BIC congestion control algorithm. More...

#include "tcp-bic.h"

Inheritance diagram for ns3::TcpBic:

Collaboration diagram for ns3::TcpBic:

Public Member Functions
	TcpBic ()
	Constructor.

	TcpBic (const TcpBic &sock)
	Copy constructor.

Ptr< TcpCongestionOps >	Fork () override
	Copy the congestion control algorithm across sockets.

std::string	GetName () const override
	Get the name of the congestion control algorithm.

uint32_t	GetSsThresh (Ptr< const TcpSocketState > tcb, uint32_t bytesInFlight) override
	Get the slow start threshold after a loss event.

void	IncreaseWindow (Ptr< TcpSocketState > tcb, uint32_t segmentsAcked) override
	Congestion avoidance algorithm implementation.

Public Member Functions inherited from ns3::TcpCongestionOps
	TcpCongestionOps ()

	TcpCongestionOps (const TcpCongestionOps &other)
	Copy constructor.

	~TcpCongestionOps () override

virtual void	CongControl (Ptr< TcpSocketState > tcb, const TcpRateOps::TcpRateConnection &rc, const TcpRateOps::TcpRateSample &rs)
	Called when packets are delivered to update cwnd and pacing rate.

virtual void	CongestionStateSet (Ptr< TcpSocketState > tcb, const TcpSocketState::TcpCongState_t newState)
	Trigger events/calculations specific to a congestion state.

virtual void	CwndEvent (Ptr< TcpSocketState > tcb, const TcpSocketState::TcpCAEvent_t event)
	Trigger events/calculations on occurrence of congestion window event.

virtual Ptr< TcpCongestionOps >	Fork ()=0
	Copy the congestion control algorithm across sockets.

virtual std::string	GetName () const =0
	Get the name of the congestion control algorithm.

virtual uint32_t	GetSsThresh (Ptr< const TcpSocketState > tcb, uint32_t bytesInFlight)=0
	Get the slow start threshold after a loss event.

virtual bool	HasCongControl () const
	Returns true when Congestion Control Algorithm implements CongControl.

virtual void	IncreaseWindow (Ptr< TcpSocketState > tcb, uint32_t segmentsAcked)
	Congestion avoidance algorithm implementation.

virtual void	Init (Ptr< TcpSocketState > tcb)
	Set configuration required by congestion control algorithm.

virtual void	PktsAcked (Ptr< TcpSocketState > tcb, uint32_t segmentsAcked, const Time &rtt)
	Timing information on received ACK.

Public Member Functions inherited from ns3::Object
	Object ()
	Constructor.

	~Object () override
	Destructor.

void	AggregateObject (Ptr< Object > other)
	Aggregate two Objects together.

void	Dispose ()
	Dispose of this Object.

AggregateIterator	GetAggregateIterator () const
	Get an iterator to the Objects aggregated to this one.

TypeId	GetInstanceTypeId () const override
	Get the most derived TypeId for this Object.

template<typename T >
Ptr< T >	GetObject () const
	Get a pointer to the requested aggregated Object.

template<>
Ptr< Object >	GetObject () const
	Specialization of () for objects of type ns3::Object.

template<typename T >
Ptr< T >	GetObject (TypeId tid) const
	Get a pointer to the requested aggregated Object by TypeId.

template<>
Ptr< Object >	GetObject (TypeId tid) const
	Specialization of (TypeId tid) for objects of type ns3::Object.

void	Initialize ()
	Invoke DoInitialize on all Objects aggregated to this one.

bool	IsInitialized () const
	Check if the object has been initialized.

void	UnidirectionalAggregateObject (Ptr< Object > other)
	Aggregate an Object to another Object.

Public Member Functions inherited from ns3::SimpleRefCount< Object, ObjectBase, ObjectDeleter >
	SimpleRefCount ()
	Default constructor.

	SimpleRefCount (const SimpleRefCount &o)
	Copy constructor.

uint32_t	GetReferenceCount () const
	Get the reference count of the object.

SimpleRefCount &	operator= (const SimpleRefCount &o)
	Assignment operator.

void	Ref () const
	Increment the reference count.

void	Unref () const
	Decrement the reference count.

