/*
* o When cwnd is less than or equal to ssthresh, an SCTP endpoint MUST
* use the slow-start algorithm to increase cwnd only if the current
* congestion window is being fully utilized, an incoming SACK
* advances the Cumulative TSN Ack Point, and the data sender is not
* in Fast Recovery. Only when these three conditions are met can
* the cwnd be increased; otherwise, the cwnd MUST not be increased.
* If these conditions are met, then cwnd MUST be increased by, at
* most, the lesser of 1) the total size of the previously
* outstanding DATA chunk(s) acknowledged, and 2) the destination's
* path MTU. This upper bound protects against the ACK-Splitting
* attack outlined in [SAVAGE99].
*/
protected void adjustCwind(bool didAdvance, int inFlightBytes, int totalAcked)
{
bool fullyUtilized = ((inFlightBytes - _cwnd) < DataChunk.GetCapacity()); // could we fit one more in?
if (_cwnd <= _ssthresh)
{
// slow start
Logger.Debug("slow start");
if (didAdvance && fullyUtilized && !_fastRecovery)
{
int incCwinBy = Math.Min(_transpMTU, totalAcked);
_cwnd += incCwinBy;
Logger.Debug("cwnd now " + _cwnd);
}
else
{
Logger.Debug("cwnd static at " + _cwnd + " (didAdvance fullyUtilized _fastRecovery inFlightBytes totalAcked) " + didAdvance + " " + fullyUtilized + " " + _fastRecovery + " " + inFlightBytes + " " + totalAcked);
}
}
else
{
/*
* 7.2.2. Congestion Avoidance
*
* When cwnd is greater than ssthresh, cwnd should be incremented by
* 1*MTU per RTT if the sender has cwnd or more bytes of data
* outstanding for the corresponding transport address.
*
* In practice, an implementation can achieve this goal in the following
* way:
*
* o partial_bytes_acked is initialized to 0.
*
* o Whenever cwnd is greater than ssthresh, upon each SACK arrival
* that advances the Cumulative TSN Ack Point, increase
* partial_bytes_acked by the total number of bytes of all new chunks
* acknowledged in that SACK including chunks acknowledged by the new
* Cumulative TSN Ack and by Gap Ack Blocks.
*
* o When partial_bytes_acked is equal to or greater than cwnd and
* before the arrival of the SACK the sender had cwnd or more bytes
* of data outstanding (i.e., before arrival of the SACK, flightsize
* was greater than or equal to cwnd), increase cwnd by MTU, and
* reset partial_bytes_acked to (partial_bytes_acked - cwnd).
*
* o Same as in the slow start, when the sender does not transmit DATA
* on a given transport address, the cwnd of the transport address
* should be adjusted to max(cwnd / 2, 4*MTU) per RTO.
*
*
*
*
*
* Stewart Standards Track [Page 97]
*
* RFC 4960 Stream Control Transmission Protocol September 2007
*
*
* o When all of the data transmitted by the sender has been
* acknowledged by the receiver, partial_bytes_acked is initialized
* to 0.
*
*/
if (didAdvance)
{
_partial_bytes_acked += totalAcked;
if ((_partial_bytes_acked >= _cwnd) && fullyUtilized)
{
_cwnd += _transpMTU;
_partial_bytes_acked -= _cwnd;
}
}
}
lock (_congestion) {
Monitor.PulseAll(_congestion);
}
}
