Ethernet, the hardwired kind, dominates the networking world simply because it's flexible, reliable, and works as advertised. Like the telephone system, it's the network we all rely on but invariably take for granted. While wireless Ethernet (IEEE 802.11 or Wi-Fi) has received all of the attention, press,
and hype recently, conventional wired Ethernet is quietly evolving. Now moving into its 31st year, Ethernet dominates the networking world (see "Happy Birthday, Ethernet," p. 48). This article is an update on this commodity, yet world-class, networking technology.
Ethernet is of course a standard, specifically the Institute of Electrical and Electronic Engineers' (IEEE's) 802.3 standard. The original version, which defined a coax-based 10-Mbit/s bus system, has evolved into a 10-Mbit/s CAT5 unshielded twisted pair (UTP) based physical star known as 10BaseT. In the mid-1990s, a 100-Mbit/s version known as Fast Ethernet or 100BaseT (802.3u) came about.
Today, virtually all companies, institutions, and other organizations are wired for these 10/100-Mbit/s versions of Ethernet. More recent developments are a 1-Gbit/s CAT5 version called 1000BaseT, as well as 1- and 10-Gbit/s optical fiber versions. Fully ratified standards cover all of these (see the table).
The standards process forges on, as both chip and equipment companies seek out ways to further harness and improve Ethernet's performance. Some of the current active standards work includes:
- 10GbaseT: 10 Gbits/s over 100 meters of CAT5/CAT6 twisted pair;
- 10GbaseCX4: 10 Gbits/s over 15 meters of coax cable;
- Ethernet fiber in the first mile; fiber to the home (FTTH) using Ethernet;
- General maintenance on previous standards.
While still a Study Group, the 10GbaseT effort is considering ways to actually transmit 10 billion bits per second over a copper cable. My first reaction was "good luck," but much progress has already been made. By using multilevel coding schemes, such as 10-level pulse amplitude modulation (PAM) and multiple simultaneous paths along with adaptive equalization, it's possible. Such a solution will allow those with installed bases of CAT5E and CAT6 twisted pair to eventually upgrade to a 10-Gbit/s path. Yet the distances will be less than the usual standard 100 meters unless an upgrade to CAT7 is made. In any case, this approach will still be less expensive than using the approved fiber-optical cable standard for 10G (802.3ae).
The 10GbaseCX4 initiative is designated 802.3ak. The Task Force defined an Ethernet physical layer (PHY) that uses a version of the InfiniBand cabling scheme with dual TwinAx coax cables. This should make for an ideal connection in data centers where high-speed connections between servers are desirable, as well as in some storage-area network (SAN) applications. Look for this standard very soon.
The Ethernet in the first mile (EFM) effort has a formal Task Force designated 802.3ah. It's developing a standard that will allow homes and businesses to hook up to local carriers directly with Ethernet. Both copper and optical versions are being developed. The copper version will be less expensive, but a low-cost passive-optical-network (PON) solution is also on the docket.
Perhaps with such a standard, we will eventually see a replacement for the 100-year-old twisted-pair copper local loop we all still rely on. It could be the main connection for new homes in the near future. You'd get your telephone, as well as high-speed Internet access and even cable TV, via Internet Protocol telephony. We'll see. In any case, a standard will make the technology a reality much faster.
RECENT DEVELOPMENTS AND APPLICATIONS
Keeping track of Ethernet activities is almost a full-time job. Nearly everyone already uses Ethernet in some form, and many new versions and uses are continuously thrown into the mix. Presented here is juat a handful of the many new methods.
First, the newest versions of Ethernet, specifically the 1-Gbit/s Ethernet (1GE) and 10-Gbit/s Ethernet (10GE) standards, ratified in 1998 and 2002 respectively, are still in the early stages of rollout. With expenditures in IT ranging from flat to down during the current economic doldrums, companies are finding out that their legacy 10/100 systems are pretty much fast enough.
However, the copper version of 1GE is beginning to appear in many places. This version of Ethernet (802.3ab) implements four twisted pairs in the available CAT5 wiring to carry specially coded baseband signals at 250 Mbits/s to achieve the 1-Gbit/s rate. It works rather well at up to 100 feet.
Organizations are gradually updating their hubs, switches, and routers to accommodate the higher speed. The wide availability of 1GE chips and their rapidly declining prices have also led most major PC manufacturers to include 10/100/1000 ports in most new models. This is by far the most successful trend going on in Ethernet right now.
Backplane design is also seeing the incorporation of 1GE and 10GE versions. The data rate on wide parallel buses has pretty much topped out, so the trend is to move to serial buses that can be more easily routed over longer distances but still achieve higher overall data rates. Designers of high-speed routers, switches, and other telecom and networking equipment are adopting serial buses in the backplanes. This has been made easier by the wide availability of whole families of serializer/deserializer (SERDES) chips from many manufacturers. Designers are achieving distances up to 50 inches with 1 Gbit/s and up to 6 inches at 10 Gbits/s in copper transmission lines on FR4 backplanes.