ECE/MAE 7750: Distributed Control Systems FISP: Focused Independent Study and Presentation Topic: Integrated congestion control and scheduling in wireless local area networks

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ECE/MAE 7750 Distributed Control SystemsFISP
Focused Independent Study and PresentationTopic
Integrated congestion control and scheduling in
wireless local area networks

• Presenter
• Yashodhan Tarte
• Dept. of Electrical and Computer Engineering
• Utah State University
• E yashodhan_at_cc.usu.edu T [phone]

02/28/2005
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Presentation Outline

• References
• QoS contract
• Problems with the present architecture
• Proposed solution
• Traffic control module
• MT i scheduler
• MT i buffer controller
• Simulation results
• Authors conclusions
• Readers comment

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References

• Francesco Delli Priscoli Alberto Isidori
  (2004). A control engineering approach to
  integrated congestion control and scheduling in
  wireless local area networks. Control Engineering
  Practice 13 (2005) 541-558
• Arindam Paul. QoS in Data Networks Standards and
  Protocols. Department of Computer Science and
  Engineering, Ohio State University

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QoS contract

• A Service Class is defined as the set of
  connections whose QoS contract is characterized
  by the same parameters
• A Quality of Service contract is agreed
  establishing
• The characteristics (e.g. minimum bit rate etc.)
  of the so-called Compliant Traffic, i.e. the
  traffic which has to be admitted in the network
  in whatever traffic condition
• The delay and jitter do not exceed maximum
  tolerable values for a given service class
• The Non-Compliant Traffic is admitted into the
  wireless network as long as this admittance does
  not affect QoS requirements of Compliant Traffic

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Problems with the present architecture

• Internet protocol only provides best-effort
  packet delivery service and may consequently be
  inadequate to allow the respect of the QoS
  contracts.
• Inefficient use of available bandwidth because
  various underlying networks (e.g. IEEE 802.11,
  GPRS etc.) use different mechanisms to respect
  the QoS contracts.
• Because of established standards, there is little
  flexibility in both the IP and the UN layers for
  improved IP with wireless.

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Proposed solution

• Wireless adaptation layer (WAL) A layer that
  works between IP and UN layers and is transparent
  to both.
• Components of WAL
• a. Traffic control module (TCM) It includes
  both the congestion control and scheduling
  roles.
• b. Logical link control translator (LLCT)
  Interface between the WAL and the considered UN.
• c. WAL coordinator For coordination between
  various WAL modules.

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Traffic control module

• A TCM consists of the following building blocks
• A Classifier in charge of sorting the IP
  datagrams arriving at the TCM according to the
  associations (i,j) they belong to.
• A Capacity-to-MT Assigner whose role is to select
  the mobile terminal which has to transmit an IP
  datagram towards the LLCT whenever it is
  possible.
• The MT i Scheduler ( i 1,., N ) which handles
  the IP datagrams directed to the ith mobile
  terminal.

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Traffic control module (contd.)
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MT i Scheduler

• The MT i scheduler consists of the following
  blocks
• one FIFO buffer for each association
• an MT i Buffer Controller which is in charge of
  deciding the admittance/discarding of the
  incoming IP datagrams
• one Admittance Handler for each association,
  implementing the decisions taken by the buffer
  controller.

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MT i Scheduler (contd.)
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MT i Scheduler (contd.)
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MT i Buffer Controller

• The decisions of the MT i Buffer Controller are
  based on
• the information about the IP datagrams arrived at
  the MT i Scheduler
• the information about the decisions performed by
  the Capacity-to-MT Assigner
• the FIFO Buffer (i,j) (j 1,., C(i))
  occupancies.

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MT i Buffer Controller (contd.)

• The aim of the buffer controller is increasing
  the (properly weighted) admitted traffic, while
  respecting the QoS constraints
• The adopted approach is based on the idea of
  periodically computing an ideal equilibrium and
  then using proportional feedback control in order
  to steer the state of the system towards such an
  ideal equilibrium

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Simulation Results

• QoS contracts associated to the connections
  relevant to the four considered services

Parameter Voice FTP Web Video
Minimum bit rate 29 kbps 200 kbps 40 kbps 1350 kbps
Maximum delay 0.1 s 4 s 1.5 s 0.5 s
Maximum jitter 0.09 s 3.8 s 1.45 s 0.48 s
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Simulation Results (contd.)

• The number of bits discarded during the
  simulation time period (20 min. for the graph
  shown below )is given by
• Bloss

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Simulation Results (contd.)

• The Link Efficiency is given as the ratio of bits
  passed towards the LLCT during the simulation
  time period (20 min for the graph shown below) to
  the bits which the LLCT would have been able to
  accept during that period.

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Simulation Results (contd.)

• The above results clearly show the advantages, at
  high traffic loads, of the closed loop option
  with respect to open loop option both in terms of
  higher Link Efficiency and in terms of lower
  number of discarded bits.

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Authors Conclusions

• The proposed Traffic Control Module performs
  better than the present arrangements because of
  the presence of a single controller which
• integrates congestion control and scheduling
  tasks
• performs these tasks in a real time closed loop
  fashion
• performs these tasks in a centralized way for all
  the connections involving the considered access
  point (or base station).

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Readers Comment

• The proposed scheme can only be used in the
  wireless networks where cost of implementing such
  a complex system can be justified (e.g. in
  real-time applications)

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• Questions?