This is the first in a two-part series of articles exploring XGS-PON vs. Active Ethernet. In this article, we will explore why operators must seriously consider ceasing the use of Active Ethernet in their new fiber deployments. The second article will discuss innovative solutions that will enable operators to leverage XGS-PON with any existing Active Ethernet network deployments, thus providing substantial power, space, and equipment cost savings.
The Storied Journey of Fiber Optic Networks
We live in a world where most people are accustomed to the joys of broadband internet, whether it be talking to their TVs, doing group calls with people across the globe, or cultivating virtual lives in cloud-hosted video games where the shackles of reality are left behind. It is absurd to think that less than three decades ago, the World Wide Web was born! The transformational impact on culture, commerce, and technology born from the internet was nothing short of revolutionary! Gigabit speeds are rapidly becoming the norm today. While many contend that users don’t need Gigabit, everyone agrees that this next speed tier is what operators are leveraging to attract customers onto their new fiber networks - Gigabit speeds today with multi-gigabit speeds just around the corner!
While most internet early adopters leveraged ‘twisted copper pairs’ used for analog telephony as dial-up internet access mechanisms, the internet truly began its journey toward democratization with the emergence of “always-on” Digital Subscriber Lines (DSL). DSL became the de facto telco technology to bring internet to homes and businesses. While cable TV companies also began bringing internet access, telephony services, along with digital TV signals, over coaxial cable systems to their end-users.
A technology that began to emerge in the early 1980s was fiber optics. Fiber-optic communication benefited from low signal loss and very-high capacity, which translated to the possibility of transporting comparatively much larger amounts of information more reliably and with better quality over much greater distances. Unfortunately, the early expense of laying down fiber optics was prohibitive for most operators. As a result, many of the early builds were closely aligned with newly built premises, where the cost of laying fiber in the ground was largely eradicated. When the first scale Fiber-to-the-Home (FTTH) deployments began to emerge in the early 90s, Ethernet was modified to facilitate transmission over longer distance fiber optic cables, with the first deployments capable of delivering up to 100Mbps, at a time when those accessing the internet over copper lines or coax cables were receiving one-hundredth of that capacity. As technology progressed and the cost of fiber optic equipment plummeted, greater adoption of this approach continued. During the original Ethernet-over-Fiber approach became standardized as Active Ethernet. At the same time, innovative thinkers in British telecom proposed an approach that they believed could leverage the sharing of fiber cables across a larger number of users to help lower the deployment cost and accelerate deployment. This approach leveraged a concept called Passive Optical Networks (PON).
What is a Passive Optical Network?
A PON is a fiber-optic network with a point-to-multipoint architecture. At its most basic level, a PON solution is comprised of a single strand of fiber optic cable, which the operator connects into its data equipment, often in a telecom exchange building. This equipment is referred to as an Optical Line Terminal (OLT). This cable then travels out towards the end-users, where it is then passed through a series of passive optical splitters. These splitters are pieces of glass that take the light signals coming in on the fiber cable coming from the OLT and spread that light across multiple other cables that travel onward to the end-user. Each of the cables that connect to the end-user, often referred to as the drop cable receives the same light signal data from the OLT. To ensure that users only receive the data signals meant for them, encryption scrambles the data so that only the equipment deployed at the end user’s premises can decipher the data meant for that user. Often referred to as the Optical Network Terminal (ONT) or the Optical Network Unit (ONU), several of these Optical Network Units (ONU) terminate the fiber from the splitters and constitute the user endpoints. The use of passive optical splitters that consume no power means that operators can utilize these components reliably out in the field to adapt the fiber network architecture to connect new locations that the fiber network can reach. With no active electronics deployed in the field, the robustness of these networks is significantly improved.
This solution enables the delivery of data from the single transmission point (the OLT) to multiple user endpoints, enabling service providers to save significantly on the amount of raw fiber needed to serve end subscribers, the space within the aggregation location or exchange building needed to manage all of the cables that connect to the end-users, and drastically reduce the size of the active equipment that transmits the data over the fiber network, along with the power and cooling demands of that equipment.
These PON fiber network architectures yielded other substantial cost and time to market-saving benefits in the field. With the PON network architecture, the number of fiber splices needed to build out a fiber network is significantly reduced, accelerating build time, and lowering costs. The added cost of a splitter is insignificant compared to the savings in raw fiber consumption and reduced fiber splicing, allowing for more efficient fiber deployment.
