From 6e5e84458fe89b22e4883364aa9f66b1005f9985 Mon Sep 17 00:00:00 2001
From: George Joseph <gjoseph@digium.com>
Date: Wed, 18 May 2016 06:54:14 -0600
Subject: [PATCH] udptl: Don't eat sequence numbers until OK is received
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
---
main/udptl.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/main/udptl.c b/main/udptl.c
index a0f533fd0c..e543b4e8ee 100644
--- a/main/udptl.c
+++ b/main/udptl.c
@@ -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)) {
--
GitLab