ICOM 6115 Computer Networks and the WWW Isidoro

ICOM 6115 – Computer Networks and the WWW Isidoro Couvertier, Ph. D. Lecture 12 ICOM 6115 ©Manuel Rodriguez-Martinez

Lecture Objectives • Understand the principles the behind the following physical layer technologies – Cellular Networks – ADSL – Wireless Local Loops – Cable TV ICOM 6115 ©Manuel Rodriguez-Martinez

Cellular Systems • Idea: Phone service without wires – Allows user to move around – Keep current call active while moving • Solution: – Divide a region into many small areas • Called cells – Each cell has a tower that send/receives calls – Phone must be associated with the cell in which it is currently located ICOM 6115 ©Manuel Rodriguez-Martinez

Cellular Basics • Each cell is served by a base station – Computer – Antenna with transmitter/receiver • Based stations connect to a MTSO – Mobile Telephone Switching Office • Similar to a Phone End Office – Groups of MTSO connect to one or more Phone End Office • Move calls over regular and long distance phone lines ICOM 6115 ©Manuel Rodriguez-Martinez

Cellular Basics (2) • Each cell uses a given frequency to move calls – Frequency Division Multiplexing – Contiguous Cells have different frequencies • As user moves the phone switches from cells and associates with new base stations – This is called handoff ICOM 6115 ©Manuel Rodriguez-Martinez

Cellular Handoff • Soft handoff – old and new base stations provide service to phone on the cell border • Prevents current calls from failing – New station exclusively acquires phone once phone is deep into cell • Hard handoff – old base station drops phone as soon as signal fades (it is going away from the cell) • Current call fails if phone does not enter new cell soon ICOM 6115 ©Manuel Rodriguez-Martinez

Cellular System Organization Letters indicate frequency of cells ICOM 6115 More capacity can be added with more cells (more towers) ©Manuel Rodriguez-Martinez

Cellular System Generations • First Generation – Analog Voice • Second Generaton – Digital Voice (PCS) • Third Generation (3 G) – Digital Voice – Digital Data (Internet Access) • Centennial Turbo. Net ICOM 6115 ©Manuel Rodriguez-Martinez

Cellular Systems Tradeoffs • Advantages – Ubiquitous Internet Access • Malls, highways, beach, parks – Reuse Existing infrastructure – No need for wires • Disadvantages – Limited bandwidth – 144 Kbps – 384 Kbps – Expensive $$$ • You get charge by air time! ICOM 6115 ©Manuel Rodriguez-Martinez

DSL System • Phone companies realized they needed high speed Internet – 56 Kbps was no match for Cable. TV system • Problem: – Regular phone line has limited bandwidth • Voice filter is used to limit data rate on line • Done to optimize the system for voice transmission • Solution: – Give people a new phone line without the filter – DSL – Digital Subscriber Line ICOM 6115 ©Manuel Rodriguez-Martinez

DSL Highlights • Based on Frequency Division Multiplexing – Divide Local Loop into 256 4 k. Hz Channels – Channel usage • • 0 : used for voice 1 -5: not used – kept as signal separation zone (voice-data) 2 channels used for move control information 248 for data exchange • DSL typically is an Asymmetric Service – Receive data faster that it sends • Downlink has more bandwidth than uplink • Uplink usually gets 32 channels to transmit • Down link usually gets 216 channels to transmit ICOM 6115 ©Manuel Rodriguez-Martinez

DSL Basics: End Office Configuration Regular Phone Line Phone Switch Codec DSL Line DSLAM Line Splitter • Do not connect line directly to Codec • Connect part of line to a new device called DSLAM – Digital Subscriber Line Access Multiplexer ICOM 6115 ©Manuel Rodriguez-Martinez

Splitting the Phone Line • DSL line must be split at both ends – Filter out frequencies depending on service – Home splitter • Divides channels – Regular phone – DSL modem – End Office splitter • Divides channels – Codec – DSLAM ICOM 6115 ©Manuel Rodriguez-Martinez

