crossover cables

pts.
Tags:
Cabling
Ethernet
I know this may be basic questions to many but can someone tell me why crossover cables would be used as opposed to straight through cables. Also, what do crossover cables do that straight through cannot? What would be a funtion for each? Thanks for the help.

Answer Wiki

Thanks. We'll let you know when a new response is added.

All 10/100/1000 Base-T copper wiring are composed of two used pairs – transmit and receive.

A hub or switch usually has these reversed from typical end objects (PC’s, Servers, Routers, etc.) so that the send pair from one goes to the receive pair from the other and vice versa.

While many newer devices have auto-detect (and auto-switch) for this, most PC’s and such do not.

If you’re connecting two pc’s to each other without an intervening switch or hub, you need a cross over cable.

Internally (to the cable) all it does is connect the pair of wires 1 & 2 to the pair of wires 3 & 6, and vice versa the other direction.

Bob

Discuss This Question: 6  Replies

 
There was an error processing your information. Please try again later.
Thanks. We'll let you know when a new response is added.
Send me notifications when members answer or reply to this question.

REGISTER or login:

Forgot Password?
By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy
  • CableInstallationTech
    The other posted response from this was good, but there are a couple of other points that may need to be covered, due to the nature of the question. Going back to the basics, all 8 conductor network patchcords (and cabling) have the conductors divided up into four pairs, with the wires of the pairs twisted together. This is many refer to this cable as "four-pair" cable, or "twisted-pair" cable. By twisting these pairs together, the idea is to minimize the amount of signal that "bleeds" through from one pair to another. As previously noted, Ethernet devices transmit on one "pair" and recieve on another "pair". Standards created to regulate this stuff have determined that, if you look into a computer port on the back of the computer, the first two conductors from the left (1 & 2) and the two pins just "outside" the center two conductors (3 & 6) are the active pins. A straight through cable makes sure that 1 & 2 are a twisted pair all the way through the cable, and 3 & 6 are a different twisted pair. The remaining pairs (4 & 5) and (7 & 8) are unused in 10 and 100Base-t, but used in 1000Base-t...still in pairs. The cross-over cable also keeps the signals in pairs, but reverses the pairs on one end. In addition to allowing two pc's (or station NIC's) to directly connect, a crossover cable also allows two hubs, switches, or routers (Head-end NIC's) to be direcetly connected to each other, which allows hubs to be cascaded, or a small hub in a workstation to be connected to a larger switch back in the telecom room.
    0 pointsBadges:
    report
  • KeithD1967
    Here's a good web site for your question: http://www.duxcw.com/digest/Howto/network/cable/cable5.htm Basically, this is how it looks: *Pin 1 on sideA (TX+) goes to Pin3 on sideB (RX+) *Pin 2 on sideA (TX-) goes to Pin6 on sideB (RX-) *Pin 3 on sideA (RX+) goes to Pin1 on sideB (TX+) *Pin 6 on sideA (RX-) goes to Pin2 on sideB (TX-) So if you really think about it, when you use a normal land-line telephone, you are hooking up two telephones with a cross-over connection. You can't have two people talking on one wire that both transmit (TX). You have to have one side that has a wire that transmits (TX), and another side that receives (RX), and vice-versa. The "+" and "-" in the example above only relates voltage. Another good web site to look at is: http://www.cisco.com/univercd/cc/td/doc/product/lan/cat3200/3200/amappexa.htm This web site can be a little confusing, but it can answer your question with regards to, ?why crossover cables would be used as opposed to straight through cables. Also, what do crossover cables do that straight through cannot?? Just look under the title ?Twisted-pair Cable and Connector Pinouts / 10BaseT / Straight-through and Cross-over? sections. This explains OK for people starting to try to understand what this whole convoluted idea of ?pin-out? is. However, I wouldn?t follow their example of the diagram of their pin-out for a cross-over and straight-through. Use the first web site I gave you. Hope this helps.
    0 pointsBadges:
    report
  • SusanFogarty
    We have quite a bit of info on crossover cables on SearchNetworking.com. You might want to take a look at these articles: Ten cabling tips in 10 minutes http://searchnetworking.techtarget.com/originalContent/0,289142,sid7_gci1007161,00.html Network cable, lesson 3: CAT5 UTP crossover cable http://searchnetworking.techtarget.com/tip/1,289483,sid7_gci993181,00.html Good luck!
    0 pointsBadges:
    report
  • DavidFigueroa
    One other minor piece of information. The number of twists per foot is different in each pair. This also helps eliminate cross-talk bleedover from the wires. Pair 1 - wires 4,5 (blue, blue white) Pair 2 - Wires 1,2 (orange white, orange) Pair 3 - Wires 3,6 (green white, green) Pair 4 - wires 7,8 (brown white, brown) This is AT&T 568B standard wiring.
    0 pointsBadges:
    report
  • Raphael7
    You can also use a crossover cable to access another computer the NIC card
    145 pointsBadges:
    report
  • Needhlp
    [...] Crossover cables [...]
    0 pointsBadges:
    report

Forgot Password

No problem! Submit your e-mail address below. We'll send you an e-mail containing your password.

Your password has been sent to:

To follow this tag...

There was an error processing your information. Please try again later.

REGISTER or login:

Forgot Password?
By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy

Thanks! We'll email you when relevant content is added and updated.

Following