howto_be_an_isp

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Subject: Re: what's involved with ISP like dialup?
From: Ramon Gandia <rfg@nook.net>
Date: Tue, 22 Jun 1999 09:54:52 -0800


Jim Priest wrote:
> 
> Our company has about 150 employees - and we are in the middle of upgrading
> most of our network to IP (from IPX), and will be getting a T1 in soon for
> WAN and net access.   I'm curious about what it would take to provide
> dial-up access  for our employees so they could hit our Intranet and maybe
> mail (Groupwise).
> 
> I'm thinking direct dial - maybe via a 1-800 # - vs. something like dialing
> up an independent ISP and making a VPN type connection...
> 
>  I'm curious how ISP's handle the simultaneous phone calls - some type of
> modem bank?  Does Linux support something like a Digiboard?  And what about
> security?
> 
> Useful links, etc. welcome.

You have 3 choices.

For 33.6K modem banks, use a Linux computer and a serial card,
or a Livingston Portmaster.

For 56K modems, use a digital terminal server, like the Livingston
PM3 or the Ascend Max 4048.

Here is the skinny on them.

1. Linux box with serial card.  The software package to do this
on multiple lines is called Portslave.  Serial cards are available
from Digi, Cyclades and a few others.  The stability of this
solution has been fair; ie, not as good as a Livingston.  It is
also expensive.  You need a PC, the serial cards which are NOT
cheap, and a lot of hours of labor to get it all working.  Any
PC so used cannot be used for other office work but needs to
work 100% of its time as an access server.  So its tied up.

2. Portmaster.  You need a PM2 model.  There are several.  The
PM2ER-xx has a WAN serial port (R=router), to connect to a
sync 56K or T1 WAN line.  It is expensive and hard to find on the
used market.  The PM2E-xx do not have this WAN port and are easy
to come by.  You probably do not need the WAN model.  Routers
are cheap, and better to get as a separate product.

The PM2E-xx have 10, 20 or 30 ports depending on the model.  The
PM2E-30 is the most common, meaning is has three 10-port cards
installed.  These have DB25 connectors in the back, in this case
a total of 30 for connecting up to 30 modems.  The connections
are the same as on a PC, but the sex is opposite.  The cables
are straight-thru serial cables.

All of these ports combine into the single ethernet port.  The
portmaster takes care of authenticating the people that dial in,
giving them a terminal login OR a PPP connection and assigning
them a dynamic IP address.  It has no disk drives, no moving parts,
and the software is dead easy to configure via a serial port or
the ethernet interface.  Used, a PM2E-30 goes for $600 to $1000,
with about $700 being most common.  Its a largish box, about
10" tall on the rack.

The PM-25 is a slim 3.5" tall box, it is functionally similar
to the PM2 series, but has one DB25 port (modem or console) and
24 async modem ports.  The ports are 8 to each high density
connector and you need a special octopus cable with RJ-45 or
DB25 connectors on them.  The cables are readily available from
Curtiss.   The PM25, due to its low profile is much easier to
handle than the PM2, but is a bit harder to find.

3. 56K digital lines.  All the above will handle normal external
modems.  If you want 56K for the people that dial IN, then you
cannot do this with analog modems.  You need a digital terminal
server.

In the typical terminal server, modems are grouped in banks of
24.   The line that comes in is a Channelized T1 or an ISDN PRI
line.  They have 24 and 23 calls each.  It saves a bunch of
wiring, and typically the CT1 lines are much cheaper than regular
analog lines.  Maybe as much as 50% discount per month.  So if
you can use 24 lines at a crack, you can save hundreds per month.

The boxes have these T1 ports for the phone calls (inbound only),
and an ethernet port.  Some have WAN serial ports too.  Prices
or fully configured 48 port boxes are like this:

Ascend Max 4048  $9000
Portmaster PM3AT  $10,500
Cisco AS5200   $20,600

The Cisco basically combines the above features with a dual WAN
router like a 2501 into one box.

All the above prices include 48 digital modems.  The cost of
a less populous box will be about 70% of the price if you go
for a 24-port box.

If you want your dial in users to have 56K speeds, you must have
one of those boxes.  The Portmaster PM3 cannot be found on the
used market, the others CAN.  Be careful of Cisco, you need the
one with MICA modems.  The Cisco uses IOS, and if you are not 
Cisco literate you will have a very hard time setting it up.
The PM3 is dead easy to set up even if you know nothing about
all this.  I have no experience with the Ascend.  All of the
above boxes do K56Flex/V90.  If you want an X2/V90 box, then
only 3COM is available.  I know little about them, other than
I think they come in 96 port and larger boxes and cost beacoup
dollars.  However, their prices are competitive if you need
96 or 192 inbound lines.

For your needs, with fewer than 16 lines or so, the PM2 is
the simplest.  Each port is really a router port, so NONE of
the dial in users is part of your ethernet segment and therefore
cannot sniff passwords and the like.  They only see the traffic
routed out to them on their dynamic IP.  You must protect the
password used to access the PM2, obviously.  If you know nothing
about PM2 and all this, you can probably be up and going with
no help whatsoever within 4 hours.  With help, maybe half an
hour.

If on the other hand, you want 24 lines (or more) and need 56K
access, the the PM3 is also dead easy to set up; similar time
frame.  The trick here is to spec your inbound CT1 or ISDN BRI
lines properly so the telco is compatible with you.  This
solution becomes involved because you and the telco are in for
a "relationship" once you do this; whereas analog lines are
fairly simple.  In fact, with analog lines you may already
have enough available right now to get started with a PM2.

For analog lines, the PM2 will cost a lot less than a PC with
a serial card.  The 8-port serial cards from Cyclades and others
cost about as much as an entire PM2 (used) and only give you
8 ports.  You still need a PC with attendant Linux or NT4RAS,
disk drives and all the attendant headaches.  In the PM2, all
the software is specialized, and in ROM or NVRAM, and all the
commands are very simple and specialized to this task.

===


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