Migrating to an Ethernet-centric Infrastructure

DWDM is alive and well! We have seen an increase in demand for DWDM systems, all driven by an increased demand for bandwidth in metro, regional and long-haul networks. While DWDM systems are generally deployed by communications service providers, one of the most interesting recent developments is the growing interest in building private long-haul DWDM networks. For many years private DWDM networks have been built in metro and regional areas. Private long-haul networks are built by governments, the research and education community, and large enterprises, such as financial institutions. The reasons for building such dedicated high capacity private networks are several. It all starts with a bandwidth need of course, but there must also be a bandwidth supply that is affordable. A number of carriers offer fiber lease arrangements, provide space to house equipment, and offer maintenance and repair services that provides users a chance to separate the procurement of fiber from the equipment that “lights” the fiber. DWDM equipment has continued to decrease in price and is now affordable for high capacity private long-haul applications. Another motivation is assurance the network will meet future capacity needs. When the network is privately controlled it is possible to add capacity by adding additional DWDM transceivers. On the other hand if individual wavelengths are purchased from a carrier there can be a concern that the carrier’s system may fill up, causing substantial delays in adding capacity.

Demand continues to grow for capacity on carrier DWDM networks. Carriers that deployed DWDM systems in the late 90’s may still have available capacity on those systems, but the incremental cost to activate that capacity may be high. Carriers have to decide if there is enough future demand to make the up-front investment to deploy modern systems, or if it is more economic to add capacity to existing systems. Modern DWDM systems have ultra-long optical reach (the distance signals can travel before electrical regeneration is required), high capacity, and much lower cost than the systems from the last millennium. In short, the combination of evolving traffic demands and continued focus on capex budgets has carriers scrutinizing the decision about whether to procure new systems or continue to add capacity to old systems. Increasingly, however, we expect they will opt to move toward new systems..

Another motivation for choosing to deploy new systems is the need to support new signal types. Many of today’s core IP networks are being interconnected using a 10Gigabit Ethernet LAN interface. Ciena’s systems carry this signal by enclosing it in a digital wrapper based on international standards. This approach allows the network to evolve to support inexpensive Ethernet interfaces while providing SONET-like management capabilities. Many of the old DWDM systems are SONET-oriented, and cannot easily carry these high speed Ethernet signals. New systems also support the introduction of yet higher speed channels, such as 40G. There is not yet widespread deployment of 40G because the costs of 40G transmission are higher per bit than 10G channels. With time the economics will improve, and all new systems must support 40G, while many old systems cannot.

So far we’ve spoken about economic motivations and service motivations, but have not directly discussed the need for growing system capacity. While your question mentions research publications on 1000 channel DWDM systems, such systems have not proved to be commercially viable. Ciena currently offers the industry’s highest capacity commercially deployed DWDM system, with a capacity of 1.92 Tb/s. We’ve found flexibility to be more important than continued increases in capacity. System flexibility allows the trade-off of ultimate capacity and optical reach for lowest network cost in a particular network design. Today’s multi-reach systems provide cost-optimized solutions for metro, regional and long-haul networks.

But what about fiber, are we running out? While there are always places in the network that may not have fiber deployed or available, in general there is plenty of fiber in the most popular traffic routes. In cities there is generally a great deal of fiber between the large central offices of local operators, both owned by those operators as well as by others. In the metro most of the fiber is not even using DWDM at present. As you suggested when fiber does run out, there will be plenty of opportunity to take currently lit, but inefficiently utilized fiber, and upgrade it with DWDM equipment with high capacity. To cite an example that demonstrates the relative unconcern of carriers today about running out of fiber in long-haul networks, some network operators have chosen to light long-distance fiber networks with equipment that only supports 40 10Gbit/sec wavelengths. The majority, however, are using systems with 80 to 192 channel capacity.