Unlike active optical network, PON network doesn’t require electrical power to send signal to customers, becoming the technology of choice of telcos. Its characteristics and several benefits will be discussed throughout this article.
What is a PON network?
PON means Passive Optical Network and, as the name implies, is a network totally built with fiber optic, without any active components between the head of the network (OLT – Optical Line Terminal) and the end user (ONT – Optical Network Terminal or ONU – Optical Network Unit).
This all-passive structure makes this type of network extremely reliable. The availability is 99,99999% a year, which means that one port has an unplanned downtime of 3 seconds per year.
Why a PON network?
Almost all the telecom companies in the world use this kind of network to deliver services to their clients because of the reliability of this type of network. Besides that, PON network:
– It’s easy and cost-effective to install
– Requires almost no maintenance
– It is immune to electromagnetic interferences
– It uses cables that can be installed in all kinds of environments and with small diameter, among many other advantages.
As it is totally in fiber optic, the PON Network can cover distances of 100Km without regenerating or amplifying the signal. This allows long distances can be covered using the same cabinet or the same technical room.
How does a Passive Optical Network work?
PON network is a Point to Multipoint (P2MP) communication, which means it can split the power in the fiber optic by 2, 4, 8, …, 128 (always in a base 2 exponential) depending on the power budget (the power available to the ONT in the downstream, and on the OLT in the upstream communication). This means that one port on the OLT can be connected with 128 ONT simultaneously.
As the communication between the OLT and the ONT is made using different wavelengths for the downstream and the upstream, we can use only one fiber for the bidirectional communication. Also, we can add several other signals, in different wavelengths, all traveling in the same fiber.
The downstream is a broadcast signal, with addressed packages. The ONT reads those files and accepts the ones that address to him, rejecting the others.
In the upstream communication, the ONT and OLT negotiate a time slot and the ONT uses that time to send information to the OLT (TDM Protocol). Any communication received by the OLT outside this time slot results in a communication breakdown, protecting the information.
Almost all the telecom operators in the world use this network to deliver TV, Ethernet and voice to their clients in an effective way, with almost no downtime and at a low cost.
Types of technologies that use the PON concept
There are different technologies that use the PON network concept:
– APON: Asynchronous transfer mode or ATM, it was the first PON Standard (ITU G983), mainly used in enterprise networks with downstream 1,25Gb/s and Upstream 622Mb/s
– BPON: Broadband PON. It has introduced the Wave division multiplexer (WDM), which allows several wavelengths and services (TV, Data, etc) in the same fiber.
– EPON or GEPON: Gigabit Ethernet PON. It uses Ethernet protocol in the data packages. The communication is synchronous 1,25Gb/s downstream and Upstream.
– GPON: Gigabit capable PON. Asynchronous communication 2,5Gb/s downstream and 1,25 Gb/s Upstream. Over time were developed several technologies using the GPON base, increasing the communication speed, changing the wavelengths used. Some of these variations keep the asynchronous velocity (XG-PON, 25G-PON, NG-PON) and some changes to synchronous (XGS-PON, 25GS-PON).
All these technologies operate as passive optical networks and the main differences between them are in how they support and transmit wavelengths and overall speed.