Chapter 10: WAN Hardware

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Chapter 10 WAN Hardware

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

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Network Types

• Wide Area Network (WAN)
• Cover large geographical areas, often crossing
  public right-of-ways
• Usually consists of several interconnected
  switching points.
• Local Area Network (LAN)
• Small scope, usually a building or cluster
• Typically owned by the same organization that
  owns the equipment.

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WAN Hardware

• See Figure 10-1 on p. 270 for possible Hardware
  Configuration of a WAN.
• Terminals
• Multiplexers
• Concentrators
• Front End Processors (FEP)
• Protocol Converters
• Diagnostic and Miscellaneous Equipment

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Terminals

• An I/O device that can be connected to a local or
  remote computer called a Host Computer.
• TERMINAL TYPES
• 1. Microcomputers
• 2. Remote Job Entry (RJE) Stations
• 3. Data Entry and Display
• 4. Sensor Devices
• 5. Display-Only Devices

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TERMINAL TYPES (Continued)

• 6. Point-of-Sale Terminals
• 7. Portable Terminals
• 8. Touch-Tone Telephones
• 9. Automatic Teller Machines (ATMs)

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TERMINAL TYPES (Continued)

• 1. Microcomputers
• (i)Uploading terminal transfers files or
  programs to the host.
• (ii)Downloading transferring programs or data
  from a host to a terminal.
• (iii) Terminal Emulation software program and
  hardware interface that allows one microcomputer
  to function as a variety of terminals in support
  of changing requirements.

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TERMINAL TYPES (Continued)

• 2. Remote Job Entry (RJE)
• Also called Remote Batch Processing
• Terminal sends recorded images to host.
• Terminal receives updated reports from host.
• 3. Data Entry and Display by
• Video Display Unit (VDU) See Figure 10-2 on p.
  271
• Video Display Terminal (VDT)
• Teletypewriter (TTY)
• Cathode Ray Tube (CRT)

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TERMINAL TYPES (Continued)

• 4. Sensor Devices
• Computer-controlled environmental monitoring
  systems
• Temperature control sensors sends a message to an
  output-only terminal devices that switches on
  heating or cooling.
• 5. Display-Only Devices examples
• Display monitors in stock market applications.
• Remote printers with control information display,
  e.g. out of paper,not ready to receive.

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TERMINAL TYPES (Continued)

• 6. Point-of-Sale (POS) Terminals
• Maintain inventory, record bill-of-sale receipts,
  money transfers, etc.
• 7. Portable Terminals
• Laptops are most popular example.
• Can be used for inputting customers orders and
  transmitted to home office via telephone or modem
  link.

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TERMINAL TYPES (Continued)

• 8. Automatic Teller Machines (ATM)
• Handle ordinary banking transactions of deposits,
  withdrawals, and account balance inquires.

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Terminal Capabilities

• Types of Terminals
• 1. Dumb
• NO MEMORY!!! (e.g. Doesnt save data!)
• NO PROCESSING OF DATA!!!
• 2. Smart
• Can SAVE DATA entered by the operator
• Advantage over dumb terminals is independence
  between terminal operator host.
• 3. Intelligent
• BOTH SAVES DATA PROCESSES DATA !!!
• Advantage over smart terminals is fact that
  control processing are local.

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Terminal Capabilities (Continued)

• Some Terminal Attributes See Table 10-2 on
  p.274
• Cost (variable costs)
• Speed (up to 56Kbps)
• Maintenance Support
• Display Attributes (e.g. screen size character
  size)
• Data Link Protocols (usually different from LAN
  protocols)

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Terminal Configurations

• 2 Options for attaching Terminals
• 1. Point-to-Point Connection
• Uses a communication line to connect one terminal
  to a host computer.
• Examples Computer-to-computer communications
• Contention or when host and terminal compete
  for control of medium.
• 2. Multipoint Connection
• Several terminals share one communications line.
• Most common approaches with terminals are
  polling multiplexing.

