FEC-Integrated Network Traffic Shaping Using the NIProxy

1
FEC-Integrated Network Traffic Shaping Using the
NIProxy

• Maarten Wijnants, Wim LamotteHasselt University
  Expertise Centre for Digital Media (EDM)
• Wetenschapspark 2, BE-3590 Diepenbeek, Belgium
• maarten.wijnants,wim.lamotte_at_uhasselt.be

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Outline

• Background and Motivation
• Error Correction Techniques
• Network Intelligence Proxy
• Objectives Methodology
• FEC Integration in NIProxy
• Evaluation
• Experiment Description
• Experimental Results Findings
• Conclusions

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Background and Motivation

• Exchanging data over computer networks can lead
  to corruption
• Data becomes (partly) unusable for receiver
• Data corruption can be caused by
• The loss of entire packets
• E.g. insufficiently capacitated network
  infrastructure
• The introduction of bit errors
• E.g. signal interference and noise on the channel
• Irrespective of its cause, data corruption is
  likely to degrade user experience
• Effort should be made to minimize it!

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Error Correction Techniques

• 2 data corruption countermeasure categories
• Retransmission-based techniques Receiver
  requests source to retransmit missing or
  corrupted data
• Forward Error Correction (FEC) Sender
  supplements source data with redundant info which
  allows receiver to repair, to a certain extent,
  errors introduced during transmission
• FEC schemes enable lost or damaged data recovery
  without incurring RTT overhead introduced in
  retransmission-based solutions

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Error Correction Techniques

• Example FEC scheme XOR-Based Parity Coding
• Input Group of n media packets
• Output Single parity packet
• Constructed by applying the XOR operator on the
  bits stored at identical locations in the n input
  packets
• At decoding side, parity packet can be used to
  recover a singly lost/corrupted packet
• By XOR-ing the (n - 1) correctly received media
  packets with the (also perfectly received) parity
  pack
• Important advantage Run-time adaptability Trade
  off protection for BW (by changing n)

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Error Correction Techniques

• Retransmission- and FEC-based schemes share a
  common disadvantage
• Both introduce overhead in terms of the amount of
  data that needs to be transmitted
• I.e. the BW requirements of data flows are raised
• The surprising scenario might occur where the
  addition of error protection yields an increased
  instead of a decreased error rate
• Deliberate decision making regarding the amount
  of protection to add to network traffic is
  advocated!

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Network Intelligence Proxy

• Network intermediary (a proxy)
• Can be incorporated in existing IP networks
• Goal Optimize QoE of users of distributed
  applications
• Approach Gather context and improve MM handling
  capabilities of transportation network to enable
  user QoE optimization
• Network traffic shaping
• Multimedia service provisioning
• NOT transparent

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Network Intelligence ProxyMethodology

• NIProxy introduces intelligence in the
  networking infrastructure
• 2 distinct sources of contextual info are queried
• Source 1 Transportation network
• Contextual knowledge Quantitative
  network-related measurements and statistics
• Obtained through active network probing
  monitoring
• Source 2 Distributed application
• Contextual knowledge Any application-related
  knowledge that is deemed relevant
• Needs to be provided by the application software

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Network Intelligence ProxyNetwork Traffic Shaping

• Orchestrate bandwidth consumption by arranging
  flows in a stream hierarchy
• Tree-like structure expresses flow relationship
• Internal nodes implement bandwidth distribution
  strategy
• Mutex Available bandwidth BW allotted to child
  with largest still satisfiable bandwidth
  requirement
• Percentage Each child i is granted its
  corresponding percentage value of
  the distributable bandwidth BW, i.e.
• Leaf nodes correspond with actual flows
• Discrete leaf Switch BW usage of associated
  flow between discrete number of levels

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Network Intelligence ProxyNetwork Traffic Shaping

• Sibling dependencies framework
• Enables dependencies to be enforced between
  sibling nodes in the stream hierarchy
• Currently only 1 type of dependency defined,
  namely SD_BW_ALLOC_CONSTRAINED
• Set of supported sibling dependency types readily
  extensible
• SD_BW_ALLOC_CONSTRAINED dependency between
  sibling nodes A and B specifies that B is allowed
  to consume bandwidth if and only if As bandwidth
  consumption is non-zero
• Node A can borrow bandwidth assigned to B

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Network Intelligence Proxy Multimedia Service
Provision

