Success in the metro optical market: designed from ground up

Feb. 1, 2001
Evaluating metro-class equipment

In a blistering metro market, success depends on the application of optical networking to meet requirements unique to metropolitan-area networks.

ONI Systems Corp.

It's no surprise that carriers are eager to serve the metropolitan-area-network (MAN) market. Metro action is heating up fast and promises to stay hot for quite some time. Carriers are clamoring for innovative and cost-effective ways to design for, and succeed in, the MAN boom. Analyst firms predict solid growth in the metro network for both traditional SONET/SDH and new all-optical equipment.

Solving the lamented bandwidth crunch at the access level depends largely on overcoming the metro "bandwidth gap" between the access and long-haul portions of the network. Nearly everyone agrees that success will depend on the application of optical networking to MANs.

Succeeding in the metro optical market requires a fresh perspective designed specifically to meet metro's unique needs. The best place to start is with equipment vendors who understand MANs from the inside out.

There are different network drivers in the MAN than can be found in the long-haul network. Long-haul networks focus on moving data and voice traffic across distances that range from several hundred to thousands of kilometers, with the primary challenge to amplify signals intermittently so they maintain the same intensity and integrity at the destination as at the source. By contrast, MANs manage traffic among enterprise networks and end users within a single or cluster of metropolitan areas, as well as provide an "on-ramp" to long-haul networks for enterprise and end-user traffic.
Existing and emerging transport service will provide the bandwidth and connectivity for an expanding array of metropolitan end-user applications. Many of these applications are driving the growth of metro optical networks.

Applications found in the MAN differ from those found traveling over long-haul networks. One will find a higher concentration of bandwidth-intensive and distance-sensitive applications, such as data storage, content delivery, interactive multimedia, and digital TV (see Table). Such applications are more efficiently deployed when information users are located within a few hops of the source. Other applications such as residential voice and Internet services require access not only to national Internet service providers (ISPs), but also to local service providers and other users. A properly designed MAN will provide a network that meets these local/regional needs.

These applications are transported using some of the same transport methods as long haul, such as OC-3 (155 Mbits/sec), OC-12 (622 Mbits/sec), OC-48 (2.5 Gbits/sec), and in some cases, even OC-192 (10 Gbits/sec). However, enterprises and end users do not typically request bandwidth in such large increments. DS-0 (64 kbits/sec), DS-1 (1.544 Mbits/sec), DS-3 (44.736 Mbits/sec) and 10/100 Fast Ethernet are more widely requested, as are traditional ATM and frame relay circuits. Other protocols, such as Fibre Channel for data storage and Gigabit Ethernet (GbE) for Internet Protocol (IP) traffic and data storage, are designed into more and more metropolitan networks to support the increasing demand for both.
Figure 1. A true optical network provides connectivity for a variety of metropolitan customers with the required bandwidth, manageability, and scalability-all over transparent optical interfaces.

In addition, there are also many different ways for customers to connect, and each connection has different requirements. The most prevalent customer connections are residential-consumer access, interoffice interconnectivity, business-to-wide-area network, business-to-business, and ISPs. The carrier must see that each connection has survivability and manageability, desired capacity, service transparency (if required), and scalability for future customer growth-all provided by the carrier at a competitive price (see Figure 1).

Furthermore, metropolitan networks have two components: the metro core and metro access. Because users interact with the network at the metropolitan rather than at the long-haul level, the metro-access level is the point at which the network needs to focus on flexible connections and connection speeds, services, protection, and manageability. The metro core acts as a collector network for the enterprise and metro-access networks, interfacing with the regional and long-haul networks. Both segments of the MAN are instrumental and also provide the perspective from which carriers and service providers need to design their future networks.

Many challenges are standing in the MAN designer's way. First of all, existing metro networks were primarily designed to carry voice-oriented time-division-multiplexing (TDM) traffic streams, and this existing infrastructure is not optimized to handle the variety of high-capacity traffic types currently emerging. Also, as mentioned, a variety of applications are driving the tremendous traffic growth for interoffice, business-to-business, ISP, content delivery, and data-storage interconnectivity over a variety of traffic types such as legacy SONET, GbE, Fibre Channel, and Escon. All of these applications and services are converging upon metro networks at the optical layer.

For a network designer at a carrier or service provider looking at this metro market, there are important issues to consider when building a differentiated business model for such service delivery. Questions include how to:

  • Deliver a broad service portfolio that differentiates itself from the marketplace.
  • Build a network that scales quickly enough to meet increasing customer demands and provide service survivability.
  • Provide integrated network management of a multivendor service-delivery platform.
  • Support (flexibly) and provision (dynamically) a variety of traffic patterns and traffic types.
  • Provide interoperability among legacy and next-generation systems.
  • Automate day-to-day network planning and end-to-end service management and operations.
  • Give customers direct feedback and control of their network parameters.
  • Accomplish all of the above cost-effectively.

End-user demands are driving the characteristics of today's and tomorrow's metro solution. Users want more affordable bandwidth for their data-intensive activities and flexibility in choosing and changing telecommunications services. From the carriers' perspective, these demands require cost-effective subwavelength transport, flexible and scalable interfaces, remote manageability, a variety of traffic patterns, lower entry cost, and optimum scalability.

