PSTN (cont'd.) - Cochise College

PSTN (cont'd.) - Cochise College

NETWORK+ GUIDE TO NETWORKS TH 6 EDITION Chapter 7 Wide Area Networks (U.S. Centered) Network+ Guide to Networks, 6th Edition 2 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 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 3 Network+ Guide to Networks, 6th Edition 4

WAN Essentials (contd.) 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 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

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

Network+ Guide to Networks, 6th Edition Figure 7-5 Full-mesh and partial-mesh WANs Courtesy Course Technology/Cengage Learning 8 Network+ Guide to Networks, 6th Edition 9 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 PSTN (contd.) PSTN elements

Cannot handle digital transmission Requires modem Signal travels path between modems Over carriers 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 10

Network+ Guide to Networks, 6th Edition 11 PSTN (contd.) 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 12 Figure 7-7 A long-distance dialup connection Courtesy Course Technology/Cengage Learning Network+ Guide to Networks, 6th Edition Figure 7-8 Local loop portion of the PSTN

Courtesy Course Technology/Cengage Learning 13 Network+ Guide to Networks, 6th Edition 14 PSTN (contd.) Optical line terminal Single endpoint at carriers central office in a PON Device with multiple optical ports Optical network unit

Distributes signals to multiple endpoints using fiber-optic cable Or copper or coax cable Network+ Guide to Networks, 6th Edition Figure 7-9 Passive optical network (PON) Courtesy Course Technology/Cengage Learning 15 Network+ Guide to Networks, 6th Edition 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

16 Network+ Guide to Networks, 6th Edition X.25 and Frame Relay (contd.) 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 17 Network+ Guide to Networks, 6th Edition 18 X.25 and Frame Relay (contd.) 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

X.25 and Frame Relay (contd.) 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 19

Network+ Guide to Networks, 6th Edition Figure 7-10 A WAN using frame relay Courtesy Course Technology/Cengage Learning 20 Network+ Guide to Networks, 6th Edition X.25 and Frame Relay (contd.) 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 21 Network+ Guide to Networks, 6th Edition

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 22 Network+ Guide to Networks, 6th Edition Types of T-Carriers

Many available Most common: T1 and T3 Table 7-1 Carrier specifications Courtesy Course Technology/Cengage Learning 23 Network+ Guide to Networks, 6th Edition Types of T-Carriers (contd.) 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 24 Network+ Guide to Networks, 6th Edition Types of T-Carriers (contd.)

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 T1s may accommodate needs TI costs vary by region Fractional T1 lease Use some T1 channels, charged accordingly 25

Network+ Guide to Networks, 6th Edition 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 26 Network+ Guide to Networks, 6th Edition

T-Carrier Connectivity (contd.) 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 27

Network+ Guide to Networks, 6th Edition T-Carrier Connectivity (contd.) 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 28 Network+ Guide to Networks, 6th Edition Figure 7-17 A point-to-point T-carrier connection Courtesy Course Technology/Cengage Learning 29 Network+ Guide to Networks, 6th Edition

T-Carrier Connectivity (contd.) 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

30 Network+ Guide to Networks, 6th Edition T-Carrier Connectivity (contd.) CSU/DSU may be integrated with router, switch Expansion card Faster signal processing, better performance Less expensive, lower maintenance solution 31 Network+ Guide to Networks, 6th Edition

Figure 7-18 A T-carrier connecting to a LAN through a router Courtesy Course Technology/Cengage Learning 32 Network+ Guide to Networks, 6th Edition 33 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 ATM (contd.)

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 34

Network+ Guide to Networks, 6th Edition ATM (contd.) 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

35 Network+ Guide to Networks, 6th Edition 36 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 Figure 7-23 A SONET ring Courtesy Course Technology/Cengage Learning

37 Network+ Guide to Networks, 6th Edition SONET (contd.) Fault tolerance Double-ring topology over fiber-optic cable SONET ring Begins, ends at telecommunications carriers facility Connects organizations multiple WAN sites in ring fashion Connect with multiple carrier facilities Additional fault tolerance Terminates at multiplexer

Easy SONET ring connection additions, removals 38 Network+ Guide to Networks, 6th Edition Figure 7-24 SONET connectivity Courtesy Course Technology/Cengage Learning 39 Network+ Guide to Networks, 6th Edition

SONET (contd.) Data rate indicated by OC (Optical Carrier) level Table 7-3 SONET OC levels Courtesy Course Technology/Cengage Learning 40 Network+ Guide to Networks, 6th Edition SONET (contd.) 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 41

Network+ Guide to Networks, 6th Edition WAN Technologies Compared Table 7-4 A comparison of WAN technology throughputs Courtesy Course Technology/Cengage Learning 42 Network+ Guide to Networks, 6th Edition 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 43

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