Rtcp.h File Reference

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Macros
#define	RTCP_PLI_PACKET_LEN   (RTCP_PACKET_HEADER_LEN + 2 * SIZEOF(UINT32))
#define	TWCC_TICKS_PER_SECOND   (1000000LL / 250)
#define	MICROSECONDS_PER_SECOND   1000000LL
#define	MILLISECONDS_PER_SECOND   1000LL
#define	TWCC_PACKET_LOST_TIME   ((UINT64) (-1LL))
#define	TWCC_PACKET_UNITIALIZED_TIME   0
#define	TWCC_ESTIMATOR_TIME_WINDOW   (4 * HUNDREDS_OF_NANOS_IN_A_SECOND)
#define	TWCC_MAX_PACKET_STATUS_COUNT   2048
#define	TWCC_FB_PAYLOAD_MIN_LEN   16
#define	TWCC_TRENDLINE_SMOOTHING_FACTOR   0.2
#define	TWCC_FB_PACKETCHUNK_SIZE   2
#define	IS_TWCC_RUNLEN(packetChunk)
#define	TWCC_RUNLEN_STATUS_SYMBOL(packetChunk)
#define	TWCC_RUNLEN_GET(packetChunk)
#define	TWCC_IS_NOTRECEIVED(statusSymbol)
#define	TWCC_ISRECEIVED(statusSymbol)
#define	TWCC_RUNLEN_ISRECEIVED(packetChunk)
#define	TWCC_STATUSVECTOR_IS_2BIT(packetChunk)
#define	TWCC_STATUSVECTOR_SSIZE(packetChunk)
#define	TWCC_STATUSVECTOR_SMASK(packetChunk)
#define	TWCC_STATUSVECTOR_STATUS(packetChunk, i)
#define	TWCC_STATUSVECTOR_COUNT(packetChunk)
#define	TWCC_PACKET_STATUS_COUNT(payload)

Enumerations
enum	TWCC_STATUS_SYMBOL { TWCC_STATUS_SYMBOL_NOTRECEIVED = 0 , TWCC_STATUS_SYMBOL_SMALLDELTA , TWCC_STATUS_SYMBOL_LARGEDELTA }

Functions
STATUS	onRtcpPacket (PKvsPeerConnection, PBYTE, UINT32)
STATUS	onRtcpRembPacket (PRtcpPacket, PKvsPeerConnection)
STATUS	onRtcpPLIPacket (PRtcpPacket, PKvsPeerConnection)
STATUS	createRtcpPLIPacket (UINT32, UINT32, PBYTE, PUINT32)
STATUS	parseRtcpTwccPacket (PRtcpPacket, PTwccManager)
STATUS	onRtcpTwccPacket (PRtcpPacket, PKvsPeerConnection)
STATUS	updateTwccHashTable (PTwccManager, PINT64, PUINT64, PUINT64, PUINT64, PUINT64)
STATUS	computeTwccTrendline (PTwccManager, PDOUBLE, PDOUBLE)
	Estimates network congestion trend using least-squares linear regression on accumulated one-way delay variations, smoothed with an exponential moving average (EMA).

Macro Definition Documentation

IS_TWCC_RUNLEN

#define IS_TWCC_RUNLEN

(

packetChunk

)

Value:

((((packetChunk) >> 15u) & 1u) == 0)

MICROSECONDS_PER_SECOND

#define MICROSECONDS_PER_SECOND   1000000LL

MILLISECONDS_PER_SECOND

#define MILLISECONDS_PER_SECOND   1000LL

RTCP_PLI_PACKET_LEN

#define RTCP_PLI_PACKET_LEN   (RTCP_PACKET_HEADER_LEN + 2 * SIZEOF(UINT32))

TWCC_ESTIMATOR_TIME_WINDOW

#define TWCC_ESTIMATOR_TIME_WINDOW   (4 * HUNDREDS_OF_NANOS_IN_A_SECOND)

TWCC_FB_PACKETCHUNK_SIZE

#define TWCC_FB_PACKETCHUNK_SIZE   2

TWCC_FB_PAYLOAD_MIN_LEN

#define TWCC_FB_PAYLOAD_MIN_LEN   16

TWCC_IS_NOTRECEIVED

#define TWCC_IS_NOTRECEIVED

(

statusSymbol

)

Value:

((statusSymbol) == TWCC_STATUS_SYMBOL_NOTRECEIVED)

TWCC_ISRECEIVED

#define TWCC_ISRECEIVED

(

statusSymbol

)

Value:

((statusSymbol) == TWCC_STATUS_SYMBOL_SMALLDELTA || (statusSymbol) == TWCC_STATUS_SYMBOL_LARGEDELTA)

TWCC_MAX_PACKET_STATUS_COUNT

#define TWCC_MAX_PACKET_STATUS_COUNT   2048

TWCC_PACKET_LOST_TIME

#define TWCC_PACKET_LOST_TIME   ((UINT64) (-1LL))

TWCC_PACKET_STATUS_COUNT

#define TWCC_PACKET_STATUS_COUNT

(

payload

)

Value:

(getUnalignedInt16BigEndian((payload) + 10))

TWCC_PACKET_UNITIALIZED_TIME

#define TWCC_PACKET_UNITIALIZED_TIME   0

TWCC_RUNLEN_GET

#define TWCC_RUNLEN_GET

(

packetChunk

)

Value:

((packetChunk) & 0x1fffu)

