Methods for Seamless Vertical Handoff between UMTS and WLAN

3G cellular networks and 802.11 wireless LANs have complementary advantages to each communication systems. Interworking between UMTS and WLAN can be used to pursue two advantages of both high speed access network and a broad cell coverage. How to reduce handoff latency between UMTS and WLAN is a so important issue, so in this paper we investigate the handoff latency and separate handoff delay into several parts in both upward handoff (from WLAN to UMTS) and downward handoff (from UMTS to WLAN). In order to reduce the handoff delay, we use cross-layer information between layer 2 and layer 3.