1. QShine 2005, Orlando, Florida
Enhancing QoS Support for Vertical Handoffs Using Implicit/Explicit Handoff Notifications
Ling-Jyh Chen, Guang Yang, Tony Sun, M. Y. Sanadidi and Mario Gerla
Computer Science Department University of California, Los Angeles
August 24, 2005
QShine 2005, Orlando, Florida

2. QoS Enhancement for Vertical Handoffs
Goal: Providing highly agile system for mobile applications.
August 24, 2005
QShine 2005, Orlando, Florida

3. QShine 2005, Orlando, Florida
Related Work
Conventional adaptive method: AIMD
TCP, RAP, …
TEAR, TFRC, …
They DO NOT perform well in vertical handoffs [Gurtov et al, MC2R ’04].
Our solution:
Handoff Notifications: Implicit Handoff Notification and Explicit Handoff Notification
Enhanced Service Agility Schemes: Fast Rate Adaptation and Early Rate Reduction
August 24, 2005
QShine 2005, Orlando, Florida

4. Implicit Handoff Notification
Vertical handoffs usually result in drastic changes in the link capacity.
By monitoring the end-to-end capacity, one can identify the occurrence of a vertical handoff.
Passive capacity monitoring tools: TFRC Probe & TCP Probe (CapProbe based)
August 24, 2005
QShine 2005, Orlando, Florida

5. Background on CapProbe
20Mbps
10Mbps
5Mbps
8Mbps T1 T3
Narrowest Link T2 T3 T3 T3
Capacity = (Packet Size) / (Dispersion)
August 24, 2005
QShine 2005, Orlando, Florida

6. TFRC: TCP Friendly Rate Control
TFRC is an equation based unicast protocol.
TFRC mimics the TCP long-term throughput by utilizing the function:
The receiver is responsible for calculating the loss event rate p and sending it back to the sender once per round-trip time.
The sender is responsible for adjusting its sending rate Tactual to be close to T.
August 24, 2005
QShine 2005, Orlando, Florida

7. QShine 2005, Orlando, Florida
TFRC Probe
Embed CapProbe algorithm within TFRC by sending two packets back-to-back every n packets
TFRC Probe was assessed in [E2EMON’04].
August 24, 2005
QShine 2005, Orlando, Florida

8. QShine 2005, Orlando, Florida
TCP Probe
CapProbe:
Delayed Ack
TCP Probe:
TCP Probe was assessed in [GI’05].
August 24, 2005
QShine 2005, Orlando, Florida

9. Implicit Handoff Notification
TCP/TFRC Probe continuously estimate the link capacity, using 50 samples per estimate.
A vertical handoff can be identified when a dramatic capacity change is observed.
An IHN is generated when
Cnew > αCpre or
Cnew < βCpre
where α =5 and β=0.2.
August 24, 2005
QShine 2005, Orlando, Florida

10. Enhancing QoS using IHN
Fast Rate Adaptation (FRA)
FRA monitors the capacity.
When vertical handoff from LOW to HIGH is observed, FRA changes ssthresh of TCP/TFRC.
TCP/TFRC enter slow start, instead of staying in congestion avoidance.
FRA+IHN is end-to-end.
However, IHN does not work with HIGH to LOW handoff.
Decreasing ssthresh does not change TCP/TFRC behavior.
Therefore, we need EHN….
August 24, 2005
QShine 2005, Orlando, Florida

11. Explicit Handoff Notification
Need an “Intelligent Handoff Manager”.
EHN is generated prior to the occurrence of handoff.
Smart Decision Model
August 24, 2005
QShine 2005, Orlando, Florida

12. Enhancing QoS using EHN
LOW-to-HIGH:
Fast Rate Adaptation (FRA)
HIGH-to-LOW:
Early Rate Reduction (ERR): Reduce rate in advance to prevent bulk packet losses.
August 24, 2005
QShine 2005, Orlando, Florida

13. QShine 2005, Orlando, Florida
Evaluation
Simulation Scenario (NS-2)
Vertical handoff between b (5.5Mbps) and 1xRTT (150kbps).
August 24, 2005
QShine 2005, Orlando, Florida

14. QShine 2005, Orlando, Florida
Evaluation
TFRC: vertical handoff from LOW to HIGH
August 24, 2005
QShine 2005, Orlando, Florida

15. QShine 2005, Orlando, Florida
Evaluation
TCP: vertical handoff from LOW to HIGH
August 24, 2005
QShine 2005, Orlando, Florida

16. QShine 2005, Orlando, Florida
Evaluation
TFRC: vertical handoff from HIGH to LOW
EHN (a): EHN when the handoff occurs
EHN (b): EHN one OWD before the handoff
August 24, 2005
QShine 2005, Orlando, Florida

17. QShine 2005, Orlando, Florida
Evaluation
TFRC: vertical handoff from HIGH to LOW
August 24, 2005
QShine 2005, Orlando, Florida

18. QShine 2005, Orlando, Florida
Summary
We have proposed IHN and EHN to notify the sender about the occurrence of vertical handoff.
We have proposed FRA (for IHN) and ERR (for IHN/EHN) for better QoS for vertical handoff.
August 24, 2005
QShine 2005, Orlando, Florida

19. QShine 2005, Orlando, Florida
Thank you
Questions are welcome.
For more info, please visit our web at
August 24, 2005
QShine 2005, Orlando, Florida