[VoIP] Zaptel.c patch?

Tue Oct 23 12:16:15 CDT 2007

I don't think John N has the SF code in place any more.
Jayson

----- Original Message ----- 
From: "Donald Froula" <dfroula at sbcglobal.net>
To: "ikjtel" <ikj1234i at yahoo.com>; <voip at ckts.info>
Sent: Tuesday, October 23, 2007 12:36 PM
Subject: Re: [VoIP] Zaptel.c patch?

> Max,
>
> Thanks! I wondered about the purpose of the SF patch.
> So, SF is being filtered and sent via robbed-bit
> signalling over A T1 channel? I remember years ago
> connecting ITT channel banks to my company's early
> celular switches. While monitoring the digital stream,
> I recall audio being passed back from FXS cards on our
> test phones, although they were on-hook. We leveraged
> this "feature" for some testing. I'd forgotten that.
>
> I have a Berry 314A test set than can do 2600 SF dial
> pulses. I'll have to fool around with John N's switch.
> Sound cool!
>
> Obviously, I need the SF modifications for ProjectMF
> intact. I wonder if the unmute parts of the patch
> would work to allow the user to hear forward MF on my
> TDMOE fake T1 trunk arrangement? I suspect that thi
> smay not work, as the MF is in the forward direction.
> If the reverse path is unmuted, I'm hoping some
> reflection of the MF may be audible to the user during
> the MF outpulsing over the trunk during initial call
> setup, before and blue box intervention. Any
> suggestions how to modify the patch to remove the SF
> signalling parts, while leaving the essential unmuting
> code intact?
>
> Thanks for the very concise reply!
>
> Best,
>
> Don
>
> --- ikjtel <ikj1234i at yahoo.com> wrote:
>
>>
>> Hi Don
>>
>> I've been following with great interest your MF and
>> 2600 project, delighted to hear from you.  If
>> there's
>> anything I might do to help, let me know.
>>
>> There are actually two separate things going on in
>> the
>> patch, perhaps should have been separated, but...
>>
>> The 2600 additions were to enable SF-to-DC
>> conversion
>> for incoming VOIP audio (assuming an FXO leg) for
>> application to an incoming selector in a SxS office.
>>
>> The intent was to allow distant callers (who must be
>> equipped for SF outpulsing) directly to dial through
>> the switches in remote EM offices *and* to hear the
>> switches operating in real time.
>>
>> The X100P (junk) cards won't do it, but most channel
>> bank FXO's will also pass audio back to the remote
>> caller EVEN WHEN ONHOOK.  On John Novack's W.E. SxS
>> machine you used to be able to hear the dialtone
>> motor/generator set winding down like an old record
>> player turntable by blasting 2600 at the 1st
>> selector
>> and listening as the FXO line goes onhook....
>>
>> I believe Mr. Ratguy (Jayson Smith) also has
>> successfully SF'ed into offices equipped with some
>> versions of this patch.
>>
>> As for the code itself, the bulk of the zaptel
>> changes
>> were simply to move the existing sf_detect()
>> function
>> upwards in the file so its fn definition is defined
>> at
>> an earlier point.  There is code added to invoke
>> sf_detect for audio received via the WAN.  This is
>> the
>> actual SF-to-DC conversion.  It implements a digital
>> LPF to try to cover up IP packet loss/latency; the
>> resulting filtered DC signal is used to toggle the
>> FXO's transmitted hook state.  If I recall
>> correctly,
>> there's code to notch out any 2600 that might appear
>> in frames of audio that are flying by (in that same
>> direction of flow), although in this particular case
>> it's sort of moot because by definition the very
>> next
>> link in the chain is in the onhook state (where no
>> audio is presumed to be proceeding to whatever
>> follows
>> next ;)
>>
>> Also, note that it's NOT true that you only need to
>> defeat the built-in audio muting just in zaptel
>> (unless you're using zaptel by itself without
>> asterisk, which most people don't do, although
>> perhaps
>> you are)...  In addition to commenting out the
>> section
>> of zaptel code you mentioned (below), there's also
>> some "undesirable" muting code in asterisk
>> (chan_zap.c) that you need to defeat.  Also, for my
>> application it seemed that native bridging needed to
>> go (an interesting feature, an optimization, not
>> strictly essential).
>>
>> Here are the current links if I recall correctly
>> http://www.lightlink.com/mhp/sf/sf2.patch
>> http://www.lightlink.com/mhp/sf/sf-0.2.tar.gz
>>
>> Best
>>
>> Max
>>
>> --- Donald Froula <dfroula at sbcglobal.net> wrote:
>>
>> > Max, I'm a CNET member on extension 1-762.
>> >
>> > On my Asterisk box, I'm running some Zaptel
>> patches
>> > that correctly enable 2600 SF/MF signalling,like
>> > that
>> > of the old blue box days. I have this working over
>> a
>> > TDMOE 24 member trunk-group using two extra looped
>> > Ethernet cards.
>> >
>> > All works very well, except the MF outpulsing over
>> > the
>> > trunks can not be heard when a call is set up. I
>> was
>> > hoping your patch on the CNET web site might help
>> > here.
>> >
>> > However, the patch seems to fool with the SF notch
>> > filter, which I am using for the trunks.
>> >
>> > I seems the only thing needed to unmute Zaptel on
>> > call
>> > setup is to comment out the following block of
>> code,
>> > which your patch does:
>> >
>> > if 0
>> >
>> >      if (ms->dialing) ms->afterdialingtimer = 50;
>> >         else if (ms->afterdialingtimer)
>> > ms->afterdialingtimer--;
>> >         if (ms->afterdialingtimer && (!(ms->flags
>> &
>> > ZT_FLAG_PSEUDO))) {
>> >                 /* Be careful since memset is
>> likely
>> > a
>> > macro */
>> >                 rxb[0] = ZT_LIN2X(0, ms);
>> >                 memset(&rxb[1], rxb[0],
>> ZT_CHUNKSIZE
>> > -
>> > 1);  /* receive as silence if dialing */
>> >         }
>> >
>> > #endif
>> >
>> > Could you explain a bit how the patch works,
>> > especially th part that affects the notch filter?
>> >
>> > Best,
>> >
>> > Don Froula
>> >
>> >
>>
>>
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>
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