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What’s The Difference Between EPON And GPON Optical Fiber Networks?

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EPON and GPON are popular versions of passive optical networks (PONs). These short-haul networks of fiber-optical cable are used for Internet access, voice over Internet protocol (VoIP), and digital TV delivery in metropolitan areas. Other uses include backhaul connections for cellular basestations, Wi-Fi hotspots, and even distributed antenna systems (DAS). The primary differences between them lie in the protocols used for downstream and upstream communications.
A PON is a fiber network that only uses fiber and passive components like splitters and combiners rather than active components like amplifiers, repeaters, or shaping circuits. Such networks cost significantly less than those using active components. The main disadvantage is a shorter range of coverage limited by signal strength. While an active optical network (AON) can cover a range to about 100 km (62 miles), a PON is typically limited to fiber cable runs of up to 20 km (12 miles). PONs also are called fiber to the home (FTTH) networks.
The term FTTx is used to state how far a fiber run is. In FTTH, x is for home. You may also see it called FTTP or fiber to the premises. Another variation is FTTB for fiber to the building. These three versions define systems where the fiber runs all the way from the service provider to the customer. In other forms, the fiber is not run all the way to the customer. Instead, it is run to an interim node in the neighborhood. This is called FTTN for fiber to the node. Another variation is FTTC, or fiber to the curb. Here too the fiber does not run all the way to the home. FTTC and FTTN networks may use a customer’s unshielded twisted-pair (UTP) copper telephone line to extend the services at lower cost. For example, a fast ADSL line carries the fiber data to the customer’s devices.
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 (see the figure). Optical splitters, passive optical devices that divide a single optical signal into multiple equal but lower-power signals, distribute the signals to users. An optical network unit (ONU) terminates the PON at the customer’s home. The ONU usually communicates with an optical network terminal (ONT), which may be a separate box that connects the PON to TV sets, telephones, computers, or a wireless router. The ONU/ONT may be one device.
In the basic method of operation for downstream distribution on one wavelength of light from OLT to ONU/ONT, all customers receive the same data. The ONU recognizes data targeted at each user. For the upstream from ONU to OLT, a time division multiplex (TDM) technique is used where each user is assigned a timeslot on a different wavelength of light. With this arrangement, the splitters act as power combiners. The upstream transmissions, called burst-mode operations, occur at random as a user needs to send data. The system assigns a slot as needed. Because the TDM method involves multiple users on a single transmission, the upstream data rate is always slower than the downstream rate.
GPON
Over the years, various PON standards have been developed. In the late 1990s, the International Telecommunications Union (ITU) created the APON standard, which used the Asynchronous Transfer Mode (ATM) for long-haul packet transmission. Since ATM is no longer used, a newer version was created called the broadband PON, or BPON. Designated as ITU-T G.983, this standard provided for 622 Mbits/s downstream and 155 Mbits/s upstream.
While BPON may still be used in some systems, most current networks use GPON, or Gigabit PON. The ITU-T standard is G.984. It delivers 2.488 Gbits/s downstream and 1.244 Gbits/s upstream.
GPON uses optical wavelength division multiplexing (WDM) so a single fiber can be used for both downstream and upstream data. A laser on a wavelength (λ) of 1490 nm transmits downstream data. Upstream data transmits on a wavelength of 1310 nm. If TV is being distributed, a wavelength of 1550 nm is used.
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. This divides the bandwidth so each user gets a fraction such as 100 Mbits/s depending upon how the service provider allocates it.
The upstream rate is less than the maximum because it is shared with other ONUs in a TDMA scheme. The OLT determines the distance and time delay of each subscriber. 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. That means each fiber can serve up to 32 or 64 subscribers. Split ratios up to 1:128 are possible in some systems.
As for data format, the GPON packets can handle ATM packets directly. Recall that ATM packages everything in 53-byte packets with 48 for data and 5 for overhead. GPON also uses a generic encapsulation method to carry other protocols. It can encapsulate Ethernet, IP, TCP, UDP, T1/E1, video, VoIP, or other protocols as called for by the data transmission. Minimum packet size is 53 bytes, and the maximum is 1518. AES encryption is used downstream only.
The latest version of GPON is a 10-Gigabit version called XGPON, or 10G-PON. As the demand for video and over the top (OTT) TV services has increased, there is an increasing need to boost line rates to handle the massive data of high-definition video. XGPON serves this purpose. The ITU standard is G.987.
XGPON’s maximum rate is 10 Gbits/s (9.95328) downstream and 2.5 Gbits/s (2.48832) upstream. Different WDM wavelengths are used, 1577 nm downstream and 1270 nm upstream. This allows 10-Gbit/s service to coexist on the same fiber with standard GPON. Optical split is 1:128, and data formatting is the same as GPON. Maximum range is still 20 km. XGPON is not yet widely implemented but provides an excellent upgrade path for service providers and customers.
Most PONs are configured like this. The number of splitters and split levels varies with the vendor and the system. Split ratios are usually 1:32 or 1:64 but could be higher.

