Network+ Guide to Networks 6th Edition Chapter 7 Wide Area Networks

Network Guide to Networks 6th Edition Chapter 7 Wide Area Networks

Objectives Identify a variety of uses for WANs Explain different WAN topologies, including their advantages and disadvantages Compare the characteristics of WAN technologies, including their switching type, throughput, media, security, and reliability Describe several WAN transmission and connection methods, including PSTN, ISDN, T-carriers, DSL, broadband cable, broadband over powerline, ATM, and SONET Network Guide to Networks, 6th Edition 2

WAN Essentials WAN – Network traversing some distance, connecting LANs – Transmission methods depend on business needs WAN and LAN common properties – Client-host resource sharing – Layer 3 and higher protocols – Packet-switched digitized data Network Guide to Networks, 6th Edition 3

WAN Essentials (cont’d.) WAN and LAN differences – Layers 1 and 2 access methods, topologies, media – LAN wiring: privately owned – WAN wiring: public through NSPs (network service providers) Examples: AT&T, Verizon, Sprint WAN site – Individual geographic locations connected by WAN WAN link – WAN site to WAN site connection Network Guide to Networks, 6th Edition 4

WAN Topologies Differences from LAN topologies – Distance covered, number of users, traffic – Connect sites via dedicated, high-speed links Use different connectivity devices WAN connections – Require Layer 3 devices Routers – Cannot carry nonroutable protocols Network Guide to Networks, 6th Edition 5

Figure 7-1 Differences in LAN and WAN connectivity Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 6

Bus Bus topology WAN – Each site connects serially to two sites maximum – Network site dependent on every other site to transmit and receive traffic – Different locations connected to another through point-to-point links Best use – Organizations requiring small WAN, dedicated circuits Drawback – Not scalable Network Guide to Networks, 6th Edition 7

Figure 7-2 A bus topology WAN Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 8

Ring Ring topology WAN – – – – Each site connected to two other sites Forms ring pattern Connects locations Relies on redundant rings Data rerouted upon site failure – Expansion Difficult, expensive Best use – Connecting maximum five locations Network Guide to Networks, 6th Edition 9

Figure 7-3 A ring topology WAN Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 10

Star Star topology WAN – Single site central connection point – Separate data routes between any two sites Advantages – Single connection failure affects one location – Shorter data paths between any two sites – Expansion: simple, less costly Drawback – Central site failure can bring down entire WAN Network Guide to Networks, 6th Edition 11

Figure 7-4 A star topology WAN Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 12

Mesh Mesh topology WAN – Incorporates many directly interconnected sites – Data travels directly from origin to destination – Routers can redirect data easily, quickly Most fault-tolerant WAN type Full-mesh WAN – Every WAN site directly connected to every other site – Drawback: cost Partial-mesh WAN – Less costly Network Guide to Networks, 6th Edition 13

Figure 7-5 Full-mesh and partial-mesh WANs Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 14

Tiered Tiered topology WAN – Sites connected in star or ring formations Interconnected at different levels – Interconnection points organized into layers Form hierarchical groupings Flexibility – Allows many variations, practicality – Requires careful considerations Geography, usage patterns, growth potential Network Guide to Networks, 6th Edition 15

Figure 7-6 A tiered topology WAN Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 16

PSTN PSTN (Public Switched Telephone Network) – Network of lines, carrier equipment providing telephone service – POTS (plain old telephone service) – Encompasses entire telephone system – Originally: analog traffic – Today: digital data, computer controlled switching Dial-up connection – Modem connects computer to distant network Uses PSTN line Network Guide to Networks, 6th Edition 17

PSTN (cont’d.) PSTN elements – Cannot handle digital transmission Requires modem Signal travels path between modems – Over carrier’s network Includes CO (central office), remote switching facility Signal converts back to digital pulses CO (central office) – Where telephone company terminates lines – Switches calls between different locations Network Guide to Networks, 6th Edition 18

PSTN (cont’d.) Local loop (last mile) – Portion connecting residence, business to nearest CO – May be digital or analog Digital local loop – Fiber to the home (fiber to the premises) Passive optical network (PON) – Carrier uses fiber-optic cabling to connect with multiple endpoints Network Guide to Networks, 6th Edition 19

Figure 7-7 A long-distance dialup connection Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 20

Figure 7-8 Local loop portion of the PSTN Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 21

