拥塞控制算法举例.docx

拥塞控制算法举例.docx

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拥塞控制算法举例

1．拥塞控制算法

NAATA（intsentByte,intRcvByte）{

staticintinit=1;//initialstateflag

staticintinit_bit;//initialbit-rate（userrequestedbit-rate）

staticintmin_bit;//minimumbit-rate

staticintmax_bit;//maximumbit-rate

staticinttmp;//temporaltargetbit-rate

staticinttarget_tr_bit;//targetbit-rate

staticintcount;//timecount

staticintflag=0;//flagforcontinousproblem

staticintthreshold_time=10;//thresholdtimetorecovertargetbit-rate

intthreshold_fail=0;//thresholdtodetecttransmissionfailure

intdiff=sentByte-RcvByte;

if（diff>threshold_fail）{//whentransmissionfailureoccurs

if（init）{//whenfirsttransmissionfailureoccurs

target_tr_bit=init_bit/2;

min_bit=max_bit=target_tr_bit;

init=0;

}elseif（flag==1）{//whencontinuoustransmissionfailureoccurs

target_tr_bit=max_bit/2;

min_bit=0;

threshold_time+=10;

}else{//whentheothertransmissionfailureoccurs

target_tr_bit=（max_bit+min_bit）/2;

min_bit=target_tr_bit;

threshold_time+=10;

}

flag=1;//transmissionfailureoccurred

count=0;

}else{//whennotransmissionfailureoccurs

flag=0;//notransmissionfailure

tmp=target_tr_bit+increasedbit-rate;//calculatetemporaltargetbit-rate

if（tmp

target_tr_bit=max_bit=tmp;

}elseif（tmp>=init_bit）{//whentmpissameasinitialbit-rate

target_tr_bit=init_bit;

count++;

if（count>=threshold_time）{//whencountisgreaterthanthreshold

min_bit=0;

threshold_time-=10;

count=0;

}

}elseif（tmp>=max_bit）{//whentmpisgreaterthanbandwidth

target_tr_bit=max_bit;

count++;

if（count>=threshold_time）{//whencountisgreaterthanthreshold

min_bit=max_bit;

max_bit=init_bit;

count=0;

threshold_time-=10;

}

}

}

returntarget_tr_bit;

}

Althoughthequalityofplaymediadropsduetothelowbit-rate,itisbetterthanthejitteringandceasingphenomenaofmediastreaming.Ifthestreamingbit-rateiskeptastheinitialbit-rateinthepoornetworkbandwidthenvironment,thejitteringandceasingphenomenacannotbeavoided.

2．轨道交换

//-------------------SetTrackQualityLevelenQTRTPFile.cpp-------------------//

voidQTRTPFile:

:

SetTrackQualityLevel（RTPTrackListEntry*inEntry,UInt32inNewQualityLevel,UInt32

inMaxQualityLevel）

{

if（inNewQualityLevel!

=inEntry->QualityLevel）

{

UInt32threshold=3*（inMaxQualityLevel/4）;

if（inNewQualityLevel>threshold&&inEntry->QualityLevel

>QualityLevel!

=0）

{

inEntry->QualityLevel=inMaxQualityLevel*0.4;

this->SwapTracks（false）;

return;

}

elseif（inNewQualityLevel==0&&inEntry->QualityLevel>inNewQualityLevel&&inEntry-

>QualityLevel!

=10）

{

inEntry->QualityLevel=0;

this->SwapTracks（true）;

return;

}

inEntry->QualityLevel=inNewQualityLevel;

}

}

//-------------------UpdateTimeAndQualityenRTPStream3GPP.cpp-------------------//

voidRTPStream3GPP:

:

UpdateTimeAndQuality（SInt64curTime）

{

fAdjustTime=kNoChange;

fAdjustSize=kNoChange;

if（!

