Chapter 17, New Technology Familiarization

Broad Band Access

Chapter 17

BROAD BAND ACCESS(Wired and Wireless) Contents • • • • • •

Introduction What is Broadband Broad Band Acess Wired Line Acess Wireless Acess Conclusion

Objectives After completion of this module you will be able to know: •

About various Broad Band access technologies being deployed around the globe.

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17.1 Introduction Advances in telecommunications and data technology are creating new opportunities for countries, businesses and individuals—just as the Industrial Revolution changed fortunes around the globe. The new economy is defining how people do business, communicate , shop, have fun, learn, and live on a global basis—connecting everyone to everything. The evolution of Internet has come into existence & Internet service is expanding rapidly. The demands it has placed upon the public network, especially the access network, are great. However, technological advances promise big increases in access speeds, enabling public networks to play a major role in delivering new and improved telecommunications services and applications to consumers .The Internet and the network congestion that followed, has led people to focus both on the first and last mile as well as on creating a different network infrastructure to avoid the network congestion and access problems. The solution to this is Broadband.

17.2 What is Broadband? A definition to broadband is a must as different service providers defines in their own terms & context. TRAI (Telecommunication Regulatory Authority of India) defines broadband as follows:An ‘always-on’ data connection that is able to support interactive services including Internet access and has the capability of the minimum download speed of 256 kilo bits per second (kbps) to an individual subscriber from the Point Of Presence (POP) of the service provider intending to provide Broadband service where multiple such individual Broadband connections are aggregated and the subscriber is able to access these interactive services including the Internet through this POP. The interactive services will exclude any services for which a separate licence is specifically required, for example, real-time voice transmission, except to the extent that it is presently permitted under ISP licence with Internet Telephony.”

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17.3 Broadband Access Broadband access technology is broadly classified into two categories. They are Wired Line & Wireless and further classified as detailed in the following diagram.

Broadband Access Technologies Wiredline

Wireless

DSL (Digital Sub’s Line)

3G Mobile

Cable Modem

Wi-Fi (Wireless Fidelity)

PLC (Power Line Communication)

WiMAX

Optical Fibre Technologies

FSO (Free Space Optics) LMDS & MMDS Satellite

17.3.1

Wired Line Access:

17.3.1.1 DSL (Digital Subscriber Line) :DSL uses the exisiting twisted-pair telephone lines as the access media. Over a period of time, a number of technologies (xDSL) have been introduced to provide faster data speeds over this medium. The various xDSL technologies are given below. 1. ADSL (Asymmetric Digital Subscriber Line) 2. VDSL (Very High-Speed Digital Subscriber Line) 3. RADSL (Rate Adaptive Digital Subscriber Line) 4. HDSL (High Data-Rate Digital Subscriber Line) 5. SDSL (Symmetric Digital Subscriber Line

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Broad Band Access ADSL (Asymmetric Digital Subscriber Line) Asymmetric Digital Subscriber Line (ADSL) is a form of DSL, a data communications technology that enables faster data transmission over copper telephone lines than a conventional modem can provide.ADSL has the distinguishing characteristic that the data can flow faster in one direction (used for download streaming) than the other(used for upload streaming) i.e., asymmetrically. WHY ADSL? ADSL is in place due to both technical and marketing reasons. On the technical side, there is likely to be more crosstalk from other circuits at the DSLAM (Digital Subscriber Line Access Multiplex) end (where the wires from many local loops are close together) than at the customer premises. Thus the upload signal is weakest, while the download signal is strongest at the noisiest part of the local loop. It therefore makes DSLAM transmit at a higher bit rate than does the modem on the customer end. Since the typical home user in fact does prefer a higher download speed, thus telecom companies chose to make a virtue out of necessity, hence ADSL come to place. HOW ADSL WORKS ? To obtain the asymmetrical data transfer to suit requirement of Internet and LAN access, ADSL works by firstly splitting the available bandwidth on the twisted copper wire (telephone wires) into three different channel: 1)A high speed downstream channel (ranges from 1.5 to 8 Mbps) 2)A medium speed upstream channel (ranges from 16 kbps to 1 Mbps) 3)POTS (Plain Old Telephone Service) channel ADSL uses two separate frequency bands. With standard ADSL, the band from 25.875 kHz to 138 kHz is used for upstream communication, while 138 kHz - 1104 kHz is used for downstream communication.