PSTN (cont’d.) Optical line terminal – Single endpoint at carrier’s central office in a PON – Device with multiple optical ports Optical network unit – Distributes signals to multiple endpoints using fiberoptic cable Or copper or coax cable Network Guide to Networks, 6th Edition 22

Figure 7-9 Passive optical network (PON) Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 23

X.25 and Frame Relay X.25 ITU standard – Analog, packet-switching technology Designed for long distance – Original standard: mid 1970s Mainframe to remote computers: 64 Kbps throughput – Update: 1992 2.048 Mbps throughput Client, servers over WANs – Verifies transmission at every node Excellent flow control, ensures data reliability Slow, unreliable for time-sensitive applications Network Guide to Networks, 6th Edition 24

X.25 and Frame Relay (cont’d.) Frame relay – Updated X.25: digital, packet-switching – Protocols operate at Data Link layer Supports multiple Network, Transport layer protocols Both perform error checking – Frame relay: no reliable data delivery guarantee – X.25: errors fixed or retransmitted Throughput – X.25: 64 Kbps to 45 Mbps – Frame relay: customer chooses Network Guide to Networks, 6th Edition 25

X.25 and Frame Relay (cont’d.) Both use virtual circuits – Node connections with disparate physical links Logically appear direct – Advantage: efficient bandwidth use Both configurable as SVCs (switched virtual circuits) – Connection established for transmission, terminated when complete Both configurable as PVCs (permanent virtual circuits) – Connection established before transmission, remains after transmission Network Guide to Networks, 6th Edition 26

X.25 and Frame Relay (cont’d.) PVCs – Not dedicated, individual links X.25 or frame relay lease contract – Specify endpoints, bandwidth – CIR (committed information rate) Minimum bandwidth guaranteed by carrier PVC lease – Share bandwidth with other X.25, frame relay users Network Guide to Networks, 6th Edition 27

Figure 7-10 A WAN using frame relay Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 28

X.25 and Frame Relay (cont’d.) Frame relay lease advantage – Pay for bandwidth required – Less expensive technology – Long-established worldwide standard Frame relay and X.25 disadvantage – Throughput variability on shared lines Frame relay and X.25 easily upgrade to T-carrier dedicated lines – Same connectivity equipment Network Guide to Networks, 6th Edition 29

ISDN Standard for transmitting digital data over PSTN Gained popularity: 1990s – Connecting WAN locations Exchanges data, voice signals Protocols at Physical, Data Link, Transport layers – Signaling, framing, connection setup and termination, routing, flow control, error detection and correction Relies on PSTN for transmission medium Dial-up or dedicated connections – Dial-up relies exclusively on digital transmission Network Guide to Networks, 6th Edition 30

ISDN (cont’d.) Capability: two voice calls, one data connection on a single line Two channel types – B channel: “bearer” Circuit switching for voice, video, audio: 64 Kbps – D channel: “data” Packet-switching for call information: 16 or 64 Kbps BRI (Basic Rate Interface) connection PRI (Primary Rate Interface) connection Network Guide to Networks, 6th Edition 31

ISDN (cont’d.) BRI: two B channels, one D channel (2B D) – B channels treated as separate connections Carry voice and data Bonding – Two 64-Kbps B channels combined Achieve 128 Kbps PRI: 23 B channels, one 64-Kbps D channel (23B D) – Separate B channels independently carry voice, data – Maximum throughput: 1.544 Mbps PRI and BRI may interconnect Network Guide to Networks, 6th Edition 32

Figure 7-11 A BRI link Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 33

Figure 7-12 A PRI link Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 34

T-Carriers T1s, fractional T1s, T3s Physical layer operation Single channel divided into multiple channels – Uses TDM (time division multiplexing) over two wire pairs Medium – Telephone wire, fiber-optic cable, wireless links Network Guide to Networks, 6th Edition 35

Types of T-Carriers Many available – Most common: T1 and T3 Table 7-1 Carrier specifications Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 36

Types of T-Carriers (cont’d.) T1: 24 voice or data channels – Maximum data throughput: 1.544 Mbps T3: 672 voice or data channels – Maximum data throughput: 44.736 Mbps (45 Mbps) T-carrier speed dependent on signal level – Physical layer electrical signaling characteristics – DS0 (digital signal, level 0) One data, voice channel Network Guide to Networks, 6th Edition 37

