Network technologies: Active (Ethernet) vs Passive (PON)

When it comes to delivering networks to support Smart Buildings, there is no doubt the near-limitless bandwidth of fibre is of benefit.  What is less clear is whether an active or passive technology is better.  The reality is that it depends on many factors including the environment, applications being used and who is going to manage or operate the infrastructure.  Let’s look at this in a little more detail.

History and background

Active Ethernet or point to point Ethernet has been used extensively in a broad range of applications and environments for many years from the early days of 10Base2 to the current Ethernet technologies that utilise copper or fibre to deliver 1G, 10G and beyond.

In order to deliver next generation services to consumers or subscribers, the aging twisted pair infrastructure that had been used for many years was simply not capable of meeting the bandwidth requirements of services like HDTV.  Fibre with its near limitless bandwidth was an easy choice but using an active or point-to-point technology would have seen thousands to tens of thousands of strands of fibre required from the exchange.  Alternately, it would have been necessary to have active equipment in the field from where fibre would have been aggregated.  Neither of these was particularly suitable so an alternative technology known as Passive Optical Networks or PON was developed.  PON had the benefit of using small fibre counts from the exchange and then branching out to deliver services to subscribers with passive splitters overcoming the limitations of active Ethernet for this application.

Application and use

There is no question that in a broadacre environment for the delivery of consumer services that PON has many benefits.  These benefits though are questionable when it comes to delivering services in other environments such as building and other services in commercial buildings or hospitality environments. 

Today, the benefits of a single converged network to support all applications within a facility are better understood.  The simplicity of managing one set of infrastructure, flexibility to add additional services and lower total cost of ownership are now being seen by organisations that head down this path.  And with 20% of commercial buildings being smart or intelligent buildings by 2020 this trend will only increase.

The requirements of these services that leverage a converged network are quite different to those of the consumer services seen in broadacre environments.  Within a commercial building services that are regularly deployed include telephony, CCTV, signage and wayfinding, wireless, access control, BMS/HVAC and lighting with who knows what new technology being around the corner.

These applications often require Power over Ethernet to power the endpoint, multicast support to manage the distribution of content, symmetric bandwidth to support both content moving in both directions, and due to the critical nature of some services, a high degree of redundancy.  These are inherent within active Ethernet networks but are not typical of passive networks.

Technology aside, another factor to consider is ownership and operation of the network.  Passive networks are typically deployed by a carrier or service provider who then takes complete responsibility for the infrastructure and service delivery.  When an add, move or change is required, this is undertaken by the organisation responsible.  This is ideal for the delivery of services such as voice, data and telephony to consumers but is less than ideal for building services. 

Within commercial buildings there is often a need by the facility owner or manager to reconfigure the network to support new services or add new endpoints.  This level of flexibility is simply not available when the network is operated or managed by a carrier or service provider and would generally incur additional costs that would not occur with an active network that is managed by the facility.

Summary

So, when it comes to deploying fibre to support services, it is not simply a case of an active topology being better than a passive topology or vice versa but consideration being given to the environment and applications and then making a considered choice based on the requirements.  And in some cases, it may be that both can co-exist – a passive topology to deliver consumer services to residents which would be managed by a carrier and an active topology for building services that would be managed by the facility.