PJSUA-LIB takes pains to preserve the RTP transmit sequence number for a
given call, across multiple sessions. However, a specific scenario
breaks its attempts:
1. Peer A calls peer B
2. Peer B answers; peer B creates a new media session with a
bidirectional stream
3. Peer A puts call on hold; peer B creates a new media session with
a receive-only stream
4. Peer A reinvites peer B; peer B creates a new media session with a
bidirectional stream
Between steps 3 and 4, B forgets the transmit sequence number. This is
because the initial sequence number is stored in the encoder channel of
stream #0 when the session is created, but before the session is
destroyed, the current sequence number is read from the RTCP statistics
of stream #0. A receive-only stream never updates the RTCP transmit
statistics, so the sequence number is initialized to zero at step 3 when
the session is created, and never updated between steps 3 and 4. When
peer B retrieves the sequence number to set in the new session, it
retrieves zero, and mistakenly restarts the sequence.
My patch fixes the issue by initializing RTCP transmit statistics to
meaningful values
--
KHAMSA SA
Michele Cicciotti
Research & Development
Mobile: + 39 339 3206609
E-mail: m.cicciotti at khamsalabs.net <mailto:m.cicciotti at khamsalabs.net>
KHAMSA SA
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