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0 pointswalrus011y ago0 comments

> The FTTH offerings from Ziply, Cox, Comcast, Google, ATT, Centurylink etc are all the same "shared media with high oversubscription" design too.

No, they're really not, you can't compare single strand FTTH XGSPON on singlemode fiber (16:1 or 32:1 contention ratio), something that is built on 10G XGSPON tech, to something that is built on bonded RF channels on coax copper. The aggregate capacity per oversubscribed network segment is radically different.

Now, all of these cable operators also ARE building actual FTTH networks in certain areas because they see the writing on the wall for the longevity of how much more they can squeeze out of the copper. So in some very specific places the Comcast 1 Gbps last mile product is functionally equivalent to the local Verizon, or Ziply, or Lumen (Centurylink, now branded as Quantum Fiber) FTTH product.

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zamadatix1y ago

DOCSIS 3.1 is extremely comparable to PON in terms of oversubscription design (in bandwidth and allocation breakout). The largest difference between the two is DOCSIS uses dynamic bonding of OFDM channels to chop up the ~10 Gbps of bandwidth while 10G-PON uses TDM to slice up the bandwidth.

The physical medium itself really has next to nothing to do with it. You can TDM and OFDM on both fiber and coax. The bandwidth is a factor of the total frequency and modulation methods.

FTTH is popular for new rollouts because it's cheaper to rollout and run. It uses less power, it goes longer distances, it's cheaper to repeat if you need to, it's cheaper to upgrade to the next generation of PON. It also has a better scaling future, but I already mentioned that above.

walrus01OP1y ago

> The physical medium itself really has next to nothing to do with it.

yes, it does, because actual fiber is significantly more future-proof. The same boring 9/125 fiber that's being built today is capable of 100/200/400 Gbps ethernet with only a change in electronics at the ends. Can't say the same for coax. Even the must rudimentary DWDM with 10G OOK optics on single strand or two strands of fiber has vastly more capacity than anything coax based.

No matter how you slice it the coax has a much more limited service lifespan and eventual capacity exhaustion problem compared to the more creative solutions that can be employed in the future to grow beyond the capabilities of 10G XGSPON.

Your typical 10G XGSPON setup like with 16:1 or 32:1 split and single strand to the home, is only using maybe 2% to 5% of the actual available THz channels that exist (in the 1470 to 1610 bandwidth range) in the fiber. There's a vast amount of empty channel space in that fiber for future bidi optic usage scenarios if you know how DWDM stuff works.

The RF on coax, on the other hand, is using pretty much every viable frequency in the bands that will work on the coax and is already at its limit.

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