The lack of a standard Ethernet interface between different carrier networks is impeding carrier plans to extend virtual private LAN services on a national and global scale.

Carriers say they require a standard network-to-network interface (NNI) between their own and other carrier networks to offer consistent multipoint Ethernet services for customers with operations across the country or the world. They say such a virtual private LAN service (VPLS) NNI would let them offer consistent service quality and more reliable service-level agreement (SLA) guarantees for meshed intercarrier Ethernet connectivity extending beyond the metropolitan-area boundary.

"We want to be able to map services" across carrier boundaries, said Michael Rouleau, senior VP of business development and strategy at Time Warner Telecom. "The last thing we want is lowest common denominator" service.

"VPLS will be very important for maintaining QoS through a multivendor infrastructure," added Craig Drinkhall, senior VP of product development and engineering at TelCove, a competitive local exchange carrier in Pittsburgh. "But not all of the standards are put together to create vendor interoperability."

However, others argued that even with a standard NNI, carriers will have to enter into lengthy negotiations and testing with specific peers to extend SLA guarantees across carrier boundaries.

The Metro Ethernet Forum (MEF) is working on an Ethernet NNI (ENNI) that would describe how carriers can pass off services between their networks. This specification could be ready next year, MEF officials said.

Work on the ENNI started three years ago but has been idle for about a year because key people working on it were reassigned at their companies and could not commit enough time to it, said Bill Bjorkman, an enterprise marketing consultant for Verizon and co-chairman of the MEF technical committee. But AT&T, Verizon and Cisco are interested in resurrecting the work and have scheduled teleconferences over the next few months to try to wrap it up, he added.

But without ENNI, Broadwing and other carriers have to hammer out individual and specific peering relationships with other carriers in order to extend VPLS-based Layer 2 Ethernet VPN service guarantees. Indeed, at the recent Supercomm conference, Broadwing announced a relationship with metropolitan service provider OnFiber to pair Broadwing's nationwide Layer 2/3 converged services offering with OnFiber's Ethernet local access network to deliver end-to-end VPLS and MPLS-based VPNs.

After intensive combined testing and evaluation, OnFiber and Broadwing have interconnected their networks in 16 of OnFiber's major US markets to provide an infrastructure for enterprise WAN communications, including jointly developed pricing, monitoring and support processes.

The combined Broadwing/OnFiber service supports hard (guaranteed) QoS using IEEE 802.1p and q virtual LAN (VLAN) tags, and four class-of-service levels - voice and video, priority, standard and best effort.

Broadwing has plans to extend its Gigabit Ethernet VPLS services globally, but must undergo similarly intensive interconnection testing and evaluation processes with select carriers to do so. But some argue that this would be necessary even with an Ethernet/VPLS NNI.

"It's more a business issue" whether carriers are willing to set up NNIs with every other carrier with which they wanted to interoperate in order to share routing data necessary to make service connections, said Steven Cotter, senior systems engineer at router vendor Riverstone Networks.

Technically, it is not difficult to pass off VLANs between networks, he noted. It could be done, for instance, with Ethernet psuedo-wires or SONET connections, the key being to map VLANs from one network to another and maintain service characteristics.

And some providers have custom arrangements to terminate VPLS services on each others' networks, using the user-to-network interface (UNI) already defined by the MEF, said Bob Mandeville, CEO of technology testing lab Iometrix and the MEF's editor of testing methods.

But the UNI lacks operations, administration and maintenance (OA&M) specifications that carriers require to connect services with other carrier networks, Verizon's Bjorkman said.

Some providers also use MPLS as the NNI to share intercarrier VPLS instances, added Ron Kaplan, an analyst at IDC. But MPLS intercarrier connectivity is a daunting challenge in and of itself, he said: "There's only a few carriers where it's taking place because of different (MPLS) implementations."

To get the ENNI work accomplished quickly, the MEF may scale back its scope. For example, rather than specify how to set up a transport network that could route traffic among three or more networks, the agreement may address only how to pass traffic between two networks.

The Ethernet/VPLS NNI issue is not unlike that which occurred with Frame Relay years ago. When Frame Relay first came out, national carriers such as AT&T sold long-haul segments of networks and tied into local carrier networks to reach customer sites, much as Broadwing and OnFiber now do.

But the local carriers didn't win big contracts at the outset because they lacked simple ways to connect to other carrier networks, Bjorkman said. Eventually the Frame Relay Forum came up with an NNI for the technology.