Now that many fiber competitors are providing gigabit Ethernet to a lot of customers we have started to stress the capability of the existing passive optical network (PON) technology. The most predominant type of PON network in place today is GPON (gigabit PON). This technology shares 2.5 gigabits of download data among up to 64 homes (although most providers put fewer customers on a PON).
My clients today tell me that their gigabit customers still don’t use much more data than other customers. I liken this to the time when the industry provided unlimited long distance to households and found out that, on the whole, those customers didn’t call a lot more than before. As long as you can’t tell a big difference in usage between a gigabit customer and a 100 Mbps customer, introducing gigabit speeds alone is not going to break a network.
But what does matter is that all customers, in aggregate, are demanding more downloads over time. Numerous studies have shown that the amount of total data demanded by an average household doubles about every three years. With that kind of exponential growth it won’t take long until almost any network will show stress. But added to the inexorable growth of data usage is a belief that, over time, customers with gigabit speeds are going to find applications that use that speed. When gigabit customers really start using gigabit capabilities the current PON technology will be quickly overstressed.
Several vendors have come out with a new PON technology that has been referred to as XGPON or NGPON1. This new technology increases the shared data stream to 10 gigabits. The primary trouble with this technology is that it is neither easily forward nor backward compatible. Upgrading to 10 gigabits means an outlay for new electronics for an only 4 times increase in bandwidth. I have a hard time recommending that a customer with GPON make a spendy upgrade for a technology that is only slightly better. It won’t take more than a decade until the exponential growth of customer demand catches up to this upgrade.
But there is another new alternative. Both Alcatel-Lucent and Huawei have come out with next generation PON technology which uses TWDM (time and wave division multiplexing) to insert multiple PONs onto the same fiber. The first generation of this technology creates four different light pathways using four different ‘colors’ of light. This is effectively the same as a 4-way node split in that it creates a separate PON for the customers assigned to a given color. Even if you had 64 customers on a PON this technology can instead provide four separate PONs of 16 customers. But with 32 customers this becomes an extremely friendly 8 customer per PON.
This new technology is being referred to as NGPON2. Probably the biggest benefit of the technology is that it doesn’t require a forced migration and upgrade to existing customers. Those customers can stay on the existing color while you migrate or add new customers to the new colors. But any existing customer that is moved onto a new PON color would need to have an upgraded ONT. The best feature of the new technology is that it provides a huge upgrade in bandwidth and can provide either 40 Gbps or 80 Gbps download per an existing PON.
This seems like a no brainer for any service provider who wants to offer gigabit as their only product. An all-gigabit network is going to create choke points in a traditional PON network, but as long as the backbone bandwidth to nodes is increased along with this upgrade it ought to handle gigabit customers seamlessly (when they actually start using their gigabit).
The big question is when does a current provider need to consider this kind of upgrade? I have numerous clients who provide 100 Mbps service on PON who are experiencing very little network contention. One strategy some of them are considering with GPON is to place gigabit customers on their own PON and limit the number of customers on each gigabit PON to a manageable number. With creative strategies like this it might be possible to keep GPON running comfortably for a long time. It’s interesting to see PON providers starting to seriously consider bandwidth management strategies. It’s something that the owners of HFC cable networks have had to do for a decade, and it seems that we are getting to the point where even fiber networks can feel stress from bandwidth growth.