Transcript
Local Area Networks
Main articles: Local Area Network and Point-to-point protocol over Ethernet Local area networks (LANs) provide Internet access to computers and other devices in a limited area such as a home, school, computer laboratory, or office building, usually at relatively high data rates that [23] typically range from 10 to 1000 Mbit/s. There are wired and wireless LANs. Ethernet over twisted pair cabling and Wi-Fi are the two most common technologies used to build LANs today, but ARCNET, Token Ring, Localtalk, FDDI, and other technologies were used in the past. Most Internet access today is through a LAN, often a very small LAN with just one or two devices attached. And while LANs are an important form of Internet access, this begs the question of how and at what data rate the LAN itself is connected to the rest of the global Internet. The technologies described below are used to make these connections. [edit]Dial-up
access
"Dial up modem noises"
Typical noises of a dial-up modem while establishing connection with a local ISP in order to get access to the Internet.
Problems listening to this file? See media help.
Main article: Dial-up Internet access Dial-up access uses a modem and a phone call placed over the public switched telephone network (PSTN) to connect to a pool of modems operated by an ISP. The modem converts a computer's digital signal into an analog signal that travels over a phone line's local loop until it reaches a telephone company's switching facilities or central office (CO) where it is switched to another phone line that [24] connects to another modem at the remote end of the connection. Operating on a single channel, a dial-up connection monopolizes the phone line and is one of the slowest methods of accessing the Internet. Dial-up is often the only form of Internet access available in rural areas as it requires no new infrastructure beyond the already existing telephone network, to connect to the Internet. Typically, dial-up connections do not exceed a speed of 56 kbit/s, as they are primarily made using modems that operate at a maximum data rate of 56 kbit/s downstream (towards the end user) and [10] 34 or 48 kbit/s upstream (toward the global Internet). [edit]Broadband
access
The term broadband includes a broad range of technologies, all of which provide higher data rate access to the Internet. These technologies use wires or fiber optic cables in contrast to wireless broadband described later. [edit]Multilink dial-up
Main article: Channel bonding Multilink dial-up provides increased bandwidth by bonding two or more dial-up connections together and [25] treating them as a single data channel. It requires two or more modems, phone lines, and dial-up accounts, as well as an ISP that supports multilinking - and of course any line and data charges are also doubled. This inverse multiplexing option was briefly popular with some high-end users before ISDN, DSL and other technologies became available. Diamond and other vendors created special modems to [26] support multilinking. [edit]Integrated Services Digital Network (ISDN) Main article: Integrated Services Digital Network Integrated Services Digital Network (ISDN), a switched telephone service capable of transporting voice and digital data, is one of the oldest Internet access methods. ISDN has been used for voice, video conferencing, and broadband data applications. ISDN was very popular in Europe, but less common in North America. Its use peaked in the late 1990s before the availability of DSL andcable [27] modem technologies. Basic rate ISDN, known as ISDN-BRI, has two 64 kbit/s "bearer" or "B" channels. These channels can be used separately for voice or data calls or bonded together to provide a 128 kbit/s service. Multiple ISDNBRI lines can be bonded together to provide data rates above 128 kbit/s. Primary rate ISDN, known as ISDN-PRI, has 23 bearer channels (64 kbit/s each) for a combined data rate of 1.5 Mbit/s (US standard). An ISDN E1 (European standard) line has 30 bearer channels and a combined data rate of 1.9 Mbit/s. [edit]Leased lines Main article: Leased line Leased lines are dedicated lines used primarily by ISPs, business, and other large enterprises to connect LANs and campus networks to the Internet using the existing infrastructure of the public telephone network or other providers. Delivered using wire, optical fiber, and radio, leased lines are used to provide Internet access directly as well as the building blocks from which several other forms of Internet access [28] are created. T-carrier technology dates to 1957 and provides data rates that range from 56 and 64 kbit/s (DS0) to 1.5 Mbit/s (DS1 or T1), to 45 Mbit/s (DS3 or T3). A T1 line carries 24 voice or data channels (24 DS0s), so customers may use some channels for data and others for voice traffic or use all 