[Asterisk-Users] T1-PRI deployment questions...

[Bruce Ferrell]

PRI is shorthand for Primary Rate Interface ISDN
BRI is Basic Rate Interface ISDN

John Harragin wrote:
> Thanks to everyone for all the info...
> 
> One more question. Until now, I had succesfully avoided isdn throughout my
> computer career... other than having the notion that it was a fairly
> troublesome line with data rates several times faster than pots.
> 
> So far from ACC (my pri vendor) my T1-PRI must be b8zs/esf. On the form I
> have to fill out most of the pri enteries are listed under ISDN/PRI so I'm
> not really sure which questions are particular to pri.
> 
> My usage will 23 voice (with an occational fax) plus the d channel. What is
> the relationship between pri & isdn - is it considered isdn? If so, what do
> I need to know about that?
> 
> John
> 
> 
> 
> -----Original Message-----
> From: asterisk-users-admin at lists.digium.com
> [mailto:asterisk-users-admin at lists.digium.com]On Behalf Of Don Pobanz
> Sent: Monday, June 02, 2003 9:42 AM
> To: 'asterisk-users at lists.digium.com'
> Subject: RE: [Asterisk-Users] T1-PRI deployment questions...
> 
> 
> I have been on vacation so didn't jump in earlier. Some of what I say
> here has been gone over earlier in this thread but I will repeat the
> results as a summery.
> 
> AMI is not lossy, but it is almost always used in conjunction with a
> ones density technique called bit7. Bit7 will change bit 7 to a 1 when
> a word (8 bits) are all zeros. In North America when someone says AMI
> they really mean AMI with bit7. PRI ISDN will not work on an AMI (with
> bit7) T1.
> 
> When validating ones density B8ZS does introduce errors but in such a
> way that the far end will know that they are errors and remove them.
> The only reasonable choice for PRI ISDN is B8ZS
> 
> Robbed bit signaling uses bit 8 of each word of every 6th frame for
> signaling. This does not introduce errors on the line but it does make
> those bits unavailable for data. Usually data services assumes that the
> 8th bit of every work of every frame are not available so that you have
> 7 of each 8 bit word. That makes 56Kbit/s of 64Kbit/s of bandwidth
> available. PRI ISDN does not use Robbed bit signaling. Instead it uses
> the D channel.
> 
> Slips are caused by a timing problem and have nothing to do with AMI or
> B8ZS.
> 
> Framing of either SF (D4) or ESF can be used on a T1 regardless of the
> line coding. (some mistakenly believe that B8ZS must be used with ESF
> and AMI must be used with SF) ESF is preferred because more robust
> performance monitoring is possible while the T1 is in service.
> 
> Don Pobanz
> 
> Ps. For a while the group I worked with back at the phone company was
> known as 'T1s are us' so I should be familiar with this stuff.  ;)
> 
> 
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