DWDM Pluggable vs Traditional Transponder/ Muxponder

IP over DWDM has been around for more than a decade. As a concept, it revolves around placing coherent pluggable optics directly into routers. The value propositions of collapsing an entire layer includes the elimination of back-to-back grey optics, lower power consumption and unification of monitoring, control planes and management. However, and although architecturally making all the sense in the world, it never really took off outside of a few niche deployment scenarios. This begs the question of what’s different this time around?

Two major differences stem from the previous sections:

1. The evolution of routing silicon has led to multi-Tbps ASICs and exponential, Moore’s Law-like, performance increases in throughput and power efficiency. This performance trajectory now exceed the needs of most networks, reduce the overall cost structures, and shift the relative spending even more to optical networks – as evident in Figure 5.
2. The partial disaggregation of optical networks with a uniform approach to deploying alien wavelengths over open optical line-systems; thus mitigating many of the traditional challenges in operations, vendor competition, culture, process, and technology

Figure 5 – Avg. CAPEX distribution per 100G Circuit
 

As recent as just last year, deploying IPoDWDM did not only incur a huge density penalty on switch-router blades. Because the application itself was revolving around the CFP2 form-factor, the other natural side effect was therefore a need for dedicated single-purpose cages/line cards. Through standardization work by the OIF and other MSAs, this all changed with the introduction of 400G-ZR(+) that can be realized using industry-standard QSFP-DD modules. This, for the very first time, enables true mix-and-matching of all client applications on the same switch-router building block at full face-plate density and in turn:

1. Predictive failure scenarios and overall improved operations
2. Simpler capacity and power planning, improving ROI
3. Fewer types of components to maintain, simpler life cycle and spare-part management
4. No switch-router to transponder speed and hardware cycle mismatches
5. Faster installations and deployments

Perhaps even more importantly as the relative spending is shifted heavily towards transponders is a standards-based DWDM layer without bookending. By being pluggable and interoperable, just-in-time investments without front-heavy discrete transponder chassis/card costs are made possible. It also enables continuous and healthy per module granularity to vendor competition and thus making it the most powerful pay-as-you-grow schema ever seen in this space. In addition, these modules can subsequently be reused in any 400GE capable host, offering unparalleled investment protection.

The latter is yet another testament as to why conventional sourcing methodologies fall short. In that model, multi-year investments and the associated lock-in is based on pricing given at a single point in time. Throughout the lifetime and fill-up of transponder systems, the mapping disconnect to bottom-up supplier COGS is usually increasing and without any credible leverage to exercise competition. This has always been true for modular systems in general as they truly are, and as mentioned in Section 1. for routers, the ultimate lock-in for vendors because of the proprietary nature of the components loaded into them. With standards-based DWDM optics, being the by far most expensive components, competition can be exercised at any given point without much operational or administrative overhead. It also serves as cheap insurance to some cases of supply chain contraints.

The other often forgotten aspect and benefit with IPoDWDM is around availability schemas. As previously mentioned, traditional transponder chassis often become front-heavy in terms of cost unless assuming high initial fill-rate. This is partially driven by discrete systems each coming with their own additional space, power and cost components including:

1. Vendor developed software, management interfaces, and monitoring stack
2. CPUs, controller cards, power feeds and fans – most in a redundant setup for intra-system availability
3. Grey back-to-back optics and cabling

As a result, you’ve effectively deployed another whole set of hardware with its own intra-system redundancies, software, support, and life-cycle management overhead. Limiting the blast radius of any single failure to for example one fiber direction in many cases necessitates deploying more (surplus) components and amplifies the negative ROI effects even further.

This is by no means to say that high-performance discrete transponders will go away, at least not in challenging fiber-scarce (ultra) long-haul and subsea applications where spectral efficiency will continue to be key for network operators needing to squeeze out every last bit. However, as a consequence of forever changed cost structures, overall topological and architectural principles have to evolve accordingly. With the existing and as-is topology of AS1299, almost 80% of the total circuit bandwidth is between router pairs less than 1,000 km apart.

It will also be interesting to see the subsequent spending effects any IPoDWDM adoption may have on conventional DWDM technologies amongst networks operators in general, as it not only has the potential to cannibalize on new deployments. As with the case of high-touch NPUs in routers discussed in the first section of this post, there is probably similar case to be made for replacing already (and recently) deployed transponder shelves and modem cards with pluggable coherent optics directly into switch-routers. The ripple effects of such a scenario for traditional DWDM components would then be, just as with high-touch NPU-based routers:

1. A stock is built as migrations are made, thus reducing or even eliminating the need for new investments in those technologies
2. Redeployment where their premium performance add value, which is arguably also a shrinking number of scenarios. At the very least, using the freed-up modem cards to consolidate and fill up already deployed chassis with slot capacity elsewhere
3. By converting to IPoDWDM, each A-Z circuit also releases four (2x back-to-back) grey optics

Conclusions

1. Minimize time spent in sourcing and validation by automating operations and reducing complexity to onboard new technologies faster as they become available
2. Map depreciation times to the (new) economically viable lifetime of equipment
3. Use the shorter cycles and a rigorous technology strategy to offset some of the traditional risk-adverseness

Open and partially disaggregated optical networks provide a framework for commissioning and operating alien wavelengths uniformly as the default deployment paradigm.

Standards-based 400G DWDM pluggable optics put directly into high-scale routing systems bring much-needed fluency to vendor competition in addition to redefining network economics, operational simplicity, and architectures.

For many network operators, this requires breaking down the cultural, process, planning, and organizational barriers that have kept the IP and Optical domains apart and as such often lead to sub-optimal decisions. With the emergence of disruptive technology innovations discussed in this post, there have never been stronger incentives to finally get it right.