DSL Modem • Device use to move bits between computer and phone line • DSL modem connect to computer via Ethernet Interface – Modem has one Ethernet Card – Computer must also have an Ethernet Card ICOM 6115 ©Manuel Rodriguez-Martinez

DSL: Complete Configuration ICOM 6115 ©Manuel Rodriguez-Martinez

DSL Tradeoffs • Advantages – Dedicated Line to user • Maximum bandwidth can be 8 Mbps – Reuse existing Infrastructure • No need to re-wire the home – Connection is always on • Disadvantages – Need to live close to phone end office! • Signal fades as distance increases ICOM 6115 ©Manuel Rodriguez-Martinez

Wireless Local Loop • Problem: Throwing new lines is expensive – New phone service providers cannot afford it • Solution 1: Lease access to existing lines – But be at the mercy of existing Phone company • Solution 2: Do not use wires – Use radio signals and antennas – This is called a Wireless Local Loop • Fixed wireless service ICOM 6115 ©Manuel Rodriguez-Martinez

Wireless Local Loop Basics • Phone service provider must install towers with several antennas – Need to put many of these on a given area • Like cellular towers • Subscribers gets an antenna on the roof of the home – Must be pointed towards one of the towers. • Like satellite TV • Bandwidth: Between 50 Mbps – 150 Mbps ICOM 6115 ©Manuel Rodriguez-Martinez

Wireless Local Loop Scheme ICOM 6115 ©Manuel Rodriguez-Martinez

Wireless Local Loop Tradeoffs • Advantages – Connection is always on – Very high bandwidth – No need to wait for wiring of neighborhood • Unlike Cable TV or DSL – Less expensive to roll out • Need many towers but not as bad a putting lines – There is a standard for it: IEEE 802. 16 • Makes it easier to adopt • Can have off-the-shelf hardware-software for it ICOM 6115 ©Manuel Rodriguez-Martinez

Wireless Local Loop Tradeoffs (2) • Disadvantages – Shared Media • Effective bandwidth decreases with number of users – Need to have a tower near by • Like DSL must have end office near by – Rain and trees cause signal distortion • Like Direc. TV – Antenna typically is not allowed on condos • “hurts the good looks” of the apartment complex ICOM 6115 ©Manuel Rodriguez-Martinez

Cable TV Internet • Cable TV provider realized they must enter Internet game – They already have • Line coming into the homes • Fiber backbone • Problem: – Cable is used to receive TV programs only • Solution: – Modify the equipment so it can send data from home ICOM 6115 ©Manuel Rodriguez-Martinez

Components of the System • Headend – – Device the receives the data and TV signals from backbone – moves them to neighborhoods • Fiber node – Device that maps optical signals into electrical signals – Feed coaxial cable for a group of homes ICOM 6115 ©Manuel Rodriguez-Martinez

Architecture of the Cable TV System Fiber Node ICOM 6115 ©Manuel Rodriguez-Martinez

Cable Modem • Device use to move bits between computer and phone line • Cable modem connects to computer via Ethernet Interface – Modem has one Ethernet Card – Computer must also have an Ethernet Card • Connection is always on ICOM 6115 ©Manuel Rodriguez-Martinez

Asymmetric Service • Like DSL, Internet Cable is asymmetric – Based on Frequency Division Multiplexing – Downstream is faster than upstream – Maximum bandwidth can be up to 40 Mbps • But most vendors provide around 1 Mbps – Cost effective issues ICOM 6115 ©Manuel Rodriguez-Martinez

Cable TV Tradeoffs • Advantages – Always on – Reuse existing infrastructure • No need to re-wire home – High bandwidth – Distance is not an issue • You do not need live near a headend ICOM 6115 ©Manuel Rodriguez-Martinez

Cable TV Tradeoffs (2) • Disadvantages – Shared Media • Effective bandwidth decreases with number of users • Service is very variable in terms of performance – Need to have Cable TV infrastructure in the neighborhood – Need to have good security mechanism to protect the data • It is a bus network ICOM 6115 ©Manuel Rodriguez-Martinez