Advances in WDM and ROADMs: The key to your success

The latest advances in multidegree ROADM and packet optical networking technologies enable independent service providers to remain competitive.

By Ronen Mikdashi, ECI Telecom

The competitive environment has become especially challenging for carriers and service providers over the last decade, thanks in part to deregulation, which has allowed new operators to penetrate the market. At the same time, existing customers are demanding higher capacity and additional services, but revenue-per-bit continues to decrease.

To gain a competitive advantage in such a challenging market, today's service providers must build optical networks that are as efficient as possible and agile enough to respond to any customer need or new revenue-generating opportunity.

Any operators deploying an optical network should ask the following questions:

How do I invest in a new telecom infrastructure that will be futureproof but also optimized from a capital expenditure (capex) perspective?
How can I reduce my network's operational expenditures (opex)?
How can I ensure reliable quality of service?
Can I respond quickly to new and unexpected traffic demands or services?
Is the network built to enable the introduction of new technologies without risking reliability?

Today, the most fashionable approach to solving these challenges is the next-generation optical network. But within this approach, it is crucial to choose the correct building blocks and technologies to most cost-effectively and optimally achieve the desired competitive advantage.

Multidegree WSS ROADM

Reconfigurable optical add/drop multiplexing (ROADM) is currently considered the technology of choice for carriers worldwide, adding flexibility and lowering total cost of ownership (TCO) for various core and regional network scenarios.

Wavelength-selective switch (WSS)-based ROADMs allow carriers to route any wavelength (or any combination of wavelengths) to any node without the need to predefine traffic demands or install additional devices—thereby significantly reducing time-to-market for new services. Furthermore, the WSS ROADM offers "colorless" ports, affording the operator increased flexibility in selecting and then reselecting a specific wavelength to add/drop at the node. This is of particular benefit for a network with hard-to-predict traffic and/or a traffic mix that is expected to change often.

Thanks to its multidegree architecture, the WSS ROADM can be deployed not only in rings and chains as in previous generations but also in the multiring and mesh topologies so common in metro core and regional WDM networks today.

One recent deployment provides an example. A new regional WDM network for a major European carrier was designed twice: once based on traditional DWDM and again based on WSS ROADMs. The network featured a mesh topology with a nodal degree from two to four. A detailed capex comparison revealed a striking and counter-intuitive result. Although the initial cost of the ROADM-based network was 10% higher than a traditional fixed network, once populated with just a few wavelengths per link, it became more cost-effective (see Fig. 1).

Figure 1. ROADM-based networks become more economical versus fixed DWDM networks as traffic load increases.

As traffic demands grow, networks become complex, even at the metro layer. Today's operators require flexible capabilities all the way from the metro to the core and cost-effective ROADMs for each segment. Metro flexibility is currently achieved by planar lightwave circuit (PLC)-based ROADMs that optimally fit budget limitations while fulfilling the bandwidth and flexibility requirements in that segment.

OTN: Any service, anytime

Optical Transport Network (OTN) is a transport-layer technology defined by ITU-T (G.709) to provide standardization for optical networks. This standard offers the best of both SONET and Carrier Ethernet, resulting in a reliable and interoperable network that enables high-capacity transport with enhanced bandwidth utilization.

Implementing OTN capabilities in a network reduces capex by providing better performance of the optical links and control channels and increases revenue opportunities with transparent multiprotocol interfaces. The main advantages of OTN include:

Higher payload granularity from 2.5 Gbits/sec to 40 Gbits/sec, improving network utilization and, as a result, reducing capex.
Transparent transmission of any known protocol without damaging its characteristics (e.g., clocking), increasing network flexibility and agility when implementing new services.
An in-band control channel (GCC), which reduces management costs and extends the network's reach compared with traditional control systems (OSC).
Quantifiable carrier-grade capabilities for optical networks, including sub-50-msec protection switching.
Subwavelength grooming or efficient bandwidth utilization that combines a number of low-rate links onto a single high-capacity wavelength, resulting in lower capex.
Extended reach with enhanced forward error correction (FEC), which minimizes the number of regenerations and reduces capex.

