Crossover Cables: Thing of the Past?

...

Background

Ever since the introduction of the Ethernet standard, hubs, routers, and switches people have had to connect them with cables. Ethernet cables come in various categories (which describe the physical characteristics of the cable, and thereby define the speed at which data can travel through them). Ethernet cables also come in two main types: straight-through and crossover.
This has been the bane of many a home-networker or LAN-gamer.

You see, when Ethernet transfers data, it transmits on two lines, and receives on two other lines. Basically, network card (NIC) “A” will send its data to NIC “B” on one pair of cables, but NIC “B” will listen for that data on another pair, because it’s sending its data back to NIC “A” on the same pair that NIC “A” is using… In otherwords, all NICs send data on the same pair of wires, and receive data on the same pair of wires, thus, you’d have both NICs talking, but neither NIC listening (which won’t work).

To address this seemingly simple problem, one NIC’s sending wires have to be “switched” to another NIC’s receiving wires, and vice versa. Hubs and Switches do this for us today. But what about those of us that still connect a computer directly to another computer (or a gaming console directly to another gaming console)? For those applications the switching has to be done physically INSIDE the cable. This, for logical reasons, is called a “crossover cable.”

Crossover cables have other uses in larger deployments, for example, in a larger network setup, a particular router (or similar network appliance) may REQUIRE a crossover cable connecting to it from a bridge (aka “modem” for those of you who insist on using incorrect and outdated terminolgy — Qwest, Comcast, SBC, etc.), similarly, a switch connected to said router may ALSO require a crossover cable to connect to each other.

Luckily for home users most consumer-grade networking appliances (switches, routers, etc.) are “autoswitching,” which means it will detect if you’re using a straight-through cable, and automatically switch the pairs internally.

Pretty cool, right? Well, yes and no.

Yes, it’s cool that networking appliances can auto-switch, but the one thing that’s lacking is the NIC: if you want to use two computers/consoles directly connected together, you still have to use a crossover cable (and to connect a computer/console to your network, you still have to use a straight-through cable).

So what’s one to do?

Lucky for all of us, we have standards to help us along our way!

More background: Ethernet comes in different speeds (which have slightly different cable requirements), including 10Mbps, 100Mbps, and “Gigabit.”

Here’s where it gets good

While the 10 and 100 Mbps speeds are certainly fast enough for most home networks, Gigabit Ethernet has its disadvantages (CAT5e/CAT6 cable is more expensive, appliances and NICs are more expensive, people have to know what “Giga” means, etc.), but it has advantages, too (it’s faster, and NO MORE CROSSOVER CABLES!).

Yes, you read that right! With a standards-compliant Gigabit Ethernet deployment, you no longer need crossover cables — the switching is part of the specification.

Leave a Reply