February 2002 - Test - lists.nanog.org

Re: Satellite latency
by Jim Mercer 28 Feb '02

28 Feb '02

On Thu, Feb 28, 2002 at 12:14:43PM -0500, Eric Oosting wrote: > Is there something else specific to one-way satellite connections that you > are attributing these problems with asymmetric routing to? There is > nothing inherently wrong with asymmetric routing that causes high latency > or perceived differences in usability of real-time connections like ssh. > For instance, a large percentage of the traffic on the Internet is > asymmetric. Anyone who is multihomed knows that half the time they send > something to one upstream, it will come back a different upstream. > > Do you believe that there is something wrong with a downlink of 400ms and > an up of 100ms? (guesses at satellite with dialup return connection one > way latencies) I can't imagine that things would be better with a 400ms > down and 400ms back up (as with a two-way sat connections) but maybe you > can do different tricks with spoofing tcp acks to the traffic over the sat > link when it is two-way. in my experience, the upstream, typically via terrestrial, is more lossy than the downlink. this has nasty effects on ssh windowing. i haven't used telnet in a long time, more specifically over sat links. asymetric traffic over high-speed, low latency, low loss links is mostly transparent. when one path is clean, and the other is dirty, then the symptoms get worse. also, asymetry is relative. in one case, i had packets go high speed across north america (uunet/teleglobe/ sprint/alternet/etc/etc) over unencumbered fiber to the UK, then up via satelite, down into the middle east into a terrestrial fiber network to the dial-up port to the user. the return path was dial-up over ancient infrastructure, to an overloaded national backbone provider, via overloaded circuits to singtel, across the pacific (using different networks depending on the phase of the moon), into north america. this is wholly different from have the outgoing packet traverse teleglobe from newyork->los-angeles, and having the return packet go via alternet from los-angeles->newyork. (although, depending on the phase of the moon, sometimes teleglobe and/or alternet resemble the previous paragraph). 8^) -- [ Jim Mercer jim(a)reptiles.org +1 416 410-5633 ] [ I want to live forever, or die trying. ]

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Line Rate vs CPU utilization info requested
by Donn Lasher 28 Feb '02

28 Feb '02

Does anyone have a table / web site / etc that talks about realized IP throughput on various routers (3600 / 7100 / 7200, 5500, 6500, etc) versus cpu load? IE even though you can put 4 x 100M ethernet cards in a 3640, IMHO, you'd never see 400/800M aggregate throughput because the CPU would be on its' knees begging long before that point. I'm looking at a project that calls for a DS3, and the suggested router is a 3640, and I'm trying to prove / document that's not a wise idea. What has your experience been? Anecdotal or personal experience appreciated. Offline replies work just as well. Thanks in advance. -donn

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RE: Satellite latency
by Rowland, Alan D 28 Feb '02

