Carrier Ethernet aggregation rings rely on 10 Gig E connectivity

CEN Feature (Oct 26 2010)

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   Although only a small fraction of enterprise users are purchasing 10 gigabit Ethernet connectivity, one area where 10 Gig E is widely used is in service provider networks to support Carrier Ethernet rings that serve as aggregation networks to support business customers and residential traffic from DSL and fiber networks.

    

   “10 Gig E is pretty widely deployed worldwide for this purpose,” commented Michael Howard, principal analyst for Infonetics Research.

    

   10 Gig is likely to be the preferred speed for Ethernet aggregation rings for at least three to five more years, Howard predicts. “You can use WDM and stack 10 Gig rings,” he said. “All you have to do is put an inexpensive WDM box in a ring and you can have multiple 10 Gig E rings on separate wavelengths.”

    

   As of today, Howard estimates that more than half of Ethernet rings in North America are built on top of SONET infrastructure, with the remainder deployed over MPLS or directly onto WDM. In the latter scenario, Ethernet-over-WDM rings may co-exist on the same fiber as wavelength services.

    

   Outside North America, the percentage of Ethernet deployed over TDM infrastructure in service provider networks is even higher, Howard said. “In the rest of the world, it’s more like 80 percent of Ethernet that’s on top of SDH.”

    

   One factor that has driven service providers to rely so heavily on TDM is that they want the network restoration capabilities of SONET and SDH. MPLS restoration options also are gaining acceptance with service providers. But Ethernet developers have struggled to come up with a solution that can give service providers the comfort level they have with TDM.

    

   The resilient packet ring (RPR) standard developed a decade or so ago initially sounded like a good idea—enabling service providers to use backup links more efficiently than with SONET. But RPR had a few serious flaws, according to Scott Knox, director of solutions development for Overture Networks. “The reason RPR didn’t take off was that the standard didn’t really leverage any of the existing Ethernet technology,” he said. “With a new packet header and a new OAM protocol, it simply wasn’t going to enjoy the economies of scale that comes with today’s Carrier Ethernet,” Knox explained.  “By contrast, G.8032 takes advantage of standard Ethernet headers and standard Ethernet OAM such as 802.1ag and Y.1731.”

    

   The new ITU-T G.8032 standard, also known as Ethernet ring protection, aims to provide self-restoration capabilities for packet networks akin to what is available with SONET and, unlike RPR, it is designed to support ring interconnection. And as for the protection switching performance, at least one vendor is claiming restoration times under 20ms for G.8032 rings. This is far better than the 50ms required by the SONET/SDH specifications.

    

   Another advantage of G.8032 Ethernet multi-node rings is that it is one of the most effective ways to increase fiber efficiency. Serving multiple locations with a multi-node ring solution instead of dedicating a fiber pair for each endpoint provides significant fiber efficiency improvement. If, for example, 10 endpoints are combined on a G.8032 Ethernet multi-node ring, only a single fiber pair is consumed instead of 10 fiber pairs.

    

   As a result, Howard said, “It’s starting to become, and will emerge as, the common way that operators build Ethernet rings.”

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