Granted, it was an MPLS-immersed conference. And Cisco had its best engineering SWAT team there to exterminate anything that threatened its router franchise.

But this week's Future-Net conference -- formerly MPLScon -- showed just what a daunting uphill climb MPLS alternatives such as Provider Backbone Transport (PBT) have to gain market momentum.

PBT -- which chief proponent Nortel now calls Provider Backbone Bridging-Traffic Engineering (PBB-TE) and is proposing as an amendment to the IEEE 802.1Q standard -- is an Ethernet derivative intended to bring connection-oriented characteristics and deterministic behavior to Ethernet. PBT turns off Ethernet's Spanning Tree and media access control (MAC) address flooding and learning characteristics to enable Ethernet to behave more like a traditional carrier transport technology.

PBT and PBB-TE are extensions of the IEEE 802.1ah specification Provider Backbone Bridging (PBB), which scales virtual LANs (VLAN) by encapsulating MAC addresses within MAC addresses.

But router vendors such as Cisco assail PBT as a limited niche technology that supports only point-to-point Ethernet applications and lacks the multipoint, multiservice capabilities of MPLS, as well as an integrated control plane.

One of the themes of this year's Future-Net was "The Great Ethernet Debate," featuring discussion and presentations on emerging Ethernet transport techniques in the face of a 10-year-old installed base of MPLS switches and routers. Nortel was virtually the lone wolf baying in the hostile wilderness on the benefits of PBT over MPLS and offspring Virtual Private LAN Service (VPLS) for Ethernet transport applications.

Small, privately held edge switch maker Hammerhead Systems tried to show how its HSX 6000 switch could function as a PBT service gateway, but may have done more to complicate the technology than to clarify its role. From a PBT perspective, the conference could have benefited from the presence of advocates Siemens, Avici or Huawei; or BT or Shanghai Telecom, two carriers that are using or plan to use the technology.

The service providers that were here this week never gave PBT a mention during their presentations on MPLS/VPLS features and functions, until prodded to do so during question and answer sessions.

"It seems like PBT in the metro is a step back from what the technology is capable of," said Keao Caindec, chief marketing officer at Ethernet service provider Yipes Enterprise Services. But Caindec acknowledged Yipes does not face the same issues as a large carrier looking to packetize its SONET access and metro infrastructures.

Verizon does, yet while acknowledging a potential role for PBT in the service edge, it has too much invested and embedded in MPLS and VPLS to carve out a niche for PBT.

"If it is not a large MPLS infrastructure, there might be a simpler role" for PBT, said Stuart Elby, vice president of network architecture for Verizon Business. He did mention, however, that there could be a role for the PBB in the Verizon Business network to perform VLAN scaling.