Hi I am about to take my CCDP EXAM, but I am finding the material on WAN services to be a little unclear. Specifically I could some one expand on SONET/SDH, RPR, WDM flavours and Ethernet. My interpretation has WDM AS THE Fiber build standard and SONET/SDM, RPR and Ethernet as the L1 transport standard that runs over WDM, although reading the cisco press book and watching CBT Nuggets don't really clear this up. Any help would be greatly appreciated
