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Optical/IP

Optical Crossconnects

Before reading this you may find the following tutorials useful:
Optical Networks, Wavelength Division Multiplexing (WDM)

Huge amounts of information traveling around an optical network need to be switched through various points known as “nodes.” Information arriving at a node will be forwarded on towards its final destination via the best possible path, which may be determined by such factors as distance, cost, and the reliability of specific routes. The conventional way to switch the information is to detect the light from the input optical fibers, convert it to an electrical signal, and then convert that back to a laser light signal, which is then sent down the fiber you want the information to go back out on.

It all sounds unnecessarily complicated, don't you think? It's as if to give money to a friend, you would have to convert it into Euros, then back into your own currency before your friend can use it. Now, even though your information is safer in electrical form than your money may be in Euros, it still seems a strange way to work. What if we could just move the light itself around, without all this ridiculous conversion to electric signals? Well, my friend, what you need is an optical crossconnect (OXC).

The advantages of being able to avoid the conversion stage are significant. “Optical switching” should be cheaper, as there is no need for lots of expensive high-speed electronics. Removing this complexity should also make for physically smaller switches. Additionally, optical switches are relatively future-proof. An electrically based switch will have electronics designed to detect the incoming light signal. If you increase the speed at which the light signals operate (increasing the “bit-rate”) then the electronics will need to be upgraded to handle the faster speeds. If you are just rerouting light, however, it doesn't matter how fast the data is coming — so you can accommodate any future upgrades of bit-rate without needing to upgrade the switch (this is called “bit-rate transparency”). Optical crossconnects are just now coming onto the market with these benefits and more.

Optical crossconnects are very much designed with simplicity in mind. You've got some light in one fiber that you want to move to a different fiber, so just redirect the light somehow and that's all you need — it's child's play. Unfortunately, the technologies used seem to come out of science fiction rather than a child's bedtime story. There is a wide range of wild and wacky ways to switch light between optical fibers. Semiconductor amplifiers, liquid crystals, holographic crystals, and tiny moveable mirrors are just a few. Truly buttock-clenching switching developments are anticipated in the future. One of the most common techniques being developed is that of the tiny moveable mirrors known as micro-electro-mechanical systems (MEMS).

MEMS Mirror MEMS Optical Cross Connect MEMS consist of mirrors no larger in diameter than a human hair. They can be arranged on special pivots so that they can be moved in three dimensions, and several hundred such mirrors can be placed together on mirror arrays no larger than a few centimeters square. Light from an input fiber is aimed at a mirror, which is directed to move the light to another mirror on a facing array. This mirror then reflects the light down towards the desired output optical fiber. It perhaps sounds a little bizarre, but it does seem to work. MEMS mirror arrays are even used successfully in some of the modern digital projectors used for computer-based presentations.

Key Points

  • Crossconnects forward signals to their destination by specific routes
  • Traditional crossconnects convert light to electricity then back to light
  • Optical crossconnect advantages include cost, size, and bit-rate transparency
  • Redirecting light from one optical fiber to another, without electrical conversion
  • Most advanced optical switching technology is MEMS, tiny moveable mirrors


Further Reading

Fiber Bragg Gratings (FBGs), Arrayed Waveguide Gratings (AWGs), Semiconductor Optical Amplifiers (SOAs)

dansteph 12/4/2012 | 7:31:42 PM
re: Optical Crossconnects If I'm right, is this company claiming to be able to give OOO from a DWDM link to dropping it off to legacy equipment. There is already a very well taken product on the market that already has all the capabilities except for the OOO to the drop offs, it still requires a little OEO at this point. Could someone explain how they take the info off the DWDM and drop it off to the legacy equipment without some form of electrical conversion? I'm definately not saying it's not possible, I would just like to know how it's achieved.

An all OOO cross connect is viable, as long as there is no info to be dropped off and it's just directing the info. At the end of the day, the structure of signals is still apparent in the DWDM link and therefore holds the required info of where it's supposed to go. How it gets there, the info doesn't care. After all DWDM doesn't care what it takes as long as the equipment interfacing the traffic type (ie the point at which traffic joins the link or leaves it)has the functionality.
manoflalambda 12/4/2012 | 7:37:43 PM
re: Optical Crossconnects Can?t speak to all MEMS switches, but ones I am aware of have no such limitation.