28 Feb '02

Not to mention that -5 degree or so look angle (negative elevation) from the poles being hard to acquire. ;) But with enough elevation and a big enough dish... Also about that satellite drift...The earth wobbles during rotation meaning geo stats do small figure 8s overhead. IIRC there is some computer software out there (from my days of TVRO in Europe) that given a latitude/longitude and sat placement would return a time where the sat was in the middle of that 8 so you could best aim the dish. Or maybe I just had too much Heineken at the bar, can't remember which. Just my 2¢. The delete key is your friend. -Al -----Original Message----- From: Michael Painter [mailto:tvhawaii@shaka.com] Sent: Wednesday, February 27, 2002 12:22 PM To: nanog(a)merit.edu Subject: Re: Satellite latency ----- Original Message ----- From: "Leo Bicknell" <bicknell(a)ufp.org> To: "Steven M. Bellovin" <smb(a)research.att.com> Cc: "Tim Devries" <zsolutions(a)cogeco.ca>; <nanog(a)merit.edu> Sent: Tuesday, February 26, 2002 5:27 PM Subject: Re: Satellite latency >>Remember that a geosynchronous satellte must orbit the equator. Let's say for the sake of argument it's over mexico, you're in New York, and the downlink station is in San Diego. The 36,000 is the distance straight "down" to mexico, It's probably more like 50,000 to New York, and 45,000 to San Diego. And if you're in New York, and your mail server is in New York, but the downlink was to San Diego, you've got another 4,000 across country. Now you're up closer to 100,000km.<< Not wanting to get picky about ~20,000 km., but the maximum -usable- slant path is ~41,000 km. --Michael > > In a message written on Tue, Feb 26, 2002 at 09:07:14PM -0500, Steven M. Bellovin wrote: > > Geosynchronous orbit is about 36,000 km from the center of the earth. > > Round-trip to the satellite is ~72,000 km; the speed of light is > > 300,000 km/sec. That works out to 240 milliseconds at the minimum for > > one-way packet delivery. > > Remember that a geosynchronous satellte must orbit the equator. > Let's say for the sake of argument it's over mexico, you're in New > York, and the downlink station is in San Diego. The 36,000 is the > distance straight "down" to mexico, It's probably more like 50,000 > to New York, and 45,000 to San Diego. And if you're in New York, > and your mail server is in New York, but the downlink was to San > Diego, you've got another 4,000 across country. Now you're up > closer to 100,000km. > > Add to this some inefficient encoding done on satellites, and most > (consumer) systems using a broadcast medium that can buffer packets > and you see why people report 1 second RTT's with services like > StarBand. > > It's better than nothing, but it's a rough primary connection. > > -- > Leo Bicknell - bicknell(a)ufp.org - CCIE 3440 > PGP keys at http://www.ufp.org/~bicknell/ > Read TMBG List - tmbg-list-request(a)tmbg.org, www.tmbg.org >

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RE: Just keep telling yourself, "Worldcom won't fail, Worldcom wo n't fail"
by Jon Stanley 28 Feb '02

28 Feb '02

What is the reasoning for thinking that WorldCom may fail? Is there something that I've missed? -----Original Message----- From: Fletcher E Kittredge [mailto:fkittred@gwi.net] Sent: Monday, February 25, 2002 12:51 PM To: nanog(a)merit.edu Subject: Just keep telling yourself, "Worldcom won't fail, Worldcom won't fail" This is an interesting NYT article (free registration required) for all of those of us trying to convince themselves that even if Worldcom goes bankrupt, UUnet will stay up. The example used is Global Crossings. If a company has complex enough finances and gets deeply enough under water, the courts might not be able to figure it out and creditors may just liquidate... whether or not it makes sense for the customers and society as a whole. If the government is not willing to step in for Enron, would they step in for UUnet? http://www.nytimes.com/2002/02/25/technology/25GLOB.html By the way, I never said to Dan Hollis and others: "You were right; I was wrong." about Global Crossing. If one had listened to Dan, one would have known 12 months that Global Crossing was in trouble. I read their press releases and balance sheets and didn't see it... Mea Culpa. regards, fletcher

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Re: Satellite latency
by Steven M. Bellovin 27 Feb '02

27 Feb '02

In message <014d01c1bf3b$44bfca00$ea9a8d18@evilinc>, "Tim Devries" writes: > >Hello, > >I think this question may have been asked before, but what is the minimum >latency and delay I can expect from a satellite connection? What kind of >delay have others seen in a working situation? What factors should be >considered in end to end connectivity architecture when utilizing a >satellite link? > >Any help appreciated, Geosynchronous orbit is about 36,000 km from the center of the earth. Round-trip to the satellite is ~72,000 km; the speed of light is 300,000 km/sec. That works out to 240 milliseconds at the minimum for one-way packet delivery. --Steve Bellovin, http://www.research.att.com/~smb Full text of "Firewalls" book now at http://www.wilyhacker.com

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Re: Fiber cut in Anaheim?
by Stephen Fisher 27 Feb '02

27 Feb '02

MCI says that there are 8 OC48's down in a fiber cut due to utility company cutting through the conduit. No ETA. On Wed, Feb 27, 2002 at 04:35:11PM -0500, Eric Whitehill wrote: > > NANOG: > > I have some customers reporting a possible fiber cut in/near Anaheim, CA. > Anyone able to confirm/deny/throw donuts at this? > > Thanks, > > -Eric

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Fiber cut in Anaheim?
by Eric Whitehill 27 Feb '02

27 Feb '02

NANOG: I have some customers reporting a possible fiber cut in/near Anaheim, CA. Anyone able to confirm/deny/throw donuts at this? Thanks, -Eric