Public Member Functions inherited from ns3::ObjectBase
virtual	~ObjectBase ()
	Virtual destructor.

void	GetAttribute (std::string name, AttributeValue &value) const
	Get the value of an attribute, raising fatal errors if unsuccessful.

bool	GetAttributeFailSafe (std::string name, AttributeValue &value) const
	Get the value of an attribute without raising errors.

virtual TypeId	GetInstanceTypeId () const =0
	Get the most derived TypeId for this Object.

void	SetAttribute (std::string name, const AttributeValue &value)
	Set a single attribute, raising fatal errors if unsuccessful.

bool	SetAttributeFailSafe (std::string name, const AttributeValue &value)
	Set a single attribute without raising errors.

bool	TraceConnect (std::string name, std::string context, const CallbackBase &cb)
	Connect a TraceSource to a Callback with a context.

bool	TraceConnectWithoutContext (std::string name, const CallbackBase &cb)
	Connect a TraceSource to a Callback without a context.

bool	TraceDisconnect (std::string name, std::string context, const CallbackBase &cb)
	Disconnect from a TraceSource a Callback previously connected with a context.

bool	TraceDisconnectWithoutContext (std::string name, const CallbackBase &cb)
	Disconnect from a TraceSource a Callback previously connected without a context.

Static Public Member Functions
static TypeId	GetTypeId ()
	Get the type ID.

Static Public Member Functions inherited from ns3::TcpCongestionOps
static TypeId	GetTypeId ()
	Get the type ID.

Static Public Member Functions inherited from ns3::Object
static TypeId	GetTypeId ()
	Register this type.

Static Public Member Functions inherited from ns3::ObjectBase
static TypeId	GetTypeId ()
	Get the type ID.

Protected Member Functions
virtual uint32_t	Update (Ptr< TcpSocketState > tcb)
	Bic window update after a new ack received.

Protected Member Functions inherited from ns3::Object
	Object (const Object &o)
	Copy an Object.

virtual void	DoDispose ()
	Destructor implementation.

virtual void	DoInitialize ()
	Initialize() implementation.

virtual void	NotifyNewAggregate ()
	Notify all Objects aggregated to this one of a new Object being aggregated.

Protected Member Functions inherited from ns3::ObjectBase
void	ConstructSelf (const AttributeConstructionList &attributes)
	Complete construction of ObjectBase; invoked by derived classes.

virtual void	NotifyConstructionCompleted ()
	Notifier called once the ObjectBase is fully constructed.

Private Attributes
uint8_t	m_b
	Binary search coefficient.

double	m_beta
	Beta for cubic multiplicative increase.

uint32_t	m_cWndCnt
	cWnd integer-to-float counter

Time	m_epochStart
	Beginning of an epoch.

bool	m_fastConvergence
	Enable or disable fast convergence algorithm.

uint32_t	m_lastCwnd
	Last cWnd.

uint32_t	m_lastMaxCwnd
	Last maximum cWnd.

uint32_t	m_lowWnd
	Lower bound on congestion window.

uint32_t	m_maxIncr
	Maximum window increment.

uint32_t	m_smoothPart
	Number of RTT needed to reach Wmax from Wmax-B.

Friends
class	::TcpBicDecrementTest
	TcpBicDecrementTest friend class (for tests).

class	::TcpBicIncrementTest
	TcpBicIncrementTest friend class (for tests).

Additional Inherited Members
Related Functions inherited from ns3::ObjectBase
static TypeId	GetObjectIid ()
	Ensure the TypeId for ObjectBase gets fully configured to anchor the inheritance tree properly.

Detailed Description

BIC congestion control algorithm.

In TCP Bic the congestion control problem is viewed as a search problem. Taking as a starting point the current window value and as a target point the last maximum window value (i.e. the cWnd value just before the loss event) a binary search technique can be used to update the cWnd value at the midpoint between the two, directly or using an additive increase strategy if the distance from the current window is too large.

This way, assuming a no-loss period, the congestion window logarithmically approaches the maximum value of cWnd until the difference between it and cWnd falls below a preset threshold. After reaching such a value (or the maximum window is unknown, i.e. the binary search does not start at all) the algorithm switches to probing the new maximum window with a 'slow start' strategy.

If a loss occur in either these phases, the current window (before the loss) can be treated as the new maximum, and the reduced (with a multiplicative decrease factor Beta) window size can be used as the new minimum.

To maintain the performance of TCP Bic as close as possible with the Linux implementation, and at the same time maintain the friendliness with other TCP flavors, the cWnd is increased only after a certain number of ACKs are received, following RFC 6356. After the slow start phase, and after each new ACK, a value is calculated by the method Update. This number (m_cnt in the code) represents the ACK packets that should be received before increasing the cWnd by one segment. After a trivial check on the arrived ACKs (represented by m_cWndCnt in the code), the cWnd can be increased and m_cWndCnt can be set to zero, or otherwise m_cWndCnt can be increased by one and the cWnd can be left untouched.

The binary search on the cWnd size space is done by varying the returned cnt, depending on the internal state of the class (e.g. the last maximum and the current cWnd size).

