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tcp: Vegas simplified

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This commit is contained in:
Natale Patriciello
2016-07-04 15:04:59 +02:00
parent 8a19cbd288
commit cd29d3dea9
1 changed files with 25 additions and 17 deletions
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42
src/internet/model/tcp-vegas.cc
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@@ -191,18 +191,25 @@ TcpVegas::IncreaseWindow (Ptr<TcpSocketState> tcb, uint32_t segmentsAcked)
* rate and the predefined thresholds (alpha, beta, and gamma).
*/
uint32_t diff;
uint64_t targetCwnd;
uint32_t targetCwnd;
uint32_t segCwnd = tcb->GetCwndInSegments ();
/*
* Calculate the cwnd we should have
* Calculate the cwnd we should have. baseRtt is the minimum RTT
* per-connection, minRtt is the minimum RTT in this window
*
* little trick:
* desidered throughput is currentCwnd * baseRtt
* target cwnd is throughput / minRtt
*/
targetCwnd = (uint64_t) segCwnd * (double) m_baseRtt.GetMilliSeconds () / (double) m_minRtt.GetMilliSeconds ();
double tmp = m_baseRtt.GetSeconds () / m_minRtt.GetSeconds ();
targetCwnd = segCwnd * tmp;
NS_LOG_DEBUG ("Calculated targetCwnd = " << targetCwnd);
NS_ASSERT (segCwnd >= targetCwnd); // implies baseRtt <= minRtt
/*
* Calculate the difference between the expected throughput and
* the actual throughput that we achieved
* Calculate the difference between the expected cWnd and
* the actual cWnd
*/
diff = segCwnd - targetCwnd;
NS_LOG_DEBUG ("Calculated diff = " << diff);
@@ -214,16 +221,18 @@ TcpVegas::IncreaseWindow (Ptr<TcpSocketState> tcb, uint32_t segmentsAcked)
* slow-start to linear increase/decrease mode by setting cwnd
* to target cwnd. We add 1 because of the integer truncation.
*/
NS_LOG_LOGIC ("We are going too fast. We need to slow down and change to linear increase/decrease mode.");
segCwnd = std::min (segCwnd, (uint32_t) targetCwnd + 1);
NS_LOG_LOGIC ("We are going too fast. We need to slow down and "
"change to linear increase/decrease mode.");
segCwnd = std::min (segCwnd, targetCwnd + 1);
tcb->m_cWnd = segCwnd * tcb->m_segmentSize;
NS_LOG_DEBUG ("Updated cwnd = " << tcb->m_cWnd);
tcb->m_ssThresh = GetSsThresh (tcb, (uint32_t) 0);
NS_LOG_DEBUG ("Updated ssthresh = " << tcb->m_ssThresh);
tcb->m_ssThresh = GetSsThresh (tcb, 0);
NS_LOG_DEBUG ("Updated cwnd = " << tcb->m_cWnd <<
" ssthresh=" << tcb->m_ssThresh);
}
else if (tcb->m_cWnd < tcb->m_ssThresh)
{ // Slow start mode
NS_LOG_LOGIC ("We are in slow start and diff < m_gamma, so we follow NewReno slow start");
NS_LOG_LOGIC ("We are in slow start and diff < m_gamma, so we "
"follow NewReno slow start");
segmentsAcked = TcpNewReno::SlowStart (tcb, segmentsAcked);
}
else
@@ -235,9 +244,9 @@ TcpVegas::IncreaseWindow (Ptr<TcpSocketState> tcb, uint32_t segmentsAcked)
NS_LOG_LOGIC ("We are going too fast, so we slow down by decrementing cwnd");
segCwnd--;
tcb->m_cWnd = segCwnd * tcb->m_segmentSize;
tcb->m_ssThresh = GetSsThresh (tcb, (uint32_t) 0);
NS_LOG_DEBUG ("Updated cWnd = " << tcb->m_cWnd);
NS_LOG_DEBUG ("Updated ssThresh = " << tcb->m_ssThresh);
tcb->m_ssThresh = GetSsThresh (tcb, 0);
NS_LOG_DEBUG ("Updated cwnd = " << tcb->m_cWnd <<
" ssthresh=" << tcb->m_ssThresh);
}
else if (diff < m_alpha)
{
@@ -246,8 +255,8 @@ TcpVegas::IncreaseWindow (Ptr<TcpSocketState> tcb, uint32_t segmentsAcked)
NS_LOG_LOGIC ("We are going too slow, so we speed up by incrementing cwnd");
segCwnd++;
tcb->m_cWnd = segCwnd * tcb->m_segmentSize;
NS_LOG_DEBUG ("Updated cWnd = " << tcb->m_cWnd);
NS_LOG_DEBUG ("Updated ssThresh = " << tcb->m_ssThresh);
NS_LOG_DEBUG ("Updated cwnd = " << tcb->m_cWnd <<
" ssthresh=" << tcb->m_ssThresh);
}
else
{
@@ -262,7 +271,6 @@ TcpVegas::IncreaseWindow (Ptr<TcpSocketState> tcb, uint32_t segmentsAcked)
// Reset cntRtt & minRtt every RTT
m_cntRtt = 0;
m_minRtt = Time::Max ();
}
else if (tcb->m_cWnd < tcb->m_ssThresh)
{