Crossover cables - Bah humbug?

Tke this URL: http://networkwire.org/what-is-crossover-cable.html

7&8 are the same, why?

Now if you go here, you get a different pinout for a crossover cable:

http://logout.sh/computers/net/gigabit/

So, someone is pulling someone's leg. I suppose #2 is right.

I was trying to repair a crossover cable and discovered this nonsese as well as a blue pair crossed at one end.

Unfortunately, I made the cable like the first diagram.

You have to be careful beliveing what you find on the Internet.

http://en.wikipedia.org/wiki/Crossover_cable also shos the #1 configuration.

Which one is right for Gigabit Ethernet? We know they will both work for 10/100.

I guess it's explained here: http://en.wikipedia.org/wiki/Ethernet_crossover_cable

You have to be careful beliveing what you find on the Internet.

Click to expand...

The internet is 100% true, especially in religion, politics, money, and pin numbers. (and unwanted comments by fools)

Hi

See this link:

http://www.zytrax.com/tech/layer_1/cables/tech_lan.htm

This shows the correct wiring scheme.

The color code can follow one of two different standards: 568A and 568B
568B is the common one but it doesn't really matter which you choose, electrically they are the same.

Straight thru cables are wired matching pin# to pin#.
Crossover cables are wired differently. Basically, the crossover cable swaps the transmit and receive pins on one end. See the diagram on the link.

If you need to connect similar devices together (router to router, or, switch to switch, for example) you have to use a crossover cable.
If connecting different devices(router to switch, PC to switch) use a straight thru cable. The only exception is if you want to directly connect a PC to a router,
then the cable must be a crossover cable.

10/100 (100BaseTx) and Gigabit Ethernet (1000BaseT) cables are wired the same way but there are more Twists/inch for the gigabit cable to help prevent crosstalk at the higher speed.
The testing specification for each is different as well.

The important thing is to wire all conductors to each respective pin as shown in the diagrams. Try to keep the wires from un-twisting as much as possible, otherwise crosstalk
will be a problem (will cause CRC errors).

Hope this helps..

eT

So, far research has indicated that Gigabit Ethernet should contain Two independent auto negotiation links (MDIX) and auto MDIX is required. If auto MDIX is not used, a switch MUST contain one port that provides a manual switch to swap all of the wires.

In theory, the other 2 pairs do not HAVE to be crossed. POE is polarity independent.

Only if the switch has the (manual cross) switch, I would think that you have to cross all of the conductors.

So, what actually happened.

I had a commercial cable that needed an end replaced.
I failed to note that it had "Crossover" written on it.
I used the EZ-RJ45 system which I like and had the blue pair that was miswird
I did it again and got the same thing. Concluded that the blue pair was swapped bt he manufacturer on the side I wasn't replacing.

I wired it, unknowingly, like the diagram that swaps the pairs used for 10/100 base T, but didn;t swap the 1000 baseT wires. While I was at it, I swapped the blue pair.

I have three testers I can use for cables

1. Will show basic wiring faults. It cannot distingush between a crossover or regular cable. I like it because I can flex a patch cable and find intermittant connecions. You can cut each individual path and make the connections manually to either side. It just uses bi-color LED's. I haven't found this tester anymore. I made a remote unit for it. It kinda needs better labeling.

2. the second tester can figure out the pair connections.

3. the third tester can figure out the pairs and is a TDR as well.

So, just picking at random a crossover cable page, I find that it isn't quite as simple. The cable will stay as it is, but I'll probably label it.
It is labeled crossover. so I might add (X 1,2,3,6) and (S 4,5, 7, 8)

I'm jsut starting to get into doing the house wiring (CAT 6) as close to right as possible and have already learned some things.

1. Check BOTH sides of the wall. (I put a hole in an air return wall space and too close to an electical box on the opposite side of the wall)
2. Inspect for AC cables. (Fortunately, I did that)
3. There is a block with angled rather than parallel terminations called Krone and it looks like a 110 block and it requires a different tool.
4. Not all of the Leviton Quickports are considered equal. Some you cannot use next to each other.
5. CAT6 is useful for Media Servers, RAID arrays etc.
6. Plans include a few wired ports.

The biggest issue wit Network relaibility was the "wall wart" power supplies. They are now plugged into a high grade Octopus power squid and lay on shelf instaed of handing upside down on on a wall. the Network stuff is also on a UPS. My DSL modem is running off of POE now. Eventual plans are to put a UPS on a repeater.

Needless to say, I'm mildly annoyed.

I've basically mounted the patch panels for phone and Ethernet, but nothing is connected. Wires are still strung haphazardly in the basement.

We use a lot of video switch's in our classrooms. We chose AMX and used a cable made by Kramer CAT6a, it is plenum rated and also shielded "on all pairs" including "around all pairs" it's a very thick cable, more so than a standard plenum CAT6a.

It uses a special connector, a normal RJ45 or a standard CAT6 plenum will not allow the cable to fully insert into the connector block, it's just to big.

The connector provided by Kramer is a really good concept but, it will test your skills and aggravate you in the beginning. But, the noise and cost of the rooms we build is worth the extra cost of insuring all packets get delivered.

We are passing 1080p and 720p through our systems with little degradation or signal loss. We have "TX boxes and RX boxes" over CAT6a to and from devices, Switcher, Computers, Cameras etc.

It's all I've been doing over the last month. We Certified the room finally yesterday, and we are ready for class on Monday. I celebrated last night, Thankfully it all worked, it's all in the planning.

Don't be to frustrated just take your time and build each one equally and your system will be robust and hearty.

Good luck, kiss

kv

So, far research has indicated that Gigabit Ethernet should contain Two independent auto negotiation links (MDIX) and auto MDIX is required. If auto MDIX is not used, a switch MUST contain one port that provides a manual switch to swap all of the wires.

Click to expand...

Just to be clear, If the device port supports Auto-MDIX or manual MDIX (where a selector switch is provided on the device to toggle the pin connections), then you can use a straight through cable.

Otherwise, a crossover cable must be used.
This is the same for Gigabit Ethernet or Fast Ethernet.

In theory, the other 2 pairs do not HAVE to be crossed. POE is polarity independent.

Click to expand...

Not sure what you mean by "the other 2 pairs", but for Gigabit Ethernet, the additional pairs are used for flow control. Gigabit Ethernet is actually 500MB full duplex Ethernet with flow control. So all eight wires are connected.

Only if the switch has the (manual cross) switch, I would think that you have to cross all of the conductors.

Click to expand...

If the device port has a manual MDIX switch, then you don't need a crossover cable.