August 24, 2005 QShine 2005, Orlando, Florida 1

Enhancing QoS Support forVertical Handoffs Using Implicit/Explicit Handoff Notifications

Ling-Jyh Chen, Guang Yang, Tony Sun,M. Y. Sanadidi and Mario Gerla

Computer Science DepartmentUniversity of California, Los Angeles

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QoS Enhancement for Vertical HandoffsQoS Enhancement for Vertical Handoffs

Goal: Providing highly agile system for mobile applications.

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Related WorkRelated 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 Implicit Handoff Notification and

Explicit Handoff NotificationExplicit Handoff Notification Enhanced Service Agility Schemes: Fast Rate AdaptationFast Rate Adaptation and

Early Rate ReductionEarly Rate Reduction

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IImplicit mplicit HHandoff andoff NNotificationotification

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 ProbeTFRC Probe & TCP Probe TCP Probe (CapProbe based)

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Background on CapProbeBackground on CapProbe

T3

T2 T3

T3

T1

T3

Narrowest LinkNarrowest Link

20Mbps 10Mbps 5Mbps 10Mbps 20Mbps 8Mbps

Capacity = (Packet Size) / (Dispersion)

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TFRC: TCP Friendly Rate Control 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.

22 33 1 32

3 8RTO

sT

p pR t p p

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Embed CapProbe algorithm within TFRC by sending two packets back-to-back every n packets

TFRC Probe was assessed in [E2EMON’04].

TFRC ProbeTFRC Probe

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TCP ProbeTCP Probe

Delayed Ack

TCP Probe:

CapProbe:

TCP Probe was assessed in [GI’05].

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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

1. Cnew > αCpre or

2. Cnew < βCpre

where α =5 and β=0.2.

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Enhancing QoS using Enhancing QoS using IHNIHN

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.

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Explicit Handoff Notification

Need an “Intelligent Handoff Manager”. EHN is generated prior to

the occurrence of handoff.

Smart Decision Model

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Enhancing QoS using Enhancing QoS using EHNEHN LOW-to-HIGH:

Fast Rate Adaptation (FRA)

HIGH-to-LOW: Early Rate Reduction (ERR):

Reduce rate in advance to prevent bulk packet losses.

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EvaluationEvaluation

Simulation Scenario (NS-2) Vertical handoff between 802.11b

(5.5Mbps) and 1xRTT (150kbps).

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EvaluationEvaluation

TFRC: vertical handoff from LOW to HIGH

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EvaluationEvaluation

TCP: vertical handoff from LOW to HIGH

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EvaluationEvaluation

TFRC: vertical handoff from HIGH to LOW EHN (a): EHN when the handoff occurs EHN (b): EHN one OWD before the handoff

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EvaluationEvaluation

TFRC: vertical handoff from HIGH to LOW

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SummarySummary

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.

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Thank you

Questions are welcome. For more info, please visit our web at

http://www.cs.ucla.edu/NRL/