Re: A New TransAtlantic Cable System
On 04/10/2010 18:24, Heath Jones wrote: I'm not clever enough to know of some way that you could do optical regeneration without converting the signal to electrical and retransmitting back as optical.. How is that done? Wikipedia has a useful article on this: http://en.wikipedia.org/wiki/EDFA Nick
Re: A New TransAtlantic Cable System
Dorn Hetzel dhet...@gmail.com wrote on 10/04/2010 06:22:58 PM: With regards to the Wired Article, I still have my copy of that issue and would consider that article perhaps my favorite magazine article of all time. Same here. A classic.
Re: A New TransAtlantic Cable System
What's that quote again...? Oh, that's it: The more you know, the more you know you don't. It feels very appropriate now :) I was wondering for quite some time if there was a scientific term for that effect, since many of us seem to run into the opposite quite often. It turns out that it's the Dunning-Kruger effect: http://en.wikipedia.org/wiki/Dunning-Kruger_effect Ignorant bliss! :)
Re: A New TransAtlantic Cable System
Heath, By the way, my recollection is the undersea regenerators do purely optical regeneration. There is no O-E conversions undersea, only at the landing stations and terrestrial components. I'm not clever enough to know of some way that you could do optical regeneration without converting the signal to electrical and retransmitting back as optical.. How is that done? Erbium Doped Fiber Amplifiers (EDFAs) do not re-shape or re-time the signals (the last 2 R's in 3R -- re-amplification, re-shaping, and re-timing). Raman is another popular amplification technology, widely used in long-haul WDM. Some systems have the flexibility of using EDFA and Raman amps on the same spans. EDFAs amplify a band of spectrum (C- and/or L-band, depending on the device) -- signal *and* noise. The amplified noise floor is clearly visible if you connect an optical spectrum analyzer to the output of an EDFA -- you see a big wide bump across the entire amplified band with spikes for each wavelength. An optical signal can only go through so many EDFAs before it becomes too degraded to be accurately converted back to an electrical signal by the receiver -- either due to dispersion (especially if uncompensated) or noise, tolerances of which are different for every device...(EDFAs introduce some amount of noise, so OSNR before EDFA != OSNR after EDFA :-) ) That being said, one can find examples of all-optical regeneration [1], but I do not know of any transport vendors who have integrated this capability into currently shipping products. (Some have developed various tricks like electronic dispersion compensation, but IIRC, these work by pre-distorting the signal.) Getting back to the original post from this thread -- when I first read it, I immediately wondered whether the vendor might be using coherent optical receivers which have much higher dispersion tolerances, allowing the optical signal to travel much further without OEO conversions (see [2] and [3] for some background). Unfortunately, I could not find any evidence one way or the other about what Hibernia is doing. In fact, Per Hansen from Ciena just so happens to be talking about coherent receiver technology [DP-QPSK encoding DSP analysis] as I write this e-mail... Cheers, -Chris [1] 3R optical regeneration: an all-optical solution with BER improvement, http://www.opticsinfobase.org/abstract.cfm?URI=oe-14-14-6414 [2] Coherent receivers enable next-generation transport, http://www.lightwaveonline.com/about-us/lightwave-issue-archives/issue/coherent-receivers-enable-next-generation-transport-53426202.html [3] Optical hybrid, http://en.wikipedia.org/wiki/Optical_hybrid -- Chris Tracy ctr...@es.net Energy Sciences Network (ESnet) Lawrence Berkeley National Laboratory
Re: A New TransAtlantic Cable System
Erbium Doped Fiber Amplifiers (EDFAs) do not re-shape or re-time the signals (the last 2 R's in 3R -- re-amplification, re-shaping, and re-timing) Thanks Chris - even more reading to do :) It's interesting stuff that's for sure. This is also pretty cool: http://en.wikipedia.org/wiki/Chirped-pulse_amplification I just had a thought about EFDA - please forgive my lack of terminology though, i'll try to explain: Say you have signal coming in to EFDA, the signal is just amplified (as you said, also noise - the whole source signal). Would it be possible to extract via PLL or similar the source clock and use that to modulate the amplifier power? Does it work with QPSK / whatever keying is used? Would that even help with the noise issue at all, or am I way off? Cheers
Re: A New TransAtlantic Cable System
