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Is it possible for a PC, if connected directly to a consumer router--but the ethernet wire has two mismatched wires (i.e.: End 1 sequences 1-2-3-4-5-6-7-8, but End 2 sequences 2-1-3-4-5-6-7-8)--to still 'see' the Internet? But badly?

If you have a simple PC→Consumer (Verizon) Modem connection with this mis-wired cable can a person still get access to the internet simply because the consumer modem/router isn’t utilizing all 8 wires?

I know someone who connects this PC to his modem and it works, but all he does is connect to the internet. If I plug this cable into my office network (Sonicwall Firewall connected to three subswitches with two Subnets running) the connection is dead.

I keep telling him the network wire is mis-sequenced (I have an ethernet wire tester: it showed me the mis-wired sequence plain as day). But he yanks out a telephone TONE generator and says the wire is OK.

random
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Rabhadur
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3 Answers3

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There are two common ways you can cause partial failures.

One is you break the electrical connections required for gigabit Ethernet (which needs all 8 connections) but leave the ones required for fast Ethernet (which only needs 4).

The other is if you mismatch the pairs, even if all 8 wires go through correctly. The matching of differential signal pairs to physical twisted wire pairs is needed for proper noise rejection. If the mapping is incorrect, performance can suffer due to data errors, particularly in electrically noisy environments.

David Schwartz
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Is it possible for a PC, if connected directly to a consumer router– but the ethernet wire has two Mismatched wires (ie: End 1 sequences 1-2-3-4-5-6-7-8, but End 2 sequences 2-1-3-4-5-6-7-8) to still 'see' the Internet?

Possible? In this specific example the answer is yes, depending on the how the circuitry is engineered in the hardware in question. However there certainly wiring problems that will prevent a cable from working.

The feature that allows this particular wiring problem is called "polarity reversal" and allows a device to detect and adjust to reversed polarity on each pair (see O'Reilly's Ethernet: The Definitive Guide for more detail). Only one of the devices in question needs to support this feature to allow normal operation.

If this feature is present in the hardware, such a cable will work just fine.

YLearn
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Ethernet and Fast Ethernet over UTP cabling use wires 1 and 2 to transmit and wires 3 and 6 to receive.

Electrically, the signals on wires 1 and 2 are based on differential signaling. It means that the signal is the difference among the two wires instead that the classical signal in one wire and ground in the other.

Because of differential signaling if you exchange wires 1 and 2 the cable is still usable, however is out of certification norms that guarantee noise reduction and crosstalk reduction, so it's prone to electromagnetic interference, specially at high speeds.

jcbermu
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