Transcript MIS 430 – Chapter 8 - Indiana State University

MIS 430 – Chapter 9
Metropolitan and Wide Area
Networks
Under construction…
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Introduction
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MANs span 3-30 miles and connect BNs
and LANs
WANs connect BNs and MANs across
wider distances
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Most companies do not build their own
WANs
They use common carriers (AT&T,
Ameritech, Sprint)
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LEC – Local Exchange Carrier
IXC – Interexchange Carrier
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I. Circuit-Switched Networks
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Basic Architecture – dial-up access
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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
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POTS (Plain Old Telephone Service)
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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
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WATS – wide area telephone services
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Special rate allows both voice and data calls to be
purchased at a discounted flat rate
ISDN – Integrated Services Digital Network
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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
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Circuit-Switched Networks
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Advantages
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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
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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
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Solves three problems:
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Much higher data rates than dial-up
Better quality because one circuit all the time
24x7 usage without significant cost penalty
Basic architecture
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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)
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Dedicated Circuit Networks
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Architectures
 Ring fig 9-3 p. 304 (accommodates failures)
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Star fig 9-4 p. 305 (faster, easy to manage)
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Uses one central computer to route messages
Mesh fig 9-5 p. 306 (full or partial)
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Can have delays in getting messages to destination
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
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T Carrier Services: most common in NA
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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
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Dedicated Circuit Networks
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SONET Services: Synchronous Optical Net
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American standard for high speed digital
Almost identical international standard
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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
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Dedicated Circuit Network – hybrid
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See figure 9.8 p. 309
6 hospitals using MAN and WAN
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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
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Common carriers allow packets (not a circuit) to
transfer data between any nodes on network
Basic architecture
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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
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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
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X.25: ITU-T packet network std. in Europe
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ATM: like BN ATM, similar to X.25
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64 Kbps up to 2.048 Mbps
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
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No error control provided
56 Kbps to 45 Mbps speeds
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Packet Switched Networks
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SMDS – Switched Multimegabit Data Service
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Like ATM, no error checking
Not yet standardized but RBOCs offer it
Ethernet/IP Packet Networks
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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
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Equivalent of private packet-switched network
over the public Internet
Basic architecture
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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
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Architecture, contd.
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Advantages
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Receiver’s VPN device strips off the VPN packet
and delivers the initial packet to destination;
decrypt here
Low cost: mainly ISP access
Flexibility: can get on network from anywhere
Disadvantages
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Traffic on the Internet is unpredictable
Security is always a concern on the Internet
despite encryption
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VPNs
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Types of VPNs
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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
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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
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Just like improving LAN performance
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Increase computer and device performance
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Upgrade devices
Change to more appropriate routing protocol
Increase circuit capacity
Reduce network demand
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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
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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…
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Low traffic: POTS, VPN, frame relay
Moderate traffic: VPN, T1, frame relay
High traffic: Ethernet, T3, frame relay
Very high traffic: Ethernet, SONET, ATM
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