[VoiceOps] "Timeout" on VoIP call traversing Verizon data

[Pete Mundy]

Precisely. And those "NAT table entries" eventually time out. On CG-NAT they often time out aggressively; <60 seconds. Hence sending OPTIONS over SIP over UDP regularly keeps the NAT table entries refreshed and active and therefore the UDP 'connection' open. I've come across firewalls with 30 second timeouts, so we use 25 second keepalives (OPTIONS).

Pete

>> On 11/06/2021, at 8:24 AM, Alex Balashov <abalashov at evaristesys.com> wrote:
>> 
>> Not to muddy the waters here with needless pedantry, but:
>> 
>> While UDP may be "connectionless", the only way UDP, and in particular, symmetric SIP signalling, can work through NAT is if a stateful firewall + NAT gateway has some awareness (that is, state) of UDP "flows", or groups of packets flowing between ports consistently in some kind of temporary logical association--one might say, the endpoints have a "connection" of sorts...
>> 
>> -- Alex
>> 
> On 6/10/21 4:07 PM, Peter Beckman wrote:
> uhhhh.... SIP here is UDP, no?
> There's no connection to close for UDP.
> The source port for UDP doesn't matter. It's not part of the whole
> conversation, unless your switch cares that all communications continue to
> come from the source port. It's connectionless.
> TCP 5060 isn't even listening on our switches.
> So, maybe you're doing SIP over TCP?
> On Thu, 10 Jun 2021, Mark Wiles wrote: