📄 net_tcp.h
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* there SHOULD be an ACK for at least every second segment".
*
* (B) RFC #2581, Section 4.2 reiterates that "an ACK SHOULD be generated for at
* least every second full-sized segment".
*
* (2) However, RFC #2581, Section 4.2 states that "an implementation is deemed to
* comply with this requirement ... by acknowledging at least every second segment,
* regardless of size".
*
* (b) (1) RFC #1122, Section 4.2.3.2 states that "an ACK should not be excessively delayed;
* in particular, the delay MUST be less than 0.5 seconds".
*
* (2) RFC #2581, Section 4.2 reiterates that "an ACK ... MUST be generated within 500 ms
* of the arrival of the first unacknowledged packet".
*
* See also 'net_tcp.c NetTCP_TxConnAck() Note #6'.
*$PAGE*
* (7) RFC #1122, Section 4.2.3.5 states that "excessive retransmission of the same segment by TCP
* indicates some failure of the remote host or the Internet path".
*
* (a) "The following procedure MUST be used to handle excessive retransmissions of data segments" :
*
* (a) "There are ... thresholds ... measuring the amount of retransmission that has occurred
* for the same segment ... measured in time units or as a count of retransmissions."
*
* (c) "When the number of transmissions of the same segment reaches a threshold ... close the
* connection."
*
* (d) "An application MUST be able to set the [threshold] value ... for a particular connection.
* For example, an interactive application might set [the threshold value] to 'infinity'."
*
* See also 'net_tcp.c NetTCP_TxConnReTxQ() Note #3'.
*
* (b) (1) (A) "The value of ... [the threshold] SHOULD correspond to at least 100 seconds."
*
* (B) Therefore, the minimum threshold value is calculated as follows :
*
* [ ] Minimum
* (1) Summation [ Exponential * (Exponential ^ (N - 1)) ] >= Retransmission
* i = 1 --> i = N [ Scalar Base ] Threshold
*
* Summation [ 3 * (2 ^ (N - 1))] >= 100 seconds
* i = 1 --> i = N
*
* N >= 5.06
*
* (2) N = 6
*
* where
* N Minimum Excessive Retransmission Threshold
* (in number of retransmissions)
* Exponential Scalar Exponential Scalar = 3 (see 'TCP ROUND-TRIP
* TIME (RTT) DEFINES Note #3ab')
* Exponential Base Exponential Base = 2 (see 'TCP ROUND-TRIP
* TIME (RTT) DEFINES Note #3c2')
* Minimum Retransmission Minimum Excessive Retransmission Threshold
* Threshold (in seconds; see Note #7b1A)
*
* (2) (A) Stevens, TCP/IP Illustrated, Volume 1, 8th Printing, Section 21.2, Page 299
* states that "on most implementations this total timeout value is not tunable
* ... and its default is ... the more common 9 minutes".
*
* (B) Therefore, the default threshold value is calculated as follows :
*
* (1) [ ]
* [ Exponential * (Exponential ^ (M - 1)) , when < Maximum Exponential ]
* [ Scalar Base Timeout Value ] Common
* Summation [ ] >= Retransmission
* i = 1 --> i = M [ Maximum Exponential ] Threshold
* [ Timeout Value , otherwise ]
* [ ]
*
* [ ]
* [ 3 * (2 ^ (M - 1)) , when < 64 seconds ]
* Summation [ ] >= 9 minutes
* i = 1 --> i = M [ 64 seconds , otherwise ]
* [ ]
*
* M >= 11.98
*
* (2) M = 12
*
* where
* M Default Excessive Retransmission Threshold
* (in number of retransmissions)
* Exponential Scalar Exponential Scalar = 3 (see 'TCP ROUND-TRIP
* TIME (RTT) DEFINES Note #3ab')
* Exponential Base Exponential Base = 2 (see 'TCP ROUND-TRIP
* TIME (RTT) DEFINES Note #3c2')
* Maximum Exponential Maximum Exponential Timeout Value (see 'TCP
* Timeout Value ROUND-TRIP TIME (RTT) DEFINES Note #3c3')
* Common Retransmission Common Default Retransmission Threshold
* Threshold (in minutes; see Note #7b2A)
*********************************************************************************************************
*/
/*$PAGE*/
/* See Note #2b3. */
#define NET_TCP_SST_UNACKD_DATA_NUMER 1
#define NET_TCP_SST_UNACKD_DATA_DENOM 2
#define NET_TCP_SST_MSS_SCALAR 2
#define NET_TCP_CONG_WIN_MSS_SCALAR_INIT 2 /* See Note #3a. */
#define NET_TCP_CONG_WIN_MSS_SCALAR_INC 1 /* See Notes #3b & #4c. */
#define NET_TCP_CONG_WIN_MSS_SCALAR_TIMEOUT 1 /* See Note #3c. */
#define NET_TCP_FAST_RE_TX_ACK_DUP_TH 3 /* See Note #4a. */
