Throughout their existence, the local-area network (LAN) and the wide-area network (WAN) have remained separate, complementary entities. Their distinct cost/performance structures were defined by the nature of their application. Broadly stated, the LAN took care of intersystem communication within a building or complex, while the WAN facilitated distance requirements ranging from a couple of km to 40 km and beyond. Their roles were clear, and never the two should meet.
As is often the case, however, cost pressures are about to change all of that. The two are now prepared to battle for the heart and soul of communications today: the metropolitan-area network (MAN). This network boasts a diameter of roughly 40 km. It's proven to be the fastest-growing segment of the networking arena, with business-to-business communication forming the bulk of the traffic. Up until a couple of years ago, it would've fallen naturally under the umbrella of the WAN, with its SONET-based architecture's rate of 9.5 Gbits/s. But a lot has changed since then.
Ethernet, the LAN protocol of choice, has come a long way since its inception in the mid-'70s. It's gone from 5 to 10 to 100 Mbits/s by 1994. Then, between 1994 and 1998, it jumped from 100 Mbits/s to 1 Gbit/s. Now, as it stands at the threshold of 10 Gbits/s, it could cater to the expanding MAN. It only needs a standard to be decided upon that would allow it to natively interface with the established, trillion-dollar SONET infrastructure. Therein lies the problem.
To date, improvements to the Ethernet standard have been dealt with by the IEEE-802 committee alone. These participants have similar LAN interests, so most decisions ended up holding a mutual benefit. Now, participants on the 802.3ae Committee for 10-Gbit Ethernet not only include members of the LAN community, but also from the WAN community. Their concerns don't exactly match up.
The top layer of contention is cost. From there the issues trace down to the media-access-control (MAC) mechanism and how it should interface with the physical-media-dependent (PMD) layer. No one is sure just what form that PMD should take. A key concern is the type of coding to be used. At 10 Gbits/s, this will really impact the demands made upon both the silicon and the optics—and hence overall cost.
Other issues to be debated include the base speed, distances, and the wavelengths of the lasers to be used. Those concerns spiral into discussion over the number of wavelengths, the number and type of fibers, and overall system quality in terms of bit error rate and component reliability. In addition, consideration must be given as to how other applications fit in, such as Fibre Channel and NGIO.
Fortunately, the structure of the IEEE is such that the concerns of both camps can be aired. No decision will be made final until 75% of the voting membership agree. So neither camp can dominate the proceedings. Also, five criteria exist under which the 802.3ae working group will entertain proposals to solve the many outstanding technical and market issues. They are: broad market potential, compatibility with IEEE 802.3, distinct identity, technical feasibility, and economic feasibility. Under these guidelines, anyone in the group has the right to shoot down any proposal, making it difficult to compromise the integrity of the proceedings.
This strict adherence to the cost principles, as outlined in the five criteria, is the chief bone of contention between the LAN and WAN proponents. Traditionally, the WAN has been technology-driven, with cost being almost an afterthought. If it could be done, it was done. Cost didn't matter. The LAN, in general, and Ethernet in particular, have taken the opposite tack. The LAN's low cost per node has been its selling point, and has helped boost the number of installed ports to over 700 million today and rising (Fig. 1).
As the number of nodes expanded, so did the technology. From 1 to 10 to 100 to 1000 Mbits/s it grew, all the while adhering to that mantra of the Ethernet community—10 times the performance for three times the cost. Not many schemes can make that claim, especially in the WAN arena. It's the low cost of implementation, in combination with its quality of service and network-management capabilities, that have pushed Ethernet beyond its original confines. In fact, predictions are that in five to 10 years, OC-192 SONET will be completely replaced by Ethernet, which will maintain its cost/performance ratio.
This doesn't bode too well for the existing WAN infrastructure and equipment. Nor will it help pad the pockets of component suppliers, particularly in the optics realm, who have long demanded high premiums from WAN box builders. Unfortunately, it also makes the decision process as much a matter of protecting turf as it is technical viability.
Reprints
