Ethernet, one of the most successful network standards ever, is poised to take a new role, as a new telco-friendly version emerges, suitable for metropolitan area networks. In order to become the ubiquitous local area network (LAN) standard that it is, Ethernet has had to see off several competitors, including token ring, ATM-on-the-LAN and FDDI. It now has an unrivalled position on company's local area networks (LANs). The only other network specification to grow significantly is the specialised Fibre Channel, used in storage area networks (SANs), and even this is predicted to eventually be superseded by Ethernet. So where next for Ethernet? Users who have Ethernet internally want to join those networks together to make global networks, and they have done this for some time, by encapsulating Ethernet traffic and carrying it over whatever private and public networks are available. Ethernet interfaces are being offered by most telcos, for long-distance services. Ethernet, once carried over coax cable, has long since jumped to fibres, and would have no problem reaching the distances over which those service providers operate. So why can't service providers run native Ethernet for those long distance networks, and simplify things immensely? The answer is that service providers have quite a lot of different requirements. Long-distance networks have different characteristics to the ones Ethernet was designed to meet, such as reliability, conserving bandwidth which may still be costly, and offering multiple clients different quality of service. Standards like ATM still rule the world in these areas, for the longest-distance and busiest networks, but a new area has opened up where Ethernet can offer significant benefits. Metropolitan area (or "metro") networks span anywhere from a city to a region as big as some European countries. There is currently a big bottleneck in the metro. During the late 1990s, masses of long-haul bandwidth was built out, and the last mile began to open out with the spread of broadband. However, for city-wide fast links, there is still not enough bandwidth. "The last decade has seen LAN capacity expand some 100-fold, and backbone capacity more like 300-fold, while the real bottleneck has been in the metropolitan area, with a bare 16-fold increase," says Nan Chen, president of the Metro Ethernet Forum (MEF). The bottleneck is partly there simply because it is difficult and expensive to lay fibre across cities. However, it is certainly true that, in the current climate, service providers would find it easier to deliver services across those distances if they had access to cheaper equipment. Most metropolitan area networks are based on the Sonet/SDH optical networking standard, which was designed to provide highly reliable networks tuned to carrying voice traffic on ring networks. To get on in this environment, Ethernet needed some (but not all) of those attributes -- and keep its cheapness.