Wednesday, November 19, 2008

Cable vs FTTH Bandwidth Throwdown

The battle of the bandwidths has begun in earnest. In one corner, the presumed high speed champion, FTTH (Fiber to the Home). In the opposite corner, the challenger, Cable Broadband. Who will be champion? That's too early to tell. But we know who the real winner is going to be - bandwidth hungry broadband users.

The latest battleground is Washington state. Comcast, the Cable giant, is rolling out 50 Mbps Internet service to compete with Verizon, the telco giant, that offers 50 Mbps FiOS Internet service. FiOS is the name Verizon has given to its PON or Passive Optical Network system that connects homes and businesses to distribution hubs via fiber optic cable. The fiber and its splitters are passive, although you do need a rather large network interface box mounted outside to terminate the cable and convert the pulsating wavelength data back to electrical signals.

So what makes Comcast think that plain old copper coaxial TV cable can take on light powered optical fibers? DOCSIS 3.0, that's what. DOCSIS or Data Over Cable System Interface Specification is the cable modem standard that allows cable system operators to transport data along with TV signals. They do this by setting aside some TV channels for Internet service and using modulation technology to create signals that are compatible with cable channels. The modem takes care of making those signals Ethernet compatible.

From a users perspective, it doesn't matter if the incoming cable is fiber or copper as long as it can handle the needed bandwidth. Ultimately, the user is simply going to connect an RJ-45 plug in the back of whatever interface box is provided.

Just what bandwidth can you squeeze out of cable, anyway? Well, it's a far cry from analog telephone lines. We know how quickly our analog modems topped out at 56 Kbps. That's all there will ever be from that technology. A telephone voice channel just hasn't got any more room to grow. Telephone companies get around that by using frequencies beyond the voice range to deliver DSL over home and business phone lines. But there is a definite speed versus distance tradeoff that limits this technology.

No so much with Cable. Those TV channels can go and go and go. Most Cable companies now use fiber optic transmission for part of the distribution distance. They just haven't gone the extra step of bringing the fiber right to the building, like Verizon has done. For users lucky to get 3 to 6 Mbps on their Cable connections, 50 Mbps may seem a bit fanciful. But they're stuck using older DOCSIS standards that don't bond multiple channels together to create a pipe capable of as much as 400 Mbps.

Wow! Comcast is sitting on 400 Mbps? Well, not so fast. That's an upper limit and could require a huge investment of both equipment and set-aside channels. For now, Comcast is figuring their 50 Mbps "Extreme 50" service will be enough to compete with 50 Mbps FiOS.

We'll see how long that lasts. Verizon is already planning to up the ante to 100 Mbps in the near future.

One thing that doesn't seem to be mentioned in the news about these fantastic broadband speeds is download limits. There's been a lot of hoopla recently as Internet Service Providers, including Comcast, have announced caps on how much data you can download per month before getting kicked off the service. The providers say the limit is set high so that only network abusers will be affected. But that's with the modest bandwidths most of us have available. You have to spend a majority of your time in constant download mode to hit the limits.

What happens as bandwidths exceed 100 Mbps and full-length high definition video downloads become commonplace? Perhaps by then the carriers will have upgraded their network backbones and have auxiliary content delivery networks in place to handle the video load. They'll need to keep on this. After all, the way technology advances we'll be clamoring for Gbps broadband service sooner than any of us expect.

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