Should there be connection problems that do not occur with a direct connection
of similar length, then we shall check the PCB for craze interruptions, "cold solders", especially around the RJ-terminals. And, believe it or not, dirty LAN sockets and plugs
may actually cause network problems, too.
After the LAN-Priority-Switch has proven to be reliable for us, it is recommended to conserve the PCB's bottom side by means of some protective coating. Make sure not to spill over the RJ45 contacts.
- This LAN-Prioriy-Switch forwards the RX and TX line pairs (1+2 and 3+6), which are being used in 10/100BASE-T Ethernet. The concept is not suitable for a Gigabit LAN (1000BASE-T), that would require two further pairs (4 + 5, 7 + 8) to be switched with more sophisticated components, as the signal requirements are higher. (BTW, if we really had one single Gigabit-LAN socket, a so-called LAN-Splitter, which is a completely passive device, may be an option.)
Unused wires are left open, i.e. unterminated by the LAN-Priority-Switch. PoE or other added-use will not pass.
Real network switches are meant to dispatch network traffic in an simultaneous fashion onto multiple network participants and likely feature firewall-related functionality as well. Setup and administrating these mighty devices requires plenty of knowledge and time and is only worthwhile if we actually want to operate a local network of mid to large dimensions. In a home scenario with only two or few more computers, an unmaintained switch rather introduces further operational risk and potential attack vectors. On the other hand, mechanical or electromechanical switching solutions may be less comfortable, yet having none of these vulnerabilities.
Relays: Data sheets promise at least 1 million switching cycles under modest load for this type of relay. In fact, we got nearly ideal conditions in this application: ethernet signal's voltage shift amount to +/-2.5 V), impedance of the Ethernet transformers is low, providing enough wetting current, and high frequency components up to some tens of MHz will gently fond their gold plated contacts to last forever...
- Power consumption: The "high-sensitive" variant of the Takamisawa relay has DC-impedance of about 165 Ohms each, 82.5 Ohms in parallel, so we can account up to 60 mA at 5 Volts (= 0,3 Watts). Any USB port may deliver the current without any problems. Running the LAN-Priority-Switch from the Master PC about 8 hours per day and every day, will sum up to an annual energy consumption of less than 1 kWh. Still affordable...
Instead of the 5-V-relays, the 6-V-versions would save some further milliamps. Their operating voltage should be sufficient in many cases. On the other hand, if we feel that those "5 Volts" in our Master machine is already at the bottom of the tolerance range, we should safely prefer the 5-V breed.
These modular connectors...
a sunday weather system! In reality, there is always a good chance that this little fixation clip will break, so we sooner or later have to replace the cable or crimp a new plug. What a waste of material and what a great deal for the manufacturers of cheap twisted telephone wire in colorful PVC hoses!
Experience: Clean contacts of RJ connectors with a fine brush (e.g. toothbrush) along the guide grooves of loose dust and dirt. (There are, who wonders, Youtube tutorials available on this topic...) In case of sticky debris, use water-free degreasant (isopropanol, acetone) for cleaning purposes. Contacts in a RJ socket may be cleaned carefully with a cotton swab soaked in alcohol. Do not apply excessive force and observe that the contacts remain in parallel order. Please make sure that all solvent has evaporated before re-connecting electricity!
And these RJ-connectors are incredibly susceptible to dust and dirt! Outside of server rooms, the air may contain lots of dust and dirt, just to mention. Appears, that all grease and dust from a normal room atmosphere will preferably deposit on these RJ-connectors!
In the modular socket, spring-contacts of basically round diameter are meant to contact with their flat-shaped counterparts in the modular-plug. So, the area of electrical contact is comparably small and friction forces that could wipe off debris when pluggin' in and out, aren't very effective, too. These connectors MUST get worse with the time. Even worse, these contact springs in the modular sockets, seem to wear with time, or just the moment they're exposed to solder heat...
- USB power-off: Some external USB Hubs have power-down features that can be activated by software drivers or software tools. These will actually switch off the USB supply voltage on the USB terminals, rather than just sending sleep command to the connected device. An attached LAN-Priority-Switch could also be de-energized by this feature, enabling the Master to deliberately switch himself "offline" from the desktop and grant LAN access to the Subordinate.
Unfortunately, this does not usually apply to internal USB
controllers that are installed directly on mainboards. More likely the USB power is hardwired to the system's 5-V-rail, only switching off when the whole device was switched off resp. going deep standby.
- USB voltage persistent? If your PC mainboard continuously delivers USB voltage even after system shutdown, you may have some of these weird configurations that will keep USB provided with standby voltage, which is - superficially - intended for "charging batteries" of USB-appliances like mobile phones etc. Yet another doubtable feature, giving rise to the danger of fire and/or data leaks (NSA papers give indication that USB-communication modules may be integrated into UEFI framework, capable of doing hidden communication with any external device, that is still powered up, even if the system was supposed to be "shut down".)
Hint: In some cases, the USB port's standby behavior may be changed by jumper on the motherboard or by a BIOS/UEFI setup - please consult the manual!
- Master voltage from PS/2: PS/2 ports could be used to provide switching voltage to the LAN-Priority-Switch. The respective pins are 3+4 on the PS/2 Mini-DIN socket. Don't feel pleased too quickly. In many cases, the voltage at PS/2 ports does not disappear after computer has shutdown. This may be due to the important feature of "wake-up" by keyboard or mouse, which needs some electrical power for these peripherals to be able to send any signal to the mainboard. You may easily check what's the case: Plug an optical mouse to PS/2 and observe the mouse's LED after system shutdown. When it keeps on lighting, we got permanent PS/2 power and therefore PS/2 is unfortunately no option for the LAN-Priority-Switch. There is a chance that something may be changed via BIOS settings. Look for options like "wake on Keyboard", deactivate them and see what will happen after the next bootup-and-shutdown cycle.