Large carriers, burned by fear of repeating boom overbuild, hesitate to install full-scale DWDM in their networks. In response, a passle of vendors large and small has released news of new CWDM gear that lets these reluctant providers start small.
These wares cater to a real or perceived need for a simpler, more manageable optical solution -- and one that costs less than DWDM (see CWDM: Low-Cost Capacity). But as products proliferate, carriers clearly need to choose among a growing range of approaches.
Let's start with the news. Following are just a few items that have surfaced in conjunction with last week's CeBIT tradeshow in Hannover, Germany, or in anticipation of next week's OFC show in Atlanta:
- ADVA AG Optical Networking (Frankfurt: ADV) announced this week an eight-channel CWDM module, set for shipment in April 2003, for its FSP 2000 transport box (see ADVA Continues Metro March). The new gear will be shown at OFC.
- Alcatel SA (NYSE: ALA; Paris: CGEP:PA) released at CeBIT the 1692 Metro Span Edge, a standalone CWDM transport system based on its own components (see Alcatel Joins CWDM Club).
- ECI Telecom Ltd. (Nasdaq/NM: ECIL) announced at CeBIT the XDM 200, a standalone, eight-channel CWDM unit for metro use that's due out in the fourth quarter of this year (see ECI Moves Deeper Into Metro).
- Movaz Networks Inc. announced this week the RAYexpress CWDM, an eight-channel transport platform based on the same architecture as its DWDM gear. It's now available and will be on display at OFC (see Movaz Launches CWDM Platform).
- Transmode Systems AB at CeBIT unveiled a new version of its System 1100 CWDM box, with a new four-channel CWDM amplifier that extends the product's range to 120 km. The optional add-on ships in the coming quarter, Transmode says (see Transmode Extends CWDM Reach).
Not only new systems, but more CWDM components are hitting the streets as well. On March 18, NKT Integration A/S, which is exhibiting at OFC, announced a CWDM mux/demux module based on a single-chip wafer fabrication technique (see NKT Launches CWDM Modules). Another component maker, Gigabit Optics Corp., says it plans OFC announcements relating to its existing product line, which includes passive CWDM components.
Other vendors that have made CWDM announcements recently include: BaySpec Inc., which launched an optical spectrum analyzer module for use in handheld CWDM testers in February; LastMile AG, which launched a 2-Gbit/s CWDM Fibre Channel mux in January; and Microsens GmbH & Co. KG, which unveiled a modular eight-channel CWDM/DWDM multiplexer last fall (see Microsens Migrates CWDM to DWDM). Bayspec will be exhibiting at OFC.
All this activity is no surprise. CWDM's been building momentum for months, thanks to its simplicity and relatively low cost (see CWDM On the Move). But recent announcements entail some debatable claims and conflicting agendas. Here's a summary of some key controversies:
Module or Standalone Unit?
Vendors are taking different approaches to the problem of how to put specific networking interfaces onto their wares. Some vendors, including ADVA, Microsens, and Movaz, use components such as ready-made, small form-factor, pluggable (SFP) modules that assign wavelengths discrete interfaces. This enables them to add CWDM as a feature to existing DWDM gear. Others, like Transmode, use proprietary components that enable interfaces to change dynamically.
These tacks show underlying differences of opinion about CWDM. Transmode, for instance, says its gear, which features an automatic sensing capability that adjusts transmission rates to match incoming protocols, adds to CWDM's hands-off manageability. ADVA and Movaz, in contrast, say CWDM is a feature, not a platform; and their execs dispute the need for a technique that involves flexible protocol changes. "Carriers don't want auto-sensing," says ADVA CEO Brian Protiva. If a carrier sells a wavelength for a 155-Mbit/s Sonet connection, they want to stop that customer from running Gigabit Ethernet over it for the same price, he says.
For its part, Transmode says this argument is "irrelevant," since their net management system offers carriers visibility into the network and allows them to "lock" the transmission rates for specific protocols.
ECI Telecom isn't drawing any firm lines yet. While its XDM 200 uses SFPs, senior product manager David O'Neill says the company is open to new approaches. ECI's Lightscape Optical Networks Division uses auto-adjustable features in other metro products, but, he says, "We'll investigate whether it's cost effective" for CWDM use.
Distance and Interoperability
Another issue with CWDM is distance limitations. CWDM has wider channel spacing and lower signal strength than DWDM, and the cost differential reflects that. But vendors have had to work hard to overcome CWDM's rep as a wavelength weakling. One way of doing this is to use proprietary techniques to boost signals. Thus, most new gear is said to be able to send signals over 100 km without optical regeneration, compared with about 60 km just last year.
On the downside, these long-distance CWDM products usually aren't interoperable with other vendors' gear. Part of the problem is that specs for distance haven't been hammered out by the International Telecommunication Union (ITU). The distance issue is being studied by the ITU and should be part of a draft later this year.
Vendors continue to seek ways of making CWDM more attractive to penny-pinching carriers. One way is through the use of cheaper components. Increased demand has led some component players, such as NKT, to focus on making elements that are mass-producible. CEO Lars Bonn claims his company's new CWDM mux/demux is based on a single-chip semiconductor process that makes it easier to manufacture than competing thin-film filters. Just how much the costs can be cut remains to be seen, he says. But, like other component players, he envisions selling his wares to OEMs that can use them with transponders from the likes of Finisar Corp. (Nasdaq: FNSR) to pop together CWDM products in Lego-like fashion.
These and other issues point to ongoing development in CWDM techniques. As CWDM continues to grow in popularity, widespread adoption will help clarify the issues and fit specific approaches more closely to real-world circumstances.
— Mary Jander, Senior Editor, Light Reading
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