[asterisk-users] Learn some terminalogy before mounting this task.

[Alex Balashov]

James,

On Tue, 10 Apr 2007, James R. Stevens said something to this effect:

> When I talk with our CLEC (USLEC) I should now expect them to tell me 
> there are only 7 channels provisioned on the Voice T1. (If I understand 
> your comments)

   It appears there are only 7 channels which are usable for the purpose of 
making and receiving PSTN calls.  Whether the remaining 17 channels are
otherwise "provisioned" is a somewhat technical fine point;  at the lowest
level, they are definitely "active" in the sense that they are built into
the T1 extended superframe.  How and where exactly those timeslots are
allocated in the equipment and how they're treated is to some extent is
the provider's matter;  either way, they won't work as additional TDM
channels for your purposes, so it is safe to say on a sufficient level
of abstraction that they are not provisioned.

> Sounds as though I should compare pricing to a PRI ISDN circuit and 
> inquire about our current Voice T1's signaling (I wonder if this is in 
> reference to CLOCKING of a TDM circuit?)

   I would do that, yes.  But no, clocking has nothing to do with it 
(although the term "clock signal" is sometimes used to describe the
timing signal distribution relationship, but it's an entirely separate
matter).  Signaling in this case refers to how call setup, teardown,
and any feature group and/or other peripheral information is transmitted
on the circuit.  PRI signaling does it out-of-band on a particular channel 
set aside specifically for this administrative purpose, while 
channel-associated signaling does it in-band using robbed-bit signaling
(1 out of the 8 bits in every sixth sample in every channel used on
the T1 is allocated to a dedicated signaling path, reducing the effective 
throughput of that DS0 channel from 64kbps to 56kbps).  You can read more 
about this here, and in various books on T-carrier technology in general:

 	http://en.wikipedia.org/wiki/Robbed_bit_signaling


>  We will need a few Analog lines for various IT Dpt. issues therefore a 
> Zapata T1 card for the Asterisk server is out.

   Why is that?  You can put multiple cards in an Asterisk server.  You can 
take a T1 card into the box, and for the analogue lines needed, break out
the phone calls (probably routed by DIDs) onto a separate card that has
FXS ports.  This way you can take fax calls, etc.  Asterisk can and does
cross-connect calls on the TDM bus / in the Zaptel kernelspace.

> Also, an earlier reference to 'A port' comes for my reading about the 
> TDM400 cards. That material states the card has 4 'ports' configurable to 
> FXO or FXS type 'ports'. If I understand your comments, 1 Channel of a T1 
> OR PRI equals 1 port on an TDM400 card or OpenSwitch12 for that matter.

   Well, in some sense of "equals," yes.  The TDM400 card will take a plain 
analogue line on each port, which in most cases is what's broken out of a 
T1 channel bank/demultiplexer.  But that's essentially equivalent to saying 
it'll take four plain copper POTS lines straight from the curb.  (Just make 
sure that if you do that, you set the channel bank to signal FXS to them,
and the signaling on the Asterisk side to FXO.)

> Lastly, I have seen recommendations to only install ONE card within an 
> Asterisk server for stability and performance reasons. Are we past that 
> need with todays current baseline server products?

   Hmmm.  I can't claim to be an eminent authority on this subject, but I 
see no reason why that ought be the case in principle.  Even if it were,
I don't think it'd be a big problem to set up another Asterisk server
with an FXS card specifically as a media server for all tasks requiring an 
analogue break-out port and pass calls to it via SIP/G.711.  This should 
not break fax over LAN network conditions, in general.  And of course, 
there are other cross-connect approaches as well depending on what sort of 
equipment you're using to terminate the T1 in the first place.  You could 
get a multispan T1 card and do T1 crossconnects or whatever.

   But this is all kind of crazy and speculative.  I see no reason why you 
shouldn't put multiple Zaptel adaptors into one box and have not found any 
reason not to in my own experience.  Perhaps others can weigh in on this?

> Again, Thank you and anyone who replies to this dialog. It is very 
> appreciated in helping raise confidence with this project.

   You are most welcome.  :)

   Honestly, I'd say your easiest approach is just to look into a PRI, get a 
single-port T1 card, and go from there.  It's the one I've seen most widely 
practised in businesses with IP PBX needs and a substantial amount of 
outside lines.

-- Alex

--
Alex Balashov <sasha at presidium.org>