Chapter 9: LAN Considerations

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Chapter 9 LAN Considerations

• MIS 3523 Business Data Communications
• Fall 2001
• Dr. Segall

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Chapter 9 Objectives

• 1. Describe several LAN alternatives.
• 2. List several LAN selection criteria.
• 3. Discuss how a specific criterion influences
  the LAN selection process.
• 4. Evaluate a companys needs and develop a basic
  LAN strategy that meets those needs.

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LAN ALTERNATIVES

• 2 Perspectives
• 1. Different types of LAN Implementation
• 2. Hardware and software alternatives to LANs
• LAN Implementation Alternatives
• 1. Dedicated Servers
• 2. Non-dedicated Servers
• 3. Peer-to-peer implementation (was discussed in
  Chapter 8!!!)

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Dedicated vs. Non-Dedicated Server

• Dedicated Server
• One or more computers that operate ONLY as
  designated file, database, or other types of
  servers.
• Non-dedicated Server
• A computer that can operate as BOTH a server and
  a workstation.

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Non-Dedicated Servers

• Advantages
• 1. Allows more effective use of resources.
• Disadvantages
• 1. Must divide its workload between its
  application work and its server work.
• 2. Increased likelihood of server failures.
• (i) Caused by running both server and
  applications software
• (ii) Caused by users application, e.g. locked
  application
• (iii) Caused by user him or her-self, e.g.
  unintentionally formats server disk.

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Other Implementations

• 1. Large, Central Computer Systems
• 2. Service Bureaus
• 3. Zero-Slot LANs
• 4. Sub-LANs

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Large, Central Computer Systems

• Traditional Approach
• Central Host Computer See Figure 8-1 on p. 251.
• Primary means for
• processing large volumes of data
• producing big reports
• supporting special-purpose hardware devices, e.g.
  checker reader/sorters.

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Large, Central Computer Systems

• Modern Approach
• Microcomputers argument large central computer
  systems.
• Downsizing to LANs is more common than replacing
  LANs with large systems.

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Service Bureaus

• A subscription service in which the user pays for
  amount of computing resources used.
• e.g. amount of disk storage, processing time, and
  printed output.
• Amount paid by Subscriber Monthly subscription
  fee Monthly usage fee

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Zero-Slot LANs

• Low-speed LANs that use standard PC components.
• Lower Cost of Implementation.
• Do not require an additional slot on the
  motherboard for a LAN adapter.
• If LAN adapter is used
• addresses of stations either factory assigned or
  set by Dual Inline Package (DIP) switch settings.

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Sub-LANs

• Provides a subset of LAN capabilities in
• 1. Peripheral sharing
• 2. File transfer
• Differences from LAN
• 1. Transfer rates Costs are lower for a Sub-LAN
  than for a LAN.
• 2. File transfer capabilities are typically less
  transparent than on a LAN.

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Sub-LANs

• Are inexpensive.
• Implemented with Data Switches.
• which provides connection between microcomputers.
• allows file transfer between microcomputers.
• See Figure 9-2 on page 252.

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Sub-LANs

• Data Switches (Continued)
• To connect peripherals devices such as printers
  plotters, see Figure 9-3.
• Manual switching using a switch selection knob.
  
• Keyboard command switching using address of
  device.
• Does NOT allow file transfer between
  microcomputers.

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Sub-LANs

• Data Switches (Continued)
• ADVANTAGES
• 1. Effective, low cost way to share peripherals
• 2. Accomplish infrequent transfers of small
  files.
• DISADVANTAGES
• 1. Low speed of communication link
• 2. Lack of user transparency
• 3. Lack of expandability (e.g. number of
  connection ports is limited).

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Sub-LANs

• Data Switches (Continued)
• DISADVANTAGES (Continued)
• 4. Lack of ability to interface to other networks
  (e.g. ability to connect to other networks is
  generally poor.)
• 5. Contention
• competing for use of one of the peripherals
• 6. NOT well suited for downloading software
  programs or large data files.
• 8. NOT well suited for frequent file exchanges.

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Comparison of LAN Alternatives

• See Table 9-1 on page 254 where
• A Large, centralized computer system
• B use of a service bureau
• C sub-LANs
• D Zero-slot and low-cost LANs
• E Conventional LAN (such as Ethernet or token
  ring)
• 1 BEST Alternative
• 5 WORST Alternative

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Comparison of LAN Alternatives

• SUMMARY of Table 9-1 on page 254
• Number of Workstations BEST for large
  centralized computer system
• Initial Cost BEST for both sub-LANs Zero-slot
  and low-cost LANs
• Initial Cost, Personnel Costs,
  Operations/Maintenance Costs WORST for large
  centralized computer systems
• For others see Table 9-1 on page 254.

