Device-transparent network-layer handoff for micro-mobility

An emerging class of applications for enterprise wireless LANs (WLAN) is voice over IP (VoIP) applications, which impose a stringent requirement on end-to-end delay. Because access points on an enterprise WLAN tend to be associated with different IP subnets, support for network-layer handoff is indispensable. Moreover, the handoff frequency is expected to be much higher for WLANs than for cellular networks because the coverage of a WLAN access point is much smaller. Although mobile IP is a mature solution to the network-layer handoff problem, no known mobile IP implementation on IEEE 802.11 WLANs can reduce the handoff latency below 100 msec, a nominal requirement for VoIP applications. This paper describes a novel Ethernet-over-IP overlay network architecture that completely does away with network-layer handoff, and thus reduces the end-to-end handoff delay to that of link-layer handoff, which is supported by WLAN hardware directly. In addition, the proposed wireless overlay network (WON) architecture, which has been implemented in a commercial WLAN access point, represents the first mobility solution that allows a mobile device to maintain its network connections while roaming across different IP subnets without requiring any modification on the mobile device. As a result, the proposed architecture can automatically provide seamless network-layer handoff to a wide variety of mobile devices (such as PDA, portable, cell phone) running on different operating systems, as long as they are equipped with 802.11 network interface.