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Broad Band Access Frequency plan for ADSL

First the POTS channel is splits off from the digital modem by filter, thus guaranteeing uninterrupted POTS. After the POTS channel are splitted from the digital data transfer bandwidth, the 26kHz to 1.1mhz data bandwidth could be further separated by using one of two ways as describe below: 1)Frequency Division Multiplexing (FDM) :- FDM assigns one band for upstream data and one band for downstream data. Time division multiplexing divides the downstream path into one or more high speed channels and one or more low speed channels. But the upstream path is only multiplexed into corresponding low speed. 2)Echo cancellation :- Echo cancellation assigns the upstream band to over-lap the downstream. To separate them is by local echo cancellation. This technique is common in V.32 and V.34 modems(Conventional Modems). By using either one of the above techniques, ADSL splits off a 4khz region for POTS at the DC end of the band.

Upstream

Downstream

Basic Telephone Service

FDM

Frequency Upstream Downstream Basic Telephone Service

Echo Cancellation Frequency

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ADSL MODULATION ADSL uses two types of Modulation i.e CAP(Carrierless Amplituse Phase Modulation) & DMT(Discrete Multi Tone) & DMT is the most widely used one. CAP(Carrierless Amplituse Phase Modulation) : It is a variation of QAM (Quadrature Amplitude Modulation).QAM generates a DSSC (Double Sideband Suppressed Carrier) signal constructed from two multi-level PAM (Pulse Amplitude Modulated) signals applied in phase quadrature to one another. CAP modulation produces the same form of signal as QAM without requiring in-phase and quadrature components of the carrier to the first be generated. The following diagrams illustrates the CAP modulation. CAP TRANSMITTER & RECEIVER In-Phase Filter

an Binary Constellatio Input n Encoder

bn

+

Passband Line Filter

D/A

Quadrature Filter

In-Phase Adaptive filter Line Input

Output To line

~ an Decision Device

A/D Quadrature Filter

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Data Decode Out r

~ bn

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Broad Band Access

Discrete Multitone Modulation (DMT) DMT is basically a multicarrier modulation technique. DMT spread the original spectrum of the input signal over numerous sub-channels each of which carries a fraction of the total information. All these sub-channels transmit data in parallel to each other and are In-Phase independently modulated with a carrier frequency. By using DSP techniques, multiple subAdaptive channels could be established using Fast Fourier Transform (FFT), where the sub-carriers filter had to have orthoganlity with each~ other. an As mentioned before, DMT utilizes the spectrum between 26kHz and 1.1Mhz.Data After Line Out Decision Decode using FDM or echo cancellation technique, this spectrum of bandwidth is split up into Input Device r A/D upstream band(26kHz to 138kHz) and downstream band (138kHz to 1.1MHz), which is then further divided into 256 discrete sub-channels each of which~ a bandwidth of bhad n 4kHz. Quadrature One of DMT most significant feature is that it is able to dynamically adapt to the line Filter condition to obtain the maximum throughput for each unique telephone line. DMT does this by framing the data bits into chunks and spreads them over the sub-channels. The allocation of data into each sub-channel is dependent on the characteristics of the line and on the SNR (Signal to Noise Ratio) of the line. There could be no data at all in a really noisy channel and there could be as high as 15 bits/Hz in a channel where SNR is optimum. By using the average signal to noise ration (SNR) of the sub-channel, the number of bits to be allocated to that sub-channel can be decided. The number of bits to be assigned to the nth channel could be calculated from this equation.

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Broad Band Access The major stages in transmitting and receiving could be seen in the following block diagram .

1

Data Input

Serial to Parallel Input Data Buffer

Output To line

2

DMT Symbol Encoder

D/A

IFFT

Line Filter

N DMT Symbols Transmitted Serially

N (Complex) Sub-channel Symbols

1 2

line

Filter

A/D

DMT Symbol Decoder

FFT

Parallel Data To Serial Out Output Data Buffer

N DMT Symbols Received Serially

N (Complex) Sub-channel Symbols

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The chunk of bits that are being assigned to each sub-channel as described above are encoded as a set of quadrature amplitude modulated subsymbols. These subsymbols are then pass into an Inverse Fourier Transform(IFFT) which combines the subsymbols into a set of real-valued time domain samples, the output of the IFFT is then send a Parallel-to-Serial block with cyclic prefix which is added to remove InterSymbol Interference (ISI) between the subchannels. The output is then pass into an digital to analog converter which is then send through the twisted copper telephone wire. The receiver would receive the signal from the twisted copper telephone wire and does the reverse process to obtained the required data. To reduce error in transmission and to counter those problem of using telephone lines as a data transfer medium, DMT had uses Reed Solomon forward error correction method .The size of this Reed Solomon codeword depends on the number of bits assigned to each subchannel. Common Elements In ADSL

