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4 October 2011
Transmode has adopted coherent detection technology for 100Gbps in metro networks.  The Swedish equipment vendor is not the first to offer a coherent solution for the metro; Ciena has 300km and 600km reach coherent line cards. But the decision contrasts with other recent metro announcements from Adva Optical Networking and MultiPhy, which are adopting 100Gbps direct detection.
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," said Sten Nordell, CTO of Transmode. Up to four TM-2000 are used with one TM-301 or TM-3000 master rack, with the architecture supporting up to 80 wavelengths at 100Gbps overall.
The system also uses daughter boards that support various client-side interfaces while keeping the 100Gbps line-side interface, which is the most expensive system component, intact.
Transmode will offer two line-side coherent options: the metro with a reach of 750km and a long-haul, 1,500km one.  The options are to make sure that the vendor can meet operators’ reach requirements that exceed traditional metro spans.
The company chose coherent technology because it is an industry-backed standard. "We can benefit from coherent technology," said Nordell. "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 reconfigurable optical add-drop multiplexers (ROADMs) are introduced in the metro. "Coherent will help simplify this," said Nordell. "Beforehand metro was more point-to-point, now we are seeing more flexibility."
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.
By Roy Rubenstein