Upon entering its fourth decade, you’d think Ethernet would show signs of age, being pushed aside for newer, stateof- the-art networking technologies. Well, ummm, no.
Rather, Ethernet has evolved in step with changing requirements and standards. In the beginning, it involved PC ports on a coax bus local-area network (LAN). Over time, the technology has morphed into many other forms of networking, from simple I/O ports on embedded controllers to metroarea- network (MAN) and wide-area-network (WAN) implementations including backbone and backhaul—not to mention wireless (see “Ethernet: A History”).
THE 10-GBIT/S ROLLOUT
The 10-Gbit/s version of Ethernet has been around for more than five years in several forms. But it has taken time for prices to moderate and companies to adopt these higher-speed versions. Usually, 10/100 Ethernet works for most small and medium businesses, and 1 Gbit/s is fast enough for an aggregation backbone.
Yet with ever-larger networks, more wireless extensions, and larger data flows, the advent of 1 Gbit/s to the desktop and 10-Gbit/s backbones has become necessary. With server virtualization, the increased growth of data centers and server farms with blade servers, the growing number of Internet searches, video downloads, and streaming video, the need for 10-Gbit/s networks is critical.
Today, 10-Gbit/s equipment is more common and becoming the main link between servers in data centers. While most 10-Gbit/s LANs are fiber, the newer copper unshielded twisted-pair (UTP) version is slowly being adopted in data centers and other short-distance (<30 to 100 m) applications.
The 10-Gbit/s copper version (10GBaseT) is an interesting technical case because it virtually defies the laws of physics. To achieve that seemingly impossible rate, the standard calls for 16 levels of pulse-amplitude modulation (PAM) simultaneously occurring at an 800-Msymbol rate over each of the four pairs in a special low-loss CAT6a UTP. A low-density parity check (LDPC) coding scheme helps overcome data errors due to cable losses and noise.
On top of that, all sorts of fancy equalization, echo, and crosstalk cancellation for near-end crosstalk (NEXT), far-end crosstalk (FEXT), and alien (adjacent cables) crosstalk are implemented with DSP. Lots of circuitry (i.e., 800-MHz 10-bit analog- to-digital converters, DSP logic) is used to achieve these connections, making most implementations power hogs. Several companies have brought the power consumption per port down to 3 to 5 W, which is barely acceptable.
Yet 10GBaseT is still significantly lower cost per port than fiber versions. While 10-Gbit/s copper network interface cards (NICs) are now available, 10GBaseT has never really taken off, primarily because of the rivalry and squabbling between the competing companies over intellectual property (IP) and other issues. This small group of companies has never come together to build a market despite the fact it did actually agree on a standard (802.3an).
A variety of Ethernet optical modules is now available in X2, XFP, SFP, and other multisource agreement (MSA) formats. With the new SFP+ optical transceiver modules for 10 Gbits/s now priced competitively, there may be fewer reasons to keep the copper version. The market will no doubt let us know.
THE 40/100-GBIT STANDARD
With Ethernet steadily increasing in speed, there have been debates on its use as a network backbone and in core MANs and WANs. It’s highly desirable due to its fully standardized nature, which includes full interoperability and backward-compatibility between the components of many different vendors. Its low cost is also attractive, as is the fact that it’s well-known among IT and network personnel. The forthcoming 40- and 100-Gbit/s versions will make Ethernet a real contender in the MAN and WAN space.
Right now, Sonet/SDH is still the leading technology in these core, edge, and access networks. Sonet/SDH networks of the OC-48 (2.5 Gbits/s) and OC-192 (10 Gbits/s) varieties see wide usage. Also, Sonet/SDH defines standards to OC-768 or 40 Gbits/s. The 40-Gbit/s versions aren’t common, but are now getting more play. Holding back their widespread adoption is the high price.
Thanks to developments in 10-Gbit/s Ethernet, semiconductors, and optical processing, data rates are reaching 100 Gbits/s. In 2006, the IEEE established the High Speed Study Group (HSSG) to investigate the development of a 100-Gbit/s standard. Then in 2007, the group agreed to add a 40-Gbit/s version as an interim technology for data centers and other markets.
Continue on Page 2
Reprints
