Best of all worlds: intelligent hybrid platforms offer reliability of legacy, flexibility of next-gen systems

The latest buzz is that the faint pulse of telecom is beating in the metro networking market. Telecom managers know that long-haul fiber capacity is abundant and high-speed, last-mile access solutions are already being deployed at breakneck pace. So the sweet spot for revenue requires metro networks that pull it all together. It is the next piece needed to enable the wonderful gigabit services everyone's talking about. However, planners and engineers can no longer simply pull out the corporate checkbook and start building.

A lot of equipment is already in place. Maybe today's low price of legacy product is enticing enough to make use of this technology. But is it ready to handle the growing demand for advanced data-centric services like native Ethernet and Gigabit Ethernet for VIANs and VPNs? Can that architecture match up with the requirements of on-demand, wavelength services?

MANs are built typically with SONET rings made up of ADMs (add/drop multiplexers). Synchronous transport brought digital telephony into the optical era with more cost-effective and reliable network elements and topologies. DCS (digital cross-connects) are used to interconnect traffic from ring to ring. They perform a "groom and fill" function that helps make better use of backhaul circuits destined for central switching locadons or POPs. Recently, DWDM has been used in some metro applications to increase fiber capacity in much the same way as it is for long haul. It may be used to offer large-capacity, carrier-to-carrier connections in the metro or for fiber-exhaust in regional networks such as the New York/Washington, D.C., corridor. Some inexpensive versions of DWDM such as low-count lambdas over shorter distances, have been used for SANs (storage area networks) and other high-bandwidth, point-to-point applications. Combine these solutions and one could have a reliable, albeit disjunctive, multiservice met ro network. Unfortunately such a network is not scalable and flexible enough for new services models.

Trying to tap into one of the few growth areas, vendors increasingly are announcing "next generation" or "metro" products that promise to help carriers do it smarter, faster and better. However, many of these god boxes have failed to find favor with carriers. It is not optimal for next-gen transport elements to possess all the functionality of service layer voice and data switches.

Among these myriad options are also a few solutions that efficiently integrate the essential transport features for these new services into a very small, dense, flexible "hybrid-optical" platform. Topped off with more intelligence, these make up a cost-effective, scalable metro infrastructure geared to handle today's traffic as well as future data-centric services.

Figure 1 shows a typical metro network built with traditional network elements. There are stacked rings of OC-3, 12 and 48 with DCS for interconnection and grooming. Two types of WDM systems are shown: A regional system is connecting two POPs in different cities and an enterprise system is used for the SAN. More detail at the metro access shows the need for customer premises or access node equipment such as frame relay access devices, ATM concentrators and WAN access routers for service-layer aggregation.

Figure 2 shows a hybrid-optical platform that combines a multi-ADM function to close multiple rings and enable mesh topologies, with built-in DCS for grooming and integrated DWDM for both long-reach regional connections and short reach for SAN or OADM applications. Some platforms even integrate data handling such as GigE, FICON, Fibre Channel and video.

At the first stages of planning and implementation, both approaches may seem about equal in cost and complexity. Depending on how small the network is, the old way can even be less expensive. A simple eight-node, OC-48 transport ring for voice and some data services is half the initial capital cost of one built using the new hybrid-optical systems. Soon after the plans go from paper to plant, though, some big differences arise. At a hub or POP site, the combination of a few gateway ADMs, a DCS and possible DWDM nodes add up to 10 times the space, seven times the power and cooling and three times the cabling of a hybrid solution. For a colocation site, that amounts to about $18,000 per month for one site.

Long-term maintenance costs differ, too. Each network element brings additional points of failure. Common spare parts are unlikely across different platforms and different vendors. For one DS3 office jumper, three or four different circuit packs may be doing the job of one in a hybrid system. Newer, high-density cards that make up hybrid equipment share universal subsystems, so an entire site spares kit may consist of only 10 components. Network engineers trained on traditional equipment are easier to find, but more than one person may have to cover the full spread of equipment. All of this amounts to a more than 65 percent savings on average. For one small, six-node MAN that's nearly $8 million saved over a five-year period, according to Probe Research.

