This section examines the key technologies that are being used to construct today’s broadband networks. Although each of these technologies can be used throughout the supply chain, they tend to be used most heavily in the international, domestic backbone, and metropolitan link segments. Each of these levels is discussed in more detail later in this chapter, as are the technologies that support wireline and wireless local access networks.

5.3.1 Fiber Optic

Much of the Internet’s content travels via fiber optic cables, particularly for long-haul transmissions. Fiber optic cable provides closed circuit transmissions with very large bandwidth and at very high transmission speeds. These two complementary features occur because these cables, made of thin strands of coated glass, can transmit signals modulated over laser-generated beams of light. Rather than transmit using lower-frequency radio waves, fiber optic cables operate at the frequencies of light, where the spectrum is larger than in the radio frequencies (the visible spectrum contains more than 100,000 gigahertz, GHz), making it possible to carry large volumes of traffic at a rate of up to several hundred gigabits per second (Gbit/s) or even terabits per second (Tbit/s). Additionally, carriers can transmit traffic at several different frequencies using a technology called Dense Wave Division Multiplexing (DWDM). Multiplexing makes it possible for carriers to aggregate traffic onto a shared channel. Demultiplexing unpacks and separates the aggregated traffic back into separate transmission streams for delivery to the intended recipients.

Because of the high expense incurred when installing cable across an ocean floor or buried underground, carriers deploying fiber optic cables typically install dozens of glass strands into one cable. Initially, not all of these individual fibers will be used; carriers can activate (“light”) individual strands as demand grows. Installed but unused “dark fiber” can be activated later, as required. In addition to installation costs, the comparative disadvantages of using fiber optic cables over copper lie primarily in the cost of the equipment and labor. While this technology can interconnect with existing copper networks, additional cross-connect switching equipment must be installed. Carriers with a large installed copper wire network may undertake a cost-benefit analysis and conclude that simply retrofitting and upgrading the existing network may help to conserve capital in the short run. Carriers opting to upgrade will install replacement fiber optic cable first on backbone routes with high volumes of traffic. As demand for bandwidth grows and investments can be justified, fiber progressively replaces copper cables throughout the network, reaching closer to the end users.

At present, most backbone networks are fiber based, even in developing economies, and the use of fiber in metropolitan and “middle-mile” links is rapidly increasing as well, particularly in developed countries. As the demand for wireless broadband grows, there is also increasing use of fiber to provide backhaul from cell sites to mobile carrier switching facilities. Fiber penetration in the local access network is still very limited, even in developed countries. But the emerging trend, especially for building out new housing and commercial developments, is to install fiber from the outset. Several deployment scenarios are possible for fiber optic cable:

• International connectivity: international undersea networks and international terrestrial networks
• National backbones: national undersea networks and national overland backbone networks
• Metropolitan rings and cellular backhaul
• Subscriber access: fiber to the premises.

5.3.2 Satellite

In the broadband supply chain, satellites are used primarily for international connectivity and some domestic backbones; they are used less frequently for metropolitan and local access networks. Geostationary communication satellites receive and transmit information from orbital slots located 35,786 kilometers (22,282 miles) above Earth. At this height, the satellite appears in a fixed location when viewed from Earth; this stable location is an advantage since subscriber satellite dishes do not need to move or track the satellite.

Satellites’ communication capabilities can be analogized to an invisible “boomerang” or “bent pipe,” with signals transmitted (uplinked) to the satellite, which then relays (downlinks) them back to Earth. Data are transmitted via the communication satellite’s transponders. Satellites usually have between 24 and 72 transponders, with a single transponder capable of handling up to 155 Mbit/s (megabits per second).4 Intelsat, “Satellite Basics,” www.intelsat.com/resources/satellite-basics/how-it-works.asp. Next-generation satellites will offer speeds in excess of 100 Gbit/s.5 ViaSat, “Meeting the Demand for Media-Enabled Satellite Broadband Satellite Services,” www.viasat.com/files/assets/Broadband%20Systems/MediaEnabledSatellite9-09.pdf.

From a geosynchronous vantage point, satellites can transmit signals covering as much as one-third of the Earth’s surface. This stable “footprint” coverage makes satellites an ideal medium for distributing television (TV) and Internet content on both a single point-to-point basis and a point-to-multipoint basis. Today’s advanced satellites also make use of “spot beams” (principally in the Ka band) that allow higher power to be concentrated in specific regions to improve bandwidth and signal quality. These beams can also be steered or reconfigured to match bandwidth to specific areas of demand.

