*3.9.2. CH stability*

The time during which a node is in the state of a CH determines stability. It is the mean time duration of the nodes, remaining its leadership role as CHs. Long CH lifetime implies, few changes and good stability. The information is disseminated by groups enhancing the communication delay, reliability, low data delivery and congestion issues, making the vehicular networks accurate and efficient. CH stability can be affected by different factors such as merging, distance between CHs, exit from the road etc. In VANETs, merging collisions can happen among vehicles moving in the same direction due to acceleration or deceleration, it is more likely to occur among vehicles moving in opposite directions (approaching each other) or between a vehicle and a stationary RSU since they approach each other with a much higher relative velocity as compared to vehicles moving in the same direction. The high mobility of the shifting nodes within the networks causes lots of challenges to face and affects stability.

If vehicles are changing their state very often in intersection scenarios and stay only for short times in the CH state, CH stability is low. In some of intersection based approaches the first vehicle to enter the intersection region in a particular direction is elected as CH to improve stability. Furthermore, some cluster-based routing algorithms, the selection of CH are based on willingness factor which defines the relative stability of a node. CH stability is also based on the threshold distance between the two CHs. Optimal distance between two CHs should be obtained.
