Thursday, November 15, 2007

Uber-Bandwidth: Verizon Testing 400Mbps Service

Last month I wrote about Verizon's 20 Mbps symmetrical FiOS service - if you haven't had a chance to read that entry follow this link - there is a good description of asymmetrical and symmetrical services along with a quick video at the end demonstrating the differences between the two types of services.

A few days ago Gizmodo posted an interesting piece titled Next Up for Verizon FiOS: Invading Manhattan, Japan-Like Uber-Bandwidth. Gizmodo describes a Pennsylvania trial Verizon is running - in the trial they are seeing peak rates of 400Mbps downstream and sustained rates of 200Mbps upstream. Incredible bandwidth that, according to Gizmodo, is enough to make even the most hardened Tokyo resident jealous with their measly 100Mbps downstream fiber service. Yes - this is incredible bandwidth and we can only imagine the voice, video, data, entertainment and communications possibilities.

Let's back up a bit and take a look at the way Verizon is delivering services using the FiOS Fiber to the Home (FTTH) system. Verizon currently uses the Broadband Passive Optical Network (BPON) standard, which has limits of 622 Mbps downstream and 155 Mbps upstream for each Optical Line Terminal (OLT). OLT's are also referred to as service provider endpoints and one Verizon OLT will connect 32 homes with fiber.

Verizon is also currently using BPON OLTs to service their 20 Mbps symmetrical service which may or may not be a problem. Let's do some math:

Downstream Bandwidth
32 homes at 20 Mbps/home downstream require: (32 homes)*(20 Mbps/home) = 640 Mbps

Upstream Bandwidth
32 homes at 20 Mbps/home upstream require: (32 homes)*(20 Mbps/home) = 640 Mbps

You may think a fully loaded (32 home) BPON OLT running symmetrical 20 Mbps service does not provide enough bandwidth and you may or may not be right. It comes close in the downstream direction (622 Mbps available and 640 Mbps required) but is not even close in the upstream direction (155 Mbps available and 640 Mbps required). It turns out this may or not be that big of a deal - for now. Telephone company traffic engineers have always calculated voice switch connections using units called Erlangs. Erlangs are dimensionless units used as a statistical measure of the volume of telecommunications traffic. Brian Whitton, Verizon's Executive Director of Broadband Access Technologies is quoted in the Gizmodo piece on this topic as follows:

Of course 32 households couldn't run 20/20 full blast all at once but simultaneous peak usage on that scale is such a remote possibility it's not really an issue. Yet.

I always like to describe Erlangs and switch connection calculations using an example - have you ever got a fast busy signal when you tried to make a call? Perhaps on Mother's Day around 11 AM - a time when many of us are calling our Moms! The fast busy means there are no voice switch connections available. Why? Because the voice switch has has been configured more lines coming in to it than available connections. Most times and days of the year this is not a problem because we are not all trying to use the phone at the same time - it's only when call volume goes way up that we typically have problems - days like Mother's Day!

Right now Verizon is calculating that BPON will be ok for 20 Mbps symmetrical service - the chances of all 32 homes on a BPON OLT all purchasing 20 Mbps symmetrical service are slim and it's even more slim that everyone subscribing to a 20 Mbps symmetrical service will all be requiring maximum bandwidth at exactly the same time - today.

So how is Verizon delivering 400 Mbps downstream and 200 Mbps upstream? BPON only supports 622 Mbps downstream and 155 Mbps upstream - there is not enough upstream bandwidth for one customer with BPON and two customers at 400 Mbps is not possible. The answer is Gigabit Passive Optical Network (GPON) technology - an evolution of the BPON standard that supports higher bandwidths. GPON provides a maximum of 2.48 Gbps downstream and 1.244 Gbps upstream - enough, using the statistical methods described above, for Verizon to be seeing peak rates of 400Mbps down and sustained rates of 200Mbps in the Pennsylvania trial.

The Gizmodo piece continues:

"Virtually" every network hub built after January will be GPON-based, says Verizon. It has the network set up for easy upgrading, so to bump current hubs to GPON, technicians just have to swap out the boxes on each end of the fiber cable they've already laid. Not too much of a hassle, in other words. As each current hub hits its bandwidth limit, it too will be updated to super-fast GPON.

For those of us that can get it [ I can't :( ] we are just seeing the beginning of these Uber-Bandwidths!

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