Re: A New TransAtlantic Cable System
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
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.Kletnieks@vt.edu wrote: From: Valdis.Kletnieks@vt.edu To: Heath Jones <hj1980@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: that runs at 1.1 and a *cladding* that's up around 2.0?
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
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.Kletnieks@vt.edu wrote: From: Valdis.Kletnieks@vt.edu To: Heath Jones <hj1980@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: that runs at 1.1 and a *cladding* that's up around 2.0?
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?
On Mon, Oct 4, 2010 at 10:24 AM, Heath Jones <hj1980@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
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=6&topic= 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 patrick@zill.net
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
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 <patrick@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=6&topic=
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 patrick@zill.net
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
Dorn Hetzel <dhetzel@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.
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.
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
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/coher... [3] Optical hybrid, http://en.wikipedia.org/wiki/Optical_hybrid -- Chris Tracy <ctracy@es.net> Energy Sciences Network (ESnet) Lawrence Berkeley National Laboratory
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 waaaaay off? Cheers
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 waaaaay 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 <ctracy@es.net> Energy Sciences Network (ESnet) Lawrence Berkeley National Laboratory
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?
participants (10)
-
Chris Tracy -
Dorn Hetzel -
Frank A. Coluccio -
Heath Jones -
Joe Loiacono -
nick hatch -
Nick Hilliard -
Patrick Giagnocavo -
Randy Bush -
Rod Beck