Path: utzoo!attcan!uunet!samsung!usc!trwind!venice!greene
From: greene@venice.SEDD.TRW.COM (John Greene)
Newsgroups: sci.electronics
Subject: Re: LAN speed?????
Keywords: Ethernet, cable, transmission line.
Message-ID: <473@venice.SEDD.TRW.COM>
Date: 13 Apr 90 15:32:17 GMT
References: <19603@boulder.Colorado.EDU>
Reply-To: greene@venice.sedd.trw.com (John Greene)
Organization: TRW System Engineering and Development Division
Lines: 38

In article <19603@boulder.Colorado.EDU> wallwey@snoopy.Colorado.EDU (WALLWEY DEAN WILLIAM) writes:
>
>Does anybody know the realistic speed limit of data transfer that can
>reliably be sent over RG-58 (or even the 75-ohm RG-59).  I think
>thin Ethernet uses the RG-58.  Is Ethernet close to the limits of this
>type of cable or if a different standard was adopted, could the performance
>upscaled a magnitude or two?

The limitation is not the data rate but the protocol.  The higher the data
rate, the 'shorter' the packet is and the end-to-end length of the network
needs to get shorter.  This is based on the idea that a transmitted packet
has to reach the last node on the network before the originating node
finishes transmitting.  One way to increase the data rate would be to use
a token bus protocol that would eliminate the need for collision detection.
This is how ChipCom gets past the distance limitation of 10broad36 with their
Marathon Bridge.  (get it?  Marathon, goes the distance?) 

Naturally, the higher the data rate the more susceptible it will be to 
flaws in the network structure.  I don't think you could get away with using
'T' connectors at 100 Mbit/sec data rates.  

In a way, a higher data rate is already being achieved because you can have
several 10broad39 units on a single RG-59 network.  They are modulating an
RF carrier at a 10 Mbit/sec rate so with three 10broad36 channels you network
data rate in 30 Mbit/sec.  It's just not between the same two nodes.

I have proposed designs in the past for 100 Mbit/sec transceivers/modems but
could never generate enough interest to have it launched as a project.  :-(
Mainly because it would utilize a token bus at a non-standard rate and they
didn't want to put money into an activty that was non-standard compliant.
"We think it's a great idea! but....."


-- 
John E. Greene    "People are just like frankfurters....You have to decide
                   if you're going to be a hot dog or just another wiener" DLR
TRW Systems Engineering and Development Division
INTERNET: greene@venice.sedd.TRW.COM  USENET: ..trwrb!venice!greene