copy srt estimated link capacity algorithm

srt/Common.hpp

@@ -14,6 +14,7 @@
 
 #include <chrono>
 #define MAX_SEQ  0x7fffffff
+#define SEQ_NONE 0xffffffff
 #define MAX_TS   0xffffffff
 
 namespace SRT {
@@ -35,6 +36,25 @@ static inline uint16_t loadUint16(uint8_t *ptr) {
     return ptr[0] << 8 | ptr[1];
 }
 
+inline static int64_t seqCmp(uint32_t seq1, uint32_t seq2) {
+    if(seq1 > seq2){
+        if((seq1 - seq2) >(MAX_SEQ>>1)){
+            return (int64_t)seq1 - (int64_t)(seq2+MAX_SEQ);
+        }else{
+            return (int64_t)seq1 - (int64_t)seq2;
+        }
+    }else{
+        if((seq2-seq1) >(MAX_SEQ>>1)){
+            return (int64_t)(seq1+MAX_SEQ) - (int64_t)seq2;
+        }else{
+            return (int64_t)seq1 - (int64_t)seq2;
+        }
+    }
+}
+
+inline static uint32_t incSeq(int32_t seq) {
+    return (seq == MAX_SEQ) ? 0 : seq + 1;
+}
 static inline void storeUint32(uint8_t *buf, uint32_t val) {
     buf[0] = val >> 24;
     buf[1] = (val >> 16) & 0xff;

srt/SrtTransport.cpp

@@ -106,7 +106,6 @@ void SrtTransport::inputSockData(uint8_t *buf, int len, struct sockaddr_storage
                 _handleshake_timer.reset();
             }
             _pkt_recv_rate_context->inputPacket(_now,len-HDR_SIZE);
-            _estimated_link_capacity_context->inputPacket(_now);
             //_recv_rate_context->inputPacket(_now, len);
 
             handleDataPacket(buf, len, addr);
@@ -126,8 +125,8 @@ void SrtTransport::inputSockData(uint8_t *buf, int len, struct sockaddr_storage
                 return;
             }
             
-            _pkt_recv_rate_context->inputPacket(_now,len);
-            _estimated_link_capacity_context->inputPacket(_now);
+            //_pkt_recv_rate_context->inputPacket(_now,len);
+            //_estimated_link_capacity_context->inputPacket(_now);
             //_recv_rate_context->inputPacket(_now, len);
 
             auto it = s_control_functions.find(type);
@@ -179,6 +178,7 @@ void SrtTransport::handleHandshakeInduction(HandshakePacket &pkt, struct sockadd
     _mtu = pkt.mtu;
 
     _last_pkt_seq = _init_seq_number - 1;
+    _estimated_link_capacity_context->setLastSeq(_last_pkt_seq);
 
     _peer_socket_id = pkt.srt_socket_id;
     HandshakePacket::Ptr res = std::make_shared<HandshakePacket>();
@@ -484,6 +484,7 @@ void SrtTransport::sendACKPacket() {
     pkt->pkt_recv_rate = _pkt_recv_rate_context->getPacketRecvRate(recv_rate);
     pkt->estimated_link_capacity = _estimated_link_capacity_context->getEstimatedLinkCapacity();
     pkt->recv_rate = recv_rate;
+    TraceL<<pkt->pkt_recv_rate<<" pkt/s "<<recv_rate<<" byte/s "<<pkt->estimated_link_capacity<<" pkt/s (cap)";
     pkt->storeToData();
     _ack_send_timestamp[pkt->ack_number] = _now;
     _last_ack_pkt_seq_num = pkt->last_ack_pkt_seq_number;
@@ -563,6 +564,8 @@ void SrtTransport::handleDataPacket(uint8_t *buf, int len, struct sockaddr_stora
     DataPacket::Ptr pkt = std::make_shared<DataPacket>();
     pkt->loadFromData(buf, len);
 