TWCC_RUNLEN_ISRECEIVED

#define TWCC_RUNLEN_ISRECEIVED

(

packetChunk

)

Value:

TWCC_ISRECEIVED(TWCC_RUNLEN_STATUS_SYMBOL(packetChunk))

TWCC_RUNLEN_STATUS_SYMBOL

#define TWCC_RUNLEN_STATUS_SYMBOL

(

packetChunk

)

Value:

(((packetChunk) >> 13u) & 3u)

TWCC_STATUSVECTOR_COUNT

#define TWCC_STATUSVECTOR_COUNT

(

packetChunk

)

Value:

(TWCC_STATUSVECTOR_IS_2BIT(packetChunk) ? 7 : 14)

TWCC_STATUSVECTOR_IS_2BIT

#define TWCC_STATUSVECTOR_IS_2BIT

(

packetChunk

)

Value:

(((packetChunk) >> 14u) & 1u)

TWCC_STATUSVECTOR_SMASK

#define TWCC_STATUSVECTOR_SMASK

(

packetChunk

)

Value:

(TWCC_STATUSVECTOR_IS_2BIT(packetChunk) ? 2u : 1u)

TWCC_STATUSVECTOR_SSIZE

#define TWCC_STATUSVECTOR_SSIZE

(

packetChunk

)

Value:

(TWCC_STATUSVECTOR_IS_2BIT(packetChunk) ? 2u : 1u)

TWCC_STATUSVECTOR_STATUS

#define TWCC_STATUSVECTOR_STATUS	(		packetChunk,
			i )

Value:

    (((packetChunk) >> (14u - (i) * TWCC_STATUSVECTOR_SSIZE(packetChunk))) & TWCC_STATUSVECTOR_SMASK(packetChunk))

TWCC_TICKS_PER_SECOND

#define TWCC_TICKS_PER_SECOND   (1000000LL / 250)

TWCC_TRENDLINE_SMOOTHING_FACTOR

#define TWCC_TRENDLINE_SMOOTHING_FACTOR   0.2

Enumeration Type Documentation

TWCC_STATUS_SYMBOL

enum TWCC_STATUS_SYMBOL

Enumerator
TWCC_STATUS_SYMBOL_NOTRECEIVED
TWCC_STATUS_SYMBOL_SMALLDELTA
TWCC_STATUS_SYMBOL_LARGEDELTA

Function Documentation

computeTwccTrendline()

STATUS computeTwccTrendline	(	PTwccManager	pTwccManager,
		PDOUBLE	pDelayTrend,
		PDOUBLE	pQueueDelay )

Estimates network congestion trend using least-squares linear regression on accumulated one-way delay variations, smoothed with an exponential moving average (EMA).

Algorithm overview:

1. For each consecutive packet pair (i-1, i), compute the inter-arrival delay variation: d_i = (recvTime_i - recvTime_{i-1}) - (sendTime_i - sendTime_{i-1}) A positive d_i means the network took longer to deliver packet i than packet i-1.
2. Accumulate these variations into a running sum (the "accumulated delay"): D_i = D_{i-1} + d_i (where D_0 = 0) This represents the total queuing delay buildup over the observation window.
3. Fit a line to the points (x_i, y_i) = (i, D_i) using ordinary least-squares regression. The slope formula is: rawSlope = (n * sum(x_i * y_i) - sum(x_i) * sum(y_i)) / (n * sum(x_i^2) - (sum(x_i))^2) A positive slope indicates delay is growing (congestion building up). A near-zero slope indicates stable network conditions. A negative slope indicates delay is decreasing (congestion clearing).
4. Smooth the slope with an EMA to reduce noise: smoothedSlope = alpha * rawSlope + (1 - alpha) * prevSmoothedSlope where alpha = TWCC_TRENDLINE_SMOOTHING_FACTOR (0.2 by default).

Parameters

[in]	pTwccManager	TWCC manager containing packet timing history
[out]	pDelayTrend	Smoothed slope in ms per sample (positive = congestion building)
[out]	pQueueDelay	Total accumulated delay variation in ms over the window

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createRtcpPLIPacket()

STATUS createRtcpPLIPacket	(	UINT32	senderSsrc,
		UINT32	mediaSsrc,
		PBYTE	pRawPacket,
		PUINT32	pPacketLen )

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onRtcpPacket()

STATUS onRtcpPacket	(	PKvsPeerConnection	pKvsPeerConnection,
		PBYTE	pBuff,
		UINT32	buffLen )

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onRtcpPLIPacket()

STATUS onRtcpPLIPacket	(	PRtcpPacket	pRtcpPacket,
		PKvsPeerConnection	pKvsPeerConnection )

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onRtcpRembPacket()

STATUS onRtcpRembPacket	(	PRtcpPacket	pRtcpPacket,
		PKvsPeerConnection	pKvsPeerConnection )

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onRtcpTwccPacket()

STATUS onRtcpTwccPacket	(	PRtcpPacket	pRtcpPacket,
		PKvsPeerConnection	pKvsPeerConnection )

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parseRtcpTwccPacket()

STATUS parseRtcpTwccPacket	(	PRtcpPacket	pRtcpPacket,
		PTwccManager	pTwccManager )

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updateTwccHashTable()

STATUS updateTwccHashTable	(	PTwccManager	pTwccManager,
		PINT64	duration,
		PUINT64	receivedBytes,
		PUINT64	receivedPackets,
		PUINT64	sentBytes,
		PUINT64	sentPackets )

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