I'll make it more clear.

a network card is unique in the whole world by it's mac address.
the mac is unique in the world, unless it's cloned.

what's similar to mac in usb that makes it unique?

Hello,

I don't think there is any unique identifier for USB ports, there isn't a need for it. MAC addresses are used for effective communication. USB ports are usually for transfer of data in some way; the source and destination address is obvious, there is no need for the USB port to be unique.

There is no need for the USB port to be unique, the same way a parallel or serial port has no unique identifier.
A device attached to USB port, however, such as webcam, may have its serial number available for access, or a WIFI dongle have its MAC address, etc available.

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