40- and 100-Gbit/sec links

The sustained high growth of IP-based traffic, as evidenced by the increased popularity of real-time video and Internet services, has important scaling implications for Carrier Ethernet network capacity. As a result, core router-to-router links are over-utilized and constantly expanding, causing increased wavelength demand in optical networks. A typical technique used to meet such expansion is the addition of 10G links per router and optical connection.

However, to improve bandwidth utilization and reduce capex, service providers are implementing high-speed links, e.g., 40G links to replace 4×10-Gbit/sec links. This number may even expand to 100G links in the near future, further reducing the number of optical ports on the core router and the optical network.

In order to understand the cost reduction of implementing 40G and 100G links, we should take a look back at history. The transition from 622 Mbits/sec to 2.5 Gbits/sec and, later, from 2.5 Gbits/sec to 10 Gbits/sec resulted in a substantial reduction in the cost of transport per bit. The rule of thumb has been that a 4× data rate increase means a 2.5× price increase for transponder cards. The same rule is expected for the transition from 10 to 40 Gbits/sec and 100 Gbits/sec, thereby reducing capex.

Additional benefits of higher-speed cards include lower power consumption, a more compact footprint, and the need for fewer cards. These benefits not only influence the capex, but are also evident in the daily opex.

Packet optical convergence

One of the leading technologies for achieving a competitive advantage—while seeing significant cost reduction and ease of operation—is convergence. To realize the full benefits, convergence should be implemented in various levels within the network:

Technological packet optical convergence to provide both data (carrier Ethernet) and wavelength (WDM, OTN, ROADM) services, along with traditional circuit services (SONET-based), on a single, space-efficient platform (see Fig. 2).
All-range convergence to provide a complete end-to-end solution, from metro to long haul, using a single platform.
Management convergence to ease operations and reduce opex. A unified management system will enable management across all network layers and technologies—optical, Ethernet-based and SONET—and support end-to-end access-to-long-haul provisioning with a single system.

Figure 2. A converged packet optical platform integrates Carrier Ethernet, WDM, and SONET-based services in a single device.

The value of converging WDM/ROADM, Carrier Ethernet, and multiservice provisioning platform (MSPP) capabilities lies both in its integration and in the flexibility it gives service providers, enabling them to almost seamlessly implement any service and technology required at a particular place and time within a unified transport platform.

Major benefits, including simplified management and reduction in service provisioning time and network complexity, complement the more expected cost savings associated with reduced sparing, training, and space requirements. Projections based on preliminary field data from users of packet optical systems indicate an average capex saving of approximately 25% and an estimated drop in TCO by about 45% over 5 years (see Fig. 3).

Figure 3. Use of packet optical network platforms can result in an estimated 25% drop in total cost of ownership due to convergence.

Ease of operation

Today's next-generation networks can easily contain a full set of features aimed at simplifying the planning, installation, operation, and maintenance tasks of WDM/ROADM networks that were previously considered fairly complex.

In order to decrease opex, increase network agility, and improve response time to customer needs, carriers should build their optical networks with automated features, including:

An enhanced Automatic Power Control to ensure network robustness, automatically adjust to changes in optical power due to variations in span loss and/or the number of active channels, and provide comprehensive data on network status. Apart from reducing opex, that feature also improves the carrier-grade reliability of services given to customers and enables an agile response to customer expansion that can ultimately increase revenue.
A comprehensive planning tool for bandwidth optimization, optical link design optimization/verification, and shelf layout to optimize installation and reduce capex. This also reduces the re-engineering duration needed for new revenue-generating services design.
An Automatically Switched Optical Network (ASON)-based automatic network element, link, and topology discovery.

Summary

Carriers and service providers are seeing challenges from all sides. They are facing a much more competitive environment due to the impact of deregulation, and their existing customers are demanding additional services and higher capacity. To face these challenges—and to transform them into a competitive advantage—carriers must find innovative ways both to increase revenue-per-investment and lower total cost of ownership. This is possible today, thanks to the next-generation optical network and its building blocks: