Transmit_Protocol_Handler.h

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00009 #ifndef TRANSMIT_PROTOCOL_HANDLER_H
00010 #define TRANSMIT_PROTOCOL_HANDLER_H
00011 
00012 #include "Retransmission_Buffer.h"
00013 #include "Packet_Queue.h"
00014 
00023 
00024 class Transmit_Protocol_Handler
00025 {
00026     enum {L2_HEADER_LENGTH=8};
00027 
00029     int m_next_Transmit_Sequence_Number;
00030 
00033     int m_next_Receive_Sequence_Number;
00034 
00036     Retransmission_Buffer m_retransmission_Buffer;
00037 
00039     Packet_Queue<Datagram> m_transmit_Queue;
00040 
00042     Protocol_Layer *m_p_Layer;
00043 
00055 
00056     void Transmit_Packet(Datagram *p_Packet)
00057     {
00058         // Add header and sequence numbers
00059         p_Packet->Add_Header(L2_HEADER_LENGTH);
00060 
00061         p_Packet->Set_Receive_Sequence_Number(m_next_Receive_Sequence_Number);
00062 
00063         // Fill the transmit sequence number and inform
00064         // retransmission queue if the packet is not
00065         // an acknowledgement packet
00066         if (p_Packet->GetType() != Datagram::ACKNOWLEDGEMENT)
00067         {
00068             p_Packet->Set_Transmit_Sequence_Number(m_next_Transmit_Sequence_Number);
00069             Modulo_Increment(m_next_Transmit_Sequence_Number);
00070             // Inform retransmission queue about the packet
00071             m_retransmission_Buffer.Add_Packet(p_Packet);
00072         }
00073 
00074         // Pass on the message for transmission to the lower layer. A pointer to the lower
00075         // layer is obtained from the parent layer.
00076         Protocol_Layer *p_Lower_Layer = m_p_Layer->Get_Lower_Layer();
00077         if (p_Lower_Layer)
00078         {
00079             p_Lower_Layer->Transmit(p_Packet);
00080         }
00081     }
00082 
00083 public:   
00084 
00093 
00094     Transmit_Protocol_Handler(Protocol_Layer *p_Layer) :
00095       m_p_Layer(p_Layer), m_retransmission_Buffer(p_Layer)
00096       {
00097       }
00098 
00106 
00107       void Handle_Transmit_Request(Datagram *p_Packet)
00108       {
00109           // Check for space in window
00110           if (m_retransmission_Buffer.Get_Window_Room() == 0)
00111           {
00112               // No space, window is full. The message waits
00113               // in the queue
00114               m_transmit_Queue.Add(p_Packet);
00115           }
00116           else
00117           {
00118               // If the window is open, transmit packet immediately
00119               Transmit_Packet(p_Packet);
00120           } 
00121       }
00122 
00133 
00134       void Handle_Send_Ack_Request(int new_Receive_Sequence_Number)
00135       {
00136           // Copy the new receive sequence number
00137           // to acknowledge a packet
00138           m_next_Receive_Sequence_Number = new_Receive_Sequence_Number;
00139 
00140           // If there are no more pending messages,
00141           // send an explicit acknowledgement message. If messages
00142           // are pending, ack can be piggy backed.
00143           if (m_transmit_Queue.Get_Length() == 0)
00144           {
00145               // No messages are pending transmission.
00146               // Send explicit ack
00147               Transmit_Packet(new Datagram(Datagram::ACKNOWLEDGEMENT));
00148           }
00149       }
00150 
00163 
00164       void Handle_Received_Ack_Notification(int acknowledged_Sequence_Number)
00165       {
00166           Datagram *p_Packet;
00167 
00168           // Delegate ack processing to Retransmission Buffer
00169           m_retransmission_Buffer.Handle_Received_Ack_Notification(acknowledged_Sequence_Number);
00170 
00171           // Check if the transmit window has opened up. If there is is room in
00172           // the window, transmit packets waiting in the transmit queue
00173           int windowRoom = m_retransmission_Buffer.Get_Window_Room();
00174           for (int i=0; i < windowRoom && m_transmit_Queue.Get_Length(); i++)
00175           {
00176               p_Packet = m_transmit_Queue.Remove();
00177               Transmit_Packet(p_Packet);
00178           }
00179       }
00180 
00181 };
00182 #endif