The common elements of ADSL are a) CPE(Customer Premises Equipment) containing a Splitter, ADSL Modem & a PC. b) Central Office Premises Equipment containing DSLAMs(Digital Subscriber Line Access Miltiplex),MDFs & PSTN. c) Aggregator and ATM core consists of Tier II,TierI switches,BRAS(Broad Band Remote access Service) ,Servers and Core routers. Factors Determining ADSL Connectivity: More the distance from the DSLAM(Digital Subscriber Line Access Multiplex) to the customer end the data rate reduces.Signal attenuation and Signal to Noise Ratio are defining characteristics, and can vary completely independently of distance (e.g., non-copper cabling, cable diameter).The performance is also dependent to the line impedance, which can change dynamically either dependent on weather conditions (very common for old overhead lines) or on the number and quality of joints or junctions in a particular cable length.

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Data Rate - Wire Size – Distance Data Rate

Wire Size

Distance

1.5-2.0 Mbps

0.5 mm

18000 Feet

5.5 Kms

1.5-2.0 Mbps

0.4 mm

15000 Feet

4.6 Kms

6.1 Mbps

0.5 mm

12000 Feet

3.7 Kms

6.1 Mbps

0.4 mm

9000 Feet

2.7 Kms

ADSL standards Standard name ANSI T1.413-1998 Issue 2 ITU G.992.1 ITU G.992.2 ITU G.992.3/4 ITU G.992.3/4 Annex J ITU G.992.3/4 Annex L¹ ITU G.992.5 ITU G.992.5 Annex L¹ ITU G.992.5 Annex M

Standard type Downstream rate Upstream rate ADSL 8 Mbit/s 1.0 Mbit/s ADSL (G.DMT) 8 Mbit/s 1.0 Mbit/s ADSL Lite (G.Lite) 1.5 Mbit/s 0.5 Mbit/s ADSL2 12 Mbit/s 1.0 Mbit/s ADSL2 12 Mbit/s 3.5 Mbit/s ADSL2 12 Mbit/s 1.0 Mbit/s ADSL2+ 24 Mbit/s 1.0 Mbit/s ADSL2+ 24 Mbit/s 1.0 Mbit/s ADSL2+ 24 Mbit/s 3.5 Mbit/s

Additionally, the non-Annex ADSL2 and ADSL2+ support an extra 256 kbit/s of upstream if the bandwidth normally used for POTS voice calls is allocated for ADSL usage.While the ADSL access utilizes the 1.1 MHz band, ADSL2+ utilizes the 2.2 MHz band.

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VDSL (Very-High-Speed DSL) Very-high-speed DSL (VDSL) promises even higher speeds than ADSL, although over much shorter distances. Originally named VADSL (A –Asymmetric) but was later extended to support both symmetric & asymmetric.Requires one phone line and supports voice & data.It works between 0.3-1.37 kms depending on speed. It supports upstream data rate of 1.6-2.3 mbps & downstream data rate of 13-52 mbps. The following figure illustrates shows the data rate, wire size & distance. Downstream

Upstream

Distance Feet Kms

12.96 Mbps

1.6-2.3 mbps

4500 Feet

1.37 Kms

25.82 Mbps

1.6-2.3 mbps

3000 Feet

0.91 Kms

51.84 Mbps

1.6-2.3 mbps

1000 Feet

0.30 Kms

RADSL(Rate-Adaptive DSL) As the name implies, rate-adaptive DSL (RADSL) modems adjust the data rate to match the quality of the twisted-pair connection. Emerging software should make this an automated process with little human intervention. HDSL(High-Data-Rate DSL) HDSL modem is viewed as equivalent of PCM stream(2 MBps) and offers the same bandwidth both upstream and downstream. It can work up to a distance of 3.66 to 4.57 kms depending upon the speed required. It can deliver 2048 kbps a) On 2 pairs of wires, each line carrying 1168 kbps b) On 3 pairs of wires, each line carrying 784 kbps. SDSL(Symmetric DSL) Symmetrical digital subscriber line (SDSL) is similar to HDSL but requires only one pair of 12

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Broad Band Access wires. Transmission speed ranges from n x 64 kbps to 2.0 Mbps in both directions. In this the upload and download streams are of equivalent bandwidth.

