quality of service support in wireless networks
Download
Skip this Video
Download Presentation
Quality of Service Support in Wireless Networks

Loading in 2 Seconds...

play fullscreen
1 / 31

Quality of Service Support in Wireless Networks - PowerPoint PPT Presentation


  • 444 Views
  • Uploaded on

Quality of Service Support in Wireless Networks. Hongqiang Zhai http://www.ecel.ufl.edu/~zhai Wireless Networks Laboratory Department of Electrical and Computer Engineering University of Florida In Collaboration with Dr. Xiang Chen and my advisor Professor Yuguang ``Michale’’ Fang. Outline.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Quality of Service Support in Wireless Networks' - Leo


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
quality of service support in wireless networks
Wireless Networks Laboratory (WINET)

Quality of Service Support in Wireless Networks

Hongqiang Zhai

http://www.ecel.ufl.edu/~zhai

Wireless Networks Laboratory

Department of Electrical and Computer Engineering

University of Florida

In Collaboration with Dr. Xiang Chen and my advisor Professor Yuguang ``Michale’’ Fang

outline
Wireless Networks Laboratory (WINET)Outline
  • Introduction
  • Performance analysis of the IEEE 802.11 MAC protocol
  • A call admission and rate control scheme
  • Conclusion and future research issues
wireless local area networks wi fi hot spots
Wireless Networks Laboratory (WINET)Wireless Local Area Networks/ Wi-Fi Hot Spots
  • Web traffic
  • Email
  • Streaming video
  • Instant messaging
  • Gaming over IP
  • Voice over IP over Wi-Fi

Next Call May Come from a Wireless Hot Spot

challenges
Wireless Networks Laboratory (WINET)Challenges
  • Unreliable physical channel
    • Time-varying propagation characteristics
    • Interference
  • Limited bandwidth
  • Limited processing power and battery life
  • Distributed control
  • Mobility
medium access control
Wireless Networks Laboratory (WINET)Medium Access Control
  • Coordinate channel access
    • Reduce collision
    • Efficiently utilize the limited wireless bandwidth

B

D

C

A

ieee 802 11 distributed coordinate function dcf mac protocol

DIFS

SIFS

SIFS

SIFS

Backoff

DIFS

NAV(RTS)

RTS

NAV(CTS)

Backoff

Transmitter

A

Receiver

B

ACK

Others

Wireless Networks Laboratory (WINET)

IEEE 802.11 Distributed Coordinate Function (DCF) MAC Protocol
  • Carrier sense multiple access with collision avoidance (CSMA/CA)
    • Carrier sensing
      • Physical Carrier Sensing
      • Virtual Carrier Sensing
    • Interframe Spacing (IFS)
      • Short IFS (SIFS) < DCF IFS (DIFS)
  • Binary Exponential Backoff
    • Randomly chosen from [0, CW]
    • CW doubles in case of collision

Contention based MAC

Can it support QoS requirements of various applications?

Request to send

DATA

RTS

DATA

CTS

ACK

Acknowledge

Clear to send

previous work on performance analysis of the ieee 802 11 mac standard
Wireless Networks Laboratory (WINET)Previous Work on Performance Analysis of the IEEE 802.11 MAC Standard
  • Previous studies focus on saturated case
    • Each device always has packets in the system and keeps contending for the shared channel.
      • Collision probability is very high
      • Delay performance is very bad
      • Only throughput and average delay have been derived.
    • Related work
      • Bianchi, JSAC March 2000
      • Cali et al., IEEE/ACM Tran. Networking, Dec. 2000

QoS requirements of real-time services can not be guaranteed if there are many contending users?

previous work on supporting qos in wlans
Wireless Networks Laboratory (WINET)Previous Work on Supporting QoS in WLANs
  • Service differentiation
    • Provide different channel access priorities for different services by differentiating
      • Contention window
      • Interframe spacing (IFS)
    • IEEE 802.11e draft (based on 802.11b)
    • Related work
      • Ada and Castelluccia, Infocom’01 (CW, IFS)
      • Veres et al., JSAC Oct. 2001 (real-time measurement in virtual MAC)
      • S.T. Sheu and T.F. Sheu, JSAC Oct. 2001 (real-time traffic periods)
      • S. Mangold et al., Wireless Communications Dec. 2003 (802.11e)

Service differentiation is still not enough to meet the strict QoS requirements

Can the IEEE 802.11 MAC protocol do better than service differentiation?

