Receiver on the NIC

[Robert M]

Does a receiver on a 10 BaseT Ethernet network interface card see its own transmitted signal on pins 3 and 6 of the twisted pair when connected to a hub?

[dougj]

Given the nature of hub-based communications, I would have to give a definate "maybe". The NIC would generate the required transmit voltage on pins 1 & 2, the hub would receive that voltage and pass it to the receive pins (3 & 6) on all ports, which presumably would include the sender's port. In other words, I might logically expect to find voltage on pins 3&6 of the sending port after a transmit on 1&2. However, hubs do not support full duplex, meaning they cannot both send and receive at the same time, so it may be that the act of sending on a specfic port disables it's ability to also receive, thereby eliminating the "hear your own transmission" scenario you describe.

[Robert M]

A "definate" maybe or a definite maybe?
Hubs make transmitted signals available to other ports.
They can accept transmitted signals at the same time they make them available to other ports.
Incoming transmitted signals entering a hub are immediately available on the receive pairs. The signal can also be seen at the receive pair of the transmitting station also I think....although it may be ignored...not sure.
Anyone else?

[Tuttle]

I can't find a good online reference, but the short answer is that the hub doesn't replay the signal back on the same port -- the transmitting interface does that itself.

In a half-duplex environment, the transmitting device maintains an internal loopback connection so anything it sends on pins 1/2 is immediately received on pins 3/6 as well. If it receives anything from the rest of the network while it's transmitting, it can detect the collision.

If you can lay hands on a copy of the Cisco Press CCNA INTRO Exam Certification Guide (Wendell Odom), pages 59-63 have a decent explanation and pictures.

[Robert M]

Well, if anyone has a hub and an ohm meter available they could check.
They can check for zero or close to zero ohms resistance between pins 1 and 3 and pins 2 and 6 at the hub port. If zero ohms resistance was observed, then the network card's receiver would "see" its own transmitted signal.

Collisions only occur if two transmitters try to transmit at the same time...not when both have data to send. Otherwise, Ethernet stations wait for absence of signals before they attempt to transmit.

[Robert M]

Bump,
Wow, all the gurus here and nobody has a simple hub and an ohm meter?

[meldan24]

Nobody wants to talk to someone whose thanks for help offered is having their grammar corrected. Also, if you know all the answers already why are you asking questions?

[Robert M]

Well, I guess you don't have a simple hub and an ohm meter....

You can speak for yourself, but I wouldn't presume to know what everyone else on the forum is all about.

If I knew the answer, I wouldn't have asked it.

[meldan24]

Wow, all the gurus here and nobody has a simple hub and an ohm meter?

Well, you asked this in a real snide manner. If it's so simple and should be so common why don't you have one? All I'm saying is lighten up on people. When it comes to being insulted by your remarks, I doubt if anyone enjoys it so I will presume.

No, I don't have a hub and ohm meter.

[Robert M]

It's you who needs to lighten up.

[Train]

Enough.