17.3.1.2 CABLE MODEM The cable network was primarily designed to deliver TV signals in one direction from the Head-End to the subscribers homes. Operators had to upgrade the cable network so that signals could flow bi-directionally.One spectrum is used for the signals that move from the Head-End towards the cable subscriber. Another spectrum of signal frequencies are used for the signals that move from the cable subscriber towards the Head-End. By way of replacing the existing one way amplifiers with two way amplifiers,Cable Operators are able to separate the upstream and downstream signals and amplify each direction separately in the right frequency range. In the downstream direction (from the network to the computer), network speeds can be up to 27 Mbps. In the upstream direction (from computer to network), speeds can be up to 10 Mbps. Most modem producers have selected a more optimum speed between 500 Kbps and 2.5 Mbps. A cable modem with a splitter can provide Internet access to multiple PCs, if they are connected via a local area network (LAN).Cable modems typically have an Ethernet output, so they can connect to the LAN with a standard Ethernet hub or router.

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A typical CABLE MODEM SETUP at CUSTOMER END.

There are 3 types of cable modem. 1). External Cable Modem  External box connected to computer through Ethernet connection  Can use USB interface too. 2). Internal Cable Modem  Is typically a PCI bus add-in card for a PC 3.). Interactive Set-Top Box  Provides a return channel –often through the POTS-giving access to webbrowsing through the TV screen. Disadvantages of Cable Modem: 1) Bandwidth Sharing: Users in a neighborhood have to share the available bandwidth provided by a single coaxial cable line. Therefore, connection speed can vary depending on how many people are using the service at the same time. Often the idea of a shared line is seen as a weak point of cable Internet access. 2) Security: A more significant weakness of cable networks using a shared line is the risk of loss of privacy, especially considering the availability of hacking tools for cable modems.

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Broad Band Access 3) Connectivity Problem :Many cable Internet providers are reluctant to offer cable modem access without tying it to a cable television subscription. 4) Cost factor: The cost of Cable modem & splitters is high as complared to ADSL modems.

17.3.1.3 Power Line Communication (PLC) PLC also called Broadband over Power Lines (BPL) or Power Line Telecoms (PLT), is a wireline technology that is able to use the current electricity networks for data and voice transmission. The carrier can communicate voice and data by superimposing an analog signal over the standard 50 or 60 Hz alternating current (AC). Traditionally electrical utilities used low-speed power-line carrier circuits for control of substations, voice communication, and protection of high-voltage transmission lines.More recently, high-speed data transmission has been developed using the lower voltage transmission lines used for power distribution. A short-range form of power-line carrier is used for home automation and intercoms.A computer (or any other device) would need only to plug a BPL "modem" into any outlet in an equipped building to have high-speed Internet access. PLC modems transmit in medium and high frequency (1.6 to 30 MHz electric carrier). The asymmetric speed in the modem is generally from 256 kbit/s to 2.7 Mbit/s. In the repeater situated in the meter room the speed is up to 45 Mbit/s and can be connected to 256 PLC modems. In the medium voltage stations, the speed from the head ends to the Internet is up to 135 Mbit/s. To connect to the Internet, utilities can use optical fiber backbone or wireless link. TYPICAL PLC LAYOUT

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High-speed data transmission, or Broadband over Power Line uses the electric circuit between the electric substations and home networks. A standard used for this is ETSI PLT. PLC uses the following frequencies bands. Low frequencies  Below 400 kHz (US)  Below 125 kHz (Europe)  Transmission rate about 1 to 10 kbps Low Band is used for Telemetry,Security & Remote Control. High frequencies  2 to 30 MHZ (HF)  Transmission rate about 1 to 40 Mbps High Band is used for Telephony & Internet. PLC Distribution Network

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Getting beyond the transformer

Insert Power Line Carrier at middle voltage

Backhaul to NAP (fiber, DSL, wireless, satellite)

ADVANTAGES The major advantage of BPL over regular cable or DSL connections is the availability of the extensive infrastructure already available which would appear to allow more people in more locations to have access to the Internet. DISADVANTAGES Utility power systems are adverse electromagnetic environments for broadband communications. 1. Network characteristics (topology, impedance, splices, terminations, grounding) and devices (regulators, capacitors, re-closers) can adversely affect signal strength and quality. 2. Electronic loads and nearby high frequency radiation sources may cause high frequency noise that interferes with BPL. 3. Equipment will be exposed to severe lightning and switching surges. 4. Utility operations and maintenance personnel may damage or improperly install equipment

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Broad Band Access 5. Some of the PLC systems are not fully operable at very low or no load without battery backup. 6. Physics limits frequency on power lines to <100 Mhz, limiting ultimate throughput in densely penetrated areas. 7. BPL is not likely to be available soon for high voltage (>66 kV) power lines. 8. Conventional electronic surge arrestors severely attenuate BPL signal. 9. Other electronic devices (plasma screen TV’s, variable speed drives) interfere with BPL signal or vice versa. 10. Existing vendors’ technologies are not interoperable. 11. There is not yet an IEEE standard for BPL 17.3.1.4

