How Much Do You Know About FTTH PON Testing?

Passive optical network (PON) is a cost-effective way to deliver high-bandwidth broadband services to users and widely deployed all over the world. FTTH uses PON technology and provides high bandwidth from the central office (CO) to subscribers. FTTH PON system achieves network reliability and makes network testing, monitoring and measuring easier. This article will tell about FTTH PON testing from the four aspects below.

Connector Inspection

Connector inspection/cleaning plays an important role in network installation and maintenance. Typically an optical microscope is used for connector inspection. To prevent accidental eye damage when inspecting fibers potentially carrying live traffic, a video microscope images the connector end-face and displays the magnified image on a handheld display. In this way, the dirt, debris or damage on the connector could be easily detected. According to the study by NTT-Advanced Technology, connector contamination and damage are the key reason for poor optical network performance.

Insertion Loss Test

In telecommunications, the term “insertion loss” expressed in dB, refers to the loss of signal power resulting from the insertion of a device in a transmission line or in an optical fiber. An insertion loss test measures the end-to-end loss of the installed link by injecting light with a known power level and wavelength at one end, and then measures the received power level output from the other end. The measured difference between the transmitted and received power levels exactly indicates the very optical loss through the network. In some occasions, insertion loss is allowed and considered acceptable when the measured loss level is lower than the budget loss level.

Optical Return Loss Test

In telecommunications, return loss expressed in dB, means the loss of power in the signal returned or reflected by a discontinuity in a transmission line which can be a mismatch with the terminating load or with a device inserted in the line. The optical return loss test injects light with known wavelength and power level into one end and measures the power level returned to that same end. Then the return loss is the difference between the injected power level and the measured return level. When the return loss is higher than the budgeted return loss target, it is considered acceptable.

Typically insertion loss test and return loss test are performed by using wavelengths at those which will be used during network operation. For FTTH PON system, 1310nm wavelength is used in the upstream direction, while 1490nm and 1550nm wavelengths are used in the downstream direction. So it is essential to have insertion and return loss testing at 1310nm, 1490nm and 1550nm wavelengths. The optical network is considered ready for activation when the insertion loss and return loss measured at each wavelength are within the budgeted levels for the link. However, in some cases, the network operator uses an optical time domain reflectometry (OTDR) as the following picture shows for more fully documented network.

Optical Time Domain Reflectometry (OTDR)

OTDR scans a fiber from one end to measure the length, loss and optical return loss of an optical network. And it also locates and measures reflective or non-reflective events in the network caused by splices, connectors, splitters, faults, etc. OTDR operates like a radar by injecting narrow pulses of light into the fiber under test. As each pulse travels down the fiber, imperfections in the fiber scatter some of the light, with some of this Rayleigh-scattered light being guided back up the fiber.

Summary

From the above description, four tests are commonly used to verify optical links. Proper testing is critical for FTTH PON installing, activating and maintaining, because excess loss or reflectance can result in poor network performance if not detected and corrected. And over time, transmission errors will occur before the need for any maintenance activity.

Article source: www.fiberopticshare.com/how-much-do-you-know-about-ftth-pon-testing.html

Introduction to PON Technologies

Passive optical network (PON) is a very significant class of fiber access system in the world and it enjoys a dominant position in the access market. GPON and EPON are the two classifications of PON. The primary differences between the GPON and EPON lie in the protocols used for upstream and downstream communications. This article will introduce PON, GPON and EPON sequentially.

Passive Optical Networks (PON)

 

A PON is a fiber network that only uses fiber and passive components like PON splitters and combiners rather than active components like amplifiers, repeaters, or shaping circuits. Thus PON network costs significantly less than those using active components, but it has a shorter range of coverage limited by signal strength. An active optical network (AON) is able to cover a range to about 100 km (62 miles), while a PON is typically limited to fiber cable runs of up to 20 km (12 miles). PON is also called FTTH (fiber to the home) network.

The typical PON arrangement is a point to multi-point (P2MP) network where a central optical line terminal (OLT) at the service provider’s facility distributes TV or Internet service to as many as 16 to 128 customers per fiber line. Dividing a single optical signal into multiple equal but lower-power signals, the optical splitters distribute the signals to users. An ONU (optical network unit) terminates the PON at the customer’s home. Usually, ONU communicates with ONT (optical network terminal). The ONU/ONT may be one device.

Gigabit Passive Optical Networks (GPON)

 

GPON utilizes optical wavelength division multiplexing (WDM) so a single fiber could be used for both upstream and downstream data. A laser on a wavelength of 1490 nm transmits downstream data, while upstream data transmits on a wavelength of 1310 nm.