The provisioning match-up is really no contest. Legacy networks, consisting of many different types of network elements purchased from multiple vendors, can be complicated and time consuming to provision. It can take a carrier weeks or even months to set up a new circuit from Washington, D.C., to New York. A few of these next-gen hybrid platforms can even offer point-and-click capability across multiple network layers (e.g., SONET, DWDM and data) for end-to-end provisioning that is done in minutes or seconds. This will shave off valuable time and promote on-demand services for additional revenues to cash-strapped carriers.

Now what about the future? How do these solutions scale up for capacity, services and flexibility for new technology? Legacy network elements alone do not support the requirements of tomorrow's networks. Even combined as one solution, they lack the flexibility for unpredictable growth. The cost of expanding legacy equipment is not linear. It quickly gets out of control in terms of cost, not to mention complexity.

By nature, ADM and DCS do not offer native support for switching data or packetized traffic. WDM systems may use entire wavelengths or simple combiners to pack data onto light. Some of the hybrid optical systems integrate efficient data handling, such as Layer 2 GigE switching, to use existing network infrastructure more efficiently for support of data-centric services through the metro. Using the GigE features of these systems, carriers can engineer their networks for over-subscription of the unpredictable IP services traffic, allowing them to get the most out of network resources. Additionally, such data-aware features give carriers the ability to offer new, differentiated bandwidth services, such as pay-by-the-slice connectivity with selectable protection. Some of these new platforms will migrate easily to support the upcoming standards for intelligent self-provisioning of core optical capacities from edge devices. They also provide dynamic restoration capabilities in a mesh environment. Currently, multipl e industry bodies are working on various items for standards such as GMPLS (generalized multiprotocol lambda switching) and O-UNI (optical-user network interface).

When it comes to deploying this new gear, one of the advantages is that it's possible to start with familiar, ubiquitous technology such as traditional SONET rings or even simple point-to-point connections. Since SONET, WDM and grooming functions are integrated on the same platform, carriers can upgrade from DS1 to 10-Gbps DWDM with a simple card change. Hybrid optical systems support a wide range of topologies, allowing easy migration from ring or star to full mesh. This flexibility is a key benefit for carriers looking for a build-as-you-grow tactic in their network deployment. It also enables them to offer on-demand, differentiated services based on various protection schemes. Carriers can offer fast, guaranteed ring-based circuit protection (gold service), less expensive but shared mesh protection (silver service) and preemptable or no protection at all (bronze service). Using the mesh capability of this integrated platform, carriers can provide geographic expansions, additional capacity and new services without having to upgrade the entire ring or network. This allows network managers to add only what they need when they need it. This build-as-you-grow approach greatly improves bandwidth utilization, aligns investment with revenues and adds a sharper competitive edge while keeping options open for the future.

Hybrid-optical platforms possess intelligence that combines the reliability of SONET rings with the flexibility of mesh into an architecture that supports data-aware and high-capacity interfaces that can be tailored to specific needs. Integrating mesh intelligence with high-density SONET, smaller distributed grooming and optical networking has produced a building block for metro networks that can be profitable even in today's financial climate. In addition, these networks also will be ready for future demands, Combining proven transport technologies in a smart, cost-effective way for the metro core enables efficient, high-capacity networks. Flexibility is key. New platforms must coexist with legacy gear while providing an infrastructure that supports the appropriate networking capability, when and where it is needed. Prudent steps must be taken to collapse metro network layers, reduce complexity and improve manageability. The resulting cost savings allows carriers to offer new high-volume, low-margin services profitably. They also will be in a better position to offer traditional services competitively.

Michael Schneider is a proposals manager for Lightscape Networks, an ECI Telecom company (michael.schneider@lightscapenet.com).

COPYRIGHT 2002 Horizon House Publications, Inc.
COPYRIGHT 2002 Gale Group