OPTIC FIBER TECHNOLOGIES

Optical fibers, clearly the chosen technology for transmission media, are beginning to find their place in the subscriber's loop. Currently fiber costs are high as compared to copper but there is a trend towards decreasing costs of optical fiber cables and photonics employed. In addition the tremendous advantages in terms of information capacity of fiber, its small weight and size over copper cable are making it a very attractive technology to replace copper in subs loop when advanced broadband services need to be offered to the customer. To carry the same information as one fiber cable we would need hundreds of reels of twisted wire Cu cables. Further, fiber is 23 times lighter than Cu cable and 36 times less in crosssectional area. These features of light weight and small size make it easier to handle fiber cable. In crowded city networks they can easily be accommodated in existing ducted systems.

Fiber in loop (FITL) can be developed in several configurations. 1) 2) 3) 4)

Fibre to the Curb(FTTC) Fibre to the building(FTTB) Fibre to the home/Office(FTTH/FTTO) PON (Passive Optical Network)

Fibre to the Curb(FTTC) in which the terminal equipment is located on the curb from where it would be convenient to serve a suitable service area. Since the distribution would still be copper, suitable location for the terminal would be one which optimizes the cost, reduces back-feeding, reduces distribution cost and takes safety factors into consideration. Space and power availability need to be confirmed before finalising the location. Fibre to the building(FTTB) in which the terminal equipment is located inside a multistoreyed building. This brings higher bandwidth closer to the subscriber. The

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Broad Band Access distribution part is still copper. For new buildings, the planners may negotiate for suitable location well in time. Fibre to the home/Office(FTTH/FTTO) in this method the fibre goes upto the subscriber premises Typical Architecture of Fibre in Local Loop

Depending upon the location of the cabinet (CAB-see above diagrams ) or the terminal equipment we call FTTC,FTTH or FTTO and FTTB. The optical fibre cabinet consists of fibre optic transmission equipment and customer access equipment. It consists of three internal chambers. A battery chamber that houses upto 2 batteries, an MDF chamber housing MDF, alarms and fibre splice box, an equipment chamber housing transmission and access equipment. Exchange side of cabinets connect to exchange on 2Mbps or channel level or on a V 5.2 interface and subscriber side of cabinets connect to subscribers via copper lines. These can be installed as outdoor or indoor cabinets. Outdoor cabinets are environmentally fitted and could be installed on curbs or in remote areas. Usual capacities of fibre optic cabinets

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Broad Band Access have capacities 120, 240,480 and 1920 channels. Each cabinet requires two fibres for operation and one dark fibre-pair is usually kept as spare. The fibre optic cabinets offer point to point connections and can take care of POTS, ISDN(BA and PRI), DID, Payphones, 64Kbps leased lines. 17.3.1.5 Passive Optical Networks (PONs) Most networks in the telecommunications networks of today are based on active components at the serving office exchange and termination points at the customer premises as well as in the repeaters, relays and other devices in the transmission path between the exchange and the customer. By active components, we mean devices which require power. With Passive Optical Networks, all active components between the central office exchange and the customer premises are eliminated, and passive optical components are put into the network to guide traffic based on splitting the power of optical wavelengths to endpoints along the way. This replacement of active with passive components provides a cost-savings to the service provider by eliminating the need to power and service active components in the transmission loop. The passive splitters or couplers are merely devices working to pass or restrict light, and as such, have no power or processing requirements and have virtually unlimited Mean Time Between Failures (MTBF) thereby lowering overall maintenance costs for the service provider.

The basic components of PON are a) Optical Line Terminal(OLT): It is located in the central office and interfaces with switch (possibly through V5 interface) .It provides system control and implements protocol for transmission. b) Splitter : It splits the source optical beam into multiple fibers. c) Optical Network Unit (ONU) : It interfaces with subscriber terminals and works under the control of OLT to implement the transmission protocol.It can be configured in FTTC, FTTB and FTTH configurations

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Typical PON Connectivity

There are different PON technologies exists and are given below. a) APON (ATM PON) b) EPON (Ethernet PON) c) GPON( Giga Bit EthernetPON) . PON benefits PON systems offer a number of benefits to the operator and the end users. 1).Fiber is less costly to maintain than copper based systems so operators can reduce costs, increase profits or lower costs to the end-users.

