TECHNOLOGY TRENDS O PTICAL NETWORKS AGILE NETWORKS: SELF SERVICE


Operators are looking foward to the holy grail of dynamic optical neworks that can reconfigure themselves to provision capacity and restore faults . By Roy Rubenstein


optical layer, to boost efficiencies and reduce costs. It is the photonic layer, the ‘plumbing’ that props up the network, where flexible optical wavelength switch- ing will make a telling contribution. “The challenge of most service provid-


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ers largely hasn’t changed for some time: dealing with growth in demand economi- cally,” says Drew Perkins, CTO of optical equipment company Infinera. “How can operators grow the capacity on each route and switch it, largely on a packet-by-packet basis, without increasing the numbers of dollars going into the network.” Improving switching at the optical layer


has been an ongoing challenge, but new more-capable photonic switch elements— dubbed reconfigurable optical add/drop multiplexers (ROADMs)—coupled with control plane and management software (see box) promise finally to deliver config- urable optical meshed networks. Ron Kline, principal analyst for network


infrastructure at Ovum, says a reconfigura- ble optical network is a holy grail: “It refers to a network that is smart enough to recon- figure itself in response to provisioning requirements and restoration events.” Dynamic optical networking has been


an industry goal for over a decade. During the dotcom boom of the late 1990s, projected bandwidth requirements led operators to believe that customers would dial up lightpaths on demand. This spurred optical system vendors to develop large optical cross-connect switches. But the business case never materialised. “The industry has been transitioning


towards this vision slower than anyone would have thought 10 years ago,” says Bill Kautz, staff portfolio planning manager at Tellabs. Instead, dynamic optical network- ing enabled at the electrical layer has taken hold. Using electrical switches, operators can set up connections quickly but at sub- wavelength capacities. “This has delivered


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arriers are assessing the trade-offs over how best to architect their networks, from the router to the


tremendous flexibility,” says Joe Berthold, VP of network architecture at Ciena. Operators have deployed ROADMs, but


currently they offer limited wavelength agility such that network restoration and wavelength provisioning are still largely manual processes. Electrical switches can set up connections within a second, support shared mesh restoration in under 100 milliseconds, and they have a proven control plane that can oversee networks of 1,000 nodes. “This is the baseline chal- lenge for dynamic optical networking, and the alternative [to electrical switching] that carriers look for,” says Berthold. AT&T’s Optical Mesh service, enabled


using Ciena’s CoreDirector electrical switches, allows customers to change their access circuits in Sonet STS-1 (50 Megabits- per-second) increments via a web interface. “We want to take that low speed service to a higher level—1 Gigabit and above,” says Jim King, executive director of new tech- nology product development and engineering, AT&T Labs. But switching at the electrical layer is


costlier than at the photonic layer, while only the photonic layer switches full wave- lengths. A dynamic photonic layer is also a prerequisite for more advanced customer services: “If you want to do cloud comput- ing but the infrastructure is fixed,


Backbone/metro ROADM market 7,000


n Backbone ROADM n Metro ROADM


6,000 5,000 4,000 3,000 2,000 1,000 0


2009 2010 2011 2012 2013 2014 Source: Ovum


‘hard-wired’ connections, that is basically incompatible,” says King. “The Layer 1 cloud should be flexible and dynamic in order to enable a much richer set of customer applications.” According to Infonetics Research, the


optical networking equipment market has been growing at an annual compound rate of 8% since 2002 while ROADMs have grown at 46% annually between 2005 and 2009. Ovum, meanwhile, forecasts that the global ROADM market will reach US$7 billion in 2014 (see chart). Verizon Business has deployed over


2,000 ROADMs in its medium-haul metro- politan networks: “Everywhere we deploy FiOS [Verizon’s optical access broadband service] we put a ROADM node,” says Glenn Wellbrock, director of backbone network design at Verizon Business. A ROADM is typically a telecoms rack


comprising optical switching blocks— wavelength-selective switches (WSS) that connect lightpaths to fibres—as well as optical amplifiers, optical channel moni- tors, and control plane and management software. Some vendors also include optical transponders as part of the ROADM definition. “ROADMs are at the core of the network and define its characteristics,” says Simon Poole, director, new business ventures at Finisar, a WSS specialist. The WSS can bundle and route wavelengths in several fibre directions, typically ranging from two or nine directions, known as 1x2 and 1x9 degree switches. Operators such as AT&T and Verizon


have long adopted tunable transponders, another key optical component needed for agile optical networking. Such a trans- ponder can be tuned to any DWDM wavelength, yet when plugged into a ROADM it becomes restricted in operating wavelength and direction. “If you take a tunable transponder that can go anywhere and plug it into Port 2 facing west, say, that is the only place it can go at that [network] ingress point,” says Wellbrock. Once passed through intermediate


www.totaltele.com July/August 2010


$ millions $2,181 $2,449 $2,834 $3,117 $3,447 $3,733


$1,356 $1,618 $2,128 $2,400 $2,807 $3,269


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