Gigabit Ethernet changes network behavior

Fast backbones require fast servers. Servers will need to have faster network interfaces and faster disks. Load balancing can be used across multiport network interface cards (nics), or a GbE nic can be used to achieve a wider path into the server. Keep in mind that if you open up your backbones and nics to GbE, then you will have to be sure that your server can deliver input/output at those speeds. You will need ultra scsi (small computer system interface) or Fibre Channel raid (redundant array

Gian Zoppo

The Designory Inc.

If you`re thinking of upgrading to Gigabit Ethernet (GbE), here are some things you should consider.

Fast backbones require fast servers. Servers will need to have faster network interfaces and faster disks. Load balancing can be used across multiport network interface cards (nics), or a GbE nic can be used to achieve a wider path into the server. Keep in mind that if you open up your backbones and nics to GbE, then you will have to be sure that your server can deliver input/output at those speeds. You will need ultra scsi (small computer system interface) or Fibre Channel raid (redundant array of independent disks) to keep up with the new demand. You will also want to upgrade to a faster bus architecture such as pci II or xio on Silicon Graphics.

You will need to examine the rest of your network, along with faster servers. Because you are already running Fast Ethernet does not mean you can put in a GbE backbone. Flatten your network to reduce the number of subnetworks and put in switched Ethernet. You need to eliminate routers wherever possible. If you are moving your network to pure Internet protocol (IP) or ip/ipx (internetwork packet exchange), then use routing switches instead of routers. If you are not running an IP or ipx network, but rather a multiprotocol environment, then you need a very fast router.

Anyone trying to sell you a routing switch for a multiprotocol environment is really selling you a router card in a routing switch, which will perform like a slow router and produce a bottleneck for any traffic that needs to leave the device. The real test of a routing switch is how many packets it moves onto and out of the device`s backplane, along the backbone. Speed within the switch only helps you if none of your traffic leaves the department. In today`s client/server-driven world, more traffic leaves the department than stays in it, which is why it is a good idea to design your network from the server out.

The goal is to deliver gigabit-per-second transactions from the servers to the wiring closets via the backbone. First figure out how to do that. Then figure out how many times you will need to replicate that transaction to serve all the ports in your organization. For example, if your server will supply line-speed input/output over the backbone to the closet, how many Fast Ethernet ports will it take to fully saturate that GbE backbone? The answer depends on your users. In a typical corporate environment, we have found that about 96 Fast Ethernet ports will fully saturate a GbE backbone. In an environment that uses a lot of graphics, audio, video, or multimedia, it will take only 48 ports or fewer to fully saturate the backbone.

Latency issues must also be considered. Not a real-world problem, you say? What if the database you need to query is in Hong Kong? How much latency does it take to make an application think that it has timed out? Does this mean you need one server for every 96 people? Of course not, but you will need sufficient infrastructure to run GbE. If you do not have it, your users will let you know in a hurry.

Importance of cable

Do not underestimate the importance of cable. Putting in Category 5 cable does not mean it will work. A poor-quality cable installation will impact your network immediately after you turn up the speed. If your cable was installed before anyone was running Fast Ethernet broadly across the enterprise or by anyone other than a properly trained installer, then look out.

Crosstalk will make itself known in a big way. Crosstalk issues should be seriously addressed when installers pull and terminate your cable. If there is any exposed copper at the connectors or patch panels, you will probably get errors. If the installers pull 20 cables in one bundle, you may get crosstalk across them. One Fast Ethernet nic manufacturer recommends a maximum of six cables in each bundle.

Also, don`t forget the patch cables, which also need to be of high quality. Make sure your end-users are not shoving their desks against the wallplates, because right-angle bends in the patch cable can cause problems. If you start having these kinds of issues, you may want to consider fiber. The price is close to copper, and the future utility is very good for GbE to the desktop. Ridiculous, you say? How much traffic do you think voice and video will add to your network?

One last thing: Spend extra time monitoring your network closely after a backbone upgrade. GbE changes network behavior. It`s a little bit like a dam breaking.

Gian Zoppo is information-systems director at the Designory inc. (Long Beach, CA).

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