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Broad Band Access 2) The technology conserves fibre,passive elements and optical interfaces. All this leads to cost effectiveness. 3) Reliabilty of the network is very high. 4) Both business and residential customers can be served on the same platform and customers get better quality of service. 5). Network can be upgraded to support future services

17.4 Wireless Technologies 17.4.1 Bluetooth It is a Wireless Technology used for short range applications ( about 10 meters) namely in Personal Area Networks(PAN). It operates on 2.4 Ghz band with 1+ Mbps speed and Frequency Hopping Spread spectrum modulation technique is employed. It is a Combination of circuit switching and packet switching supporting both voice and data. Bluetooth lets these devices talk to each other when they come in range, even if they are not in the same room, as long as they are within up to 100 metres (328 feet) of each other, dependent on the power class of the product. Products are available in one of three power classes: Class 1 (100 mW) [still readily available]: It has the longest range at up to 100 metres (328 ft). Class 2 (2.5 mW) [most common]: It allows transmission to a distance of 10 metres (33 ft). Class 3 (1 mW) [rare]: It allows transmission of 10 cm (3.9 in), with a maximum of 1 metre (3.3 ft). With UWB (Ultra Wide Band technology) speed upto a maximum of 400Mbps is achieved.

17.4.2

3G Mobile Of late cellular mobile telephony has started maturing in delivering data access over the air. The evolution of cellular mobile telephony has taken place in following steps 1. 2G – GSM, CDMA 2. 2.5G – GSM(GPRS/EDGE), CDMA 2000 1x 3. 3G – UMTS/WCDMA, CDMA 2000 1xEVDO/EVDV The speeds achieved with above different cellular mobile telephony is given below. 1).2G GSM/CDMA 9-14 Kbps 2).2.5G GSM GPRS 115 Kbps 22

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Broad Band Access EDGE 3).2.5G CDMA 2000 1x 4).3G 3G UMTS/WCDMA 5).3G CDMA 2000 EVDO/EVDV

384 Kbps 170 Kbps 384K (M), 2048K(S) 1x 384K (M), 2048K(S)

However the technologies 2.5G GSM(EDGE) & 3G (Both CDMA 2000 1x EVDO*/EVDV* & UMTS*/WCDMA*) falls into the category of Broadband access. (*Note:_EVDO-Evolution Data Optimised ,EVDV-Evolution Data and Voice ,UMTSUniversal Mobile Telephony System & WCDMA – Wideband Code Division Multiple Access) 17.4.3 Wi-Fi( Wireless Fidelity) Wi-Fi (also WiFi or wifi) is an abbreviation for "wireless fidelity” & is a trademark controlled by the Wi-Fi Alliance (formerly the Wireless Ethernet Compatibility Alliance), the trade organization that tests and certifies equipment compliance with the IEEE 802.11 standards for wireless local area networks( WLANs). Wi-Fi was intended to allow mobile devices, such as laptop computers and personal digital assistants (PDAs) (PDAs) to connect to local area networks, but is now often used for wireless Internet access and wireless. Many computers are sold today with Wi-Fi built-in; others require adding a Wi-Fi network card (Wireless Ethernet/LAN card). A Wi-Fi-enabled device is able to connect to a local area network when near one of the network's access points (see the figure below). The connection is made by radio signals; there is no need to plug the device into the network. If the local area network is connected to the Internet, the Wi-Fi device can have Internet access as well. The geographical region covered by several access points is called a hotzone. The range of an access point varies. The access point built into a typical Wi-Fi home router might have a range of 45 m (150 ft) indoors and 90 m (300 ft) outdoors.

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Wireless Ethernet standards Wi-Fi is based on the IEEE 802.11 specifications. There are currently four deployed 802.11 variations: 802.11a, 802.11b, 802.11g and 802.11n. The b specification was used in the first Wi-Fi products. The n variant is most recent. IEEE 802.11 The Initial release of the standard capable of transmissions of 1 to 2 Mbps and operates in 2.4 GHz band using either frequency hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS). IEEE 802.11a Capable of transmissions upto 54 Mbps and operates in 5 GHz band and uses an orthogonal frequency division multiplexing OFDM encoding scheme . IEEE 802.11b Capable of transmissions of upto 11 Mbps and operates in 2.4 GHz band and uses only DSSS encoding scheme. IEEE 802.11g Capable of transmissions upto 54 Mbps and operates in 2.4 GHz band and uses an orthogonal frequency division multiplexing(OFDM) encoding scheme. IEEE 802.11n Capable of transmissions upto 100 Mbps and operates in 2.4 GHz band and uses an orthogonal frequency division multiplexing(OFDM) encoding scheme. Advantages of Wi-Fi •Unlike packet radio systems, Wi-Fi uses unlicensed radio spectrum and does not require regulatory approval for individual deployers. •Allows LANs to be deployed without cabling, potentially reducing the costs of network deployment and expansion. Spaces where cables cannot be run, such as outdoor areas and historical buildings, can host wireless LANs. •Wi-Fi products are widely available in the market. Different brands of access points and client network interfaces are interoperable at a basic level of service. •Competition amongst vendors has lowered prices considerably since their inception. •Many Wi-Fi roaming, in which a mobile client station such as a laptop computer can move from one access point to another as the user moves around a building or area.

