RTO.c

/************************************************************************************
* Copyright (C) 2023                                                                *
* TETCOS, Bangalore. India                                                          *
*                                                                                   *
* Tetcos owns the intellectual property rights in the Product and its content.      *
* The copying, redistribution, reselling or publication of any or all of the        *
* Product or its content without express prior written consent of Tetcos is         *
* prohibited. Ownership and / or any other right relating to the software and all   *
* intellectual property rights therein shall remain at all times with Tetcos.       *
*                                                                                   *
* This source code is licensed per the NetSim license agreement.                    *
*                                                                                   *
* No portion of this source code may be used as the basis for a derivative work,    *
* or used, for any purpose other than its intended use per the NetSim license       *
* agreement.                                                                        *
*                                                                                   *
* This source code and the algorithms contained within it are confidential trade    *
* secrets of TETCOS and may not be used as the basis for any other software,        *
* hardware, product or service.                                                     *
*                                                                                   *
* Author:    Shashi Kant Suman                                                      *
*                                                                                   *
* ----------------------------------------------------------------------------------*/
#include "main.h"
#include "TCP.h"
#include "TCP_Enum.h"
#include "TCP_Header.h"
 
//RFC 6298
#define alpha   (1/8.0)
#define beta    (1/4.0)
#define G       (0.5*SECOND) /* Min RTO value is set to 0.5 s.
                              * The RFC states this should be 1 s
                              * Linux seems to be currently using 200 ms.
                              */
#define K       (4)
 
double calculate_RTO(double R,
                     double* srtt,
                     double* rtt_var)
{
    double rto;
    if (!R) //2.1
        rto = 1 * SECOND;
    else if (!*srtt) //2.2
    {
        *srtt = R;
        *rtt_var = R / 2.0;
        rto = *srtt + max(G, K*(*rtt_var));
    }
    else //2.3
    {
        *rtt_var = (1 - beta) * (*rtt_var) + beta *  fabs(*srtt - R);
        *srtt = (1 - alpha) * (*srtt) + alpha * R;
        rto = *srtt + max(G, K*(*rtt_var));
    }
    return min(max(rto, G), (60 * SECOND)); //2.4 and 2.5
}
 
static void Backoff_RTO(double* rto)
{
    *rto = min(max((*rto*2), G), (60 * SECOND));
    print_tcp_log("New RTO = %0.2lf", *rto);
}
 
void add_timeout_event(PNETSIM_SOCKET s,
                       NetSim_PACKET* packet)
{
    NetSim_PACKET* p = fn_NetSim_Packet_CopyPacket(packet);
    add_packet_to_queue(&s->tcb->retransmissionQueue, p, pstruEventDetails->dEventTime);
    if (s->tcb->isRTOTimerRunning) return;
    s->tcb->isRTOTimerRunning = true;
    NetSim_EVENTDETAILS pevent;
    memcpy(&pevent, pstruEventDetails, sizeof pevent);
    pevent.dEventTime += TCP_RTO(s->tcb);
    pevent.dPacketSize = packet->pstruTransportData->dPacketSize;
    pevent.nEventType = TIMER_EVENT;
    pevent.nPacketId = packet->nPacketId;
    if (packet->pstruAppData)
    {
        pevent.nApplicationId = packet->pstruAppData->nApplicationId;
        pevent.nSegmentId = packet->pstruAppData->nSegmentId;
    }
    else
        pevent.nSegmentId = 0;
    pevent.nProtocolId = TX_PROTOCOL_TCP;
    pevent.pPacket = fn_NetSim_Packet_CopyPacket(p);
    pevent.szOtherDetails = NULL;
    pevent.nSubEventType = TCP_RTO_TIMEOUT;
    s->tcb->RTOEventId = fnpAddEvent(&pevent);
    s->tcb->eventPacketptr = pevent.pPacket;
    print_tcp_log("Adding RTO Timer at %0.1lf", pevent.dEventTime);
}
 
static void handle_rto_timer_for_ctrl(PNETSIM_SOCKET s)
{
    if (isSynbitSet(pstruEventDetails->pPacket))
        resend_syn(s);
    else
        fnNetSimError("Unknown packet %d arrives at %s\n",
                      pstruEventDetails->pPacket->nControlDataType,
                      __FUNCTION__);
}
void handle_rto_timer()
{
    PNETSIM_SOCKET s = find_socket_at_source(pstruEventDetails->pPacket);
    if (!s)
    {
        //Socket is already close. Ignore this event
        fn_NetSim_Packet_FreePacket(pstruEventDetails->pPacket);
        return;
    }
    if (!s->tcb || s->tcb->isOtherTimerCancel)
    {
        fn_NetSim_Packet_FreePacket(pstruEventDetails->pPacket);
        return;
    }
 
    s->tcb->isRTOTimerRunning = false;
    bool isPresent = isAnySegmentInQueue(&s->tcb->retransmissionQueue);
    
    if (isPresent)
    {
        NetSim_PACKET* segment = get_earliest_copy_segment_from_queue(&s->tcb->retransmissionQueue);
        
        print_tcp_log("\nDevice %d, Time %0.2lf: RTO Time expire.",
                      pstruEventDetails->nDeviceId,
                      pstruEventDetails->dEventTime);
        
        s->tcpMetrics->timesRTOExpired++;
 
        Backoff_RTO(&TCP_RTO(s->tcb));
 
        if (isTCPControl(segment))
        {
            handle_rto_timer_for_ctrl(s);
        }
        else
        {
            //Call congestion algorithm
            s->tcb->rto_expired(s);
 
            resend_segment(s, segment);
        }
 
        fn_NetSim_Packet_FreePacket(segment);
    }
    else
    {
        //Ignore this event
    }
    fn_NetSim_Packet_FreePacket(pstruEventDetails->pPacket);
}
 
void restart_rto_timer(PNETSIM_SOCKET s)
{
    fnDeleteEvent(s->tcb->RTOEventId);
    fn_NetSim_Packet_FreePacket(s->tcb->eventPacketptr);
    s->tcb->eventPacketptr = NULL;
    s->tcb->isRTOTimerRunning = false;
 
    bool isPresent = isAnySegmentInQueue(&s->tcb->retransmissionQueue);
    if (isPresent)
    {
        s->tcb->isRTOTimerRunning = true;
        NetSim_PACKET* segment = get_earliest_copy_segment_from_queue(&s->tcb->retransmissionQueue);
        NetSim_EVENTDETAILS pevent;
        memcpy(&pevent, pstruEventDetails, sizeof pevent);
        pevent.dEventTime += TCP_RTO(s->tcb);
        pevent.dPacketSize = segment->pstruTransportData->dPacketSize;
        pevent.nEventType = TIMER_EVENT;
        pevent.nPacketId = segment->nPacketId;
        if (segment->pstruAppData)
        {
            pevent.nApplicationId = segment->pstruAppData->nApplicationId;
            pevent.nSegmentId = segment->pstruAppData->nSegmentId;
        }
        else
            pevent.nSegmentId = 0;
        pevent.nProtocolId = TX_PROTOCOL_TCP;
        pevent.pPacket = segment;
        pevent.szOtherDetails = NULL;
        pevent.nSubEventType = TCP_RTO_TIMEOUT;
        s->tcb->RTOEventId = fnpAddEvent(&pevent);
        s->tcb->eventPacketptr = segment;
        print_tcp_log("Adding RTO Timer at %0.1lf", pevent.dEventTime);
    }
}