Keywords. Vertical handoff, Heterogeneous wireless mobile networks, new call blocking probability 1. Introduction. As we are moving towards expeditious development and rapid evolution in wireless networks, we faced different type of challenges i-e combining a diverse number of networks. The fourth generation (4G) of mobile communication networks is expected to integrate a possibly huge amount of heterogeneous wireless network in that could be investigated towards the universal seamless access. there will be many challenges in the process of seamless mobility one of the main is efficient vertical scheme availability, that is decision for a mobile point (i.e. mobile cell phone, tab-pc, Laptop) to handover among the various types of networks i.e, cellular, wireless area network (WAN, wide local area network (WLAN) [1]. As we look back to the traditional cellular approach to the communication which also mention with name GSM, the predefine threshold which compare different parameters in specific order is basically used to handle handover decisions [2] the handover are not only cause of ongoing call connections but it can be helpful in order to provide best services package and to fulfill their requirements for stable communication with the comparison to horizontal handover the newly presented vertical handover not only based on the received signal gain which is known as RSS but also the different services i-e class mapping among the handoff-out and handoff-out networks [3] high data rate services (HDS) and Nonpareil global roaming (NGR) eminent fourth generation 4G from the previous of wireless networks (WN) [4], [5].the 4g networking model contains, mobile nodes or handsets terminals connects by different multiple interfaces which will be able to select the best suitable link for access among the all available alternatives. Those ace links consist of IEEE 802.11 access of wireless local area network (WAN) [6]. When we talking about the idea behind connectivity in best way through various networks, a good QoS and also decrease in the call dropping level after unnecessary and wrong handover a phone call in process might be drop or interrupted. The wrong decision of handover cause by unnecessary handover directly affects the QoS makes interruption with ongoing transmission. The more important is the process of handover accurately and seamlessly executes to enhance the QoS. The application of multimedia i-e video streaming, web browsing depend upon good QoS the mandatory is to identify the