I Feel the Need, the Need for Speed

When the IEEE took over Ethernet standards development from Xerox in the early 1980s, Ethernet used a 10-Mbps transmission rate. Whether you were using a hub or a switch, when it came down to the actual transmission of data, the bits crossed the wires at 10 Mbps.

Over the years, the IEEE has created many enhancements to the Ethernet standards. One of the enhancements made over time was an increase in speed. This short section outlines some of the changes to Ethernet over the years, including increases in speed.

A New, Improved, and Faster EthernetLet's Call It Fast Ethernet

My mom always used Tide laundry detergent when I was a kid. Every time she bought a new box of detergent, it had a new marketing blurb on it. "New and Improved," it would state. Or "Newer, and Even More Improved" the next time around. Then someone got smart and started looking for Greek and Latin root words that meant really super good, like my personal favorite "Ultra-Cleaning Power," or "Super-Dooper Cleaning Power," and the like.

The first time Ethernet speed was enhanced, the IEEE created a working group and named it 802.3u. (The "u" has no special meaning. The IEEE chooses to name new 802.3 (Ethernet) working groups using letters after the base 802.3 name, and they hadn't used "u" before.) So, the 802.3u working group created a specification for Ethernet to run 10 times faster, at 100 Mbps. So, if Ethernet ran at 10 Mbps, what do you call Ethernet that runs at 100 Mbps? "New and Improved Ethernet"? "Ultra Ethernet"? Well, the IEEE settled on another termFast Ethernet. So does that mean "normal" Ethernet is slow? Not really. But for today's enterprise networks, Fast Ethernet does help tremendously.

When the IEEE created 802.3u Fast Ethernet, it chose to do something incredibly smart. Yes, I'm overemphasizing this point, but it's hugely important. The IEEE decided that the rest of Fast Ethernet worked the same as plain old Ethernet. So, both Ethernet and Fast Ethernet use the same headers and trailers. The same CSMA/CD logic is used, too. In addition, the same 6-byte MAC addresses are used. The only differences come in how the bits are encoded to cross the wires, including the speed at which they are encoded. In fact, Fast Ethernet fell under a working group of 802.3 because it was only amending the original 802.3 Ethernet, rather than creating a whole new type of LAN.

Why am I so ultra-hyper about this design choice? (There's that "ultra" word again. It's so easy to use!) Well, that one design choice has had a lot of impact on Ethernet's acceptance in the marketplace. If you already knew Ethernet, you could learn Fast Ethernet easily. Also, vendors only needed to make small changes to existing Ethernet products to create Fast Ethernet products, meaning that those products' prices fell quickly, making them popular in the marketplace and making it harder for anyone to choose anything except Ethernet.

Along the way, many new terms were introduced to describe Fast Ethernet. For instance, Fast Ethernet is often simply abbreviated as FE. The older 10 Mbps Ethernet, when using twisted pair cabling, was called 10BaseT, meaning 10 Mbps Ethernet using twisted pair. As a result, FE was called 100BaseT.

If Fast Ethernet Is Good, Even Faster Is Better: Gigabit Ethernet

Yep, 100 Mbps is fast, but 1000 Mbpsalso known as 1 gigabit per second (Gbps)is even faster. So, the IEEE eventually created even faster Ethernet, using 802.3 working groups 802.3z and 802.3ab. What do you call really super fast Ethernet that runs at 1 Gbps? Well, the IEEE got smart this time, avoiding the pitfalls of the laundry detergent industry, and cleverly called this one Gigabit Ethernet (GigE).

The difference between Gigabit Ethernet and Fast Ethernet is speed. To support the speed, the standards call for better cabling, but everything else is the samesame frame header and trailer, same CSMA/CD (as needed), same MAC addresses, same relatively quick acceptance in the market, same death-knell for all other LAN technologies. Historically speaking, by the time Gigabit Ethernet was becoming accepted in the marketplace, the competition between Ethernet and other LAN technologies was over. Ethernet had won, being faster, better, and cheaper than the competition. That is, in part, why you won't be reading about other types of LANs in this bookthey just don't matter much anymore.

By the way, in case you were wondering, the 802.3z working group defined how to do GigE over optical cable, and the 802.3ab working group defined how to do GigE over copper cabling. Optical cabling uses glass fibers instead of copper wire. The devices that are attached to an optical cable send light across the cable, instead of electricity, to encode 0s and 1s. As it turns out, the physics behind optical signals over optical glass-fiber cabling allow for higher speeds, longer distances, fewer errors, and better security, but at a higher cost than copper wiring.

The optical version of GigE(802.3z) came out first, with the copper version (802.3ab) coming out a little later. And because each standard required different types of engineering effort based on whether optical or electrical cabling was used, the IEEE created two working groups to create the standards.

