We've run into that too, something goofy in 4.x firmware. The sofia profile param tcp-keepalive can be set to like 60000 to send a packet once a minute to keep them open. I think I also added the flag to the socket in linux to do this tcp ping pong stuff but it appears that the polycom is doing it some other way and even with a steady flow of these, it gives up and disconnects. So this param above may fix it but I think the polycom is actually not behaving properly and we have to pay for it now with scheduler overhead in the lib. On Mon, May 13, 2013 at 2:37 PM, Spencer Thomason < spencer@5ninesolutions.com> wrote:
Understood, I though it was quite strange to see these unsolicited ACKs from the Polycoms followed by a RST.
Thanks, Spencer
On 05/13/2013 02:07 PM, Steven Schoch wrote:
On Sun, May 12, 2013 at 2:54 PM, Spencer Thomason < spencer@5ninesolutions.com> wrote:
The phones periodically send a TCP ACK ping to Freeswitch which goes unanswered and then phone then tears down the TCP connection. I'm not at all a TCP expert but should Freeswitch be responding to this unsolicited ACK?
I've been working with TCP for 25 years, and this is the first I have heard of ACK ping. A quick Google search told me that this technique involves sending a normal TCP ACK packet (which all TCP packets except the initial one have, by the way) to a random TCP port. The host will then respond with a RST packet. (Which means reset the connection because the ACK was not sent to an established connection.)
However, a firewall may filter and discard these random ACK packets. Since they're not part of "normal" TCP, no one cares.
In answer to your question, this is in the TCP layer much deeper than Freeswitch. There is nothing Freeswitch can do at this level.
-- Steve
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