An implementation of TCP Vegas. More...

#include "tcp-vegas.h"

Inheritance diagram for ns3::TcpVegas:

Collaboration diagram for ns3::TcpVegas:

Public Member Functions
	TcpVegas ()
	Create an unbound tcp socket.

	TcpVegas (const TcpVegas &sock)
	Copy constructor.

	~TcpVegas () override

void	CongestionStateSet (Ptr< TcpSocketState > tcb, const TcpSocketState::TcpCongState_t newState) override
	Enable/disable Vegas algorithm depending on the congestion state.

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 slow start threshold following Vegas principle.

void	IncreaseWindow (Ptr< TcpSocketState > tcb, uint32_t segmentsAcked) override
	Adjust cwnd following Vegas linear increase/decrease algorithm.

void	PktsAcked (Ptr< TcpSocketState > tcb, uint32_t segmentsAcked, const Time &rtt) override
	Compute RTTs needed to execute Vegas algorithm.

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

	TcpNewReno (const TcpNewReno &sock)
	Copy constructor.

	~TcpNewReno () override

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

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

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

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, bool permissive=false) 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.

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::TcpNewReno
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.

Private Member Functions
void	DisableVegas ()
	Stop taking Vegas samples.

void	EnableVegas (Ptr< TcpSocketState > tcb)
	Enable Vegas algorithm to start taking Vegas samples.

Private Attributes
uint32_t	m_alpha
	Alpha threshold, lower bound of packets in network.

Time	m_baseRtt
	Minimum of all Vegas RTT measurements seen during connection.

SequenceNumber32	m_begSndNxt
	Right edge during last RTT.

uint32_t	m_beta
	Beta threshold, upper bound of packets in network.

uint32_t	m_cntRtt
	Number of RTT measurements during last RTT.

bool	m_doingVegasNow
	If true, do Vegas for this RTT.

uint32_t	m_gamma
	Gamma threshold, limit on increase.

Time	m_minRtt
	Minimum of all RTT measurements within last RTT.

Additional Inherited Members
Protected Member Functions inherited from ns3::TcpNewReno
virtual void	CongestionAvoidance (Ptr< TcpSocketState > tcb, uint32_t segmentsAcked)
	NewReno congestion avoidance.

virtual uint32_t	SlowStart (Ptr< TcpSocketState > tcb, uint32_t segmentsAcked)
	Tcp NewReno slow start algorithm.

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.

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

Detailed Description

An implementation of TCP Vegas.

TCP Vegas is a pure delay-based congestion control algorithm implementing a proactive scheme that tries to prevent packet drops by maintaining a small backlog at the bottleneck queue.

Vegas continuously measures the actual throughput a connection achieves as shown in Equation (1) and compares it with the expected throughput calculated in Equation (2). The difference between these 2 sending rates in Equation (3) reflects the amount of extra packets being queued at the bottleneck.

         actual = cwnd / RTT        (1)
         expected = cwnd / BaseRTT  (2)
         diff = expected - actual   (3)

To avoid congestion, Vegas linearly increases/decreases its congestion window to ensure the diff value fall between the 2 predefined thresholds, alpha and beta. diff and another threshold, gamma, are used to determine when Vegas should change from its slow-start mode to linear increase/decrease mode.

Following the implementation of Vegas in Linux, we use 2, 4, and 1 as the default values of alpha, beta, and gamma, respectively.

More information: http://dx.doi.org/10.1109/49.464716

Definition at line 54 of file tcp-vegas.h.

Constructor & Destructor Documentation

◆ TcpVegas() [1/2]

ns3::TcpVegas::TcpVegas ( )

Create an unbound tcp socket.

Definition at line 52 of file tcp-vegas.cc.

References NS_LOG_FUNCTION.

◆ TcpVegas() [2/2]

ns3::TcpVegas::TcpVegas ( const TcpVegas & sock )

Copy constructor.

Parameters

sock	the object to copy

Definition at line 66 of file tcp-vegas.cc.

References NS_LOG_FUNCTION.

◆ ~TcpVegas()

ns3::TcpVegas::~TcpVegas ( )

override

Definition at line 80 of file tcp-vegas.cc.

References NS_LOG_FUNCTION.

Member Function Documentation

◆ CongestionStateSet()

void ns3::TcpVegas::CongestionStateSet	(	Ptr< TcpSocketState >	tcb,
		const TcpSocketState::TcpCongState_t	newState )

overridevirtual

Enable/disable Vegas algorithm depending on the congestion state.

We only start a Vegas cycle when we are in normal congestion state (CA_OPEN state).

Parameters

tcb	internal congestion state
newState	new congestion state to which the TCP is going to switch

Reimplemented from ns3::TcpCongestionOps.

Definition at line 132 of file tcp-vegas.cc.

References ns3::TcpSocketState::CA_OPEN, DisableVegas(), EnableVegas(), and NS_LOG_FUNCTION.

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◆ DisableVegas()

void ns3::TcpVegas::DisableVegas ( )

private

Stop taking Vegas samples.

Definition at line 124 of file tcp-vegas.cc.

References m_doingVegasNow, and NS_LOG_FUNCTION.

Referenced by CongestionStateSet().

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◆ EnableVegas()

void ns3::TcpVegas::EnableVegas ( Ptr< TcpSocketState > tcb )

private

Enable Vegas algorithm to start taking Vegas samples.

Vegas algorithm is enabled in the following situations:

at the establishment of a connection
after an RTO
after fast recovery
when an idle connection is restarted

Parameters

tcb	internal congestion state

Definition at line 113 of file tcp-vegas.cc.

References m_begSndNxt, m_cntRtt, m_doingVegasNow, m_minRtt, ns3::Time::Max(), and NS_LOG_FUNCTION.

