Reality → Tech → Internet → Infrastructure
The Net's massive physical infrastructure is accumulated from bits and pieces of greatly varying size and type provided by a plethora of participants [1] . Typical components include:
To access the Net, a router establishes a duplex connection over the 'last mile' with the nearest server of the internet service provider (ISP) [13] . The residential router is usually an integral part of a 'gateway' [14] which frames internet packets and transmits them in line with TCP/IP protocols [15] .
Phone and cable companies, internet infrastructure and service companies, corporations, universities, and governmental institutions are among the owners of Wide Area Networks and portions of the Internet Backbone. In addition, all Local Area Networks and single devices connected to the Net form part of the physical Net.
A server is a stripped down computer (no GUI, audio, and USB) focussed on high performance (fast CPU, large RAM), high reliability (through built-in redundancy), 24/7 availability, and compactness for standard rack mounting. For further reduction of space and energy use, blade servers packed in adapted enclosures have become popular in large enterprises.
Big data centers (e.g., Google, Microsoft) may require more than 100 MW power, capital investment exceeding $5 billion, and employ almost no people. Power use efficiency and water use for cooling are important operating parameters (e.g., see Facebook Prineville data center). Leasing of facilities and services through colocation and tight management are common (e.g., see Equinix).
Routers send packets to the next point (node), while switches send them to specific destination points. Bridges connect different subnets (segments), and gateways (protocol converters) connect segments that run under different protocols. Other devices and systems may be installed at nodes, e.g., repeaters to amplify signals, or multiplexers to maximize data transmission.
A Coaxial cable (a single transmission line for many frequency channels carrying TV, Internet, and telephone signals) usually connects home TV and cable modem to the cable company's hybrid fibre-coaxial network. High-speed Ethernet connections of enterprise and institutional networks use twisted pair and/or optical fiber cables. Modern Gigabit Ethernet may transmit at bit rates exceeding 100 Gbit/s over distances ranging from 10 m to more than 40 km, depending on the type of cable and protocol.
Long-distance optical fiber cables conduct light (invisible infrared of about 200 THz frequency or 1.5 μm wavelength) in hair-thin (10 μm) single-mode fibers of highly purified glass through total internal reflection (see FOA Guide). To transmit digital data, the carrier frequency can be modulated with bitstreams (voltage pulses) at rates up to 100 Gbit/s, allowing the simultaneous transmission of 200-300 channels through a single fiber ("1 g fiber replaces 10 kg copper"). The very high bit rates and cable lengths of 100 km between EDFA repeaters have been made possible through dramatic advances in solid states physics and manufacturing processes. Original groundbreaking work, carried out by Kao already in the 1960s, was honored with one half of the 2009 Nobel Prize in Physics (see also Lighting the way to a revolution).
Ocean-crossing underwater cables, originally built for telegraph and telephone communication, transmit now primarily the high-volume, rapid data streams of the global Internet. The first successful telegraph cable transmitted 8 words per minute (equivalent to 300 Morse code bits per minute, or 5 bit/s), while the transmission capacity of a modern fiber optic cable amounts to tens of Tbit/s (an increase by 13 orders of magnitude). Historical milestones of trans-Atlantic cable connections include: 1858-1866 first telegraph cable (laid by Great Eastern); 1956 first telephone cable (TAT-1); 1988 first fiber optic cable (TAT-8); 1996 optical amplifiers (TAT-12/13); and 2001 wavelength-division multiplexing (TAT-14). Other submarine optical cables cross the Pacific and Indian oceans and also surround Africa and South America. Due to their superior carrying capacity and high reliability, modern optical cables also superseded telecommunication via satellite.
Cellular networks were originally conceived for mobile telephony and integration with the public fixed telephone net, but since the advent of smartphones and tablets, cellular networks have to cope with rapidly increasing data transfer from the Internet. A countrywide grid of wireless cell sites (often towers) now links with the fiber optic terrestrial backbone of the Internet. Adjoining cells work at different frequencies, but same frequencies are reused when cells are sufficiently apart. The distance between cells varies from less than 1 km to several tens of kilometers depending on user density and technology (e.g., GSM-based nets (carrier frequency up to 900 MHz, most common standard worldwide) can have spacing up to 35 km, whereas CDMA (frequency higher than 2 GHz) requires tighter spacing). To meet capacity demand in urban areas, small and very small cells with low power output but large bandwidth fill the spacing between larger cells.
Wi-Fi, wherever available, is the preferred method of Internet data transfer for smartphones and tablets, due to lower cost and higher speed (a 802.11ac Wi-Fi connection theoretically can provide data rates exceeding 1 Gbit/s, though in practice they are much lower, in some cases even below a good cellular LTE connection).
An increasing number of apps for smartphones and tablets integrate Web and GPS data. The Global Positioning System employs 24-32 navigation satellites (24 needed, up to 8 for redundancy). Arranged in 6 different orbital planes, they circle the Earth at 20 km altitude in 12 hours, always providing a constellation of at least 6 satellites in line of sight from any point (except the poles) on Earth. The satellites continuously send signals with encoded time and position data. Receivers integrated into phones and tablets continuously capture these signals, from which special processor circuits calculate the device's position as well as direction and speed of movement. The process depends on precision measurement of signal transit time, taking into account relativity effects.
Mobile satellite phones allow poor, low-bandwidth Internet access from anywhere via geostationary (36,000 km altitude) or, alternatively, low Earth orbit (e.g., 800 km altitude Iridium) satellites. In rural US, Broadband residential satellite Internet access (roundtrip signal travel time (latency) 0.5 s, maximum data rate 25 Mbit/s) is available via geostationary satellites (e.g., Hughes). As potentially lower-cost alternatives, futuristic projects such as Google's Loon or solar-powered drones are being explored.
The access server (BRAS) establishes a connection with the ISP network and from there, through another router, with the Internet. Data transfer speed of the point-to-point connection between the residential client router and the BRAS is restricted by the weakest physical link of the ' last mile'. While routers with a design rating of several gigabits per second (Gbps) are available, the average download speed of fixed broadband service is only about 70 Mbps in the US, where rates of 150 Mbps and higher are considered very fast (upload rates are much lower).
The 'gateway' can be described as a router cable modem combo. A modem transcribes, through modulation, data onto a high-frequency carrier signal; when receiving data, the modem retrieves, through demodulation, the transcribed data from the carrier signal. Cable modems use a narrow (6 MHz) channel reserved for Internet data flow among the many TV channels (also 6 MHz, each) transmitted simultaneously through a coaxial or fiber cable according to the Data Over Cable Service Interface Specification (DOCSIS) standard.
Under IEEE 802.11 standards, channels are automatically selected for low interference and high speed (a connection in the 5 GHz band can achieve data rates exceeding 1 Gbit/s). The service provider assigns a single (public) IP address for the local network, adding firewall protection for connected devices by hiding their individual (private) addresses generated by the local router.