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Retransmission_Buffer Class Reference

Collaboration diagram for Retransmission_Buffer:

Detailed Description

The messages are retransmitted If no ack is received.

The interactions of this object are listed below:

• The Transmit_Protocol_Handler calls Add_Packet to save a transmitted packet.
• The Retransmission_Buffer saves the message according to its sequence number. A retransmission timer is started for the ack.
• The message is deleted from the buffer if an acknowledgement is received from the remote end. The retransmission timer is stopped.
• If an ack is not received, the message is retransmitted on a retransmission timer time-out.

See also:

Transmit Protocol Handler Design Pattern

Definition at line 30 of file Retransmission_Buffer.h.

Public Member Functions
	Retransmission_Buffer (Protocol_Layer *p_Layer)
	The constructor for the class.
void	Add_Packet (const Datagram *p_Packet)
	Store a packet for possible retransmission in the future.
void	Handle_Received_Ack_Notification (int new_Acknowledged_Sequence_Number)
	Handle the acknowledgement received from the remote end.
int	Get_Window_Room () const
	Obtain the total free room available in the window.
void	Handle_Await_Ack_Timeout ()
	This method is invoked when the protocol times out for an acknowlegement from the remote end.

Constructor & Destructor Documentation

Retransmission_Buffer::Retransmission_Buffer (  Protocol_Layer *  p_Layer  )  [inline]

The constructor for the class. The constructor needs a pointer to the parent layer. The Retransmission Buffer will use this pointer to obtain a pointer to the lower layer. Parameters: p_Layer  Pointer to the parent layer. See also: Transmit Protocol Handler Design Pattern Definition at line 52 of file Retransmission_Buffer.h. 00052 : m_p_Layer(p_Layer) 00053 { 00054 }

Member Function Documentation

void Retransmission_Buffer::Add_Packet (  const Datagram *  p_Packet  )  [inline]

Store a packet for possible retransmission in the future. This method takes the following actions: Obtain the transmit sequence number of the packet. Make a copy of the packet for the retransmission buffer Save the packet according to the transmit sequence number. Retart the ack timer. Parameters: p_Packet  Packet that needs to be saved for possible retransmission in the future. See also: Transmit Protocol Handler Design Pattern Definition at line 67 of file Retransmission_Buffer.h. 00068 { 00069 00070 m_last_Transmitted_Sequence_Number = p_Packet->Get_Transmit_Sequence_Number(); 00071 00072 // Make a copy of the packet for the retransmission buffer 00073 m_p_Pending_Packets[m_last_Transmitted_Sequence_Number] = new Datagram(p_Packet); 00074 00075 // Restart the ack timer. Timer is started if its not running 00076 Restart_Await_Ack_Timer(); 00077 }

void Retransmission_Buffer::Handle_Received_Ack_Notification (  int  new_Acknowledged_Sequence_Number  )  [inline]

Handle the acknowledgement received from the remote end. The following actions are taken on receiving an ack: Run a loop from the last acknowledged sequence number to the new acknowledged sequence number In each iteraction, delete the buffer corresponding to that sequence number. (As the message has been acknowledged and will not be retransmitted) Record the new acknowledged sequence number as the last acknowledged sequence number. Stop the ack timer if no packets are pending retransmission. Parameters: new_Acknowledged_Sequence_Number  The transmit sequence number that has been acknowledged by the remote end. See also: Transmit Protocol Handler Design Pattern Definition at line 91 of file Retransmission_Buffer.h. 00092 { 00093 // Delete the buffers allocted to retransmission buffers 00094 // for all allocated packets. 00095 for (int i=m_last_Acknowledged_Sequence_Number; i != new_Acknowledged_Sequence_Number; 00096 Modulo_Increment(i)) 00097 { 00098 delete m_p_Pending_Packets[i]; 00099 m_p_Pending_Packets[i] = NULL; 00100 } 00101 00102 // Save the new sequence number as the last acknowledged seq num 00103 m_last_Acknowledged_Sequence_Number = new_Acknowledged_Sequence_Number; 00104 00105 // If all packets have been acknowledged, stop timer 00106 if (m_last_Transmitted_Sequence_Number == m_last_Acknowledged_Sequence_Number) 00107 { 00108 Stop_Await_Ack_Timer(); 00109 } 00110 }

int Retransmission_Buffer::Get_Window_Room (   )  const [inline]

Obtain the total free room available in the window. Return the room in window by determining the current count of messages awaiting acknowledgement. Return values: int  Number of free entries available before the window will be full. See also: Transmit Protocol Handler Design Pattern Definition at line 120 of file Retransmission_Buffer.h. 00121 { 00122 // Return the room in window by determining the current count of messages 00123 // awaiting acknowledgement 00124 return (WINDOW_SIZE - 00125 Modulo_Difference(m_last_Transmitted_Sequence_Number, m_last_Acknowledged_Sequence_Number)); 00126 }

void Retransmission_Buffer::Handle_Await_Ack_Timeout (   )  [inline]

This method is invoked when the protocol times out for an acknowlegement from the remote end. This method will retransmit all the packets that are pending acknowledgement. The sequence of actions is: Initiate retransmission of all unacknowledged packets by looping from the last unacknowledged sequence number to the sequence number of the last transmitted message. Restart the await ack timer to keep track of acknowlegements to these as well as previous transmissions. See also: Transmit Protocol Handler Design Pattern Definition at line 137 of file Retransmission_Buffer.h. 00138 { 00139 Datagram *p_Packet; 00140 00141 // Initiate retransmission of all unacknowledged packets by 00142 // looping from the last unacknowledged sequence number to 00143 // the sequence number of the last transmitted message 00144 for (int i=Modulo_Add(m_last_Acknowledged_Sequence_Number, 1); 00145 i != m_last_Transmitted_Sequence_Number; Modulo_Increment(i)) 00146 { 00147 00148 // Get the packet corresponding to the sequence number i 00149 p_Packet = m_p_Pending_Packets[i]; 00150 00151 // Pass on the message for transmission on the serial port 00152 (m_p_Layer->Get_Lower_Layer())->Transmit(p_Packet); 00153 } 00154 00155 // Now restart the timer 00156 Restart_Await_Ack_Timer(); 00157 }

• Retransmission_Buffer.h

Generated on Sun Feb 13 21:30:37 2005 for Object Oriented Design Examples by 1.3.4

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