Transmode chooses coherent for 100 Gigabit metro

Transmode has detailed its 100 Gigabit metro strategy based on a stackable rack, a concept borrowed from the datacom world. 

The Swedish system vendor has adopted coherent detection technology for 100 Gigabit-per-second (Gbps) optical transmission, unlike other recent metro announcements from ADVA Optical Networking and MultiPhy based on 100Gbps direct-detection. 

"Metro is a little bit diverse. You see different requirements that you have to adapt to."

Sten Nordell, Transmode

"We are getting requests for this and we think 2012 is when people are going to put in a low number of [100Gbps] links into the metro," says Sten Nordell, CTO at Transmode. 

The 100Gbps requirements Transmode is seeing include connecting data centres over various distances. The data centres can be close - tens of kilometers - or hundreds of kilometers apart. 

"They [data centre operators] want to get more capacity over longer distances over the fibre they have rented," says Nordell. "That is why we are going down the standards path of coherent technology that gives you that boost in power and distance."

Nordell says that customers typically only want one or two 100Gbps light paths to expand fibre capacity or to connect IP routers over a link already carrying multiple 10Gbps light paths. "Metro is a little bit diverse," he says. "You see different requirements that you have to adapt to."

Rack system approach

Transmode has adopted a stackable approach to its 100Gbps TM-series of chassis. The TM-2000 is a 4U-high dual 100Gbps rack that implements transponder, muxponder or regeneration functions.  "We have borrowed from Ethernet switches - you add as you grow," says Nordell. 

Up to four TM-2000 are used with one TM-301 or TM-3000 master rack, with the architecture supporting up to 80, 100Gbps wavelengths overall.

"If you have too many ROADMs in the way it is going to hurt you. We have seen that with 40 Gig."

The system also uses daughter boards that support various client-side interfaces while keeping the 100Gbps line-side interface - the most expensive system component - intact. "You can install a muxponder of 10x10Gig modules,” says Nordell. "When an IP router upgrades to a 100 Gig interface, you take out the daughter board and put in a 100 Gig transponder."

Transmode will offer two line-side coherent options, with a reach of 750km or 1,500km. "We want to make sure that customers' metro and long-haul requirements will be covered," says Nordell.

The reach of various 100Gbps technologies for the metro edge, core and regional networks. Source: Gazettabyte

The company chose coherent technology because it is an industry-backed standard. "We can benefit from coherent technology," he says. "If the industry aligns, the volumes of the components come down in price." 

Coherent also simplifies the setting up and commissioning of agile photonic networks, especially as more ROADMs are introduced in the metro. "Coherent will help simplify this. All the others are more complex," he says. "Beforehand metro was more point-to-point, now we are seeing more flexibility." 

Transmode recently announced it is supplying its systems to Virgin Mobile for mobile backhaul. "That is a metro network with all ROADMs in it," says Nordell. Such networks support multiple paths and that translates to a need for greater reach. "The power budget we need to have in the metro is going up a little bit."

Direct-detection technology was considered by Transmode but it chose coherent as it gives customers a better networking design capability. 

Direct detection is also not as spectrally efficient as coherent: 200GHz or 100GHz-wide channels for a 100Gbps signal rather that coherent's 50GHz. "If you have too many ROADMs in the way it is going to hurt you, says Nordell.”We have seen that with 40 Gig." 

The TM-2000 rack will begin testing in customers' networks at the start of 2012, with limited availability from mid-2012.  The platform and daughter boards will be available in volume by year-end 2012.