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udptl: Don't eat sequence numbers until OK is received

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Scenario:
Local fax -> Asterisk w/ firewall -> Provider -> Remote fax

* Local fax starts rtp call to remote fax
* Remote fax starts t38 call back to local fax.
* Local fax sends t38 no-signal to Asterisk before sending an OK.
* udptl processes the frame and increments the expected sequence number.
* chan_sip drops the frame because the call isn't up so nothing goes out
  the external interface to open the port for incoming packets.
* Local fax sends OK and Asterisk sends OK to the remote fax.
* Remote fax sends t38 packets which are dropped by the firewall.
* Local fax re-sends t38 no-signal with the same sequence number.
* udptl drops the frame because it thinks it's a dup.
* Still no outgoing packets to open the firewall.
* t38 negotiation fails.

The patch drops frames t38 received before udptl sequence processing
when the call hasn't been answered yet.  The second no-signal frame
is then seen as new and is relayed out the external interface which
opens the port and allows negotiation to continue.

ASTERISK-26034 #close

Change-Id: I11744b39748bd2ecbbe8ea84cdb4f3c5943c5af9
This commit is contained in:
George Joseph
2016-05-18 06:54:14 -06:00
committed by Mark Michelson
parent ae81b55361
commit 6e5e84458f
1 changed files with 12 additions and 0 deletions
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12
main/udptl.c
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@@ -769,6 +769,18 @@ struct ast_frame *ast_udptl_read(struct ast_udptl *udptl)
return &ast_null_frame;
}
/*
* If early media isn't turned on for the channel driver, it's going to
* drop this frame. By that time though, udptl has already incremented
* the expected sequence number so if the CPE re-sends, the second frame
* will be dropped as a dup even though the first frame never went through.
* So we drop the frame here if the channel isn't up. 'tag' is set by the
* channel drivers on T38_ENABLED or T38_PEER_REINVITE.
*/
if (udptl->tag == NULL) {
return &ast_null_frame;
}
if (udptl->nat) {
/* Send to whoever sent to us */
if (ast_sockaddr_cmp(&udptl->them, &addr)) {