Uplink and MDI ports

shiraforkosh1 · ‎01-26-2016

I wanted to learn about the types of Ethernet physical ports,especially the RJ-45 ports.

I strated with serach what is Uplink port, and then I continue to serach about MDI, MDI-X and auto MDI.

I don't understand if Uplink port is type of MDI port or isn't, because the Tx and Rx are in the same order in their both.

And if it is type of MDI, so why it called differently?

I know this maybe a stupid question, but I realy want to undertasnd it, and I didn't find an answer yet.

Jon Marshall · ‎01-26-2016

An uplink port is simply a port that connects a network device to an upstream device typically used with switches.

So an access switch connected to a distribution would use uplink port(s) to connect.

If it is copper it is no different from what you have read and you used to need a crossover cable to interconnect switches but nowadays a lot of switches support auto-mdix.

This isn't usually an issue though as most uplinks use fibre for interconnections between switches.

The difference between uplink ports and the other ports on the switch is not the wiring (if using copper) but uplink ports generally support more media types (eg. fibre) and they often support higher bandwidth rates both in terms of the actual link and the connection to the switch fabric.

It is just a networking term for ports that interconnect network devices.

Jon

Peter Paluch · ‎01-26-2016

Dear friends,

To add to Jon's response, I believe that the term "uplink port" is a legacy term coined with first 10BaseT hubs that, for the sake of simplicity, had one of ports dedicated for interconnection to another hub, and this port was either hardwired to the cross-over mode or even had a tiny button nearby that allowed you to choose between straight-through and cross-over modes so that, no matter what device, you could always use a straight-through cable. Besides that, however, this "uplink port" was absolutely no different from all other ports on the hub. It wasn't even necessarily faster than other ports, as dual-speed hubs came in later.

When switches became prevalent, it was quite common to install a couple of ports (one or two) into these switches that were faster than the rest of the ports (say, 100Mbps vs. 10Mbps), with the obvious intention of providing extra bandwidth for aggregated traffic coming from the slower ports. These ports were also dubbed "uplink ports" because they were naturally suited to connect the switch along with all attached stations to another device, thanks to their bandwidth allowance. Again, however, apart from being faster, there was no technical difference between these "uplinks" and the other ports on the switch.

The presence of MDI or MDI-X depended entirely on the manufacturing choice of the vendor. Some vendors could have chosen MDI-X, some went with MDI. All reasonably recent devices implement Auto-MDIX, so this question is really no longer relevant.

Nowadays, with the obvious need for more and more bandwidth, it is quite common to see dedicated uplink ports using a different kind of medium than the normal ports on the switch, usually going for fiber, and providing speeds 10 or 40 times higher than the normal ports.

Once again, however, an uplink port is really just an intended role of the port, not its technical nature.

My $0.02...

Best regards,
Peter