Bandwidth Aggregation in Heterogeneous Networks

1
Bandwidth Aggregation in Heterogeneous Networks

• Kameswari Chebrolu, Ramesh Rao
• Department of ECE
• University of California, San Diego

2
Introduction

• Recent mobile Internet growth spurred deployment
  of different wireless technologies
• e.g. GPRS, CDMA2000, HDR, 802.11, Bluetooth,
  Iridium etc
• End-Users have flexibility regarding Interface
  choice
• Can choose any number of interfaces to best fit
  application needs
• Simultaneous use of multiple interfaces opens
  interesting possibilities
• Bandwidth Aggregation, Mobility Support,
  Security, Reliability
• Problem Statement
• How to effectively aggregate bandwidth across
  multiple network interfaces?

3
Motivation

• Applications will drive next-generation network
  deployments
• Video Applications
• Video-on-demand
• Interactive video
• Video conferencing
• Multiplayer games
• Bandwidth requirements 250 Kbps to 2-3 Mbps
• Problem
• Wireless interfaces have bandwidth limitations
• 50 Kbps 384 Kbps (GPRS, CDMA2000)
• TCP applications can also benefit from bandwidth
  aggregation

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Challenges in Bandwidth Aggregation

• Use of multiple interfaces ? Reordering
• Video applications have stringent QoS
  requirements
• Interactive applications
• One way latency of 150ms , Max limit 400ms
• Frame loss rate lt 1
• Video on Demand (with VCR functions)
• One way latency of 1-2 sec
• Frame loss rate lt 1
• Cannot tolerate excess delay due to reordering
• TCP applications
• More than 3 duplicate acks invokes congestion
  control
• Bandwidth probing issues
• Inter arrival between acks does not reflect
  available bandwidth

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Related Work

• Link-Layer Solutions
• Bonding aggregates circuit switched lines
• IMA ATM technology for aggregating multiple
  point-to-point links
• Multilink PPP
• Stripe Protocol
• Generic load-sharing protocol based on Surplus
  Round Robin (SRR)
• Minimizes packet processing overhead
• SRR similar to WRR
• Accounts for variable sized packets
• Surplus (unused bandwidth) is carried on to next
  round

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Related Work (Contd.)

• Transport-Layer Solutions
• RMTP
• Reliable rate-based transport protocol
• Flow and congestion control based on bandwidth
  estimation
• Parallel TCP (pTCP)
• Opens multiple TCP connections on each interface
• Handles congestion and blackout through data
  reallocation and redundant striping
• Network-Layer Solutions
• Based on tunneling
• Weighted round-robin based scheduling

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Research Contibution

• Solution Approach
• Bandwidth aggregation at IP-level
• Meet application requirements using multiple
  interfaces
• Contributions
• Architecture for using multiple interfaces based
  on Mobile-IP
• Scheduling algorithm based on estimated delivery
  time

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Outline

• Architecture
• Scheduling algorithm
• Evaluation
• Analysis
• Trace-based simulation
• Ongoing work

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Outline

• Architecture
• Scheduling algorithm
• Evaluation
• Analysis
• Trace-based simulation
• Ongoing work

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Architecture for Bandwidth Aggregation

• Link-Layer Solutions infeasible
• End point is an IP address
• Application/Transport Layer Solutions
• Need to modify/rewrite code
• Ensure compatibility with existing infrastructure
• Network Layer solution
• IP a single standard
• Application transparency and interoperability
• Cleanest Solution

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Our Architecture
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Architecture Details

• Mobile IP based
• Packets pass through Home Agent (HA)
• Simultaneous Binding - multiple Care-of-Address
  registration
• Intelligent scheduling of packets to multiple
  addresses
• Radio Access Network Selection Unit (RSU)
• Located on Mobile Host (MH)
• Selects right interfaces based on app. reqmts.
  and cost
• Update bindings with HA
• Traffic Management Unit (TMU)
• Located on HA and MH
• Processes and schedules the incoming traffic onto
  multiple paths
• Conveys application type and end goal
  requirements to HA
• Scheduling Algorithm in TMU is crucial
• Focus on Interactive Real-Time Applications

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Scheduling Algorithm Design Considerations

• Bandwidth
• Interested in WWAN system (CDMA2000, GPRS etc)
• Provide only a few hundred kbps
• Not interested in WLAN/WPAN systems
• Wireless hop is the bottleneck link
• Delay/Jitter
• Wireline Delay between HA and Base-Station (BS)
• Delay values and variation small
• If large, variation may likely be masked at BS
  as wireless hop is bottleneck
• Wireless Delay between Base-Station and MH
• Queuing delay and transmission delay

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Scheduling Algorithm Design Considerations

• Qos Support
• Interested in systems that provide QoS (CDMA2000,
  UMTS etc not HDR)
• Negotiated bandwidth and loss rate guaranteed
  for duration of session

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Design Possibility Weighted Round Robin

• Schedules packets based on bandwidths of
  interfaces
• Not suitable for real-time applications
• Example
• Three interfaces with bandwidth ratios 521
• Packets 1-5 sent on IF1, 6-7 sent on IF2, 8 on
  IF3
• Packet 6 arrives ahead of packets 3,4,5
• Packet 3 suffers excess delay due to reordering
• Ideal ordering IF1 1,2,4,5,6 IF2 3,7 IF3
  8
• Variants of WRR Surplus Round Robin (SRR),
  Shortest Queue First face similar problems