Heath, I just had a thought about EFDA - please forgive my lack of terminology though, i'll try to explain: Say you have signal coming in to EFDA, the signal is just amplified (as you said, also noise - the whole source signal). Would it be possible to extract via PLL or similar the source clock and use that to modulate the amplifier power? Does it work with QPSK / whatever keying is used? Would that even help with the noise issue at all, or am I way off? Although you can amplify just a single wavelength with an EDFA (has to be in the 1550nm range, not 1310nm), most deployments are using EDFAs in a DWDM environment. The C-band alone consists of ~5THz (5000GHz) of spectrum between 191.00-195.95 Thz. Some systems pack 40 wavelengths into this space at 100GHz spacing, some 80 channels @ 50GHz spacing, others 160 @ 25GHz. Each of these signals is independent, they can each be using different modulation/bitrate/etc. The amplifiers are completely ignorant to what is going on with each channel, only the devices performing conversion back to the electrical domain need to care about these details (after the incoming light has been demultiplexed into individual signals, of course). Re: amplifier power... Amplifier gain should really stay constant unless new wavelengths are added/removed from the fiber. There are fixed-gain and variable-gain amps. VGAs have the advantage that engineers do not need to manually re-balance power levels whenever a large number of wavelengths are added or removed from a span, they adjust automatically. Newer DWDM systems should all have VGAs whereas a lot of earlier generation DWDM systems still use fixed-gain amps. With the older fixed-gain amps, you had to have the input power just right -- hence the need to re-balance if your aggregate signal changes a lot -- too low and the EDFA would not kick on at all, too high and you'd saturate the amp. -Chris -- Chris Tracy ctr...@es.net Energy Sciences Network (ESnet) Lawrence Berkeley National Laboratory
Re: A New TransAtlantic Cable System
Would it be possible to extract via PLL or similar the source clock and use that to modulate the amplifier power? Although you can amplify just a single wavelength with an EDFA (has to be in the 1550nm range, not 1310nm), most deployments are using EDFAs in a DWDM environment. The C-band alone consists of ~5THz (5000GHz) of spectrum between 191.00-195.95 Thz. Some systems pack 40 wavelengths into this space at 100GHz spacing, some 80 channels @ 50GHz spacing, others 160 @ 25GHz. Each of these signals is independent, they can each be using different modulation/bitrate/etc. The amplifiers are completely ignorant to what is going on with each channel, only the devices performing conversion back to the electrical domain need to care about these details (after the incoming light has been demultiplexed into individual signals, of course). I'm wondering if it could be done per wavelength? I guess that would be pretty ridiculous having demux + 160 * decoder + 160 * efda + mux.. Just wondering if the theory works though?
RE: A New TransAtlantic Cable System
Hi Frank, Yes it does include all the O-E conversions. By the way, my recollection is the undersea regenerators do purely optical regeneration. There is no O-E conversions undersea, only at the landing stations and terrestrial components. Since the system is just in the planning stage, the latency estimate is conversative. It is better to surprise than disappoint ... Hi All. It appears we're discussing theoretical limits of silica-based glass here. The Press Release assertion talks about what a trader might experience. Hm. I would ask Rob Beck to clarify this point and inform whether the stated objective in the release accounts for the many o-e and e-o conversions on the overland part of the end-to-end trader connection, including the handoffs that occur in the NY and London metros. I know that terrestrially, i.e., here in the US, some brokerage firms and large banks (is there any longer a distinction between those two today?:) have used their clout to secure links that are virtually entirely optical in nature on routes that are under a thousand miles, but this is not an option on a submarine system that's intrinsically populated with electronics, never mind the tail sections that assume multiple service providers getting into the act. Rob? Anyone? FAC --- valdis.kletni...@vt.edu wrote: From: valdis.kletni...@vt.edu To: Heath Jones hj1...@gmail.com Cc: nanog@nanog.org Subject: Re: A New TransAtlantic Cable System Date: Fri, 01 Oct 2010 10:08:50 -0400 On Fri, 01 Oct 2010 15:01:25 BST, Heath Jones said: http://finance.yahoo.com/news/Hibernia-Atlantic-to-bw-3184701710.html ?x=0.v=1 Sales spam - but still - very close to minimum possible latency! 3471 miles @ 186,282 miles/s * 1.5 in glass * 2 round trip = 55.9ms. My first thought is that they've found a way to cheat on the 1.5. If you can make it work at 1.4, you get down to 52.2ms - but get it *too* low and all your photons leak out the sides. Hmm.. Unless you have a magic core that runs at 1.1 and a *cladding* that's up around 2.0?
