[Asterisk-Users] Qs about FXO/FXS cards

[Damon Estep]

Brian,

People are making 100's of excuses for *'s inability to deal with analog
lines and extensions, the bottom line is that it is a serious issue that
we all hope to see resolved. The best one is "analog lines are for
babies"

Bottom line, the economics of analog vs. t1 usually work out so a T1 is
easily justified when you have about 10+ analog lines, that means that
offices with 20 to 30 users are borderline on being able to justify the
expense of a T1.

As best I can tell * can not really handle more than 50 to 100 calls at
a time (on a single box), and then only if there is not a lot of other
stuff (transcoding, vmail, etc.) going on.

This makes * a slam dunk for environments that handle somewhere between
10 and 100 simultaneous calls, and a not so easy decision for users with
less than 10 or more than ~100 simultaneous calls.

The best workarounds at this time for small (analog) implementations is
to use an external VoIP to PSTN gateway or a T1 interface and a used
FXO/FXS channel bank.

For larger installations (more than 2 to 4 t1s) there are other
scalability issues, such as no SIP reinvite, meaning all of the call
data streams must run across the PCI bus of the PC. This can be solved
with a proxy like SIP Express Router aka SER and a media gateway like
the Lucent Max TNT so * is only in the data stream when the features it
provides are needed.

Our range of customers and applications spans from 5 or 6 analog lines
to a DS3 (672 digital lines), and we have quickly determined that the
TDM400 in the majority of hardware combinations we have tried is not
100% reliable. We have tried old Dell PII 500s, New HP Xeon 3.0s, and
everything in between, all quality system boards, power supplies,
dedicated IRQs, hardware raid controllers, high quality NICs, etc.

We have tried machines that can pass real time HDTV video/audio streams
across the PCI bus with bit for bit accuracy (translate: no PCI
latency).

As far as all of the power supply related issues are concerned, it is
not really the job of the power supply to FULLY regulate the power, it
provides GOOD power to the system board and other components which are
then expected to have integral voltage and current regulators suitable
for their application.

It is my understanding that all of the power for an FXO module comes off
of the PCI bus, and only the FXS module requires power straight from the
power supply, yet they both suffer from the same lock up issue, and the
funny part is the driver has no idea the hardware is not responding.
This is clearly a problem with the hardware/driver design. There does
appear to be some combinations that work, but that is not acceptable,
unless the exact requirements can be quantified and advertised.

Find a good PSTN to VoIP gateway and forget the headaches... in time the
TDM400 might improve, but not as a result of the long running rants in
this forum.

> -----Original Message-----
> From: asterisk-users-bounces at lists.digium.com [mailto:asterisk-users-
> bounces at lists.digium.com] On Behalf Of brian at txshirts.com
> Sent: Monday, January 03, 2005 7:23 PM
> To: asterisk-users at lists.digium.com
> Subject: RE: [Asterisk-Users] Qs about FXO/FXS cards
> 
> My cost analysis showed that * is a slam dunk for the $ per feature.
> 
> Heck adding voicemail from Nortel is about a $1000 venture by itself
> (call pilot, used).
> 
> And that is just the start.  Granted, programming text files is
> vexing... But if you hate that try programming with a 10 key and a 2
> line interface on a nortel KSU.  And btw, Nortel is one of the better
> ones for documentation.
> 
> TDM400 has been reliable, it's just a bit squirrelly to get the
options
> set right.  I think in the greater scheme of things Digium produces a
> nice product and * is hard to beat.
> 
> I think the quality of the power, system, and power supply can't be
> underrated when doing telephony.  Everything I've read points to less
> then desirable results with sketchy hardware.
> 
> 
> Brian Greul
> Texas Shirt Company
> www.txshirts.com
> 713-802-0369 / 713-861-6261 (fax)
> 
> -----Original Message-----
> From: Andrew Kohlsmith [mailto:akohlsmith-asterisk at benshaw.com]
> Sent: Monday, January 03, 2005 2:25 PM
> To: asterisk-users at lists.digium.com
> Subject: Re: [Asterisk-Users] Qs about FXO/FXS cards
> 
> On January 3, 2005 03:07 pm, Steven Critchfield wrote:
> > And we come full circle to a comment I made before that TDM cards
are
> > more for hobbyist than for real serious installs. A real install is
> > probably going to use a T1/E1 interface and bypasses all the
troubles
> > listed in this thread.
> 
> Unfortunately that makes Asterisk installs for small businesses more
> expensive than necessary.  At US$500 for a T100P and US$300ish for a
> channel bank (FXS only, FXO is significantly more expensive!) plus
your
> time and system for an Asterisk install it raises the bar for the
small
> business to adopt Asterisk.
> The TDM400P would fit a very nice little niche if it worked reliably.
> 
> Let's face it -- most businesses are looking at VOIP to reduce their
> telephone bills and if the time it takes for the install to pay for
> itself is raised significantly (like an added $1000 price tag for
> reliable equipment)...
> well... the writing on the wall is pretty clear.
> 
> -A.
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