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slanbuas2
join:2002-01-06

slanbuas2

Member

Good way to build an analog modem pool

Hi,
Does anyone know a good way to build an analog modem pool for dial-out. We are currenly using external USR modems but as we grow it's becoming hell to manage..

What we need:
- We have 5 modem which need to connect (dialout) to remote ones (our clients) at only 2400 bauds.
- We may have to grow our number of modems (a week for turn around is acceptable)
- All our lines are centrex. Maybe we should look for digital solution?
- Our main focus is reliability and redundancy

After a first research here are my two solutions ideas:

A) Using two servers (redundancy) each with integrated cards:
»www.digi.com/products/se ··· overview

B) Using a modem rack in combination with serial servers
Modem rack:
»www.blackboxcanada.ca/St ··· I/RM421A

Serial servers:
»www.digi.com/products/se ··· servers/

Any suggestions/recommandations ?
Thanks
JoelC707
Premium Member
join:2002-07-09
Lanett, AL

JoelC707

Premium Member

How many lines do you need? You say you have 5 modems that dial out but to me 5 modems doesn't seem too hard to manage but maybe there is something I'm not seeing. Also, what is your goal after establishing these connections? Is it for out of band management where you need to dial in to a customer router or something similar?

I know Cisco makes small and large access servers as they call them to do basically what you are wanting to do. I have an old AS2511RJ that has 16 ASYNC serial ports on them that you can hang modems off of similar to what you are doing now. I also have an AS5200 that has two slots in it and I have it populated with a pair of dual T1 (PRI) cards. Four T1's at 23 voice channels each totals a max of 92 "modems" in one 2U router. The AS5200 is more intended for dial-in applications, think dial-up ISP, which actually was it's use before I got it.

Depending on how many lines you want and what you want to do with them I would suggest something like that. The week turnaround time you mention, is that for getting a new voice circuit installed and everything? I would suggest you do some cost comparison as well, when I researched a PRI for my old company the break even point was 9 analog lines I think (I could get a PRI with 23 lines for the same cost as 9 analog lines).

RockyBB
Premium Member
join:2005-01-31
Steamboat Springs, CO

RockyBB

Premium Member

said by JoelC707:

I would suggest you do some cost comparison as well, when I researched a PRI for my old company the break even point was 9 analog lines I think (I could get a PRI with 23 lines for the same cost as 9 analog lines).
careful. analog modems are looking for analog signals ... you'll need something to do the analog to digital conversion, so it's not just a per line cost thing. also, a PRI would not be the right circuit for the application .. a regular T1 would be better (one more channel, non-PRI equipment, almost always less expensive). this application is for dial out, so he doesn't need DID numbers or incoming caller ID which are the main advantages of PRI over local T1. OP didn't say where he's calling, but if all the calls are long distance, the whole think might be cheaper and work better with a long distance T1 instead of a local T1.
JoelC707
Premium Member
join:2002-07-09
Lanett, AL

1 edit

JoelC707

Premium Member

I know that. Channel banks can be had for $1000 or less, a small one time investment to save LOTS more per month buying a bunch of individual analog lines. I suppose a channel bank can take any input really but I always assumed a voice T1 of any flavor (local, LD) was called a PRI.

Of course it really depends on how many lines he actually needs.

RockyBB
Premium Member
join:2005-01-31
Steamboat Springs, CO

RockyBB

Premium Member

said by JoelC707:

I always assumed
PRI is a T1 in ISDN format, 23B + D, each of the B (bearer) channels running at 64K clear channel, with the D (data) channel handling the signaling for the others. a regular T1 is 24 B channels running at 56K robbed bit with in-band signaling. gotta sweat the details ... ordering the wrong thing makes an unpleasant turn-up day!
JoelC707
Premium Member
join:2002-07-09
Lanett, AL

JoelC707

Premium Member

True and considering voice nor his data requirements even needs 56K let alone 64K that extra channel could be useful as well.