Referenced by CongestionStateSet().

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◆ Fork()

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

overridevirtual

Copy the congestion control algorithm across sockets.

Returns: a pointer of the copied object

Reimplemented from ns3::TcpNewReno.

Definition at line 86 of file tcp-vegas.cc.

References ns3::Object::CopyObject.

◆ GetName()

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

overridevirtual

Get the name of the congestion control algorithm.

Returns: A string identifying the name

Reimplemented from ns3::TcpNewReno.

Definition at line 273 of file tcp-vegas.cc.

◆ GetSsThresh()

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

overridevirtual

Get slow start threshold following Vegas principle.

Parameters

tcb	internal congestion state
bytesInFlight	bytes in flight

Returns: the slow start threshold value

Reimplemented from ns3::TcpNewReno.

Definition at line 279 of file tcp-vegas.cc.

References NS_LOG_FUNCTION.

Referenced by IncreaseWindow().

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◆ GetTypeId()

TypeId ns3::TcpVegas::GetTypeId ( )

static

Get the type ID.

Returns: the object TypeId

Definition at line 28 of file tcp-vegas.cc.

References m_alpha, m_beta, m_gamma, ns3::MakeUintegerAccessor(), ns3::MakeUintegerChecker(), and ns3::TypeId::SetParent().

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◆ IncreaseWindow()

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

overridevirtual

Adjust cwnd following Vegas linear increase/decrease algorithm.

Parameters

tcb	internal congestion state
segmentsAcked	count of segments ACKed

Reimplemented from ns3::TcpNewReno.

Definition at line 146 of file tcp-vegas.cc.

References ns3::Time::GetSeconds(), GetSsThresh(), ns3::TcpNewReno::IncreaseWindow(), m_alpha, m_baseRtt, m_begSndNxt, m_beta, m_cntRtt, m_doingVegasNow, m_gamma, m_minRtt, ns3::Time::Max(), NS_ASSERT, NS_LOG_DEBUG, NS_LOG_FUNCTION, NS_LOG_LOGIC, and ns3::TcpNewReno::SlowStart().

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◆ PktsAcked()

void ns3::TcpVegas::PktsAcked	(	Ptr< TcpSocketState >	tcb,
		uint32_t	segmentsAcked,
		const Time &	rtt )

overridevirtual

Compute RTTs needed to execute Vegas algorithm.

The function filters RTT samples from the last RTT to find the current smallest propagation delay + queueing delay (minRtt). We take the minimum to avoid the effects of delayed ACKs.

The function also min-filters all RTT measurements seen to find the propagation delay (baseRtt).

Parameters

tcb	internal congestion state
segmentsAcked	count of segments ACKed
rtt	last RTT

Reimplemented from ns3::TcpCongestionOps.

Definition at line 92 of file tcp-vegas.cc.

References ns3::Time::IsZero(), m_baseRtt, m_cntRtt, m_minRtt, NS_LOG_DEBUG, and NS_LOG_FUNCTION.

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Member Data Documentation

◆ m_alpha

uint32_t ns3::TcpVegas::m_alpha

private

Alpha threshold, lower bound of packets in network.

Definition at line 146 of file tcp-vegas.h.

Referenced by GetTypeId(), and IncreaseWindow().

◆ m_baseRtt

Time ns3::TcpVegas::m_baseRtt

private

Minimum of all Vegas RTT measurements seen during connection.

Definition at line 149 of file tcp-vegas.h.

Referenced by IncreaseWindow(), and PktsAcked().

◆ m_begSndNxt

SequenceNumber32 ns3::TcpVegas::m_begSndNxt

private

Right edge during last RTT.

Definition at line 153 of file tcp-vegas.h.

Referenced by EnableVegas(), and IncreaseWindow().

◆ m_beta

uint32_t ns3::TcpVegas::m_beta

private

Beta threshold, upper bound of packets in network.

Definition at line 147 of file tcp-vegas.h.

Referenced by GetTypeId(), and IncreaseWindow().

◆ m_cntRtt

uint32_t ns3::TcpVegas::m_cntRtt

private

Number of RTT measurements during last RTT.

Definition at line 151 of file tcp-vegas.h.

Referenced by EnableVegas(), IncreaseWindow(), and PktsAcked().

◆ m_doingVegasNow

bool ns3::TcpVegas::m_doingVegasNow

private

If true, do Vegas for this RTT.

Definition at line 152 of file tcp-vegas.h.

Referenced by DisableVegas(), EnableVegas(), and IncreaseWindow().

◆ m_gamma

uint32_t ns3::TcpVegas::m_gamma

private

Gamma threshold, limit on increase.

Definition at line 148 of file tcp-vegas.h.

Referenced by GetTypeId(), and IncreaseWindow().

◆ m_minRtt

Time ns3::TcpVegas::m_minRtt

private

Minimum of all RTT measurements within last RTT.

Definition at line 150 of file tcp-vegas.h.

Referenced by EnableVegas(), IncreaseWindow(), and PktsAcked().

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

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

Public Member Functions

Static Public Member Functions

Private Member Functions

Private Attributes

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

◆ TcpVegas() [1/2]

◆ TcpVegas() [2/2]

◆ ~TcpVegas()

Member Function Documentation

◆ CongestionStateSet()

◆ DisableVegas()

◆ EnableVegas()

◆ Fork()

◆ GetName()

◆ GetSsThresh()

◆ GetTypeId()

◆ IncreaseWindow()

◆ PktsAcked()

Member Data Documentation

◆ m_alpha

◆ m_baseRtt

◆ m_begSndNxt

◆ m_beta

◆ m_cntRtt

◆ m_doingVegasNow

◆ m_gamma

◆ m_minRtt