This chapter describes the wireless model that was originally ported as CMU's Monarch group's mobility extension to ns. This chapter consists of two sections and several subsections. The first section covers the original mobility model ported from CMU/Monarch group. In this section, we cover the internals of a mobilenode, routing mechanisms and network components that are used to construct the network stack for a mobilenode. The components that are covered briefly are Channel, Network-interface, Radio propagation model, MAC protocols, Interface Queue, Link layer and Address resolution protocol model (ARP). CMU trace support and Generation of node movement and traffic scenario files are also covered in this section. The original CMU model allows simulation of pure wireless LANs or multihop ad-hoc networks. Further extensions were made to this model to allow combined simulation of wired and wireless networks. MobileIP was also extended to the wireless model. These are discussed in the second section of this chapter.