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Background for new protocols (was Re: ISDN & CCIE) [7:71071] posted 06/21/2003
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At 5:35 PM +0000 6/21/03, The Road Goes Ever On wrote:
>""John Neiberger""  wrote in message
>>  We use ISDN for dial backup where DSL is not available and we need more
>>  bandwidth than a standard modem connection would provide, which is a lot
>>  locations.  It seems that there is a lot of ISDN out there and plenty of
>>  being ordered, but I might be mistaken.  I'd love to get rid of it
>>  it has too many quirks.  :-)
>just my two cents, but ISDN is one of the old and arguably obsolete
>technologies that still is quite relevant today. I prefer to sell RLAN ( ATM
>host and DSL spokes ) but when the customer requires relaibale backup, ISDN
>is always the choice. Happens a lot because although DSL is generally very
>reliable, when a link develops troube it still can take a long time for a
>telco to get around to fixing it. Sometimes over a week, in my experience.
Another two cents, but I strongly recommend studying X.25 and ISDN 
simply for the background they give for other protocols. I don't 
think, for example, you really understand FR until you understand why 
and how that it was stripped down from X.25, and was also designed as 
a low-speed access protocol to ATM.  Understanding Q.931 leads to 
better understanding of Q.931, and, especially if you also look at 
Q.932, helps you understand motivations for IP telephony protocols.

I was developing some AVVID courseware and found it extremely useful 
to present the ISDN reference model that the students _thought_ they 
knew, and then started filling in the blanks that are usually skipped 
in pure data instruction -- such as an NT2 being the prototype for a 
PBX.  Also usually skipped are anything going beyond (toward the 
carrier) the NT1.

It turns out that the ISDN conceptual architecture has quite a number 
of interworking abstractions of what goes on in the "cloud", which 
again can help in understanding what IP telephony has to do.

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