Optical fiber has been in use for many years to build data communications networks. The Internet backbone and undersea cables use fiber.
Optical fiber cable has a series of advantages when compared with copper cables.
Signal attenuation of fiber is much less than copper so a cable run can be much longer.
The data capacity of fiber is much higher than copper cables.
The data traveling along fiber has no interference from surrounding magnetic fields, unlike copper cables.
The data velocity is higher for fiber than for copper cables so latency is lower.
Many data centers use #fiber cables to interconnect LAN segments when distances exceed the maximum length of Ethernet copper cables (100m).
The inter-LAN connection uses two Ethernet to fiber bridges and the data is sent over the fiber link in Ethernet format. The connection can use Gbit or 10Gbit Ethernet to fiber.
Internet service providers have built networks using existing copper cables installed for voice or TV. Phone companies have installed ADSL #networks over twisted pair copper to a home router and cable companies have installed DOCSIS networks over coaxial cable to a cable modem installed in the home. The problem that the phone and cable companies face is the limited transmission distance. ADSL can be extended in a 3Km radius around the central office, and cable distances are similar. Distances can be extended but powered repeater equipment is required and the number of repeater hops is limited. In many cases the Telcos and cable companies have been installing fiber trunk circuits to neighborhood hubs where the data signal is converted from the fiber trunk circuit to copper cables.
Fiber cable distances are much greater than for copper. A single fiber can communicate over a distance of 60Km while a fiber that is optically split into drop cables for homes can extend to 20 Km.
Fiber has been used to build out Internet service provider networks for fiber to the home (#FTTH) in areas where there is no existing copper cable however service providers with copper networks have deployed faster transmission technologies over copper to maximize the return of the copper cable networks rather than make the investment to upgrade all networks to fiber.
Meanwhile customers want faster Internet data services. The pandemic lockdown created hybrid working which in turn put pressure on service providers to improve the speed of home Internet services. The mobile wireless companies took advantage of this situation by offering fixed broadband over 5G wireless and many ADSL and cable customers switched to 5G fixed broadband wireless services. The biggest selling products for IT distribution businesses during the pandemic were 5G wireless modems and antennas.
The federal government dramatically changed the situation by launching a plan to connect every home in the USA with #opticalfiber and required providers to guarantee a fast minimum data speed. The proposal for connecting everyone with fiber is that better connectivity will improve the productivity of citizens and so the USA will become more competitive in world markets. The funding that the federal government provided has persuaded many established Telcos and cable companies to upgrade their networks to fiber. Wireless Internet service providers (WISP’s) are also in the process of switching their networks to fiber as they can offer higher data speeds with a more reliable service; wireless is affected by atmospheric and terrestrial conditions. Many new companies have been established to become fiber installers and possibly future Internet service providers.
Installing optical fiber cables has a very high cost. Cables are either installed below ground, which requires trenches to be dug, or else strung along existing utility poles. A construction company has to install fiber cable using heavy machinery. In addition many types of permits have to be pulled to install fiber over long distances, which requires a significant bureaucracy. Often the reason that a cable cannot be installed is due to problems with bureaucracy rather than a technical or geographic reason.
An Internet service provider will follow a specific design for the construction of a fiber network to the home (FTTH) that is determined by the type of equipment available for the installation. The popular fiber network design is called a passive optical network (PON) because the components between the central office and the home are passive, they do not require power. This is in contrast with large ADSL and cable networks that require powered repeaters, which are the boxes with the humming noise along the side of a road. These are called active networks, as the network requires active or powered components. Active networks cost much more to build out and operate. An active hub has to be provided with metered power from the electricity grid. The hub needs backup batteries to power the network equipment in the case of an outage. The powered equipment gets hot and so the hub cabinet requires cooling and as the cabinet is hermetically sealed to protect the electronic components then a heat exchanger is required to transfer the heat out of the cabinet. Power equipment sometimes breaks and batteries need replacing so the maintenance cost of the powered network hub is high.
In contrast the fiber ISP central office has fiber connections to neighborhood passive optical splitters and then drop cables connect each house. The fiber network is illustrated in the next diagram.
A wholesale provider installs a high speed Internet backbone connection at a central office. The circuit may have a speed of 10 Gbits/s The Internet router connects to a fiber optical line terminal (OLT) with either a 10Gb Ethernet connection or a 10Gb Ethernet over fiber connection. The OLT has multiple fiber connections; the number depends on the OLT model selected. Each OLT fiber port connects to a neighborhood optical splitter hub. Fiber drop cables are then extended from the hub to each home and terminate at an optical network terminal (ONT) usually mounted on an outside wall of the home and powered from the home's electricity. The ONT converts the fiber connection to an Ethernet connection for devices in the home. A wireless router will be connected to the ONT for the home WiFi network.