• NIProxy acts as service provision platform
• In-network execution of (context-aware) services
  on transported data
• Implemented using a plug-in based design
• Each service corresponds to a NIProxy plug-in
• Service cooperation through chaining
• NTS and MM service provision integrated in an
  interoperable manner!
• Services can query/influence the bandwidth
  distribution strategy devised for clients
• Unlocks extra QoE optimization possibilities

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FEC Integration in NIProxy

• Given its negative impact on user experience,
  techniques to counter lost or damaged data are
  meaningful extensions of the NIProxys feature
  list
• Adaptive XOR-Based Parity coding implemented as
  NIProxy service
• Integrated approach with NIProxy NTS
• FEC-generated network traffic might consume
  significant amounts of bandwidth
• Should be reckoned with by NIProxys NTS
  mechanism
• Necessitates FEC traffic inclusion in stream
  hierarchy

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FEC Integration in NIProxy

• FEC incorporation in stream hierarchy
• Redundant FEC parity data is represented as
  discrete stream hierarchy leaf node
• Defines a discrete bandwidth consumption level
  for each supported input packet grouping size
• FEC data also needs to be adequately related to
  the media stream it protects (JSCC)
• Deliberately amortize BW that has been reserved
  for FEC-protected traffic among the media data
  and its FEC overhead
• In this paper By using a Percentage node
• Adjusting the percentage values assigned to both
  nodes allows the JSCC process to be controlled
• SD_BW_ALLOC_CONSTRAINED dependency between the
  nodes representing the media and its FEC
  protection
• FEC can consume BW if and only if associated
  media flow is enabled

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FEC Integration in NIProxy

• Operation of the NIProxy FEC service
• Performs 2 initialization tasks on discovery of
  network stream eligible for FEC protection
• Instantiate a XOR-based parity encoder
• Inform NTS process of possibility to FEC protect
  the stream and the thereby associated BW
  requirements
• Main processing loop
• Service exploits its interface with NTS to
  determine discrete level to which the FEC data
  for the media flow that is being processed is
  currently set
• FEC encoder is switched to the input grouping
  size that is associated with this level
• Packet is fed encoder (possibly producing parity
  packet)

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EvaluationExperimental Setup

• FEC support advantageously influences NIProxys
  user QoE optimization capabilities?
• Video streaming case study

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EvaluationExperiment Description

• MM server maintained 2 simultaneous RTP video
  sessions with client VS1 and VS2
• Video data emitted in unprotected form
• NIProxy had its FEC service loaded
• Parity coding per 3 or per 6 input packets
• Only video session VS2 was marked as being
  eligible for receiving FEC protection
• Identical video fragment streamed over both
  sessions to allow meaningful comparison
• NIProxy video transcoding service also loaded
• To address bandwidth shortage on the access
  network

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EvaluationExperiment Description

• Experiment was executed twice
• Once without and once with the netem component
  introducing packet loss on last mile
• Access network throughput artificially modified
  at predefined points in time (5 times in total)
• Investigate effect on the way the NIProxy shaped
  the network traffic destined for the receiving
  client
• All other conditions remained constant
• Bandwidth modifications conceptually divided the
  experiment into 6 discrete intervals

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EvaluationExperiment Description

• Stream hierarchy which steered the shaping of the
  network traffic

XOR disabledn 3 n 6
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EvaluationExperimental Results

• Execution 1 Error-free environment

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EvaluationExperimental Results

• Execution 2 10 packet loss

Playback VS2 less distorted! ?
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EvaluationExperimental Results

• Findings and observations
• Capacity of clients access connection respected
• Delineated BW distribution strategy successfully
  enforced
• Access bandwidth shared equitably among video
  sessions
• Example of potential of supporting interoperation
  between NIProxy services and bandwidth brokering
• E.g. JSCC process steered entirely by NIProxys
  NTS
• JSCC might require quality of MM data to be
  reduced to accommodate its FEC protection
• Therefore quality VS2 sometimes lower than VS1
• FEC overhead however enables packet loss recovery
• Playback VS2 smoother and less perceptually
  degraded
• Lower quality yet less distorted More enjoyable
  viewing experience than high-quality distorted
  video (subjective)

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Conclusions

• MM data might arrive in corrupted form during its
  propagation through error-prone networks
• Typical outcome Deteriorated media presentation
• Likely source for user frustration
• FEC schemes possess the ability to alleviate
  detrimental effects of data corruption
• Enable receivers to repair compromised data
• FEC incorporated in NIProxy (XOR parity code)
• FEC operations directed by NTS ? Ensure XOR BW
  justified
• Evaluated using video streaming case study
• Results corroborate that FEC coding is valuable
  addition to NIProxys toolset to improve user QoE