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Our approachEarliest Delivery First

• For each path (between HA and MH), estimate
  arrival time of a packet at MH
• Estimation based on
• Bandwidth of the interface
• One-way wireline delay (estimated) on the
  Internet path
• Schedule the packet on the path that delivers the
  packet the earliest
• Quick remarks
• No need for synchronized clocks (relative one-way
  delay counts)
• EDF is not work conserving
• EDF cannot totally eliminate reordering
• Multiple applications can be handled by combining
  EDF with Weighted Fair Queuing (WFQ)

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EDF Details

• Each path l is associated with three quantities
• A variable , which is the time the channel
  becomes available next.
• , the one-way wireline delay (estimate) of
  the path
• , the bandwidth negotiated
• - the arrival time, - the size of packet
  i,
• Packet i scheduled on path l would be delivered
  at the MH at
• EDF schedules the packet on the path p for which
• is updated to

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Performance of EDF

• How well can EDF perform?
• Can the application QoS requirements be met?
• Is performance as good as having a Single-Link
  (SL) with the same aggregated bandwidth?
• Approach
• Analysis
• Prove fairness of EDF in distributing bits across
  different links
• Compare EDF with SL in terms of work, delay,
  jitter and buffering
• Simulation
• Consider application performance level metrics
• Measure sensitivity of the algorithm to bandwidth
  asymmetry, number of interfaces, delay variation,
  channel losses

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Properties of EDF

• Notation
• - max packet Size, number of
  interfaces, - bandwidth of link l, -
  weight of link l (normalized bandwidth)
• Assumptions
• , and
• When packets are of constant size, they arrive in
  order at the client
• For variable sized packets Given P packets to
  transmit, the maximum difference in normalized
  bits allocated to any two pair of links is
  
• For WRR, this amount is a function of P and can
  be unbounded
• For SRR it is

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Properties of EDF (Contd.)

• For any time t, the difference between the total
  number of bits W serviced by SL and EDF is
• The difference in delay experienced by a packet i
  in SL and EDF is bounded by
• The jitter experienced by a packet i without
  buffering is upper bounded by
• The jitter experienced by a packet I with
  buffering is upper bounded by
• The buffer size needed to deliver the packets in
  order is

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Experimental Methodology

• Trace driven simulation
• Server
• Video frame traces office cam (Mpeg4 and H.263)
• For MPEG-4, avg 400kbps, peak - 2Mbps, frame
  period - 40ms
• For H.263, avg 260kbps, peak 1.5Mbps, frame
  period - variable
• Maximum packet size assumed is 1400 byte
• Home Agent
• Employs scheduling algorithm
• Base-Station
• No cross traffic
• Serve packets first-come-first-serve basis

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Experimental Methodology (Contd.)

• Client
• Begin video display after a fixed delay startup
  latency L
• Afterwards, display frames consecutively every t
  seconds (frame period)
• Arrival after playback deadline results in frame
  loss
• Startup latency bounds one-way delay of packets
• Internet Path
• Packet delay traces collected over different
  Internet paths
• Hosts on UCSD, UCB, Duke, CMU
• Wireline delay range used 15ms 22 ms (one-way)
• Algorithms under comparison
• Single Link SL
• Surplus Round Robin - SRR

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Application Performance Metrics

• Backlog in the system
• Delay experienced by packets
• Frame Loss probability - Fraction of packets that
  miss playback deadline
• Glitch Duration Number of consecutive frames
  that cannot be displayed
• Glitch Rate Number of glitches/sec

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Bandwidth Allocation
Bandwidth Needed over SL to achieve 0 frame
loss, MPEG-4, BS 3
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Backlog

• Bandwidth fixed at 600kbps

SL
EDF
SRR
Backlog in the system between HA and Client
application, MPEG-4
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Delay Distribution
Cumulative Percentage of Delay, Mpeg-4, BS3
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Frame Loss probability
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Sensitivity to Bandwidth Asymmetry
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Sensitivity to Number of Interfaces
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Extensions to EDF
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Other Results

• Delay Variation EDF
• Truncated Gaussian with mean 22ms, std. devn.
  0-10ms
• For a split 531 at 225ms,
• No variation introduces 0.26 frame loss
• 5ms variation, 0.27 frame loss
• 10ms variation, 0.28 frame loss
• Channel Losses
• Limited retransmissions help
• Other Applications
• Non-Interactive Applications
• Large tolerance for delay ? no big difference in
  relative perf.
• Video-On-Demand Applications
• High peak-to-mean rates imply over-provisioning
  of bandwidth
• Choice of scheduling algorithm does not matter

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Summary

• Network-layer architecture to enable multiple
  communication paths
• EDF scheduling algorithm reduces delay
  experienced by packets in presence of multi-path.
• An analysis of the algorithm shows that it
  doesnt differ much from idealized SL
• Trace-driven simulations
• EDF mimics SL closely
• Outperforms by a large margin WRR based approaches

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Ongoing Work

• Bandwidth Aggregation in Best-Effort Systems
• Bandwidth Estimation at MH
• Work ahead scheduling
• TCP
• Support TCP applications
• Network layer solutions
• Ad-hoc Networks
• Security