Timing: T1s and E1s carry a clock signal that Ethernet lacks. Without it, performance of voice and video traffic could suffer. Plenty of standards are being kicked around here, and companies like Brilliant Telecommunications Inc. and Symmetricom Inc. (Nasdaq: SYMM) are chipping in with timing products. (See Luminous Crew Gets Brilliant.)

Some proposed answers are based on using a GPS clock, but that's a $50,000 expense, Easley says. Others rely on standards -- Institute of Electrical and Electronics Engineers Inc. (IEEE) 1588v2 or International Telecommunication Union (ITU) G.8261. No option has emerged as an obvious winner, although 1588v2 seems to be a favorite.

Reliability: As with carrier Ethernet services, wireless backhaul has to be as sturdy as a T1. Ethernet demarcation boxes, already a hot topic in carrier Ethernet, are going to be key here, says Brian McCann, chief marketing and strategy officer for ADVA Optical Networking .

That's because cell sites are so spread out. Operators will want ways of pinpointing the location of a line break, for instance, without sending trucks all over the place. They'll also want a means of monitoring network performance to compare it to service level agreements, McCann says.

The outdoors: In many cases, McCann notes, cell sites will require temperature-hardened gear that can survive a long, lonely life inside a telecom hut.

800-pound gorillas: As with any Ethernet market, Cisco Systems Inc. (Nasdaq: CSCO) could cause trouble for smaller companies. A Cisco offering "may be more expensive and more complicated, but it's comfortable," McCann says.

It's worth noting Alcatel-Lucent (NYSE: ALU) wants a stake in this market, too. And even without those two giants, startups in this space would have to contend with offerings from Adtran Inc. (Nasdaq: ADTN) and Tellabs Inc. (Nasdaq: TLAB; Frankfurt: BTLA). (See AlcaLu Targets Wireless Backhaul and Tellabs Snares Euro Backhaul Deal.)

— Craig Matsumoto, Senior Editor, Light Reading

Interested in learning more on this topic? Then come to Ethernet Expo 2007, a conference and exhibition that will explore major carrier Ethernet networking and service trends. To be staged in New York City, October 15-17, admission is free for attendees meeting our prequalification criteria. For more information, or to register, click here.