O'Reilly System & Network Administration Center -- An Interview with Charles Spurgeon

Ethernet's origins date back to an early 1970s experiment at Xerox to interconnect a couple of Altos computers with servers and printers to share a communications channel and exchange data without conflict. Ethernet creator Bob Metcalfe's fundamental concept for local area networks forever altered the world of computing with its hardware-neutral nature and flexible design. Because Ethernet has kept pace with technological advances and evolving standards for the past 30 years, it continues to be the most widely adopted, low cost network design.

Charles Spurgeon is a senior network architect whose career progressed in tandem with Ethernet's evolution. He first became involved with Ethernet in 1981 while building campus networks at Stanford University, part of the ARPANet, the network that became the basis for the Internet. In fact, several core Internet technologies grew out of Stanford's SUNet. Spurgeon also contributed to another university group whose experiments became the founding technology for a couple of little startup enterprises: Sun Microsystems and Cisco Systems.

Charles Spurgeon talked with Web reporter Lori Houston about Ethernet's ubiquity, where it's headed, and his recently released book, Ethernet: The Definitive Guide.

Houston:

To begin with, how about a concise definition of Ethernet?

Spurgeon:

Ethernet is a very flexible network technology that has become the most widely adopted way of linking computers. A more precise definition from my book describes the Ethernet system in terms of its four basic building blocks:

• The frame, which is the standardized set of bits used to carry data over the system.
• The media access control protocol, which is the set of rules embedded in each Ethernet interface that enables multiple computers to access a shared Ethernet channel equitably.
• The signaling components, or standardized electronic devices that send and receive signals over the Ethernet.
• The physical medium, that is, the cables and other hardware carrying those digital signals between computers on the network.

Houston:

What is the current "state of affairs" with Ethernet technology and standards?

Spurgeon:

The current state of affairs is that Ethernet is evolving yet again, with a new 10 gigabit-per-second Ethernet standard now under development. All Ethernet standards are published by the IEEE (Institute of Electrical and Electronics Engineers), and those interested in following the standards can find them listed on the IEEE Web site. The presentations and meeting notes for the evolving 10 Gigabit/sec standard can also be found on the IEEE site.

Houston:

Ethernet has been around since the 70s, and both computer and networking technology have exploded since then. How has Ethernet technology been able to keep pace?

Spurgeon:

I think that Ethernet has been able to keep pace because the original design was kept as simple as possible. The basic simplicity of the system also made it possible for Ethernet to more readily evolve to meet the needs of new generations of computer technology. Also, the success of Ethernet has spawned more evolution since the widespread popularity of the system has meant that there is constant pressure from the marketplace to develop ever-faster Ethernet technology.

Another advantage is that Ethernet's simplicity of operation means that it will typically continue functioning even when conditions are less than optimal. Like the Energizer Bunny on the television commercials, the Ethernet system "... just keeps on going."

Houston:

Tell us more about the newest 10Gbps Ethernet standard.

Spurgeon:

The 10 Gbps standard is being designed to support not only the traditional local area networks (LANs), but also metropolitan area networking (MAN) and wide area networking (WAN). Building MANs and WANs involves sending Ethernet signals over considerably longer distances than are usually seen in LANs. This will open up a new market for Ethernet technology, providing high bandwidth links within a city or to the Internet. It will be very interesting to see what happens when that occurs.

The new 10 Gbps standard is still evolving, and specific details are not available. However, the current scheme is that two signaling systems will be provided. One will operate at 10 Gbps over the same fiber optic cables currently used to support 1 Gbps Ethernet signals on campus networks. The second scheme will provide 10 Gbps Ethernet signals over WANs. The WAN interface will provide mechanisms to map the 10 Gbps Ethernet signals onto the synchronous optical network (SONET) and wave division multiplexing (WDM) technology used in WANs to carry high bandwidth signals over long distances.

Houston:

What kinds of issues are raised by the development of multi-Gigabit Ethernet?

Spurgeon:

The 802.3z fiber optic Gigabit Ethernet standard has performed like all other Ethernet technology, providing very solid interoperability between equipment from different vendors. The major issues raised by this and the even faster Ethernet technologies under development typically have to do with the current limitations in disk and bus I/O bandwidth inside computers. In other words, gigabit Ethernet networks frequently provide more bandwidth than many server computers can handle at this time. Of course, this will change as the speed of disk and bus I/O continues to improve.

Houston:

Would different or new types of cabling, hardware, software, or other equipment be necessary?

Spurgeon:

In some cases, yes. For example, when the 1 Gbps fiber optic Ethernet system was developed in 1998, it was discovered that the most widely used multimode fiber optic cables did not perform as well at that speed as had been hoped. As a result, the achievable segment length was shorter than the original goals. This was not due to any limitation in Ethernet. It was simply that this was the first time that the industry had attempted to send signals this rapidly through these cables. In response, cable vendors are now producing better fiber optic cables that can support this signaling rate over longer distances.