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POLLING

• Polling
• Process of asking terminals if they have data to
  transmit.
• Host is usually designated as Primary Station.
• Other stations designated as Secondary Stations.
• Illustration in Benjamin-Cummings Software
  Module.
• Types of Polling
• 1. Roll-Call uses list of addressesSee
  Figure10-4 on p.278
• 2. Hub-Polling requires terminals to be
  involved in the polling.See Figure 10-5 on p.279

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MULTIPOINT CONNECTIONS

• Advantages of Multipoint Connections
• Economical
• Only ONE communication link is required for a
  host to communicate with several terminals.
• If modems are required, FEWER modems are
  necessary.
• Disadvantages of Multipoint Connections
• Terminals more expensive than those in
  point-to-point connections, as not dumb
  terminals.
• Waiting time for message or data transmission.

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MULTIPLEXERS

• Line-sharing technique that allows multiple
  signals to be transmitted over a single link.
• Also called muxes
• Does not generally require the use of smart
  terminals.
• Provides an alternative to point-to-point
  connection and polling.
• The mux combines the data from all incoming lines
  and transmits it via one line to a mux at the
  receiving line.

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TYPES OF MULTIPLEXERS

• 1. Frequency Division Multiplexing (FDM)
• Divides the available bandwidth of circuit into
  sub-channels of different frequency ranges.
• See Figure 10-8 on p. 282 NOTE that can NOT have
  four (4) 300-bps lines becasue need to eliminate
  crosstalk.

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TYPES OF MULTIPLEXERS (Continued)

• 2. Time Division Multiplexing (TDM)
• Allots to each device a time slot during which it
  can send or receive data.
• See Figure 10-9 on p. 282 NOTE CAN have 4 lines
  of 300-bps each!!!
• See also Figure 10-10 on p. 283 4 lines of
  2400-bps each.

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TYPES OF MULTIPLEXERS (Continued)

• 3. Statistical Time Division Multiplexing (STDM)
• Transmits data only for lines with data to send,
  rather than allowing idle lines to occupy
  carrying capacity of the communication circuit.
• Also called a Stat Mux.
• See Figure 10-11 on p. 284.

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MULTIPLEXERS CONFIGURATIONS

• Daisy Chaining (also called Cascading)
• Allows some circuits to be extended to another
  remote point.
• See Figure 10-12 on p. 285 which has 16 ports at
  host which transmits to Mux with 12 ports to
  terminals and 4 ports to another Mux.
• Inverse Multiplexer
• Accepts one line from a host and separates it
  into multiple lower-speed communication circuits.
• See Figure 10-13 on p. 285. Note 9600bps X 6
  lines 57.6Kbps !!!

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CONCENTRATORS

• A computer that provides line-sharing
  capabilities including data editing, polling,
  error handling, code conversion, compression, and
  encryption.
• See Figure 10-14 on p. 286.

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Differences between Concentrators and Muxes

• 1. Concentrators are used ONE at a time.
  Multiplexers are used in PAIRS.
• 2. (i)Concentrator may have number of incoming
  lines NOT equal to number of outgoing lines.
• (ii) Multiplexer merges a set of incoming
  lines into ONE LINE, and then converts back to
  the same number of outgoing lines.

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Differences between Concentrators and Muxes

• 3. Concentrator is a computer and may have
  auxiliary storage for use in support of an
  application.
• 4. Concentrator may perform some data processing
  functions, such as device polling and data
  validation.

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FRONT-END PROCESSORS (FEP)

• A communications component placed at the host end
  of a circuit to take over a portion of the line
  management work from the host.
• Also called a Communications Controller or
  Message Switch
• See Figure 10-15 on page 287.

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PROTOCOL CONVERTER

• A special-purpose device that allows a terminal
  to look like a different type of terminal in
  order to facilitate interconnection between
  different computer systems.
• See Figure 10-16 on page 287.