+    _estimated_link_capacity_context->inputPacket(_now,pkt);
+
     std::list<DataPacket::Ptr> list;
     //TraceL<<" seq="<< pkt->packet_seq_number<<" ts="<<pkt->timestamp<<" size="<<pkt->payloadSize()<<\
     //" PP="<<(int)pkt->PP<<" O="<<(int)pkt->O<<" kK="<<(int)pkt->KK<<" R="<<(int)pkt->R;

srt/Statistic.cpp

@@ -1,5 +1,5 @@
 #include <algorithm>
-
+#include <math.h>
 #include "Statistic.hpp"
 
 namespace SRT {
@@ -47,47 +47,121 @@ uint32_t PacketRecvRateContext::getPacketRecvRate(uint32_t &bytesps) {
         ++bp; // advance bytes pointer
     }
 
-    // claculate speed, or return 0 if not enough valid value
-
+    if(count>(SIZE>>1)){
         bytesps = (unsigned long)ceil(1000000.0 / (double(sum) / double(bytes)));
         auto ret = (uint32_t)ceil(1000000.0 / (sum / count));
-    if(_cur_idx == 0)
-        TraceL << bytesps << " byte/sec  " << ret << " pkt/sec";
         return ret;
     }
+    bytesps = 0;
+    return 0;
+    // claculate speed, or return 0 if not enough valid value
+
     
-void EstimatedLinkCapacityContext::inputPacket(TimePoint &ts) {
-    if (_pkt_map.size() > 16) {
-        _pkt_map.erase(_pkt_map.begin());
 }
-    auto tmp = DurationCountMicroseconds(ts - _start);
-    _pkt_map.emplace(tmp, tmp);
+EstimatedLinkCapacityContext::EstimatedLinkCapacityContext(TimePoint start) : _start(start) {
+    for (size_t i = 0; i < SIZE; i++) {
+        _dur_probe_arr[i] = 1000;
+    }
+    _cur_idx = 0;
+};
+void EstimatedLinkCapacityContext::inputPacket(TimePoint &ts,DataPacket::Ptr& pkt) {
+    uint32_t  seq = pkt->packet_seq_number;
+    auto diff  = seqCmp(seq,_last_seq);
+    const bool retransmitted = pkt->R == 1;
+    const bool unordered = diff<=0;
+    uint32_t  one = seq&0xf;
+    if(one == 0){
+        probe1Arrival(ts,pkt,unordered || retransmitted);
+    }
+    if(diff>0){
+        _last_seq = seq;
+    }
+    if(unordered || retransmitted){
+        return;
+    }
+    if(one == 1){
+        probe2Arrival(ts,pkt);
+    }
+}
+
+/// Record the arrival time of the first probing packet.
+void EstimatedLinkCapacityContext::probe1Arrival(TimePoint &ts, const DataPacket::Ptr &pkt, bool unordered) {
+    if (unordered && pkt->packet_seq_number == _probe1_seq) {
+        // Reset the starting probe into "undefined", when
+        // a packet has come as retransmitted before the
+        // measurement at arrival of 17th could be taken.
+        _probe1_seq = SEQ_NONE;
+        return;
+    }
+
+    _ts_probe_time = ts;
+    _probe1_seq = pkt->packet_seq_number; // Record the sequence where 16th packet probe was taken
+}
+
+/// Record the arrival time of the second probing packet and the interval between packet pairs.
+
+void EstimatedLinkCapacityContext::probe2Arrival(TimePoint &ts, const DataPacket::Ptr &pkt) {
+    // Reject probes that don't refer to the very next packet
+    // towards the one that was lately notified by probe1Arrival.
+    // Otherwise the result can be stupid.
+
+    // Simply, in case when this wasn't called exactly for the
+    // expected packet pair, behave as if the 17th packet was lost.
+
+    // no start point yet (or was reset) OR not very next packet
+    if (_probe1_seq == SEQ_NONE || incSeq(_probe1_seq) != pkt->packet_seq_number)
+        return;
+
+    // Reset the starting probe to prevent checking if the
+    // measurement was already taken.
+    _probe1_seq = SEQ_NONE;
+
+    // record the probing packets interval
+    // Adjust the time for what a complete packet would have take
+    const int64_t timediff = DurationCountMicroseconds(ts - _ts_probe_time);
+    const int64_t timediff_times_pl_size = timediff * SRT_MAX_PAYLOAD_SIZE;
+
+    // Let's take it simpler than it is coded here:
+    // (stating that a packet has never zero size)
+    //
+    // probe_case = (now - previous_packet_time) * SRT_MAX_PAYLOAD_SIZE / pktsz;
+    //
+    // Meaning: if the packet is fully packed, probe_case = timediff.
+    // Otherwise the timediff will be "converted" to a time that a fully packed packet "would take",
+    // provided the arrival time is proportional to the payload size and skipping
+    // the ETH+IP+UDP+SRT header part elliminates the constant packet delivery time influence.
+    //
+    const size_t pktsz = pkt->payloadSize();
+    _dur_probe_arr[_cur_idx] = pktsz ? int64_t(timediff_times_pl_size / pktsz) : int64_t(timediff);
+
+    // the window is logically circular
+    _cur_idx = (_cur_idx + 1) % SIZE;
 }
 
