I have the following topology setup.
User B does a SUBSCRIBE and INVITE to Focus A
At some point, User B loses connectivity due to a WiFi dropout or other such network interface change that is transient.
If Focus A sends a NOTIFY to User B, the NOTIFY to User B will fail with a locally generated 408 before Proxy B sends back a 503 or 504 message. Also because this is a non-INVITE transaction, no 100 Trying is sent by Proxy A or Proxy B.
Now because this was a locally generated 408 error a DNS graylist entry is added for the IP Address of Proxy A since it was an in-dialog message that was sent based on a numerical IP Route header.
This then causes all of Focus A's other traffic which is Routed through Proxy A to temporarily fail including new transactions.
Another interesting side effect is that even though the original Route header did not include a transport= value (Route: x.x.x.x:port), resip will try to contact that IP:Port with TCP even though TCP was never part of the original DNS lookup (not in the SRV records).
I can see a few possible ways to fix this issue:
- Change Proxy A to send 100 Trying for non-INVITE transactions. This will change the TransactionState from "Trying" to "Connecting" which then won't trigger a graylist (requires Proxy changes)
- Change TransactionState class to only graylist entries for INVITE transactions based on "mMachine==ClientInvite" since those are the only ones which seem to send 100 Trying messages.
- Allow Application writer control over black/gray list.
- If we don't want to break source compatibility, we could modify the MarkListener class to add a new virtual function "before" insertion which could return true/false or allow modifying the Mark or Expirery.
- If we wanted to break source compatibility, we could modify the current onMark callback to have a new signature and be called before insertion allowing changing of the values.
If anybody is interested, I have a full resip debug log showing this issue from Focus A's perspective.
Aron Rosenberg
Sr. Director, Engineering,
LifeSize, a division of Logitech