Fiber-optic communication offers a number of well-known advantages over electrical and RF transmission. Optical cables have very high bandwidth. The absence of electrical power over the line means there’s no spark hazard. The signal can’t be tapped by electromagnetic methods, so it’s more secure. Likewise, EM interference isn’t a problem. Maintenance is low, and the thin cables can be packed densely.
Several options are available for getting fiber optics close to the end user. They include active optical networks (AON) as well as passive optical networks (PON). Within PON, the main options are BPON (broadband passive optical network), GPON (gigabit passive optical network), and EPON (Ethernet passive optical network). GPON offers the fastest speeds of any current PON option.
How GPON Works
The GPON technology is based on the ITU-T G.984 standard. It’s considered the successor to BPON, which is built on G.983. A single network consists of an optical line terminal (OLT) belonging to the service provider, a splitter, and up to 64 optical network units (ONU). The ONU may or may not be on the end user’s premises, but it serves a single customer. It converts the optical signal to electrical or RF signals which the end user’s equipment can connect to.
An ONU is sometimes called an ONT (optical network terminal). An ONT is usually on the customer premises and an ONU somewhere outside, but there’s otherwise no real difference. The distance from the OLT to the ONU or ONT can be up to 20 km.
The information is sent over the short-wavelength infrared band, using wavelength division multiplexing (WDM). Downstream data goes over a 1490 nm signal, with a maximum speed of 2.488 gigabits per second. The upstream data uses the 1310 nm wavelength and can carry up to 1.244 Gb/second.
The next generation of GPON, called 10G GPON or XG-PON, offers symmetric 10 Gb/second upload and download speeds.
GPON customers are typically homes or small businesses. The technology delivers data, voice, and IP video. It may be packaged with an RF overlay at 1550 nm so that it can deliver standard cable video as well.
The Best Cases for GPON
GPON technology can be very cost-effective, provided it meets certain conditions. The OLT is relatively expensive, so the number of ONUs connected to it should be at or not much below either 32 or 64. Going above 32 ONUs requires adding a second port to the OLT, so there’s a cost jump at that point. Of course, the more users there are on an OLT, the more likely it is that service will degrade under peak use.
A PON offers low maintenance costs and has a high MTBF, since passive components don’t fail as often. Its advantage is especially strong where minimizing maintenance work is important.
The GPON design includes ATM encapsulation. This makes it convenient to deploy in networks which use an ATM backbone.
A GPON can replace existing copper-wire cabling and deliver higher data speeds with greater reliability. The question is when the improvement justifies the work of replacing it. High-density areas require less fiber and make it easier to optimize the allocation of ONUs to OLTs. With a large office building, it may make sense to put an OLT on the premises. Compact OLTs are available which don’t have to be deployed in a central office.
GPON vs. Other Optical Technologies
While GPON is growing in popularity, it isn’t the only option for bringing optical communication lines to the end user. Other technologies have their place, and a service provider needs to consider their relative costs and benefits.
AON vs. PON
Active optical networks have their own advantages. They use electrically powered switching rather than passive splitters. An AON has a greater range, as much as 70 km from the central switch to an Ethernet device. Users can be more widely dispersed. The costs are more nearly proportional to the number of users, so there’s less need to optimize end-user groupings.
GPON includes QoS features to keep latency down, but an active network allocates bandwidth more effectively and provides better latency when the user load is high. It’s easier to locate faults in an active network, since the switches can report points of failure.
An AON has higher power consumption, and active components are more prone to failure than passive ones. Costs and maintenance requirements will be higher. AONs don’t support RF overlays.
BPON, EPON, and GPON
The PON competition today is basically between EPON and GPON. BPON networks are still around and will be for a long time, but they’re a previous generation of technology. BPON is slower than GPON and offers no advantages to compensate. It’s simply a matter of how long it will take to replace all existing installations.
EPON is sometimes called GEPON (gigabit EPON), which is confusing, since people will tend to pronounce it like GPON.
EPON and GPON are both available in 10G versions, but the architectures are noticeably different.
GPON uses two different types of encapsulation. It uses GPON Encapsulation Mode, or GEM, to provide a frame-oriented service. In addition, it uses ATM encapsulation for when working in an ATM network rather than Ethernet. EPON doesn’t add any encapsulation but treats everything as Ethernet data. It’s a subject of ongoing debate whether GPON is more flexible this way or just adds complexity.
Choosing between GPON and EPON is difficult. GPON has ATM compatibility, better data speeds, and better QoS features. EPON is more economical and treats Ethernet natively.
Making the Right Choices
Getting fiber to the customer allows greater data speeds and opens new business opportunities. The questions are when to upgrade and which technology to use. The first choice is between active and passive networking. Within passive optical networking, GPON and EPON are the leading choices. Each approach has its advantages. Careful research and planning are needed to decide which will provide the greatest benefits.
Regarding the experience taken by Intraway, in projects with clients that offer services on optical fiber, it could be said that the most particular advantage of GPON networks is that a single shared optical fiber can support multiple users through the use of splitters passive optics, and this at a very low cost. On GPON networks, up to 64 ONT can share a fiber connection with the OLT. This allows the Gigabit passive optical network to be one of the first options for service providers who want to replace copper networks with fiber.
In conclusion, we could be talking about the following points to highlight about PON networks:
The provisioning of the platforms that manage the access, management and traffic of a service delivered by FTTX, being network elements that obey one of the new technologies, is much faster efficient to carry out.
Allow service providers to offer more capacity to transport bandwidth intensive applications.
Provide one of the most cost effective ways for service providers to implement fiber.
Future speed improvements can be achieved through equipment upgrades before any update on the fiber itself.