Active (Ethernet) vs Passive (PON)
When it comes to delivering networks to support smart buildings and applications like CCTV, IPTV and Internet service delivery, there is no doubt that the near-limitless bandwidth of optical fiber is of benefit. What is less clear is whether an active, or passive technology is better. In reality, 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 utilize copper or optical fiber 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. Optical fiber with its near limitless bandwidth was therefore an easy choice. Using an active or point-to-point technology, however, would have seen thousands to tens of thousands of strands of optical fiber required from the exchange. Alternately, it would have been necessary to have active equipment in the field from where optical fiber had aggregated. Neither of these options was particularly suitable so an alternative technology known as Passive Optical Networks (PON) was developed. PON had the benefit of using small counts of optical fiber 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 – one covering large distances – PON has many benefits for the delivery of consumer services. These benefits, however, are questionable when it comes to delivering services in other environments such as buildings, 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 organizations that head down this path. With 20% of commercial buildings predicted to be smart or intelligent by 2020, this trend will only increase. The requirements of services that leverage a converged network are quite different to those of the consumer services seen in ‘broadacre’ environments. Services regularly deployed within commercial buildings include telephony, CCTV, signage, wayfinding, wireless, access control, BMS/ HVAC and lighting. These applications often require Powerover-Ethernet (PoE) to power the endpoint, multicast support to manage the distribution of content, symmetric bandwidth to support content moving in both directions, and a high degree of redundancy due to the critical nature of some services. 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 adds, moves or changes are required, this is undertaken by the organization 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 for 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. This would not occur with an active network that is managed by the facility. Summary So, when it comes to deploying optical fiber to support services, it is not simply a case of an active topology being better than a passive topology or vice versa. Consideration needs to be given to the environment and applications before a choice is made based on the requirements. In some cases, 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. By – Scott Penno Regional Marketing Manager, APAC, Allied Telesis