Ethernet Cable ??? 3

[Frank4d]

I have a test setup at work that has a PC with 10/100/1000 ethernet connected to a Gigabit switch, and a unit under test (UUT) with 10/100/1000 ethernet connected to the same switch. The PC and UUT are both supposed to auto-negotiate speed.

If the cable between the UUT and switch has eight wires, the PC and UUT can communicate at 100 or 1000 Mbps.

If the If the cable between the UUT and switch has four wires, the UUT complains "no link detected" and the PC and UUT cannot communicate.

My guess is that the UUT is not auto-negotiating speed as it should. It doesn't find a gigabit link and gives up. (The four wire cable has been verified good at 100 Mbps).

The switch is Netgear GS105 and the UUT is a DY4 Systems DMV-182 running vxWorks.

Note: The other DMV-182 ethernet port is connected to another 10/100 switch with four wires and is working.

 

[LawnBoy]

I have never heard of 4 wire ethernet cable. 2 wire (coax) or 8 wire (utp).

What is this 4 wire stuff?

 

[technome]

Frank4D
One hundred full duplex uses 4 wires of a 4 pair cable,Gigabit uses all 8 wires

........................................
Chernobyl disaster..a must see pictorial

http://www.kiddofspeed.com/default.htm

 

[Frank4d]

One hundred full duplex uses 4 wires of a 4 pair cable

.

Correct. So a 10/100/1000 device that is capable of auto-negotiating the connection should work with four wires at 100 Mbps.

Anyway, problem solved, the unit under test ethernet port was bad. The replacement unit works properly.

 

[Frank4d]

I have never heard of 4 wire ethernet cable. 2 wire (coax) or 8 wire (utp).

What is this 4 wire stuff?

It is commonly used in aircraft avionics wiring when the requirements specification drawing calls for 100 Mbps. Weight is a big deal in an aircraft environment, so 4 wires weighs 1/2 as much as 8 wires. I/O pins are also a precious commodity.

 

[edfair]

I've also seen them in low price bins at computer stores. They can be built cheaper, therefore sold cheaper.
You would never notice it in normal cat5 operations.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[LawnBoy]

Thanks for the education!

 

[jdeisenm]

10/100 ethernet uses wires 1,2,3 and 6. When looking at the rj45 end, it's the side opposite the tab. On a straight through (normal) cable, if you put the 2 ends of an rj 45 cable next to each other, you'll see the wire colors match