Most textbooks no longer cover Telnet (undoubtedly because they deem remote terminal support a thing of the past). This is precisely what is wrong with today’s networking textbooks. The reason for covering Telnet is not because it provides remote terminal support, but because it teaches lessons in understanding networking problems.
Telnet takes a problem that everyone else saw as asymmetrical (terminal-host) and found an elegant symmetrical solution. That solution made Telnet much more useful than mere terminal support. Telnet also finds an elegant solution to a classic “oil and water” problem (the handling of half/full duplex) that makes both degenerate cases of a more general solution.
We consider Telnet because these concepts are important in the education of network designers (the goal of a university education), even though they might not be for the training of network technicians.
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DAY, John D., 2008. Patterns in network architecture: a return to fundamentals. Upper Saddle River, N.J: Pearson Education. ISBN 978-0-13-225242-3, p. 101.