From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail239c25.carrierzone.com (mail146c25.carrierzone.com [64.29.147.216]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id D51513CB35; Tue, 19 Dec 2017 07:45:22 -0500 (EST) X-POP-User: hmurray@megapathdsl.net Received: from ip-64-139-1-69.sjc.megapath.net (ip-64-139-1-69.sjc.megapath.net [64.139.1.69]) by mail239c25.carrierzone.com (8.14.9/8.13.1) with ESMTP id vBJCjKxR013501; Tue, 19 Dec 2017 12:45:21 +0000 Received: from shuksan (localhost [127.0.0.1]) by ip-64-139-1-69.sjc.megapath.net (Postfix) with ESMTP id 16C4340605C; Tue, 19 Dec 2017 04:45:20 -0800 (PST) X-Mailer: exmh version 2.7.2 01/07/2005 with nmh-1.3 To: bloat@lists.bufferbloat.net, cerowrt-devel@lists.bufferbloat.net cc: hmurray@megapathdsl.net From: Hal Murray Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Tue, 19 Dec 2017 04:45:20 -0800 Message-Id: <20171219124520.16C4340605C@ip-64-139-1-69.sjc.megapath.net> X-CSC: 0 X-CHA: v=2.2 cv=WtpbCZXv c=1 sm=1 tr=0 a=OWgXOY7Tc8w5m7k7nGX6Zw==:117 a=OWgXOY7Tc8w5m7k7nGX6Zw==:17 a=kj9zAlcOel0A:10 a=ocR9PWop10UA:10 a=m0iwk5PbAAAA:8 a=69R-NtAiHnPuYq18qvAA:9 a=CjuIK1q_8ugA:10 a=nBnehqrKFnTNgoiqJ76Z:22 X-CTCH-RefID: str=0001.0A010202.5A3909E2.0013, ss=1, re=0.000, recu=0.000, reip=0.000, cl=1, cld=1, fgs=0 X-CTCH-VOD: Unknown X-CTCH-Spam: Unknown X-CTCH-Score: 0.000 X-CTCH-Rules: X-CTCH-Flags: 0 X-CTCH-ScoreCust: 0.000 Subject: [Cerowrt-devel] Fiber bandwidth vs distance X-BeenThere: cerowrt-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: Development issues regarding the cerowrt test router project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 19 Dec 2017 12:45:23 -0000 > I don't know the physics behind it, but people who have better insight than > I do tell me "it's hard" to run longer hops (if one wants any kind of high > bitrate). The buzzword is dispersion. The speed of the photon varies slightly with color. All the photons in a pulse are not the same color. The farther they go, the more they spread out. If they spread out far enough, they overlap neighboring bits and the receiver can't sort things out. You would like all the photons in a pulse to be the same color. Lasers are close. Just not close enough. The dimension of quality for fibers used to be megabit*miles. (actually megabits/second) That probably assumed a specific bandwidth of the light. For a given transmitter, you could go X miles at Y bits/sec, or 2*X at Y/2... Sample data sheet: https://www.corning.com/media/worldwide/coc/documents/Fiber/SMF-28%20Ultra.p df Dispersion is the next to bottom section on the right of the first page. > Todays laser links are in the few km per hop range, with is easily at least > one magnitude shorter than radio based equivalents. What's the bandwidth of those radio links? -- These are my opinions. I hate spam.