/usr/include/ns3.27/ns3/tcp-tx-buffer.h is in libns3-dev 3.27+dfsg-1.
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/*
* Copyright (c) 2010-2015 Adrian Sai-wah Tam
* Copyright (c) 2016 Natale Patriciello <natale.patriciello@gmail.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation;
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
* Original author: Adrian Sai-wah Tam <adrian.sw.tam@gmail.com>
*/
#ifndef TCP_TX_BUFFER_H
#define TCP_TX_BUFFER_H
#include "ns3/object.h"
#include "ns3/traced-value.h"
#include "ns3/sequence-number.h"
#include "ns3/nstime.h"
#include "ns3/tcp-option-sack.h"
namespace ns3 {
class Packet;
/**
* \ingroup tcp
*
* \brief Item that encloses the application packet and some flags for it
*/
class TcpTxItem
{
public:
/**
* \brief Constructor
*/
TcpTxItem ();
/**
* \brief Copy-constructor
* \param other TcpTxTag to copy values from
*/
TcpTxItem (const TcpTxItem &other);
/**
* \brief Print the time
* \param os ostream
*/
void Print (std::ostream &os) const;
Ptr<Packet> m_packet; //!< Application packet
bool m_lost; //!< Indicates if the segment has been lost (RTO)
bool m_retrans; //!< Indicates if the segment is retransmitted
Time m_lastSent; //!< Timestamp of the time at which the segment has
// been sent last time
bool m_sacked; //!< Indicates if the segment has been SACKed
};
/**
* \ingroup tcp
*
* \brief Tcp sender buffer
*
* The class keeps track of all data that the application wishes to transmit to
* the other end. When the data is acknowledged, it is removed from the buffer.
* The buffer has a maximum size, and data is not saved if the amount exceeds
* the limit. Packets can be added to the class through the method Add(). An
* important thing to remember is that all the data managed is strictly
* sequential. It can be divided into blocks, but all the data follow a strict
* ordering. That order is managed through SequenceNumber.
*
* In other words, this buffer contains numbered bytes (e.g., 1,2,3), and the
* class is allowed to return only ordered (using "<" as operator) subsets
* (e.g. 1,2 or 2,3 or 1,2,3).
*
* The data structure underlying this is composed by two distinct packet lists.
* The first (SentList) is initially empty, and it contains the packets
* returned by the method CopyFromSequence. The second (AppList) is initially
* empty, and it contains the packets coming from the applications, but that
* are not transmitted yet as segments. To discover how the chunks are managed
* and retrieved from these lists, check CopyFromSequence documentation.
*
* The head of the data is represented by m_firstByteSeq, and it is returned by
* HeadSequence(). The last byte is returned by TailSequence(). In this class,
* we also store the size (in bytes) of the packets inside the SentList in the
* variable m_sentSize.
*
* SACK management
* ---------------
*
* The SACK information is usually saved in a data structure referred as
* scoreboard. In this implementation, the scoreboard is developed on top of
* the existing classes. In particular, instead of keeping raw pointers to
* packets in TcpTxBuffer we added the capability to store some flags
* associated with every segment sent. This is done through the use of the
* class TcpTxItem: instead of storing a list of packets, we store a list of
* TcpTxItem. Each item has different flags (check the corresponding
* documentation) and maintaining the scoreboard is a matter of travelling the
* list and set the SACK flag on the corresponding segment sent.
*
* Inefficiencies
* --------------
*
* The algorithms outlined in RFC 6675 are full of inefficiencies. In
* particular, traveling all the sent list each time it is needed to compute
* the bytes in flight is expensive. We try to overcome the issue by
* maintaining a pointer to the highest sequence SACKed; in this way, we can
* avoid traveling all the list in some cases. Another option could be keeping
* a count of each critical value (e.g., the number of packets sacked).
* However, this would be different from the algorithms in RFC. There are some
* other possible improvements; if you wish, take a look and try to add some
* earlier exit conditions in the loops.
