> >With ISDN, the conversion is done in your phone > > Exactly. Or in the case of Asterisk, it is a 4 wire digital right into = > the switch--no degradation. Even converting back and forth between = > analog and digital multiple times compromises quality. Try doing a = > dial-up modem across such a path. The best you will get is 20 - 30 K.
A single D/A hop destroys the ability to do 56k. Successful 56k requires that there be a single A/D hop at the far end (the user's POTS interface) and then digital delivery of signal the remainder of the way to the terminating equipment. (modem -> phone co A/D -> digital to ISP modem bank). If you stick an extra D/A (maybe plus A/D) transformation in there, you will probably get fairly clean speeds in the upper ranges of 28.8-33.6, but that'll be it (modem -> phone co A/D -> digital network -> phone co D/A -> your buddy's modem). If you're unlucky enough to get some crummy phone co arrangement where they punt you back and forth from digital to analog and back to digital within their network, that's even worse. >From an Asterisk point of view, it's interesting that you can get digital delivery of the signal, and route the signal around internally digitally, if you have ISDN. This means, for example, that our USR Courier I-Modem, which can terminate a 56K call *digitally*, results in my being able to make a 56K connection from most modern cities here in the US, without wasting an ILEC ISDN BRI line dedicated to that purpose, by having the PBX connect an extension to the I-Modem. I just dial into a general purpose number, and dial the appropriate extension, and voila, I'm on our network at "high speed." This is clearly obvious to you, but I thought I'd expand for the others who might be reading along and didn't understand the implications of all- digital. > >IF you can get a PRI-line for the same price. > > Not to mention that the interfaces for PRI are about five times as = > expensive. I'm not sure why. It doesn't seem like it ought to take a = > lot of electronics to break down the bit stream. It may not take a lot of electronics. However, the sad truth of it all is that any electronic device produced at low volume tends to be expensive to produce. This is largely the result of costs such as retooling, and in most cases the significantly higher cost of small-run integrated circuits. For example, a PC board manufacturing house (I'll use the following shop, no affiliation, as an example, because they have transparent pricing) http://www.expresspcb.com/ExpressPCBHtm/Specs4LayerStandard.htm http://www.expresspcb.com/ExpressPCBHtm/Specs4LayerProduction.htm for a 30 sq in board. To produce 10 boards would cost $404, or $40/board. To produce 50 boards would cost $1109, or $22/board. To produce 1000 boards would cost $15516, or $15/board. Even 1000 isn't really a large run, though. You're paying premium board rates for small runs, because the shop has to stop and retool for your run. I haven't bothered to get a large-run quote, but I bet you can get that down to well under $10/board if you're ordering a hundred thousand at a time... You then have to add on assembly costs, which are typically higher than the PCB costs. It could very easily end up costing $50/board *just* for PCB and assembly, no parts included, for runs in the hundreds of cards range. The problem with telephony stuff, especially in this market, will be that the demand for a T1(/PRI/etc) interface is going to be very low. You would need to be a relatively big shop to be able to buy by the thousand, as even at one bulk buy per year, that translates to several cards departing inventory daily. I expect that some of the ISDN BRI interfaces are dirt cheap because they're popular over in Europe. I've been told that in many places, they're sold in lieu of a modem. Once you are moving product in high volumes, the pricing tends to come down. It stinks, yes. ... JG -- Joe Greco - sol.net Network Services - Milwaukee, WI - http://www.sol.net "We call it the 'one bite at the apple' rule. Give me one chance [and] then I won't contact you again." - Direct Marketing Ass'n position on e-mail spam(CNN) With 24 million small businesses in the US alone, that's way too many apples. _______________________________________________ -- Bandwidth and Colocation Provided by http://www.api-digital.com -- asterisk-users mailing list To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users