From: gvb@telly.on.ca (George VandeBunte)
Subject: Re: ZyXEL Caller-ID Problem
Organization: Somewhere just far enough out of Toronto
Date: Tue, 17 Nov 1992 15:55:24 GMT
Keywords: Caller-ID ZyXEL 

 
 
>I am a subscriber to Caller-ID here in Michigan Bell territory.  I have
>utilized this service on the 1A ESS switch that I am connected to since
 
>During that time I have had limited problems with the service.  In this
 
 
>Out of the box everything but Caller-ID worked just great.  
>.. I took my modem to another
>friends house, and it worked.  This friend is connected to the
>SAME 1A ESS that serves me!  Well, I guess its probably not the 1A ESS.
>However, he is about 16,000 feet from the central office, I am about
>11,000.
>
 
>Through experimentation I discovered that a 2 MF non-polar cap in 
>series with a 2700 ohm resistor across tip and ring "loades" the
>line sufficiently so that the ZyXEL will work.
>
>Some comments and questions:
...
>2.  I wonder what the Bell Core specification says about the level,
>    amount of distortion, etc. that a Caller-ID receiving device must
>    be able to tolerate?
  The bellcore tr tsy 3o document states that the interface should perform
  correctly for loops having the characteristcs of:  loop resistance less
  than 1300 ohms, insertion loss @3k less than 14 db , total bridge
  tap length less than 6000 feet.  The level is only spec-ed at
  13.5 dbm at point of data application into a resistive load of 900
  ohms.  (bear in mind the signal only has to go from the office to your
  phone). I don't know how you verify your bridge tap length is less
  than 6000 feet. 
 
 
>5.  How do I measure this distortion so that I can assess wether it
>    is a MBT or ZyXEL problem (assuming that it is the problem)?
 
  I have a ZyXEL  --works great with caller id here. I suggest the 
  following:
  1. Use the spiffy modem to record the signal from the phone company,
  both with and without your 'fix'.
  To do this connect a .2 ufd to 4 ufd non polarized cap from tip to
  the recording modem, so the modem can pick up the line with out 
  really answering.  I have had no problem getting a really good recording
  this way.  (use the included ZFAX recording software-recording from telco
  line mode).
  Record the CID signal, with and without the gadget you have (should be
  about 20Kilobytes).  To make sure your measuring equipment does not
  reduce the 'problem' also use your friend modem to make sure it doesn;t
  work.
 
  I suggest recording
both the 2 bit and 3 bit voice mode.
 
Next step is to analyse it.  The best place to start is to find the
150 ms mark signal.  Now mark is a 1200 hz signal and you are sampling
at 9600 bits.  so you can use a hex editor to locate the mark section.
A clean mark signal should be 2 repetitive bytes in 2 bit sampling mode,
and 3 repetive bytes in 3 bit mode (since 9600/1200 is 8).  
Another way would be to convert the file to say a soundblaster file and use
an oscilloscope program to play-- however keeping it simple is not a bad idea.
You should look for differences in the two cases.  
 
 
 
>6.  Does anyone have any other suggestions as to how to correct this
>    problem?
 I have been coordination some of the caller id testing
for zyxel -- or at least helping in Canada.
 
I suggest after you do your analysis, beat up Bell, and get your 
money back  ;-).,  
you could provide the two or 4
files to ZyXEL.  
They could then use the recordings to possibly tweek the dsp algorithm
if they figure they could improve it.  I could do the introductions or ....
I think this is a pretty neat way to gather data in the field.  
 
The company I work for, OCOMP, distributes the modems in Canada, 
and has managed the DOC approval cycle etc.  If anyone in Canada
needs a ZyXEL, or update etc check out our company.
OCOMP  416 5341508
gvb@telly.on.ca
 
.