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Crossover Adapter
visser Aug-14-01 07:36 PM

I have experience making straight-thru cables and cross-over cables. What I want to make is a cross-over adapter using a male connector, a female connector, and a 4 inch piece of cable. An example of what I want to make can be seen at:
Basically, I need to know if:
Male ---> Female
T568B ---> T568A or
T568A ---> T568B or
T568A ---> T568A or
T568B ---> T568B

The reason that I want to make one of these is because I am running a length of network cable through my house which will eventually be connected to a router/switch, but currently is not because I don't own one yet. For now, I want to test the cable by using such an adapter and connecting two computers. I would just go out and buy one of these adapters, but I already have most of the hardware, so I might as well just make it. I am also curious to know the answer to this just to understand the wiring better.

Thanks for your time.

1. RE: Crossover Adapter
lbyard Aug-14-01 09:07 PM
In response to message 0
Mike, It would certainly be cheaper and less time consuming overall to wire the cable as a crossover cable until you obtain the switch and then cut the plug off the cable a rewire it as a straight-thru cable. Also, you will not have to change the cable at all if your router/switch has an uplink port. If you want to fabricate the adapter anyway, it makes absolutely no difference whatsoever which of the two color codes you use. “The electrons couldn’t care less.” They do however care that each set of transmitter pins be connected to the corresponding receiver pins by wires in the same pair (see the right diagram in the FAQ below).

Wire your jack for 568A following the color code on the jack. Wire your plug for 568B. Or do it the other way around. Again, it makes not difference which way you do it and it makes no difference which of the two color codes you use for the straight-thru cable. The color codes will not change the colorless diagram in the FAQ. All your straight-thru cable does is extend the length of the adapter. Be sure you do not untwist your wires more than ˝”, and make sure you use CAT 5 or 5e jacks and plugs, that wire is solid core, and that your plugs are designed for solid core wire. The jacks are designed for use only with solid core wire. They are expensive; plugs are cheap. Larry

Q. What is an uplink port and what are the ways to connect two hubs/switches together?

A. There is no big mystery about the difference between an uplink and a regular port. Each Ethernet interface has two transmit pins + and - and two receive pins (the other pins may have wires running between them, but they are not used). The transmit pins at one end of a cable have to be connected to the receive pins at the other end and vice versa. An uplink port does not crossover the transmit and receive pins and a regular port does.

If two hubs/switches (What is the difference between a hub and switch?) are connected together with a straight-thru cable then one end must crossover (regular port) and one end must not (uplink port). If a crossover cable is used to connect them, then the ports at both ends must be the same kind of port. If a straight-thru cable is used to connect them, then the ports must be different. A PC can be connected to an uplink port with a crossover cable and to a regular port with a straight-thru cable. Also, be aware that many hubs/switches share the uplink port with one of the regular ports, usually port 1. Both ports will not work if they are both connected at the same time. Finally, many hubs and switches have a switch associated with the uplink port that can switch the port between uplink and regular port configurations.

2. RE: Crossover Adapter
visser Aug-15-01 03:32 PM
In response to message 1
Thanks Larry,

I was actually thinking that was the answer before you responded. I have built the adapter and it works great. I also built a crossover cable to compare the adapter to - and ironically enough I screwed up the crossover cable - somehow the end wiring wasen't good (i.e bad connection or wrong order).

Anyways... thanks again for your help and a speedy reply.


3. RE: Crossover Adapter
lbyard Aug-15-01 03:51 PM
In response to message 2
I do that on occassion (and one of the reasons I know custom cables are the first place to look when there is a network problem--and know that cables made for customers have to be tested before they go out the door) and have to cut-off a plug, sometimes both, and start over. Larry

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