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Department of Information EngineeringUniversity
of Padova, ITALY
On Providing Soft-QoS in Wireless Ad-Hoc Networks
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Department of Information EngineeringUniversity
of Padova, ITALY
Special Interest Group on NEtworking
Telecommunications
On Providing Soft-QoS in Wireless Ad-Hoc Networks
Andrea Zanella, Daniele Miorandi, Silvano
Pupolin, Paolo Raimondi
andrea.zanella, daniele.miorandi,
silvano.pupolin_at_dei.unipd.it
WPMC 2003, 21-22 October 2003
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Motivations

• Ad-hoc networks are a valuable solution to
• Extend in a multi-hop fashion the radio access to
  wired networks
• Interconnect wireless nodes without any fixed
  network structure
• In these contexts, providing QoS is a key issue
• audio/video streaming
• interactive games
• multimedia
• A possible QoS support method
• QoS-routing Call-Admission-Control (CAC)
  mechanisms
• Constrained Shortest Path Routing Problem
  (NP-complete)?
• MAC-layer Resource Reservation (MRR) and
  scheduling strategies

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Hard Soft QoS
Hard-QoS
Soft-QoS

• Widely used in wired networks
• Integrated Services flow based (RSVP)?
• Differentiated Services class based

• Suitable for wireless networks
• Applications may work even if, for short periods
  of time, QoS requirements are not satisfied
• Deals with limited bandwidth and radio channel

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Aim of the study

• Reference network scenario
• Low-profile multi-hop wireless networks
• Intermediate nodes capable of basic
  functionalities
• Routing Link monitoring Basic computation
• Border nodes capable of rather complex
  functionalities
• Call Admission Control (CAC) MAC layer Resource
  Reservation (MRR)?
• Goal
• Providing Soft-QoS support over low-profile
  multi-hop networks
• Define Soft QoS parameters
• Define distributed statistical CAC
• Define statistical MAC-layer Resource Reservation
  (MRR) mechanism
• Modify AODV in order to support Soft-QoS routing

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Whats Soft-QoS?

• Soft-QoS definition

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Soft-QoS parameters

• QoS parameters required per link
• Minimum peak band Br
• End-to-End Delay Dr
• Soft QoS parameter Target Satisfaction index
• ?r percentage of pcks expected to satisfy QoS
  constrains
• ?r 1 ? hard QoS (or wealthy clients)?
• ?r 0 ? pure best-effort (or poor clients)?

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Call Admission Control

• Distributed CAC mechanism

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Path Service Levels

• Path P (p1,, pN)?
• Service levels
• Path Bandwidth minimum available bandwidth along
  the path
• Path Delay total delay introduced by the path
• Bandwidth bpj and delay dpj of each link are
  assumed to be (independent) random variables
  BP Dp are random variables!

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Call Admission Control

• Path is feasible if
• Bandwidth constrained requests
• Delay constrained requests
• However, this would require the collection of the
  complete statistics of link bandwidth and link
  delay

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Gaussian approx

• But when statistics are tough to be determined
  we may (always?) resort to the Gaussian
  approximation!
• Statistics are univocally determined by mean and
  standard deviation values of link delay and
  available bandwidth
• Such values can be easily determined by each
  intermediate node
• QoS routing algorithm collects and delivers such
  statistics to the destination node
• Destination node performs CAC in a
  straightforward manner
• Bandwidth constrained requests
• Delay constrained requests

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MRR

• Statistical MAC-layer Resource Reservation

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Resource Bounds

• Once a connection is accepted, resources should
  be reserved
• To avoid complex static reservation mechanisms
  and flow differentiation we resort to statistical
  resource reservation
• Each node processes all the packets in the same
  way
• Packets of different flows get the same service
  from the same link
• For each link, nodes compute the Resource Bounds,
  i.e., the minimal residual resources that should
  be guaranteed to preserve QoS levels of accepted
  connections that go through that link

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Example of Bandwidth bound
Actual Sat. Index ?
Bandwidth Bound
P(bj gt B)?
Target Satisfaction Index ?r
Required Path Bandwidth Br
Bandwidth B
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Bandwidth Bounds

• Bandwidth-constrained requests

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Delay Bounds

• Delay-constrained requests
• Extra-delay margin is computed for the entire
  path
• Each link along the path is assigned a fraction
  of the extra delay time inversely proportional to
  the average link delay

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Maximum Sustainable traffic

• The tightest resource margins of the links along
  the path are made available at the source
• The source derives the maximum sustainable
  traffic rate, i.e., the maximum traffic that may
  be injected into the network without violating
  the QoS agreements of the connections already
  established

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How to create a path

• Soft-QoS routing algorithm

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Path creation maintenance

• Soft-QoS routing is largely inspired to AODV
• Each Route Request (RREQ) packet gathers
  statistical information on the minimum bandwidth
  and maximum delay along that portion of the path
• RREQ is propagated only whether bandwidth request
  is satisfied
• The destination node back propagates a Route
  Reply (RREP) packet along the selected path
• RREP acquaints intermediate nodes with new
  resource bounds and updates maximum sustainable
  traffic rate limit
• Source node is required to respect the maximum
  sustainable traffic rate limit or to refuse the
  connection

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Simulation Results

• Simulation of Soft-QoS routing algorithm

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Simulation Scenario

• Bluetooth Scatternet
• Round Robin Polling
• Gateways spend 50 slots in each piconet
• Poisson packets arrival process
• Mixed packet formats with average length of 1500
  bits
• Delay-constrained requests

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Gaussian Approximation

• Local slave-to-slave connections in each piconet
• Data rate9.6 Kbit/s

• 1 hop

• 6 hops

• Gaussian approx is fairly close to empirical
  delay CDF
• Gap increases for long-distance and high traffic
  connection

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Simulation setup

• Target connection c1
• Dr 50 ms
• ?r 0.2
• r 20 kbit/s
• Target connection c2
• Dr 200 ms
• ?r 0.9
• r 30 kbit/s
• Target connection c3
• Dr 200 ms
• ?r 0.9
• r 20 kbit/s

• Target connection c4
• Dr 50 ms
• ?r 0.2
• r 60 kbit/s
• Transversal connections
• Starting after 20 s, last for 10 s
• On average 1 request/s
• Random source, destination QoS requests
• Rate 5?20 kbit/s

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Satisfaction Delay dynamics

• Satisfaction

• Delay

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Conclusions

• We have proposed a basic Soft QoS routing
  algorithm for low-profile ad hoc networks
• Provides Soft-QoS guarantees
• Requires
• basic nodes functionalities
• statistical link state monitoring (mean and
  standard deviation)?
• Does not require
• service differentiation
• static resource reservation
• Drawbacks
• Lower resource utilization
• Higher rate of connection request rejection

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Department of Information EngineeringUniversity
of Padova, ITALY
On Providing Soft-QoS in Wireless Ad-Hoc Networks
Andrea Zanella, Daniele Miorandi, Silvano
Pupolin, Paolo Raimondi
Questions?
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Extra Slides

• Spare Slides

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Statistical Resource Reservation

• Resource bounds
• Minimal residual resources that should be
  guaranteed to preserve QoS levels of accepted
  connections

• Bandwidth-constrained

Actual Satisfaction
Resource bounds

• Delay-constrained
• Extra-delay margin given to each link along the
  path is inversely proportional to the mean link
  delay