Enhancing QoS Support for Vertical Handoffs Using ImplicitExplicit Handoff Notifications

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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 Handoffs

• Goal Providing highly agile system for mobile
  applications.

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Related Work

• Conventional adaptive method AIMD
• TCP, RAP,
• TEAR, TFRC,
• They DO NOT perform well in vertical
  handoffsGurtov 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

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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 toolsTFRC Probe
  TCP Probe (CapProbe based)

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Background on CapProbe
Capacity (Packet Size) / (Dispersion)
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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.

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TFRC Probe

• Embed CapProbe algorithm within TFRC by sending
  two packets back-to-back every n packets
• TFRC Probe was assessed in E2EMON04.

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TCP Probe

• TCP Probe was assessed in GI05.

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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
• Cnew gt aCpre or
• Cnew lt ßCpre
• where a 5 and ß0.2.

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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.
• FRAIHN 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 tothe occurrence of
  handoff.
• Smart Decision Model

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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.

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Evaluation

• Simulation Scenario (NS-2)
• Vertical handoff between 802.11b (5.5Mbps) and
  1xRTT (150kbps).

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Evaluation

• TFRC vertical handoff from LOW to HIGH

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Evaluation

• TCP vertical handoff from LOW to HIGH

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Evaluation

• 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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Evaluation

• TFRC vertical handoff from HIGH to LOW

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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.

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Thank you

• Questions are welcome.
• For more info, please visit our web
  athttp//www.cs.ucla.edu/NRL/