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SSDR for Mac - Network Stats - Radio RTT vs Radio Latency

AF3K Member ✭✭
edited September 2022 in Networking

I'm curious what others are getting for Radio RTT and Radio Latency using the SSDR for Mac Network Stats tool.

In my case Radio RTT = 3ms, and Radio Latency = 40ms, seems about the average.

According to the smartsdr-mac documentation these values should be similar so I'm wondering if this explains some of the glitchy behavior I'm seeing on a 6600. BTW, the fix recommended in the manual is to power cycle the radio but that didn't change things for me.

73, John AF3K


  • AA5SH
    AA5SH Member ✭✭

    My RTT runs about the same and the Latency on average around 24ms on the local lan. Goes higher when running remote. But to me looks good with no errors reported.

    Michael, AA5SH

  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin

    Those are pretty good numbers. All LANs will have latency and Jitter which is the variance in latency.

    What we see almost daily in the support group are network issues that can impact the radio.

    The first thing we have people check is their DHCP server settings and make sure the time is long (days) and that on an IP address renewal, the same IP address is issued. Most DHCP servers issue the same IP address. Some don't.

    The first thing we ask people to test is to run a very simple test using the link.local feature of today's networking. And, that is correct a LAN cable directly between the radio and the user client with no switch in between. If you see your glitchy behavior go away, then that is good. Now, you can look elsewhere. If you still have an issue, please open a support ticket.

    The next step would be to isolate part of your network. Personally, I have found some Gig switches to be problematic (not all). I have asked customers to swap out a Gig switch to an older 100mb/sec switch and see if the problem changes. In some cases, they have found the 100mb/sec more reliable.

    Those are some ideas.


  • AF3K
    AF3K Member ✭✭

    Hello Mike,

    Thank you for your response. That's interesting about the Gig router/switches sometimes being less reliable than the 100 Mbps ones. I don't have one to swap out right now but will try that. The IP addresses for the Flex and the Mac were reserved in the router, so DHCP wasn't involved.

    At your suggestion I did configure using link.local (Flex and Mac connected directly via ethernet cable). The results (screenshot below) are similar to the LAN. It does seem like network latency isn't an issue here for now.

    What I'm curious about is the "Radio Latency" measurement, which according to the SSDR-Mac manual it is the time the radio itself takes to answer commands. I assume this is different from network latency, and that it is a measure of radio response time as if Radio RTT (i.e. network latency) was subtracted out? The manual says Radio Latency should be 1.5x to 2x the Radio RTT latency, so I'm way over that.

    Do you have any background info on the Radio Latency measurement? Shouldn't two radios operating properly give pretty much the same measurement once network latency is out of the equation? If so, what is the range? Is it 2 x 2.5ms or is 37ms acceptable, etc.

    As always, your thoughts are appreciated.

    John, AF3K

    Here is the relevant text from section 6.5 Network Stats of the SSDR-Mac manual

  • John KB4DU
    John KB4DU Member ✭✭✭✭

    I replaced my 1 gig switch with an older 100 Mb router/WAP with the wireless disabled. No more intermittent disconnects.

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