First it was BT Group plc (NYSE: BT; London: BTA). Now, Verizon Communications Inc. (NYSE: VZ) reportedly says it's not interested in using Provider Backbone Transport (PBT) in its long haul intercity networks.

Sources have said that the carrier once asked suppliers Nortel Networks Ltd. and Ciena Corp. (NYSE: CIEN) to employ some form of PBT -- or PBB-TE, as it's called in standards circles. (See A Guide to PBT/PBB-TE.)

But it now appears Verizon will stick with virtual private LAN services (VPLS), the technology it has recently adopted as the standard in its long-haul network. (See 2007 Top Ten: Services Stories.)

Nortel, the vendor that originally championed PBT as a cheaper and simpler form of carrier Ethernet, had been hoping that Verizon, one of its long-time customers, would sign on to use PBT.

Nortel and Ciena declined to comment for this story.

Verizon's decision would be another sign that PBT is not catching on with Tier 1 carriers the way Nortel, in particular, had hoped. Last week, Light Reading reported that the technology’s biggest carrier supporter, BT, had opted against using PBT as its main strategy for data services and would instead stick with MPLS. (See PBT Sidelined at BT.)

Verizon is exploring the use of Provider Backbone Bridging (PBB) -- a similar technology to PBT without some of its traffic engineering capabilities -- in its metro Ethernet networks as an additional access technology in order to address some of the scaling limitations in bigger cities.

But Verizon has decided PBT requires a suite of management capabilities that will make it just as complex to operate as VPLS. Since VPLS is already widely deployed within Verizon’s network, it doesn’t make sense to make the switch to PBT, the carrier reasons.

That decision raises the question of whether PBT has any long-term play with Tier 1 carriers that are already running large MPLS-type networks.

Many PBT customers so far are Tier 2 carriers, says Nortel’s director of carrier Ethernet, EMEA, Mervyn Kelly. But Kelly expects that Nortel will be signing on some new Tier 1 customers in the coming months. (See Nortel: There's More to PBT Than BT.)

Some analysts agree it's still too early to count PBT out and that Tier 1s are simply slower in adopting new technology than the more nimble Tier 2s. (See Analyst: PBT’s Not Dead Yet.)

It comes down to costs, says Stan Hubbard, senior analyst with Heavy Reading. "You can probably have the MPLS guys be competitive on the capex front, so then it becomes an opex debate. There are still some studies that can be done on that topic to see what makes sense."

Indeed, many Tier 1s have yet to be heard from on the technology. "I wouldn't write it off yet," says Hubbard. "It'll be part of the mix."

— Raymond McConville, Reporter, Light Reading