Cognitive Radio Ad-Hoc Network (CRAHN) is an emerging class of mobile ad hoc networks that provides each network node with a list of available channels. It is expected that the traditional routing approach will not work well in CRAHN, by which its performance may be determined by user and channel interferences, as well as by frequent topology changes. The result is varying connectivity conditions being experienced by the mobile nodes. Therefore, to achieve a realistic cognitive routing in CRAHN, the routing protocol and its routing metrics shall be chosen to adapt to propagation and channel conditions. Typically, the aim of any routing protocol is to provide QoS that could be measured by some performance parameters such as average delay and packet delivery ratio. The focus of this work is to justify the effect of user and channel interferences on QoS routing function in CRAHN. Hence, if this justification can be explained, the routing operating conditions can be controlled and the achievement for QoS routing can be more objectively obtained. © 2012 IEEE.