Types of T-Carriers (cont’d.) T1 use – Connects branch offices, connects to carrier – Connects telephone company COs, ISPs T3 use – Data-intensive businesses T3 provides 28 times more throughput (expensive) – Multiple T1’s may accommodate needs TI costs vary by region Fractional T1 lease – Use some T1 channels, charged accordingly Network Guide to Networks, 6th Edition 38

T-Carrier Connectivity T-carrier line requires connectivity hardware – Customer site, switching facility – Purchased or leased – Cannot be used with other WAN transmission methods T-carrier line requires different media – Throughput dependent Network Guide to Networks, 6th Edition 39

T-Carrier Connectivity (cont’d.) Wiring – Plain telephone wire UTP or STP copper wiring STP preferred for clean connection – Coaxial cable, microwave, fiber-optic cable – T1s using STP require repeater every 6000 feet – Multiple T1s or T3 Fiber-optic cabling Network Guide to Networks, 6th Edition 40

Figure 7-13 T1 wire terminations in an RJ-48 connector Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 41

Figure 7-14 T1 crossover cable terminations Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 42

T-Carrier Connectivity (cont’d.) CSU/DSU (Channel Service Unit/Data Service Unit) – Two separate devices – Combined into single stand-alone device Interface card – T1 line connection point CSU – Provides digital signal termination – Ensures connection integrity Network Guide to Networks, 6th Edition 43

T-Carrier Connectivity (cont’d.) DSU – Converts T-carrier frames into frames LAN can interpret (and vice versa) – Connects T-carrier lines with terminating equipment – Incorporates multiplexer Smart jack – Terminate T-carrier wire pairs Customer’s demarc (demarcation point) Inside or outside building – Connection monitoring point Network Guide to Networks, 6th Edition 44

Figure 7-17 A point-to-point T-carrier connection Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 45

T-Carrier Connectivity (cont’d.) Incoming T-carrier line – Multiplexer separates combined channels Outgoing T-carrier line – Multiplexer combines multiple LAN signals Terminal equipment – Switches, routers – Best option: router, Layer 3 or higher switch Accepts incoming CSU/DSU signals Translates Network layer protocols Directs data to destination Network Guide to Networks, 6th Edition 46

T-Carrier Connectivity (cont’d.) CSU/DSU may be integrated with router, switch – Expansion card – Faster signal processing, better performance – Less expensive, lower maintenance solution Network Guide to Networks, 6th Edition 47

Figure 7-18 A T-carrier connecting to a LAN through a router Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 48

DSL (Digital Subscriber Line) Operates over PSTN Directly competes with ISDN, T1 services Requires repeaters for longer distances Best suited for WAN local loop Supports multiple data, voice channels – Over single line – Higher, inaudible telephone line frequencies Uses advanced data modulation techniques – Data signal alters carrier signal properties – Amplitude or phase modulation Network Guide to Networks, 6th Edition 49

Types of DSL xDSL refers to all DSL varieties – ADSL, G.Lite, HDSL, SDSL, VDSL, SHDSL Two DSL categories – Asymmetrical and symmetrical Downstream – Data travels from carrier’s switching facility to customer Upstream – Data travels from customer to carrier’s switching facility Network Guide to Networks, 6th Edition 50

Types of DSL (cont’d.) Downstream, upstream throughput rates may differ – Asymmetrical More throughput in one direction Downstream throughput higher than upstream throughput Best use: video conferencing, web surfing – Symmetrical Equal capacity for upstream, downstream data Examples: HDSL, SDSL, SHDSL Best use: uploading, downloading significant data amounts Network Guide to Networks, 6th Edition 51

Types of DSL (cont’d.) DSL types vary – – – – Data modulation techniques Capacity Distance limitations PSTN use Table 7-2 Comparison of DSL types Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 52

DSL Connectivity ADSL: common example on home computer – Establish TCP connection – Transmit through DSL modem Internal or external Splitter separates incoming voice, data signals May connect to switch or router Network Guide to Networks, 6th Edition 53

DSL Connectivity (cont’d.) ADSL (cont’d.) – DSL modem forwards modulated signal to local loop Signal continues over four-pair UTP wire Distance less than 18,000 feet: signal combined with other modulated signals in telephone switch – Carrier’s remote switching facility Splitter separates data signal from voice signals Request sent to DSLAM (DSL access multiplexer) Request issued from carrier’s network to Internet backbone Network Guide to Networks, 6th Edition 54

Figure 7-20 A DSL connection Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 55

