textbook from a university course on ICT that is considered particularly good?
IMO, text book covers more on theory. Generally text book are outdated when it comes out due to relatively longer time required for preparation and publishing.
But a lot of the underlying technology is unchanged for a long time, right? So to get a deeper grasp of e.g. different protocols and data flows, I imagine it could at least be a good starting point.
The Wikipedia-article on the Internet protocol suite of course provides a lot of information on this, but my issue with learning from Wikipedia is that it provides a long article on one topic with tons of links, but often no natural flow to the next topic. This could lead to reading up on things in the wrong order, making the learning process more difficult that it has to be. A text book on the other hand, if written well, is more a curated set of texts that introduces topics in a logical order, so that a topic is not introduced until the required prerequisites have already been treated.
A YouTube-channel (or perhaps rather a YouTube-playlist) can also provide such a curated set of material, although in my experience these videos can often be a little to superficial to get any proper understanding of the subject. There are of course exceptions.