[H-GEN] Beware the JabberRIMy my friend (X2/K56Flex/V90)

[Brent Wesley]

Cris Bourke is one of my work mates.  He was kind enough to eplain what is
the actual cause.

All 56k modem use what is called PET encoding for the wave form.   This form
of encoding is very subseptable to bandwith changes.  Basically with the
encoding method is a form of frequency modulation.  When it recieves a
signal it mesures the width of the wave to decide what the information is 
eg: sign wave
 
    |       ---
    |     /    \
    |     |     |
----|--------------
    |    |---a--|

  Witdth of a determines what the encode data is.

When it goes through an analog to digital converter is sightly alters the
witdth if the wave.  This can normally be tollerated if it only hapens once
but with the RIMs in place the A/D conversion happns more times, it alters
the width too much making it unable to use the 56k encoding.

If you want to know more see me at the next meeting.

Cya
Brent.    
> -----Original Message-----
> From:	Ross Camm [SMTP:rossco-humbug at powerup.com.au]
> Sent:	Friday, May 08, 1998 5:00 PM
> To:	Humbug General List
> Subject:	Re: [H-GEN] Beware  the JabberRIMy my friend
> (X2/K56Flex/V90)
> 
> From my understanding of RIMS, they take the digital signal straight from
> the system 12 or AXE, before the line cards, and de-multiplex teh 2 meg
> stream and convert it to analog. In other words the line cards are
> utilised
> in the RIM, not the exchange.
> 
> Some early RIMS were 'non-intergrated' and as such did require an extra
> a/d-d/a conversion, but I doubt this exists in new suburbs.
> 
> RIMS were introduced by telstra to save laying more copper cables. They
> wizely prefered fibre.
> 
> So the RIMS are no doubt helping your modem transfer rates, as you only
> have twisted pair to the RIM, not the exchange.
> 
> Rossco
> 
> 
> 
> At 07:40 PM 5/7/98 +1000, you wrote:
> >A very interesting post from Christopher Burke to uq.general
> >
> >cheers,
> >James
> >
> >---
> >
> >Path: nargun.cc.uq.edu.au!bunyip.cc.uq.edu.au!not-for-mail
> >From: zzcburke at uq.net.au (Christopher Burke)
> >Newsgroups: bne.general
> >Subject: Beware  the JabberRIMy my friend (X2/K56Flex/V90)
> >Date: Thu, 07 May 1998 08:34:21 GMT
> >Organization: University of Queensland
> >Lines: 30
> >Message-ID: <355171fe.66381762 at news.uq.net.au>
> >NNTP-Posting-Host: zzcburke.dialin.uq.net.au
> >X-Newsreader: Forte Free Agent 1.11/32.235
> >Xref: nargun.cc.uq.edu.au bne.general:3155
> >
> >Well I have found out why I will never ever get better than V34 on my
> >phone - its called a RIM and is used in new estates (last 5 years).
> >
> >I thought to myself that being 2kms from a brand new System-12
> >exchange in a new suburb with new cables that I wouldn't have the
> >problem, but not the case.
> >
> >A RIM is an amazing 'corner cutting' device that means all our local
> >phone lines get digitised onto a fibre, then at the exchange all the
> >lines get converted back to analog and then into the exchange which
> >immediately digitises them again.
> >
> >So when you see the error on your X2 modem 'Multiple CODECS in
> >channel' thats what it means - only one D/A or A/D conversion allowed
> >between your modem and the ISP's system.
> >
> >Well I've got three, and whats worse if I dial up my other line in the
> >house the best I get is 19.2k - you guessed it - because there is now
> >6 D/A or A/D lines.
> >
> >Apart from high speed modems, I will not be able to receive calling
> >number display either - and who knows what other advanced facilities.
> >
> >So lesson of the day - if you want advanced comms facilities don't
> >move into a new suburb.
> >
> >So if anyone else has this problem - e-mail me, maybe we will start up
> >a RIM support group.
> >
> >C.L.Burke
> >
> >-- 
> >
> >James
> >
> >:>
> >Computer Science/Music Student
> >The University of Queensland.
> ><e9322899 at student.uq.edu.au>
> >
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