[mythtv-users] Strange Issue with Myth and HDHomeRun

Stroller linux.luser at myrealbox.com
Tue Feb 13 19:46:04 UTC 2007

Sorry for my premature reply.  I do that all the time, which is why  
I'll be spending tomorrow alone. :(

I didn't appreciate you knew the difference between a hub & a switch,  
so here's the full explanation. I'm afraid I have hacked your post  
apart to support my analysis, and so I have quoted some of your  
sentences out of order. I do hope you don't feel I'm dismissing your  
view that you "can't see how it could be" the network, but the my  
visualisation of the problem seems so clear to me, I don't see how it  
can be anything else (although I'd love for you to prove me wrong).

On 13 Feb 2007, at 04:41, John Welch wrote:
> I'll try to describe my network the best I can.  The myth B/E [and]  
> The HDHR ... are both connected to an 8-port 10/100 hub.  Also  
> connected to this hub is the 'orange' network card of the IPCop  
> box ...  The 'green' network card of the IPCop box ... is connected  
> to an el-cheapo 8-port fast ethernet switch in the same room.  The  
> F/E is located in another room where it is connected to another 8- 
> port fast ethernet switch (same model as the first).
>>>  I can record content from the HDHR as long as I don't do  
>>> anything with Myth on my F/E system while the recording is taking  
>>> place.  However, as soon as I bring up MythTV on my F/E

.... introducing collisions on the hub...

>>> the HDHR recording becomes "corrupt", for a lack of a better  
>>> term.  By corrupt I mean there are severe video and audio  
>>> breakups and dropouts to the point where the recording is  
>>> unwatchable.  This is not just a playback issue; the corruption  
>>> is actually in the file.

When you record content from the HDHR packets are able to stream  
through the hub at full 100mBit. The FE starts interrupting them, as  
it makes requests to the BE for guide & programme data.

The HDRD is saying "and then this bloke walks in to the room, look at  
that bullet go flying, oh, it's a goal, well done Ayrton Senna, at  
pole pos..."
"hello, I'm the front end. Can I have the icon for BBC 1 please?"
BE: "I'm sorry, HDRD, I missed that. There was a packet collision.  
Can you wait 0.2 seconds and stay that again, please?"

Naturally the video stutters here.

> In the process of troubleshooting this problem I tried eliminating  
> the switch in the F/E room and also swapping out the hub with a  
> switch.  Neither change seemed to make any difference, although I  
> have to say I didn't really test it that thoroughly.

I think a longer look at this would be warranted.

> Right now I'm in the process of setting up another myth B/E on the  
> green network.

I don't understand the need for this. IMO the simple way to  
troubleshoot this is set the subnet mask on all machines to (manually allocated IP addresses), plug them all into a  
single switch (or range-extend using only the two switches, but  
definitely not the hub) and switch the IPcop box off. They'll all be  
on the same network then and I am absolutely convinced you'll see  
this issue go away. It shouldn't take more than an hour or two to do  
this, and I'm convinced you'll see the problems go away.

I know it seems like a chore to mess around with your whole network,  
and maybe have to connect keyboards & monitors to servers to assign  
IPs manually (if they're issued by DHCP at the moment?) before  
changing the subnet mask, but I'm utterly convinced you could  
essentially resolve the problem in a couple of hours.

> Even if this proves to be the answer I'd still like to know why my  
> original setup isn't working.

I hope I've answered this clearly.

I know you've said:
>  I would also think if it was a network issue I should be able to  
> see errors popping up somewhere; netstat, ipconfig, dmesg, /var/ 
> logs, etc. and I'm not.  Maybe I'm just not looking in the right  
> place.  Also, if I was saturating the network I would think  
> performance on the F/E would suffer, but I don't see any evidence  
> of that ( i.e. jumping from menu to menu is fine, playing back  
> recordings from other inputs is fine, etc.).

But it seems obvious to me that the hub is the core issue (and I'd  
like the IPcop box out of the way in the first instance, just to  
absolutely prove that the configuration I describe above solves the  
problem). As soon as I properly read your description of your  
topology I just see all these collisions taking place between the  
HDDR & the FE.

I've already said I'm not so familiar with `netstat`, but I wouldn't  
expect to see network collisions in dmesg or /var/logs (and I'm not  
sure about `ipconfig`).

> Maybe I'm being a little too paranoid, but this setup has never  
> caused me any issues in the past.

Have you been streaming a lot of hi-def video in the past?

> I even asked the question about this configuration on the HDHR  
> forums prior to purchasing the device.  Other than one minor issue  
> with not being able to use the Windows GUI 'hdhomerun_config'  
> program because it couldn't cross networks there were no objections  
> raised; and one of the responses was from the main tech guy on  
> there (Nick).

Maybe these guys didn't realise you were using a hub & not a switch.  
Unfortunately the words are often used interchangeably.

> My thinking for putting the IPCop system in the DMZ was always on  
> system, connected to the Internet, which I wanted to be able to  
> connect to remotely.

I can't really comment on this, because it's just not the way I'd do  
things. I have all my machines on a single LAN & simply forward or  
open ports to the machines to which I wish to allow external access.


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