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Re: Satellite latency
by Dickson, Brian 27 Feb '02

27 Feb '02

"Tim Devries" <zsolutions(a)cogeco.ca> wrote: > I think this question may have been asked before, but what is the minimum > latency and delay I can expect from a satellite connection? What kind of > delay have others seen in a working situation? As others have pointed out, GEO is about 22,000 miles, plus offsets for both sending and receiving station, both in lat. and long. There are a lot of satellites up there, on the equator, spaced every 0.5 degrees or so. Another latency factor is something not normally factored in land-based systems. Doppler shift! Satellites are seldom in perfect orbits - they drift up and down, returning to zero (thus in stable orbit), but the relative motion results in clocking issues. Satellite modems usually have 8ms receive buffers to accommodate drift, and when local clocking is not available, clocking transmit from receive requires at least double. On the down-swing, the buffer drains; on the up-swing it fills (both rates are slow, but last a long time). Regardless, the buffer itself adds 8ms to each way delay. A good working value is 280ms each way, *plus* any router serialization delay and terrestrial backhaul at both ends (unless you live at an earth station). > What factors should be considered in end to end connectivity architecture > when utilizing a satellite link? If you have end users, put in a huge web cache, as big as you can afford. Not only will it reduce bandwidth usage, it lowers average latency considerably. Doesn't help non-cacheable content, or other applications, directly, but lowering usage minimizes latency at least. Another approach is asymmetric - buy a low-speed terrestrial link for return path. Round-trip time is the sum of transmit and receive paths, so reducing even one of them helps most applications. Brian Dickson

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Cogent picks up PSInet
by David Ulevitch 27 Feb '02

27 Feb '02

Hello Nanog, Interesting news.... http://washington.bizjournals.com/washington/stories/2002/02/25/daily19.html Cogent Communications Group said Wednesday it will purchase PSINet's major U.S. assets, including part of the Ashburn, Va.-based Internet infrastructure company's customer base and network, certain equipment and three hosting facilities. The companies did not disclose the financial terms of the deal, nor would they provide specific details as to how much of PSINet's network the Washington-based high-speed Internet access provider wants to buy. Cogent (http://www.cogent.com) and PSINet (http://www.psinet.com) officials were not immediately available for comment. PSINet, which filed for Chapter 11 bankruptcy protection with more than $3 billion in debt late last spring, has been selling itself piece-meal -- including international assets in Latin America, Chile, Canada and Hong Kong -- ever since. Cogent's offer to buy part of PSINet's assets is also subject to bankruptcy court approval and requires a court-sanctioned auction. Thanks, David Ulevitch mailto:davidu@everydns.net Founder, EveryDNS.net http://www.everydns.net

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Re: Satellite latency (fwd)
by Ukyo Kuonji 27 Feb '02

27 Feb '02

>The radius of the earth is about 6400km. Geostationary orbit is, as >you note, 36000km above the equator. The path from the satellite to >the North Pole is the hypotenuse of a right triangle with legs of >6400km and (6400+36000)km. That gives a distance from the North Pole >to the satellite of 43000km. It's reasonable to conclude that the >distance from either New York or San Diego is less than that. Is that 36000 km above the equator measures from the surface of the earth, or the center of the earth? I would assume that most companies would use the surface of the earth to determine the orbit, or sea level. Looking at a spam I just received from satcast.com, it looks like they are considering the distance from the dish to the satellite to be roughly 44000 miles. That's roughly 70000 km. Assuming that they are stating that from the dish to the bird, that would account for the larger RTT times that people see. My real problem with these directpc type systems are two fold. The first is that these systems use a USB connection. I use wireless at home since I have a number of laptops. I certainly am not willing to tie myself down to a usb cable. The second problem is that the users are addressed using rfc1918 address space and are translated via nat to the Internet. This may mess up any number of applications that I use, including VPN software. Add to this the first problem, and suddenly I have two levels of NAT that I have to contend with, one on my windows machine connected to the USB cable (with Internet sharing), and one at earthlink's edge. Those are what's keeping me at dialup, even though I only get 28.8 at best. Well... that and the fact that I can't get cable where I live, and the CO is sonething like 15 miles away (not that they can spell DSL out here). _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com

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