Optical systems target metro networks

Aug. 1, 2000

By Meghan Fuller


Fiber installations and DWDM equipment have increased bandwidth capacity and lowered the cost per bit, resulting in the availability of more raw bandwidth than ever before. At the same time, increasing access connectivity requirements and new access technologies and equipment are driving consumers to demand more customized services at even higher speeds. Trapped in this "metro gap," service providers are often unable to access the long-haul bandwidth to provision usable, revenue-generating services.

To bridge this gap, Alidian Networks Inc. (Mountain View, CA) has introduced its Optical Service Network (OSN) 4000 family of service add/drop multiplexers (ADMs), targeted at bandwidth-usage efficiency and wavelength scalability. The OSN 4000 line scales from 2.5 Gbits/sec at the edge of the metropolitan area network (MAN) to 80 Gbits/sec at the MAN's major hubbing and aggregation points and implements the company's patent-pending WavePack, WaveSwitch, and WaveMux technologies.
While the OSN 4200 platform can be scaled to DWDM, it is lower-capacity and geared more for the access part of the metro space.

The OSN 4100 and 4200 are metro access platforms located at either the customer's premises or the first carrier-edge location. They tap into ring bandwidth to provide access to and aggregation of local services onto the ring. They have a 2.5-Gbit/sec (one OC-48c wavelength) service-bearing capacity but can be scaled to support DWDM capability at 10-Gbits/sec (four OC-48c wavelengths).

The high-end OSN 4800 is a metro core platform and serves as the aggregation or collection point for access traffic flowing from the OSN 4200s at the network edge into the points-of-presence or central office. A single OSN 4800 provides up to 40 Gbits/sec of trunk capacity (16 OC-48c wavelengths) in a single shelf. Alternatively, two systems may be physically connected and managed as one network element to provide 80-Gbit/sec (32 OC-48c wavelengths) capacity in a 7-ft, two-shelf configuration.

Alidian is marketing its OSN 4000 line on the strength of its Intelligent Service Multiplexing (ISM) architecture, which includes the WavePack, WaveSwitch, and WaveMux technologies.

Unlike technologies that require a separate wavelength for each traffic type, the WavePack technology enables each OSN system to carry multiple services and protocols on one SONET-framed wavelength, which allows service providers to maximize available bandwidth. The technology also enables providers to pre-provision a service to a fraction of its physical interface, freeing unused bandwidth for customers, who may even use other protocols. Packets, frames, cells, and circuits are carried in their native mode and do not require conversion to a common protocol or rigid time slot like ATM or TDM. The technology's service intelligence maintains the quality of service of each protocol traveling on the wavelength.

While voice services fit well into a SONET circuit-based ADM's time-division multiplexing (TDM) hierarchy, provisioning data services in such systems wastes both time and capacity, says the company. Alidian's WaveSwitch technology allows providers to use only the capacity each service requires and can add or drop individual services and application flows at multiple nodes around the infrastructure. It functions like a miniature crossconnect or switch and overcomes the limitations of traditional SONET-ring architecture by creating a logical mesh, similar to a distributed switch infrastructure, that allows every node to tap any service.

The WaveMux technology, which is also found in all three OSN products, is the integrated DWDM optical subsystem and provides the additional DWDM capacity necessary to scale the infrastructure. It allows service providers to deploy several different Alidian products, all scaled to different wavelengths, on the same metro infrastructure.

Alidian has also introduced the MetroSAN interface cards, which create direct connections between the OSN ADMs and Escon or Fibre Channel/Ficon storage area network (SAN) devices, allowing the OSN line to interconnect with previously isolated SAN "islands" across metro networks.
The OSN 4800 scales up to 32 wavelengths and is designed for the larger aggregation points in a metro network or for larger metro networks in general.

Alidian's proprietary technology aims to position the OSN 4000 line ahead of traditional SONET and metro WDM systems, which must deploy separate networking equipment for each service they provide, often resulting in the over-provisioning of equipment and capacity for services that may or may not succeed. The Alidian system, asserts Scott Clavenna, principal analyst at Pioneering Consulting (Cambridge, MA), "stacks up very well against SONET and metro WDM systems, because it's very flexible and it's as scalable as metro WDM."

The future competition will not come from SONET/WDM systems, however; Alidian must differentiate itself from the host of new startups, including Chromatis Networks (now part of Lucent Technologies), Sirroco Systems (now part of Sycamore Networks), and Astral Point, all of which have recently introduced systems similar to the OSN 4000 line. Because none of the new offerings have had any significant deployments, it's difficult to compare them in any real detail, although Alidian's proprietary ISM technology may prove to be a selling point.

Explains Clavenna, "What the other systems tend to do is package all services into either TDM or ATM and then bring them back to a hub and perform switching there. The Alidian network is a bit more distributed in the way it does that. [It] has a proprietary way of tagging each service flow through the network and only performing switching on that service at the location that it's terminated. Ideally, this allows a network operator more control over latency-sensitive services and better use of the bandwidth that it has deployed already."

Two competitive local-exchange carriers, Enkido (Hackensack, NJ) and Everest Broadband (Fort Lee, NJ), have agreed to conduct trials of the OSN 4000 line, though Clavenna is quick to note that without significant deployments, it remains unclear how the technology will affect the market. "It's a matter of, once these [systems] get deployed, seeing how real [they] are and whether [they] do create new service economics or not," he says.