a multi-service carrier that separates services onto wavelengths to ensure simplicity and manageability. And WDM aggregation rings are preferable to creating cascaded chains of Ethernet switches, which invariably creates undesirable dependencies. WDM is also very effective network wide, offers a smooth upgrade path and can be Layer 2 aware. Making upgrades to the network to bring WDM connectivity direct to the bottleneck node in the access network can alleviate network congestion, and channel upgrades can add capacity as needed. WDM also has advantages in scalability and security. Thanks to recent advances in ROADM technology, WDM has also become the best technology on which to base a more flexible optical network that will help operators reduced operations costs and profitably offer new services.

Introducing Transmode’s Flexible Optical NetworksHow can service operators build a flexible optical network with the kind of flexibility, operational efficiency, and simplicity they need? By using Transmode’s Flexible Optical Network solutions! Based on an innovative approach that leverages the state of the art in commercially viable WDM and ROADM technologies, Transmode’s Flexible Optical Network incorporates intuitive planning and management systems that are tightly integrated with efficient planning tools, a complete suite of cost optimized ROADM technologies and other innovative optical components. Based on Transmode’s extensive experience designing and building a large installed base of WDM and ROADM systems in many countries around the globe, Transmode’s Flexible Optical Network gives operators the levels of operational efficiency they need to survive and thrive in the rapidly evolving services market.

Designed from the ground up to provide comprehensive, flexible and granular control of the network throughout the entire life cycle process, the Transmode Flexible Optical Network sets a new benchmark for simplicity in operations by making the planning and management of the network a highly intuitive, integrated, and automated process. This creates a whole new level of efficiency that directly translates into minimizing operators’ costs, building new revenues, enhancing competitive position, and maximizing profitability-a future proof solution leveraging proven technology.

ROADM applications ROADMs are used in bus and ring networks to give operators flexible add/drop and hitless upgrade capability. But they can also be used in a meshed network to provide full flexibility to route wavelengths among a number of nodes. ROADMs can be used to make quick changes in carrier networks, for remotely provisioning upgrades and changes in any network in response to new service demand or to compensate for changing traffic patterns. They can be an important enabler of core router offload. Furthermore, they can also support shared protection and restoration capabilities in a meshed architecture, or dynamic provisioning capabilities for special applications.

Pros and cons of current ROADM deploymentsThe first generation of ROADMs eliminated the stranding of capacity associated with wavelength banding, and simplified traffic engineering to make optimization and rerouting easy. They enabled wavelength path setup without having to send technicians out to intermediate nodes. Finally, they allowed for per channel power control to enable optimization of transmission and simple capacity upgrades.

Networks based on the first generation of ROADMs have offered greater flexibility and eliminated the need for some truck rolls, but they have not created the full degree of operational efficiency that service operators will need in future. A site visit is still required to change the fixed direction assignment for the add/drop and to reassign the wavelength assigned to specific ports at the end nodes. So full automation and rapid end-to-end provisioning is not possible, which limits flexible options in protection that can be offered and does not allow acceleration of time to market. Legacy ROADMS can also experience contention for use of a wavelength when traffic is rerouted due to a failover. These early ROADMS can experience bandwidth constraints by traffic being limited to a single instance of a specific wavelength.

Future proofing a traditional ROADM-based network for scaling beyond 100Gbps line rates can also be a problem, since 400Gbps will be unlikely to conform to the 50 GHz grid that is typically used at 100Gbps line rates and below. Future proofing ROADMs partially addresses the challenges of moving to line rates of greater than 100Gbps as other network components will require replacement for 400Gbps, e.g. amplifiers. Where it makes economic sense to use future-proof ROADM modules operators should do so, but they should not pay a premium for this capability due to the rest of the upgrade costs associated with line speeds in excess of 100Gbps.

Finally, lower cost ROADMs may be required closer to the customer premise, residence, or cell site – and it might be more cost effective to deploy a partial mesh there or even to use a logical mesh architecture leveraging the assets of existing ring topologies.

That is why building efficient WDM and ROADM-based meshed networks that maximize operational efficiency requires the use of a full and flexible suite of advanced ROADM technologies that is cost optimized and provides the flexibility and features required for each part of the network.