Ultra Super-Fast Fast Ethernet: 10 Gigabit Ethernet

Yep, it's an old storythere's an even faster option now. 10 Gbps Ethernet, or 10 GigE for short, defined by the IEEE 802.3ae working group, does have a few more distinguishing characteristics than normal. For instance, you cannot use hubs for 10 GigE. Also, 802.3ae calls for optical cabling only, with no option for copper wiring as of the time this book went to press. If history is any indication, the thought of 10 GigE using copper wires is more than a twinkle in someone's eye already, though!

As usual, 10 GigE uses the same framing, addresses, and so on as other forms of Ethernet, with the only differences being in the physical encoding details and the requirements on the cabling, which allow the faster speeds.

And yes, there's already talk of 40 Gig Ethernet, but that's still in the working stages.

Summary of Ethernet Speeds

Although you shouldn't feel the need to memorize the IEEE standard names about each type of Ethernet, you should at least know about the different speeds. Table 6-1 lists several of the details in one place for your convenience.

Table 6-1. Ethernet Specifications

Common Name	IEEE Standard	Speed	Type of Cabling
Ethernet	802.3	10 Mbps	Both
Fast Ethernet	802.3u	100 Mbps	Both
Gigabit Ethernet	802.3z	1 Gbps	Optical
Gigabit Ethernet	802.3ab	1 Gbps	Copper
10 Gigabit Ethernet	802.3ae	10 Gbps	Optical

Interestingly, if you walked around asking long-time network engineers things like, "Which IEEE standard defines GigE over optical cabling?," I'd guess at least half the people wouldn't remember. Knowing that standards exist for Ethernet at varying speeds is what's important.

A Switch for All Speeds

LAN switches use logic that relies on information in the Ethernet header. Because all the more advanced forms of Ethernet use the same header, switch forwarding and learning logic do not change based on what speed Ethernet is used. The switch can behave the same way as always, with some ports using Ethernet, some Fast Ethernet, some Gigabit Ethernet, and so on.

Imagine that you want to support a bunch of users on a building floor, some with NICs that only support 10 Mbps 802.3, and some that only support 100 Mbps 802.3u Fast Ethernet. You might buy a switch that has 24 ports12 10-Mbps ports and 12 100-Mbps ports. Figure 6-12 shows the basic setup, with Fred using a 10-Mbps NIC and Wilma using a 100-Mbps NIC.

Figure 6-12. Supporting Multiple Speeds on a Single Switch

The switch can easily support both speeds in the single switch, mainly because the only difference between Ethernet and Fast Ethernet is in how the bits are transmitted over the cable, and at what speed. Because the headers and trailers are the same, and the addresses are the same, the switch still learns MAC addresses, makes forwarding and filtering decisions, and buffers frames, just like always.

The switch in Figure 6-12 has physical ports that only support 10 Mbps or 100 Mbps; this type of switch does not provide an easy migration path from 10 Mbps to 100 Mbps. For instance, imagine that you have 12 devices migrated to use Fast Ethernet, so you have plugged them all into the 12 Fast Ethernet ports on the switch. Now Fred gets a new 100-Mbps NIC, puts it in his computer, and wants to be moved to a 100-Mbps switch port. Uh oh. No more ports.

To solve problems like this one, the IEEE created a standard, called autonegotiation, that provides an easy migration path from 10 Mbps Ethernet to 100 Mbps Ethernet, or even to 1000 Mbps Ethernet (GigE). Vendors build switches with physical ports that can run at various speeds. Autonegotiation allows the switch and NIC on either end of the cable to automatically negotiate to determine the speed. The switch and computer also happen to negotiate whether to use full duplex or half duplex. Figure 6-13 shows the general idea.

Figure 6-13. Autonegotiation with 10/100 Cards

To perform autonegotiation, the switch and the NIC must support multiple speeds, as well as autonegotiation logic. To perform autonegotiation, the switch and NIC send some messages back and forth. These messages simply state things like, "I want to use 100 Mbps," with a response like, "Okay, me, too. Let's do it." Of course, the IEEE specifications aren't so informal, but that's the gist of the mean.

And if the switch and NIC simply can't agree, they fall back to 10 Mbps, half duplex.

Many of the Ethernet NICs in use today are called 10/100 cards, meaning that they will run at either speed, and they will negotiate with the switch. In Figure 6-13, Fred has a new 10/100 card, and Wilma has her same old 10/100 card. Both have negotiated for 100 Mbps, full duplex. Barney, using an older 10-Mbps only card that does not support autonegotiation, settles for 10 Mbps, half duplex.

Because GigE products keep falling in price, you can now find 10/100/1000 NICs and switch ports, meaning that the NICs and the switches will negotiate the use of Gigabit Ethernet as well.