Path: utzoo!attcan!uunet!ns-mx!iowasp!deimos.cis.ksu.edu!ux1.cso.uiuc.edu!iuvax!cica!tut.cis.ohio-state.edu!ucbvax!bloom-beacon!ftp!jbvb
From: jbvb@ftp.COM (James Van Bokkelen)
Newsgroups: comp.dcom.lans
Subject: Re: Ethernet *WAN* (can it be done?)
Summary: Remote bridges using 9.6 lines may have problems...
Message-ID: <915@ftp.COM>
Date: 22 Mar 90 00:51:33 GMT
References: <173@mnopltd.UUCP>
Organization: FTP Software Inc., Cambridge, MA
Lines: 28

In article <173@mnopltd.UUCP>, neal@mnopltd.UUCP writes:
> Is it possible to run 10Mbps Ethernet over a star topology of offices up to 80
> miles apart connected via 9.6 dedicated voice grade lines? 

1. Under un-loaded conditions, you will get a large variance in transit time
depending on packet length.  This may result in unnecessary retransmissions.

2. Under loaded conditions, when the number of packets that need to traverse
the link exceed the capacity for significant periods of time, you may get
a syndrome of repeated retransmits, and possibly what is called "congestive
collapse".  In this condition, the load is so high that packets are delayed
or dropped, which generates more retransmitted packets, etc.

3. Depending on how many packet the bridges will queue for transmit, some
protocols (e.g. ARP) may fail under some conditions, because implementations
frequently assume that the round-trip time *can't* exceed X on an Ether.

I'd advise that you investigate other people using similar software across
slow links; If you can't find any, you might not want to be the first.  If
you can, go cautiously when trying anything that you haven't seen working
in a similar environment.  Above all, *don't* let the demand across any of
the serial links exceed capacity for long.



-- 
James B. VanBokkelen		26 Princess St., Wakefield, MA  01880
FTP Software Inc.		voice: (617) 246-0900  fax: (617) 246-0901