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MIS 430 – Chapter 9

MIS 430 – Chapter 9. Metropolitan and Wide Area Networks Under construction…. Introduction. MANs span 3-30 miles and connect BNs and LANs WANs connect BNs and MANs across wider distances Most companies do not build their own WANs They use common carriers (AT&T, Ameritech, Sprint)

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MIS 430 – Chapter 9

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  1. MIS 430 – Chapter 9 Metropolitan and Wide Area Networks Under construction… MIS 430 Chapter 9

  2. Introduction • MANs span 3-30 miles and connect BNs and LANs • WANs connect BNs and MANs across wider distances • Most companies do not build their own WANs • They use common carriers (AT&T, Ameritech, Sprint) • LEC – Local Exchange Carrier • IXC – Interexchange Carrier MIS 430 Chapter 9

  3. I. Circuit-Switched Networks • Basic Architecture – dial-up access • Operate over PSTN – public switched telephone network • Cloud architecture (network is cloud) • Users lease access points (not wireless) • A connection is temporarily established, data is exchanged, and connection is dropped (e.g., hang up) MIS 430 Chapter 9

  4. Circuit Switched Networks • POTS (Plain Old Telephone Service) • Common dial-up services • Lease the phone line connection • Use special equipment (modem) to talk to PSTN • Dial via modem; can hang up and dial a different ISP or computer. • Quality and line speed vary with each call: UGH MIS 430 Chapter 9

  5. Circuit Switched Networks • WATS – wide area telephone services • Special rate allows both voice and data calls to be purchased at a discounted flat rate • ISDN – Integrated Services Digital Network • Digital phone connection: voice, data, video on one phone line (but not your regular POTS line) • Not widely adopted in US: DSL clobbered it; ISDN=“It Still Does Nothing” • 64 Kbps + 64 Kbps service • Can have data and voice on same line or several voice MIS 430 Chapter 9

  6. Circuit-Switched Networks • Advantages • Very flexible: establish circuits as needed from any point to any other point • Sometimes used when network demand is unknown • Simpler – management is done by the common carrier, not the organization • Disadvantages • Data only transmitted while circuit is established • More expensive – users pay for each connection and often for the time used MIS 430 Chapter 9

  7. II. Dedicated Circuit Networks • Solves three problems: • Much higher data rates than dial-up • Better quality because one circuit all the time • 24x7 usage without significant cost penalty • Basic architecture • Circuits leased from a common carrier • All connections are point to point • Connections run through common carrier’s cloud but it appears you have your own private network (no sharing) MIS 430 Chapter 9

  8. Dedicated Circuit Networks • Architectures • Ring fig 9-3 p. 304 (accommodates failures) • Can have delays in getting messages to destination • Star fig 9-4 p. 305 (faster, easy to manage) • Uses one central computer to route messages • Mesh fig 9-5 p. 306 (full or partial) • Uses decentralized routing – requires more processing • Billing: usually a flat rate regardless of volume sent • Very hard to make changes in locations MIS 430 Chapter 9

  9. Dedicated Circuit Networks • T Carrier Services: most common in NA • T1 (DS1): 1.544 Mbps • T2 (DS2): 6.312 Mbps (inverse mux 4 T1) • T3 (DS3): 44.736 Mbps (ISU) • T4 (DS4): 274.176 Mbps • Fractional T1 (DS0): 64 Kbps and up • Can be used for voice: a T1=24 voice channels MIS 430 Chapter 9

  10. Dedicated Circuit Networks • SONET Services: Synchronous Optical Net • American standard for high speed digital • Almost identical international standard • SDH – synchronous digital hierarchy (STM) • OC-1: 51.8 Mbps (faster than a T3) • OC-3: 155.5 Mbps (STM-1) • OC-9: 466.6 Mbps (STM-3) • OC-12: 622.1 Mbps (STM-4) • OC-24: 1.244 Gbps (STM-8) • OC-48: 2.488 Gbps (STM-16) • OC-192: 9.953 Gbps (STM-24) MIS 430 Chapter 9

  11. Mgt Focus 9-1 Caregroup • Dedicated Circuit Network – hybrid • See figure 9.8 p. 309 • 6 hospitals using MAN and WAN • 3 have OC-1 SONET ring topology • Central data center • 3 use T-3 star topology • Physician offices MIS 430 Chapter 9

  12. III. Packet Switched Networks • Common carriers allow packets (not a circuit) to transfer data between any nodes on network • Basic architecture • PAD (packet assembler/disassembler) to go between LAN and the common carrier network – Fig. 9.9 p. 310 • Packets travel ala Internet … store and forward – Fig 9.10 p. 311 • Datagram – connectionless service • Virtual Circuit – looks like one end-to-end circuit • Permanent Virtual Circuit – for higher data volumes between same nodes (very common and results in higher data rates) MIS 430 Chapter 9

  13. Packet Switch Networks • X.25: ITU-T packet network std. in Europe • 64 Kbps up to 2.048 Mbps • ATM: like BN ATM, similar to X.25 • No error control is done: responsibility of users • Speed same as SONET by muxing ATM lines • Offers QoS to set priorities for packets • Frame Relay: speed between X.25 and ATM • No error control provided • 56 Kbps to 45 Mbps speeds MIS 430 Chapter 9

  14. Packet Switched Networks • SMDS – Switched Multimegabit Data Service • Like ATM, no error checking • Not yet standardized but RBOCs offer it • Ethernet/IP Packet Networks • Extends Ethernet beyond LAN, BN and avoids introducing a new protocol and new addresses • Speeds from 1 Mbps to 1 Gbps at ¼ cost! • Emerging technology MIS 430 Chapter 9

  15. IV. Virtual Private Network-VPN • Equivalent of private packet-switched network over the public Internet • Basic architecture • 1st lease an Internet connection at your speed • Connect a VPN device (router or switch) to each Internet access circuit: purpose is to create a VPN tunnel through the Internet • Sender VPN device encapsulates packet for transfer through the Internet; may encrypt for security MIS 430 Chapter 9

  16. VPNs • Architecture, contd. • Receiver’s VPN device strips off the VPN packet and delivers the initial packet to destination; decrypt here • Advantages • Low cost: mainly ISP access • Flexibility: can get on network from anywhere • Disadvantages • Traffic on the Internet is unpredictable • Security is always a concern on the Internet despite encryption MIS 430 Chapter 9

  17. VPNs • Types of VPNs • Intranet VPN: provides virtual circuits between organization’s offices over the Internet • Extranet VPN: connects different organizations (often customers and suppliers) over the Internet • Access VPN: allows employee to access organization’s networks from a remote location • Cheaper (and faster) than having a toll free number and bank of modems to dial back to the organization • More secure than regular remote control over Internet MIS 430 Chapter 9

  18. V. Improving MAN/WAN Performance • Just like improving LAN performance • Increase computer and device performance • Upgrade devices • Change to more appropriate routing protocol • Increase circuit capacity • Reduce network demand • Change user behavior: peak/off-peak • Analyze network needs of all new systems • Move data closer to users (regional not central) MIS 430 Chapter 9

  19. VI. Best Practice MAN/WAN • Figure 9-15 p. 321 shows service, data rate, relative cost, reliability, and network integration • Fig. 9-16 p. 321 shows best practice recommendations for traffic conditions… • Low traffic: POTS, VPN, frame relay • Moderate traffic: VPN, T1, frame relay • High traffic: Ethernet, T3, frame relay • Very high traffic: Ethernet, SONET, ATM MIS 430 Chapter 9

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