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End-to-End Performance and Fairness in Multihop Wireless Backhaul Networks

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... good economics ... Without any modifications to TCP Inter-TAP performance isolation Outline Fairness reference model Performance study Capacity and fairness ... – PowerPoint PPT presentation

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Title: End-to-End Performance and Fairness in Multihop Wireless Backhaul Networks


1
End-to-End Performance and Fairness in Multihop
Wireless Backhaul Networks
  • V. Gambiroza, B. Sadeghi, and E. Knightly
  • Rice University

2
Backhaul Networks
Residential user or small business
  • Backhaul networks technologies
  • Wireline coax-, copper-based, fiber
  • Wireless

3
Wireless Backhaul Networks TAP Networks
Residential user or small business
  • Multihop wireless infrastructure
  • High bandwidth, good economics, deployability
  • Transit Access Point (TAP)

4
Fundamental Scenario
  • One branch of the access tree

5
Parking Lot Scenario
  • Similar to parking lot with one exit

Internet
TAP3
TAP1
TAP2
TAP4
6
Fairness Problem
7
Fairness Problem
8
Fairness Problem
We need multihop fairness
9
Contributions
  • Fairness reference model
  • Performance study
  • TCP
  • Inter-TAP fairness algorithm
  • Capacity and fairness

10
Outline
  • Fairness reference model
  • Limitations of existing models
  • Fairness objectives
  • Algorithm solution space
  • Performance study
  • Capacity and fairness

11
Limitations of Existing Fairness Models
Ingress-Egress Flow Granularity
  • Fairness with Ingress-Egress (IE) flow
    granularity
  • Provide fair share to each ingress-egress pair
  • Node corresponds to TAP
  • TAP is small business/residence
  • Provide fair shares to TAPs independent of
    number of flows
  • Treat TAPs traffic as a single aggregate
  • Ingress Aggregate (IA) flow granularity
  • Provide fairness on both IA and IE flow
    granularities -Fundamentally different

12
Our Objectives (Our Objectives vs. Classical
Objectives)
Our Objectives
Classical Objectives
  • Flow granularity
  • Ingress aggregate (IA) and Ingress-Egress
  • Ingress-Egress (IE)
  • Spatial properties
  • Provide fair shares independent of spatial
    location
  • Maximize spatial reuse flows sufficiently
    spatially separated can transmit simultaneously

Depends on fairness model
  • Resource
  • Channel access time
  • Bandwidth
  • Medium
  • Multirate shared wireless channel
  • Wired link

13
Problem Statement
  • Fairness reference model defined
  • Distributed algorithm
  • Targeted at achieving shares defined by reference
    model
  • Solution space
  • Local solution insufficient
  • Example Parking lot
  • Multihop solution
  • Flow e2e TCP
  • Multihop wireless network e2e Inter-TAP
    Fairness Algorithm (IFA)

14
Outline
  • Fairness reference model
  • Performance study
  • Performance factors
  • TCP fairness
  • Inter-TAP Fairness Algorithm (IFA)
  • Capacity and fairness

15
Performance Factors (1/2)
  • Goal
  • Study end-to-end performance and fairness
  • Factors investigated
  • Fairness algorithms
  • Uncontrolled UDP, TCP, IFA
  • Media access control
  • 802.11 with two-way and four-way handshake
  • Antenna technologies
  • Omni directional, sector
  • Carrier sense range, multiple topologies and flow
    scenarios
  • Other simulation specs
  • Channel rate constant 2 Mb/sec
  • 1000 byte packets

16
Performance Factors (2/2)
Topology
Well understood topologies
17
Performance Factors (2/2)
Topology
Parking lot
MU-TAP and TAP-TAP transmissions on orthogonal
channels
18
Fairness with TCP MAC, Hidden Terminals and
Information Asymmetry
MUs generate long lived TCP-Sack flows Carrier
sense range transmission range
19
Fairness with TCP MAC, and Hidden Terminals and
Information Asymmetry
MUs generate long lived TCP-Sack flows Carrier
sense range transmission range
  • TAP1 and TAP2 traffic starved
  • Both are hidden terminals
  • Timeouts significant throughput penalty
  • TCP generates bursts of packets

ACK Traffic
20
Fairness with TCP MAC, and Hidden Terminals and
Information Asymmetry
MUs generate long lived TCP-Sack flows Carrier
sense range transmission range
  • Capacity and fairness need to be considered
    jointly
  • Total is up to 125 of objective while two flows
    are starved
  • RTS/CTS exchange introduces information asymmetry
    KSSK02
  • TAP1 has no information of TAP3-TAP4 trans.

ACK Traffic
21
TCP and Sector Antennas
MUs generate long lived TCP-Sack flows TAPs use
sector antennas
  • Severe spatial bias
  • TAP1 traffic obtains 26 of objective
  • Total goodput increased
  • Total goodput is 67 of the objective

22
Inter-TAP Fairness Algorithm (IFA)
  • Idealized version of algorithm
  • Omniscient calculation of fair rates
  • Practical algorithm needs messaging
  • Limit traffic rate at ingress

23
TCP and IFA
MUs generate long lived TCP-Sack flows Carrier
sense range transmission range
  • End-to-end performance considerably improved
  • TAP-aggregated throughput is 59 to 75 of the
    objective
  • Hidden terminal problem
    mitigated
  • Contention considerably decreased
  • TCP cannot inject bursts of packets
  • Spatial bias
  • IFA alone cannot eliminate it
  • Rates lower than the objective

24
Inter-TAP Performance Isolation
  • Provide inter-TAP performance isolation
  • independent of traffic types

25
Summary of Findings (1/2)
  • Starvation of upstream flows (UDP, TCP, with or
    w/o RTS/CTS)
  • Parking Lot scenario results in hidden
    terminals and information asymmetry
  • Sector antennas and carrier sense range mitigate
    the hidden terminal problem
  • Severe spatial bias
  • SA Throughput as low as 26 of targeted values
  • CSR Throughput as low as 34 of targeted values
  • TCP able to exploit spatial reuse

26
Summary of Findings (2/2)
  • IFA approximates reference model performance
  • The impact of hidden terminal problem and
    information asymmetry mitigated
  • Without any modifications to CSMA/CA
  • TCP over IFA achieves 59 to 75 of idealized
    objective
  • Without any modifications to TCP
  • Inter-TAP performance isolation

27
Outline
  • Fairness reference model
  • Performance study
  • Capacity and fairness
  • Maximum throughput without fairness
  • Fairness objectives and throughput

28
Problem Statement
  • Compute maximum aggregate throughput
  • No fairness constraint
  • System model
  • One transmission possible at time
  • Perfect collision-free MAC

Single contention neighborhood
29
Aggregate Throughputwith and without Fairness
Constraints
Assign time-shares to maximize network throughput
Solution
No spare time-capacity
  • Fairness constraints
  • Temporal fairness constraint
  • Spatial bias removal constraint
  • Ingress aggregate constraint

30
Conclusions
  • Fairness
  • Fairness reference model formally defined
  • Designed for multihop wireless networks
  • Performance study
  • Starvation of upstream flows
  • Sector antennas, larger carrier sense range, IFA
    mitigate the problem
  • IFA approximates performance of reference model
  • Capacity and fairness
  • Need to be considered jointly

31
End-to-End Performance and Fairness in Multihop
Wireless Backhaul Networks
  • V. Gambiroza, B. Sadeghi, and E. Knightly
  • Rice University
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