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Broad Band Access •Many access points and network interfaces support various degrees of encryption to protect traffic from interception. •Wi-Fi is a global set of standards. Unlike cellular carriers, the same Wi-Fi client works in different countries around the world (although may require simple software configuration). Disadvantages of Wi-Fi •Though the use of the 2.4 GHz Wi-Fi band does not require a license in most of the world, local regulations do require that Wi-Fi devices stay below the local regulatory limits on transmission power and accept interference from other sources, including interference which causes the devices to no longer function. Legislation/regulation is not consistent worldwide. •The 802.11b and 802.11g flavors of Wi-Fi use the 2.4 GHz spectrum, which is crowded with other equipment such as Bluetooth devices, microwave ovens, cordless phones (900 MHz or 5.8 GHz are, therefore, alternative phone frequencies one can use to avoid interference if one has a Wi-Fi network), or video sender devices, among many others. This may cause a degradation in performance. Other devices which use these microwave frequencies can also cause degradation in performance. •Closed access points can interfere with properly configured open access points on the same frequency, preventing use of open access points by others. •Power consumption is fairly high compared to other standards, making battery life and heat a concern. 17.4.4 WiMAX WiMAX is an acronym that stands for Worldwide Interoperability for Microwave Access, a certification mark for products that pass conformity and interoperability tests for the IEEE 8802.16 standards.(IEEE 802.16 is working group number 16 of IEEE 802 specializing in point-to-multipoint Broadband wireless access).WiMAX covers wider, metropolitan or rural areas. It can provide data rates up to 75 megabits per second (Mbps) per base station with typical cell sizes of 2 to 10 kilometers. This is enough bandwidth to simultaneously support (through a single base station) more than 60 businesses with T1/E1type connectivity and hundreds of homes with DSL-type connectivity. It is similar to Wi-Fi in concept, but has certain improvements are done at improving performance and should permit usage over much greater distances. IEEE 802.16 networks use the same Logical Link Controller(standardized by IEEE 802.2) as in other LANs and WANs, where it can be both bridged and routed to them. An important aspect of the IEEE 802.16 is that it defines a MAC (Media Access Control) layer that supports multiple physical layer specifications in 2 to 11 Ghz & 10 to 66 Ghz bands. It will provide fixed, portable, and eventually mobile wireless broadband connectivity and also provides POTS services.

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Broad Band Access

802.16 Last Mile Networks

WiMAX Subscriber Station

AX l iM hau W ck Ba

POTS

WiFi

WiMAX Access Pt to Multipt.

Internal Access Point with hub Ethernet

PSTN Internet Telco core network Or private (fiber) network

WiMAX Base Station

Customer Premise (Home, Business or HOTSPOT)

The MAC is significantly different from that of Wi-Fi (and ethernet from which Wi-Fi is derived). In Wi-Fi, the MAC uses contention access—all subscriber stations wishing to pass data through an access point are competing for the AP's(Access points) attention on a random basis. This can cause distant nodes from the AP to be repeatedly interrupted by less sensitive, closer nodes, greatly reducing their throughput. By contrast, the 802.16 MAC is a scheduling MAC where the subscriber station only has to compete once (for initial entry into the network). After that it is allocated a time slot by the base station. The time slot can enlarge and constrict, but it remains assigned to the subscriber station meaning that other subscribers are not supposed to use it but take their turn. This scheduling algorithm is stable under overload and oversubscription (unlike 802.11). It is also much more bandwidth efficient. The scheduling algorithm also allows the base station to control Quality of Service by balancing the assignments among the needs of the subscriber stations. This is also an important aspect of why WiMAX can be described as a "framework for the evolution of wireless broadband" rather than a static implementation of wireless technologies.

