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Nortel's BT 21CN win puts focus on PBT(Total Telecom Via Thomson Dialog NewsEdge) As part of the implementation of its next-generation 21st Century Network, BT this week announced it would be using Ethernet technology from both Siemens and Nortel. The move sparked interest not only because it brings Canada's Nortel into the 21CN fold, but also because it has highlighted the debate over the use of Provider Backbone Transport (PBT) technology, which some are heralding as an alternative to MPLS in Ethernet networks. According to Nortel, PBT is a set of enhancements to Ethernet incorporated in the emerging IEEE standard PBB-TE (Provider Backbone Bridging Traffic Engineering) that allows the use of Ethernet for a carrier class transport network. BT will be using Metro Ethernet routing switches from Nortel and Ethernet carrier-class switches from Siemens, all supporting PBT. Nortel is one of the main promoters of PBT, claiming that it represents far simpler technology. "The simpler the technology, the easier to interoperate it is, and PBT is simple technology," said Melvyn Kelly, carrier Ethernet leader, EMEA, at Nortel. But both Nortel and BT conceded that there would probably be some minor interoperability issues. "The potential problems I see come with the physical task of installing the new network infrastructure," commented Kelly. Overall, BT is very confident about the decision it has made: "I think they [Siemens and Nortel] will deliver proven technology that is interoperable, and will provide the network solution that will give our customers the level of service that 21CN promises to deliver," said Matt Beal, director core convergence, BT 21CN. Beal added: "BT 21CN has been a multi-vendor project from the very beginning, and building out a carrier-class Ethernet has been part of the plan since 2003." BT has also pointed out that PBT, which uses destination address-based network switching, will not replace its IP-based MPLS architecture, which uses routers at the edge of the network to label data packets. Beal stressed that PBT would complement BT's MPLS strategy, and not replace it. But Mark Seery, vice president of IP service infrastructure at Ovum, said that although MPLS and PBT could reside in the same network, they represent entirely different architectures. "In the MPLS world Ethernet is just an interface," Seery said, adding, "if it is not Ethernet, then it cannot be carrier Ethernet." Until MPLS, the size of an Ethernet network was limited. Beyond a certain size the amount of data flowing between multiple switches could cause instability and fluctuations in performance across the entire network. PBT, meanwhile, works by designating specific routes across a network for certain data packets, which results in a more stable network with a performance that is far more predictable, according to proponents of the technology. It does this by making network switches behave slightly differently to how they would in a normal LAN, and doesn't require additional routers to label data packets. It is being promoted as the more cost-effective solution for network operators because it does not require additional MPLS routers to sit at the edge of the core network. Seery said that with these two different systems a "battle between Ethernet over Ethernet and Ethernet over IP/MPLS," was emerging, concluding, "It is a detailed issue, with much controversy." Copyright 2007 Terrapinn Ltd |