RateAdaptationEnabled（））

return;

Bool16limitTargetDelay=true;

UInt32maxTargetDelayMilli=10000;//5000;

UInt32adjustedFreeBuffer=fLastReportedFreeBufferSpace;

UInt32adjustTargetDelay=fTargetBufferingDelay;

if（limitTargetDelay）

{

if（adjustTargetDelay>maxTargetDelayMilli）//makethisconstantapref

adjustTargetDelay=maxTargetDelayMilli;

}

if（fBufferSize>RTCPNaduPacket:

:

kMaximumReportableFreeBufferSpace）

fBufferSize=RTCPNaduPacket:

:

kMaximumReportableFreeBufferSpace;

UInt32maxUsableBufferSizeBytes=fBufferSize;

UInt32extraBufferMultipleInSeconds=2;//useupto3timestherequestedtargetdelayin

bytes

UInt32maxUsableDelaySecs=extraBufferMultipleInSeconds*（adjustTargetDelay/1000）;

UInt32movieByteRate=fMovieBitRate>>3;//bitstobytes

UInt32bufferUsage=fBufferSize-fLastReportedFreeBufferSpace;

UInt32bufferDelay=fLastReportedBufferingDelay;

if（bufferUsage>fBufferSize）//thereismorereportedfreebufferthanthemaximum--not

goodforourratiosbutagoodsituationattheclienti.e.nobufferoverrunhere.

{

bufferUsage=fBufferSize/2;//Havetopicksomethingsouse50%.

}

DEBUG_PRINTF（（"reportedbuffersize=%"_U32BITARG_"reportedFreeBuffer=%"_U32BITARG_"

currentcalculatedbufferUsage=%"_U32BITARG_"\n",fBufferSize,

fLastReportedFreeBufferSpace,bufferUsage））;

DEBUG_PRINTF（（"AvgMovieBitRate=%luoriginaltargetdelay=%luadjustedTargetDelay=%ld

\n",fMovieBitRate,fTargetBufferingDelay,adjustTargetDelay））;

if（qtssVideoPayloadType==fRTPStream.GetPayLoadType（）&&fMovieBitRate>0&&

adjustTargetDelay>0）//limithowmuchweuse

{

maxUsableBufferSizeBytes=maxUsableDelaySecs*movieByteRate;//buffertime*bitratefor

movieisbiggerthananysinglestreambuffer

if（maxUsableBufferSizeBytes>fBufferSize）//reportedsizeissmallerthanourbuffer

target

{maxUsableBufferSizeBytes=fBufferSize;

if（maxUsableBufferSizeBytes

maxUsableBufferSizeBytes=movieByteRate;

UInt32newTargetDelay=（maxUsableBufferSizeBytes/movieByteRate）*1000;

if（newTargetDelay

adjustTargetDelay=newTargetDelay;

}

if（adjustedFreeBuffer>maxUsableBufferSizeBytes）

adjustedFreeBuffer=maxUsableBufferSizeBytes;

UInt32freeBytes=fBufferSize-bufferUsage;

if（freeBytes>fBufferSize）

bufferUsage=maxUsableBufferSizeBytes/2;

DEBUG_PRINTF（（"ADJUSTINGbufferusageandtargetdelay:

maxUsableBufferSizeBytes=%lu

adjustedFreeBuffer=%lubufferUsage=%luadjustedTargetDelay=%lu\n",maxUsableBufferSizeBytes,

adjustedFreeBuffer,bufferUsage,adjustTargetDelay））;

}

DEBUG_PRINTF（（"CalculatedmaxUsableBufferSize=%"_U32BITARG_"reported

fBufferSize=%"_U32BITARG_"reportedbufferdelay=%"_U32BITARG_"currentcalculatedbufferUsage=

%"_U32BITARG_"\n",maxUsableBufferSizeBytes,fBufferSize,bufferDelay,bufferUsage））;

//bufferDelayshouldreallybethenetworkdelaybecauseifbufferdelaywerereallylargethat

wouldbeok

//itissupposedtobe-1ifnotsupportedorarealvalue.Someclientssend0incorrectly.

//ifbufferdelayissmallthatshouldmeanthebufferisemptyandaunder-runfailure

occurred.

if（bufferDelay==0）

bufferDelay=kUInt32_Max;

doublebufferUsageRatio=static_cast（bufferUsage）/maxUsableBufferSizeBytes;

doublebufferDelayRatio=static_cast（bufferDelay）/adjustTargetDelay;

DEBUG_PRINTF（（"bufferUsageRatio=%fbufferDelayRatio=%f\n",bufferUsageRatio,

bufferDelayRatio））;

if（!

fStartDoingAdaptation）

{

//ThisisusedtopreventQTSSfromthinninginthebeginningofthestream,whenthebuffering

delayandusageareexpectedtobelowRateadaptationwillstartwhenEITHERofthetwolow

watermarksforthinninghavepassed,ORthemediahasbeenplayingforthetargetbufferingdelay.

