IDC: PBT ‘wildly over-hyped’

Provider Backbone Transport (PBT) technology has been “wildly over-hyped” as a way to reduce carrier capital and operating expenditures, IDC analyst Eve Griliches said in a new report published today.

“Carriers are struggling with, ‘How can we make this simpler but not lose intelligence?’” Griliches said. “With PBT, you do lose a lot.”

A point-to-point technology, PBT has been proposed by vendors including Nortel Networks and Siemens (and accepted by British Telecom) as a simpler alternative to multiprotocol label-switching (MPLS) in certain applications. Nortel is marketing PBT in metro networks in particular, while Meriton Networks is applying it to transport networks.

PBT disables some functions of traditional Ethernet networks to allow “tunnels” of dedicated bandwidth for network traffic. It creates those tunnels by affixing headers to incoming packet traffic and removing those headers on the far end of the tunnel. Those tunnels would be set up and taken down by the network’s provisioning system, which would be forced to take on some of the work routers would perform in an MPLS network.

“PBT does strip complexity out of the Ethernet control plane, but it adds complexity to the provisioning system,” Griliches said. “This effectively becomes a ‘zero sum’ game, where the complexity is now shifted from one component of the system (the control plane) to the provisioning plane.”

In addition, PBT is not suited for multicast traffic, which limits its applicability to triple-play networks, one of the most important sources of carrier revenue in coming years, she said. Nortel has proposed using PBT and Provider Backbone Bridging—a more mature layer-two protocol with superset of PBT functionality, including multicasting capabilities—in different parts of the same switch.

For all the attention PBT has gotten lately, with several vendors vowing support for it, from Extreme Networks and Ciena to Hammerhead Systems, the technology has only been truly embraced by one major carrier, BT, and it is not yet standardized.

Carriers interested in PBT tend to favor its use in small networks with limited, predictable scale, Griliches said. “The holy grail for most providers is a multi-service infrastructure with switch/routers that is less expensive than traditional routers and provides the flexibility of control-plane centralization. PBT makes Layer 2 transport look like Layer 3 without the complexity, but it is at the expense of flexibility and multi-service capabilities.”