Understanding the FTTx Network

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FTTx technology plays an important role in providing higher bandwidth for a global network. And FTTx (fiber to the x) architecture is a typical example of substituting copper by fiber in high data rate traffic. According to the different termination places, the common FTTx architectures include FTTH, FTTB, FTTP, FTTC, and FTTN. This article will introduce these architectures respectively.
What is FTTx Network?
FTTx also called as fiber to the x, is a collective term for any broadband network architecture using optical fiber to provide all or part of the local loop used for last mile telecommunications.
Different FTTx Architectures
FTTP: fiber-to-the-premises, is a loosely used term, which can encompass both FTTH and FTTB or sometimes is used a particular fiber network that includes both homes and businesses. It depends on how the context is used and a specific location of where the fiber terminates. FTTP can offer higher bandwidth than any other broadband services, so operators usually use this technology to provide triple-play services.
FTTH: as indicated by the name fiber-to-the-home, fiber from the central office reaches the boundary of the living space, such as a box on the outside wall of a home. Once at the subscriber’s living or working space, the signal may be conveyed throughout the space using any means, such as twisted pair, coaxial pair, wireless, power line communication, or optical fiber. Passive optical networks (PONs) and point-to-point Ethernet are architectures that deliver triple-play services over FTTH networks directly from an operator’s central office.
FTTB (fiber to the building) — Fiber terminates at the boundary of the building. A fiber cable in FTTB installation goes to a point on shared property and the other cabling provides the connection to single homes, offices or other spaces. FTTB applications often use active or passive optical networks to distribute signals over a shared fiber optic cable to individual households of offices.
FTTC( fiber-to-the-curb or -cabinet), is a telecommunication system where fiber optic cables run directly to a platform near homes or any business environment and serve several customers. Each of these customers has a connection to this platform via coaxial cable or twisted pair. The term “curb” is an abstraction and just as easily means a pole-mounted device or communications closet or shed. Typically any system terminating fiber within 1000 ft (300 m) of the customer premises equipment would be described as FTTC. A perfect deployment example of FTTC is a DLC/NGDLC (digital loop carrier) which provides phone service.
FTTN (fiber to the node) — Fiber terminates in a street cabinet, which may be miles away from the customer premises, with the final connections being copper. One of the main benefits of FTTN is the ability to deliver data over more efficient fiber optic lines, rather than other fiber optic lines with the greater speed restriction
Conclusion
The advent of the FTTx network is of great significance for people around the world. As it has a higher speed, costs less, and carries more capacity than twisted pair conductor or coaxial cables.

WHAT IS FTTX OR FIBER TO THE X?

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“Fiber to the X” sounds like something really big, like to the “Nth degree.” It is one of the reasons that around 20,000 professionals plan to meet up at CommunicAsia June 26 – 28, 2018 in Singapore to gather info and develop business around it. FTTX is a situation in which all available optical fiber topologies from a telecommunications or cable carrier point to its customers. This is based on (not outside) the location of the fiber termination point. FTTC and FTTN (curb and neighborhood) are similar because the fiber ends outside the building.
Whereas, FTTC and FTTN (curb and neighborhood) are a little different. The fiber, in these cases, ends outside a building, not inside the building. FTTH and FTTP (home and premises) mean the same. FTTE (enclosure) refers to a junction box on a floor or in a department in a bigger facility.
FTTX, FTTH and FTTP are a must-have because of individuals’ and organizations’ increasing appetite for network, network and more network. The number of voice, image and video files shared on networks is bigger than ever and will continue to increase.
FTTx offers a huge amount of bandwidth to meet today’s needs better than ever. It lines up well with the triple play of voice, video and data and now people expect a converged multi-play services environment with huge bandwidth requirements. Apps and services like Hulu, Pluto, Amazon Alexa, WhatsApp, GoDaddy (web hosting, ISP, and DID number provider) and Zoom.us as well as, in general VOIP, RF video, online gaming that enables video and voice while playing, cyber security, and smart everything are depend upon FTTx networks.

