The Compass DeRose Guide to Saving on Multiple Ethernet Drops

This page was written by Steven J. DeRose, and was last updated on 2003-03-29.

Instead of pulling a whole bundle of wires to a particular location, you can save money and time by pulling one or two, and then using a local hub or switch to expand it into as many as you need. This can save a lot of wiring or rewiring work in some cases. The drawback is that the speed of the main connection is shared across the several machines -- so if you have many machines with very high speed requirements, this won't be ideal.

Professional wiring can cost hundreds of dollars per connection. And there are never enough connection points (or "drops"). Only a year after my old company had completely rebuilt a building, with 3 to 6 drops per office, I came in one day and found people pulling a huge bundle of additional cables over my ceiling.

There has to be a better way. And there is: Use hubs or switches where you would have put extra drops.

An 8-port 10MB Ethernet hub is now about $20 (probably less by the time you read this). That's far less than the labor to add a single drop. It's less than just the wire and connectors for the 7 added drops you get. 100MB hubs are a bit more; but still way less than wiring.

So my general principle is: pull one or two drops to each relevant wall, and when you need more add a hub. If you put the drops into inside walls between adjacent rooms, or in corners where they can reach two walls easily enough, you can get by with even fewer "real" drops.

I was on a plane recently with an administrator who was about to order 150 drops to wire his school. He was quoted $350 per drop: $52,500. Every drop he can drop (ahem) saves him enough to buy 8 routers and lunch.

The problem with this plan is when traffic gets high. Since all the machines on one hub have to share that hub's connection back to the main net, You can't get simultaneous maximum performance on all the machines. To minimize this problem, take these steps:

• Buy high-quality switches and hubs; there are various details of their design that can make a big speed difference.
• Try to group related machines onto the same switch.
• Use very high speed interconnects between the switches -- 1,000Mb twisted pair, or perhaps even fiber.
• Don't carry the idea of adding hubs and switches to extremes.... One reader reported having seen someone string 25 hubs in a row -- which is really a bit much. If nothing else, it raises the number of failure points so high that you'll see some kind of failure pretty soon, and you won't enjoy never tracking it down. Buy bigger hubs instead of many little ones.

Larger networks deal with this by using sub-nets: use a switch instead of a hub, and plug machines that will have a lot of talk between them, on the same switch. Then the wires between the switches don't see any of the local traffic within each switch's subnet. Getting this to work right requires assigning IP addresses, subnet masks, and other configuration settings right.

If you do add layers of switches (not just hubs), accept that you'll have to be much more careful about managing their configurations to make sure packets actually get through.

So any time someone wants to sell you more wire-pulling, ask them why you can't just stick a hub into the outlet you have, and have 7 new drops for half the price of one.

Nuff said.

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