As described in Chapter 16 of my book, the maximum segment length for 1000BASE-SX short wavelength Gigabit Ethernet signals carried over the most commonly installed multimode fiber optic cable is about 220 meters (721.78 feet). This is based on worst-case assumptions of signal loss. To achieve longer segment lengths for new multimode fiber optic installations, network administrators need to be sure to install the enhanced versions of multimode cables, which are available from a number of vendors. These fiber optic cables can typically provide 1000BASE-SX multimode segment lengths from 300 to 500 meters. The Siecor "Gigabit Plus" product line is one example of enhanced multimode cabling.

As noted in Chapter 16, the 1000BASE-LX Gigabit Ethernet long wavelength segments do not have these distance issues. Typical 1000BASE-LX segments can reach 550 meters on multimode fiber, and 5,000 meters on single-mode fiber, based on worst-case signal loss assumptions as listed in the standard. In the real world, vendors are providing 1000BASE-LX equipment that can achieve segment lengths of 10,000 meters and more.

Houston:

It sounds like a lot has to change to support it?

Spurgeon:

Yes, cable vendors are developing new cable types. Computer vendors are developing higher performance network interface cards that can assist the computer when it comes to supporting gigabit Ethernet data rates. Switch vendors are working on better switches with faster switch fabrics that can support more gigabit Ethernet ports in a given switch.

All of these developments are happening now. The 1-gigabit fiber optic Ethernet standard has been a major success, and the 1 gigabit twisted-pair Ethernet is expected to result in more and more sites adopting Gigabit Ethernet. Vendors are developing pre-standard versions of 10 Gbps, and you can expect to see that gear appearing later in 2000, and during 2001. The target date for the completion of the new 802.3ae 10-Gigabit Ethernet standard is late 2001.

The development of technology for this new standard is moving fast. At least one vendor has asked if I would be interested in beta testing their new pre-standard 10 Gbps Ethernet module for their high-end switching hub, which they expect to have available around July-August 2000.

Houston:

What are some important tips for upgrading or migrating from older versions of Ethernet to newer ones, for example, from 10BASE5 /2 to 10/100BASE-T?

Spurgeon:

These days, the typical upgrade is to purchase a switching hub with 10/100 ports. That's a major increase in bandwidth from a single 10 Mbps shared channel system such as 10BASE5 or 10BASE2 segments linked with one or more repeater hubs. As part of your upgrade you need to find out how many clients and servers you may have, and what the traffic patterns may be. Are all the clients using a single server, or do you have multiple servers with a more balanced traffic load? You want to make sure that any servers you might have can handle the increased traffic loads they will encounter now that client machines will have more bandwidth at their disposal. You can do that by upgrading the servers and making sure that the servers are located on high speed links.

Houston:

How did Ethernet: The Definitive Guide come about for you?

Spurgeon:

My writing on Ethernet stems from my involvement in the design and development of large campus networks based on Ethernet technology, which began in the early 1980s. Based on that experience, I wrote an annotated reading list called the "Network Reading List: TCP/IP, Unix, and Ethernet," which I published on the Internet in 1987. I updated and maintained that list for several years. In those days, the Internet consisted only of a few hundred research and educational sites worldwide.

In 1994, I created a Web site for Ethernet information. I wrote a set of Ethernet tutorial and configuration guides that I made available on that Web site for free, and tens of thousands of people have used that information. After that, I wrote this book.

Houston:

What do you feel distinguishes Ethernet: The Definitive Guide from other books about Ethernet?

Spurgeon:

There are a number of books about Ethernet on the market, and they each have their virtues. I think one of the main things that distinguishes my book is the scope of its coverage. Ethernet has evolved over the years to include quite a wide range of technology. My goal was to cover all of the widely used Ethernet technologies in a single volume, which is what makes this an O'Reilly "definitive guide." Readers will find coverage of the entire range of Ethernet systems, from the original 10 Mbps system to the 100 Mbps Fast Ethernet system and Gigabit Ethernet. The twisted-pair and fiber-optic versions of each technology are covered for each Ethernet speed. Readers will also find extensive coverage of a wide range of topics, including repeater hubs, switching hubs, full-duplex operation, the Auto-Negotiation system, structured cabling systems, twisted-pair and fiber optic cables, network performance, and troubleshooting.

Houston:

What do you hope to achieve with your book?

Spurgeon:

The book is written to be understandable by anyone with a basic computer background who needs to know more about how Ethernet works. The current IEEE 802.3 Ethernet standard contains over 1,200 pages of "standards-speak" and dense engineering details. My goal for this book was to describe the standard in something closer to plain English, and to include only those items that explain how Ethernet works or contribute to keeping an Ethernet operational. The book includes enough technical information to provide a good understanding of how the system works, while not overwhelming the reader with the sort of engineering details that only the designers of Ethernet chips really need to know. Another goal was to provide a practical, real-world orientation with emphasis on the sorts of things that one needs to know to build and troubleshoot Ethernet systems.

Houston:

Are you planning any more books?

Spurgeon:

Writing this book has been a major project that consumed all of my spare time, weekends, and even vacation time for a solid year. Having just finished this book, I am looking forward to taking a break for a bit. However, I have to admit that I am developing a new book idea, around the general topic of network management.

Sponsored by: