After initially being shut out of BT's £10 billion network overhaul, Nortel will now be one of two suppliers of Ethernet gear to the carrier's 21st Century Network (21CN) programme.

Nortel and Siemens will provide BT with Ethernet equipment that will support Provider Backbone Transport (PBT), an Ethernet derivative for metropolitan networks, positioned by Nortel as a lower-cost alternative to MPLS for traffic engineering and other tasks. BT will use the PBT gear to backhaul high-bandwidth business and full-streaming video applications in domestic and international markets onto an MPLS backbone.

The value of the five-year contract was not divulged. Under 21 CN, BT is attempting to consolidate 16 separate networks into one.

PBT is intended to bring connection-oriented characteristics and deterministic behaviour to Ethernet communications. PBT turns off Ethernet's Spanning Tree and MAC address flooding and learning characteristics to enable Ethernet to behave more like a traditional carrier-transport technology.

In part because of its simplicity, Nortel says PBT and an emerging IEEE standard called Provider Backbone Bridging Traffic Engineering (PBB-TE) can provide a 40% to 80% capital and operating expense savings over MPLS and virtual private LAN services (VPLS) – an MPLS augmentation of Ethernet – in the metropolitan network. PBB-TE incorporates PBT and is designed to control data paths within very large carrier networks to enable quality of service and service-level agreements, and to set aside specific paths for certain traffic.

Even though some carriers, such as Verizon and AT&T, are opting for VPLS in their Metro Ethernet service networks, Nortel indicated it may not be in the running to supply equipment for these projects.

BT will deploy Nortel's Metro Ethernet Routing Switch 8600 and Metro Ethernet Services Unit 1850 this quarter. BT may also deploy Nortel's Optical Multiservice Edge 6500 product after PBT is added to it in the second half of the year.

BT will also deploy Siemens' PBB-TE-enabled SURPASS hiD Ethernet switches and element management system.

BT and Shanghai Telecom publicly endorsed PBT last year. Shanghai Telecom is deploying the technology.