A PRI gives you 23 digital data paths which can be used for either 64k B
channel ISDN calls or analog modems (see below). They are completely
interchangable but they can't do both at the same time.
A T1 gives you 24 digital data paths which can be used for analog modem
calls only (for now, rumor has it that they will support 56k ISDN calls
soon). PRI is ussually more $$
Once you have the data paths you need to get digital modems to handle the
analog part. A PRI with NO digital modems can only to ISDN. A T1 with no
digital modems can't do anything. The modems slide into 6 slots in the
chassis and you can get 10 or 8 port modem cards (8 * 6 = 48 = 24 * 2 = 2
* T1). The 10 port modem card is for Europe which has E1 instead of T1
and gives you 30 data paths.
The T1/PRI ports can be configured for one of the following.
ISDN PRI: Inbound/Outbound. ISDN & analog modem calls
Channelized T1: Inbound only. analog modem calls
T1 leased line (or fractional T1): Bandwidth (i.e. to connect a POP)
T1 Frame Relay (or fractional T1): Bandwidth (i.e. to connect a POP)
If you go for the pure modem pool route (like I do, I use cisco for my
network bandwidth backbone) you can get a PM-3 2T1 with 48 modems and run
two Channelized T1's into it for 48 digital modems, or one T1 and one PRI
for 47 digital modems and/or 23 ISDN B channels, *OR* 2 PRI for 46 digital
modesm and/or 46 ISDN B channels.
-Matt
-- ---------------------------------------------------------------------- Matthew S. Crocker - Systems Administration matthew@crocker.com Crocker Communications Phone: (413) 587-3350 PO BOX 710 Fax: (413) 587-3352 Greenfield, MA 01302-0710 http://www.crocker.com ----------------------------------------------------------------------