I know session keys are exchanged (in SSL e.g.) over public-key cryptography channels but I was wondering if there are already known algorithms/methods for exchanging session keys over a symmetric-key channel? More specifically, is it possible/feasible to e.g. exchange 128-bit AES keys over a channel already using 128-bit AES keys?
If so, where can I read about them? IF not, why not? Is it not a good idea or can't be secured?
Possibly related: Deriving Keys for Symmetric Encryption and Authentication