What Is WDM?

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WDM is a technique in fiber optic transmission that enables the use of multiple light wavelengths (or colors) to send data over the same medium. Two or more colors of light can travel on one fiber and several signals can be transmitted in an optical waveguide at differing wavelengths.
Early fiber optic transmission systems put information onto strands of glass through simple pulses of light. A light was flashed on and off to represent digital ones and zeros. The actual light could be of almost any wavelength—from roughly 670 nanometers to 1550 nanometers.
WDM is a technique in fiber optic transmission for using multiple light wavelengths to send data over the same medium.
During the 1980s, fiber optic data communications modems used low-cost LEDs to put near-infrared pulses onto low-cost fiber. As the need for information increased, so did the need for bandwidth. Early SONET systems used 1310 nanometer lasers to deliver 155 Mb/s data streams over very long distances.
But this capacity was quickly exhausted. Advances in optoelectronic components allowed the design of systems that simultaneously transmitted multiple wavelengths of light over a single fiber. Multiple high-bit rate data streams of 2.5 Gb/s, 10 Gb/s and, more recently, 40 Gb/s, 100 Gb/s, and 200 Gb/s could be multiplexed through divisions of several wavelengths. Thus, WDM was born.
There are two types of WDM today:
Coarse WDM (CWDM): WDM systems with fewer than eight active wavelengths per fiber. CWDM is defined by wavelengths. DWDM (see below) is defined in terms of frequencies. DWDM’s tighter wavelength spacing fits more channels onto a single fiber, but cost more to implement and operate.
CWDM is for short-range communications, so it employs wide-range frequencies with wavelengths spread far apart. Standardized channel spacing permits room for wavelength drift as lasers heat up and cool down during operation. CWDM is a compact and cost-effective option when spectral efficiency is not an important requirement.
Dense WDM (DWDM): DWDM is for systems with more than eight active wavelengths per fiber. DWDM dices spectrum finely, fitting 40-plus channels into the same frequency range used for two CWDM channels.
DWDM is designed for long-haul transmission, with wavelengths packed tightly together. Vendors have found various techniques for cramming 40, 88, 96, or 120 wavelengths of fixed spacing into a fiber. When boosted by Erbium Doped-Fiber Amplifiers (EDFAs)—a performance enhancer for high-speed communications—these systems can work over thousands of kilometers. For robust operation of a system with densely packed channels, high-precision filters are required to peel away a specific wavelength without interfering with neighboring wavelengths. DWDM systems must also use precision lasers that operate at a constant temperature to keep channels on target.
Ciena’s 6500 Packet-Optical Platform converges packet, Optical Transport Networks (OTNs), and flexible WaveLogic Photonics in a single platform to streamline operations and optimize footprint, power, and capacity. Built for efficient network scaling from the access to the backbone core, it offers the full gamut of CWDM and DWDM solutions, with DWDM solutions ranging from 10 Gb/s to beyond 200 Gb/s.
The 6500 has the following advantages:
Industry-leading 10G, 40G, 100G, and 200G coherent and control plane capabilities for scale and service differentiation
Hybrid OTN and packet-switching technologies for the most efficient use of network resources
Embedded and discrete software tools that increase programmability, visibility, and control of the optical network
Minimal equipment needed to adapt to a wide variety of requirements, reducing standardization and operational costs
The ability to tailor customer solutions via various chassis, power, and configuration options to maximize operational efficiencies

