Since the introduction of unshielded twisted pair (UTP) and category cabling, telecommunications networks have largely been based on copper cables. Beginning in the mid-1990s, CAT 5 cabling was used to provide connectivity for Ethernet networks. Over the past 30 years since, several enhancements have been made to copper cabling specifications in order to support increasing bandwidth demands, each of them driving a new type of category cable – CAT 5e, CAT 6, CAT6a, etc. As a result, enterprises increasing their LAN speeds from 1Mbps, to 100Mbps, 100Mbps, 1Gbps, and beyond have been forced to periodically replace the costly copper cables in their buildings and campuses to support the higher speeds.
As bandwidth needs continue to increase in the enterprise, Passive Optical Networking (PON) technology is uniquely positioned to support that bandwidth evolution for decades without costly changes to the structured cabling. This application of PON technology within the enterprise local area network is known as Passive Optical LAN or POL. Standards bodies and PON equipment manufacturers continue to drive more bandwidth over the same POL topology and fiber infrastructure through advancements in PON technologies. Over the long-term, the ability to leverage the existing fiber infrastructure will help reduce the total cost of ownership of a fiber-based passive optical LAN
Today, most enterprise POL implementations are based on GPON, which was standardized in 2003 and delivers 2.5Gbps downstream and 1.25Gbps upstream over a point-to-multipoint fiber network as shown below.
As bandwidth needs have increased and become more symmetrical, newer PON technologies have been developed to leverage the same point-to-multipoint network topology as well as the fiber investment itself. Several 10Gbps PON technologies like XGS-PON and TWDM-PON (or NGPON2) have evolved from GPON and were standardized in the 2015/2016 timeframe. These technologies are deployed in networks today and can either deliver symmetrical 10Gbps bandwidth or asymmetric 10Gbps downstream and 2.5Gbps upstream. XGS-PON is based on a single fixed wavelength which contributes to its cost-effectiveness and wide market deployment. TWDM-PON can support multiple 10G wavelengths over the same fiber, but the associated ONTs require more costly tunable lasers to support the different wavelengths.
The uniqueness of fiber and PON technology is that bandwidth upgrades and enhancements can occur with the active electronics (OLT and ONT) and without any disturbance of the fiber cabling. GPON, XGS-PON and TWDM-PON use different wavelengths such that all three technologies can co-exist on the same fiber. This allows all splitter output ports to be lit with multiple PON technologies and, for example, either GPON or 10G PON ONTs could be attached to any splitter port. This allows for higher speeds to be supported simultaneously, and on an as needed basis, without a cabling retrofit. As an example, delivering multi-gig services for 802.11ac Wave 2 access points or a 10Gbps circuit for server or research applications in a higher education environment can easily be accommodated by a network primarily intended for 1Gbps desktop VoIP and data connections.
In early 2019, trials of 25G PON were launched and the 25G PON standard is expected to be ratified in 2020 with both symmetric and asymmetric bandwidth options. A 50G PON standard is expect in 2021. Standards bodies and equipment manufacturers will continue to define new PON technologies to deliver more bandwidth for the POL market. This continued evolution of bandwidth without a need for cabling change increases the longevity of the fiber network and reduces the total cost of ownership of POL compared to traditional Ethernet LANs.