GPON Explained and Definition

GPON Explained

GPON stands for Gigabit Passive Optical Network. It's a type of high-speed network standard for internet access, primarily used in fiber-optic broadband services. Here's a breakdown of GPON and its primary features:

1. Network Structure:  GPON is based on a point-to-multipoint architecture. This means that a single optical fiber can serve multiple premises with the help of passive optical splitters. This contrasts with point-to-point models, where each premise would require its dedicated fiber line.

2. OLT & ONT/ONU:  OLT (Optical Line Terminal): This is the device located at the service provider's central office. It sends out the data to multiple users and also collects data from them.  ONT (Optical Network Terminal) or ONU (Optical Network Unit): This is the device placed at the user's premise. It receives data sent by the OLT. The terms ONT and ONU are sometimes used interchangeably, but ONT is typically customer-facing, while ONU can refer to a larger device serving multiple customers in some contexts.

3. Speed & Efficiency:  GPON offers asymmetric bandwidth with downstream rates of up to 2.5 Gbps and upstream rates up to 1.25 Gbps. However, there are advancements and newer standards that can offer even higher rates.The use of passive splitters in the network means that no power is required in the distribution network, reducing maintenance costs and increasing reliability.

4. Wavelengths:  GPON uses wavelength division multiplexing (WDM), allowing multiple signals to be sent over a single fiber using different wavelengths (colors) of light. Typically, two wavelengths are used: one for downstream data and another for upstream data.

5. Layer 2 Protocols:  GPON utilizes Ethernet and TDM (time division multiplexing) for data and voice services respectively. This makes it highly versatile in delivering various services over a single infrastructure.

6. Distance & Coverage:  The GPON standard allows for coverage of up to 20 kilometers (around 12.4 miles) between the central office and the end user. This makes it suitable for both densely populated urban areas and more spread-out rural settings.

7. Security:  GPON has inherent security features. Data encryption is used to ensure that even if someone taps into the fiber, they cannot interpret the data flowing through it.

8. Applications:  GPON is primarily known for providing high-speed internet access, but it's also used for delivering IP television (IPTV), Voice over IP (VoIP), and other digital services.

Gigabyte Passive Optical Networks (GPON’s) are networks which rely on optical cables to deliver information.  GPON’s are currently the leading form of Passive Optical Networks. GPONS offer up to a 1:64 ratio on a single fiber. As opposed to a standard copper wire in most networks, GPON’s are 95% more energy efficient. In addition to efficiency, gigabyte passive optical networks provide a low cost solutions to adding users through splitters which make GPON’s desirable in populated areas. 

A TDMA, time division multiple access, format is used in GPON in order to designate bandwidths to each ONU. Depending on the service provider and how they decide to allocate the bandwidth, each ONU can receive a downstream rate of 2.488 Gbits/s. 

The upstream rate however will receive less than its maximum due to the sharing of other ONUs. The ONUs will communicate with the OLT and it will determine the distance and time delay for every subscriber. 

Over the years, as technology has advanced, there have been discussions about the evolution from GPON to XGS-PON (10 Gbps symmetric) and even higher-speed variants. However, GPON still remains one of the most widely deployed fiber-to-the-home (FTTH) technologies worldwide.

To see more on how GPON works, click here.