Blowing Past the Bottleneck

Expanding Bandwidth to the Edge--and Beyond

Fast forward to the 1990s and this device has proved invaluable, revolutionizing a variety of industries from communications to medicine.

Still, the impact of optical technology remains a question mark to some. Even when the first dense wavelength division multiplexing (DWDM) systems were introduced in 1995--when Internet usage was just gearing for take-off--some industry experts were ambivalent about the need. While transporting vast amounts of information through multiple wavelengths of light on a fiber was awesome in concept, many questioned whether service providers would really fill all that capacity.

Today, DWDM is a given in long distance networks. The next logical step for service providers is to move DWDM into regional and enterprise networks. Consider that in the next 15 to 20 years, 700 million phone lines will be installed. (It took more than a century to install the first 700 million lines.) Internet traffic likely will double in the next three to four months, with Internet users driving demand for bandwidth to the enterprise, the desktop and the home. So far, nobody is complaining of too much capacity.

Graph: Blowing Past the Bottleneck

Yet, when multigigabit signals come off a long-haul route or urban ring, they are often slowed once they reach edge-of-the-network equipment--whether it's enterprise servers and routers or cramped loop facilities that choke the bit stream down to a trickle. But with advances in DWDM technology, optical signals soon will be racing unhindered all the way to the desktop, and eventually, the home. In fact, the time is now for both metropolitan area networks (MANs) and optical area networking in the enterprise and service provider markets.

Different Strokes

Unlike DWDM in long distance networks, there's no one-size-fits-all solution for metropolitan, or optical area networking. In the next two years alone, it's estimated there will be 1,000 new providers of telephone, Internet and wireless communications services--each with varying network needs. Hence, short-haul systems should vary considerably. These can range from DWDM systems designed especially for densely-populated metropolitan areas and short-haul transmission in between central offices (COs), to systems that send optical signals beaming through the air--all of which can affordably circumvent server and loop bottlenecks. Such products push bandwidth to the very edge of the network and beyond, as well as boost capacity in areas already reaching fiber exhaust. Just as important, they let service providers deliver high bandwidth and application services in a choice of ways that suit their local conditions and their customers, while opening new possibilities for generating revenue.

As well as vast bandwidth, these systems deliver flexibility to meet needs that grow more specific as they reach the local loop. Nodes of different sizes can carry traffic designated for a specific local area or placed near major customers. Airborne optics can route signals where fiber cannot go while variable bandwidth interfaces drop off just the capacity customers need. Within the enterprise, new approaches to high bandwidth raise storage area networks and local area networks (LANs) to the optical level.

Getting Around a City or Campus

Some large enterprises already are fueled by fiber optics via high-speed synchronous optical network (SONET) interfaces like OC-3/STM-1, 155 megabit per second (mbps) feeds. A few get OC-48/STM-16, 2.5 gigabit per second (gbps) drop-offs, but the number is still low. Only about 5 percent of enterprises in the United States are served by fiber to deliver such capacity. Yet for enterprise LANs, the standard is fast becoming 1gbps or more. Microsoft Corp. is one example, as Lucent Technologies Inc., Murray Hill, N.J., and US WEST announced last year the software company would be testing a DWDM network on its Redmond, Wash., campus. Many homebuilders are now routinely running fiber to homes, at rates up to 10mbps, expecting that fiber will soon replace or augment traditional copper lines.

A variety of ring-based and point-to-point DWDM systems and optical access systems are now offered that beef up regional backbone fiber capacity and support routine delivery to customers of as much bandwidth as they require--even many gigabits per second.

Graph: Optical Area Network

For example, ring-based DWDM systems are designed especially for regional or urban networks where traffic volume is in constant flux. These systems can answer service providers' loudest and clearest demand: flexibility, flexibility, flexibility. They may be scalable from two wavelengths up to 40, permitting providers to deliver as many as 100gbps per fiber between COs--the equivalent of 1.3 million simultaneous calls on one fiber. This presents a major cost benefit to urban carriers who can't afford to trench new fiber below busy streets.