Theidealsituationforthecurrentcodeis2xormorebuffersizetotargettime.Sotargettime

convertedtobytesshouldbe50%orlessthebuffersizetoavoidoverrunthisoneisagressiveand

workswellwithNokiawhenallisgoodandthereisextrabandwidthsoitmakesagoodnetworklook

good.

if（bufferUsageRatio>=0.7）//startactiverateadaptwhenclientis70%full

{fStartDoingAdaptation=true;/*qtss_printf（"bufferusage\n"）;*/}

elseif（curTime-fRTPStream.GetSession（）.GetFirstPlayTime（）>=15000）//butdon'twait

longerthan15seconds

{fStartDoingAdaptation=true;}

else//neithercriteriawasmet.//speedupwhilewaitingforthebuffertofill.

{fAdjustTime=kAdjustUpUp;

}

if（fStartDoingAdaptation）

{fNumLargeRTT=0;

fNumSmallRTT=-3;//Delaythefirstrateincrease

}

}

if（fStartDoingAdaptation）

{

SInt32currentQualityLevel=fRTPStream.GetQualityLevel（）;

if（currentQualityLevel>（fRTPStream.GetNumQualityLevels（）*0.75）||currentQualityLevel<1）

{

fRTPStream.SetQualityLevel（20）;

}

//newcodeworksgoodforNokiaN93onwifiandokforslowlinks（needssomemorecomparison

testingagainstnonrateadaptcodeandagainstbuild520orearlier）

if（bufferDelay!

=kUInt32_Max）//notsupported

{

DEBUG_PRINTF（（"rateadaptisusingdelayratioandbuffersize\n\n"））;

//Thebufferingdelayinformationisavailable.

//shouldIspeeduporslowdown?

ADelayRatioof100%isatargetnotaminimumandnotamaximum.

if（bufferDelayRatio<2.0）//allowupto200%

fAdjustTime=kAdjustUpUp;

else

fAdjustTime=kAdjustDown;

if（bufferUsageRatio>=0.7）//ifyouareindangerofbuffer-overflowingbecausethe

buffersizeistoosmallforthemovie,alsoslow

fAdjustTime=kAdjustDown;

elseif（bufferUsageRatio<0.5&&bufferDelayRatio>2.5）//stoppushing.

fAdjustTime=kAdjustDownDown;

elseif（bufferUsageRatio<0.5&&bufferDelayRatio>2.0）//stoppushing.

fAdjustTime=kAdjustDown;

elseif（bufferUsageRatio<0.5&&bufferDelayRatio>0.5）//trytopushuphard.

{fAdjustTime=kAdjustUpUp;

fAdjustSize=kAdjustUp;

}

//shouldIthinorthicken?

if（bufferUsageRatio<0.2&&bufferDelayRatio>2.5）//avoidunderflowsincethe

bandwidthislow.

{fAdjustSize=kAdjustDown;

fAdjustTime=kAdjustUpUp;

}

elseif（bufferUsageRatio<=0.1）//trythickening

{fAdjustSize=kAdjustUpUp;

fAdjustTime=kAdjustUpUp;

}

elseif（bufferUsageRatio<=0.3&&bufferDelayRatio<1.0）//stillindangerofunderflow

fAdjustSize=kNoChange;

elseif（bufferUsageRatio<0.7）//nolongerindangerofunderflow;oktothick

fAdjustSize=kAdjustUp;

else

fAdjustSize=kNoChange;

}

else

{

DEBUG_PRINTF（（"rateadaptisusingonlybuffersize\n"））;

//Thebufferingdelayisnotavailable;wemakethin/slowdecisionsbasedonjustthe

bufferusagealone

if（bufferUsageRatio>0.9）//needtoslowandthintoavoidoverflow

{

fAdj