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DIAGNOSTIC AND MISCELLANEOUS EQUIPMENT

• 1. Security Hardware
• Call-Back Units
• Encryption Equipment
• 2. Line Monitors
• 3. Breakout Boxes
• 4. Auto-Call Units (ACU)
• 5. Port Concentrators
• 6. Port Selector or Data Switch
• 7. Cluster Controllers

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DIAGNOSTIC AND MISCELLANEOUS EQUIPMENT

• 8. Private Branch Exchanges (PBXs)
• 9. Matrix Switches

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DIAGNOSTIC AND MISCELLANEOUS EQUIPMENT

• 1. Security Hardware
• (i)Call-Back Units a security device for
  switched connections. It operates by receiving a
  call, verifying the user, severing the call, and
  calling the user back.
• 2 PROBLEMS
• Host computer becomes responsible for the
  connection cost.
• Prohibits portable terminal connections.
• (ii) Encryption Equipment
• scrambles transmitted data
• one standard is data encryption standard (DES)
  approved by US NIST(national Institute for
  Standards and Technology)
• See Figure 10-17 on p. 289 for Data Encryption
  Box.

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DIAGNOSTIC AND MISCELLANEOUS EQUIPMENT

• 2. Line Monitors
• Devices used to diagnose problems on a
  communications link.
• Also called Protocol Analyzer.
• 2 Types of DIGITAL ANALOG.
• See Figure 10-18 on p. 290 for DIGITAL LINE
  MONITOR
• See page 289 for Common Available Features of
  Line Monitors.
• No industry standard recording mode, so tape or
  disk recorded on one manufacturers machine is
  probably NOT readable on another manufacturers
  equipment.

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DIAGNOSTIC AND MISCELLANEOUS EQUIPMENT

• 3. Breakout Boxes
• A passive, multipurpose diagnostic device that is
  patched or temporarily inserted into a circuit at
  an interface.
• Used to
• monitor activity on each of the circuits
• change circuit connections
• isolate a circuit to prevent its signals from
  passing through to the receiver
• measure circuit voltage levels.
• See Figure 10-19 for a Programmable Breakout Box

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DIAGNOSTIC AND MISCELLANEOUS EQUIPMENT

• 4. Auto-Call Units (ACU)
• A device used to place a telephone call
  automatically without manual intervention.
• Interface to ACU equipment in US using the
  RS-232-C or RS-366 interface.
• 5. Port Concentrator
• A device that allows multiple input streams from
  a multiplexer to be passed to the host through a
  single communication port.
• See Figure 10-20 on page 292.

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DIAGNOSTIC AND MISCELLANEOUS EQUIPMENT

• 6. Port Selector or Data Switch
• A device that helps determine which users are
  granted access to applications when the number of
  potential terminal users far exceed the number of
  available lines.
• Also known as a Data Switch.
• See Figure 10-21 on page 293 for Port Selector
  Schematic.

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DIAGNOSTIC AND MISCELLANEOUS EQUIPMENT

• 7. Cluster Controller
• A device that manages multiple terminals by
  buffering data transmission to and from the
  terminals and performing error detection and
  correction.
• See Figure 10-22 on page 293.

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DIAGNOSTIC AND MISCELLANEOUS EQUIPMENT

• 8. Private Branch Exchange (PBX)
• A private telephone switch
• Switches call internally while routing external
  calls through the telephone companys system.
• Disadvantages of using PBX systems for LANs
• lower transmission speed
• competition between data and voice for available
  transmission capacity.

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DIAGNOSTIC AND MISCELLANEOUS EQUIPMENT

• 9. Matrix Switches
• A device that allows terminal connections to be
  switched among the available processors
• Use when have multiple host processors.
• See Figure 10-23 on page 294 for Matrix Switch
  Hardware.
• 3 Uses of Matrix Switches
• 1. Users can be evenly distributed over several
  processors.
• 2. If a failure occurs in one line, the terminals
  attached to that line are switched to a
  functional line.
• 3. More terminals can be distributed than direct
  physical line attachments would permit.

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WAN Hardware

• THE END!!!