The passive optical network can be one of two types; Ethernet passive optical network (EPON) or gigabit passive optical network (GPON). EPON is limited to 1Gb/s speed although there are 10Gb/s EPON versions. GPON has a 2.5Gb/s download speed and 1.25GB/s upload speed. Some GPON installations are symmetrical, 2.5Gb/s down and up. EPON implements the IEEE 802.3 Ethernet standard while GPON implements the International Telecommunications Union (ITU-T) G.984 standard with synchronous optical networking (SONET) and synchronous digital hierarchy (SDH) protocols to transfer multiple digital bit streams using asynchronous transfer mode (ATM) encoding. GPON supports multiple types of data transmission that includes Internet data, voice telephony and video streaming (Telco’s call this triple-play), which permits the implementation of quality of a service (QoS) to prioritize different data streams. Ethernet has one data stream and so additional equipment such as a VLAN router is required with VLAN equipped devices in the home to implement a QoS strategy. Most of the fiber equipment currently manufactured is for the GPON standard as it is considered superior to EPON with the same cost. Therefore many installations are built using the GPON standard.
Optically splitting one fiber cable into many drop cables to each home is very efficient and minimizes the cable installation work. However the attenuation at the optical splitter reduces the total maximum distance of the fiber. The type of optical splitter is determined by the split-ratio required. A popular splitter is one to 32 splits; this means that one fiber from the central office is split optically into 32-drop fibers to homes. In addition to 1:32, splitters are available for 1:8 1:16, 1:64, and 1:128. However the greater the number of splits, the shorter the maximum distance between the central office and the home. With a split ratio of 1:16 the maximum distance between the central office and the home is 20Km. With a split ratio of 1:32 the maximum distance between the central office and the home is reduced to 10Km.
The ISP can overcome distance limitations by installing a multi-fiber cable from the central office to the optical splitter hub. Each fiber connects to a port on the OLT at the central office. An example with 8 fibers in the cable; each fiber can connect to a 1:16 splitter so a total of 128 homes can be connected at a distance of 20Km from the central office using one cable from the central office to the optical splitter. The installation location of the splitter is determined by the fiber cable installation. If the cable is strung on utility poles then the fiber splitter can be mounted on the utility pile or hung from the supporting wire. If the cable is underground then the splitter can be installed in an underground enclosure with an access cover. There are many pre-fabricated components for all types of fiber installations.
When the fiber network is built out from the central office to homes, the installation is only half completed. Each home is a paying subscriber and it is necessary to have additional technical and management infrastructure to charge the subscribers for the Internet service. Some features of the management infrastructure are listed below.
Add a new subscriber to the management system.
Provision the subscriber, which means start the process of connecting the subscriber to the network.
Manage the workflow; create a work order for technical staff with instructions about the subscriber installation.
Set the subscribers rate plan, this is the maximum speed of data that the subscriber has chosen to receive based on the cost.
Charge the subscriber for the service each month.
Disable the subscriber’s service temporarily in the case of a late payment and reconnect the service after the payment is received.
Maintain a help desk to provide support for the subscribers.
Provide a customer relationship (CRM) portal for the subscriber to check the account status, review past invoices and make payments on-line.
Monitor the operation of the network, if a failure is detected alert technical staff and generate a repair work order.
Management of the Internet service requires two components, one is hardware and one is software, to be added to the network. The hardware component is called the broadband network gateway (BNG). The BNG has a throughput of 10Gb/s and is installed in the network between the Internet backbone router and the fiber OLT. All subscriber data traffic passes through the BNG from one or more OLT’s. This is shown in the next diagram.
The BNG is controlled by the management software and has the following specific tasks.
Activate the subscribers network access after installation of the ONT.
Authenticate the subscriber onto the network.
Set the subscriber’s maximum data rate (the rate plan).
Enable or disable the subscriber according to the status of the billing system account.
Test the circuit through to the subscribers ONT when requested.
Monitor the network components for failure and alert the management system if this occurs.
The final step is to incorporate the management software into the system. The next figure illustrates the management system features.
The management system shown in the diagram is hosted in the cloud. The staff login to the cloud server to manage the service delivery to the customers. The areas of activity and responsibilities of each staff member are shown in the diagram.
The cloud system can manage multiple BNG’s so the ISP can expand geographically with many central offices to cover a much larger area than the maximum distance of the fiber will permit.
If the ISP wishes to add a triple-play service (Internet, phone and video) then it is necessary to add infrastructure and the administration system features to bill the additional services of voice and video.
One important decision when configuring the system is the Contention Ratio. This parameter determines by how many times the backbone bandwidth can be oversold. This is described using an example below.
Assume that the backbone circuit is 10Gb/s and each subscriber has a 100Mb/s rate plan. Dividing the backbone speed by the subscriber circuit speed determines that the backbone bandwidth can be divided between 100 subscribers. However we can connect many more subscribers to the backbone circuit.
ISP’s know that the average data speed of the home with four people using the Internet will be about 5Mb/s. If we divide 10Gb/s by 5Mb/s we get 2000 subscribers. In this case the contention ratio will be 100:2000 or 1:200. Each subscriber may have peak traffic speeds when downloading a large file but these will be of short duration. The contention ratio can be higher when the subscriber maximum data speed (rate plan) is a small percentage of the backbone data speed.
The ISP must monitor network data use as subscribers are added to the network to calculate the ideal contention ratio for the subscriber base.
There are many companies that offer fiber equipment, infrastructure components, the BNG and the software management system. The companies can be located using Google. The features of the easyFTTH system (www.easyftth.com) were used to illustrate this article.
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