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From: howard@cos.COM (Howard Berkowitz)
Newsgroups: comp.dcom.modems
Subject: Re: Multiplexor Advice
Message-ID: <179@cos.COM>
Date: Thu, 19-Mar-87 07:46:50 EST
Article-I.D.: cos.179
Posted: Thu Mar 19 07:46:50 1987
Date-Received: Sat, 21-Mar-87 03:12:34 EST
References: <116@medivax.UUCP>
Distribution: na
Organization: Corporation for Open Systems, McLean, VA
Lines: 36
Keywords: HELP
Summary: Multiplexers work, but there's no general solution.  Here are more questions.

In article <116@medivax.UUCP>, jgb@medivax.UUCP (J. Grant Bristow) writes:
> Our department is currently communicating with 5 remote sites
> via 10 leased lines and  20 2400 baud modems.  We are running Ultrix 1.2
> on an VAX 11/750.  Obviously, one leased line to each site is
> mandatory, but surely not 4.  All lines are normal serial tty ports.
> 
> Questions:
>     Are you using multiplexors over leased lines?  What brand?
>     What speed?  What modems?  How much did the multiplexor cost?
>     Any advice?

I've run multiplexers (GDC, Codex, Vidar, Micom, Timeplex, Bridge, DEC,
etc.) and related technologies on lines from 2400 BPS
to 10 megabits.  There is no general answer to what multiplexer is
best.  Just think of the various types that are available for wide
area (i.e., using long-haul telephone-based transmission, rather
than campus or LAN wiring):  statistical, fixed bit-interleaved,
fixed character-interleaved, etc.  X.25 PAD's also can be very
effective multiplexers.

To give you more help, I need more information:
    How far are the remote sites from the host?   There may
  be some viable alternatives between LAN and telephone multiplex
  technologies, such as limited distance modems.
    What speeds and protocols are used by the terminals?  What
  sort of applications (e.g., do they receive lots of reports
  back which have lots of blanks which could be suppressed by
  an intelligent multiplexer)?
    Do the terminals ever need connectivity to other than the
  VAX?  If they do, you variously may need dial-out ports on
  the VAX or X.25 may be a better solution than standard 
  multiplexing.

Howard C. Berkowitz
(703) 848-2100 (office)
(703) 998-5017 (home)