 uint32_t EstimatedLinkCapacityContext::getEstimatedLinkCapacity() {
-    decltype(_pkt_map.begin()) next;
-    std::vector<int64_t> tmp;
+   int64_t tmp[SIZE];
+   std::copy(_dur_probe_arr, _dur_probe_arr + SIZE , tmp);
+   std::nth_element(tmp, tmp + (SIZE / 2), tmp + SIZE);
+   int64_t median = tmp[SIZE / 2];
 
-    for (auto it = _pkt_map.begin(); it != _pkt_map.end(); ++it) {
-        next = it;
-        ++next;
-        if (next != _pkt_map.end()) {
-            tmp.push_back(next->first - it->first);
-        } else {
-            break;
+   int64_t count = 1;
+   int64_t sum = median;
+   int64_t upper = median << 3; // median*8
+   int64_t lower = median >> 3; // median/8
+
+   // median filtering
+   const int64_t* p = _dur_probe_arr;
+   for (int i = 0, n = SIZE; i < n; ++ i)
+   {
+      if ((*p < upper) && (*p > lower))
+      {
+         ++ count;
+         sum += *p;
       }
-    }
-    std::sort(tmp.begin(), tmp.end());
-    if (tmp.empty()) {
-        return 1000;
+      ++ p;
    }
 
-    if (tmp.size() < 16) {
-        return 1000;
-    }
-
-    double dur = tmp[0] / 1e6;
-    return (uint32_t)(1.0 / dur);
+   return (uint32_t)ceil(1000000.0 / (double(sum) / double(count)));
 }
 
 /*

srt/Statistic.hpp

@@ -23,14 +23,25 @@ private:
 
 class EstimatedLinkCapacityContext {
 public:
-    EstimatedLinkCapacityContext(TimePoint start) : _start(start) {};
+    EstimatedLinkCapacityContext(TimePoint start);
     ~EstimatedLinkCapacityContext() = default;
-    void inputPacket(TimePoint &ts);
+    void setLastSeq(uint32_t seq){
+        _last_seq = seq;
+    }
+    void inputPacket(TimePoint &ts,DataPacket::Ptr& pkt);
     uint32_t getEstimatedLinkCapacity();
-
+    static const int SIZE = 16;
+private:
+    void probe1Arrival(TimePoint &ts,const DataPacket::Ptr& pkt, bool unordered);
+    void probe2Arrival(TimePoint &ts,const DataPacket::Ptr& pkt);
 private:
     TimePoint _start;
-    std::map<int64_t, int64_t> _pkt_map;
+    TimePoint _ts_probe_time;
+    int64_t _dur_probe_arr[SIZE];
+    size_t _cur_idx;
+    uint32_t _last_seq = 0;
+    uint32_t _probe1_seq = SEQ_NONE;
+    //std::map<int64_t, int64_t> _pkt_map;
 };
 
 /*