100BASE-TX signal received by 10BASE-TX port

100BASE-TX signal received by 10BASE-TX port
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Subject Author Date
100BASE-TX signal received by 10BASE-TX port Jay Kim 11-29-2005
Posted by Jay Kim on November 29, 2005, 7:27 pm
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Hi, I have an interesting question for you all.

When two 10/100 Ethernet devices are configured statically, but
differently configured,
say, one device port is configured to 10M, while the other device port
is configured to
100M. And the two wronfully configured ports are connected with a
copper cable.

In this situation, the 10M device port looks working ok, while the 100M
device port looks
'link down'. My question is why the 10M device port looks working ok
(link-up).

The 10M device company claims the following statement;
---
If a speed mismatch were configured and an attempt at communication was
made, the 100BASE-TX data received by the 10BASE-T device could look
like real data and cause
the 10BASE-T device link to activate, causing errored data to be
received.
---

I wonder whether the above statement is correct or not. If correct, I'd
like to have
any document or comment explaining the behavior at 10M side. Thanks.

- jay


Posted by Jay Kim on November 30, 2005, 1:22 am
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I found the following information in IEEE 802.3 by myself. Just FYI.

---

1.4.116 Fast Link Pulse (FLP) Burst: A group of no more than 33 and not
less than 17 10BASE-T compatible link integrity test pulses. Each FLP
Burst encodes 16 bits of data using an alternating clock and data pulse
sequence. (See Figure 14-14, IEEE 802.3 Clause 14 and Figure 28-4,
IEEE 802.3 Clause 28)

1.4.117 Fast Link Pulse (FLP) Burst Sequence: The sequence of FLP
Bursts transmitted by the local station. This term is intended to
differentiate the spacing between FLP Bursts from the individual pulse
spacings within an FLP Burst. (See IEEE 802.3 Clause 28)

1.4.185 Normal Link Pulse (NLP): An out-of-band communications
mechanism used in 10BASE-T to indicate link status. (See IEEE 802.3
Figure 14-12.)

1.4.186 Normal Link Pulse (NLP) Receive Link Integrity Test function: A
test function associated with Auto-Negotiation that allows backward
compatibility with the 10BASE-T Link Integrity Test function of IEEE
802.3 Figure 14-6. (See IEEE 802.3 Clause 28)

- jay


Posted by glen herrmannsfeldt on November 30, 2005, 3:59 am
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Jay Kim wrote:

> When two 10/100 Ethernet devices are configured statically, but
> differently configured,
> say, one device port is configured to 10M, while the other device port
> is configured to
> 100M. And the two wronfully configured ports are connected with a
> copper cable.

> In this situation, the 10M device port looks working ok, while the 100M
> device port looks
> 'link down'. My question is why the 10M device port looks working ok
> (link-up).

A 10baseT device signals link up when it sees link pulses. While there
are specific timing specs for link pulses, the detector may accept a
wider range than the specification. If the 100baseT signal looks enough
like link pulses, it might believe it. This would be more likely for
devices designed before 100baseTX.

-- glen


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other useful resources:
The Federal Communications Commission (FCC)
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Electronic and Software Security Products and Services
International Telecommunication Union

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