There has been recent changes made to structure of Node../ns-2/node.h in . This revised node architecture would allow more flexible and modularised construction of different node definitions like a MobileNode capable of wireless communication or a HierNode that supports hierarchical routing or just a simple Node or a completely new node type. In this chapter we will introduce the new node APIs, discuss the differences between the old and new OTcl interfaces and compare the advantages of this new structure over the old one. The functions and procedures relevant to the new node APIs may be found in /tcl/lib/ns-lib.tcl.