What You Need to Know When Using 10G over CWDM

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Both Passive CWDM and DWDM have been viable solutions in the telecommunications industry, but now, 10G Ethernet is appearing to be the most preferred solution over CWDM, everyone is migrating to the use of 10G Ethernet. This encourages many engineers to figure out how they ought to adjust their new designs to support the transition from 10G to CWDM. If you’re one of these designers who’s attempting to navigate the transition, the following is what you need to know.
Bandwidth Exts are Easier
In past years, designers who want to increase or improve their bandwidth could achieve this easily over a single or duplex mode fiber. During this period, the 1G Ethernet and CWDM solutions were sufficient, and the only limiting element was the power budget of the optical transceiver or the attenuation of your fiber. That it was possible to transmit up to 200 kilometers and utilize just a 1G Ethernet when designers preferred cheap CWDM.
Now, many people are considering the 10G Ethernet solutions, and that’s why it’s necessary to understand how everything will differ when using 10G over CWDM. When intending to migrate to 10G, you need to know the fiber type. For the dispersion and attenuation calculation, every designer need to know the recommended parameters from ITU-T and understanding the vendor and product kind of the fiber could also help. Remember that the physical fiber will work better than the standards claim most of the time.
Chromatic dispersion is referred to as the time variance of a single pulse of a signal. To summarize, chromatic dispersion is “the spreading of a light pulse per unit source spectrum width in an optical fibre due to the various group velocities of the different wavelengths composing the source spectrum” or in layman’s terms, “the signal is stretched on the fiber transmission path due the dispersion characteristics of the transporting fiber.”
Chromatic dispersion always exists, but the higher the link speed is, the greater important it becomes. For instance, a wavelength of 1310nm have a 0 ps/nm chromatic dispersion and 5, 25 dB fiber attenuation. In comparison, a wavelength of 1610 nm have a 330 ps/nm chromatic dispersion and a 3,45 dB fiber attenuation.
CWDM Over DWDM 10G is Cost-Effective
Designers should bear it in mind that CWDM implementation is more cost effective than passive DWDM infrastructure. These solutions will be more expensive because DWDM lasers cost more. DWDM lasers are essentially DFB lasers which are cooled, however, they are recommended as they contain the longevity that are required in these solutions. If you would like transmit a signal over a large distance, you should think about large metro ring topologies.
Though 10GBASE DWDM is more expensive, it’s become the first choice because users have started to consider the costs after dividing it over the quantity of customers served. Some customers are more cost-conscious and have lower bandwidth capacity requirements; so, the cheap CWDM infrastructure will make more sense.
Remember that the new 10GBASE DWDM services is usually added over the same fiber. This will enhance the support of the initial CWDM infrastructure capacity by 4 times. This is irresistible to many designers.

How to Use OADM in WDM Network ?

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OADM is a cost-effective and easy to use passive fiber optic component, which can provide easy to build and grow connectivity environment for WDM network. The optical add-drop multiplexer is one of the key devices to implement such optical signal processing. Use of OADM makes it possible to freely add or drop signals with arbitrary wavelengths over multiplexed optical signals by assigning a wavelength to each destination. In this article, let us introduce how to use OADM in WDM Network.
Inside an OADM
A traditional OADM consists of three parts: an optical demultiplexer, an optical multiplexer and between them a method of reconfiguring the paths between the optical demultiplexer, the optical multiplexer and a set of ports for adding and dropping signals. The multiplexer is used to couple two or more wavelengths into the same fiber. Then the reconfiguration can be achieved by a fiber patch panel or by optical switches which direct the wavelengths to the optical multiplexer or to drop ports. The demultiplexer undoes what the multiplexer has done. It separates a multiplicity of wavelengths in fiber and directs them to many fibers.
Main Function and Principle of OADM
For an OADM, “Add” refers to the capability of the device to add one or more new wavelength channels to an existing multi-wavelength WDM signal while “drop” refers to drop or remove one or more channels, passing those signals to another network path. The OADM selectively removes (drops) a wavelength from a multiplicity of wavelengths in fiber, and thus from traffic on the particular channel. It then adds in the same direction of data flow the same wavelength, but with different data content. The main function of the OADM function is shown in the following picture. This function is especially used in WDM ring systems as well as in long-haul with drop-add features.
How to Connect OADM With WDM MUX/DEMUX
In most cases, OADM is deployed with CWDM or DWDM MUX/DEMUX. It is usually installed in a fiber optic link between two WDM MUX/DEMUXs. The following picture shows a CWDM network using a 1-channel dual fiber OADM between two CWDM MUX/DEMUXs. Signals over 1470 nm are required to be added to and dropped from the dual fiber link. On the OADM, there is usually one port for input and one port for output. The OADM can be regarded as a length of fiber cable in the fiber link. The point is the one or more strand of signals is added or dropped when the light goes through the OADM.
Summary
OADM is still evolving, and although these components are relatively small, they are immeasurable in the future. Optical Add-Drop Multiplexer (OADM) is used for multiplexing and routing different channels of fiber into or out of a single fiber. The CWDM OADM is designed to optically add/drop one or multiple CWDM channels into one or two fibers.