The difference between high-speed communication interface and protocol

I am confused by these two issues: interface and protocol, for a while. I try to understand their difference and want to discuss them here.

Based on my understanding, interface determines hardware level issues, like port, cable, connector type. On the contrast, protocol defines software level issues, like encoding scheme, channel bonding, data characteristics.

This looks like: if two people want to communicate, they need decide how to talk. They can talk face to face, through phone, through online chat. These are like interface. But they also need to decide which language, English, Chinese, Germany……

I don't know whether my understand is right. Hope anyone who is familar with this can help me understand.

Another question confused me does all protocol has specific interface? My understanding is no. E.g, when we talk such as PCIe, SATA, Ethernet, we can easily know what the port and cable looks like. However, when I think InfiniBand, Interlaken, I don;t know what their ports, and cables look like. So whether they have their specific port and cable? what does the port and cables for these protocol look like?

Thanks in advance.