roy@phri.UUCP (03/26/87)
As a relative neophyte a datacomm, I recently had tossed in my lap
the assignment of "getting our computers talking with their computers". I
think we've figured out that running IP over a point-to-point link is what
we have to do. What I don't know anything about is how to set up the
physical link. My "normal" alternatives so far seem to be:
1) Leasing a D1 conditioned analog line from the phone company,
over which we can supposedly run 9.6kbps. This will cost about $1000 to
install and about $140/month.
2) Leasing a 9.6 kbps DDS line for $600 up front and $360/month.
3) Leasing a 56 kbps DDS line for $600 up front and $700/month.
4) Leasing a T1 "superpath" line. This costs about $2500 to
install and $700-1500 per month, depending on details of distance which
aren't known yet.
In each case, we need to purchase random boxes to go at each end
(DSU/CSU, MUX, modems, etc). Assuming we can get by with 9.6 kbps, what is
there to choose between the first two alternatives? Are we going to see
any better performance with a DDS line instead of the D1 analog line. Just
what is D1 conditioning anyway? What if we wanted to really cheap out and
get a POTS line and something like a Microcom AX/9624c which claims to be
able to do 19.2 kbps over an unconditioned dial-up line? Is this a viable
alternative? Considering how much cheaper it is, there must be *some*
reason why it won't work, but I don't see it.
--
Roy Smith, {allegra,cmcl2,philabs}!phri!roy
System Administrator, Public Health Research Institute
455 First Avenue, New York, NY 10016
"you can't spell deoxyribonucleic without unix!"pavlov@hscfvax.UUCP (03/28/87)
In article <2619@phri.UUCP>, roy@phri.UUCP (Roy Smith) writes: > > As a relative neophyte a datacomm, I recently had tossed in my lap > the assignment of "getting our computers talking with their computers". I > think we've figured out that running IP over a point-to-point link is what > we have to do. What I don't know anything about is how to set up the > physical link. My "normal" alternatives so far seem to be: > 1) Leasing a D1 conditioned analog line .... > 2) Leasing a 9.6 kbps DDS line for $600 up front and $360/month. > 3) Leasing a 56 kbps DDS line for $600 up front and $700/month. > 4) Leasing a T1 "superpath" line... > ... Assuming we can get by with 9.6 kbps, what is > there to choose between the first two alternatives? Are we going to see > any better performance with a DDS line instead of the D1 analog line... > What if we wanted to really cheap out and > get a POTS line and something like a Microcom AX/9624c which claims to be > able to do 19.2 kbps over an unconditioned dial-up line? Is this a viable > alternative? Considering how much cheaper it is, there must be *some* > reason why it won't work, but I don't see it. > -- We have been leasing a 9.6k DDS line for 3 years (formerly 2.4, then 4.8k). Distance: apx. 450 miles direct, tho actual path is apx. 650. It has been extremely reliable. Apx. 8 hours' down time per year, apx. 15 hours' "flake time" per year. I do not believe that the Microcom modem operates in true duplex mode; it, and other modems like it, either "simulate" duplex or allocate a very small band- with to one direction (dynamically, in response to traffic patterns). If this is suitable to your application, I would suggest looking at the Telebit modem. From my point of view it utilizes a more robust transmission scheme and I believe it is likely to yield better throughput under various adverse conditions (since baud rate can be varied in much smaller increments/decrem- ents). But I am not well-versed in this and I have no experience with any of these modems. But I would certainly like to hear from those who have, since I am considering purchasing several myself. greg pavlov, fstrf, amherst, ny