The historical industry model has an access circuit 1) terminating inside the central office, 2) going from there to a traditional cross-connect or Ethernet switch for grooming, aggregation and switching and 3) then moving out onto the transport network--at each and every network node. Now, having deployed the Tellabs 7100 and the Fujitsu 9500 packet optical networking platforms (PONPs) at more than 2,000 nodes thus far, the carrier combines in one box all three functions. One result is that from a CAPEX perspective, Verizon can cap its investments in stacked SONET rings, independent cross-connects and independent Ethernet switches.
Verizon is continuing to deploy the centralized fabric, on an as-traffic-demands-it basis, and Wellbrock says that although the TDM version is becoming "quite prevalent," the demand for the packet version is also gathering steam. Currently, most Ethernet still goes over SONET, and nowhere is that more evident than in the mobile-backhaul network. Wellbrock says the PONPs are proving their value there as well.
Today, he says, requirements vary from one cell-tower customer to another, with some wanting all-Ethernet point to point, others wanting switching in between and still others simply requiring DS1 transport--some SONET and some Ethernet--as they migrate their services from DS1.
"So for us, the transition is slow, and we can see all three service types at every cell tower," he says. "Everyone has different ways they want to carry this Ethernet handoff, even though it may all be Ethernet."
Were it not for a PONP solution that incorporates the switching functionality in the transport gear, the carrier would have had to build "separate pipes and separate switching elements back in the CO for each one of those services, even though they're all out at the same location," Wellbrock says, noting that mobile-backhaul service requirements are similar to those of many enterprise customers. "But that's exactly why we went down this path, because that transition certainly varies by customer."