Re: A New TransAtlantic Cable System
By the way, my recollection is the undersea regenerators do purely optical regeneration. There is no O-E conversions undersea, only at the landing stations and terrestrial components. I'm not clever enough to know of some way that you could do optical regeneration without converting the signal to electrical and retransmitting back as optical.. How is that done?
Re: A New TransAtlantic Cable System
On Mon, Oct 4, 2010 at 10:24 AM, Heath Jones hj1...@gmail.com wrote: I'm not clever enough to know of some way that you could do optical regeneration without converting the signal to electrical and retransmitting back as optical.. How is that done? I'm not sure how it's done in practice, but check out doped fiber amplifiers for one possibility. One has to grok laser fundamentals to get what's going on, but it's not an especially complex topic. -Nick
Re: A New TransAtlantic Cable System
On 10/4/2010 1:24 PM, Heath Jones wrote: By the way, my recollection is the undersea regenerators do purely optical regeneration. There is no O-E conversions undersea, only at the landing stations and terrestrial components. I'm not clever enough to know of some way that you could do optical regeneration without converting the signal to electrical and retransmitting back as optical.. How is that done? A halfway-decent description of the physics of how this is done, is covered in Neal Stephenson's excellent article on Wired: http://www.wired.com/wired/archive/4.12/ffglass.html The specific page covering optical regeneration: http://www.wired.com/wired/archive/4.12/ffglass.html?pg=6topic= quote: These signals begin to fade after they have traveled a certain distance, so it's necessary to build amplifiers into the cable every so often. In the case of FLAG, the spacing of these amplifiers ranges from 45 to 85 kilometers. They work on a strikingly simple and elegant principle. Each amplifier contains an approximately 10-meter-long piece of special fiber that has been doped with erbium ions, making it capable of functioning as a laser medium. A separate semiconductor laser built into the amplifier generates powerful light at 1,480 nm - close to the same frequency as the signal beam, but not close enough to interfere with it. This light, directed into the doped fiber, pumps the electrons orbiting around those erbium ions up to a higher energy level. The signal coming down the FLAG cable passes through the doped fiber and causes it to lase, i.e., the excited electrons drop back down to a lower energy level, emitting light that is coherent with the incoming signal - which is to say that it is an exact copy of the incoming signal, except more powerful. Cordially Patrick Giagnocavo patr...@zill.net
RE: A New TransAtlantic Cable System
By the way, my recollection is the undersea regenerators do purely optical regeneration. There is no O-E conversions undersea, only at the landing stations and terrestrial components. I'm not clever enough to know of some way that you could do optical regeneration without converting the signal to electrical and retransmitting back as optical.. How is that done? Erbium doped fibers.
Re: A New TransAtlantic Cable System
What's that quote again...? Oh, that's it: The more you know, the more you know you don't. It feels very appropriate now :) Cheers Patrick for that great info to everyone who contacted me off-list also! A halfway-decent description of the physics of how this is done, is covered in Neal Stephenson's excellent article on Wired: http://www.wired.com/wired/archive/4.12/ffglass.html
Re: A New TransAtlantic Cable System
With regards to the Wired Article, I still have my copy of that issue and would consider that article perhaps my favorite magazine article of all time. On Mon, Oct 4, 2010 at 1:41 PM, Patrick Giagnocavo patr...@zill.net wrote: On 10/4/2010 1:24 PM, Heath Jones wrote: By the way, my recollection is the undersea regenerators do purely optical regeneration. There is no O-E conversions undersea, only at the landing stations and terrestrial components. I'm not clever enough to know of some way that you could do optical regeneration without converting the signal to electrical and retransmitting back as optical.. How is that done? A halfway-decent description of the physics of how this is done, is covered in Neal Stephenson's excellent article on Wired: http://www.wired.com/wired/archive/4.12/ffglass.html The specific page covering optical regeneration: http://www.wired.com/wired/archive/4.12/ffglass.html?pg=6topic= quote: These signals begin to fade after they have traveled a certain distance, so it's necessary to build amplifiers into the cable every so often. In the case of FLAG, the spacing of these amplifiers ranges from 45 to 85 kilometers. They work on a strikingly simple and elegant principle. Each amplifier contains an approximately 10-meter-long piece of special fiber that has been doped with erbium ions, making it capable of functioning as a laser medium. A separate semiconductor laser built into the amplifier generates powerful light at 1,480 nm - close to the same frequency as the signal beam, but not close enough to interfere with it. This light, directed into the doped fiber, pumps the electrons orbiting around those erbium ions up to a higher energy level. The signal coming down the FLAG cable passes through the doped fiber and causes it to lase, i.e., the excited electrons drop back down to a lower energy level, emitting light that is coherent with the incoming signal - which is to say that it is an exact copy of the incoming signal, except more powerful. Cordially Patrick Giagnocavo patr...@zill.net