24 channels for clear channel data. A DS3 (T3) line carries 28 DS1 (T1) channels. Fractional T1 lines are also available in multiples of a DS0 to provide data rates between 56 and 1,500 kbit/s. T-carrier lines require special termination equipment that may be separate from or integrated into a router or switch and which may be [29] purchased or leased from an ISP. In Japan the equivalent standard is J1/J3. In Europe, a slightly different standard, E-carrier, provides 32 user channels (64 kbit/s) on an E1 (2.0 Mbit/s) and 512 user channels or 16 E1s on an E3 (34.4 Mbit/s). Synchronous Optical Networking (SONET, in the U.S. and Canada) and Synchronous Digital Hierarchy (SDH, in the rest of the world) are the standard multiplexing protocols used to carry high data rate digital bit streams over optical fiber using lasers or highly coherent light from light-emitting diodes (LEDs). At lower transmission rates data can also be transferred via an electrical interface. The basic unit of framing is an OC-3c (optical) or STS-3c (electrical) which carries 155.520 Mbit/s. Thus an OC-3c will carry three OC-1 (51.84 Mbit/s) payloads each of which has enough capacity to include a full DS3. Higher data
rates are delivered in OC-3c multiples of four providing OC-12c (622.080 Mbit/s), OC-48c (2.488 Gbit/s), OC-192c (9.953 Gbit/s), and OC-768c(39.813 Gbit/s). The "c" at the end of the OC labels stands [28] for "concatenated" and indicates a single data stream rather than several multiplexed data streams. The 1, 10, 40, and 100 Gigabit Ethernet (GbE, 10GbE, 40GbE, and 100GbE) IEEE standards (802.3) allow digital data to be delivered over copper wiring at distances to 100 m and over optical fiber at [30] distances to 40 km. [edit]Cable Internet access Main article: Cable Internet access Cable Internet or cable modem access provides Internet access via Hybrid Fiber Coaxial wiring originally developed to carry television signals. Either fiber-optic or coaxial copper cable may connect a node to a customer's location at a connection known as a cable drop. In a cable modem termination system, all nodes for cable subscribers in a neighborhood connect to a cable company's central office, known as the "head end." The cable company then connects to the Internet using a variety of means – usually fiber [31] optic cable or digital satellite and microwave transmissions. Like DSL, broadband cable provides a dedicated continuous connection with an ISP. Downstream, the direction toward the user, bit rates can be as much as 400 Mbit/s for business connections, and 100 Mbit/s for residential service in some countries. Upstream traffic, originating at the user, ranges from 384 kbit/s to more than 20 Mbit/s. Broadband cable access tends to service fewer business customers because existing television cable networks tend to service residential buildings and [32] commercial buildings do not always include wiring for coaxial cable networks. In addition, because broadband cable subscribers share the same local line, communications may be intercepted by neighboring subscribers. Cable networks regularly provide encryption schemes for data traveling to and [31] from customers, but these schemes may be thwarted. [edit]Digital subscriber line (DSL, ADSL, SDSL, and VDSL)
DSL technologies Standard ADSL ANSI T1.413 Issue 2 ITU G.992.1 (G.DMT) ITU G.992.2 (G.Lite) ADSL2 ITU G.992.3 ITU G.992.4 ITU G.992.3 Annex J ITU G.992.3 Annex L ADSL2+ ITU G.992.5 ITU G.992.5 Annex M HDSL HDSL2 ITU G.991.1
Main article: Digital subscriber line Digital Subscriber Line (DSL) service provides a connection to the Internet through the telephone network. Unlike dial-up, DSL can operate using a single phone line without preventing normal use of the telephone line for voice phone calls. DSL uses the high frequencies, while the low (audible) frequencies of the line are left free for regular [10] telephone communication. These frequency bands are subsequently separated by filters installed at the customer's premises.
IDSL MSDSL PDSL RADSL SDSL
SHDSL ITU G.991.2 DSL originally stood for "digital subscriber loop". In telecommunications marketing, the term digital subscriber line is widely understood to UDSL mean Asymmetric Digital Subscriber Line (ADSL), the most commonly VDSL ITU G.993.1 installed variety of DSL. The data throughput of consumer DSL services typically ranges from 256 kbit/s to 20 Mbit/s in the direction to the VDSL2 ITU G.993.2 customer (downstream), depending on DSL technology, line conditions, and service-level implementation. In ADSL, the data throughput in the upstream direction, (i.e. in the direction to the service provider) is lower than that in the downstream [33] direction (i.e. to the customer), hence the designation of asymmetric. With a symmetric digital [34] subscriber line (SDSL), the downstream and upstream data rates are equal.
