Re: tlug: Linux telecom nexus

[craigoda@example.com]

From: "J. David Beutel" <jdb@example.com>
Subject: Re: tlug: Linux telecom nexus
Date: Tue, 2 Jun 1998 12:41:51 +0900 (PST)


Hi,
I haven't been following this thread.  However, as a user of Linux,
ISDN, a TA, and a modem connected to the TA, I'll give it a shot.
I'm just guessing and don't really know the answers. 

jdb> On Tue, 2 Jun 1998, Scott Stone wrote:
jdb> 
jdb> > > 	2. I think I understand dialing out, but how can I dial-in to
jdb> > > 	   my box at home via a digital channel?  (E.g., see the Mobile
jdb> > > 	   Phase below.)  Do I need to rent a second phone number from
jdb> > > 	   NTT?
jdb> > 
jdb> > You should be able to dial in.  Haven't tried it on isdn, but it should
jdb> > just be a matter of having Linux run mgetty and answer the phone.

The digital channel can accept both ISDN and analog calls, with the TA 
doing the detection and conversion to analog automatically.  However, 
the TA can probably only route the analog call to a port. 

jdb> I still don't understand this part.  When I call my ISDN number,
jdb> does it ring one of the analog ports, or does it "RING" the serial port?

If the signal is an analog signal, the TA most likely cannot receive it
without a modem.  If you have a modem attached to one of the analog ports,
the TA can probably route the incoming analog signal to that port. 
However, some equipment like Ascend 4000 contains modems and some
other equipment contains a DSP chip to handle both analog and digital
signals.  However, unless this is for your work place, I don't think you
have that equipment at home.  (I didn't read the earlier part of the
thread). 

jdb> Or both?  When a call comes in, does the TA know whether it's digital
jdb> or analog?  

Yes.  Most equipment can detect it.  

jdb> Can I receive both types of calls on the same number?  

Yes.  However, on inexpensive equipment, it will route the analog
call to an analog port and you need to connect an analog device
(like a phone or modem) to the port in order to use the digital
signal. 

jdb> And,
jdb> a digital call is just a bit stream?  

Umm,,, I think so.  I'm not sure what your question is.
The ISDN line consists of two bearer channels operating at 64Kbps 8-kHz
(I think) and one data channel.  It is a circuit-switched technology, so the
ISDN frames don't have the same type of information that would be
useful for your computer.  They're bits, but unless you're programming
something that uses a special card, you don't have to worry about it.
The signal that comes out of the serial port is more useful and is
not the same as the ISDN signal, which most people don't deal with. 

jdb> If an analog call comes in to 
jdb> the same number while a digital call is connected, will the analog call
jdb> go to an analog port simultaneously?  Naomi at Bricks isn't sure.

I'm not sure what the question is, but it will drop down to the 2nd
bearer channel.  There only needs to be one phone number.  If you 
are using B-1, the call is routed to B-2.  If you have a TA and a digital
phone like I do, the incoming call sends some info over the D channel and
the appropriate device rings.  Thus, using the same phone number, either
my phone or the router rings depending on the type of incoming signal.


jdb> PPP is layered on top of the digital stream by Linux?  Does PIAFS replace
jdb> PPP in the PHS scenario?  Or, does PIAFS replace IP?

I'm not sure about PIAFS.  I suspect it replaces the ISDN frames.  
Wireless is a whole new world for me.  It seems to work fine though.  

Regards,
Craig

----
Craig Oda craigoda@example.com http://tlug.linux.or.jp/~craigoda (my PGP)


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