Re: [hylafax-users] Hardware suggestions to get Hylafax running?

[Lee Howard <faxguy@xxxxxxxxxxxxxxxx>]

Joshua Kinard wrote:
> How about this Wedging issue I saw mentioned w/ Multitechs?  Non-issue when dealing with emulated modems?

I'm not entirely certain of what the Multitech wedging issue is, and so 
it's not entirely accurate for me to make a claim that iaxmodem will 
never do the same thing.

I have seen iaxmodems "wedge" before in somewhat rare cases.  Most of 
those times it has had to do with the iaxmodem process crashing entirely 
and that iaxmodem was not being run from iniittab with "respawn" (i.e. 
it was being run in daemon mode, and thus the parent process did not 
automatically restart the child process when it crashed).  I have seen 
cases where an iaxmodem seemed to get "stuck" somehow... and it thus 
required being restarted.

The beauty of it, though, is that it *can* be entirely restarted.  So in 
the case of a crash or "wedge" the modem can be restarted without 
rebooting the server or power-cycling power to an external modem, and 
automating the restart of the iaxmodem is very easy to do.

That said, let me emphasize that crashes are quite rare.  If I can 
reproduce it then I will generally have it fixed promptly.

> Any other known cases involving runaway children (i.e., from IAXmodem) possibly grinding the server down?

There have been cases in the history of iaxmodem where a process would 
hit a bug and get into some kind of infinite loop and then start 
devouring otherwise idle CPU.  To the best of my knowledge all of those 
bugs have been fixed, and I have not heard of any cases of this 
happening in the latest releases.

>   Or is this kind of setup, while a touch complex, more bulletproof than dealing with multiport modem hardware?

Well, a modem is a modem is a modem... whether it be coded and stored in 
firmware on a chip or whether it be coded and loaded into system RAM and 
CPU it's still computer code; it's still got a DSP; and all modems are 
subject to bugs in their coding.

On hardware vs. software ... they each have their advantages and 
disadvantages.  For example, if the system will be subject to regular, 
frequent heavy loads on CPU from other activities (i.e. a public mail 
server or network file server) then running modems on CPU probably will 
be unwise.  But, at the same time, it certainly makes modem development 
and debugging relatively easy.

Thanks,

Lee.


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