17.4.5

Free Space Optics FSO is optical, wireless, point-to-point, line-of-sight broadband technology that is an alternative to fiber optic cable systems without expense of fiber. Speed is comparable to fiber optic transmissions and transmits up to 1.25 Gbps at distance of 4 miles (6.4 kilometers) in full-duplex mode. It uses low-powered infrared (IR) beam sent through open air by transceivers. Uses unlicensed higher frequency. Currently FSO uses two different wavelengths(780nm & 1550nm), but expect worldwide standard in near future. 26

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Broad Band Access

FSO TRANSCEIVER Advantages of FSO 1.Significantly less expensive than fiber optic or leased lines 2.Much faster installation, days or weeks compared to months for fiber optic cables 3.Transmission speed can be scaled to meet user’s needs; from 10 Mbps to 1.25 Gbps 4.Security is key advantage; not easy to intercept or decode Disadvantage of FSO 1.Scintillation is temporal and spatial variations in light intensity caused by atmospheric turbulence that acts like prism to distort FSO signals 2. Loss of Signal due to Fog (Intensity of Light is reduced) . 3. Interference of signal due to bird/flies obstructing the signal path. 4. Obstruction of signal by swaying of tall structures/buildings due to winds and seismic activity.

17.4.6 (a) Local Multipoint Distribution Service(LMDS) LMDS is a broadband wireless access technology that uses microwave signals operating between the 26GHz and 29GHz bands. It is a point-to-multipoint service, hence is typically deployed for access by multiple parties. Throughput capacity and distance of the link depends on the modulation method used - either phase-shift keying or amplitude modulation. Links up to 5 miles from the base station are possible.

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Broad Band Access

Video

Central Office

PSTN Internet

Content &  Application  Providers Backhaul for Hotspots

Data,PSTN Video Access

Data,PSTN Video Access

LMDS Cell Site

LMDS TYPICAL LAYOUT Factors determining LMDS 1).Line-of-sight—LMDS requires direct line.Tall buildings may obstruct line of sight and the solution is to divide area into smaller cells. 2). Antenna height—placed on taller buildings can serve larger cells without obstructions Advantages a)Lower cost for both user and carrier than wired alternatives b)Increased service area; network may be expanded one cell at a time c)Capacity; with as much as 1,300 MHz of spectrum in a local market, carriers can support 16,000 telephone calls and 200 video channels simultaneously Disadvantages a)Requires line-of-sight between buildings; LMDS network is limited by surrounding objects b)Affected by precipitation; LMDS systems are susceptible to interference from rain and fog 17.4.6 (b) Multichannel Multipoint Distribution System(MMDS) Multichannel multipoint distribution service, also known as MMDS or wireless cable, is a wireless telecommunications technology, used for general-purpose broadband networking .

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Broad Band Access Similar to LMDS, MMDS can transmit video, voice, or data signals at 1.5 Mbps downstream and 300 Kbps upstream at distances up to 35 miles.Mounted MMDS hub uses point-tomultipoint architecture. Pizza box (13 x 13 inch) directional antennas are mounted at receiving location & a cable runs from antenna to MMDS wireless modem, which converts analog signal to digital and may be attached to single computer or LAN.

Advantages a)Signal strength—low frequency MMDS RF signal travels farther and with less interference than high-frequency LMDS RF signals b)Cellsize—seven times larger than area covered by LMDS transmitters c)Cost—MMDS is less expensive than LMDS Disadvantages a)Requires direct line-of-sight—makes installation difficult and eliminates locations blocked by taller obstructions b)Shared signals—decreased speed and throughput since users share same radio channel c)Security—Unencrypted transmissions may be intercepted and read d)Limited markets—available in limited areas in USA

17.4.7 SATELLITE Satellite broadband offers two-way internet access via satellites orbiting the earth about 22,000 miles above equator. The PC through a special satellite modem broadcasts the requests to the satellite dish ,located on top of the roof/building which in trun transmits and receives signal from the satellites. But satellite broadband is slower in both uplink and downlink compared to any DSL technology for example.

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Broad Band Access At present we use VSAT (Very Small Aperture Terminals) & DTH (Direct To Home) terminals for satellite transmission. C, Ku & Ka bands are used for services involving fixed terminals and L band is used for mobile services. It Offers data rates 9.6 Kbps for a handheld terminal and 60 Mbps for a fixed VSAT terminal at present. Satellite broadband has got an advantage, that it can be deployed in every region in a country. Satellite explores the possibility of usage in rural areas where tough terrain conditions prevails. It provides an always on Connection without dialling .It offers incredible reliability, better than 99.9%. and need not worry about dropped connections during critical transactions, or missed emails..

21.5 Conclusion With the advent of new technologies in the field of communication which has brought the world closer and closer, the consumer will be in a better position to choose and reap the benefits, the broadband technology offers viz. High Speed Internet, Video Conferencing, Telemedicine, Video on Demand ,Internet Radio, Instant messaging, etc.

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