dyer@spdcc.COM.UUCP (05/29/87)
I've been running for several months with a LADS circuit between my
house and the university, running at 9600 baud with a pair of Gandalf
LDS 309A short-haul modems. I'm quite happy with this setup, but I
am wondering how much of the available bandwidth I am using. If the
leased line is truly just a length of copper which runs from both endpoints
into the central office, and the total length of the wire is probably no more
than a mile, wouldn't there be a chance that the capacity of the line was
greater than 9600 or 19.2kb? Actually the distance between my house
and the other end is about 2 blocks, but I assume these lines always
must pass through the central office. Note that this isn't a "voice
grade" line, but something NETel calls "LADS" which presumably means
"Local Area Data Service" or some such. I think that this is
the same as a metallic line, although it's hopeless to talk to anyone
at the phone company who knows enough about what they're providing.
Are there are bandwidth restrictions imposed on this type of line by
the telco in addition to those imposed by the length? How would you
recommend measuring the effective capacity of the line? Is there any
chance of exploiting the residual bandwidth (if there is any at all)
using something other than the LDS309As (or would the expense of such
equipment argue that a DDS line would be cheaper!) As you can tell,
I'm dreaming of a poor-man's 56kb+ line and am trying to gauge how
much of a pipe dream it is.
---
Steve Dyer
dyer@harvard.harvard.edu
dyer@spdcc.COM aka {ihnp4,harvard,linus,ima,bbn,halleys}!spdcc!dyerGene.Hastings@H.CS.CMU.EDU (05/31/87)
We have several LADS lines in service, all at 56kbs, synchronous. There should be information available from the vendor of an arbitrary short-haul modem telling you what speed it can push how far (longer distance-> lower speed). We were frustrated and slightly amused when we called the person who was the official Point-of-Contact for our campus asking what the milage was on one of our lines and got the reply that they didn't know and had never heard the question before. Gene
dp@JASPER.PALLADIAN.COM.UUCP (06/03/87)
Date: Saturday, 30 May 1987 17:55:14 EDT
From: Gene.Hastings@h.cs.cmu.edu
We have several LADS lines in service, all at 56kbs, synchronous. There
should be information available from the vendor of an arbitrary short-haul
modem telling you what speed it can push how far (longer distance-> lower
speed).
We were frustrated and slightly amused when we called the person who was the
official Point-of-Contact for our campus asking what the milage was on one
of our lines and got the reply that they didn't know and had never heard the
question before.
Gene
the easiest answer to this question is to simply short out the line and use an
ohmmeter. the number is ~6k ohm/mile but look in the aprop telco documents for the
exact number. (you could also use a TDR if you happen to have on hanging around...
that is also the only easy way to be sure that they didn't leave the loading coils on the
line.)
<dp>