Does the transposition cipher have a network application? So I'm reading a chapter in my networking book, and it talks about substitution and transposition ciphers. I know that most network security uses public key or symmetric encryption, but I wonder whether a simple transposition is also used. I ask because I'm not sure how they would quickly decode the message on the other side. It would seem they would need to use something like the DH Key Exchange, and even then, they could just use the traditional symmetric encryption at that point anyway. 

If “transposition” and “substitution” do have applications, what are they and how secure are they?
Transposition and substitution are heavily used in today's block ciphers. S-box means substitution box, and P-boxes transpose bits.

When you say transposition cipher you are referring to classical cryptography.  The heyday of the transposition cipher was before the end of World War I. The ADFGX and the ADFGVX were fractionated transposition ciphers used by the Germans (and broken by the French).  Double fractionation is stronger, especially when at least one iteration is disrupted (VIC cipher). But all of this belongs to the last century because it is now trivial to break classical transposition ciphers. 

But transposition itself has not gone away, and modern methods are much better than those of 1918.