/* See Note #4b2. */
#define NET_TCP_FAST_RECOVERY_MSS_SCALAR NET_TCP_FAST_RE_TX_ACK_DUP_TH
/* See Note #5a1D. */
#define NET_TCP_RX_SILLY_WIN_NUMER 1
#define NET_TCP_RX_SILLY_WIN_DENOM 2
/* See Note #5b3. */
#define NET_TCP_TX_SILLY_WIN_NUMER 1
#define NET_TCP_TX_SILLY_WIN_DENOM 2
/* See Note #5b4. */
#define NET_TCP_TX_SILLY_WIN_TIMEOUT_MIN_MS 100
#define NET_TCP_TX_SILLY_WIN_TIMEOUT_MAX_MS 1000
#define NET_TCP_TX_SILLY_WIN_TIMEOUT_DFLT_MS NET_TCP_TX_SILLY_WIN_TIMEOUT_MAX_MS
#define NET_TCP_ACK_DLY_CNT_TH 2 /* See Note #6a. */
#define NET_TCP_ACK_DLY_TIME_MIN_MS 0
#define NET_TCP_ACK_DLY_TIME_MAX_MS 500 /* See Note #6b. */
#define NET_TCP_RE_TX_TH_MIN 6 /* See Note #7b1B2. */
#define NET_TCP_RE_TX_TH_MAX DEF_INT_16U_MAX_VAL /* See Note #7ad. */
#define NET_TCP_RE_TX_TH_DFLT 12 /* See Note #7b2B2. */
/*$PAGE*/
/*
*********************************************************************************************************
* TCP ROUND-TRIP TIME (RTT) / RE-TRANSMIT TIMEOUT (RTO) DEFINES
*
* Note(s) : (1) See the following RFC's for TCP Round-Trip Times (RTT) & Re-transmit Timeout (RTO) summary :
*
* (a) RFC #2988 TCP Round-Trip Time Calculations (RTT) /
* (b) RFC #1122 TCP Retransmission Timeout (RTO)
* (1) Section 4.2.2.15
* (2) Section 4.2.3.1
* (c) RFC # 793, Section 3.7 'Retransmission Timeout'
* (d) Jacobson/Karels, "Congestion Avoidance and Control"
* (e) Karn/Partridge, "Improving Round-Trip Time Estimates in Reliable Transport Protocols"
*
*
* (2) (a) RFC #793, Section 3.7 'Data Communication : Retransmission Timeout' states that
* "because of the variability of the networks that compose an internetwork system
* and the wide range of uses of TCP connections the retransmission timeout must be
* dynamically determined. One procedure for determining a retransmission time out
* is given here as an illustration".
*
* (b) However, RFC #1122, Section 4.2.2.15 states that "the algorithm suggested in
* RFC-793 for calculating the retransmission timeout is now known to be inadequate"
* & Section 4.2.3.1 states that "a host TCP MUST implement Karn's algorithm and
* Jacobson's algorithm for computing the retransmission timeout".
*
* (c) Further, RFC #2988, Section 1 states that "this document codifies the algorithm
* for setting the RTO ... expands on the discussion in section 4.2.3.1 of RFC 1122
* ... [but] does not alter the ... retransmission ... behavior outlined in RFC 2581".
*
* (3) (a) (1) (A) (1) RFC #1122, Section 4.2.3.1 states that "the following values SHOULD be
* used to initialize the estimation parameters for a new connection" :
*
* (a) RTT = 0 seconds
* (b) RTO = 3 seconds
*
* where
* RTO Retransmission Timeout
* RTT Round-Trip Time
*
* (A) RFC #2988, Section 2.1 reiterates that "until a round-trip time (RTT)
* measurement has been made ... the sender SHOULD set RTO <- 3 seconds".
*
* (B) Furthermore, RFC #1122, Section 4.2.3.1.(b) states that "the smoothed
* variance is to be initialized to the value that will result in" these
* values.
*
* Since computing the RTT retransmit timer is given by the following
* equation (see RFC #2988, Section 2.3) :
*
* (1) RTO = RTT_Avg + (RTT_RTO_Gain * RTT_Dev)
*
* then the RTT deviation, or smoothed variance, is given by the following
* equation :
*
* (2) RTT_Dev = (RTO - RTT_Avg) / RTT_RTO_Gain
*
* where
* RTT_Avg RTT Average
* RTT_Dev RTT Deviation
* RTT_RTO_Gain RTT-RTO Gain
*
*
* (2) However, since RFC #2988, Section 2.2 amends the RFC #1122, Section
* 4.2.3.1 RTT initialization; the smoothed RTT average & deviation do
* NOT truly require explicit initialization. Nonetheless, these RTT
* values are initialized to conform with RFC #1122, Section 4.2.3.1.
*
* See also 'net_tcp.c NetTCP_TxConnRTT_Init() Note #1'
* & 'net_tcp.c NetTCP_TxConnRTO_Init() Note #2'.
*$PAGE*
* (B) RFC #2988, Section 2 states that "the rules governing the computation of SRTT
* (smoothed round-trip time), RTTVAR RTTVAR (round-trip time variation), and RTO
* are as follows" :
*
* (a) RFC #2988, Section 2.2 states that for "the first RTT measurement R ...
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