One vendor quotes in data sheets three ?bands? or windows. The data sheets are available on companies web site.
1570 to 1610 nm
1530 to 1570 nm
1290 to 1330 nm
If a DWDM signal was wider than one of the windows, perhaps you would have to do something before you switch, but I don?t think that is the case.


As Lambdaswitching says, and from I have read, the limitations in range are not the mirrors, which work for 13xx, 15xx and L band, but the components married around them. Hence the mirrors can handle DWDM streams at any currently use wavelength.

Certainly any opaque (OEO) ports would be wavelength dependent. The transparent (OOO) ports might be limited by characteristics of fiber built into the system and/or monitoring devices.

Salute,
Manoflalambda
lambdaswitching 12/4/2012 | 7:37:45 PM
re: Optical Crossconnects gladysnight saidGǥ

My understanding is that it may be even more restrictive than that. I've read in some press release or other that you have to have the dwdm manage the demux because the mirrors have small angle of reflection (not sure of specific terminology?) which cannot deal effectively with (for example) 100 different wavelengths simultaneouslyGǥ

CanGt speak to all MEMS switches, but ones I am aware of have no such limitation.

One vendor quotes in data sheets three GǣbandsGǥ or windows. The data sheets are available on companies web site.

1570 to 1610 nm

1530 to 1570 nm

1290 to 1330 nm

If a DWDM signal was wider than one of the windows, perhaps you would have to do something before you switch, but I donGt think that is the case.
gladysnight 12/4/2012 | 7:37:46 PM
re: Optical Crossconnects ".....
It's all done optically in the above example, while today you need to put one DWDM box in front of every fiber coming to an OOO OXC (Unless you don't plan to extract any lambads from any fiber at that particular OXC)." -Belzebutt
----------------------------

My understanding is that it may be even more restrictive than that. I've read in some press release or other that you have to have the dwdm manage the demux because the mirrors have small angle of reflection (not sure of specific terminology?) which cannot deal effectively with (for example) 100 different wavelengths simultaneously.

So that the OOO is ONLY a lambda switch - i.e. it is NOT a really expensive automated fibre patch panel that switches a whole fibres worth of traffic irrespective of its lambda content.

Maybe manoflalambda can discuss? . . . . .
MKTG_Hack 12/4/2012 | 7:37:47 PM
re: Optical Crossconnects Hey Mono:
This still isn't making sense. Is what you are talking about similar to an SS7 network? And if an OXC is storing preselected maps, that sounds like curcuits to me. If either of these are true then I don't get it. Where's the whoop? It might make sense if the OXC is like an old railroad tack switch that simply helps the train get on a specific track without caring where that train might want to go. Give us some more details PLEASE!
laserman 12/4/2012 | 8:14:21 PM
re: Optical Crossconnects I heard that there is a new company making optical cross connect under a $50/port. Is it true?. Sorry for my ignorance, but I am not very familiar with this subject. Can some one tell me which company is it?. Thanks

Laserman
manoflalambda 12/4/2012 | 8:14:45 PM
re: Optical Crossconnects Do you mean move the mirrors? Databases of mirror positioning info and D/A converters/Op-Amps and the like.

Salute,
Manoflalambda
nightRaider 12/4/2012 | 8:14:47 PM
re: Optical Crossconnects . . . "Most advanced optical switching technology is MEMS, tiny moveable mirrors "

But what is used to switch mems. DSPS?





manoflalambda 12/4/2012 | 8:25:56 PM
re: Optical Crossconnects http://www.lucent.com/press/05...

Global Crossing bought 1 or more LambdaRouters
from Lucent.

Salute,
Manoflalambda
shun_y 12/4/2012 | 8:27:02 PM
re: Optical Crossconnects "Optical transistors"--

Having an optical device that has some transistor-like bahavior is one thing, packing godzillions of transistors and gates into one chip is another. I didn't see their website because it was not working, but one thing I am sure of is that we won't see anything like the velio switch chip in the optical domain anytime soon.

