Salisbury's FTTH Blog

One other item that I mentioned at Tuesday’s council meeting that I forgot to mention in my last post, was the discussion about Salisbury using 1×16 splitters in place of 1×32. I didn’t really forget it, it was just late and my mind was too fuzzy to try and explain it. So I thought I would try today.

Salisbury is using a technology called GPON (Gigabit Passive Optical Network) to provide service. In a GPON system, a strand of fiber leaves the headend and runs to a LCP (Local Convergent Point) cabinet. In the cabinet is a device called a splitter. This is a passive device (doesn’t require electricity) that takes the lightwave signal it receives and splits it. The GPON standard allows for up to 64 way splitters. We were originally going to use 32 way splitters. At the urging of AEG, we have now decided to use 16 way splitters.

I know this doesn’t mean a lot right now but let me see if I can explain it. A GPON system has two major pieces of equipment, the OLT (Optical Line Terminal) and ONT (Optical Network Terminal). The OLT is located in the headend and the ONT at the homes/businesses. The OLT is the device that takes signals from all the electronics that generate the video, phone, Internet and any other service we may provide, and turns it into light pulses that travel down the fiber. Each port (a connection that feeds one fiber) can provide 2.5G of bandwidth downstream and 1.2G upstream. Each port feeds one splitter so if we were using 32 way splitters, then each home could receive 75Meg down, 37.5Meg up. Since we try and talk about symmetric bandwidth (the upstream and downstream bandwidth being the same) and we try to round down to a number ending with a zero, we usually say we can provide up to a 30Meg symmetric connection using 32 way splitters. You can see we can offer a much greater speed than we are actually saying. We just don’t want to get into the same habit as the current providers by saying we can provide high speeds when we really can’t.

Now if we use 16 way splitters in place of 32 way, then the numbers change rather dramatically. If you now take the 2.5G available downstream bandwidth from one port and divide by 16, you get 150Meg down and 75Meg up. So with 16 way splitters we can offer a 70Meg symmetric connection.  This means we can provide enough bandwidth for now and in the foreseeable future. This doesn’t mean you have to sign up for this speed. We are going to offer in our base package a 10Meg symmetric service. If you want more speed, there will be options for additional bandwidth. As a side note we will also have ONT’s that can deliver 1Gigabit Per Second to businesses/schools and any high demand customers.

Just like with computers, the GPON system is continually being improved. Industry is already working on equipment that can provide 10G speeds so at some point, all we will have to do is replace the OLT and ONT’s and we will be able to provide even higher speeds. The good thing is, the OLT and ONT’s don’t have to be all replaced at the same time, we can do it over several years as the demand occurs. This is the reason we say FTTH, especially the fiber, is future proof.  

This is already too long, so I will wait until another day to discus what the ONT does and how it works. I know you can hardly wait.