FEC-Integrated Network Traffic Shaping Using the NIProxy

Maarten Wijnants, Wim Lamotte

Hasselt University – Expertise Centre for Digital Media (EDM)Wetenschapspark 2, BE-3590 Diepenbeek, Belgium

{maarten.wijnants,wim.lamotte}@uhasselt.be

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 transparent15/10/2009 EMERGING2009 7

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 A’s 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 NIProxy’s 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 NIProxy’s 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 NIProxy’s user QoE optimization capabilities?

• Video streaming case study

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High capacity; Error-free Resource constrained; Error-prone

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

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Unprotected Video Session VS1

FEC protected Video Session VS2

SD_BW_ALLOC_CONSTRAINED

Static JSCC(90%-10%)

XOR disabledn = 3; n = 6

Split access bandwidthequitably

EvaluationExperimental Results

• Execution 1: Error-free environment

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All streams at max qualityAccess BW gradually more constrainedIncreasing flow BW reductions required

VS2 transcoded to lower quality

FEC coding disabled

EvaluationExperimental Results

• Execution 2: 10% packet loss

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Residual vs original packet loss VS2 = 92 vs 210

Video playback at destination no longer perfect!

Playback VS2 less distorted!

EvaluationExperimental Results

• Findings and observations– Capacity of client’s 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 NIProxy’s 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

NIProxy’s toolset to improve user QoE

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