Same story with optical memory, storing a few kilo bits in some bulk optical meterial is one thing, storing a few giga bits in a chip is totally different.

If they claim their 'optical transistor' will revolutionize the industry, be very skeptical.

-Shun
Half-Inch Stud 12/4/2012 | 8:27:15 PM
re: Optical Crossconnects Good thread folks. Time to summarize the Tech Career pursuit [go grab a beer for this..]:

Good Career: exist only in a maturely-managed Co.
Options : find a job you like, and invest in publically-traded stocks rather than startup options. That's the real option for peace of mind.
Intellectual Property: you-wreak-ah; who cares unless it saves money in production. Otherwise, it's "hey mom, dad I got a Patent at work"

OOO : Oh give it a rest. I hear the Iridium Sat-Birds need OOO to be successful...Let's upgrade them [note to the wisest; Optical Crosslinks were not used on these birds, mmWave crosslinks were more cost and performance effective].

Remember: If it can be done Electrically, then it will be. People only use fiber when they have to.
OXCs : As real as Everlasting Gobstoppers. Next network systems advancement step is telepathy..

Good ideas/products will contine to be judged on cost and performance, with all the usual caveats of multi-source, reliability, and helping the customer solve their problem.

Wireless Phones : here to stay
Wireless 'Net : BWAHAHAHA! be afraid of hype, very afraid. email vs voice [duh!]
Internet : Email remains the killer app. Downloading music and 'pictures' seems to be the other killer app. Will remain a wired demand.

Wired phones :wake up and smell the decaying reptile.
DSL : another example of something that works but does not make a good business model. I figure $10/month rate is the "Satisfied Customer" charging for Broadband-to-home connection. Time marches on and the chargings for Mbit/month will necessarily walk down.

CATV : won the last mile 20 years ago...silly people.
Metro : Can grow to look like a Long-Haul CO.
Long-Haul fiber : Need the E to complement the O.

Sat-Phones: dead
Sat-Internet: needs return path - go DSL
Sat-CATV: here to stay
Sat-Radio: jump-on!

Work at home..
Farming : alive and well.
Therapy/Counseling : alive and well.

"The grass is just grass on the other side. Call your mom and say hi before Mother's Day"

Burrrrp!
sords 12/4/2012 | 8:27:22 PM
re: Optical Crossconnects caddy, given that you used words from aon's previous web site, I assume you are familiar with the company. what do you think of them? their technoloy certainly sounds promising and they have apparently attracted good people, but they seem to be having difficulty raising money. if things are as good as they say they are, it seems to me that money would be banging on the door despite market conditions. any thoughts?
caddy 12/4/2012 | 8:27:23 PM
re: Optical Crossconnects goodbye mems; controling light, with light, at the speed of light. say goodnite gracie.....
sords 12/4/2012 | 8:27:24 PM
re: Optical Crossconnects This message may apply to several of the inquiries. A company, All Optical Networks, aoncorp.com, a startup, claims to have developed a photonic transistor that would ultimately elliminate the need for electrons in many aspects of optical networking. Utimately, even a photonic computer. They will have an exhibit at SUPERCOMM. To the extent anyone can learn something about their technology, I would like very much to hear opinions. I am a complete novice in this field, but understand that the possibilites provided by a photonic transistor are endless.

They are hiring.

Thank you all in advance.
networking_legend 12/4/2012 | 8:27:33 PM
re: Optical Crossconnects (1) Mems is a proven technology in other industries, and since some companies have already developed mems based OXCS (Xros, now NT), then it looks doable. The port count for their product was low, but others, such as Calient claim to be able to produce high port count boxes.

