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Point-to-point VOIP?

Discussion in 'General Technical Questions and Answers' started by NN5RR, Feb 7, 2011.

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  1. NN5RR

    NN5RR Ham Member

    Hi all,

    I used IP Sound briefly for streaming audio across our company's LAN from the remote radio. Then it quit working.

    Are some of you using Skype, Teamspeak, or something else for this? What's got the highest audio bandwith and is fairly easy to set up & maintian? I'm a computer/networking guy, so I should be okay with it.

  2. N5KRC

    N5KRC Ham Member

    You can't beat Skype in terms of cost, quality, and latency. I use it for remote operation, be it from the office or from the recliner and never have any issues.

    Scott, N5KRC
  3. K7ZRZ

    K7ZRZ Ham Member


    Are you still trying to do VOIP just across the LAN or are you working outside of a LAN and the remote station somewhere off premisis? Why did your IP Sound setup quit working?? Was it something to do with a firewall change or other routing issues?

    It seems if you are just working across a LAN that shipping your VOIP out to Skype and back again is not very sensible. And also it seems as though if you are having routing/firewall issues with a local VOIP setup, you might have similar issues with Skype.

    Just some things to think about.
  4. VE3MAL

    VE3MAL Ham Member

    VLC will give you excellent control of quality/bandwidth for streaming audio. Heck, you could use loss-less Theora for CD quality audio if you were so inclined. For ease of setup, some SIP VOIP clients (like Ekiga) are able to "find" each other on a network without any server setup.
  5. NN5RR

    NN5RR Ham Member

    Wow, thanks to you and the others for great responses! Brian, I'm doing this on the LAN at the school where I teach, and both nodes are on the same subnet, so I'm not going through a firewall, bridge, or router. IP Sound started off great, then I switched it to use higher-quality settings. It worked great for a bit, then it started cutting out and/or being very noisy. I switched to the original settings, but it didn't get any better. I uninstalled and reinstalled at both locations, but it still had my entries, so I think there are registry fields that I would need to find and clean.

    So, I'm hearing that Skype won't do point-to-point VoIP. What's a good, lightweight alternate to IP Sound? I only need listening capability right now (SWL, PSK, APRS, SSTV), but I want to go to USB headset and PTT hotkey soon and get on the air, so maybe I should start out with all features from the get-go.

    Thanks for the help!
  6. N5KRC

    N5KRC Ham Member

    VOIP traffic isn't routed out to Skype's servers and back again, if both clients are on the same LAN segment; It's smart enough to realize that, and will initiate a point-to-point connection. You can easily verify this with tcpdump or wireshark.

    There's reference to it on Skype's forums. There's more documentation about it elsewhere, I just don't have it handy. I thoroughly researched VOIP solutions a few years ago when I first built my station primarily for remote operation, and my conclusion was that Skype fit the bill perfectly. Cross-platform, free, point-to-point connections, video support, auto-answer, etc. Just my opinion, of course!

    Scott, N5KRC
  7. N5KRC

    N5KRC Ham Member

    I'm bored, so did a test to confirm.... is the shack machine, is my laptop.

    As soon as the call was placed, we see the shack machine looking for the MAC address of the laptop:
    21:11:21.265020 ARP, Request who-has (00:26:bb:08:XX:XX (oui Unknown)) tell, length 46
    21:11:21.265118 ARP, Reply is-at 00:26:bb:08:XX:XX (oui Unknown), length 28
    Next we see the call setup:
    21:11:22.769468 IP > Flags [S], seq 1679465483, win 65535, options [mss 1460,nop,wscale 1,nop,nop,TS val 533948508 ecr 0,sackOK,eol], length 0
    21:11:22.770551 IP > Flags [S.], seq 380582617, ack 1679465484, win 8192, options [mss 1460,nop,wscale 8,sackOK,TS val 18333453 ecr 533948508], length 0
    21:11:22.770586 IP > Flags [.], ack 1, win 33304, options [nop,nop,TS val 533948508 ecr 18333453], length 0
    21:11:22.773961 IP > Flags [P.], seq 1:70, ack 1, win 33304, options [nop,nop,TS val 533948508 ecr 18333453], length 69
    21:11:22.776759 IP > Flags [P.], seq 1:52, ack 70, win 260, options [nop,nop,TS val 18333453 ecr 533948508], length 51
    21:11:22.776803 IP > Flags [.], ack 52, win 33278, options [nop,nop,TS val 533948508 ecr 18333453], length 0
    21:11:22.777548 IP > Flags [P.], seq 52:60, ack 70, win 260, options [nop,nop,TS val 18333453 ecr 533948508], length 8
    21:11:22.777572 IP > Flags [.], ack 60, win 33300, options [nop,nop,TS val 533948508 ecr 18333453], length 0
    21:11:22.777824 IP > Flags [P.], seq 70:78, ack 60, win 33300, options [nop,nop,TS val 533948508 ecr 18333453], length 8
    21:11:22.778802 IP > Flags [P.], seq 60:105, ack 78, win 260, options [nop,nop,TS val 18333453 ecr 533948508], length 45
    21:11:22.778835 IP > Flags [.], ack 105, win 33281, options [nop,nop,TS val 533948508 ecr 18333453], length 0
    21:11:22.779102 IP > Flags [P.], seq 78:140, ack 105, win 33304, options [nop,nop,TS val 533948508 ecr 18333453], length 62
    And then finally we start passing audio via UDP:
    21:11:22.780400 IP > UDP, length 59
    21:11:22.781662 IP > UDP, length 56
    21:11:22.781840 IP > UDP, length 28
    21:11:22.781953 IP > UDP, length 28
    21:11:22.782148 IP > UDP, length 28
    21:11:22.782767 IP > UDP, length 28
    So there ya go. Hope you find a solution that works for you, Ross!

    Scott, N5KRC
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