*
* \see Size
* \see SizeFromSequence
* \see CopyFromSequence
*/
class TcpTxBuffer : public Object
{
public:
/**
* \brief Get the type ID.
* \return the object TypeId
*/
static TypeId GetTypeId (void);
/**
* \brief Constructor
* \param n initial Sequence number to be transmitted
*/
TcpTxBuffer (uint32_t n = 0);
virtual ~TcpTxBuffer (void);
// Accessors
/**
* \brief Get the sequence number of the buffer head
* \returns the first byte's sequence number
*/
SequenceNumber32 HeadSequence (void) const;
/**
* \brief Get the sequence number of the buffer tail (plus one)
* \returns the last byte's sequence number + 1
*/
SequenceNumber32 TailSequence (void) const;
/**
* \brief Returns total number of bytes in this buffer
* \returns total number of bytes in this Tx buffer
*/
uint32_t Size (void) const;
/**
* \brief Get the maximum buffer size
* \returns the Tx window size (in bytes)
*/
uint32_t MaxBufferSize (void) const;
/**
* \brief Set the maximum buffer size
* \param n Tx window size (in bytes)
*/
void SetMaxBufferSize (uint32_t n);
/**
* \brief Returns the available capacity of this buffer
* \returns available capacity in this Tx window
*/
uint32_t Available (void) const;
/**
* \brief Append a data packet to the end of the buffer
*
* \param p The packet to be appended to the Tx buffer
* \return Boolean to indicate success
*/
bool Add (Ptr<Packet> p);
/**
* \brief Returns the number of bytes from the buffer in the range [seq, tailSequence)
*
* \param seq initial sequence number
* \returns the number of bytes from the buffer in the range
*/
uint32_t SizeFromSequence (const SequenceNumber32& seq) const;
/**
* \brief Copy data from the range [seq, seq+numBytes) into a packet
*
* In the following, we refer to the block [seq, seq+numBytes) simply as "block".
* We check the boundary of the block, and divide the possibilities in three
* cases:
*
* - the block have already been transmitted (managed in GetTransmittedSegment)
* - the block have not been transmitted yet (managed in GetNewSegment)
*
* The last case is when the block is partially transmitted and partially
* not transmitted. We trick this case by requesting the portion not transmitted
* from GetNewSegment, and then calling GetTransmittedSegment with the full
* block range.
*
* \param numBytes number of bytes to copy
* \param seq start sequence number to extract
* \returns a packet
*/
Ptr<Packet> CopyFromSequence (uint32_t numBytes, const SequenceNumber32& seq);
/**
* \brief Set the head sequence of the buffer
*
* Set the head (m_firstByteSeq) to seq. Supposed to be called only when the
* connection is just set up and we did not send any data out yet.
* \param seq The sequence number of the head byte
*/
void SetHeadSequence (const SequenceNumber32& seq);
/**
* \brief Discard data up to but not including this sequence number.
*
* \param seq The first sequence number to maintain after discarding all the
* previous sequences.
*/
void DiscardUpTo (const SequenceNumber32& seq);
/**
* \brief Update the scoreboard
* \param list list of SACKed blocks
* \returns true in case of an update
*/
bool Update (const TcpOptionSack::SackList &list);
/**
* \brief Check if a segment is lost per RFC 6675
* \param seq sequence to check
* \param dupThresh dupAck threshold
* \param segmentSize segment size
* \return true if the sequence is supposed to be lost, false otherwise
*/
bool IsLost (const SequenceNumber32 &seq, uint32_t dupThresh, uint32_t segmentSize) const;
/**
* \brief Get the next sequence number to transmit, according to RFC 6675
*
* \param seq Next sequence number to transmit, based on the scoreboard information
* \param dupThresh dupAck threshold
* \param segmentSize segment size
* \param isRecovery true if the socket congestion state is in recovery mode
* \return true is seq is updated, false otherwise
*/
bool NextSeg (SequenceNumber32 *seq, uint32_t dupThresh, uint32_t segmentSize,
bool isRecovery) const;
/**
* \brief Return the number of segments in the sent list that
* have been transmitted more than once, without acknowledgment.