DSL Connectivity (cont’d.) DSL competition – T1, ISDN, broadband cable DSL installation – Hardware, monthly access costs Slightly less than ISDN; significantly less than T1s DSL drawbacks – Throughput lower than broadband cable Network Guide to Networks, 6th Edition 56

Broadband Cable Cable companies connectivity option Based on TV signals coaxial cable wiring – Theoretical transmission speeds 150 Mbps downstream; 10 Mbps upstream – Real transmission 10 Mbps downstream; 2 Mbps upstream Transmission limited ( throttled) Shared physical connections Best uses – Web surfing – Network data download Network Guide to Networks, 6th Edition 57

Broadband Cable (cont’d.) Cable modem – Modulates, demodulates transmission, reception signals via cable wiring – Operates at Physical and Data Link layer – May connect to connectivity device Figure 7-21 A cable modem Courtesy Zoom Telephonics, Inc. Network Guide to Networks, 6th Edition 58

Broadband Cable (cont’d.) Infrastructure required – HFC (hybrid fiber-coax) Expensive fiber-optic link supporting high frequencies Connects cable company’s offices to node – Cable drop Connects node to customer’s business or residence Fiber-optic or coaxial cable Connects to head end Provides dedicated connection Many subscribers share same local line, throughput Network Guide to Networks, 6th Edition 59

Figure 7-22 Cable infrastructure Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 60

BPL (Broadband Over Powerline) High-speed Internet access over the electrical grid – Began around 2000 Advantages – Potential for reaching remote users Roadblocks to development – – – – Opposition from telecommunications groups Costly infrastructure upgrades Signals subject to more noise than DSL, cable Signals interfere with amateur radio Network Guide to Networks, 6th Edition 61

ATM (Asynchronous Transfer Mode) Functions in Data Link layer Asynchronous communications method – Nodes do not conform to predetermined schemes Specifying data transmissions timing – Each character transmitted Start and stop bits Specifies Data Link layer framing techniques Fixed packet size – Packet (cell) 48 data bytes plus 5-byte header Network Guide to Networks, 6th Edition 62

ATM (cont’d.) Smaller packet size requires more overhead – Decrease potential throughput – Cell efficiency compensates for loss ATM relies on virtual circuits – ATM considered packet-switching technology – Virtual circuits provide circuit switching advantage – Reliable connection Allows specific QoS (quality of service) guarantee – Important for time-sensitive applications Network Guide to Networks, 6th Edition 63

ATM (cont’d.) Compatibility – Other leading network technologies – Cells support multiple higher-layer protocol – LANE (LAN Emulation) Allows integration with Ethernet, token ring network Encapsulates incoming Ethernet or token ring frames Converts to ATM cells for transmission Throughput: 25 Mbps to 622 Mbps Cost: relatively expensive Network Guide to Networks, 6th Edition 64

SONET (Synchronous Optical Network) Key strengths – – – – WAN technology integration Fast data transfer rates Simple link additions, removals High degree of fault tolerance Synchronous – Data transmitted and received by nodes must conform to timing scheme Advantage – Interoperability Network Guide to Networks, 6th Edition 65

Figure 7-23 A SONET ring Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 66

SONET (cont’d.) Fault tolerance – Double-ring topology over fiber-optic cable SONET ring – Begins, ends at telecommunications carrier’s facility – Connects organization’s multiple WAN sites in ring fashion – Connect with multiple carrier facilities Additional fault tolerance – Terminates at multiplexer Easy SONET ring connection additions, removals Network Guide to Networks, 6th Edition 67

Figure 7-24 SONET connectivity Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 68

SONET (cont’d.) Data rate indicated by OC (Optical Carrier) level Table 7-3 SONET OC levels Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 69

SONET (cont’d.) Implementation – Large companies – Long-distance companies Linking metropolitan areas and countries – ISPs Guarantying fast, reliable Internet access – Telephone companies Connecting Cos Best uses: audio, video, imaging data transmission Expensive to implement Network Guide to Networks, 6th Edition 70

WAN Technologies Compared Table 7-4 A comparison of WAN technology throughputs Courtesy Course Technology/Cengage Learning Network Guide to Networks, 6th Edition 71

Summary WAN topologies: bus, ring, star, mesh, tiered PSTN network provides telephone service FTTP uses fiber-optic cable to complete carrier connection to subscriber High speed digital data transmission – Physical layer: ISDN, T-carriers, DSL, SONET – Data Link layer: X.25, frame relay, ATM – Physical and Data link: broadband Network Guide to Networks, 6th Edition 72