In addition, these carriers have the option of using different size nodes, enabling them to install rings that match both capacity and cost needs. In the case of leasing bandwidth to an enterprise, a metropolitan provider may need to drop only a few wavelengths at one node, the smaller node may work just fine. Or, a carrier may choose to deploy a very small DWDM system in business customers' basements within a given vicinity, then tying these into a larger, higher-capacity DWDM ring that circles the city.

Rings, Point-to-Point and Other Flavors

Although designed primarily for the relatively short-haul needs of urban areas, rings based on metro DWDM systems can handle sizable distances. Nodes may be up to 40 kilometers (km) apart and configured into rings 200km around without the need for regeneration. With regeneration, the rings may be larger. With some systems, the network architecture can be designed to be ready for 10gbps transmission, which means nodes will not have to be added or moved when stepping up to the OC-192/STM-64 rate.

Metro DWDM systems also may offer other types of flexibility to the enterprise for LANs connection. Line cards may handle variable bandwidth signals ranging from 100mbps to 2.5gbps, with reshaping, reamplifying and retiming at each node. Cards capable of the lower bandwidths are crucial to serving 12gbps or lower speed LANs; cards that can handle a range of bandwidths give providers flexibility in configuring their systems. So, if a customer has a gigabit Ethernet, it can have a 1gbps feed. If all it needs is 100mbps, it can get that, too.

In addition, some DWDM systems soon will be able to multiplex the lower bit-rate optical signal to a 2.5gbps channel--a real breakthrough that will help service providers fully utilize the capacity of each wavelength.

DWDM systems may become available that permit providers to use the 1,400 nanometer (nm) spectrum as well as the 1,500nm band, getting up to 80 wavelengths on one fiber. Such systems will work ideally with fiber designed especially for carrying signals in the 1,400nm spectrum. Carriers with this combination of 1,400nm-ready fiber and equipment made for this spectrum will be able to upgrade their metro systems to higher channel counts gracefully. This solution may be adopted by a carrier's carrier, for example, transporting large amounts of traffic in a mesh network.

There are cases where a provider, such as a competitive local exchange carrier (CLEC) targeting enterprise customers, doesn't need all the capabilities and bandwidth of a ring-based 40-wavelength system. This customer could use a smaller point-to-point or access ring DWDM system, which are also becoming available. This type of system is ideal for addressing fiber exhaust between certain spans in the network or delivering service to specific enterprise customers or Internet service providers (ISPs)--even for linking a computer directly to a router or Internet protocol (IP) or asynchronous transfer mode (ATM) switch.

Access rings may also offer considerable flexibility. For example, variable bit rate (VBR) line cards with retiming that can be configured remotely allow signals to pass cleanly through a series of nodes and rings. In addition, non-amplified point-to-point systems can reach up to 70km., making them very cost-effective for fiber exhaust over longer spans.

Flexibility also is enhanced when DWDM systems for regional and loop applications work with a common operating system for ease of network operations, administration, maintenance and provisioning (OAM&P). Ideally, the same operating software should manage optical systems from the backbone to regional facilities to the network edge, including access.

Photons Through Free Space

Congested urban streets and conduits can severely limit carriers from getting fiber out to more enterprises and homes. However, metro DWDM poses yet another solution: beaming photons through the air. Photons can travel reliably and safely even through snow, sleet, rain and fog, although systems must be engineered to take local weather into account.

On a clear day--typical of the U.S. Southwest, say--an open-air DWDM system can transmit signals 5km or more. Free-space photonics is a great solution in cases where fiber connections simply aren't practical due to cost, geography or other constraints.

This technology certainly can be used for permanent links to urban buildings, for ships at sea communicating with a base on land, over desert or rocky terrain, or over the walled canyons of a big city. It's also a great solution when transmission facilities must be set up quickly, and not necessarily just temporarily.

Airborne photonics can signal instant market entry for new service providers. They need invest only a small amount in infrastructure before rolling out service to customers, and their networks can grow in step with their subscriber bases.

Other applications for DWDM systems through the air might include temporary voice and data links for special events such as conventions or major sporting events. The equipment is much smaller and easier to transport than satellite or microwave systems--about the size of a rural mailbox. The airborne photonic signals also are extremely secure, making them useful for military and financial purposes as well.

