latency difference between RTT numbers and actual experience

K9SO

Operating "Hunt and Pounce" in the ARRL DX contest this weekend clearly brought forward my disadvantages due to latencies in my remote setup. I wonder if someone could help me understand the sources and particularly the difference between my displayed RTT times and my actual experienced delays. 

I operate my Wisconsin station from nearly 700 miles away in North Carolina. I use a Maestro in NC to link back to a 6600 in Wisconsin. On the NC side, I have a local station running a 6500 controlled by a local PC. I'm using SmartLink on the Maestro for the remote link. Previous posts have indicated that SmartLink does not contribute to latencies after the initial setup. 

My RTT as shown on the NC Maestro ranges between 120-175mS and I only drop 1-2 packets out of every million or so sent (a "GOOD" connection).  But when I send a CW "DIT" from NC [MAESTRO ==>6600 in Wis] and wait to hear it back in NC on the local 6500, the latency is easy much more like 500mS and I'm trying to understand the difference between the RTT  number and the actual round trip "DIT" times I'm experiencing. 

I run a PFSense site-to-site VPN running on two boxes each with Celeron N3160 processors. I know this contributes a lot to the overall latency, but it doesn't seem to be reflected in the RTT times.

Is it possible that the RTT measurement doesn't include the VPN encryption delays? That might explain why I'm seeing such a difference. If not, can anyone help me understand what's going on?

Bob K8RC

Chip Swett

I have the same issues between my remote base in Maine and home base in South Carolina.  I prefer to 'run' in contests rather than S&P, but the latencies make running almost impossible.

JohnSweeney

The Flex radios have inherent latency in their design, typically 150 ms or so. If you are using Flex radios on both ends, that is already 300 ms. I operate my IL station from FL and I see the same delays on CW but it has not caused any problems working stations. You do not need VPN for the Maestro, but I do not know the latency involved utilizing the Smartlink server. I also use a VPN connection for other things back home, but use OpenVPN. OpenVPN latency has been about 50 ms. (Comcast to COmcast) I have tested FT8 running on a local PC in IL and also running in FL over DAX and have no problem making FT8 QSO’s. Typically the time delay in FT8 shows up as .2 or .3 seconds. I know this does not answer your question, but thought it might help knowing others are operating in a similar manner.

Stan VA7NF

K9SO

K9SO

K9SO

Bob, you're right, but even if I quadruple the 700 mile path length to account for multiple skip it doesn't add up to much more than 20mS. I'm trying to understand hundreds of milliseconds added delay here. 

Fred

Jim Gilliam

Mike-VA3MW

If you do some searching in the community, you will find a few posts regarding Ping and RTT, which are 2 different measurements.

RTT, if I remember correctly is measured between applications.  Ping is measured at the machine level.  RTT is usually longer (not always).

As for 100ms latency, I have yet to see it make a difference despite people saying it does.  If you are a run station you will work the first station you can copy 100% of the callsign and calling first is not always the right way to break a pile up unless you are the loudest.   

When I run, I might hear a weak station, start to copy the first 2 letters and then someone blows him away with a much stronger signal that I easily copy.  I will work that person and then go back to the weaker station.  This is how run stations keep their numbers up.

The process on breaking pileups is well discussed in various Contest University's.   First in does not always win.

Mike 

K9SO

K1ESE

K9SO