Ling-Jyh Chen, Mario Gerla Computer Science Department, UCLA Vertical Handoff Ling-Jyh Chen, Mario Gerla Computer Science Department, UCLA

Handoff Illustration Horizontal Handoff Vertical Handoff Occurs when the user switches between different network access points of the same kind. Vertical Handoff Involves two different network interfaces which usually represent different technologies.

Seamless Handoff Defined as a handoff scheme that maintains the connectivity of all applications on the mobile device when the handoff occurs. Aims to provide continuous end-to-end data service in the face of any link outages or handoff events. Design Goal: low latency Minimal packet loss

The “ideal” solution – Mobile IP The mobile users need a “practical” solution NOW! Pros Cons Mobile IP is standardized. The deployment cost is high. Mobile IP solutions provide Internet servers the ability to track the mobility. Mobile IP solutions need to negotiate with Internet routers to relay/redirect the data flows. Thus, the handoff latency is higher. An ideal solution for mobile scenarios. Real deployment is still rare.

Universal Seamless Handoff Architecture (USHA) A “simple” and “practical” handoff solution. NAT server NAT Server All packets are encapsulated and transmitted using UDP Applications are bound to the tunnel and transparent to the handoff.

Detecting handoff events and performing service adaptation Transcoding according to available bandwidth and MH properties Smart Decision: decide the “best” time and target interface to handoff

Smart Decision Model With USHA, mobile hosts are able to select any network interface for its connection at any time. However, still need a model that knows which interface to use based on various factors such as Link Capacity, Available Bandwidth Loss Rate, Delay Power Consumption Cost Solution: Smart Decision Model

Smart Decision Model HCC—Handoff Control Center Provides connection between network interfaces and the upper layer applications. Composed of DM (Device Monitor) SM (System Monitor) SD (Smart Decision) HE (Handoff Executor)

Service Agility Vertical handoff usually results in a dramatic change in the path capacity. “Fast Rate Adaptation” forces TCP/TFRC to enter Slow Start when detecting a handoff from LOW to HIGH “Agility” is triggered by Explicit handoff notification Implicit handoff notification

Service Agility – TFRC Probe TFRC Probe with “fast rate adaptation” Vertical handoff from 1xRTT to 802.11b

Service Agility – TCP Probe TCP Probe with “fast rate adaptation” Vertical handoff from 10Mbps to 100Mbps Unit: bps

Summary We proposed a practical vertical handoff solution, called USHA. We proposed a Smart Decision Model to determine the “best” time and target interface to perform vertical handoff. We evaluated Service Agility in vertical handoff scenarios.