Reconfigurable Optical ADM (Add/Drop Multiplexers)

ROADM is a solution that long-distance data carriers have prayed for, for many years.  We can best describe ROADM by the problem that it solves.

The Problem - carriers want to build a SONET fiber network, provision high-speed connections, then re-provision it as many times as required from a workstation - but they can't !!  This has been impossible in metropolitan area networks, where setting up and tearing down high-capacity optical wavelength connections for business service transport has been hamstrung by the exorbitant costs of manual configuration.  Setting up ADM's has always been a long, complex task, which cements a particular configuration in place.  

The Solutiona ROADM allows the service provider to sit down at a workstation, and dynamically provision an end-to-end, inter-office connection that can tavel thousands of miles, across a DWDM SONET ring.  This can be for a Gigabit Ethernet, a SAN (storage area network), or any other high-speed service. If a ring is configured with multiple ROADM's, the re-configuration capabilities make it analogous to an MPLS virtual private network (VPN) configuration.  The administrator can click on the end-points and go.

Current DWDM technology with ADM's does not afford this luxury. Instead it requires manual configuration of each inter-office service connection, not only at the ingress and egress end-points of the service, but at each of a dozen or more add/drop nodes between. Consequently, provisioning a new high-speed, inter-office connection forces carriers to stack one expensive Sonet/SDH ring atop another.

To understand the ROADM, one must first understand the ADM.


The ADM, or Add/Drop Multiplexer, is a gateway into and out of a SONET ring.  For example, a carrier may have an OC-12 SONET ring that passes through a POP, and they need to use an OC3 of bandwidth from the ring.  One OC12 consists of 4 OC3 data streams.  The only way to ADD (or insert) traffic to the ring, and to DROP (or remove) traffic from the ring, is to splice it and place an ADM directly in series with the ring.  

At the POP, the ADM will send/receive data, and demux the OC-12 into four separate OC-3 streams.  It will allow 3 of them to pass through to the other port, but strip one off of them for use by that site.  The POP location can also insert an OC3 data stream, which will be muxed back together with the other 3 OC3's, back into an OC12. 

The ROADM (Reconfigurable Optical ADM) Explained

Since there are no ROADM standards right now - it is difficult to explain.  Actually, the concept of ROADM is still undergoing a lot of dramatic changes.  In addition, the vendors are coming out with proprietary stuff.  

But carriers have been starved for provisionable dense wavelength division multiplexing (DWDM) in their metro and access networks but have been unable to swallow the costs.  Thanks to ROADM technology, that dilemma is changing.  

Using emerging generic multi-protocol label switching (G-MPLS) control plane standards, ROADM maps wavelengths from metro access through metro core. Eventually, it could take over all grooming of traffic above OC-3 (155-megabit-per-second) speeds and push the Sonet ADM's traditional job of grooming sub-wavelength DS-1 and DS-3 traffic out of the core toward the customer.

ROADM uses DWDM, which replaces the method of deploying Sonet, such as the stacking of Sonet rings, with the stacking of 32 wavelengths on a single pair of fibers."

Multiple benefits may accrue in stages. First ROADM equalizes signal loss across all wavelengths, reducing the need for costly signal boosting equipment. Then, as customers demand service connections to support SAN and other applications from office to office, reconfigurability "comes essentially for free," says Movaz chief technology officer Zouheir Manzourati. "If the node requires no add/drop, we don't charge for add/drop functionality at that node."

Further, ROADM employs switching fabrics that can multiply fiber ring flexibility beyond east-west ring ins and outs to an integrated wavelength selectable switch (IWSS) mesh of multiple directions at each node, relieving carriers of unnecessary optical-to-electrical-to-optical conversion of pass-through traffic.

"We see increasing migration to a world where it's a service per wavelength," Manzourati says. If so, Sonet Multi-Service Provisioning Platform (MSPP) sub-wavelength grooming becomes an edge, collector ring job only. And push-button provisioning becomes a reality in the metro core.


ROADM Vendors

A new wave of DWDM vendors, led in particular by Movaz Networks Inc., Photuris Corp. and Tropic Networks Inc., has all but solved the challenge. They are delivering working reconfigurable optical add/drop multiplexing (ROADM) products at affordable price points. Movaz characterizes the cost of ROADM as "a small premium" with a typical return counted in months. Photuris claims there is no real premium at all.

In any case, the price may now be called irresistible, says Michael Howard, principal analyst for Infonetics Research. He adds that prices will drop further over the next two years with help from leading DWDM and synchronous optical network Sonet/SDH equipment suppliers such as Cisco Systems Inc., Lucent Technologies Inc. and Nortel Networks Ltd., as well as ECI Telecom Ltd.'s Lightscape division, Internet Photonics Inc., Lumentis AB and Photonic Bridges Inc.

Photuris claimed the first ROADM platform delivering live traffic for a Texas A&M University inter-office network, as well as a place in three RBOC) labs.

Lucent was impressed enough with Movaz Networks' RAYstar wavelength switching platform and RAYtracer management system to enter a DWDM and ROADM co-development deal with Movaz..

Tropic Networks' Wavelength Tracker technology for identification and management of every wavelength traveling throughout an optical network across its TRX-24000 metro-optical transport platform has drawn more than $80 million in funding and former Global Crossing chief Robert Annunziata as its chairman.

Further, according to Photuris and Infonetics, RBOCs have issued one request for proposals (RFP) and one request for information (RFIs), with a second RFI expected later this year; several competitive local exchange carriers have issued RFPs; and one inter-exchange carrier plans an RFI this spring.

Infonetics Research Inc. estimates that the market for "systems sold with ROADM capability" will be worth about $85 million in 2004.

One vendor already beating the pavement about its new ROADM solution is Movaz Networks. The company's RAYROADM is an integrated, metro box that boasts the ability to reconfigure any wavelength or any combination of up to 40 wavelengths. The ROADM box can be deployed separately or as an upgrade to existing RAYexpress customers, Movaz says.

Movaz says the 10 RU RAYROADM and the 4 RU RAYexpress products are managed by the same network management software, an appeal to the company's current set of 46 customers. That number is probably set to grow, because Tokyo-based reseller Netmarks Inc. says it plans to test Movaz's gear.

Movaz's next product release for its ROADM gear, early next year, will include the ability to interconnect up to four rings, says King. The so-called multi-ring ROADM will provide the ability to add and drop wavelengths from multiple rings, and the ability to switch wavelength from any ring to any other ring.

Within one year, Movaz says it will have colorless, or tunable, ROADMs, an improvement that enhances the ability of the device to drop any wavelength to any add/drop port on the ROADM.

Movaz is, of course, but one of many competitors in the space.

Tropic Networks' Lane says his company's ROADM box has been generally available since last year, but it hasn't been in any network deployments or trials "that we've admitted to publicly." Tropic and Alcatel SA (NYSE: ALA - message board; Paris: CGEP:PA) constitute one paired set of vendors reportedly on the shortlist for SBC's ROADM RFP.

Mahi Networks Inc., interestingly, just acquired some ROADM capability with its purchase of Photuris's remains (see Mahi Nabs $70M, Photuris Assets and Photuris & SBC: The Inside Story ). And Lucent is said to be close to announcing a new piece in its Metropolis line based on Movaz technology and with ROADM capabilities in mind.

It's worth pointing out that ROADMs supplied by Marconi Corp. plc (Nasdaq: MRCIY - message board; London: MONI) have been carrying live traffic in BT Group plc's (NYSE: BTY - message board; London: BTA) network for several years (see Tropic: Hot or What? ).