Topic/pull dctcp #536
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Topic/pull dctcp #536
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ecnEnabled was the previous name
DUPTHRESH is now configurable via dupthresh parameter in Tcp.ned
The initial value for Slow Start threshold is now configurable via NED parameter initialSsthresh in Tcp.ned. The default value is set arbitrarily high (0xFFFFFFFF)
Raw amount of payload bytes received at the Tcp including duplicates, out of order, etc) for TCP throughput calculation
Additional handling of IP/ECN (on top of settig gotCeIndication) can be implemented by overriding processEcnInEstablished() Marking strategy can be implemented by overriding shouldMarkAck(). The default implementaion (in TcpAlgorithm) marks an Ack when in ecnEchoState. ecnEchoState is reset when CWR (congestion window reduced) is received.
Since DcTcp MUST adhere to standard Tcp behaviour (Slow Start, Fast-Retransmit, Congestion Avoidance, Fast-Recovery, packet drops, ...) the implementation is based on TcpReno class by overriding receivedDataAck(). It reduces the cwnd window by a fraction of marked data DCTCP.Alpha = DCTCP.Alpha * (1 - g) + g * M cwnd = cwnd * (1 - DCTCP.Alpha / 2) Addional state variables are in dedicated class. Overrides processEcnInEstablished() - set state->dctcp_ce based on gotCeIndication - set ack_now if necessary It also overrides shouldMarkAck() - marks only when state->dctcp_ce is set (only one marked Ack for one received marked data segment) Tcp.ned extended with configurable dtcpGamma (default 0.0625 (1/16))
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merged. |
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This is a DCTCP implementation based on RFC 8257.
It based on the TCP Reno (slow start, fast retransmit, fast recovery, congestion avoidance).
In case of ECN (Explicit Congestion Notification) the DCTCP behaves differently than typical TCP.
Each ECN marked data packet is reflected in one Ack packet (normal TCP sends ECE marked Acks until it receives CWR).
The sender then uses two equations to reduce cwnd
where g is preconfigured variable and M is the ration of bytesMarked/bytesAcked.
and
Also included is one scenario (Incast) with DcTcp config and TcpReno for easy comparison.