Earlier quoted context omitted.
Just as a historical note, classic Mac OS (versions 7-9) used STREAMS for TCP, in the Open Transport networking API. Sockets were provided as a wrapper around STREAMS, which worked about as well as you might expect. It had its fans but most of us were pleased to get real sockets in Mac OS X.
I wasn't aware classic MacOS worked that way. The "sockets-emulated-over-STREAMS" was the standard way of doing things in SVR4-based UNIXes. In the early-to-mid 90s this gave them a poor reputation among early web admins since they just didn't handle high rates of connections as well as BSD or even the early linux stacks. In the case of Solaris, this was largely fixed in the 2.6 release where they went back to a sock…
In the age of System 6 and early System 7, before Open Transport, there was MacTCP, an add-on TCP stack, originally sold by Apple for $2500.