[CentOS] Centos 7: UPD packet checksum verification?

Tue Jan 28 20:55:43 UTC 2020
hw <hw at gc-24.de>

On Tuesday, January 28, 2020 1:50:57 PM CET Stephen John Smoogen wrote:
> On Sun, 26 Jan 2020 at 20:45, hw <hw at gc-24.de> wrote:
> > > I'm not sure I understand what you are asking.
> > 
> > It is about VOIP calls via SRTP being interrupted at irregular intervals. 
> > The intervals appear to depend on the time of day:  Such phone calls can
> > last for a duration of about 5--25 minutes during the day to up to 1.5
> > hours at around 3am before being interrupted.
> UDP is called Unreliable Datagram Protocol for a reason. It can be
> dropped at all kinds of places in between the two users depending on
> how busy the routers/firewalls between 2 users can be.

How would packets being dropped explain the replay errors and authentication 

> Packets can get
> out of order or a dozen other things which then relies on the
> application layer to put the things back in 'order'.

libsrtp seems to have provisions to deal with packets arriving out of order.

> For voice, that
> usually means a drop or other ugliness because it is assumed that if
> the quality is too bad, the people would just call each other again.

That's a funny idea.  Phone calls just worked fine and were good quality 25 
years ago, and mostly long before that.  I have never expected to have to call 
anyone back because of poor quality in over 40 years, and I'm not going to 
start to expect that now.

It's unacceptable, and it's not feasible, either.  For example, try to call 
paypal to solve some issue with your account.  It can take an hour before they 
call you back because everyone is busy.  Finally you talk to someone and just 
after you explained the problem, the call is interrupted.  Good luck calling 
the same person back.  You won't get anywhere because your next try will only 
result in another interrupted call.

> For the most part this works pretty well but all it takes is a
> firewall to get busy on something else and you have a bunch of UDP
> packets out of order and people's calls dropping.

VOIP calls are worlds away from what phone calls used to be.  Dropping calls 
has never been an option and is not an option now.