  • Research issues
    • Performance in both non-saturated and saturated case
    • Probability distribution of medium access delay
mac service time

3

3

2

2

1

Wireless Networks Laboratory (WINET)

MAC Service Time

Packet arrival

  • Probability Generating Function (PGF)
    • Pr{Ts=tsi}=pi (0 ≤ i < ∞)
  • MAC service time is discrete in value
    • SIFS, DIFS, EIFS
    • Backoff time is measured in time slots
    • Packet to be transmitted is also discrete in length

Transmit

queue

3

MAC

1

2

3

mac service time13
Wireless Networks Laboratory (WINET)MAC Service Time
  • Generalized state transition diagram (GSTD)
    • Mark the PGF of the transition time on each branch along with the transition probability
    • PGF of the transition time between two states is the corresponding system transfer function

start

end

  • Widely used method
    • Calculate the average # of retransmissions NR = p/(1-p)
    • Average transition time is NR × τ1 + τ2=
mac service time of ieee 802 11
Wireless Networks Laboratory (WINET)MAC Service Time of IEEE 802.11

State variable (j, k): j is the backoff stage, k is the backoff timer

Wj: the contention window at backoff stage j

p: collision probability perceived by a node

: maximum # of retransmissions

mac service time of ieee 802 1115

MAC service time (ms)

PDF

Collision probability p

payload size = 8000 bits, with RTS/CTS

MAC service time (ms)

Wireless Networks Laboratory (WINET)

MAC Service Time of IEEE 802.11

Observation:

When p is small, both the mean and standard deviation of MAC service timeare small.

delay and delay variation

TS

3

2

TR

1

Wireless Networks Laboratory (WINET)

Delay and Delay Variation

Packet arrival

Transmit

queue

TW

MAC

network throughput

Channel utilization:

Normalized throughput:

Channel busyness ratio:

With RTS/CTS

n: # of nodes

: the prob. that a node transmits in any slot

Without RTS/CTS

Wireless Networks Laboratory (WINET)

Network Throughput

(Tidl pi )(Tcol pc)(Tsuc ps )

network throughput18
Wireless Networks Laboratory (WINET)Network Throughput

Maximum throughput

with good delay performance

Collision Probability p

Channel Busyness Ratio is an accurate, robust, and easily obtained sign of network status.

packet loss rate
Wireless Networks Laboratory (WINET)Packet Loss Rate
  • Given the collision probability p, the MAC layer may drop the packet with the probability

Avg. queue length

Pkt loss rate

Channel busyness ratio

model validation
Wireless Networks Laboratory (WINET)Model Validation

Channel Busyness Ratio

The optimal operating point denoted by Umax

  • Simulation settings
        • 50 nodes, RTS/CTS mechanism is used
        • Each node has the same traffic rate.
        • We monitor the performance at different traffic rates.
call admission control
Wireless Networks Laboratory (WINET)Call Admission Control
  • Channel utilization/channel busyness ratio for a flow
  • Admission control test

R: flow data rate (bps)

L: average packet length (bits)

Up to Urt (= γUmax, 0<γ<1) can be assigned to real-time traffic

rate control
Wireless Networks Laboratory (WINET)Rate control
  • Notation:
    • r: Channel resource r allocated to each node
      • Allowable channel time occupation ratio
    • tp: channel time for packet p
      • Time that a successful transmission of packet p will last over the channel.
    • ∆: scheduled interval
      • Time between two consecutive packets that DRA passes to the MAC layer
    • br: channel busyness ratio
      • brth = Umax
rate control24
Wireless Networks Laboratory (WINET)Rate control
  • Initialization Procedure: r=rstart
  • Three-Phase Resource Allocation Mechanism:
    • multiplicative-increase if underloaded, i.e., br < BM=α×brth
    • Additive-increase if moderately loaded, i.e., BM ≤ br < brth
    • Multiplicative-decrease if heavily loaded, i.e., br ≥ brth
theoretical results of carc
Wireless Networks Laboratory (WINET)Theoretical Results of CARC

Convergence of Multiplicative-Increase Phase

simulation studies
Wireless Networks Laboratory (WINET)Simulation Studies
  • Simulation settings in ns2
    • Channel rate = 11 Mbps
    • Voice traffic with an on-off model
      • The on and off periods are exponentially distributed with an average value of 300 ms each.
      • During on periods, traffic rate is 32kb/s with a packet size of 160 bytes.
    • Greedy best effort traffic
      • Saturated CBR traffic with a packet size of 1000bytes.
throughput and mac delay
Wireless Networks Laboratory (WINET)Throughput and MAC delay

Each node is a source of greedy traffic

CARC improves the throughput by up to 71.62% with RTS/CTS,

and by up to 157.32% without RTS/CTS

CARC achieves up to 95.5% of maximum throughput with and without RTS/CTS

fairness

Throughput

Throughput

Time (s)

Time (s)

Wireless Networks Laboratory (WINET)

Fairness

A new greedy node joins the network every other 10 seconds

Higher aggregate throughput

Fairness convergence speed: 0-2 s

Short term fairness

quality of service for voice traffic
Wireless Networks Laboratory (WINET)Quality of Service for Voice Traffic

50 greedy nodes

A new voice node joins the network every other 10 seconds.

conclusion
Wireless Networks Laboratory (WINET)Conclusion
  • The IEEE 802.11 MAC protocol can support strict QoS requirements of real-time services while achieving maximum throughput.
  • Channel busyness ratio is a good network status indicator of the IEEE 802.11 systems.
  • An efficient call admission and rate control framework is proposed to provide QoS for real-time service and also to approach the maximum throughput.
ad