LIHP: a low latency layer-3 handoff scheme for 802.11 wireless networks

This paper presents the design and implementation of a low latency layer-3 handoff scheme for 802.11 wireless mobiles roaming between access points that are connected to different IP subnets. Called LIHP (link-layer initiated handoff protocol), the scheme uses link-layer frames (e.g., ARP and 802.11 management frames) as triggers to send route updates to the mobiles and to an access gateway, which serves as the gateway to the Internet for the mobiles. This approach allows for IP packet routing to and from a mobile to begin immediately after the mobile establishes a link-layer association with a new access point. Furthermore, the design does not require any modification to the mobiles. Each mobile is assigned a single IP address and maintains its IP address as it moves from one access point to another, thus preserving TCP connections across hand-offs. The access points (called access routers in LIHP) and the access gateway cooperate to track each mobile and forward packets using IP tunnelling. Experimental results from a prototype implementation show that the scheme can achieve layer-3 handoff latency on the order of a few milliseconds