Re: Std. Serial ports beyond 115K?
On Tue, 23 Feb 1999, Dimitri Patakidis wrote:
>> I want to connect an external ISDN to my system using the MB's
>> standard serial ports. However, everything's telling me I can only
>> push 115K through these serial ports - far less than the theoretical
>> max of an ISDN TA that does V.42bis.
>> Any comments/suggestions on
>> "overclocking" ;-) built-in serial ports to 230 (or 460) Kbps?
How good are you at making changes to multilayer PC boards?
The limitation of 115.2Kbps is a limitation of the bit-rate clock on PCs.
You cannot go faster than this without having a higher bit-rate clock.
However, with a higher bit-rate clock you can get speeds of up to 1.5Mbps.
The problem is that you can't change that clock without modifying the
circuit that generates it, which is kind of tough if the serial port is
built in to your motherboard.
>> Note: I realize that HS serial ports/boards are available, but I don't
>> want to shell out the money if I don't have to....
>> Note2: If you can recommend a good external ISDN TA (North America) or
>> an internal that supports DialD, I'd love to hear from you.
> The best way to get the most bang for your ISDN buck is to use an ISDN
> router. ISDN IN ---> ETHERNET OUT
> No RS-232 translation in between.
Speaking as the owner of an ISP that has to support this sort of thing,
I'd like to encourage Mr. Traas to get a router. It's a whole lot easier
to make a router work than an ISDN TA.
However, if he doesn't want to spend the $50 to use a high-speed serial
port, he sure isn't going to want to spend $500 extra to get a router.
My recommendation would be to look for someone who is using an old, say,
Pipeline 25 that wants to move up. I believe my company got one for $100
six-eight months ago. That's less than a decent ISDN TA is going to cost
and it does routing. Not that I'm wedded to Ascend equipment, or
anything, I just have more experience with them than other things. You
can also use the Netgear or the Cisco or the 3com. I would recommend you
stay away from the "Danube" and its ilk. They are not pleasant devices to
set up.
You'll need to do some work to find used equipment, though. Ebay is a
definite option, here. Drop me a private line and I'll give you the Web
addresses of a couple of people that deal in used equipment that you may
not be aware of because they mostly sell to ISP's. You will need to get
something that knows how to do NAT (like masquerading, only different) if
you want to use it with a regular dial-up account. (With Ascend gear,
it's mostly a matter of making sure you have a recent enough firmware
revision, and you can update the firmware for most models. I don't know
about the others.)
--
Jonathan Guthrie (jguthrie@brokersys.com)
Brokersys +281-895-8101 http://www.brokersys.com/
12703 Veterans Memorial #106, Houston, TX 77014, USA
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