NetNews Usenet Archive 1992 #30/NN_1992_30.iso/spool/comp/dcom/isdn/1006

Text File | 1992-12-20 | 3.1 KB | 63 lines

Newsgroups: comp.dcom.isdn
Path: sparky!uunet!psinntp!adcmail!bcapps
From: [e-mail] (Brent Capps)
Subject: The ISDN network
Message-ID: <[e-mail]>
Organization: Atlas Telecom Inc.
References: <[e-mail]> <[e-mail]> <[e-mail]>
Date: Thu, 17 Dec 1992 18:22:30 GMT
Lines: 52


In article <[e-mail]> [e-mail] (Curt Welch) writes:
>First, I don't know how ISDN charges work, but I doubt that you will be
>charged anything for trying to place the 64K UDI call.  The network
>will just return an error - like a busy signal - if the destination
>can't answer that type of call.  At most, I'd expect that you would be
>charged $.10.

These systems are operated by *carriers*.  Carriers get charged by the RBOCs
for ALL trunk group usage, completed or not.  Unrecoverable charges represent
about 25-30% of their overhead.

>And I think G4 includes more advanced compression
>algorithms, which could give you an even greater speed up.

Nope.  The two-dimensional encoding algorithm which G4 uses is also defined
for G3, but nobody bothers to support it because it is a lot of effort for
an algorithm that doesn't really achieve that much in way of compression.
In tests we ran internally we found that T.4 (G3) and T.6 (G4)-encoded
files differed by less than 10% for typical business correspondence-type
images.  As often as not the G4 files were *bigger* than the G3 files.
It makes a great deal of difference whether your documents are mostly
whitespace.  G4 is optimized for graphics, which doesn't represent the
most frequent type of fax transmission.

>The Fax will just automatically do this (so the user doesn't have to
>try to fax everything twice - once G4 and then once G3).  It will first
>try to use G4, and if that fails, it will use G3.

G4 machines aren't designed this way.  The G3 and G4 capabilities
use physically separate lines, one analog POTS and the other digital.
In theory the digital line is used for ISDN, but in practice it's
usually a leased line to another G4 machine over the pond.  To
switch from G4 to G3 requires a second phone call to a different DN.

>Once you switch to G4 fax, you can get 400 dpi resolution (higher
>resolution the the current de facto 300 dpi laser printer standard.)
>So if you have these G4 fax/printer/copier/scaners, the best way to
>connect them to your computer is not through a local LAN, but through
>the phone system.

The standard G4 application is to suck in faxes from G3 machines in the
local calling area and blast them over a leased line to another G4 machine
where they are broadcast locally.  As such your resolution is only as
good as the sending G3 machine.  That extra resolution G4 buys you does
you no good.  This is the niche G4 has carved out for itself, and it
does a pretty good job at it.  But if you're looking for G4 to drive
increased ISDN acceptance, you'd better think again.
--
Brent Capps                          |
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