The reference paper for BIC can be found in: http://an.kaist.ac.kr/courses/2006/cs540/reading/bic-tcp.pdf

This model has a number of configurable parameters that are exposed as attributes of the TcpBic TypeId. This model also exports trace sources, for tracking the congestion window, slow start threshold, and the internal state of the protocol.

More information on this implementation: http://dl.acm.org/citation.cfm?id=2756518

Config Paths

ns3::TcpBic is accessible through the following paths with Config::Set and Config::Connect:

"/NodeList/[i]/$ns3::TcpL4Protocol/SocketList/[i]/CongestionOps/$ns3::TcpBic"

Attributes

Beta: Beta for multiplicative decrease
- Set with class: ns3::DoubleValue
- Underlying type: double 0:1.79769e+308
- Initial value: 0.8
- Flags: constructwriteread
BinarySearchCoefficient: Inverse of the coefficient for the binary search. Default 4, as in Linux
- Set with class: ns3::UintegerValue
- Underlying type: uint8_t 2:255
- Initial value: 4
- Flags: constructwriteread
FastConvergence: Turn on/off fast convergence.
- Set with class: ns3::BooleanValue
- Underlying type: bool
- Initial value: true
- Flags: constructwriteread
LowWnd: Threshold window size (in segments) for engaging BIC response
- Set with class: ns3::UintegerValue
- Underlying type: uint32_t 0:4294967295
- Initial value: 14
- Flags: constructwriteread
MaxIncr: Limit on increment allowed during binary search
- Set with class: ns3::UintegerValue
- Underlying type: uint32_t 1:4294967295
- Initial value: 16
- Flags: constructwriteread
SmoothPart: Number of RTT needed to approach cWnd_max from cWnd_max-BinarySearchCoefficient. It can be viewed as the gradient of the slow start AIM phase: less this value is, more steep the increment will be.
- Set with class: ns3::UintegerValue
- Underlying type: uint32_t 1:4294967295
- Initial value: 5
- Flags: constructwriteread

No TraceSources are defined for this type.
Size of this type is 104 bytes (on a 64-bit architecture).

Definition at line 81 of file tcp-bic.h.

Constructor & Destructor Documentation

◆ TcpBic() [1/2]

ns3::TcpBic::TcpBic ( )

Constructor.

Definition at line 74 of file tcp-bic.cc.

References NS_LOG_FUNCTION.

◆ TcpBic() [2/2]

ns3::TcpBic::TcpBic ( const TcpBic & sock )

Copy constructor.

Parameters

sock	The socket to copy from.

Definition at line 84 of file tcp-bic.cc.

References NS_LOG_FUNCTION.

Member Function Documentation

◆ Fork()

Ptr< TcpCongestionOps > ns3::TcpBic::Fork ( )

overridevirtual

Copy the congestion control algorithm across sockets.

Returns: a pointer of the copied object

Implements ns3::TcpCongestionOps.

Definition at line 280 of file tcp-bic.cc.

◆ GetName()

std::string ns3::TcpBic::GetName ( ) const

overridevirtual

Get the name of the congestion control algorithm.

Returns: A string identifying the name

Implements ns3::TcpCongestionOps.

Definition at line 237 of file tcp-bic.cc.

◆ GetSsThresh()

uint32_t ns3::TcpBic::GetSsThresh	(	Ptr< const TcpSocketState >	tcb,
		uint32_t	bytesInFlight
	)

overridevirtual

Get the slow start threshold after a loss event.

Is guaranteed that the congestion control state (TcpAckState_t) is changed BEFORE the invocation of this method. The implementer should return the slow start threshold (and not change it directly) because, in the future, the TCP implementation may require to instantly recover from a loss event (e.g. when there is a network with an high reordering factor).

Parameters

tcb	internal congestion state
bytesInFlight	total bytes in flight

Returns: Slow start threshold

Implements ns3::TcpCongestionOps.

Definition at line 243 of file tcp-bic.cc.

References m_beta, m_epochStart, m_fastConvergence, m_lastMaxCwnd, m_lowWnd, ns3::Time::Min(), NS_LOG_FUNCTION, and NS_LOG_INFO.

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◆ GetTypeId()

TypeId ns3::TcpBic::GetTypeId ( )

static

Get the type ID.

Returns: the object TypeId

Definition at line 30 of file tcp-bic.cc.

References m_b, m_beta, m_fastConvergence, m_lowWnd, m_maxIncr, m_smoothPart, ns3::MakeBooleanAccessor(), ns3::MakeBooleanChecker(), ns3::MakeDoubleAccessor(), ns3::MakeUintegerAccessor(), and ns3::TypeId::SetParent().

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◆ IncreaseWindow()

void ns3::TcpBic::IncreaseWindow	(	Ptr< TcpSocketState >	tcb,
		uint32_t	segmentsAcked
	)

overridevirtual

Congestion avoidance algorithm implementation.

