Improving Delay Performance in UMTS/WLAN Integrated Networks with Global Gateway Router

This paper presents efficient methods of vertical handoffs from UMTS to WLAN and vice versa in a loose coupling architecture. When a mobile terminal (MT) moves from UMTS to WLAN, it performs mobile IP (MIP) registration with home agent (HA). Subsequently, HA needs to perform location update signaling with UMTS network to make the MT reachable from UMTS. If HA is deployed at gateway GPRS support node (GGSN), all incoming packets from the Internet to an MT are routed via GGSN and average packet-delay increases when the MT is in loosely-coupled WLAN. MIP registration is also affected by the traffics between the Internet and UMTS. To avoid this problem, HA can be deployed in WLAN IP network, but handoff delay from WLAN to UMTS will be more because an MT cannot send MIP-registration request to HA before the establishment of PDP context in UMTS network. We propose efficient handoff methods with simple modification in GPRS tunneling protocol (GTP) and HA functionality by placing a global gateway router. Our ns-2 based simulation results show that the proposed technique improves MIP registration during handoff from UMTS to WLAN and vice versa. It also provides lower end-to-end packet delay for Internet services when an MT is residing in WLAN.