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Monday, July 25, 2011

100 - Gbit/s Ethernet: How it will influence METRO – ACCESS NETWORKS’ outlook

Currently, the standardization of a next - generation 100 Gbit/s Ethernet data transport is under development in the IEEE P802.3ba 40 Gbit/s and 100 Gbit/s Ethernet Task Force. The transport of data traffic in metropolitan area distances through Ethernet - based equipment has been mostly motivated by the fact that the Ethernet has been very successful in LANs due to its simplicity, low cost, standardization, and compelling market penetration.
The migration of the Ethernet protocol from LAN to MAN environments has been possible mainly because of the separation of the medium access control (MAC) layer from the physical (PHY) layer since the very former times of this protocol. As a result, the progress to newer Ethernet standards over different physical layer technologies and transmission media has preserved almost the same frame format of the previous standards, which have allowed the leverage of existing Ethernet installations. The choice of the 100 - Gbit/s rate came naturally from the conventional evolution of the Ethernet over its previous generation — that is, a 10 - fold increase in the speed over 10 Gbit/s.

Ethernet as a metro - service architecture must be able to support a large number of terminals and high - capacity links in a scalable way, as well as offer OAM capabilities and network resilience guarantees for service providers. In other words, the Ethernet as a carrier - grade platform should be able to provide almost all the benefits that the SONET/SDH networks have, but using a packet - switched platform. It is not clear yet, however, if the inclusion of all these acclaimed benefits in the Ethernet will keep its cost - effectiveness. Most of the standards activities to accomplish these goals are developed by the IEEE 802 LAN/MAN Standard Committee (LMSC), who is responsible for the evolution of Ethernet in LANs and MANs. The Metro Ethernet Forum (MEF), an industry consortium that aims at fostering the adoption of the Ethernet as a carrier - class platform, has been also defining Ethernet service types, management, and service level agreements (SLA) for metro and wide area environments. Parallel standardization efforts led by the ITU have mostly focused on the definition of the transport of Ethernet over TDM circuits, Ethernet protection switching, and OAM functionalities.

The 100 - Gb Ethernet transmission over metropolitan networks will require very stringent component tolerances with respect to the chromatic dispersion (CD) and polarization mode dispersion (PMD) effects, since the impact of these impairments in the optical transmission increases with the square of the data rate. Moreover, whereas interchannel effects strongly affect mostly dispersion - compensated optical transmission systems at per - channel rate of 10 Gbaud and below, intrachannel nonlinearities (e.g. intrachannel cross - phase modulation (iXPM) and intrachannel four - wave mixing (iFWM)) severely impact such systems at per - channel rates of 10 Gbaud and above. Advanced, spectrally efficient modulation formats will play a central role in the design of 100 – Gbit Ethernet optical transmission systems, since an appropriate choice of the data modulation scheme can alleviate the impact of such impairments on the transmission and make a more efficient utilization of the channel spectrum at such high - speed data rates.

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