TCP_ESTATS_PATH_ROD_v0 structure (tcpestats.h)
The TCP_ESTATS_PATH_ROD_v0 structure contains read-only dynamic information for extended TCP statistics on network path measurement for a TCP connection.
Syntax
typedef struct _TCP_ESTATS_PATH_ROD_v0 {
ULONG FastRetran;
ULONG Timeouts;
ULONG SubsequentTimeouts;
ULONG CurTimeoutCount;
ULONG AbruptTimeouts;
ULONG PktsRetrans;
ULONG BytesRetrans;
ULONG DupAcksIn;
ULONG SacksRcvd;
ULONG SackBlocksRcvd;
ULONG CongSignals;
ULONG PreCongSumCwnd;
ULONG PreCongSumRtt;
ULONG PostCongSumRtt;
ULONG PostCongCountRtt;
ULONG EcnSignals;
ULONG EceRcvd;
ULONG SendStall;
ULONG QuenchRcvd;
ULONG RetranThresh;
ULONG SndDupAckEpisodes;
ULONG SumBytesReordered;
ULONG NonRecovDa;
ULONG NonRecovDaEpisodes;
ULONG AckAfterFr;
ULONG DsackDups;
ULONG SampleRtt;
ULONG SmoothedRtt;
ULONG RttVar;
ULONG MaxRtt;
ULONG MinRtt;
ULONG SumRtt;
ULONG CountRtt;
ULONG CurRto;
ULONG MaxRto;
ULONG MinRto;
ULONG CurMss;
ULONG MaxMss;
ULONG MinMss;
ULONG SpuriousRtoDetections;
} TCP_ESTATS_PATH_ROD_v0, *PTCP_ESTATS_PATH_ROD_v0;
Members
FastRetran
Type: ULONG
The number of invocations of the Fast Retransmit algorithm.
Timeouts
Type: ULONG
The number of times the retransmit timeout has expired when the retransmission timer backoff multiplier is equal to one.
SubsequentTimeouts
Type: ULONG
The number of times the retransmit timeout has expired after the retransmission timer has been doubled.
For more information, see section 5.5 of RFC 2988 discussed in the Remarks below.
CurTimeoutCount
Type: ULONG
The current number of times the retransmit timeout has expired without receiving an acknowledgment for new data.
The CurTimeoutCount member is reset to zero when new data is acknowledged and incremented for each invocation of Section 5.5 of RFC 2988.
AbruptTimeouts
Type: ULONG
The number of timeouts that occurred without any immediately preceding duplicate acknowledgments or other indications of congestion. Abrupt timeouts indicate that the path lost an entire window of data or acknowledgments.
Timeouts that are preceded by duplicate acknowledgments or other congestion signals (Explicit Congestion Notification, for example) are not counted as abrupt, and might have been avoided by a more sophisticated Fast Retransmit algorithm.
PktsRetrans
Type: ULONG
The number of segments transmitted containing at least some retransmitted data.
BytesRetrans
Type: ULONG
The number of bytes retransmitted.
DupAcksIn
Type: ULONG
The number of duplicate ACKs received.
SacksRcvd
Type: ULONG
The number of Selective Acknowledgment (SACK) options received.
SackBlocksRcvd
Type: ULONG
The number of SACK blocks received (within SACK options).
CongSignals
Type: ULONG
The number of multiplicative downward congestion window adjustments due to all forms of congestion signals, including Fast Retransmit, Explicit Congestion Notification (ECN), and timeouts. This member summarizes all events that invoke the Multiplicative Decrease (MD) portion of Additive Increase Multiplicative Decrease (AIMD) congestion control, and as such is the best indicator of how a congestion windows is being affected by congestion.
Note that retransmission timeouts multiplicatively reduce the window implicitly by setting the slow start threshold size, and are included in the value stored in the CongSignals member. In order to minimize spurious congestion indications due to out-of-order segments, the CongSignals member is incremented in association with the Fast Retransmit algorithm.
PreCongSumCwnd
Type: ULONG
The sum of the values of the congestion window, in bytes, captured each time a congestion signal is received.
This member is updated each time the CongSignals member is incremented, such that the change in the PreCongSumCwnd member divided by the change in the CongSignals member is the average window (over some interval) just prior to a congestion signal.
PreCongSumRtt
Type: ULONG
The sum, in milliseconds, of the last sample of the network round-trip-time (RTT) prior to the received congestion signals. The last sample of the RTT is stored in the SampleRtt member.
The PreCongSumRtt member is updated each time the CongSignals member is incremented, such that the change in the PreCongSumRtt divided by the change in the CongSignals member is the average RTT (over some interval) just prior to a congestion signal.
PostCongSumRtt
Type: ULONG
The sum, in milliseconds, of the first sample of the network RTT (stored in the SampleRtt member) following each congestion signal.
The change in the PostCongSumRtt member divided by the change in the PostCongCountRtt member is the average RTT (over some interval) just after a congestion signal.
PostCongCountRtt
Type: ULONG
The number of RTT samples, in bytes, included in the PostCongSumRtt member.
The change in the PostCongSumRtt member divided by the change in the PostCongCountRtt member is the average RTT (over some interval) just after a congestion signal.
EcnSignals
Type: ULONG
The number of congestion signals delivered to the TCP sender via ECN.
This is typically the number of segments bearing Echo Congestion
Experienced (ECE) bits, but also includes segments failing the ECN nonce check or other explicit congestion signals.
EceRcvd
Type: ULONG
The number of segments received with IP headers bearing Congestion Experienced (CE) markings.
SendStall
Type: ULONG
The number of interface stalls or other sender local resource limitations that are treated as congestion signals.