2)
Customers do not care whether you are using mems, bubble technology, or whatever. What they want is an OXC that can scale to high port counts and actually works in a pratcial setting. You should really be asking whether or not all optical OXCs will be in demand. To tell you the truth I can't say. Last year i would have said yes, definintely. Now I am skeptical. Just look at how much the stock price of Corvis has plummeted (I believe they use couplers for their switching fabric not mems). They seem to have trouble finding new customers, and maybe that says something about the current demand for a box that does not switch at granularities lower than a wavelength. If internet growth contintues at the pace it has in the past, then I think this wont be as serious an issue. There are other drawbacks to going all optical over traditional o-e-o, such as performance monitoring capabilites.

By the way, many of my friends who did their graduate level work in queueing theory are doing fine today, and working for the big name companies. As for the information theory guys, everything was o.k. until turbo codes came along. Now they don't know what to do :)

tony1athome 12/4/2012 | 8:27:33 PM
re: Optical Crossconnects "Since you brought up GMPLS, what's your take on that? Will it be useful and well implemented by
transport and router vendors? I've heard that Juniper for example is not too excited about it, even though they're working on it. Are there competing standards coming up?"


Well, you should know that I'm a big supporter and am somewhat biased. I believe that Yakov is working on GMPLS, so I'm surprised to hear that Juniper isn't too excited about it. Tho Juniper's general style isn't to hype features. Of course there will be competing standards. Too many people think that they can get advantage by abusing the process. Sigh.

"That's true, the all-optical scenario I described is pretty much science-fiction. Oh well, it's interesting to consider the possibilities."


Agreed. The tough part is discerning the commercial reality.

Tony
move 12/4/2012 | 8:27:36 PM
re: Optical Crossconnects Hi networking_legend,

Thank you very much for your reply. I appreciate
it very much.

Briefly, explained what I come up with "too late".
It is from the "fear" caused by my past experience. While I was in graduate program in EE,
I did not like quite a few courses in EE due to its "ad-hoc incomplete theory". I gave up the chance to do VLSI and computer areas, instead I
did research work in information theory with minor
in math. I ended up taking the classes such as
advanced calculus, real analysis, functional analysis, H-infinite, probability theory, queueing
theory, and ...... It was such a "beautiful theory and so challenging and interesting. I did
not care whether it is "hot or not hot".

In the end, I had hard time getting a job, partly due to the stuff I had learned partly due to my
own shyness and language skills too. There are
more sad story happened to me during those period
time.

After a few years of struggle (people knew my
backgrounds always repeatly asked me questions which I did not like to answer), I finally became
an software engineer like most people around me, i.e., those who never suffered like I went through. Well, I will not repeat the same mistakes I made, i.e., only "interesting and challenging".
I did not mean to make big money. I was asking the question of "too late" means:

(1) Techincally, whether high port count MEM based
OXC is still years away ?
Since there are some companies working on it,
what will the late comer be if they run out of
money in a year or two. Is any possible job
after it since I did not expect quitting work.

(2) Possible market size for high-port count MEM
based OXC ? If this is not a hype-technology,
there should have a market for it.

I will appreciate it very much if you could answer
these questions.

Thanks a lot.


networking_legend 12/4/2012 | 8:27:41 PM
re: Optical Crossconnects I'm not sure what you mean by "too late". If you are interested in working on developing the next-generation mems based OXC, then, by all means - go for it.

If you are asking on whether or not its too late to cash in on the hype of all-optical networking, then I'm afraid I have to say yes.

Forget about trying to become a millionaire and just work on something that you find both interesting and challenging.
move 12/4/2012 | 8:27:42 PM
re: Optical Crossconnects Hi Network_legend and others,

I was wondering whether it is too late
to join an early stage startup working
on OOO based upon MEM technology at this
point ?

I appreciate any of your opinions.

Belzebutt 12/4/2012 | 8:27:42 PM
re: Optical Crossconnects "Do you guys know what industry might be a better in the next 3 years, Optical or San? Trying to decide joining a San startup or optical startup."

Whatever happened to choosing the field that interests you the most? :)
move 12/4/2012 | 8:27:43 PM
re: Optical Crossconnects Hi Network_legend and others,

I was wondering whether it is too late
to join an early stage startup working
on OOO based upon MEM technology at this
point ?

