IP over DWDM: Pros and Cons
Optical Networking Industry
IP over DWDM (IPoDWDM) is making waves in the industry – by shrinking the typical rack-mounted optical transponder to the size of a pluggable transceiver that fits in a router port. Eliminating the transponder saves money, but there’s more to it than just a simple drop-in replacement.
In this article, we dive into the costs, the impact on the network and network management, and the scaling of the IPoDWDM solution. We weigh the pros and cons to help you understand where and when IPoDWDM makes sense.
What is IP Over DWDM?
IPoDWDM combines IP switching/routing with DWDM (dense wave division multiplexing) optics. The idea is to install DWDM optical transceivers directly in the switch/router instead of the typical grey-optics transceivers. Add an external Mux/Demux filter, amplifiers, and dispersion compensation (if necessary), and traffic can now cross the city (or even the state) directly without the need for a transponder. Each router port is a channel, and single-mode fibers can support up to 192 DWDM channels, depending on data rate and channel passband requirements.
In network architecture terms, IPoDWDM collapses the IP and optical networking layers. The router now has direct visibility into the health of optical links, so new strategies for bandwidth management and fault tolerance across sites can be implemented to optimize the converged network — not just the individual layers. A holistic approach improves performance metrics such as packet latency, utilization, and rerouting times.
DWDM transceivers for router interfaces
IPoDWDM is not new – the concept and its various implementations have been on the table for some twenty years. What’s new is the widespread availability of 100G and 400G transceivers, with 800G on the horizon, that effectively shrink the rack-mounted transponder into a small pluggable form factor that fits in a switch or router port. These DWDM transceivers are coherent and “colored,” meaning that the operating wavelength (or color) is tunable and not the standard 850/1310/1550 nm wavelengths of grey transceivers. By using a different wavelength (or channel) for each router interface and then combining all the interfaces with a Mux/Demux filter, multiple channels can be transmitted using only a single fiber pair.
Higher-end switches and routers are often required for IPoDWDM, because they support the enhanced processing capabilities and advanced management features to handle the complexities of DWDM integration. Such features include:
- Cooling: DWDM transceivers generate more heat than grey transceivers and require sufficient cooling mechanisms within the switch/router to maintain optimal performance and extend its lifespan.
- Tuning: The transceivers need to be tuned to specific wavelengths. Tunable optics allow for dynamic adjustment of wavelengths as network demands change.
- Management: The switch/router management software must be able to interface with the transceiver’s Digital Diagnostic Monitoring or CMIS (Common Management Interface Specification), which is the standard used by transceivers supporting 100G or greater data rates.
DWDM transceivers have been available in the market for many years and come in a variety of form factors – OSFP, QSFP, QSFP28, and more. More recently in the past few years, transceivers for long-distance transmission based on the ZR/ZR+ standard have become available and require a QSFP28 (100G) or QSFP-DD (400G) port.
Management Challenges
IPoDWDM merges the IP and optical layers of the network, and hence the management model changes with the switch/router controlling the optics. This introduces several management challenges:
- Color Management: Managing multiple wavelengths directly in a switch/router increases complexity due to the need for precise wavelength assignment and continuous monitoring to prevent overlap and interference. This process requires robust software for real-time wavelength management.
Example: If two data channels are mistakenly assigned the same wavelength, then one channel will not work and will be blocked by the Mux/Demux filter.
- Telemetry and Monitoring: Comprehensive monitoring tools are essential for maintaining network health. This includes reading a variety of counters, optical power level monitoring, OSNR (Optical Signal to Noise Ratio), eSNR (electrical Signal to Noise Ratio), a variety of optical link performance metrics, and robust event handling (alarms, traps, threshold-crossing alerts, etc.).
However, not all switches/routers support the full suite of telemetry tools required for such detailed monitoring. This limitation would pose significant challenges for network teams lacking the resources to regularly review this data for events, traps, or for long-term trends in the data.
Cost Considerations
The cost dynamics of IPoDWDM can be attractive because less hardware is needed, and entry costs are lower. However, the savings are often marginal in the long-term and are contingent on specific network configurations and needs. Note that Mux/Demux filters, amplifiers, equalizers, and dispersion compensators are still necessary, depending on the topology and modulation techniques being used in the transceivers. Other features may also need to be added, like optical protection switching at the DWDM layer and integrated OTDR capabilities.
