[asterisk-users] how to find out one way latency

[Adam Moffett]

>> a ping is the time a packet needs for travelling to a destination and
>> back to you. So the one way latency you are refering to, should be half
>> the time your ping took.
>>
>> In your case this will be 130ms, I would say this is still reasonable.
I am probably splitting hairs, but that's not always true because 
there's no guarantee that the reply traveled the same path as the echo 
request.  If you dig into BGP issues you'll see sometimes that traffic 
one direction takes a different route than traffic the other direction.  
I don't know of any simple and accurate way to learn the "one way" 
latency so I'm surprised they specified anything other than round trip time.

> 'Ping time' is not an accurate predictor of SIP quality.
>
> A 'ping' is an ICMP Echo/reply packet and some routers consider them 
> less important than 'data' packets and service them on an 'as 
> resources permit' basis. 
That's possibly maybe true if someone's router or connection is 
overloaded and they are trying to make up for it with CoS policies while 
they save up for an upgrade.  Otherwise it's an apology for a crappy 
network.  That's the brutally honest truth.

You can make a pretty good prediction with ping.
"sudo ping -f -i .02 -s 180 -Q 0xb8 [ip]" gives a tolerable simulation 
of voip traffic.  let it run for awhile, then press ctrl+c and see how 
many packets were dropped and also check the mdev number.  If mdev is 
low and packet loss is almost nothing then you can expect decent voice 
quality.  It may not be a 100% perfect test, but I'll bet you a vast 
majority of the time I can do that test and tell you whether it's going 
to suck.

latency by itself with low jitter and no packet loss just means delay.  
It's a matter of opinion and circumstance how tolerable delay is, but I 
think your 230ms ping is at the upper edge of what most people can live 
with.  Much more than that and you'll be tempted to say 'over' at the 
end of sentence.