A Tutorial of 802.11 Implementation in ns-2 -Ns-2 [1] is a packet-level simulator and essentially a centricdiscrete event scheduler to schedule

the events such as packet and timer expiration. Centric event scheduler cannot accurately emulate

“events handled at the same time” in real world, that is, events are handled one by one. However,

this is not a serious problem in most network simulations, because the events here are often

transitory. Beyond the event scheduler, ns-2 implements a variety of network components and

protocols. Notably, the wireless extension, derived from CMU Monarch Project [2], has 2

assumptions simplifying the physical world:

(1) Nodes do not move significantly over the length of time they transmit or receive a packet.

This assumption holds only for mobile nodes of high-rate and low-speed. Consider a node with the

sending rate of 10Kbps and moving speed of 10m/s, during its receiving a packet of 1500B, the

node moves 12m. Thus, the surrounding can change significantly and cause reception