*
* This method is to support the retransmits count for determining PipeSize
* in NewReno-style TCP.
*
* \returns number of segments that have been transmitted more than once, without acknowledgment
*/
uint32_t GetRetransmitsCount (void) const;
/**
* \brief Return total bytes in flight
*
* The routine follows the "SetPipe" function in RFC 6675 and assumes that
* SACK is enabled for the session
*
* \param dupThresh duplicate ACK threshold
* \param segmentSize segment size
* \returns total bytes in flight
*/
uint32_t BytesInFlight (uint32_t dupThresh, uint32_t segmentSize) const;
/**
* \brief Set the entire sent list as lost (typically after an RTO)
*
* Used to set all the sent list as lost, so the bytes in flight is not counting
* them as in flight, but we will continue to use SACK informations for
* recovering the timeout.
*/
void SetSentListLost ();
/**
* \brief Reset the Scoreboard from all SACK informations
*/
void ResetScoreboard ();
/**
* \brief Check if the head is retransmitted
*
* \return true if the head is retransmitted, false in all other cases
* (including no segment sent)
*/
bool IsHeadRetransmitted () const;
/**
* \brief Reset the sent list
*
* Move all but the first 'keepItems' packets from the sent list to the
* appList. By default, the HEAD of hte sent list is kept and all others
* moved to the appList. All items kept on the sent list
* are then marked as un-sacked, un-retransmitted, and lost.
*
* \param keepItems Keep a number of items at the front of the sent list
*/
void ResetSentList (uint32_t keepItems = 1);
/**
* \brief Take the last segment sent and put it back into the un-sent list
* (at the beginning)
*/
void ResetLastSegmentSent ();
/**
* \brief Craft a SACK block. Used in case the other end does not support
* SACK
*
* \param seq Look to usable block starting from this sequence number (seq will
* not be included in the block)
* \param available Space left in the header for that SACK option
* \return a SACK option that SACK the first un-SACKed segment in our sentList.
*/
Ptr<const TcpOptionSack> CraftSackOption (const SequenceNumber32 &seq, uint8_t available) const;
private:
friend std::ostream & operator<< (std::ostream & os, TcpTxBuffer const & tcpTxBuf);
typedef std::list<TcpTxItem*> PacketList; //!< container for data stored in the buffer
/**
* \brief Check if a segment is lost per RFC 6675
* \param seq sequence to check
* \param segment Iterator pointing at seq
* \param dupThresh dupAck threshold
* \param segmentSize segment size
* \return true if the sequence is supposed to be lost, false otherwise
*/
bool IsLost (const SequenceNumber32 &seq, const PacketList::const_iterator &segment, uint32_t dupThresh,
uint32_t segmentSize) const;
/**
* \brief Get a block of data not transmitted yet and move it into SentList
*
* If the block is not yet transmitted, hopefully, seq is exactly the sequence
* number of the first byte of the first packet inside AppList. We extract
* the block from AppList and move it into the SentList, before returning the
* block itself. We manage possible fragmentation (or merges) inside AppList
* through GetPacketFromList.
*
* \see GetPacketFromList
* \param numBytes number of bytes to copy
*
* \return the item that contains the right packet
*/
TcpTxItem* GetNewSegment (uint32_t numBytes);
/**
* \brief Get a block of data previously transmitted
*
* This is clearly a retransmission, and if everything is going well,
* the block requested is matching perfectly with another one requested
* in the past. If not, fragmentation or merge are required. We manage
* both inside GetPacketFromList.
*
* \see GetPacketFromList
*
* \param numBytes number of bytes to copy
* \param seq sequence requested
* \returns the item that contains the right packet
*/
TcpTxItem* GetTransmittedSegment (uint32_t numBytes, const SequenceNumber32 &seq);
/**
* \brief Get a block (which is returned as Packet) from a list
*
* This function extract a block [requestedSeq,numBytes) from the list, which
* starts at startingSeq.
