MIS 430 Chapter 9

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MIS 430 Chapter 9

• Metropolitan and Wide Area Networks
• Under construction

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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 (ATT, Ameritech,
  Sprint)
• LEC Local Exchange Carrier
• IXC Interexchange Carrier

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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)

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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

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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
  ISDNIt Still Does Nothing
• 64 Kbps 64 Kbps service
• Can have data and voice on same line or several
  voice

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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

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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 carriers cloud
  but it appears you have your own private network
  (no sharing)

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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

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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 T124 voice channels

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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)

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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

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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)

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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

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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

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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

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VPNs

• Architecture, contd.
• Receivers 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

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VPNs

• Types of VPNs
• Intranet VPN provides virtual circuits between
  organizations offices over the Internet
• Extranet VPN connects different organizations
  (often customers and suppliers) over the Internet
• Access VPN allows employee to access
  organizations 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

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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)

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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