I appreciate any of your opinions.

dd_lr 12/4/2012 | 8:27:43 PM
re: Optical Crossconnects Hi,

Do you guys know what industry might be a better in the next 3 years, Optical or San? Trying to decide joining a San startup or optical startup.

Thanks,
DD_LR

networking_legend 12/4/2012 | 8:27:44 PM
re: Optical Crossconnects Joining any optical networking startup isn't as easy as before, given the downturn in the industry as a whole.

However, if you have the right skills (for example, optical/photonic engineers are always in demand) there shouldn't be too much difficulty.
Otherwise, you might be screwed.

Take a look at:
1) Calient networks
2) Movaz networks
3) OMM
Belzebutt 12/4/2012 | 8:27:44 PM
re: Optical Crossconnects "That, or the OXC's could also participate in GMPLS."

Since you brought up GMPLS, what's your take on that? Will it be useful and well implemented by transport and router vendors? I've heard that Juniper for example is not too excited about it, even though they're working on it. Are there competing standards coming up?

"Yup. This is not a bad thing. It is far more likely to succeed than something that is much more aggressive and much more complicated. The technology is hard enough as it is."

I guess it just seems like it's far from the full glory of the all-optical network some vendors are pitching, where it's actually useful to have line systems that can reach 5000 km. They would be able to use that long range to do some OOO switching at the core...

"But now, that's much more than an OXC. That's an entire God-box transmission system. Yes, that would require all optical lambda converters. The history of technology suggests that this will not be the first product brought to market, especially since we still really haven't deployed a simplistic OOO OXC yet."

That's true, the all-optical scenario I described is pretty much science-fiction. Oh well, it's interesting to consider the possibilities.
tony1athome 12/4/2012 | 8:27:44 PM
re: Optical Crossconnects "In that case, the lambda assignments will all have to be done on the OEO boxes, controlling the OOO OXCs, would they not?"

That, or the OXC's could also participate in GMPLS. That's not out of the question, but it muddies the water in that now some of the control traffic will arrive optically and get an OE conversion. Some poor marketing person will get confused.


"So the only real advantage of the OOO OXC would be the bitrate independence and the ease of provisioning."


Yup. This is not a bad thing. It is far more likely to succeed than something that is much more aggressive and much more complicated. The technology is hard enough as it is.

"The way I pictured a "true" OOO OXC is a box would replace a whole OEO cross-connect and any adjacent DWDM line systems, and you could just send a lambda from one end of your network and terminate that lambda anywhere else on your network, switching optically all the way. For that, you would need all-optical lambda converters inside the OOO OXC."


But now, that's much more than an OXC. That's an entire God-box transmission system. Yes, that would require all optical lambda converters. The history of technology suggests that this will not be the first product brought to market, especially since we still really haven't deployed a simplistic OOO OXC yet.

Tony

move 12/4/2012 | 8:27:44 PM
re: Optical Crossconnects Hi Everyone,

I would like to know what is the prospects of
joining a small company working on OOO OXC
based upon MEM technology ?

Based upon the potential market demands for
OOO OXC and the feasibility of the MEM technology
and others, could someone kindly give me the opinions on this ?
Belzebutt 12/4/2012 | 8:27:45 PM
re: Optical Crossconnects "The control plane for an OXC is likely to be GMPLS. The routed overlay on top of the optical network understands and can optimize the traffic assignment thru lamba assignment computations."

In that case, the lambda assignments will all have to be done on the OEO boxes, controlling the OOO OXCs, would they not? So the only real advantage of the OOO OXC would be the bitrate independence and the ease of provisioning. In that POP scenario, the OOO switch would not really be able to function as an all-optical unit, but more like an automated patch pannel connecting a bunch of OEO DWDM terminals.

The way I pictured a "true" OOO OXC is a box would replace a whole OEO cross-connect and any adjacent DWDM line systems, and you could just send a lambda from one end of your network and terminate that lambda anywhere else on your network, switching optically all the way. For that, you would need all-optical lambda converters inside the OOO OXC.
tony1athome 12/4/2012 | 8:27:46 PM
re: Optical Crossconnects Most of the practical applications for an OXC are going to reside within a single POP, where they interconnect OEO devices.

