DWDM optical transport networks are at the turning point from simply providing semi-permanent connections to start being engineered for efficiently supporting dynamic optical connection services. A successful transition can only be accomplished via augmenting existing/adding new functionalities to the DWDM transport networks and has implications spanning from optical node design to network planning and network operation. This paper discusses current trends in DWDM networks with emphasis on the expected evolution in the architecture of the optical nodes for dynamic connection establishment and rerouting. In order to gain insight on the relevance of having nodes characterized as colourless, directionless and contentionless, the impact of node architecture in blocking performance of a DWDM transport network is assessed using network simulation.