Very-high-bit-rate digital subscriber line (VDSL or VHDSL, ITU G.993.1) is a digital subscriber line (DSL) standard approved in 2001 that provides data rates up to 52 Mbit/s downstream and 16 Mbit/s [36] [37] upstream over copper wires and up to 85 Mbit/s down- and upstream on coaxial cable. VDSL is capable of supporting applications such as high-definition television, as well as telephone services (voice over IP) and general Internet access, over a single physical connection. VDSL2 (ITU-T G.993.2) is a second-generation version and an enhancement of VDSL. Approved in February 2006, it is able to provide data rates exceeding 100 Mbit/s simultaneously in both the upstream and downstream directions. However, the maximum data rate is achieved at a range of about 300 meters and performance degrades as distance and loop attenuation increases. [edit]DSL Rings Main article: DSL Rings DSL Rings (DSLR) or Bonded DSL Rings is a ring topology that uses DSL technology over existing [39] copper telephone wires to provide data rates of up to 400 Mbit/s. [edit]Fiber to the home Main articles: Fiber to the x and Fiber in the loop Fiber-to-the-home (FTTH) is one member of the Fiber-to-the-x (FTTx) family that includes Fiber-to-thebuilding or basement (FTTB), Fiber-to-the-premises (FTTP), Fiber-to-the-desk (FTTD), Fiber-to-the-curb [40] (FTTC), and Fiber-to-the-node (FTTN). These methods all bring data closer to the end user on optical fibers. The differences between the methods have mostly to do with just how close to the end user the delivery on fiber comes. All of these delivery methods are similar to hybrid fiber-coaxial (HFC) systems used to provide cable Internet access. The use of optical fiber offers much higher data rates over relatively longer distances - up to 150 Mbit/s downstream (toward the end user) and up to several kilometers. Most high-capacity Internet and cable
[38]
[35]
television backbones already use fiber optic technology, with data switched to other technologies (DSL, [41] cable, POTS) for final delivery to customers. Australia has already begun rolling out its National Broadband Network across the country using fiber[42] optic cables to 93 percent of Australian homes, schools, and businesses. Similar efforts are underway [43][44][45][46] in Italy, Canada, and many other countries (see Fiber to the premises by country)., Similar to that, India also started to show its mark in Fiber based connectivity [edit]Power-line Internet Main article: Power-line Internet Power-line Internet, also known as Broadband over power lines (BPL), carries Internet data on a conductor that is also used for electric power transmission. Because of the extensive power line infrastructure already in place, this technology can provide people in rural and low population areas access the Internet with little cost in terms of new transmission equipment, cables, or wires. Data rates [47] are asymmetric and generally range from 256 kbit/s to 2.7 Mbit/s. Because these systems use parts of the radio spectrum allocated to other over-the-air communication services, interference between the services is a limiting factor in the introduction of power-line Internet systems. The IEEE P1901 standard specifies that all powerline protocols must detect existing usage and [47] avoid interfering with it. Power-line Internet has developed faster in Europe than in the U.S. due to a historical difference in power system design philosophies. Data signals cannot pass through the step-down transformers used and so a [47] repeater must be installed on each transformer. In the U.S. a transformer serves a small clusters of from one to a few houses. In Europe, it is more common for a somewhat larger transformer to service larger clusters of from 10 to 100 houses. Thus a typical U.S. city requires an order of magnitude more [48] repeaters than in a comparable European city. [edit]ATM and Frame Relay Main articles: Asynchronous Transfer Mode and Frame Relay Asynchronous Transfer Mode (ATM) and Frame Relay are wide area networking standards that can be used to provide Internet access directly or as building blocks of other access technologies. For example many DSL implementations use an ATM layer over the low-level bitstream layer to enable a number of different technologies over the same link. Customer LANs are typically connected to an ATM switch or a [49][50] Frame Relay node using leased lines at a wide range of data rates. While still widely used, with the advent of Ethernet over optical fiber, MPLS, VPNs and dedicated broadband services such as cable modem and DSL, ATM and Frame Relay no longer play the prominent role they once did. [edit]Wireless
broadband access
Main article: Wireless broadband Wireless broadband is used to provide both fixed and mobile Internet access. [edit]Wi-Fi
Wi-Fi logo
Main articles: Wi-Fi , Wireless LAN , and 802.11 Wi-Fi is the popular name for a "wireless local area network" that uses one of the IEEE 802.11 standards. It is a trademark of the Wi-Fi Alliance. Individual homes and businesses often use Wi-Fi to connect laptops and smart phones to the Internet. Wi-Fi Hotspots may be found in coffee shops and various other [51][52][53] public establishments. Wi-Fi is used to create campus-wide and city-wide wireless networks. Wi-Fi networks are built using one or more wireless routers called Access Points. "Ad hoc" computer to computer Wi-Fi" networks are also possible. The Wi-Fi network is connected to the larger Internet using DSL, cable modem, and other Internet access technologies. Data rates range from 6 to 600 Mbit/s. Wi-Fi service range is fairly short, typically 20 to 250 meters or from 65 to 820 feet. Both data rate and range are quite variable depending on the Wi-Fi protocol, location, frequency, building construction, and [54] interference from other devices. Using directional antennas and with careful engineering Wi-Fi can be extended to operate over distances of up to several kilometers, see Wireless ISP below. [edit]Wireless ISP Main articles: Wireless Internet service provider and Long-range Wi-Fi See also: Mobile broadband, below Wireless ISPs typically employ low-cost 802.11 Wi-Fi radio systems to link up remote locations over great distances, but may use other higher-power radio communications systems as well. Traditional 802.11b is an unlicensed omnidirectional service designed to span between 100 and 150 meters (300 to 500 ft). By focusing the radio signal using a directional antenna 802.11b can operate reliably over a distance of many kilometres (miles), although the technology's line-of-sight requirements hamper connectivity in areas with hilly or heavily foliated terrain. In addition, compared to hard-wired connectivity, there are security risks (unless robust security protocols are enabled); data rates are significantly slower (2 to 50 times slower); and the network can be less stable, due to interference from [55] other wireless devices and networks, weather and line-of-sight problems. Rural Wireless-ISP installations are typically not commercial in nature and are instead a patchwork of systems built up by hobbyists mounting antennas on radio masts and towers, agriculturalstorage silos, very tall trees, or whatever other tall objects are available. There are currently a number of companies [56] that provide this service. Motorola Canopy and other proprietary technologies offer wireless access to rural and other markets that are hard to reach using Wi-Fi or WiMAX.