The Return of Active Ethernet

WDM_FORecently I have been seeing new fiber construction for residential service favoring Active Optical Networks (AON) over Passive Optical Networks (PON). This reverses a decade-long trend where PON had clearly won in the US market. The reemergence of AON has been sparked by Google and others who have pushed the industry to be able to offer gigabit connections to homes.

When fiber was first built to residential neighborhoods both technologies had some success in the market in the US. But once Verizon chose PON to build its FiOS network, other builders took advantage of the price reductions driven by Verizon’s large deployment and there were very few new active networks built. Around the world the choice of technology varies. Europe also has largely chosen PON technology due to a success there by Alcatel-Lucent. But South Korea went with active Ethernet due to the large number of apartment buildings in the network, where AON is a better solution.

AON technology has never disappeared in the US and it’s the technology of choice when building fiber networks to serve business districts and business parts. Metro Ethernet is one form of an AON technology. In fact, most fiber networks have a mix of technologies and many networks use PON to serve residences and small businesses but use active connections to serve large data customers like schools and large businesses.

There are pros and cons to both technologies when building in residential neighborhoods. But the two most distinctive characteristics are the way that bandwidth is delivered and the configuration of the physical fiber network. Active Ethernet requires a dedicated fiber for each customer. PON can put up to 32 customers onto a single fiber, although it’s generally some smaller number in actual field deployment. This means that the physical fiber bundles in the network have to be significantly larger in an AON deployment. This won’t make much of a difference when deploying in small towns or rural areas. But in a densely-packed urban area the extra fiber pairs required by AON can cause some concerns, particularly for fiber management where fiber connections are aggregated at headends and hubs.

Bandwidth is handled very differently with the two technologies. With Active Ethernet each customer gets whatever bandwidth the network provider supplies. Active networks routinely can deliver 1 gigabit to 10 gigabits. Larger connections are also possible but can get significantly costlier. A PON network shares bandwidth between customers. The mostly widely deployed PON technology in the country is GPON which delivers a gigabit path dedicated to delivering cable TV and a separate data Ethernet path of 2.4 gigabits to share among the customers on a given PON. That is sufficient bandwidth to give everybody a 100 Mbps connection, but it’s not enough bandwidth if you want to guarantee a gigabit connection. There is a new PON today that can deliver 10 gigabits to each PON, but many network operators still see that as inferior to direct gigabit connections when shooting for a gigabit delivery.

The other trade-off is cost and there are cases where each technology can cost less. The customer electronics generally cost more with PON. A PON network of any size requires placing huts in neighborhoods used to terminate the feeder fibers and electronics. But an active network has a greater cost for fiber since there are more fiber pairs in each bundle. But in many cases these two costs somewhat cancel out and we have seen small town deployments that price out almost identically under the two different technologies.

There was a time five years ago when anybody building a residential fiber network could not even consider active Ethernet. There were very few vendors active in the space that supported US markets. PON had won the US marketplace and when building a network once simply decided between the various PON vendors. But today it’s all up for grabs again and anybody building a new fiber network needs to give strong consideration to both technologies.

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