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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

VPNs Architecture, contd. Advantages Disadvantages 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

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

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

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