The value add is the ease and speed of provisioning, which is a strategic advantage that should not be underestimated.

The control plane for an OXC is likely to be GMPLS. The routed overlay on top of the optical network understands and can optimize the traffic assignment thru lamba assignment computations.

While all-optical switching thru a POP would be a wonderful thing, simplicity says that the first practical step will be DWDM units that use standard SONET wavelengths for their common interconnect. The ability to connect ANY port in the POP to ANY other port is a major improvement in flexibility.

Others will argue that this is more expensive. Granted. Carriers already pay more so that they can have operational flexibility. A fine example is the set of carriers that prefer to use single mode fiber throughout their POP, paying much more than multimode just so that they never have to deal with having the wrong type of fiber on hand.

Tony
manoflalambda 12/4/2012 | 8:27:47 PM
re: Optical Crossconnects FiberSystems International, May 01, pg 14....
1296 port OXC, its coming!

Salute,
Manoflalambda
Belzebutt 12/4/2012 | 8:27:48 PM
re: Optical Crossconnects Having optical lambda conversion would make it possible to have an all-optical network with lambda granularity end-to-end.

If you're using today's all optical switches, you have some DWDM equipment at both endpoints. These DWDM boxes aggregate lambdas into one single fiber, and shoot it off towards the core. When that fiber gets to the first OOO OXC, _all_ the lambdas on that fiber must get routed together to the same output. The OOO cannot separate the lambdas by itself, and send lambda 4 to one output and lambda 5 to another. If you want to switch lambdas you need to demultiplex all the lambdas before the fiber gets to the OOO switch, then put each lambda on a separate fiber, send them all to a different port on the OOO switch, and then the OOO switch will route them to the proper output ports. There, they will have to go through another DWDM box that will aggregate several separate lambdas and put them on the same fiber.

So basically, you could do all OOO if you didn't use DWDM to its full extent by managing your labmbas as logical "pipes". That is what most carriers do however, from what I understand.

So to truely use OOO OXCs with lambda management in your network, you'd need to have OXCs that can optically demultiplex all the lambdas coming from a fiber, switch them optically, convert the original wavelenghts to different wavelengths as required so that you don't get "lambda blocking" at each output, multiplex all these lamdas that should go on the same output fiber, and send that traffic off to the next OOO OXC or to the end point.

It's all done optically in the above example, while today you need to put one DWDM box in front of every fiber coming to an OOO OXC (Unless you don't plan to extract any lambads from any fiber at that particular OXC).
optinuts 12/4/2012 | 8:27:48 PM
re: Optical Crossconnects thanks bezlebutt
optinuts 12/4/2012 | 8:27:51 PM
re: Optical Crossconnects "Today's OOO OXCs have to be coupled with OEO DWDM line systems in order to switch lambdas, which defeats the purpose of OOO (except for express traffic)."


belzebutt,
what other application is there for an OOO other than 2.5G or 10G (or 40G) express traffic. what does wavelength conversion do for an OOO other than find empty slots in a dwdm system. you still need the dwdm system anyway.

i don't understand the comment, thanks.
opticaltoys 12/4/2012 | 8:27:54 PM
re: Optical Crossconnects At least two companies discuss all optical XC:
Luxcore presented a small 2x2 switch demo, covered by LR:
Luxcore to Demo Optical Switch Advance

Lucent claims to have demonstarted a 100x100 all optical XC based on mems and SOA WC, See OFC 2001 post deadline paper PD16.
OT
Belzebutt 12/4/2012 | 8:27:57 PM
re: Optical Crossconnects As further reading, I would love to see an article here that talks about possible techniques for designing all-optical wavelength converters for OOO OXCs. Today's OOO OXCs have to be coupled with OEO DWDM line systems in order to switch lambdas, which defeats the purpose of OOO (except for express traffic).