*
* The cases we need to manage are two, and they are depicted in the following
* image:
*
*\verbatim
|------| |----| |----|
list = | | --> | | --> | |
|------| |----| |----|
^ ^
| ^ ^ | (1)
seq | | seq + numBytes
| |
| |
seq seq + numBytes (2)
\endverbatim
*
* The case 1 is easy to manage: the requested block is exactly a packet
* already stored. If one value (seq or seq + numBytes) does not align
* to a packet boundary, or when both values does not align (case 2), it is
* a bit more complex.
*
* Basically, we have two possible operations:
*
* - fragment : split an existing packet in two
* - merge : merge two existing packets in one
*
* and we reduce case (2) to case (1) through sequentially applying fragment
* or merge. For instance:
*
*\verbatim
|------|
| |
|------|
^ ^ ^ ^
| | | |
start | | |
| | end
seq |
seq + numBytes
\endverbatim
*
* To reduce to case (1), we need to perform two fragment operations:
*
* - fragment (start, seq)
* - fragment (seq + numBytes, end)
*
* After these operations, the requested block is exactly the resulting packet.
* Merge operation is required when the requested block span over two (or more)
* existing packets.
*
* While this could be extremely slow in the worst possible scenario (one big
* packet which is split in small packets for transmission, and merged for
* re-transmission) that scenario is unlikely during a TCP transmission (since
* MSS can change, but it is stable, and retransmissions do not happen for
* each segment).
*
* \param list List to extract block from
* \param startingSeq Starting sequence of the list
* \param numBytes Bytes to extract, starting from requestedSeq
* \param requestedSeq Requested sequence
* \param listEdited output parameter which indicates if the list has been edited
* \return the item that contains the right packet
*/
TcpTxItem* GetPacketFromList (PacketList &list, const SequenceNumber32 &startingSeq,
uint32_t numBytes, const SequenceNumber32 &requestedSeq,
bool *listEdited) const;
/**
* \brief Merge two TcpTxItem
*
* Merge t2 in t1. It consists in copying the lastSent field if t2 is more
* recent than t1. Retransmitted field is copied only if it set in t2 but not
* in t1. Sacked is copied only if it is true in both items.
*
* \param t1 first item
* \param t2 second item
*/
void MergeItems (TcpTxItem &t1, TcpTxItem &t2) const;
/**
* \brief Split one TcpTxItem
*
* Move "size" bytes from t2 into t1, copying all the fields.
*
* \param t1 first item
* \param t2 second item
* \param size Size to split
*/
void SplitItems (TcpTxItem &t1, TcpTxItem &t2, uint32_t size) const;
/**
* \brief Find the highest SACK byte
* \return a pair with the highest byte and an iterator inside m_sentList
*/
std::pair <TcpTxBuffer::PacketList::const_iterator, SequenceNumber32>
GetHighestSacked () const;
PacketList m_appList; //!< Buffer for application data
PacketList m_sentList; //!< Buffer for sent (but not acked) data
uint32_t m_maxBuffer; //!< Max number of data bytes in buffer (SND.WND)
uint32_t m_size; //!< Size of all data in this buffer
uint32_t m_sentSize; //!< Size of sent (and not discarded) segments
TracedValue<SequenceNumber32> m_firstByteSeq; //!< Sequence number of the first byte in data (SND.UNA)
std::pair <PacketList::const_iterator, SequenceNumber32> m_highestSack; //!< Highest SACK byte
};
/**
* \brief Output operator.
* \param os The output stream.
* \param tcpTxBuf the TcpTxBuffer to print.
* \returns The output stream.
*/
std::ostream & operator<< (std::ostream & os, TcpTxBuffer const & tcpTxBuf);
} // namepsace ns3
#endif /* TCP_TX_BUFFER_H */
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