Re: A New TransAtlantic Cable System
With regards to the Wired Article, I still have my copy of that issue and would consider that article perhaps my favorite magazine article of all time. i too thought that a great article and often point folk to it. sadly, the copy on the wired web site does not have the figures :( randy
RE: A New TransAtlantic Cable System
Is that a straight line calculation or did you take into account that a straight line is not the shortest path on a curved surface? -Original Message- From: d...@hetzel.org on behalf of Dorn Hetzel Sent: Fri 10/1/2010 3:11 PM To: Heath Jones Cc: Rod Beck; nanog@nanog.org Subject: Re: A New TransAtlantic Cable System Yeah, I wonder when we're gonna see cable that's pumped down to a vacuum in the center? :) On Fri, Oct 1, 2010 at 10:01 AM, Heath Jones hj1...@gmail.com wrote: http://finance.yahoo.com/news/Hibernia-Atlantic-to-bw-3184701710.html?x=0.v=1 Roderick S. Beck Director of European Sales Hibernia Atlantic Sales spam - but still - very close to minimum possible latency! 3471 miles @ 186,282 miles/s * 1.5 in glass * 2 round trip = 55.9ms.
Re: A New TransAtlantic Cable System
On 2 October 2010 10:52, Rod Beck rod.b...@hiberniaatlantic.com wrote: Is that a straight line calculation or did you take into account that a straight line is not the shortest path on a curved surface? Well that is pretty obvious to most, but no - I didn't go to the effort of factoring in curvature of the earth - especially given that 1.5 is very rough figure anyway for RI of glass. If anything, my comment was compliment to your network being close to minimum possible latency!
Re: A New TransAtlantic Cable System
One of the ways that I have tormented WAN vendors over the years is with a plot of RTT vs. great circle distance between the end points of a circuit. Most RTTs usually sit at some constant offset above that Physics limit straight line. Circuits taking a less than ideal have their RTT far above the Physics limit line and we have used that information to get routes fixed. Using my great circle program that accounts for the non-spherical Earth for locations we have West of London and North of NYC, assuming a 1.5 index of refraction I get: One way distance: 5520.6 km Round Trip Delay: 55.2 ms So Heath's estimate is right on, although depending on where he got the distance maybe it does account for the shape of the Earth. Jon On Sat, Oct 2, 2010 at 6:17 AM, Heath Jones hj1...@gmail.com wrote: On 2 October 2010 10:52, Rod Beck rod.b...@hiberniaatlantic.com wrote: Is that a straight line calculation or did you take into account that a straight line is not the shortest path on a curved surface? Well that is pretty obvious to most, but no - I didn't go to the effort of factoring in curvature of the earth - especially given that 1.5 is very rough figure anyway for RI of glass. If anything, my comment was compliment to your network being close to minimum possible latency!
Re: A New TransAtlantic Cable System
http://www.gcmap.com/mapui?P=lga-lhr -- kris On Oct 2, 2010, at 7:31 AM, Jon Meek wrote: One of the ways that I have tormented WAN vendors over the years is with a plot of RTT vs. great circle distance between the end points of a circuit. Most RTTs usually sit at some constant offset above that Physics limit straight line. Circuits taking a less than ideal have their RTT far above the Physics limit line and we have used that information to get routes fixed. Using my great circle program that accounts for the non-spherical Earth for locations we have West of London and North of NYC, assuming a 1.5 index of refraction I get: One way distance: 5520.6 km Round Trip Delay: 55.2 ms So Heath's estimate is right on, although depending on where he got the distance maybe it does account for the shape of the Earth. Jon On Sat, Oct 2, 2010 at 6:17 AM, Heath Jones hj1...@gmail.com wrote: On 2 October 2010 10:52, Rod Beck rod.b...@hiberniaatlantic.com wrote: Is that a straight line calculation or did you take into account that a straight line is not the shortest path on a curved surface? Well that is pretty obvious to most, but no - I didn't go to the effort of factoring in curvature of the earth - especially given that 1.5 is very rough figure anyway for RI of glass. If anything, my comment was compliment to your network being close to minimum possible latency!
