Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!bu-cs!kwe
From: kwe@bu-cs.BU.EDU (kwe@bu-it.bu.edu (Kent W. England))
Newsgroups: comp.dcom.lans
Subject: Re: Request For Opinions: FDDI follow-up
Summary: Do you want optical bypass?
Message-ID: <29548@bu-cs.BU.EDU>
Date: 13 Apr 89 18:42:23 GMT
References: <4824@charon.unm.edu> <29505@bu-cs.BU.EDU> <1507@Portia.Stanford.EDU> <825@oregon.uoregon.edu>
Reply-To: kwe@buit13.bu.edu (Kent England)
Followup-To: comp.dcom.lans
Organization: Boston U. Information Technology
Lines: 18

In article <825@oregon.uoregon.edu> dsmith@oregon.uoregon.edu
 (Dale Smith) writes:
>FDDI has an 11dB loss budget.  If you want to survive a failed
>station that has gone into bypass, then you need to figure you'll lose
>4dB through the bypassed station, giving you 7dB.  But, you have to spit
>the 7dB between runs on each side of the failed station, giving you a
>3.5dB budget between any two stations.  Figuring 1dB per inactive

	Now this is interesting.  This is the second person I've heard
talk about optical bypass and FDDI.  I don't understand why you want
or need optical bypass for FDDI.

	With the dual counter-rotating ring you have the secondary
ring in standby in case of node failure.  If a node on the ring fails,
then the adjacent nodes "wrap" and use the primary and secondary paths
to create a new ring that bypasses the failed node.

	Why do you want optical bypass fault tolerance as well?