1. Metropolitan and Wide Area Networks Under construction…
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): Mbps
T2 (DS2): Mbps (inverse mux 4 T1)
T3 (DS3): Mbps (ISU)
T4 (DS4): 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: Mbps (faster than a T3)
OC-3: Mbps (STM-1)
OC-9: Mbps (STM-3)
OC-12: Mbps (STM-4)
OC-24: Gbps (STM-8)
OC-48: Gbps (STM-16)
OC-192: 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 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. 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

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 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