FTTx/PON Network Overview

FTTx Network Basics

The FTTx architecture consists of a passive optical network (PON) that allows several customers to share the same connection, without any active components (i.e., components that generate or transform light through optical-electrical-optical conversion).

A feeder fiber is brought from an optical line terminal (OLT) in the CO to a fiber distribution hub (FDH) near a group of customers. From that point, a passive splitter is used to typically connect up to 32 or 64 customers to the same feeder fiber. Then, each customer premises is provided with an optical network terminal (ONT) connected to each splitter branch. This point-to-multipoint architecture dramatically reduces network installation, management, and maintenance costs (see Figure 1).

Figure 1. Providing triple-play services over a high-bandwidth passive optical network

The OLT provides voice and data downstream transmission using a 1490-nm wavelength band, while the ONT provides upstream transmission with a 1310-nm wavelength band, allowing for bidirectional transmission on the same fiber without the signals interfering with one another.

In addition, the OLT may be connected to a wavelength-division multiplexing (WDM) coupler to provide video together with voice and data (triple-play) services over a single fiber. The video is provided in the downstream direction only, usually in a 1550-nm wavelength band (traditional analog video).

Figure 2. Wavelengths and services delivered over an FTTx network

There are also many variations of the FTTx architecture (see figures 1-2), including:

» Fiber-to-the-cabinet (FTTCab)
» Fiber-to-the-curb (FTTC)
» Fiber-to-the-home (FTTH)
» Fiber-to-the-premises (FTTP)
» Fiber-to-the-office (FTTO)
» Fiber-to-the-user (FTTU)

Figure 3. FTTH, FTTB and FTTC

Services Enabled by PONs

Table 1 summarizes the possible services that can be provided over PONs by a single carrier. For more information on testing these services, please visit the Triple-Play/IPTV applications page.

PON Testing: The Right Gear

Adequate testing during network installation minimizes time-consuming and costly troubleshooting efforts by locating faulty components before they disrupt service.

In order to achieve this, it is important to test during the different construction and deployment phases with the appropriate test equipment.

		FTTH Deployment Phase
Type of Test Equipment	Test Applications	Construction	Service Activation	Troubleshooting
Portable OTDR	End-to-end fiber characterization: Loss and attenuation Fiber length Event location Reflectance and ORL Fiber identification
Handheld OTDR	End-to-end fiber characterization: Loss and attenuation Fiber length Event location Reflectance and ORL Fiber identification Live OTDR testing (out-of-band)
OLTS	Fully automated: Loss and attenuation Fiber length ORL Bidirectional Fiber identification
PON Power Meter	PON signal power (1310/1490/1550 nm)
Fiber Inspection Probe	Fiber inspection
Ethernet Tester	Ethernet performance verification at Layer 2 and Layer 3