Mimic the function cong_avoid in Linux. New segments have been ACKed, and the congestion control duty is to update the window.

The function is allowed to change directly cWnd and/or ssThresh.

Parameters

tcb	internal congestion state
segmentsAcked	count of segments acked

Reimplemented from ns3::TcpCongestionOps.

Definition at line 101 of file tcp-bic.cc.

References m_cWndCnt, NS_LOG_FUNCTION, NS_LOG_INFO, and Update().

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◆ Update()

uint32_t ns3::TcpBic::Update ( Ptr< TcpSocketState > tcb )

protectedvirtual

Bic window update after a new ack received.

Parameters

tcb	the socket state.

Returns: The number of segments acked since the last cwnd increment.

Definition at line 140 of file tcp-bic.cc.

References m_b, m_epochStart, m_lastCwnd, m_lastMaxCwnd, m_lowWnd, m_maxIncr, m_smoothPart, ns3::Time::Min(), ns3::Simulator::Now(), NS_LOG_FUNCTION, and NS_LOG_INFO.

Referenced by IncreaseWindow().

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Friends And Related Function Documentation

◆ ::TcpBicDecrementTest

friend class ::TcpBicDecrementTest

friend

TcpBicDecrementTest friend class (for tests).

Definition at line 125 of file tcp-bic.h.

◆ ::TcpBicIncrementTest

friend class ::TcpBicIncrementTest

friend

TcpBicIncrementTest friend class (for tests).

Definition at line 120 of file tcp-bic.h.

Member Data Documentation

◆ m_b

uint8_t ns3::TcpBic::m_b

private

Binary search coefficient.

Definition at line 139 of file tcp-bic.h.

Referenced by GetTypeId(), and Update().

◆ m_beta

double ns3::TcpBic::m_beta

private

Beta for cubic multiplicative increase.

Definition at line 129 of file tcp-bic.h.

Referenced by GetSsThresh(), and GetTypeId().

◆ m_cWndCnt

uint32_t ns3::TcpBic::m_cWndCnt

private

cWnd integer-to-float counter

Definition at line 135 of file tcp-bic.h.

Referenced by IncreaseWindow().

◆ m_epochStart

Time ns3::TcpBic::m_epochStart

private

Beginning of an epoch.

Definition at line 138 of file tcp-bic.h.

Referenced by GetSsThresh(), and Update().

◆ m_fastConvergence

bool ns3::TcpBic::m_fastConvergence

private

Enable or disable fast convergence algorithm.

Definition at line 128 of file tcp-bic.h.

Referenced by GetSsThresh(), and GetTypeId().

◆ m_lastCwnd

uint32_t ns3::TcpBic::m_lastCwnd

private

Last cWnd.

Definition at line 137 of file tcp-bic.h.

Referenced by Update().

◆ m_lastMaxCwnd

uint32_t ns3::TcpBic::m_lastMaxCwnd

private

Last maximum cWnd.

Definition at line 136 of file tcp-bic.h.

Referenced by GetSsThresh(), and Update().

◆ m_lowWnd

uint32_t ns3::TcpBic::m_lowWnd

private

Lower bound on congestion window.

Definition at line 131 of file tcp-bic.h.

Referenced by GetSsThresh(), GetTypeId(), and Update().

◆ m_maxIncr

uint32_t ns3::TcpBic::m_maxIncr

private

Maximum window increment.

Definition at line 130 of file tcp-bic.h.

Referenced by GetTypeId(), and Update().

◆ m_smoothPart

uint32_t ns3::TcpBic::m_smoothPart

private

Number of RTT needed to reach Wmax from Wmax-B.

Definition at line 132 of file tcp-bic.h.

Referenced by GetTypeId(), and Update().

The documentation for this class was generated from the following files:

src/internet/model/tcp-bic.h
src/internet/model/tcp-bic.cc

Public Member Functions

Static Public Member Functions

Protected Member Functions

Private Attributes

Friends

Additional Inherited Members

Detailed Description

Config Paths

Attributes

Constructor & Destructor Documentation

◆ TcpBic() [1/2]

◆ TcpBic() [2/2]

Member Function Documentation

◆ Fork()

◆ GetName()

◆ GetSsThresh()

◆ GetTypeId()

◆ IncreaseWindow()

◆ Update()

Friends And Related Function Documentation

◆ ::TcpBicDecrementTest

◆ ::TcpBicIncrementTest

Member Data Documentation

◆ m_b

◆ m_beta

◆ m_cWndCnt

◆ m_epochStart

◆ m_fastConvergence

◆ m_lastCwnd

◆ m_lastMaxCwnd

◆ m_lowWnd

◆ m_maxIncr

◆ m_smoothPart