A satellite network can be configured in various ways, ranging from a simple one-direction link to a more complex mesh network. Communications with the satellite take place via an earth station or individual antenna. The size of the antenna depends partially on the frequency being used and also affects the volume of information that can be exchanged with the satellite. Large antennas are typically installed at earth stations for high-bandwidth applications, while smaller antennas, such as very small aperture terminals (VSAT) or direct to home (DTH) dishes are used for applications such as lower-bandwidth Internet access in rural areas or satellite TV reception. An estimated 3 million commercial VSATs are used for commercial and consumer purposes around the world, with the majority supporting broadband Internet or high-data-rate services.6 Telesat, “Satellite’s Growing Role in Data Networking,” www.telesat.ca/en/Satellites_Growing_Role_in_Data_Networking.

Each communication satellite requires several hundred million dollars in investment to cover its construction, insurance, launch, and tracking. These satellites have a limited usable life (usually around 20 years) because operators cannot make repairs or add fuel to the propulsion motors to keep them in proper orbit and pointed at the correct angle toward Earth. Additionally, satellites have comparatively less transmission capacity than terrestrial options, such as fiber optic cables. The large distance between the satellite and users on Earth also results in delays, known as latency, due to the time it takes for instructions to reach a satellite and content to arrive on Earth. Despite these limitations, satellites excel in their ability to distribute broadband content, such as television, to many locations and are advantageous for different developing-country characteristics such as archipelagos or difficult terrain as well as for emergency and disaster situations.

5.3.3 Microwave

“Microwave” systems are named for the wavelengths they use to communicate and are generally implemented using frequencies between 6 GHz and 38 GHz (Hansryd and Eriksson 2009). Microwave systems provide a point-to-point or point-to-multipoint broadband transmission option using very high frequencies that transmit a highly directional, pencil-thin beam of energy. Unlike satellite beams that cover thousands of square miles, microwave is usually used to transport broadband data signals from one specific location to another over relatively short distances (generally 40–70 kilometers, depending on the frequency used). The installation of several microwave receiving and transmission facilities arranged in a chain is needed for longer links, with each transmission link known as a “hop.”

Microwave radio transmissions use antennas that concentrate radio energy to generate a naturally amplified signal. To achieve this signal gain, the very high frequencies of microwave—in the single or multiple GHz range—are concentrated using antennas shaped in a parabola. With advanced modulation, typical microwave networks can support up to 500 Mbit/s. In 2010 Ericsson demonstrated a microwave radio connection with a capacity of 2.5 Gbit/s (Ericsson 2010). WiMAX (Worldwide Interoperability for Microwave Access) is a specific type of microwave standard that is designed for connecting end users, but it can also be used for backbone connectivity at high costs. Ranges up to 120 kilometers (75 miles) have been advertised, with speeds up to 100 Mbit/s.7 RADWIN, “IP Backhaul,” www.radwin.com/Content.aspx?Page=ip_backhaul.

Before the advent of fiber optic cables, microwave systems were a leading provider of backbone and metropolitan (long-distance) connectivity. As fiber technology improved and costs fell, however, operators began to replace their microwave systems with fiber cables. This trend started on the highest-volume traffic routes and continues to push into more local parts of the network. Today, microwave technology is used almost extensively for point-to-point backhaul and last-mile line-of-sight communications, especially when available capital expenditures are limited. The main advantages of a microwave system are its relative immunity to interference, its straightforward deployment, and easy reconfiguration. Thus it can be a practical alternative in some cases compared to the cost and logistics of laying cable.8 NEC, “Pasolink (Egypt),” www.nec.com/global/onlinetv/en/business/pasolink_l.html#NF-project. The main drawbacks are that it requires line-of-sight and transmission capacity may be too limited for heavy broadband uses.

5.3.4 Copper

Another terrestrial technology still in use for long-haul transmission is copper wire. While fiber optic cable will eventually replace legacy copper, replacement costs create financial incentives to use and upgrade existing networking technology. Copper wire offers significantly less channel capacity and commensurately slower bit transmission speeds than other media, but it can often suffice for low-traffic routes. Even in developed nations, backbone fiber optic routes may exist only for links between major cities, with copper wire links still serving smaller towns and rural areas. A recent issue with copper cabling is theft, due to the high price of copper (Gallagher 2010).