Understanding optical transport networks

Understanding optical transport networks

Beth Schultz  |   January 12, 2011
SearchTelecom.com
Optical transport network (OTN) is a series of standards created to combine the benefits of SONET/SDH with the bandwidth-expanding capabilities of DWDM in order to build more network functionality into optical networks. As defined by the ITU, OTN is a set of optical network elements connected by optical fiber links capable of providing optical channel transport, multiplexing, routing, management, supervision and survivability.
 
Relevant ITU standards include G.878, which specifies OTN architecture, and G.709, which defines the frame format and payload mapping for carrying Ethernet, storage and SONET/SDH signals. With OTN, also called digital wrapper, these disparate traffic types are multiplexed onto and carried over a single optical transport unit (OTU) frame, either at 2.7 Gb/s (OTU-1), 10.7 Gb/s (OTU-2) or 43 Gb/s (OTU-3).
 
With the ITU standards available since the early 2000s, carriers have widely deployed optical transport technology in their long-haul and metro-area networks.
 
The tendency among industry watchers of late has been to dismiss the optical networking market as all-physics and low-margin, but in actuality, it continues to be a lucrative market, with more than a dozen vendors jockeying for position in the long haul and metro area, according to optical networking analyst Eve Griliches, managing partner at ACG Research. The market analysis firm pegs the worldwide optical networking market at an estimated $14 to $15 billion a year, a substantial market that is comparable in size to that of Ethernet switches.
 
Service providers continue to deploy OTN with the goal of boosting bandwidth and increasing network functionality. OTN has provided them a way to support different traffic types in a more cost-effective manner than by using SONET/SDH networks. Carriers are placing particular emphasis on OTN in the metro area, where they are shifting rapidly from SONET/SDH to wavelength-division multiplexing (WDM), Griliches said.
 
Griliches attributes the uptake to the increased spectral efficiency of the latest WDM equipment, which can handle two or more times the number of wavelengths -- 80, or in some cases, 96 -- than earlier systems. “This means it can handle bandwidth far better and at higher bit rates,” she said.
 

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