The power savings yielded from PON deployments vs. Active Ethernet point-to-point fiber deployments are extremely important for operators. With an ever-increasing focus from actors across society on climate change and the urgent need for both individuals and corporations to reduce their impact on the environment, operators can no longer choose to deploy a technological approach just because they have always done it that way. Operators must take control of the environmental impact of their business. They must stand accountable in their society, amongst their customers and peers. They must demonstrate proactive measures to reduce power consumption and get to a carbon neutral status to maintain parity with the larger operators in their market. They must also commit to strategies that will see them achieve a Net-Zero carbon status where they are on a path to reverse the environmental damage their company has caused historically. With an expected lifespan of at least 10 years for any active equipment placed in an operator’s network, it is vital that the architectural and technological selection choices mirror the 10-year environmental strategies of the business.
What is Active Ethernet?
Active Ethernet is a fiber access technology built on a point-to-point fiber architecture, in which there is a direct connection between each OLT port and an ONU on the end of that fiber strand. In such a solution, an operator can deliver Gigabit speeds to every subscriber without being concerned with the use of a shared resource, as is the case with PON solutions.
A point-to-point architecture dictates that there needs to be an active port on the OLT allocated solely to that subscriber for every end subscriber. While this is great from a bandwidth allocation standpoint, providing certainty regarding the capacity from that port to the end-user can be challenging. This certainty of capacity is often cited as justification for continuing with point-to-point fiber deployments; however, this is a fallacy, as the Active Ethernet OLT equipment shares in a similar fashion to a passive PON splitter a finite amount of uplink capacity amongst all the users. It is not economical to provide dedicated uplink capacity from the OLT that matches the access capacity sold across all the end-users. Hence even in an Active Ethernet network, the capacities are shared.
From a fiber management perspective, point-to-point Active Ethernet can be a nightmare. Frequently consuming between 10 and 20 times the amount of cable handling space in central exchange buildings, cable ducts, and cable distribution cabinets in the field, point-to-point architectures drive real and substantial costs for operators.
A close look at the number of splice points needed will also point to inefficiencies of about 100% relative to the same needed for a PON solution – 128 splice points versus 66 splice points needed in a PON based solution. The greater the number of splice points, the greater are the number of points of failure.
Making a Case for XGS-PON vs. Active Ethernet
PON arrived much later after few operators had already got their point-to-point deployments underway. Moving to a PON architecture proved very expensive at that time, especially given that in the early days of APON and BPON, PON as an approach versus a point-to-point solution was inferior. Even when Gigabit PON (GPON) first emerged with 2.5 Gbps downstream capacity and 1.25 Gbps upstream capacity, the choice was anything but clear for many operators. This was primarily attributed to the asymmetry associated with GPON and the issue of bandwidth sharing, which implied that guaranteeing gigabit service to a subscriber over a PON solution was difficult because the active port on an OLT was a shared resource between several subscribers.
In 2010, ITU-T introduced XGS-PON (G.9807.1) with 4x downstream (10 Gbps) and 8x upstream capacity (10Gbps) of GPON. ADTRAN was a major proponent of XGS-PON and had a strong influence on its standardization by ITU. Being a PON solution, XGS-PON benefited from the efficiencies of a point-to-multipoint architecture but enabled operators to assure Gigabit and multi-Gigabit speeds to end subscribers. Falling transceiver costs and the availability of multiple ONU chipset providers are making XGS-PON the technology of choice for many operators, as is indicated in the following forecast report presented by Omdia.
Advances in transceiver optical technology that enables simultaneous operation of GPON and XGS-PON on the same active port on an OLT also referred to as Combo PON, brings amazing flexibility in deployment scenarios for operators to further improve efficiencies in fiber optic deployment.
XGS-PON benefits from sufficient volumes that the associated transceiver cost has come down the cost curve far enough, enabling XGS-PON to be a credible and viable alternative to Active Ethernet electronics.
Comparatively, the options for an analogous a 10-Gigabit capable Active Ethernet solution isn’t very attractive, as 10-gigabit ONU suppliers are fewer in number, which renders the cost of ONUs to be exponentially higher, and expenses in electricity associated with having to support a larger number of active ports on the OLT are an order of magnitude higher.
The backdrop of the current and future costs of power and space are helping bring focus to the discussion. The rising need for marketers to have a multi-gig service offering to demonstrate the technical caliber of their networks is forcing the operators to do something new. Operators must either upgrade their Active Ethernet network to support 10GE or take the opportunity to move to a PON architecture and use symmetric XGS-PON.
Is There a Better Solution?
Operators who want to avoid a rip-and-replace of old networks on Active Ethernet but want to jump over to PON can do so by using a coexistence element (CEx) module. The CEx module multiplexes the two signals as each operates on a different wavelength. The ability to multiplex light on a single fiber strand enables operators to make the most of their investment in fiber and leverage the highest returns through the versatility and capacity of XGS-PON.