I remember reading a story on LR about a company announcing some all-optical wavelength converter product, does anyone know how these things work in more detail? Perhaps someone at LR could write a piece on this...
Half-Inch Stud 12/4/2012 | 8:27:59 PM
re: Optical Crossconnects Let's keep clear the OEO Cross-connect medium can be Optical or/and Electrical signals and still be hit the catagory of an OEO OXC with STS-1 granularity. Network system functionality [and revenue] is enables with these approached by adding processing value [protocol stripping and packet streaming].

Yet, the OOO OXC is truely a wavelength path-changer that is limited to the input DWDM granularity of a typical 2.5Gbit/s. Tough to add revenue-enhancing functionality to such a system.
Seems to me the OOO is a hyped-up wavelength groomer that will hit the optical DeMuxs anyhow, before discreet wavelength photodetection.

My bet is Signal/Noise ratios will drive wavelength photodetection to occur as soon as possible, thus showing that added functionality in the Optical [OOO] systems designs to be more expensive and quite simply delaying the inevitable photodetection..

...we'll see.

That what I think and I'm sticking to it.
H.I. Stud
ranon 12/4/2012 | 8:28:01 PM
re: Optical Crossconnects OXC's are not really practically viable. There are a large number of Electrical cross connects availaibe.

But the biggest problem with optical cross connects is that they do not have the granularity required. There are chips with 72*72 OC-48 cross connects at STS-1 granularity. While an optical corss sonnect would be at a wavelength granularity (OC-48).
manoflalambda 12/4/2012 | 8:28:03 PM
re: Optical Crossconnects Micah,

The controller of the OXC decides which input ports are mapped to which output ports. That info comes via some sort of external management/messaging software into the OXC and is stored internally.

Some OXCs also maintain some number of pre-stored maps of cross-connects to handle either pre-configured situations or emergencies.

Salute,
Manoflalambda
micahvoiers 12/4/2012 | 8:28:06 PM
re: Optical Crossconnects My understanding of a cross connect is that we can map an input to a desired output(route the optical signal from one fiber to another). My question is where is the decision being made to route a signal to a specific output? It doesn't appear that a cross connect is looking at the specific signal. Is this done electronically from another location? How frequently can we expect the mapping to change?

Thanks,

Micah
debasish71 12/4/2012 | 10:50:09 PM
re: Optical Crossconnects what are the possible implementation scenarios for ooo? how can a lower level tributary like stm-1 be dropped off from an stm-16 or higher optical signal without converting it into electrical signals?
manoflalambda 12/5/2012 | 12:54:10 AM
re: Optical Crossconnects BuzzLightwave:
My understanding is that an AON works on a TDM basis. At a preconfigured time slot T, traffic is allowed to go from source port A to destination port X and from source port B to destination port Y. At time slot T+1, traffic is allowed to traverse from port A to port Y and from port B to destination port X. This makes makes switching rather simple - each MEMs based switch just needs to know where to aim its mirrors at each time slot.


Interesting. I have have missed this, but how long are the time slots and how much switching time is allowed for the mirrors when you go from T to T+1?

Just curious since some of the mirror systems have a variety of switching times depending on distance to move the mirror, charge-discharge effects,etc.

Salute,
Manoflalambda
BuzzLightwave 12/5/2012 | 12:54:11 AM
re: Optical Crossconnects My understanding is that an AON works on a TDM basis. At a preconfigured time slot T, traffic is allowed to go from source port A to destination port X and from source port B to destination port Y. At time slot T+1, traffic is allowed to traverse from port A to port Y and from port B to destination port X. This makes makes switching rather simple - each MEMs based switch just needs to know where to aim its mirrors at each time slot. There is theoretically no need to even parse the packet headers to determine the destination.

While the switch configuration, i.e. the mapping of time slots to mirror positions, is electrical, the packets themselves never leave the optical realm.

This approach limits network utilization, since source the amount of bandwidth between a given source and destination will usually be a fraction of the available capacity when the network is otherwise idle. In the above example, if there is no traffic between B and X during time slot T+1 but port A does have traffic for port X (but none for Y), then the available bandwidth to port X at time slot T+1 still cannot be used - it is wasted. That's a drawback of the OOO switches. An OEO switch can parse the packet, determine that there is no other traffic for the destination X, and send it on. The price you pay is latency.
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