Transmode’s Flexible Optical Network ROADM technology Transmode’s Flexible Optical Network utilizes the Transmode WDM portfolio and a complete suite of state-of-the-art commercially viable ROADM technologies, applying each for the right application and in the right part of the network to give service operators the kind of flexibility, efficiency, and control that they need. The Flexible Optical Network ROADM portfolio includes 2-degree and multi-degree ROADMs as well as contentionless, colorless and directionless ROADM technologies – each of which provides distinct benefits and can be combined for ultimate in operational efficiency.

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Multi-degree ROADMs: Multi-degree ROADM nodes allow service operators to route wavelengths in a number of directions. The first generation of multi-degree ROADMs required that an operator visit the end nodes to change the Mux/DeMux port to change direction, or to change both the Mux/DeMux port and Transponder color whenever a new wavelength is required. However, a number of enhancements have increased the flexibility of both 2-degree and multi-degree ROADMs considerably – and the design of Transmode’s Flexible Optical Network means that step by step upgrades to colorless, directionless and contentionless capabilities today, and ultimately gridless capabilities, can be accomplished when needed.

Transmode offers 1x2, 1x4 and 1x8 multi-degree ROADM units to match cost to the degree of flexibility and number of links that need to be supported. A ROADM module can easily be added to existing Transmode chassis, and a straightforward design means step by step upgrades to colorless, directionless and contentionless capabilities are possible. Figure 3 shows a simple 8-degree WSS ROADM node architecture (i.e. not colorless, directionless or contentionless).

Fig 3. 8-degree ROADM node.

WSS Multi-degree ROADMs enable failover of a wavelength to a fixed, predefined backup path.

Fig 4. How protection and traffic engineering occur with multi-degree ROADMs

Colorless ROADMs: An upgrade to colorless ROADM technology provides wavelength transparent access to DWDM network ports and helps an operator manage wavelength allocation issues with any add/drop traffic. With the first generation of ROADMs, manual intervention was required to connect non-tunable transceivers to a specific mux/demux port at the add/drop site,

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Transmode’s Flexible Optical Network also partially uses gridless-ready technology where it makes economic network complexity sense. As previously mentioned this only partially addresses the issues associated future proofing with speeds in excess of 100Gbps so should not be done if it drives up the cost of ROADM deployments today. As component technology matures the Transmode Flexible Optical Network will gradually bring more gridless ROADM options onboard when the economics are right.

The role that these Metro ROADM technologies fulfill as part of Transmode’s Flexible Optical Network solution is summarized below:

2-degree ROADMs: 2-degree ROADM nodes in the Flexible Optical Network solution allow simple add/drop functionality optimized for wavelengths at the edge of the network where cost issues predominate and the architecture is typically ring based. A cost efficient Wavelength Selective Switch (WSS) design simplifies network planning, freeing up wavelength allocation and allowing operators to make more efficient use of wavelengths while simplifying fiber management as compared to using static optical filters. WSS technology on the add side of the ROADM gives full control of optical power levels for both added and passed channels – reducing transmission problems and providing greater security.

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Explanation of Transmode’s modular architecture:Transmode’s Flexible Optical Networking ROADM nodes are built using a range of ROADM and other plug-in units such as fixed or co-lourless filters and optical channel monitors. This offers the network designer great flexibility in network design.

These units provide either 1x2, 1x4 or 1x8 capabilities and support both 50 and 100 GHz spaced networks. All Transmode ROADM units use a Wavelength Selective Switch (WSS) on the add side of the module which provides additional benefits to the network operator over some ROADM designs, namely:

● Increased security against networking errors. By using the WSS on the add side instead of the drop side, passing traffic is protected against erroneously added traffic impacts.

● Simpler power balancing of all pass-through and add/drop channels by a single optical channel monitor and control loop. The alternative approach with the WSS on the drop port and a simple optical coupler for the add traffic has much more complex power balancing as locally added traffic can be balanced via a local Variable Optical Attenuator (VOA) but pass through traffic must be balanced in the various remote nodes where the wavelength was first added which may cause issues elsewhere in the network.

See below illustration of Transmode’s ROADM architecture.

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Contentionless ROADMs: Contentionless ROADMs ensure that no wavelength blocking can occur in the case that two wavelengths of the same color are encountered, a scenario that can potentially happen with colorless and directionless ROADMs as add/drop traffic is rerouted.

