Processors Toolkit

Prepare for Gigabit Ethernet

Tags:
Gigabit,
Switch,
Network,
Workstation

Brien M Posey Tech Republic

Published: 28 Jan 2003 09:32 GMT

If you've been working with networks as long as I have, you probably remember the days when 10-Mbps Ethernet seemed fast. And when 100-Mbps "Fast" Ethernet debuted -- Wow! Just when it seemed as if Ethernet couldn't get any faster, along came Gigabit Ethernet with speeds up to 1,000 Mbps (1 Gbps).

Even if you're not deploying Gigabit Ethernet right now, eventually you will. After all, just look at all of the Fast Ethernet equipment in your wiring closet. However, just because you're not deploying Gigabit Ethernet today doesn't mean you can't get your network ready to handle it. In this article, I'll show you what you need to do to prepare for Gigabit Ethernet.

What's so great about Gigabit Ethernet?
Although Gigabit Ethernet is growing in popularity, few people I know are actually running it yet. When I ask why, many explain that they'd been burned by ATM and weren't ready to go through that whole experience again. ATM was originally touted as the replacement for Ethernet. It was faster than Ethernet and avoided some of Ethernet's initial problems, such as packet collisions.

However, ATM can be costly. It's also difficult to set up and doesn't work well in environments that require routing between many subnets. In the end, ATM's performance can be disappointing.

This is what makes Gigabit Ethernet such a great technology. While Gigabit Ethernet is a high-speed medium, it's still Ethernet-based. This means that setting up a Gigabit Ethernet network isn't much different from setting up any other type of Ethernet network.

Best of all, since Gigabit Ethernet is a true Ethernet medium, it will interface with your existing Ethernet network. A Gigabit Ethernet switch can move packets between 10/100-Mbps and 1,000-Mbps networks without any type of packet translation. This not only leads to better efficiency than you'd get with ATM, but it also means less complexity and therefore less chance that something will go wrong.

How fast is it really?
Because Gigabit Ethernet supports transmission speeds of roughly 1,000 Mbps, many network gurus assume that installing a few Gigabit Ethernet NICs and attaching the cabling and a high-speed switch will make their networks perform at warp speeds. However, for several reasons, the actual network speed will probably be a bit less.

Suppose for a moment that you were to install Gigabit Ethernet NICs in a server and a workstation and then connect the two machines with a gigabit switch. Assuming there is no other traffic on the network, you'd probably expect traffic to flow between the two machines at 1,000 Mbps. Unfortunately, you'd be sadly disappointed. The truth is that, in most installations, Gigabit Ethernet implemented in the manner I've just described doesn't even come close to reaching gigabit speeds. In the example above, the best you could hope for is typically between 700 and 800 Mbps.

While 700 Mbps is a huge improvement over the 100-Mbps speed of Fast Ethernet, you're probably wondering why traffic is flowing at 200 to 300 Mbps below its potential. There are several factors that reduce Gigabit Ethernet's performance. One of the most common factors is the cabling.

Cabling considerations
One of the biggest issues to take into account when implementing Gigabit Ethernet is cabling. When you first read the specs on Gigabit Ethernet, it sounds like an ideal technology, in part because it's compatible with the Category-5 (Cat-5) cable that you already have. However, just because you can use your existing Cat-5 cable for Gigabit Ethernet, it doesn't necessarily mean that you should.

Most big companies will probably be OK with existing copper Cat-5 cable. However, I've done network repair for many small organisations, and the cabling just wasn't up to par in more of them than I can count. For example, in one location, most of the PCs had 10/100 NICs, but the company was still using a 10-Mbps hub. I swapped the hub out for a 10/100 model, and all of the PCs with 100-Mbps cards began to fail. Upon closer examination, I found that voice-grade phone cabling had been used instead of Cat-5 cable. When I explained the problem to the facility's manager, he said that he had told the installers to use phone cable because it was cheaper than Cat-5 cable.

This is an extreme example, but other cable issues tend to be much more common. For instance, although Cat-5 cable has eight wires, 10/100-Mbps Ethernet uses only four of them. I've seen quite a few organisations in which the cable installer saved time by connecting only the four wires that were actually used. In most cases like this, the other four wires are simply cut off. But I've also seen situations in which the additional wires were used to attach a second PC to the network or as wiring for a phone jack.

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