While each ONU gets the full downstream rate of 2.488 Gbits/s, GPON uses a time division multiple access (TDMA) format to allocate a specific timeslot to each user. It divides the bandwidth, so each user gets a fraction such as 100 Mbits/s depending on the way the service provider allocates it. The upstream rate is less than the maximum as it is shared with other ONUs in a TDMA scheme. The distance and time delay of each subscriber are determined by the OLT. Then software provides a way to allot timeslots to upstream data for each user. The typical split of a single fiber is 1:32 or 1:64, which means each fiber can serve up to 32 or 64 subscribers. Split ratios up to 1:128 are possible in some systems.

Ethernet Passive Optical Networks (EPON)

 

Based on the Ethernet standard 802.3, EPON 802.3ah specifies a similar passive optical network with a range up to 20 km. EPON uses WDM with the same optical frequencies as GPON and TDMA. The raw line data rate is 1.25 Gbits/s in both the upstream and downstream directions.

EPON technology provides bidirectional 1Gb/s links using 1490nm wavelength for downstream and 1310nm wavelength for upstream, with 1550nm wavelength reserved for future extensions or additional services. EPON is fully compatible with other Ethernet standards, so no encapsulation or conversion is necessary when connecting to Ethernet-based networks on either end. The same Ethernet frame is used with a payload for up to 1518 bytes. As Ethernet is the primary networking technology utilized in local area networks (LAN) and now in metro area networks (MAN), no protocol conversion is needed.

Summary

 

PONs are used to provide triple-play services including TV, and Internet service to subscribers. The lower cost of passive components means simpler systems with fewer components failing or requiring maintenance. The primary disadvantage is shorter range possible, commonly no more than 12 miles or 20 kilometers. As the demand for faster Internet service and more video grows, PONs are growing in popularity. The age of PON has begun. It is a new era of access network upon us.

Article source: www.fiberopticshare.com/introduction-to-pon-technologies.html

Passive Optical Network–A Superior Network Solution

With the explosive growth of Internet, the introduction of a broadband access network based on fiber-to-the-office (FTTO) and fiber-to-the-home (FTTH) has been triggered. Under this circumstance, access and metro networks should be scalable in terms of capacity and accommodation as well as flexible with regard to physical topology. Passive optical network (PON), one class of fiber access system, can deal with the various demands.

Definition

A passive optical network (PON) is a telecommunication network that uses point-to-multipoint fiber to the end-points in which unpowered optical splitters are used to enable a single optical fiber to serve multiple end-points. It consists of an optical line terminal (OLT) at the service provider’s central office and a number of optical network units (ONUs) or optical network terminals (ONTs), near end users (see below figure). PON takes advantages of wavelength division multiplexing (WDM) and uses one optical wavelength for upstream traffic while another for downstream traffic on a single-mode fiber. The upstream signals are combined at the splitters by using a multiple access protocol (time division multiple access). The downstream signals are directed to multiple users by passive optical splitter technology.

Advantages

There are two ways that the signals can be broken out in shared fiber architectures. One is active Ethernet (AE), with which the individual signals are split out using electronic equipment near the subscriber. The other one is PON, in which the signals are replicated passively by the splitter. Compared with AE, a network based on a PON system is more superior. The advantages of PON are as below.

PON incurs lower capital expenditures because it has no electronic components in the field. Also PON lowers the operational expenditures as there is no need for the operators to provide and monitor electrical power in the field or maintain backup batteries. Besides, a PON has a higher reliability because in the PON outside plant there are no electronic components which are prone to failure. Additionally, one of the most crucial features of a PON-based access network is its signal rate and format transparency. It is much simpler for a PON to upgrade to higher bit rates. Both AE and PON require upgraded electronics in the CO and customer premises, but unlike AE, PON does not need to upgrade in the outside plant as the passive splitters are agnostic to PON speed. Lastly, a PON solution has the ability to span long distances without degrading performance. The low-loss characteristics of single-mode fiber enable PON to support a maximum physical reach of 20 kilometers.

Applications

There are some applications for which PON is well suited, such as fiber-to-the-home (FTTH) delivery of voice, Internet data, and cable access broadband video. More specifically, PON is used when the applications require anticipated system to upgrade to high-security areas or where the rerouting of cable may be difficult. Or in the cases that installations involving widely dispersed nodes require long runs of fiber. And PON is utilized for the projects where costs, especially initial deployment costs, are a key concern. At the same time, using PON can help user bandwidth to be adequately managed.

By reading the above illustration, have you got a basic understanding about the passive optical network? Fiberstore, a professional manufacturer and supplier in the optical industry, has many high-quality PON products including PON splitters, optical network units and optical line terminal. Choosing a PON product in Fiberstore can help to deploy your network more efficiently.

Originally published: www.fiber-optic-components.com/passive-optical-network-a-superior-network-solution.html