QuenchRcvd
Type: ULONG
Reserved for future use. This member is always set to zero.
RetranThresh
Type: ULONG
The number of duplicate acknowledgments required to trigger Fast Retransmit.
Note that although this is constant in traditional Reno TCP implementations, it is adaptive in many newer TCP implementations.
SndDupAckEpisodes
Type: ULONG
The number of Duplicate Acks Sent when prior Ack was not duplicate. This is the number of times that a contiguous series of duplicate acknowledgments have been sent.
This is an indication of the number of data segments lost or reordered on the path from the remote TCP endpoint to the near TCP endpoint.
SumBytesReordered
Type: ULONG
The sum of the amounts SND.UNA advances on the acknowledgment which ends a dup-ack episode without a retransmission.
Note the change in the SumBytesReordered member divided by the change in the NonRecovDaEpisodes member is an estimate of the average reordering distance, over some interval.
NonRecovDa
Type: ULONG
The number of duplicate acks (or SACKS) that did not trigger a Fast Retransmit because ACK advanced prior to the number of duplicate acknowledgments reaching the RetranThresh.
Note that the change in the NonRecovDa member divided by the change in the NonRecovDaEpisodes member is an estimate of the average reordering distance in segments over some interval.
NonRecovDaEpisodes
Type: ULONG
The number of duplicate acknowledgment episodes that did not trigger a Fast Retransmit because ACK advanced prior to the number of duplicate acknowledgments reaching the RetranThresh.
AckAfterFr
Type: ULONG
Reserved for future use. This member is always set to zero.
DsackDups
Type: ULONG
The number of duplicate segments reported to the local host by D-SACK blocks.
SampleRtt
Type: ULONG
The most recent raw network round trip time measurement, in milliseconds, used in calculation of the retransmission timer (RTO).
SmoothedRtt
Type: ULONG
The smoothed round trip time, in milliseconds, used in calculation of the RTO.
RttVar
Type: ULONG
The round trip time variation, in milliseconds, used in calculation of the RTO.
MaxRtt
Type: ULONG
The maximum sampled round trip time in milliseconds.
MinRtt
Type: ULONG
The minimum sampled round trip time in milliseconds.
SumRtt
Type: ULONG
The sum of all sampled round trip times in milliseconds.
Note that the change in the SumRtt member divided by the change in the CountRtt member is the mean RTT, uniformly averaged over an enter interval.
CountRtt
Type: ULONG
The number of round trip time samples included in the SumRtt member.
CurRto
Type: ULONG
The current value, in milliseconds, of the retransmit timer.
MaxRto
Type: ULONG
The maximum value, in milliseconds, of the retransmit timer.
MinRto
Type: ULONG
The minimum value, in milliseconds, of the retransmit timer.
CurMss
Type: ULONG
The current maximum segment size (MSS), in bytes.
MaxMss
Type: ULONG
The maximum MSS, in bytes.
MinMss
Type: ULONG
The minimum MSS, in bytes.
SpuriousRtoDetections
Type: ULONG
The number of acknowledgments reporting segments that have already been retransmitted due to a Retransmission Timeout.
Remarks
The TCP_ESTATS_PATH_ROD_v0 structure is used as part of the TCP extended statistics feature available on Windows Vista and later.
The TCP_ESTATS_PATH_ROD_v0 is defined as version 0 of the structure for read-only dynamic information on network path measurement for a TCP connection. This information is available after the connection has been established.
The TCP_ESTATS_PATH_ROD_v0 structure is retrieved by calls to the GetPerTcp6ConnectionEStats or GetPerTcpConnectionEStats functions when TcpConnectionEstatsPath is passed in the EstatsType parameter. Extended TCP statistics need to be enabled to retrieve this structure.
The path MTU discovery and maximum segment size are discussed in detail in the IETF RFC 1191 on Path MTU discovery. For more information, see http://www.ietf.org/rfc/rfc1191.txt.
TCP congestion control and congestion control algorithms are discussed in detail in the IETF RFC 2581 on TCP Congestion Control. For more information, see http://www.ietf.org/rfc/rfc2581.txt.
SACK and an extension to the SACK option are discussed in detail in the IETF RFC 2883 on An Extension to the Selective Acknowledgment (SACK) Option for TCP. For more information, see http://www.ietf.org/rfc/rfc2883.txt.
The TCP retransmission timer (RTO) and the smoothed round-trip-time (RTT) are discussed in detail in the IETF RFC 2988 on Computing TCP's Retransmission Timer. For more information, see http://www.ietf.org/rfc/rfc2988.txt.
Explicit Congestion Notification in IP is discussed in detail in the IETF RFC 2581 on The Addition of Explicit Congestion Notification (ECN) to IP. For more information, see http://www.ietf.org/rfc/rfc3168.txt.
The members of this structure are defined in the IETF RFC on the TCP Extended Statistics MIB. For more information, see http://www.ietf.org/rfc/rfc4898.txt.
The following is the mapping of the members in the TCP_ESTATS_PATH_ROD_v0 structure to the entries defined in RFC 4898 for extended TCP statistics:
The TCP_ESTATS_FINE_RTT_ROD_v0 structure has members that provide similar data to the RttVar, MaxRtt, MinRtt, and SumRtt members of the TCP_ESTATS_PATH_ROD_v0 structure. However, the time is reported in microseconds for the similar members of the TCP_ESTATS_FINE_RTT_ROD_v0 structure.
Requirements
| Requirement | Value |
|---|---|
| Minimum supported client | Windows Vista [desktop apps only] |
| Minimum supported server | Windows Server 2008 [desktop apps only] |
| Header | tcpestats.h |