Passive Optical Networks (PON) have developed and matured since their inception. In the late 1990s and early 2000s, as Telecommunications providers sought a fibre to the home (FTTH) solution for the delivery of multiple consumer services, two major PON standards emerged.
The ITU produced the Gigabit PON (GPON) standard with 2.5Gbs downstream and 1.25Gbps upstream bandwidths. The IEEE ratified the Ethernet PON or Gigabit Ethernet PON (EPON or GEPON) standard that grew as an extension of the existing wired Ethernet standard and utilised symmetrical 1Gbps for the downstream and the upstream.
The PON solution provides a certain elegant simplicity in delivering a high capacity channel to the end user. Whilst PON and Ethernet networks share the need for a core tier, PON affects a single layer 2 domain across the distribution and access tiers. The Optical Line Terminal (OLT) that sits in the PON distribution tier aggregates traffic coming from Optical Network Terminals (ONTs) connected to end user devices and presents it to the core for layer 2 or 3 processing.
This architecture is ideal for fibre to the home. However, PON has evolved to beyond simply being a FTTH technology. Over a series of blog posts, we’ll look at what PON has to offer now and in the future.
In FTTH deployments, PON is often lauded as “future proofed” because it offers the near unlimited bandwidth of optical fibre. However, “future proofed” is more than just capacity. If not more important is the technology’s robustness when it comes to protection mechanisms across varying network topology requirements.
SDH and similar optical technologies have for many years offered 1+1 protection of some form. Whilst these technologies have been developed primarily for backhaul purposes, in recognition of the fact that the local and access networks proceed to generate greater and more significant traffic, PON offers methods for maintaining traffic in the event of optical path failure.
PON protection is achieved through a standards-based method of providing OLT chassis redundancy in the head-end, fibre path redundancy to a 2:N splitter in the optical network, and dual homing on ONTs. Vendors also offer blade-based redundancy for hot standby applications. Using these methods PON offers 1+1 as well as 1:1 optical path protection mechanisms that enable PON networks to achieve in excess of five-nines (99.999%) carrier grade availability and eliminate single points of failure.
The choice of a passive network between OLT and ONT, with carefully selected optical interfaces means that the optical distribution network can be designed for differing user densities, cost constraints, physical infrastructure constraints, and distance limitations. By developing design rule sets that describe why, how and where optical splitters are clustered, network designers can roll out optimized and scalable PON deployments.
What other network deployments could you implement PON in your business?
In the next instalment of this series on PON we consider network reach, throughput capacity and quality of service.