[CentOS-virt] Setting up serial ports on kvm guests

Ed Heron Ed at Heron-ent.com
Wed Feb 8 14:31:46 EST 2012

On Wed, 2012-02-08 at 13:29 -0500, James B. Byrne wrote:
> On Wed, February 8, 2012 11:06, Ed Heron wrote:
> > On Tue, 2012-01-31 at 14:01 -0500, James B. Byrne wrote:
> >> CentOS-6.2
> >>
> >> We have a dedicated CentOS-5.7 host used for fax
> >> reception
> >> and transmission that we wish to move to a CentOS-6.2
> >> virtual guest instance. The CentOS-6.2 virtual host has
> >> a
> >> 4-port serial card installed.
> >
> >   Consider replacing your multi-serial port card with a
> > VoIP analog
> > gateway and use a pre-rolled Asterisk with virtual
> > faxmodems, like
> > Elastix.  Just make sure your codec is high enough
> > quality.  We used to
> > receive faxes using a dedicated Linux box with a Comtrol
> > Rocketport and
> > an USRobotics MP8.  We Converted to SIP trunks and managed
> > to get our
> > faxes in the SIP trunks, as well.
> >
> >   This will remove the PCI pass-through from the equation.
> >
> After a brief read this seems to me the approach we should
> take. Recently I have discovered more about irqs, timing
> delays, and the difficulties/impossiblities of switching
> hardware from vm instances than I ever wanted to know.
> Given that we have three dedicated fax lines and 6 voice
> is there any hardware that would you suggest for a 4 core
> x86_64 Intel based host system?
> We have looked at going completely to v/f-oip but I do not
> have the time to deal with those intricacies and get this
> move completed at the same time.  So, for the nonce it
> appears that we would have to employ an FXO gateway to
> connect our existing POTS lines to the host.

  It might be OK to virtualize a fax server, but I wouldn't switch to a
new voice tech and virtualize it at the same time.

  If you are interested in moving to a VoIP phone system, you should get
familiar with how it works before adding the virtual component.

  Currently, I'm running a couple of locations using Elastix with
dedicated hardware.  One location supports 6 users with an Intel D845G
integrated desktop board with a 1.7 Celeron and 1G RAM, so the hardware
requirements are pretty low, but virtualized machines are not
necessarily real-time.

  I would consider virtualizing it if I dedicated a server CPU and
network card, but you'd need to find an external analog VoIP gateway
that you are comfortable with.  I'm currently using internal Digium
cards for T1 and analog connectivity, but obviously I'd want to move to
an external gateway or move to pure SIP before virtualizing to avoid
having a PCI passthrough issue of my own.

  Just make sure that your phone line vendor is not using VoIP
internally and handing you an emulated analog interface.  I had quite a
mess when I tried connecting an analog/VoIP external gateway to some
emulated analog lines.  The 2 analog emulations didn't quite mesh and I
had miscellaneous dropped calls.  The issue hurt my department's
credibility and led to a longer implementation schedule for our VoIP

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