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LAN Selection Criteria

• See Table 9-2 on page 255 and pp. 254-261.
• Cost
• Number of Workstations
• Type of Workstations
• Number of Concurrent Users
• Type of Use
• Number of Printers

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LAN Selection Criteria (Continued)

• Medium Distance
• Speed
• Applications
• Expandability
• Device Connectivity
• Connectivity with Other Networks
• LAN Software Hardware
• Vendor

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LAN Selection Criteria (Continued)

• Adherence to Established Standards
• Vendor Support
• Manageability
• Security

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COST

• Hardware Cost
• Software Cost
• Immediate Cost (See Table 9-3 on pg. 255)
• example installing a LAN
• Recurring Cost (See Table 9-3 on pg. 255)
• operating cost
• updating cost
• training cost for LAN users and administrators.

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LAN Selection Criteria

• NUMBER OF WORKSTATIONS
• Maximum number of workstations can support
• Methods for extension of maximum number
• Upgrade existing workstations to maintain current
  number
• TYPE OF WORKSTATIONS
• compatibility of LAN hardware software with
  workstations used.

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LAN Selection Criteria

• NUMBER OF CONCURRENT USERS
• Limits on number of concurrent users.
• Increases workload on system resulting in
• 1. slower system responsiveness
• 2. higher costs incurred as needed to increase
  the work potential of system by
• (i) purchasing a faster LAN
• (ii) adding more powerful servers
• (iii) use more efficient LAN software.

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LAN Selection Criteria

• TYPE OF USE
• Example in text of Word Processing use vs.
  Database Access.
• Type of use governs LAN performance with the
  frequency of LAN requests needed and size of data
  transfers.
• Overlay Module
• computer memory management technique

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TYPE OF USE (Continued)

• Word Processing
• LAN requests could be infrequent
• Amount of data transfers can be large.
• Class in lab with multiple concurrent users
  illustrates
• LAN response is slow at beginning of significant
  workload
• LAN response improves as LAN usage becomes more
  intermittent.
• Data Base Applications
• System could be continuously busy accessing
  updating a database.

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LAN Considerations (Continued)

• Number Type of Printers
• LAN must be able to support both the printers you
  plan to use and in the manner you plan to use
  them, e.g. printing text and printing graphics.
• Distance
• Distance in LAN is measured in wiring length.
• Most microcomputer LANs range from few 100s m to
  several 1000s m

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LAN Considerations (Continued)

• Medium
• Coaxial cable and fiber optic cables are more
  noise-resistant mediums.
• Example in text of replacing the cabling in th
  elevator shaft with more error-resistant wiring
  eliminated periodic failures of data
  transmission.
• Speed
• Common LAN speeds for PCs are 1, 2.5, 4, 10, 16,
  20 and 100 Mbps.
• Trend is for higher speeds so can transmission
  greater volumes of data.

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LAN Considerations (Continued)

• Applications
• Application Program Interfaces (APIs) are used to
  interface with networks.
• Some software is not LAN compatible.
• Expandability
• Adding workstations or more workstations from one
  location to another.
• Ease of expandability depends on medium
  installed.
• Adding nodes is more difficult for fiber optic
  cables than for twisted-pair wires or coaxial
  cables.

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LAN Considerations (Continued)

• Device Connectivity
• Ability to attach devices such as an optical
  disk.
• Some LANs may or may not have appropriate LAN
  interface devices.
• Connectivity to Other Networks
• Ability to connect to WANs and/or other LANs.

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LAN Considerations (Continued)

• LAN Software and Hardware
• Selecting software hardware that is compatible
  with existing equipment.
• Adherence to established Standards
• We discussed some of these Standards in Chapter 7.

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LAN Considerations (Continued)

• Vendor and Support
• You can be more successful with a good vendor,
  and a less capable LAN than with a poor vendor
  and a superior LAN.
• Vendor speed of resolving problems, obtaining
  needed equipment, etc. are factors of
  consideration in LAN operations.

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LAN Considerations (Continued)

• Manageability
• Do not underestimate the time and effort required
  to operate manage a LAN.
• LAN Management Tasks are listed in Table 9-4 on
  page 260.
• Security
• LAN software must have ability to control access
  to data, unlike stand-alone microcomputer systems
  which are usually single-server systems.

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Chapter 9 Summary

• LAN alternatives include
• At HIGH ENDlarge mainframes and service bureaus
• AT LOW END multi-user microcomputers, sub-LANs,
  and zero-slot LANs
• FIRST STEP MUST decide if whether a LAN is
  required or whether a LAN alternative will
  suffice.

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Chapter 9 Summary

• SECOND STEP IF LAN is REQUIRED then factors to
  consider include
• cost-effectiveness, available system and
  application software, security, compatibility
  with existing hardware and software, LAN
  organization, adherence to established standards,
  number of concurrent users supported, ability to
  interconnect with networks and computers, vendor
  support and expertise.
• WEIGHTS associated with EACH SELECTION CRITERION
  may differ among organizations.
• In making selections, you need to evaluate the
  alternatives from the perspectives of your
  organizations immediate and future communication
  objectives.

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LAN Considerations

• THE END!!!