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

2. 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.

3. 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

4. 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.

5. 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.

6. 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

7. 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

8. 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)

9. 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

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

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

12. 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.