[asterisk-dev] [Code Review] chan_sip: more accurate retransmissions

[David Vossel]

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https://reviewboard.asterisk.org/r/747/
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Review request for Asterisk Developers and Russell Bryant.


Summary
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Yes, there is some red in this diff, ignore it I'll fix it.

RFC3261 states that Timer A should start at 500ms (T1) by default.  In chan_sip this value initially started at 1000ms and I changed it to 500ms recently. After doing that I noticed in my packet captures that it still occasionally retransmitted starting at 1000ms instead of 500ms like I told it to.  This occurs because the scheduler runs in the do_monitor thread.  If a new retransmission is added while the do_monitor thread is sleeping then it may not detect that retransmission for nearly 1000ms.  To fix this I just poke the do_monitor thread to wake up when a new packet is sent reliably requiring retransmits.  The thread then detects the new scheduler entry and adjusts its sleep time to account for it.


Diffs
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  /trunk/channels/chan_sip.c 272526 

Diff: https://reviewboard.asterisk.org/r/747/diff


Testing
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I tested it with sipp.  sipp sends and invite and nothing more.  I watch the 200oks get retransmitted and verify the retransmission times are correct.


Thanks,

David