Ethernet penetrates mobile backhaul

The barrier that separates the next-generation metro network from the legacy world of mobile backhaul may finally be crumbling. Vendors in the U.S. are no longer just talking about the benefits of carrier Ethernet in wireless operators' backhaul and transport networks; mobile operators are actually deploying it. In March, Verizon Wireless announced a deal with its parent company to provision fiber Ethernet links to 90% of the cell sites in Verizon's territory over the next five years, coordinating with VZW's rollout of its 4G long-term evolution mobile broadband network.

It's one of the first major carrier commitments to an end-to-end IP transport network, and now that there are sizable cracks in the wall, metro Ethernet suppliers and service providers expect other mobile operators to bust through. “We've pitched these products to wireless carriers for the last two years,” said Larry O'Neill, manager of all Ethernet services for Verizon Partner Solutions. “They are now more prepared to move to Ethernet, and they're prepared to move en masse.”

While the benefits of Ethernet backhaul were readily apparent to most mobile operators, technical and business obstacles often stood in the way. TDM has held tremendous sway with operators because all of their voice traffic depends on the legacy transmission framework for call quality and channel integrity. Sending that TDM voice traffic over Ethernet wasn't an option until synchronization issues were worked out. While Ethernet-over-copper technologies are on the market, most Ethernet transport is dependent on fiber, which only goes to a small, but growing, percentage of U.S. base stations. In order to gain a large-scale commitment to Ethernet from VZW, Verizon had to commit to a large-scale deployment of fiber. Other barriers were much simpler. Until recently most base stations simply didn't have Ethernet ports, O'Neill said.

But in the last year operators have experienced huge upticks in mobile data growth. In many cases data has surpassed voice in overall volume of network traffic, making TDM an increasingly more inefficient means of transport. That volume will only increase with 4G technologies such as LTE, and carriers are starting to turn to Ethernet sooner rather than later.

“2008 was a transition year,” said Steve Dyck, director of mobile backhaul solutions in the Americas for Alcatel-Lucent. “We saw real volume deployments. Still, there are 1.8 million cell sites in the world. It will take a long time to deploy an Ethernet-based network to all of them.”

Part of the problem with popularizing carrier Ethernet to mobile operators has been the issue of cross communications. Ethernet emerged from the enterprise as a LAN technology, and when it migrated into the metro network it became an access and transport technology that, again, primarily served the enterprise. Enterprises have far different requirements than mobile operators, said John Sauer, senior principal engineer for Tellabs and Metro Ethernet Forum member. Enterprises have different requirements for reliability and redundancy than mobile operators; they have different service expectations and different capacity demands. But most of all they talk about Ethernet coming from an IT background — a language that operators serving those enterprises have adopted, he said.

Meanwhile mobile operators are still firmly grounded in a world of TDM. “It's understood what's being said when you order a T-1 or an OS-3,” Sauer said. “All this has long been worked out in TDM.”

The MEF recently launched an implementation agreement for Ethernet targeted at mobile backhaul called MEF 22. It's neither a standard, nor a set of specifications — those were worked out long ago — but rather a common set of definitions that will translate “Ethernet-speak” into a language operators can understand, Sauer said. In addition, MEF 22 defines the unique requirements that must be applied to Ethernet to make it suitable as a mobile backhaul technology. The most significant of these is synchronization — imperative for wireless networks to maintain channel integrity and voice quality. TDM inherently supports precise timing, but Ethernet does not, meaning either GPS or master clocks must be spread throughout the network.

“The Metro Ethernet Forum is trying to put everyone on the same page,” Sauer said.