Cost Structure
An upfront purchase of a pluggable optics solution can result in significant savings compared to using dedicated DWDM optical transport equipment. The savings come from two main fronts:
- The elimination of transponders or muxponders.
- Instead of a full-featured OLS (optical line system), the optical transport equipment can be simplified to Mux/Demux filters and optical amplifiers. The intelligence now resides on the switch/router to manage the interfaces, links, and traffic.
On the switch and router side, a higher-end model is required for IPoDWDM. If the switch or router needs to be upgraded, that cost should also be considered. DWDM transceivers are more expensive than grey transceivers, but the additional expense is more than offset by eliminating transponders. The reduced hardware requirement also means space and footprint savings, which can be important when rack space is limited.
Breakeven Point
IPoDWDM is cost-effective and manageable for networks with a relatively lower number of channels It is well suited for users with a manageable number of sites and a relatively stable network topology (i.e. without a constant stream of moves, adds, and changes).
As the number of channels increases, management complexities grow, and incremental costs rise, making IPoDWDM less attractive. More DWDM channels also mean larger Mux/Demux filters. Depending on the filter technology, more channels mean more insertion loss, which in turn could mean more amplifiers and the need to actively manage these amplifiers.
The specific breakeven point of how many channels or links beyond which IP over DWDM loses its competitiveness depends very much on the specific use cases and the legacy equipment that can be leveraged. In addition to the CapEx, the OpEx of IPoDWDM is higher than for transponder/muxponder solutions. More optical transport knowledge and training is needed for the IPoDWDM solution. The management aspect of IPoDWDM must also be considered. Wavelength management and amplifier controls and monitoring are often an afterthought, but should be addressed early on in the decision-making process.
Licensing and Compatibility when using IPoDWDM with an OLS
If an OLS is used instead of a Mux/Demux and amplifier, the OLS vendor may charge an additional licensing fee for carrying non-native wavelengths. When the wavelength originates from a DWDM transceiver instead of the vendor’s transponder, it is considered an alien wavelength.
These alien wavelength licensing fees, in addition to port activation and software usage fees, can add to the overall cost and complexity of the network. Evaluating the total cost of ownership across a 5-year time horizon is essential. The upfront savings are significant but become diluted over time once annual fees are included.
Ensuring compatibility between different types of equipment and DWDM optics is crucial for a seamless and scalable network. Selecting vendors with flexible and interoperable solutions can mitigate these issues.
Scaling Up
Can IP over DWDM effectively scale up to create a mesh backbone for your core routers? Effective solutions involve a combination of traditional DWDM components and advanced IPoDWDM technologies. Here are two solutions for scaling the optical transport network to support IPoDWDM:
IPoDWDM With Mux/Demux Filters and Amplifiers
This approach leverages the switches and routers for network intelligence. The optical transport equipment is streamlined and relatively static – its main job is to deliver data reliably across the fiber. If the Mux/Demux filters and amplifiers can be configured and managed by the same tools used for the switches/routers, then this approach can be scaled effectively.
Full OTN (Optical Transport Network)
At a certain scale, DWDM vendors can offer more comprehensive solutions. Having dedicated DWDM equipment allows the end user to support a wide range of DWDM optics, ensuring robust cooling of components, more comprehensive monitoring and control of the optical elements, and a complete end-to-end management solution for every aspect of the network. More network intelligence resides in the optical transport layer to perform functions such as switching, traffic grooming, and rerouting. This flexibility enables customers to scale their networks efficiently. Layer 1 optical protection and OTDR features are typically not available to IPoDWDM solutions.
Integrate IPoDWDM with Ease
Deploying an IPoDWDM solution can result in capital cost savings. Integrating DWDM optics directly into switches and routers introduces complexities in management and scalability problems. Organizations can make an informed decision about introducing IPoDWDM into their networks by understanding the technical drivers, cost considerations, and solutions that provide scalability.
When considering a comprehensive DWDM solution, XKL provides flexible and robust solutions that facilitate the integration of IPoDWDM with traditional DWDM systems. We make the entire process simple for your network team with easy-to-manage systems that are specifically built to your requirements. Give your network team true peace of mind with zero licensing fees and 24/7 engineering support.