Metro-network designers and service providers need to fashion solutions that meet both the current and evolving needs of users of the network, ranging from enterprises to residential users. Here are some of the specifications that need to be designed into the network:

  • Flexibility of service delivery. Users want a variety of services to meet their particular communication needs and dynamic provisioning of these services as their needs change. This requires transparent, optical interfaces for multiservice diversity and fast, on-demand, end-to-end service activation. An open-management platform will enable an interface with other systems and applications, enhancing a network's provisioning capabilities. In addition, because not every customer will connect to the MAN in the same way, the service provider needs the ability to provide flexible and scalable network configurations to meet customer demands.
  • Reliability and manageability. Users expect a high level of reliability from their data service provider. From a network perspective, optical technologies help carriers and service providers achieve this high reliability through fast, optical-layer protection, including network recovery within 50 msec or less. A comprehensive network-management system that is a standards-based, open platform for multivendor interoperability enhances the reliability of a network by managing and monitoring services from end to end across a multivendor network.
  • Service differentiation. As carriers and service providers face increased competition for users' business, they need to offer a wider range of communications services at lower prices. A sophisticated network-management system can help a service provider achieve this by reducing network operational and maintenance costs while increasing complete network reliability and service survivability. Also, by providing customer management of their own network through a customer network-management system, service providers can provide a value-added service.

Applications drive technology in the metropolitan marketplace-not simply raw bandwidth as required in long-haul networks. The ability to deliver bandwidth will be assumed. Two emerging service drivers for the metropolitan-area market that deserve special attention are Ethernet services and storage connectivity (see Figure 2).

Enterprise connectivity to the MAN is exploding with LAN infrastructure fueling that growth. These Ethernet services come in a range of speeds from 1 Mbit/sec to 1 Gbit/sec. Enterprise data is typically distributed, and enterprise customers want to extend their local networks to remote offices or campuses. They also want this metro-wide extension to be transparent. Service providers generate new revenue streams by offering native Ethernet services over a GbE wavelength to these enterprise customers.
Figure 2. Growing demands for data storage and Ethernet services are driving service providers to build networks that can accommodate such traffic requirements.

There has also been an increased demand for data storage necessitated by the need for data backup, recovery, and replication. Today's storage solutions are inadequate to meet these growing needs, so storage-centric service providers are emerging to take advantage of this storage outsourcing trend. They are building networks designed around Fibre Channel and/or GbE transport protocols.

Furthermore, as service providers begin to shift their focus from bandwidth to services, they need a network that provides the greatest flexibility and simplicity for these new services. An all-optical network allows for transparent, native protocol transmission, significantly reducing the number of protocols required for data transport. In this scenario, IP, TDM, and other data-centric services are delivered directly via optical wavelengths without inefficient conversion to electrical signals.

Until recently, economics still favored electrical transmission for all but long-haul applications. Prices for optical components such as transceivers and pump sources have been very high, largely because they are extremely difficult and time-consuming to manufacture. Only a few companies possessed the skills to build them, keeping supplies low and prices high. In addition, metro networks by definition and topology need far more components than long-haul networks as they switch and route wavelengths around the MAN. As a result, there's even greater price pressure on optical components for metro-network designers.

Technological advancement in the design and manufacture of optical components is helping matters, with more reliable and less complex manufacturing processes driving costs down. With prices finally coming more in line with metro-network designers' budgets, it's becoming cost-effective for metro-core rings and metro-access networks to deploy all-optical technology.

So where does a metropolitan service provider go from here? Metropolitan operators need to deploy equipment in a complex environment that includes a mixture of legacy voice and new data equipment such as SONET terminals, DSL access multiplexers, ATM switches, gigabit IP routers, digital-crossconnect systems, and long-haul terminals. This equipment will require high density and must be flexible enough for installation in a variety of network locations.

Furthermore, when it comes to the creation of revenue-generating services, carriers should evaluate their equipment needs on the basis of the following capabilities:

  • Dynamically provisioned services with capacity on demand.
  • Scalable and survivable customer capacity.
  • Comprehensive set of network offerings that include multiprotocol, protected, and unprotected services.
  • A complete network-management system that can manage multiple, multivendor subnetworks through a single-client interface with customer-managed internetworking options.
  • New revenue-generating services such as lambda virtual private networks available without deploying additional equipment.

Also, to maximize carriers' return on investment and competitive advantage, metropolitan service providers must incorporate equipment that allows them to grow top-line revenue while decreasing the time-to-revenue and minimizing operational expenses. Top-line revenue can be achieved by providing multiprotocol support for comprehensive service offerings and protected and unprotected options for different service-level agreements. By incorporating a sophisticated management system that automates provisioning processes and deploying flexible network architecture to support modular build-outs, a service provider can rapidly fulfill customer-driven requests and reduce time-to-revenue.

Reducing operational and maintenance expenses requires a mixture of the following:

  • A scalable network architecture that allows a service provider to increase network capacity by changing out or adding new cards in-service.
  • A highly dense platform, with respect to physical size and port count, that reduces floor space and power requirements within points of presence.
  • Protection schemes that allow channel reuse around a network, reducing the need for additional equipment or network overlays to support the additional bandwidth.
  • Automated network planning tools that improve network design as well as reduce initial network design costs by minimizing future operational and maintenance costs.
  • Improved network efficiency by leveraging common infrastructure over multiple user types through a transparent optical network.

Carriers planning now for all-optical metropolitan networks that directly meet their customers' service will be in the best position to take advantage of the revenue and market-share advantages that all-optical MANs can deliver. Forward-looking carriers owe it to themselves-and their customers-to put their faith in metropolitan optical solutions built from the ground up to serve the distinctive requirements of this market.

Hugh Carspecken is senior product marketing manager at ONI Systems Corp. (San Jose, CA). He can be reached at the company's Website,