Colorless, Directionless, and Contentionless (CDC) ROADMs offer the same advantages as a colorless and directionless ROADM, and also leverages colorless ports to allow several lambdas of the same color to be added or dropped rather than only one. It can also route traffic in any direction using any wavelength.

Gridless ROADMs: Gridless ROADMs enable the passband of the ROADM to be changed to allow channels of a speed greater than 100 Gbps to be efficiently mapped into available spectrum. Gridless ROADMs are required at every node in the network, and must offer flexible channel spacing settings to accommodate the still unknown passband that will be required at 400Gbps and beyond.

A gridless WSS makes it possible to change to new modulation formats that require new channel spacing without having to swap out all the filters in the network, and also makes it possible to optimize frequency utilization to accommodate multiple passbands of different channel spacing so that different line rates can be utilized within the same band. However, the complexity of doing so makes it difficult to optimize spectrum utilization and periodic defragmentation may be required as a result. A gridless ROADM also makes the use of any fixed filters in the network very difficult to manage.

As previously mentioned, gridless technology can be useful if the economics are right and currently not all ROADM units are best served with gridless technology. Overtime as component technology matures this will change. However, this only partially addresses the issues associated with line rates above 100Gbps as it is anticipated that a significant portion of other network components such as amplifiers will also require upgrading for these line rates.

Fig 7. Shows the passband being reconfigured over time for a gridless ROADM

Optical design flexibilityIn addition to the broad range of ROADM options, Transmode also offers a very extensive range of fixed filter modules and other optical units that allow network designers great design flexibility. This includes a broad range of fixed filter options that has grown from Transmode’s early heritage as an innovative Metro WDM vendor. This range encompasses modules for single fiber and fiber pair applications, CWDM, DWDM and mixed applications, and a complete portfolio of terminal and fixed 1, 2 and 4 wavelength add/drop modules supporting the full spectrum. The range also contains unique interleavers that allow networks to grow from 40 channel 100 GHz spaced designs to 80 channel 50 GHz spaced designs while still allowing the use of 100 GHz spaced optics on the first 40 channels.

meaning wavelengths were fixed. Colorless ROADMs replace this architecture and enable remote, automated wavelength assignment via wavelength tunable traffic units to be carried out by the control plane, reducing normal operations costs and the potential for errors.

Figure 5 shows how colorless ROADMs can be used to change the wavelength on a new protection path due to lack of availability of the initial wavelength being used on one of the links in the span.

Note that although a colorless ROADM can change the wavelength to be used for the backup path, it cannot change the direction of the backup path. Doing both of these tasks requires a ROADM that is both colorless and directionless.

Fig 5. Colorless ROADM changing wavelengths to a free lambda

Directionless ROADMs: Directionless ROADMs enable dynamic multi-directional capabilities, i.e the ability to launch a wavelength into a ROADM network in any direction as directed remotely by control plane software. This offers greater flexibility and automation than did previous fixed add/drop ROADM designs, which had a fixed relationship between the transponders and add/drop ports. These fixed designs dictated a single, fixed direction over which an outbound wavelength could be routed until manually reconfigured.

However, in addition to the advantages of the directionless ROADM, they have a number of disadvantages as well - such as potentially introducing a single point of failure unless a duplicated WSS is used, and high capex if that is the case.

Directionless ROADMs are required at the end nodes and can provide fixed or colorless add/drop capabilities.

Fig 5. Directionless ROADM picking a new path.

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The broad range fully compliments the ROADM solutions, espe-cially when combined with the range of amplifiers offered, which includes a range of EDFA options and Raman and Power Booster amplifiers.

Overall, this range of additional components provides optical network designers with the broadest possible toolkit to enable the best possible and most flexible optical network design.

Resilience FeaturesTransmode’s Flexible Optical Network solutions also has benefits in terms of Resilience

● Sub-50 ms protection switching

● Client/equipment, line, fiber, and L2 protection schemes

● Transmode’s unique 1+3 line protection

Transmode’s suite of network management and planning toolsThe Transmodes planning tools and the Transmode Network Manager (TNM) Software provide integrated software tools that are compliant with the TMForum’s eTOM framework and support the entire service life cycle.

