There's a gap in today's carrier networks. And it's keeping service providers and their customers apart.
It's the old "last mile" problem, on steroids. Business customers want higher bandwidth services and carriers have most of the infrustructure in place to deliver them. There's only one thing holding everything up - a low cost method of providing access lines between the carrier's central office and user sites.
Enter the PON--Passive Optical Network. With PONs, one access line can be shared among multiple buildings--and it can be done at a minimal cost. That's because PONs use low-cost components that don't require a lot of care and upkeep. As a result, PONs cost a fraction of what it takes to run new fiber or rework existing Sonet (synchronous optical network) rings.
Moreover, the use of passive optical components - ones that aren't powered by electricity - make PONs future-proof. They won't need upgrading to support higher transmission speeds to reap the rewards of advances in technology.
To understand how PONs work, it's best to go back to basics. Essentially, carriers want to connect each customer site with a wavelength of light, but they want to avoid having to dedicate a fiber to every wavelength.
PONs address this issue by bundling together multiple wavelengths (up to 32 at present) so they can be carried over a single access line from the carrier's central office (CO) to a manhole or controlled environmental vault close to a cluster of customer sites. At that point, the wavelengths are broken out and each one is steered into a different short length of fiber to an individual site.
A different scheme is used for collecting traffic traveling in the opposite direction - from user sites to the CO. In this case, each site is given a specific time slot to transmit, using a polling scheme similar to the one used in old IBM networks.
Eleven vendors so far are readying PON products for the business market:
Can someone explain for a dummy how the downstream 155 is split optically? Say, for example, does a 155 Sonet framed stream split it's optical power and get copied to two pipes? There's no electrical stuff going on here, so what else is it? Do the downstream ports get provisioned to grab their "slice" of the frame, say one DS3's worth?
I understand there are two different flavors; ATM and Ethernet and that bandwidth is determined by the standards for each. Provided that you had a physical switching medium capable of Terabits, could you implement a PON on that infrastructure? Would it be ATM or Ethernet? Something else?
I'd welcome anyone's articulation as to how bandwidth's are determined as a standard is being created. I'm in the dark.
From a physics perspective, I am not qualified to answer about bw limits imposed by the application of optical splitters. Hopefully somebody else will answer and we both will learn something new today.
Lets be clear, optics is cheap, optoelectronics is cheap. Even fiber is relatively cheap (cheaper than copper with better performance in terms of loss group delay etc.). Digging up the streets to lay the fiber is expensive. These days, for new residential construction (read subdivisions), when the ground is open for sewers etc., fiber is put in. The telcos and/or cities and/or developers know that eventually it will get used and whoever owns it makes dough. Otherwise I think it's not there (I've heard some sad stories from former phone company engineers about lost opportunities in the 90s when 2 fibers were pulled instead of a larger number)
In response to zman, in what percentage of residential areas is there enough fiber to support PON but not point to point? If you split 64 ways then you need 100 fibers starred out from your central offices to serve 6400 homes, and 1000 fibers starred to do 64000 homes. Neither sounds too likely to me. Unless something changes (like intense government support ala Japan) fiber to the home is likely to remain on the horizon. The PON companies who've built there business plan around curbside ONUs serving multiple businesses via copper have some hope but where are the residential PON guys going to install there systems?
For residential applications I believe there will always be some sharing somewhere (in the sense of logical sharing) - it just may be cheaper to put it higher in the network. DSL is popint to point in the analog world but as soon as you get to ATM your sharing again, DSLAM means DSL access multiplexor but the muxing happens at the cell/packet level.
Sir, Again you seem to have missed the point. You seem to believe that tomorrow's networks will all look exactly like today's networks simply because that's how today's networks are. I suspect that I will not be able to change your prevailing view of the world. Aloha,
Zman, Now we get to the crux of the biscuit - as they say (what does that mean anyway?)
I disagree with your base assumption - 30 to 50% cost differential. That was true for optics a few years ago. The products that were developed then are being sold now. The economics of optical components has changed fundamentally. The cost of lasers has dropped to the point where the cost of additional electronics necessary to support shared optics is now more expensive than the savings from shared optics. It should be noted that shared optics are inherently more expensive (more powerful lasers, burst mode etc.)than point to point optics. I suspect at this point, we will agree to disagree. Only time will tell to whom the spoils go. Aloha mi amigo, Nomad
Shared medium infrastucture is 30-50% lower in cost than point to point. If you don't believe me, ask SBC, BellSouth, NTT, British Telecom, etc... And if you don't believe them, go ask Time Warner, AT&T Broadband, Cox Cable, etc.
Example: HFC networks have the highest penetration of broadband so far... they are shared, tree (use optical couplers just like xPON) networks. They work, they make $ profits. Imagine point to point HFC!
> Consider your office LAN
Why - it is not a good analogy. An office LAN has little resemblence to a telecom network. Do you need to deploy broadcast video in an office LAN? Do you need to dig up streets in an office LAN? Of course point to point works better there, but the requirements and environment are different.
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