Electronic Design

Ethernet: 30 Years And Still Going Strong

Wireless Ethernet grabs the headlines, but a steady stream of technology advances fortify Ethernet's wired side.

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.

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.

The optical versions of 1GE and 10GE have not fared as well yet. They are, of course, being adopted. But that's happening at a slower rate due to the overall higher cost of optical fiber components and the lesser need for such high speeds. Nonetheless, progress is under way in areas that require the benefits of optical fiber.

The 1GE optical version is emerging as the backbone in some larger enterprise local-area networks (LANs), and 10GE optical versions will no doubt adopt that role eventually. Right now, though, metropolitan-area networks (MANs) are the key application for these versions. MANs cover a large campus or local area within a town or city. Sonet currently dominates the MAN space, but Ethernet is working its way in. This is mainly because it's less expensive and simpler as no protocol conversion is necessary to link to the LANs using it.

One version of optical 1GE uses coarse wavelength division multiplexing. Another MAN option is Ethernet over Sonet. Techniques such as virtual concatenation (VCAT) and the generic framing procedure (GFP) permit Ethernet packets to be carried efficiently over Sonet/synchronous-digital-hierarchy (SDH) networks. In some applications, 10GE could eventually replace Sonet/SDH in WANs.

Another interesting development is the recently ratified Power over Ethernet (PoE) standard 802.3af. It outlines a way to transmit dc power over the twisted pair in CAT5/CAT6 cables. The power level is 48 V nominal at 12.95 W or less. This is still a substantial power source that's expected to power Internet telephones (VoIP), wireless LAN (WLAN) access points, and remote devices like security cameras, data loggers, or small data terminals.

Other possibilities include charging laptops, cell phones, and PDAs. In any case, with such power available, it will make remote network nodes like WLAN access ports less expensive to install.

Also, any device powered with PoE will be immune to conventional ac power failures because the dc typically comes from an uninterruptible power supply associated with the Ethernet server. PoE is just now becoming available, but it should quickly gain popularity.

Another trend is the widespread use of Ethernet in industrial applications. As companies further automate manufacturing and production in factories and chemical/petroleum plants, networking plays a larger than ever role in connecting the sensors, machines, and computers used in the process. Many of the special networking systems created to facilitate this automation have been abandoned or assigned a lesser role in place of Ethernet everywhere.

A whole new sub-industry has developed to supply hardened Ethernet products that can withstand the temperature, noise, and other environmental problems that would seriously degrade office-type Ethernet products. Another problem has been Ethernet's nondeterministic nature, but the high-speed versions and use of Ethernet switches all but eliminated this problem. Furthermore, vendors are finding ways to operate their many proprietary industrial protocols in the higher layers of Ethernet PHY/media-access-controller (MAC) systems. Finally, the industrial networks easily link to the IT side of the business to form complete computer-integrated-manufacturing (CIM) systems.

Ethernet is also making headway in the SAN and network-attached-storage (NAS) fields. Remote-storage usage of all types continues to grow, as does the need for fast, inexpensive methods to connect it to the servers. The entrenched networking technology for storage is Fibre Channel, which offers a robust 1- and 2-Gbit/s standard that fills most needs. However, it's expensive, range is limited compared to Ethernet, and the current upper speed limit is 2 Gbits/s.

The standards are being updated to accommodate 4- and 10-Gbit/s systems, but 1GE and 10GE equipment is available right now for lower prices. This has led many to take a hard look at Ethernet for this application.

One of the best efforts is an Ethernet-based serial version of the previously popular parallel interface known as the Small Computer Systems Interface (SCSI). This new standard, developed by the Internet Engineering Task Force (ITEF), is called Internet SCSI (iSCSI). It uses the familiar transmission-control-protocol/Internet-protocol (TCP/IP) to transmit SCSI commands and data over Ethernet to achieve access to storage over very long distances with familiar low-cost equipment. There has already been a number of systems developed by many different vendors.

Another IEEE standard project tied to Ethernet is the Resilient Pack Ring (RPR) access protocol. Designated 802.17 by the IEEE, its charge is to define and develop a ring topology and protocol that's optimized for packet transmission over a ring.

Currently, there's no high-speed ring system designed to handle packets at data rates over 1 Gbit/s. Sonet/SDH, of course, incorporates a ring fully capable of speeds up to about 40 Gbits/s (OC-768), but it can't handle packets. It was optimized for time-division multiplexing (TDM) transport in the telecommunications industry.

While ways exist to transmit packets over Sonet, it's by no means an optimum solution. The RPR effort is in response to many customers and vendors who believe that a scalable packet ring for LAN, MAN, or WAN is essential for the future.

The ring topology includes at least two counter-rotating rings in which multiple nodes negotiate for and share the bandwidth of the ring without provisioning capability. The RPR is a layer 2 (MAC) protocol that provides exceptional reliability or resilience with its multiple rings and can protect against fiber or node failure within 50 ms. Every node has two paths to any other node on the ring.

RPR offers bandwidth efficiency that's achieved by using both rings to carry data and by stripping unicast packets at their destination, permitting spatial reuse of the medium. RPR doesn't define a physical layer, and it works with Sonet/SDH or Ethernet. Because most future traffic is expected to be IP, Ethernet is expected to be the main physical layer. Look for a final standard next year, along with new equipment from Cisco, Corrigent, and Nortel for metro applications.

What does the future hold for Ethernet? Expect continued fine-tuning and development of the standard, as well as increased penetration in all areas of networking. As for speed increases, the world has yet to absorb the latest 10-Gbit/s technology, so further increases in the near future aren't a priority. You can bet, though, that there are engineers working on 40-Gbit/s or even 100-Gbit/s plans right now. Don't hold your breath, but don't be surprised to see them in the future.

Overall, Ethernet seems secure enough right now, but many manufacturers are hedging their bets because of the unbelievable surge in wireless Ethernet installations. Will standard wired LAN extensions or new wired LANs be replaced with wireless equipment?

To an extent, that is already happening. Wireless will probably never replace wired systems entirely, but wireless will undoubtedly make a big dent in the marketplace as more and cheaper equipment hits the market and/or is built into PCs, laptops, PDAs, and other equipment. But so what? It may be wireless, but it's still Ethernet.

Need More Information?
Charles Spurgeon's Ethernet Web Site

For more on Industrial Ethernet

Institute of Electrical and
Electronic Engineers


Internet Engineering Task Force

InterOperability Laboratory

Resilient Packet Ring Alliance

10 Gigabit Ethernet Alliance

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