The Transmode planning tools provide planning and provisioning within Transmode’s Flexible Optical Network to support:

● Resource and Service Planning

● Route selection

● What-if scenario analysis

● Optical design

● Service restoration planning

● Service pre-provisioning

● Resource and Service documentation

The Transmode Network Manager (TNM) element and network management software provides:

● Resource Management (FCAPS)

● Service Provisioning/Activation

● Service Management

● Bidirectional northbound interfaces

Optimized Wavelength Management FeaturesTransmode’s Flexible Optical Network supports a number of optimized wavelength management features which simplify network operations. Both active and passive network elements can be registered in the network inventory, which has the benefit of greatly simplifying the wavelength planning process. Because the TNM includes ROADMs in its end-to-end configuration management, automated remote power balancing of each channel can be performed across the network. The TNM allows alien wavelengths to be remotely managed and balanced in exactly the same way as native wavelengths.

Ease of useEase of use is the key to achieving unprecedented operational efficiency, and is the driving force behind the design of Transmode’s Flexible Optical Networks. Transmode’s TNM achieves this through automation and simplification of

• Thecommissioningandoperationofamplifiednetworks

• Theprovisioningofnewservices

• Networkplanning

Transmode’s Flexible Optical Networks enables remote commissioning, upgrades, and optimization of amplified optical networks. The optical control plane simplifies monitoring and control of the amplified optical network from the Transmode Network Manager, while local control loops simplify commissioning of nodes and control of long term drift. Optical channel monitoring enables control of channel power to optimize performance. Integrated and separate variable optical amplifiers enable control of added power in both terminal and OADM nodes.

The flexibility, control, and simplicity offered by Transmode’s Flexible Optical Network relies on the interaction of a suite of network planning tools, design tools, and management software with the ROADM and WDM hardware. Transitioning from static point-to-point networks to a flexible and dynamic optical network requires this kind of tight integration.

Operators need a multi-layer view that converges the optical and Ethernet layers. By providing visualization and correlation of Layers 1 and 2, the Transmode Network Manager provides a comprehensive end-to-end understanding of Ethernet service performance and its relation to what is going on in the underlying transport network.

Transmode’s Flexible Optical Network also provides operators with an integrated solution that results in efficient work flow progression from planning and design through network commissioning, service provisioning and ongoing operations - streamlining both network and service operation and providing valuable proactive diagnostic tools.

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Benefits of Transmode’s Flexible Optical NetworksTransmode’s Flexible Optical Networks ROADM technology supports offering a variety of protection and restoration services, and provides the added benefit of enabling operators to offer dynamic service provisioning. The proper choice and use of the colorless, directionless, contentionless and gridless ROADMS allows Transmode’s Flexible Optical Networks to provide the following benefits:

● Enables remote configuration while accelerating time to market

● Reduces the need for truck rolls and the possibility of human error

● Supports automation and scheduling of changes to the network

● Simplifies planning and engineering tasks

● Increases bandwidth efficiency by eliminating stranded wavelengths

● Eliminates the potential for blocking to occur in meshed networks as they failover

● Supports optimization of amplification in the network by attenuating and equalizing all the wavelengths at many points in the network

● Enables scalability to future channel speeds while ensuring efficient use of spectrum and backwards compatibility for the installed base

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SummaryService opportunities are rapidly evolving, resulting in much greater bandwidth requirements, more frequent need for upgrades, and less predictable traffic patterns. Demand is highly variable, and high bandwidth services are creating less revenue per bit than they once did while increasing overall costs. A new degree of flexibility, automation, and control of the optical and data layers is going to be required.

Based on extensive experience designing and building optical and ROADM networks, Transmode’s Flexible Optical Networks provides a complete portfolio of advanced commercially viable ROADM technologies, and a suite of well designed network planning and management tools that integrate Layer 1 and Layer 2 views to correlate wavelengths with Ethernet-based services. Transmode’s Flexible Optical Network gives operators unprecedented degree of operational efficiency, enabling them to maximize the revenue potential of the network while minimizing total cost of ownership and maximizing profitability.

Application Note

The specifications and information within this document are subject to change without further notice. All statements, information and recommendations are believed to be accurate but are presented without warranty of any kind. Contact Transmode for more details.

www.transmode.com