Teardown of two dual-port Ethernet Adapters

StarTech US1GC301AU2R and Tripp-Lite U336-022-GB

Last Update: May 15th, 2022

Introduction

Two adapters, both alike in dignity,
In fair Silicon Valley, where we lay our scene.

Nevermind. Sounded funnier in my head.

I found myself in a position where I was designing a consumer device that needed multiple Ethernet ports, of which one needed to be USB.

My general policy when doing something I've never done before is to see how others did it.

In this case, I ordered two devices that provided two Ethernet ports via 8P8C Modular connectors, plus a USB connection. I was secretly hoping for some magic chip that integrated a switch, USB-Ethernet adapter, MACs, and PHYs all into one part - two-port adapters were common and cheap enough that there was hope of this.

Spoiler alert: sadly no magic chip, but I did discover that adapters are not made equal. It's actually really interesting to see how two companies solved the same problem. Read on to find out more.

StarTech US1GC301AU2R

I generally consider StarTech to be a 'good' company - they make all sorts of interesting adapters, their products are of good and consistent quality, their products are widely available, and the prices are reasonable. They're not exactly Keysight or Fluke, but if you need a box of odd USB cables, there are a lot worse companies to buy from. If I need some adapter and their name pops up, it's usually an immediate buy.

Let's pop it open! Screws under the rubber feet, as typical.

Interesting to note that this adapter comes in two variants: one with a USB 3 Type A cable, and one with a USB Type C cable (as shown).

They went with actual connectors for the cable swap, which is a pleasant surprise - usually for something of this price point they just solder wires to pads on the PCB.

Note the white sticker - presumably to prevent shorts on the board from the cable shield.

Other side. Not much going on here. Gold plated, good silkscreen, RoHS, don't recognize the fab house logo. Board text: PU4V811-3G2B

Not all the modular connectors have full solder wicking, probably manual process.

Heart of the operation - it's a USB hub! A VLI VL811-Q8P, specifically - four ports, USB 3, nothing to write home about, really.

It's listed as EOL by the way.

The Ethernet jacks are controlled by ASIX AX88179 Gigibit MAC/PHY chips, total of two on the board.

Bottom line: there is no Ethernet switch in this device!
It adds two USB ports to your computer, but any switching or routing operation will need to be done in software - can't be done on consumer Windows installs AFAIK, and not something I would call trivial even for the daily driver Linux user.

To be fair, it wasn't really designed to be used as a stand-alone switch anyway, but it's a small "gotcha" if you don't look carefully.

Tripp-Lite U336-002-GB

Is that my MAC address? Meh, probably not.

Tripp-Lite? Don't they make UPSs?

Yessir, but also odd adapters, apparently!
I consider this product outside of Tripp-Lites "comfort zone" as it were, which means the design could be unusual and may show techniques and priorities from their core business.
Kind of like Saab making cars as well as fighter aircraft.

Not much going on here. I bet that's an EEPROM but I didn't look too closely.
Let's flip it over.

Right off the bat, GIANT power filter caps - always a good sign, and right on brand, now that I think about it.
Unpopulated status LED spots, might be interesting to fill those in and see what happens. Note the SMD crystals vs the through-hole cans on the StarTech parts. The wires in the cable are soldered to pads, not connectorized.
But most importantly...

It's a switch! A Realtek RTL8367N five port switch, in fact. The traces to the magnetics gave it away, as soon as I opened the case.
One of the very few Ethernet switch chips still available in this blasted semiconductor shortage apocalypse we find ourselves in.

My initial instincts said that using only three ports on a five port switch was a waste, but it almost certainly would drive up the price to roll custom silicon and stock parts for the exact number of ports you need. A more cost effective solution would be to use the same lithography mask and some rubylith tape to disable blocks of logic, or just use a smaller package and not wire bond other ports to external pins.

Makes a lot more sense to make a chip with the number of ports most commonly used, and people can ignore the pins they don't want.

And, somewhat surprisingly, exactly the same Ethernet MAC/PHY as the StarTech part! An ASIX AX88179 - another part that seems to be fairly widely available still.

All done? Not quite. Check this out:

A microB USB connector? A device port? Why two USB cables?

If you look closely at the board image at the top, you'll note two 0 ohm resistor and no connections to the data pins.

That's right! It's a power connector! You can plug this into a computer or (presumably) a battery bank of your choice.
It's an unusual decision: I'm not sure why the same couldn't be accomplished by using the built-in USB cable, and a two port stand-alone Ethernet switch is only useful for boosting cable length.

Actually, now that I think about it, I wonder if this is a power fail-over connection, because - again - that would be right on brand.
Think about it: you have a couple devices talking over this thing, and you want them to keep talking to each other even when the computer is off. So they put this in, and when the computer turns off and the USB bus power is switched off, the power adapter attached here keeps it powered on.

Note that this is completely conjecture on my part - I haven't actually probed the power bus on the board, or tested it, but I can't think of any other reason why a company would spend money on connectors and board space for this. It's a neat gadget, but at thirty bucks you can also buy a stand-alone Ethernet switch, and those come with their own power adapters and probably more ports.
Like I said: unusual!