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Metropolitan Networks
Dr.Suresh Gopalakrishnan
Thursday, January 30, 2003
“FASTER AND CHEAPER” ARE FREQUENTLY HEARD rallying cries from the supporters of the bandwidth revolution. At the height of the bandwidth revolution, telecommunications carriers drastically increased the capacity of their networks, which now run at speeds of up to 10 Gbps. However, even today businesses are typically connecting their networks at speeds of less than 2 Mbps—just as they did in the late ‘80s. Worse off still are home users who typically connect to the Internet over dial-up lines at speeds of 28-56 Kbps.

The last few years saw the rise and fall of a set of carriers who tried to offer cheap, Ethernet-based bandwidth access lines using new optical fiber build outs or leasing lines from regional bell operating companies (RBOCs). The large amount of money required to build or lease their networks and the inability to convince corporate customers to switch to a new and unproven carrier, ultimately doomed these carriers to failure.

While these carriers failed, the concept of high-speed broadband access and services at affordable prices has remained. Now, carriers are attempting to reconcile the capital costs of deploying new Ethernet networks with the potential return on investment from Ethernet-based services.

Let's take a look at how the industry is adopting Ethernet to provide faster and more cost effective broadband access.

Where We Are Today
Deployments by the new competitive telecommunications carriers proved that Ethernet as an access technology can provide the scalable, affordable and flexible bandwidth to satisfy even the most demanding of users. This technology has the simplicity and ubiquity to enable a wide range of value-added services, such as storage area networks, outsourced applications and virtual private networks (VPNs). These deployments also revealed a new set of considerations that would impede any large-scale roll out:

• Managing and provisioning bandwidth

• Prioritizing and segmenting traffic

• Operation, administration and maintenance (OAM)

• Integrating Ethernet equipment with existing
operations support software (OSS)

Bandwidth Provisioning
Most end users do not need one Gigabit, or even 100 Mbps, of bandwidth that Ethernet can provide. Instead, carriers found that they could deliver tiered levels of bandwidth at different price points, effectively servicing a wide range of small, medium and large businesses. The tools to groom raw bandwidth are not inherent in Ethernet technology and carriers found they needed to enhance their networks with rate limiting and rate shaping technologies that would allow them to increase or decrease bandwidth based on customer demands.

Traffic Prioritization and Segmentation
Traffic prioritization and segmentation enables carriers to build and sell reliable and predictable connections over an Ethernet infrastructure. While the Ethernet connection to the end user is dedicated and only contains their traffic, at the first network aggregation point, it mixes with other customers’ traffic. To bring traffic segmentation capabilities to Ethernet, two primary protocols have emerged; DiffServ and multi-protocol label switching (MPLS).

DiffServ classifies traffic according to different classes. Once assigned a class, these packets are prioritized, rate shaped or blocked accordingly as they progress through the network.

MPLS sets up the equivalent of an asynchronous transfer mode (ATM) virtual circuit and labels packets entering the network. With a label attached, the traffic can be switched through the network without the need for time-consuming packet header analysis at each network router. MPLS allows carriers to assign different types of traffic to different paths in the network.

OAM Capabilities
OAM capabilities allow carriers to trouble shoot their networks. While trouble shooting standards have long since been developed for local area networks (LANs), carrier networks still lack many of the same solutions. Today vendors are building proprietary OAM capabilities into networking equipment that will provide carriers with trouble shooting tools, and standards bodies are actively engaged in defining industry standards for Ethernet OAM. The Institute of Electrical and Electronics Engineers (IEEE) 802.3ah working group is developing an OAM for Ethernet in the first mile while the Metro Ethernet Forum is working on OAM for Ethernet services. The Internet Engineering Task Force (IETF) and the International Telecommunication Union (ITU) are also working on their own Ethernet OAM standards.

OSS Integration
Prior to any service delivery, carriers are required to integrate many operational processes at the service, equipment and network level with their OSS suite. A typical OSS suite uses tools from a collection of vendors to handle these processes.

Today, the industry's software vendors and equipment vendors have defined application program interfaces (APIs) and made these APIs public, easing the integration process.

Next Steps: Network Re-use to Reduce Cost
While technical progress has been made, carriers still face a number of business issues that have stalled the deployment of new services. Their networks are handling increasing amounts of data, with traffic doubling every quarter for some carriers. They are also under significant pressure to lower operational costs and improve profitability.

Today’s carrier networks are built around legacy ATM and synchronous optical network/synchronous digital hierarchy (SONET/SDH) technology and services. Using these technologies, carriers have built a highly profitable business delivering traditional data services, leased voice lines and broadband services based on digital subscriber loop (DSL) technology. Carriers need a migration strategy that will allow them to leverage their significant investment in ATM while rolling out new Ethernet-based services without cannibalizing this large source of revenue. As the traditional carrier preferred technology, ATM is expected to continue playing a major role in public network infrastructure. In fact, this established infrastructure offers carriers a convenient way to migrate to Ethernet-based networks.

Carriers have underutilized ATM networks and typically have the capacity to support access rates of one Mbps to 100 Mbps. This under-utilization presents an ideal way for the carriers to enter the Ethernet services market quickly and cost effectively. By expanding their ATM core networks with Ethernet technology, carriers can offer Ethernet access and point-to-point LAN extension services within the same metro or between different metro areas.

The Future
This is where I get to take out my crystal ball and make some predictions that the industry can look back and laugh at in ten years. Using Ethernet in the access or last mile network to deliver value-added services, carriers can increase revenue per subscriber by tailoring services and bandwidth quickly and economically for each individual customer.

Carriers operating in countries that are slow to roll out broadband access to the masses will take baby steps towards this ideal state. They will initially extend the life of their existing networks by deploying products that allow them to offer Ethernet services over ATM and SONET/SDH networks. As traffic continues to grow, carriers will begin to migrate to Ethernet technology, deploying it where and when it will enable carriers to reduce operational costs and increase revenue from the delivery of advanced services.

Suresh Gopalakrishnan, Executive Vice President, Engineering brings more than 10 years of senior engineering management experience to Riverstone Networks (NASD:RSTN). He was previously senior director of corporate strategy at Cabletron Systems. Prior to that, he has held engineering and management positions at ZSP Corporation, Sun Microsystems and Hewlett Packard. He holds a Ph.D. in electrical engineering from the University of Idaho.

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