One such system eventually will transmit up to eight wavelengths point-to-point, with each wavelength carrying an OC-48/STM-16 signal.

To the Endpoints

With regional networks fueled by DWDM, the name of the game for the next few years will be access--high-bandwidth access at the end of the loop to the enterprise, the server, the desktop, or other information appliance, and eventually, the home.

Coming soon are access technologies incorporating DWDM, suitable for links within businesses and even to homes. One ring-based system, which transmits up to six add/drop wavelengths on one fiber, uses coarser (broader) frequency bands than its higher-capacity cousins, permitting significant cost reductions. Designed for use within a metropolitan area, a campus, or a neighborhood, a metro access system employs a central node that aggregates the six wavelengths, which can each serve various locations.

Variable capacity line cards will permit delivery of the specific amount of bandwidth needed, up to 2.5gbps. If more wavelengths are needed, DWDM channels can be inserted and delivered to that customer. This allows the carrier to match capacity to its customers that demand it, when they demand it.

The delivery of high bandwidth and low-latency capabilities to enterprise and service provider networks will open the opportunity for enhanced data transport between servers and routers as well as new applications. In addition to reducing complexity and points of failure in the data networks, an optical approach enables high-speed LANs and storage area networks to connect to other endpoints across the metro and wide-area DWDM network. This "optical area networking" approach supports server-based network interface cards such as OC-48c and OC-12c and gigabit Ethernet; storage adapter cards that bridge data transport into the optical domain and edge devices that bridge enterprise networks to metro DWDM offerings.

Once an optical signal reaches its destination, it may have to be segmented into smaller chunks, depending on customer needs. A 2.5gbps signal may need to be divided into 1gbps signals for gigabit Ethernet or fiber channel LANs, for example. Bottlenecks still may have to be overcome, particularly on enterprise systems such as servers. Today, in local area or storage networks, servers can expend much of their processing power just dealing with IP and other protocol stacks as data enters or exits the server and moves from one part to another.

Effective strategies and systems for the very edge of the network are being developed. For example, interface systems can be configured by the service provider to segment higher bandwidth signals even down to gigabit chunks if needed. Then, edge devices can interface these lower bandwidth signals--or OC-48/STM 16s or OC-12/STM- 4s--directly into workstations or servers, in IP rather than ATM format.

Interfaces also can format signals directly into gigabit Ethernet or fiber channel protocols. Such devices permit enterprises to link servers and workstations into optical area networks for voice and data communications operating at high bandwidth, and connect them directly to optical wide area networks (WANs).

On-premises optical interfaces can be especially valuable when a company links geographically dispersed servers into a storage network, so everybody in the enterprise has instant access to data or applications located on any server. Servers also could tie directly into public optical networks, perhaps over frame relay links, in a virtual private network (VPN). Direct connection to the optical network eliminates overhead, management and port costs associated with traditional gateway routers.

The capacity today of DWDM systems tailored to enterprise needs--delivering up to 80 wavelengths, each carrying a 2.5gbps signal, and potentially a 10gbps signal--combined with new interface technologies, indicate that it may soon be possible to deliver any amount of bandwidth to any workstation.

To the Limits

Thanks to the power of photons, applications once considered futuristic dreams are becoming not only near-term realities, but feasible and cost-effective: real-time transmission of medical and engineering images, real-time video, real-time disk mirroring, the whole litany. The new regional, local, loop and access systems being introduced are pushing optical networking to the edge, and to the limit.

As metro DWDM systems migrate from the long distance backbone to the local networks, the next steps are clear. Optical area networking can unleash an entirely new level of communications, unrestricted by bandwidth, and put an end to the "world-wide wait" on the web. No longer does the last mile have to be the missing link.

The authors are with Lucent Technologies Inc.'s Optical Networking Group. Frank Galuppo is director of WaveStar OpticAir Market and Product Development in Holmdel, N.J. and can be reached at frankgaluppo@lucent.com. Tim Sullivan is vice president and general manager of Optical Area Networking in Richardson, Texas and can be reached at tpsullivan1@lucent.com. Jeffrey Wilensky is product manager, WaveStar Metro OLS products in Holmdel, N.J. and can be reached at jwilensky@lucent.com.

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