Re: A New TransAtlantic Cable System
Hi All. It appears we're discussing theoretical limits of silica-based glass here. The Press Release assertion talks about what a trader might experience. Hm. I would ask Rob Beck to clarify this point and inform whether the stated objective in the release accounts for the many o-e and e-o conversions on the overland part of the end-to-end trader connection, including the handoffs that occur in the NY and London metros. I know that terrestrially, i.e., here in the US, some brokerage firms and large banks (is there any longer a distinction between those two today?:) have used their clout to secure links that are virtually entirely optical in nature on routes that are under a thousand miles, but this is not an option on a submarine system that's intrinsically populated with electronics, never mind the tail sections that assume multiple service providers getting into the act. Rob? Anyone? FAC --- valdis.kletni...@vt.edu wrote: From: valdis.kletni...@vt.edu To: Heath Jones hj1...@gmail.com Cc: nanog@nanog.org Subject: Re: A New TransAtlantic Cable System Date: Fri, 01 Oct 2010 10:08:50 -0400 On Fri, 01 Oct 2010 15:01:25 BST, Heath Jones said: http://finance.yahoo.com/news/Hibernia-Atlantic-to-bw-3184701710.html ?x=0.v=1 Sales spam - but still - very close to minimum possible latency! 3471 miles @ 186,282 miles/s * 1.5 in glass * 2 round trip = 55.9ms. My first thought is that they've found a way to cheat on the 1.5. If you can make it work at 1.4, you get down to 52.2ms - but get it *too* low and all your photons leak out the sides. Hmm.. Unless you have a magic core that runs at 1.1 and a *cladding* that's up around 2.0?
A New TransAtlantic Cable System
http://finance.yahoo.com/news/Hibernia-Atlantic-to-bw-3184701710.html?x=0.v=1 Roderick S. Beck Director of European Sales Hibernia Atlantic Budapest, New York, and Paris http://www.hiberniaatlantic.com Landline: 36+1+784+7975 AOL Messenger: GlobalBandwidth rod.b...@hiberniaatlantic.com i...@globalwholesalebandwidth.com ``Unthinking respect for authority is the greatest enemy of truth.'' Albert Einstein.
Re: A New TransAtlantic Cable System
http://finance.yahoo.com/news/Hibernia-Atlantic-to-bw-3184701710.html?x=0.v=1 Roderick S. Beck Director of European Sales Hibernia Atlantic Sales spam - but still - very close to minimum possible latency! 3471 miles @ 186,282 miles/s * 1.5 in glass * 2 round trip = 55.9ms.
Re: A New TransAtlantic Cable System
On Fri, 01 Oct 2010 15:01:25 BST, Heath Jones said: http://finance.yahoo.com/news/Hibernia-Atlantic-to-bw-3184701710.html?x=0.v=1 Sales spam - but still - very close to minimum possible latency! 3471 miles @ 186,282 miles/s * 1.5 in glass * 2 round trip = 55.9ms. My first thought is that they've found a way to cheat on the 1.5. If you can make it work at 1.4, you get down to 52.2ms - but get it *too* low and all your photons leak out the sides. Hmm.. Unless you have a magic core that runs at 1.1 and a *cladding* that's up around 2.0? pgptPpQq6miQN.pgp Description: PGP signature
Re: A New TransAtlantic Cable System
Yeah, I wonder when we're gonna see cable that's pumped down to a vacuum in the center? :) On Fri, Oct 1, 2010 at 10:01 AM, Heath Jones hj1...@gmail.com wrote: http://finance.yahoo.com/news/Hibernia-Atlantic-to-bw-3184701710.html?x=0.v=1 Roderick S. Beck Director of European Sales Hibernia Atlantic Sales spam - but still - very close to minimum possible latency! 3471 miles @ 186,282 miles/s * 1.5 in glass * 2 round trip = 55.9ms.
Re: A New TransAtlantic Cable System
Yeah, I wonder when we're gonna see cable that's pumped down to a vacuum in the center? :) Start pumping.. :) Actually, to my surprise, the refractive index in air is quite close to a vacuum - so I figured we could set up a laser link between NY and London, with 'yo mama' sitting in a boat in the middle of the Atlantic to give it the required bend... ps. that concludes my very poor attempt at humour.
