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ntp: don't accumulate old samples in interleaved client mode

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Check how many responses were missing before accumulating a sample using
old timestamps to avoid correcting the clock with an offset extrapolated
over a long interval.

This should be eventually done in sourcestats for all sources.
This commit is contained in:
Miroslav Lichvar 2017-07-21 12:16:21 +02:00
parent 992590e99c
commit 16afa8eb50
1 changed files with 11 additions and 4 deletions
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15
ntp_core.c
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@ -266,6 +266,10 @@ static ARR_Instance broadcasts;
/* Maximum number of missed responses to follow peer's polling interval */
#define MAX_PEER_POLL_TX 8
/* Maximum number of missed responses to accept samples using old timestamps
in the interleaved client/server mode */
#define MAX_CLIENT_INTERLEAVED_TX 4
/* Maximum ratio of local intervals in the timestamp selection of the
interleaved mode to prefer a sample using previous timestamps */
#define MAX_INTERLEAVED_L2L_RATIO 0.1
@ -1498,11 +1502,14 @@ receive_packet(NCR_Instance inst, NTP_Local_Address *local_addr,
/* Test A requires that the minimum estimate of the peer delay is not
larger than the configured maximum, in client mode that the server
processing time is sane, and in the interleaved symmetric mode that
the delay is not longer than half of the remote polling interval to
detect missed packets */
processing time is sane, in the interleaved client mode that the
timestamps are not too old, and in the interleaved symmetric mode
that the delay is not longer than half of the remote polling interval
to detect missed packets */
testA = delay - dispersion <= inst->max_delay && precision <= inst->max_delay &&
!(inst->mode == MODE_CLIENT && response_time > MAX_SERVER_INTERVAL) &&
!(inst->mode == MODE_CLIENT &&
(response_time > MAX_SERVER_INTERVAL ||
(interleaved_packet && inst->tx_count > MAX_CLIENT_INTERLEAVED_TX + 1))) &&
!(inst->mode == MODE_ACTIVE && interleaved_packet &&
delay > UTI_Log2ToDouble(message->poll - 1));