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Optical-electrical network convergence primer

Optical-electrical (opto-electrical) network convergence, also known as optical IP convergence, is the process by which optical transport combines with electrical layer services -- in other words, it is where synchronous optical network (SONET)/

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Time-division multiplexing (TDM) circuits meet Ethernet/IP packets. Historically, carriers have handled the circuit-packet network duality by wrapping Ethernet/IP packets for transport across the optical network in TDM frames. This approach has meant maintaining and managing discrete optical and electrical infrastructures, with all the resultant capital and operational expenses.

The goal of optical-electrical network convergence is to collapse the network layers by mapping Ethernet/IP directly onto optical wavelengths. With full opto-electrical convergence comes the ability to support basic optical transport and electrical layer connectivity using a single layer of devices, which will reduce capital equipment costs and cut management complexity and operational expenses while efficiently supporting next-generation IP services.

Why do you need to know about opto-electrical convergence?

Optical-electrical network convergence is not a passing-in-the-night trend. IP is on the rise while TDM is waning.

After years of discussing how best to handle optical transport in an increasingly Ethernet/IP world, carriers are now watching the barriers to opto-electrical convergence topple down at the same time that market drivers ramp up. For example, older optical and electrical plant is nearing full depreciation while requirements for such bandwidth-hungry IP services as 4G wireless, enterprise Ethernet and consumer broadband offerings such as IPTV increase.

These factors make increased near-term activity inevitable. "We're getting to the point where to meet traffic growth requirements, a native packet solution will be required because it's more efficient and scalable," said Jason Marcheck, Current Analysis director of custom research for the service provider infrastructure group.

"By the beginning of 2011, opto-electrical convergence is going to be a really hot area -- maybe the hottest in all of networking" predicts Tom Nolle, president of CIMI Corp., a strategic consulting firm specializing in telecommunications and data communications. "Within five years, we could see 60% or more of the incremental metro equipment investment being in converged opto-electrical devices."

What do you need to know about opto-electrical convergence?

Many carriers are already are using IP-over-SONET or IP-over-dense wave division multiplexing (DWDM) technology to merge the Ethernet and TDM worlds, but they will need to move beyond those efforts to full opto-electrical convergence. They must remember that opto-electrical convergence is about simplifying connectivity, not transport.

Operating in an environment in which the optical and electrical layers have been converged means not having to know -- or care -- about the transport route. That might comprise a single lambda, multiplexing as part of a wavelength and short-haul copper between two devices, which would be handled by device management. Opto-electrical convergence requires a management system that recognizes the concept of media-independent paths and can map traffic onto the underlying structure, even if composed of discrete optical and electrical layers, transparently to the operator, Nolle said.

This is imperative for operators stitching together older and newer, converged technology, which all of them will do unless planning a green-field opportunity.

Optical-electrical devices meet a variety of carrier needs

Telecom operators will have to determine which type of convergence device best suits their needs. Opto-electrical convergence devices are available from a wide variety of service provider equipment vendors, including Alcatel-Lucent, Ciena, Huawei and Tellabs. Also in the fray, but slower to jump in, are the big router vendors, Cisco Systems and Juniper Networks.

Depending on functionality, these devices carry general names such as converged optical switches, Ethernet switches with Ethernet-over-SONET capabilities, add/drop multiplexers or reconfigurable optical add/drop multiplexers (ROADM). Naturally, devices coming from traditional optical vendors feature SONET and add/drop multiplexing capabilities while gear from the IP-oriented manufacturers finesse the management of electrical flows. An operator's choice will depend on what it needs to accomplish at the convergence layer.

Generally speaking, carriers that must accommodate a heavy optics-based infrastructure will require an opto-electrical convergence device that provides fine-grained management at the electrical layer. Conversely, the more a carrier must support existing electrical-layer technology, the more important it will be to select a convergence box that provides add/drop multiplexing and other SONET management functions.

Once optical-electrical network convergence is achieved, operators can expect to lower their capex and opex costs by having an efficient, scalable way to handle new broadband services.

About the author: Beth Schultz is an IT writer and editor based in Chicago.

This was first published in May 2011

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