Next Generation (4G) network can be achieved through the interworking of several existing architecture to form a seamless global network. The need for a high speed (mobility) support, ubiquitous network is an emerging trend in the wireless domain. In this paper, the focus is on the interworking between Universal Mobile Telecommunication System (UMTS) and outdoor WLAN 802.11g, respectively. Many mobility management protocols are used to support vertical handover between UMTS and WLAN. Each protocol works as a standalone protocol but resides in a separate layer. The Real Time (RT) and Non Real Time (NRT) applications can be influenced by different parameters during the handover. The effect of using different mobility protocols on the performance of RT and NRT applications are studied.